Inverter Combis are increasingly getting more and more popular, and are ideal for most peoples needs on board their barges (and other boats), whether live aboard or leisure. They not only combine an inverter with battery charger but also include many other useful features, essential for comfortable cruising.
Whilst not an electronics expert, I have attempted to analyse product data and specifications of some of the more commonly available units, and give a few guidelines to features below. Please note they are only guidelines, obtained from manufacturers catalogues and web sites and as such are prone to changes and updates. If a certain function is important for your needs double check with the manufacturer that it is included before buying.
.http://www.victronenergy.com/DatasheetsPDF/SinusInverterChargers/GBPhoenixMulti.pdf
http://www.studer-inno.com/SITESTUDER/page/ANGLAIS/DescriptionE/HPCompactFichetechE.PDF
http://www.sterling-power.com/documents/bros04gb.pdf
http://www.mastervolt.com/dakarcombi/index.asp
http://www.powermastersystems.com/
Notes
May need powerman transfer switch when used together with generator
only one 230v AC input. Separate master switch required (£150) if shore and generator or both to be connected
New product, available soon
only one 230v AC input. Separate master switch required (£150) if shore and generator or both to be connected
Free technical & installation advice line - 01480 455060
Direct Mail order
Other similar versions available
7 other versions incl 24/300/70 and 12/1200/50 without power assist
3 other versions available incl 24v/2300w/55a and 24v/4000w/100a
.
6 other versions incl 12v,1500w,65a charger, 24/1800-35 and 24/3000-100
3 other versions (1500w and 24v) available
Manufacturers rated output
Care needs to be taken when buying an inverter as a 3000w inverter from one company could be less powerful than a 2000w inverter from another. This is because some manufactures base their rating on their maximum output, others at 30 minutes (P30) and others at continuous use at 40 deg C. Those that rate their outputs based on maximum power make them appear more powerful than they really are under normal operating conditions. For example, an inverter rated at 1500 watts (at 0 deg C) may only give 1000 watts if continuously rated at 20 deg C, or only 500 watts when rated continuously at 40 deg C.
The Victron 2500 watt combi is only 1600 watt at 40 deg C
The Mastervolt Dakar 2500 is only 2000 va (around 1600w) at 40 deg C
Sterling seem to be one of the few companies to rate their inverters at 40 deg C, so a 3000 watt Sterling inverter is 3000 watt at 40 deg C.
The problem in Europe is the absence of an agreed standard, unlike in North America where they have the A,B,Y,C. standards, which specify inverters (and battery chargers) at continuous use at 40 deg C ambient. If you want to compare inverter output power ratings then the best way is to compare the ABYC continuous use at 40 deg C rating, this way at least you will be comparing apples to apples, and 40 deg C is a more realistic temperature anywhere near the engine compartment than 20 deg C.
Wave Form
There are three inverter waveform types, square wave, quasi sine (or step square wave), and sine wave.
If you wish to run all appliance (especially washing machines, microwaves and timers) and you want to ensure there are no black lines on the TV, then you need to ensure you purchase a sine wave inverter. Quasi sine will run around 95% of most appliances and is very much cheaper with around 99% of all inverters sold being quasi sine. Most Combis have built in sine wave inverters, but check to make sure.
All inverters are attempting to mimic the mains 230 volt sine wave form. This ensures that all equipment to be run on an inverter receives the same input waveform for which it was designed. With some equipment such as heaters and lights the input waveform is not important. However with things like electric motors, and especially microwaves, the waveform is absolutely critical to achieve correct running.
The good side of a sine wave is it will run all equipment as well as the mains supply, however, the bad side is its cost and the fact that the quiescent current is about 2- times (and as much a 5 times) more than conventional quasi sine wave inverters
Automatic changeover - Uninterrupted A/C Power / Uninterrupted Crossover (UPS)
Most combis will automatically switch over to inverter power if shore power is disconnected, without loss of power. For example, the tv, pc etc. will remain switched on during transfer of power from shore power to inverter.
Built in power sharing / Power Control
Most combis have built in power sharing features, which will automatically reduce battery-charging power when other appliances are switched on, and have the ability to manually set maximum available incoming AC power. For example, if you are on an 8 amp shore power connection the incoming AC would be manually set to 8amps then if the battery charger is using 4 amps and a 1,400w (6amp) hair dryer is switched on the charging output is reduced to around 2 amps (35amps at 12v), giving full power to the hair dryer. When the hair dryer is switched off the battery charger will up it's power output to charge the batteries as fast as possible. Without this feature (or if separate charger and inverters installed) the 8amp shore power circuit breaker would trip as soon as the hair dryer is turned on. The Power Control function makes sure that only whatever current is “left over” is used to charge the batteries.
