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.
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
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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.
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.
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).
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
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.
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
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.
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 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.
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.
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/
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Created 26th December 2003 - Last updated 18 March 2008