Power Assist
Some combis have the ability to combine their inverter output to that of the shore power and / or generator output. So that when a peak power is required for a limited period, the combi will make sure that insufficient shore or generator power is immediately compensated for by power from the battery. When the load reduces, the spare power is used to recharge the battery. For example if you have a limited shore power supply of 8 amps (1840watts) and a 2500 watt inverter you will be able to run appliances up to around 4340 watts, and even more for short periods at a time (because most 2500w inverters are capable of supplying more than 2500w for short periods, up to 6000w for a few seconds). Same with generator, for example a 4Kw generator plus 2500w inverter will give 6500w output.
It would appear that this 'power assist' function is presently unique to the Victron Phoenix Multi Plus Combi. Because it boosts the output AC, a smaller (more efficient and cost effective) genset can be considered, plus the combi reduces the harmonic distortion of the genset output (which can this can be important for certain sensitive loads such as an induction cookers).
Parallel Connection
Some combis have the ability to be installed in parallel to each other, combining their available output. For example two 2000w combis connected together in parallel will provide 4000w output. Up to 5 combis can be installed on some systems, giving 5 x 2000w = 10Kw output
Efficiency
Most inverters (and combis) run at up to around 90% efficiency. This means that a 1,000w load (say a hair dryer) will in fact take 1,100w out of the battery. This efficiency rating is often the maximum obtained, depending on load applied, the actual power taken from the battery can be considerably more, it is quite possible that the efficiency may be only around 80%, especially when the ambient temperature is high.
Maximum Power / Surge Capacity
A high surge capacity is essential, and should be around three times it's rated output. This is because many appliances (drills, fridge compressors etc.) have a higher start up power requirement. But this 'surge' capacity adds considerably to the manufacturing cost, so some manufacturers limit it.
Low Quiescent Current
When running low power equipment for long periods, such as televisions, videos, refrigerators or computers, it is best to have an inverter with low 'quiescent' current (the actual current the inverter takes to run itself when in operation). This quiescent current can vary dramatically from 0.7 amps for switch mode inverters, 2 -5 amps for transformer inverters and 25 amps for rotary converters. Most combis are switch mode.
A typical portable phone battery on recharge would require about 1 amp an hour for 12 hours, a total of 12 amp/hours. To provide this output a good switch mode inverter would actually use about 15 amp/hours, a transformer based inverter about 40 amp/hours and a rotary converter about 250 amp/hours, all to do the same task.
This information is not clearly available from most companies. Some consume power even when switched off, others consume around 5w when 'on' but under 'no load' conditions. How much power is consumed when just a small load, eg. a 25w fridge is applied is not clear from any of the product specifications, which indicates it is likely higher than the customer thinks!.
Multi Function Relay
Used to start generators or sound alarms based on power demand or battery voltage. Most combis have this function.
IP Protection
The IP number consists of two numbers, the first of which describes the protection against solid bodies, and the second describes the protection given against liquids. IP2x Enclosure provides protection from objects larger than 12 mm. e.g. contact with finger. IP20 - No protection from liquid provided. IP21 - Enclosure provides protection from vertically falling water only. For more information on IP ratings, click here
Remote Controls
If you intend to install you combi inverter in an engine room, or an area that is not accessible on a day to day basis, a remote control needs to be purchased. This is normally an optional extra, costing between £100 and £350). But it needs to be taken into consideration when comparing different unit total costs.
Battery Charger
Most combis have a built in switch mode, multi step, battery charger. Switch mode plus multi step, together with power sharing and a high amp rating are the key features that make a good battery charger.
Switch Mode
Switch mode chargers easily out perform all conventional transformer battery chargers. Eight years ago there were no switch mode chargers on the market, they were all conventional transformer based. However most marine based chargers are now switch mode, but the transformer charger is still cheaper and more reliable than switch mode chargers (because of their poor performance and simple construction). One of the most popular manufacturers of marine battery chargers (Sterling) state that they have spent the last 10 years reducing their failure rate down to below 1%, but do not believe that a switch mode charger could ever be made as reliable as a transformer-based unit, but that the performance of Switch Mode charger units more than compensate for this. Also, because the switch mode output is pure D/C, and not half wave rectified D/C (as per conventional transformer chargers) there is no 50 Hz pulsing, which damage the batteries.
Most (if not all) Combi units have switch mode chargers, but if comparing separate charger units and stand alone inverter units to combis, this needs to be taken into account.
Multi Step Charging
Without question it is now accepted that 3 or 4 step battery charging, is the best way to charge any battery, with adjustable equalizing or absorption time control (depending on battery bank size). In order to do this the charger must have some programmable system to establish what type of batteries you have and what size of battery bank you have. Most (if not all) Combi units have this facility, but if comparing separate charger units and stand alone inverter units to combis, this needs to be taken into account.
Power Pack
The ability of a battery charger to become a power pack is one of the most important parts of marine battery charger, especially for live aboards and those spending considerable time on board.
Most people on boats only require the battery charging aspect of a charger for a relatively small amount of the time that the charger is used, i.e. if you return to your shore supply and plug in your battery charger then the battery charging is done within 5 to 10 hours. The rest of the week the charger must act as a power supply supplying D/C power directly to the boat and not permitting the batteries to be used. When looked at from this perspective, the battery charging aspect is quite small
Most Combis have the built in Power Pack function. This means that after the battery has been charged the power pack mode allows all the D/C power on the boat to be directly produced from the 240 volt input, thus saving the onboard batteries from cycling and premature destruction. This allows the charger to be fitted to a new boat under construction without any batteries onboard. The boat can be wired with only the power pack onboard.
Restricted Power
With larger chargers it is important to be able to restrict their output power, i.e. a 12 volt 100 amp battery charger requires about 2000 watts of power which is about 8 amps. The problem is that you may visit a marina with only a 5 amp supply. This will render your expensive charger useless, unless it has power reduction facilities. Most combis have this facility, some infinitely variable, some with simple 50% / 75% reduction power switching.
Most battery chargers work well at 230 volts, but at many marinas especially at the end of the pontoon the voltage can drop to as low as 180 volts. Most battery chargers will work at these voltages, but ideally look for high input voltage range 180-260 volts and 40-400 Hz frequencies range which offers maximum performance with poor input power supply.
Size of Charger / Batteries and Inverter
Battery charger size is dependent upon battery bank size, the larger the battery bank, the larger the charger needs to be. The battery bank size is dependant upon the inverter size and applied loads. Reading through various reference books and manufacturers information it seems that, as a rule of thumb;-
Battery size needs to be around 20% of the inverter size
Charger needs to be around 25% of battery capacity for optimum fast charging (10% absolute minimum is recommended).
For example a 2500w inverter needs to have a battery bank in the region of around 420ah, which would ideally need a 100a charger, but 42a minimum - at 12v (210ah batteries and 50a charger at 24v). It would seem charging at anything less than 10% and greater than 30% would not be good for the batteries.
However the battery bank size also needs to take into account the power used. Again, reading through various reference books the ‘ Battery capacity should total at least 2.5 and preferably 4 times the anticipated need between charges’. To establish the ‘anticipated need’ between charges an electrical audit / power usage on board needs to be done. I have calculated this (on our 60ft barge) to be 1,400w average per day (3,250w per day worst case – wash m/c, vac, hair dryer etc, and 800w per day minimum – no wash, no vac, no hair dryer etc.). With around 30% usable power from each battery, this equates to needing a 4,700wh battery bank (400ah at 12v).
This analysis is still being worked on, and will be updated as new information becomes available / clearer. If you know of any other useful features built in to some of the Combis please let me know and I will add them to the list, also if you see any errors or poor interpretations, please advise and I will change accordingly.
Again, this is only a guide. Please check with supplier before making a purchase.
It should be noted that I have no practical experience of combis, only of a 150w inverter on a narrowboat connected to 220ah batteries, the reason for putting the data together is to make a judgment on which one suits our needs best. Price will be a deciding factor, as is local availability / installation assistance. With boat fit-out taking us into 2006, there is no real hurry, but may buy if the right offer comes along.
27th October 2004
We have now bought and installed a Victron Phoenix Multiplus 24/3000/70.
1st impression of the Victron is very good, a 'wonderful blue' box'. I have not checked out everything it should do yet, but everything I have checked works well, eg. If on shore power it will increase available 230v supply (say 4, 8 or 16 amp) by another 16 amps from the battery, giving 20, 24 or 32amps, thus enabling simultaneous use of high power electrical appliances, say an electrical kettle (12 amp) and immersion heater (4 amp) and still have lights and battery charging. To my knowledge only the Victron combi can do this, no other combi has this facility. When boiling the electrical kettle, I unplugged the shore power connection and nothing happened, the kettle still continued to boil, 230v lights remained on, as did the mini drinks cooler.... the power switched over to inverter / battery automatically. I have also pluged in my laptop pc into the Victron 'blue box' and can see incoming and outgoing power usage, plus change voltage charging parameters etc.
I have run the combi through a Victron Isolation transformer with auto transfer of power between shore and engine driven Electrolux 230v generator ..... Have not tested / wired up Electrolux yet. But everything else has worked 1st time with no problems. We purchased the Victron Combi (and other equipment) from Energy Solutions, and they came along to check over the installation prior to switching on. Good service, advice and price from Energy Solutions, if you are fitting out around the London area it would be well worth talking over your requirements with them. http://www.energy-solutions.co.uk/
Back to Equipment Pages Replica Dutch Barge Home Page
Created 26th December 2003 - Last updated 18 March 2008
Showing posts with label Inverters. Show all posts
Showing posts with label Inverters. Show all posts
Saturday, December 27, 2008
Wednesday, April 23, 2008
Inverters
What is an inverter?
How does an inverter work?
Why are most inverters are 115 volts
What size wire, fuse, or breaker will I need?
What is an inverter?
An inverter changes DC voltage from batteries or solar panels, into standard household AC voltage so that it can be used by common tools and appliances.
Converters: What are sometimes called "converters", especially in the RV world, are actually battery chargers and/or DC power supplies. Why they are called converters in RV's and no place else we have not a clue. A "converter" is basically the opposite of an inverter.
Essentially, it does the opposite of what a battery charger or "converter" does. DC is usable for some small appliances, lights, and pumps, but not much else. Most systems should include an inverter of some type, even if it is just an el-cheapo $29 Walmart thing to run the TV occasionally. Some DC appliances are available, with the exception of lights, fans and pumps there is not a wide selection. Most other 12 volt items we have seen are expensive and/or poorly made compared to their AC cousins. The most common battery voltage inputs for inverters are 12, 24, and 48 volts DC - a few models also available in other voltages.
There is also a special line of inverters called a utility intertie or grid tie, which does not usually use batteries - the solar panels or wind generator feeds directly into the inverter and the inverter output is tied to the grid power. The power produced is either sold back to the power company or (more commonly) offsets a portion of the power used. These inverters usually require a fairly high input voltage - 48 volts or more. Some, like the Sunny Boy, go up to 600 volts DC input.
A few grid tie inverters can also be used with batteries, but there will be some loss in overall efficiency for feeding the grid. How much loss can vary considerably, depending on the inverter and the size and type of batteries. If you need battery backup power for a grid tie system, we recommend the Outback Power inverters, as they have the best efficiency with batteries - you will get about a 5-10% loss. With some older inverters, such as the Xantrex SW series, that can sell back excess power to the grid overall losses can be as high as 50%.
Back to Top
How does an inverter work?
An inverter takes the DC input and runs it into a pair (or more) of power switching transistors. By rapidly turning these transistors on and off, and feeding opposite sides of a transformer, it makes the transformer think it is getting AC. The transformer changes this "alternating DC" into AC at the output. Depending on the quality and complexity of the inverter, it may put out a square wave, a "quasi-sine" (sometimes called modified sine) wave, or a true sine wave.
Square wave inverters are usually only suitable for running some type of electrical tools and motors and incandescent lights. They are pretty rare nowadays, some of the old 1970's Triplite and a few others, and some old military surplus is about the only place you find it now.
Quasi-sine (modified sine, modified square) wave inverters have more circuitry beyond the simple switching, and put out a wave that looks like a stepped square wave - it is suitable for most standard appliances, but may not work well with some electronics or appliances that electronic heat or speed control, or uses the AC for clocks or a timer.
What May Not Run: Appliances that use electronics to control temperature or timers may have problems with modified sine waves. This includes anything - tool or appliance - that is variable speed, bread makers, some microwaves, some washers and dryers that use electronic timing for cycling. Most computers, TV's and similar items will have no problem. Anything with a motor will use about 20% more power with a modified sine wave than with a true sine wave.
Also, some of the chargers used for battery operated tools (such as Makita) may not shut off when the battery is charged, and should not be used with anything but sine wave inverters unless you are sure they will work. Sine wave inverters put out a wave that is the same as you get from the power company - in fact, it is often better and cleaner. Sine wave inverters can run anything, but are also more expensive than other types. The quality of the "modified sine" (actually modified square wave), Quasi-sine wave, etc. can also vary quite a bit between inverters, and may also vary somewhat with the load. The very bottom end put out a wave that is nothing but a square wave, and is too "dirty" for all but universal motor driven tools, coffee makers, toasters, and other appliances that have only a heating element.
One solution to the problem of a few small appliances not working well with modified sine wave inverters is to get a large standard inverter, and a small (such as the Exeltech or Samlex) true sine wave for use only with that equipment. This would also allow you to keep the small appliance (such as an answering machine) powered up without having to run the larger inverter full time.
Back to Top
Why are most inverters 115 volts?
Most utility connected homes in North America have dual AC voltages - 115 and 230. On a typical home there are three wires coming in - 115-neutral-115. It is 230 volts across the two outside ones. The 115 is used for most things, while 230 is used for water heaters, electric clothes driers, well water pumps, and air conditioning. Since these high-power items are not practical in a solar powered home, they are either not used or are replaced with gas appliances.
Most off-grid homes have little use for 230 volt AC power - but even so many newer ones are wired just like a standard home to meet electrical and building codes. If it IS required, you can "stack" two 115 volt inverters to get 230. The one exception to the above is that many AC well pumps are 230 volt. If the well pump is the only 230 volt item you have, the best choice is probably to get a step up transformer, such as the Xantrex or Outback Power 120 to 240 step up transformer.
There are export versions of most inverters for 100 volts, 105 volts, 205 volts, and 220/230 volts, in both 50 and 60 Hz.
Inverter-Chargers:
Inverters come in two basic types - with and without built in battery chargers. The ones with built in chargers are handy if you charge your batteries from AC, especially for RV's. They are also essential if using an inverter for setting up a UPS system for backup power. But not everyone needs them - and most small inverters under 1000 watts or so are simply not available with a built in charger.
Nearly all inverter-chargers made in the past few years have 3-stage chargers, so you can usually leave them powered up all the time. Nearly all inverters with chargers also have a built in transfer relay - what that means is that if you are running from AC or shore power, the power feeds through the inverter, with some being tapped off for the battery charger. If the AC power goes out, the inverter automatically switches to battery power. In most cases you won't even see a light flicker, it is so fast.
Inverter (and other) Efficiency:
Inverter efficiency is a question we get asked about a lot. The efficiency of an inverter has to do with how well it converts the DC voltage into AC. This usually ranges from 85% to 95%, with 90% being about average.
However, there is more to the story. Efficiency ratings are usually given into a resistive load (basically something like a light bulb or electric heater). When running such things as motors, the efficiency actually breaks down into two parts - the efficiency of the inverter, and the efficiency of the waveform. Waveform efficiency means that most motors and many electronic appliances run better and use less power with a sine wave. Typically, an electric motor (such as a pump or refrigerator) will use from 15% to 20% more power with a modified sine wave than with a true sine wave. When choosing an inverter based on efficiency, you should also consider what you are going to be running.
A 90% efficient modified sine wave inverter is not 90% when running a compressor motor, for example, because electric motors are less efficient. They use about 20% more power on a modified sine wave.
Inverters are also much less efficient when used at the low end of their maximum power. For example, using a 1000 watt inverter to power a 20 watt radio may actually be using 30 to 40 watts from the battery, as the inverter itself is eating up a lot just to run. Most inverters are most efficient in the 30% to 90% power range.
Back to Top
What size wire, fuse, or breaker will I need?
Inverters have two or three sets of power carrying wires to be concerned about: the wires from the battery to the inverter, the wires from the inverter to the home (or other AC load), and in some cases the wiring from a backup generator or other AC source. The wiring for the AC to the home and from the generator is sized just like you would for AC wiring in a utility connected home. It is usually #10, 12, or 14 standard AC wire. For the small inverters, 800 watts or less, #16 can be used but the mechanical strength of small wire leaves much to be desired.
The wire or cables from the batteries to the inverter are much more critical, and are often undersized. In some cases, the cable may be large enough to carry the "static" load of a motor, but on start up will drop so much voltage in the cable that the inverter will shut down on low voltage cutoff. The same thing can happen with small inverters and TV sets - a TV may only use 100 watts, but the start up surge may be 300 watts for a few seconds. Wire lengths from the battery should always be kept as short as possible, but not so tight that there is a strain on the connections.
Recommended Fuses, Breakers, and Wire Sizes for Inverters
Inverter Watts Inverter DC voltage Input Fuse/Breaker DC Wire Size
Minimum !
50-150 12 20 amp 12 to 14
200-250 12 30-40 amp 8 to 10
300-500 12 50-60 amp 6 to 8
600-1000 12 110 amp 4 to 6
1100-1500 12 200 amp/175 bkr 2/0 to 2
1100-1500 24 110 amp 2/0 to 4
1800-2500 12 300 to 400 amp/250 4/0
1800-2500 24 200 amp/175 2/0
2600-3600 24 400 amp/250 4/0
4000 24 400 amp/250 4/0
4000 48 200 amp/175 2/0
5500 48 200 amp/175 2/0
These are the recommended cable sizes for a ten-foot distance from the batteries to the inverter. Note that the larger wire size is the recommended, the smaller wire size is the absolute minimum for safe operation. The sizes recommended are from a combination of maximum wire amperage capacity and voltage drop. You can't go wrong using bigger wire.
The fuse and breaker sizes shown are approximate. Since transformer based (Outback Power, Xantrex) inverters usually have a much higher maximum surge rating than electronic based (Samlex, Exeltech, Statpower), they should always use the larger if more than one size is shown. The reason some show a smaller breaker size than fuse size is that breakers do not blow as fast on a temporary surge.
The fuse should NEVER be bigger than 125% of the maximum surge power of the inverter. For example, an inverter is rated at 1000 watts, and 1800 watts surge. For a 12 volt inverter, divide 1800 by 12, which gives you 150. 150 x 1.25 = 190 amp. The nearest standard size fuse is 200 amp. You are always safe going to a smaller fuse, but if too small it might blow on heavy loads. DC breakers should be rated for about the maximum amperage draw, as they have a slight time delay on over current.
Which inverter has the best sine wave?
In general, from best down, it is Exeltech, Outback Power, Statpower, Samlex. All are good enough for 99% of all applications, but the Exeltech may be better for low power critical applications, such as recording or studio vans, or noise sensitive medical equipment. For higher power systems that need the best sine wave, either the Outback Power series or the Xantrex SW+ series.
Which is the "best" inverter?
There is no "best" for all purposes. Although the Outback Power & Xantrex are considered by many to be the top of the line, it does not make sense to spend $500 to $3000 when all you need is a little Statpower Prowatt or Exeltech 125 watt sine wave to power up a laptop. The best way to decide on what inverter is best is to work backwards - figure out what you are going to use it for, and then find one that fits those requirements. Also, some inverters have built in chargers, which may be needed in some systems. The Outback & Xantrex sine wave units include software and hardware for remote generator start, alarms, remote control and monitoring, computer data, and other functions - in many applications this is very important. If you are running pumps or other large motors, Xantrex or Outback are the only one we will recommend, even though some others might work.
How does an inverter work?
Why are most inverters are 115 volts
What size wire, fuse, or breaker will I need?
What is an inverter?
An inverter changes DC voltage from batteries or solar panels, into standard household AC voltage so that it can be used by common tools and appliances.
Converters: What are sometimes called "converters", especially in the RV world, are actually battery chargers and/or DC power supplies. Why they are called converters in RV's and no place else we have not a clue. A "converter" is basically the opposite of an inverter.
Essentially, it does the opposite of what a battery charger or "converter" does. DC is usable for some small appliances, lights, and pumps, but not much else. Most systems should include an inverter of some type, even if it is just an el-cheapo $29 Walmart thing to run the TV occasionally. Some DC appliances are available, with the exception of lights, fans and pumps there is not a wide selection. Most other 12 volt items we have seen are expensive and/or poorly made compared to their AC cousins. The most common battery voltage inputs for inverters are 12, 24, and 48 volts DC - a few models also available in other voltages.
There is also a special line of inverters called a utility intertie or grid tie, which does not usually use batteries - the solar panels or wind generator feeds directly into the inverter and the inverter output is tied to the grid power. The power produced is either sold back to the power company or (more commonly) offsets a portion of the power used. These inverters usually require a fairly high input voltage - 48 volts or more. Some, like the Sunny Boy, go up to 600 volts DC input.
A few grid tie inverters can also be used with batteries, but there will be some loss in overall efficiency for feeding the grid. How much loss can vary considerably, depending on the inverter and the size and type of batteries. If you need battery backup power for a grid tie system, we recommend the Outback Power inverters, as they have the best efficiency with batteries - you will get about a 5-10% loss. With some older inverters, such as the Xantrex SW series, that can sell back excess power to the grid overall losses can be as high as 50%.
Back to Top
How does an inverter work?
An inverter takes the DC input and runs it into a pair (or more) of power switching transistors. By rapidly turning these transistors on and off, and feeding opposite sides of a transformer, it makes the transformer think it is getting AC. The transformer changes this "alternating DC" into AC at the output. Depending on the quality and complexity of the inverter, it may put out a square wave, a "quasi-sine" (sometimes called modified sine) wave, or a true sine wave.
Square wave inverters are usually only suitable for running some type of electrical tools and motors and incandescent lights. They are pretty rare nowadays, some of the old 1970's Triplite and a few others, and some old military surplus is about the only place you find it now.
Quasi-sine (modified sine, modified square) wave inverters have more circuitry beyond the simple switching, and put out a wave that looks like a stepped square wave - it is suitable for most standard appliances, but may not work well with some electronics or appliances that electronic heat or speed control, or uses the AC for clocks or a timer.
What May Not Run: Appliances that use electronics to control temperature or timers may have problems with modified sine waves. This includes anything - tool or appliance - that is variable speed, bread makers, some microwaves, some washers and dryers that use electronic timing for cycling. Most computers, TV's and similar items will have no problem. Anything with a motor will use about 20% more power with a modified sine wave than with a true sine wave.
Also, some of the chargers used for battery operated tools (such as Makita) may not shut off when the battery is charged, and should not be used with anything but sine wave inverters unless you are sure they will work. Sine wave inverters put out a wave that is the same as you get from the power company - in fact, it is often better and cleaner. Sine wave inverters can run anything, but are also more expensive than other types. The quality of the "modified sine" (actually modified square wave), Quasi-sine wave, etc. can also vary quite a bit between inverters, and may also vary somewhat with the load. The very bottom end put out a wave that is nothing but a square wave, and is too "dirty" for all but universal motor driven tools, coffee makers, toasters, and other appliances that have only a heating element.
One solution to the problem of a few small appliances not working well with modified sine wave inverters is to get a large standard inverter, and a small (such as the Exeltech or Samlex) true sine wave for use only with that equipment. This would also allow you to keep the small appliance (such as an answering machine) powered up without having to run the larger inverter full time.
Back to Top
Why are most inverters 115 volts?
Most utility connected homes in North America have dual AC voltages - 115 and 230. On a typical home there are three wires coming in - 115-neutral-115. It is 230 volts across the two outside ones. The 115 is used for most things, while 230 is used for water heaters, electric clothes driers, well water pumps, and air conditioning. Since these high-power items are not practical in a solar powered home, they are either not used or are replaced with gas appliances.
Most off-grid homes have little use for 230 volt AC power - but even so many newer ones are wired just like a standard home to meet electrical and building codes. If it IS required, you can "stack" two 115 volt inverters to get 230. The one exception to the above is that many AC well pumps are 230 volt. If the well pump is the only 230 volt item you have, the best choice is probably to get a step up transformer, such as the Xantrex or Outback Power 120 to 240 step up transformer.
There are export versions of most inverters for 100 volts, 105 volts, 205 volts, and 220/230 volts, in both 50 and 60 Hz.
Inverter-Chargers:
Inverters come in two basic types - with and without built in battery chargers. The ones with built in chargers are handy if you charge your batteries from AC, especially for RV's. They are also essential if using an inverter for setting up a UPS system for backup power. But not everyone needs them - and most small inverters under 1000 watts or so are simply not available with a built in charger.
Nearly all inverter-chargers made in the past few years have 3-stage chargers, so you can usually leave them powered up all the time. Nearly all inverters with chargers also have a built in transfer relay - what that means is that if you are running from AC or shore power, the power feeds through the inverter, with some being tapped off for the battery charger. If the AC power goes out, the inverter automatically switches to battery power. In most cases you won't even see a light flicker, it is so fast.
Inverter (and other) Efficiency:
Inverter efficiency is a question we get asked about a lot. The efficiency of an inverter has to do with how well it converts the DC voltage into AC. This usually ranges from 85% to 95%, with 90% being about average.
However, there is more to the story. Efficiency ratings are usually given into a resistive load (basically something like a light bulb or electric heater). When running such things as motors, the efficiency actually breaks down into two parts - the efficiency of the inverter, and the efficiency of the waveform. Waveform efficiency means that most motors and many electronic appliances run better and use less power with a sine wave. Typically, an electric motor (such as a pump or refrigerator) will use from 15% to 20% more power with a modified sine wave than with a true sine wave. When choosing an inverter based on efficiency, you should also consider what you are going to be running.
A 90% efficient modified sine wave inverter is not 90% when running a compressor motor, for example, because electric motors are less efficient. They use about 20% more power on a modified sine wave.
Inverters are also much less efficient when used at the low end of their maximum power. For example, using a 1000 watt inverter to power a 20 watt radio may actually be using 30 to 40 watts from the battery, as the inverter itself is eating up a lot just to run. Most inverters are most efficient in the 30% to 90% power range.
Back to Top
What size wire, fuse, or breaker will I need?
Inverters have two or three sets of power carrying wires to be concerned about: the wires from the battery to the inverter, the wires from the inverter to the home (or other AC load), and in some cases the wiring from a backup generator or other AC source. The wiring for the AC to the home and from the generator is sized just like you would for AC wiring in a utility connected home. It is usually #10, 12, or 14 standard AC wire. For the small inverters, 800 watts or less, #16 can be used but the mechanical strength of small wire leaves much to be desired.
The wire or cables from the batteries to the inverter are much more critical, and are often undersized. In some cases, the cable may be large enough to carry the "static" load of a motor, but on start up will drop so much voltage in the cable that the inverter will shut down on low voltage cutoff. The same thing can happen with small inverters and TV sets - a TV may only use 100 watts, but the start up surge may be 300 watts for a few seconds. Wire lengths from the battery should always be kept as short as possible, but not so tight that there is a strain on the connections.
Recommended Fuses, Breakers, and Wire Sizes for Inverters
Inverter Watts Inverter DC voltage Input Fuse/Breaker DC Wire Size
Minimum !
50-150 12 20 amp 12 to 14
200-250 12 30-40 amp 8 to 10
300-500 12 50-60 amp 6 to 8
600-1000 12 110 amp 4 to 6
1100-1500 12 200 amp/175 bkr 2/0 to 2
1100-1500 24 110 amp 2/0 to 4
1800-2500 12 300 to 400 amp/250 4/0
1800-2500 24 200 amp/175 2/0
2600-3600 24 400 amp/250 4/0
4000 24 400 amp/250 4/0
4000 48 200 amp/175 2/0
5500 48 200 amp/175 2/0
These are the recommended cable sizes for a ten-foot distance from the batteries to the inverter. Note that the larger wire size is the recommended, the smaller wire size is the absolute minimum for safe operation. The sizes recommended are from a combination of maximum wire amperage capacity and voltage drop. You can't go wrong using bigger wire.
The fuse and breaker sizes shown are approximate. Since transformer based (Outback Power, Xantrex) inverters usually have a much higher maximum surge rating than electronic based (Samlex, Exeltech, Statpower), they should always use the larger if more than one size is shown. The reason some show a smaller breaker size than fuse size is that breakers do not blow as fast on a temporary surge.
The fuse should NEVER be bigger than 125% of the maximum surge power of the inverter. For example, an inverter is rated at 1000 watts, and 1800 watts surge. For a 12 volt inverter, divide 1800 by 12, which gives you 150. 150 x 1.25 = 190 amp. The nearest standard size fuse is 200 amp. You are always safe going to a smaller fuse, but if too small it might blow on heavy loads. DC breakers should be rated for about the maximum amperage draw, as they have a slight time delay on over current.
Which inverter has the best sine wave?
In general, from best down, it is Exeltech, Outback Power, Statpower, Samlex. All are good enough for 99% of all applications, but the Exeltech may be better for low power critical applications, such as recording or studio vans, or noise sensitive medical equipment. For higher power systems that need the best sine wave, either the Outback Power series or the Xantrex SW+ series.
Which is the "best" inverter?
There is no "best" for all purposes. Although the Outback Power & Xantrex are considered by many to be the top of the line, it does not make sense to spend $500 to $3000 when all you need is a little Statpower Prowatt or Exeltech 125 watt sine wave to power up a laptop. The best way to decide on what inverter is best is to work backwards - figure out what you are going to use it for, and then find one that fits those requirements. Also, some inverters have built in chargers, which may be needed in some systems. The Outback & Xantrex sine wave units include software and hardware for remote generator start, alarms, remote control and monitoring, computer data, and other functions - in many applications this is very important. If you are running pumps or other large motors, Xantrex or Outback are the only one we will recommend, even though some others might work.
Subscribe to:
Posts (Atom)
visitors
