question

Size of generator to charge batteries

I am having a 10kw victron solar system installed part of this system is 2 x 5kw inverter chargers. Type Multiplus 48/5000/70-100, I already have a 6kw back-up auto start generator, I am informed that I need a minimum of 12kw or best to have a 15kw generator? the 6kw generator will not sufficient for load and charge. Any load in principle would be intermittent and indeed most likely be around 4kw even when intermittent. It is possible with some inverter/charger units to utilise the inverter Gen Support function and its on-board charger, so a smaller generator set can power loads (in this case 6kw generator) and provide some charging via the inverter, example if the water heater (1200w) switches on by its thermostat to maintain water temperature for say 15 to 20 minutes the inverter then throttles back off from charging. I am really stuck with answers to this issue. Any help would be very much appreciated

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Hi, what you call Gen Support is what we call PowerAssist, and I think its might be fair to say that we invented the feature for this market. (!). So yes; normally there is no need for a large generator.

I dont have time to help with all calculations (anyone, please help Peter); but, I would be surprised if you’d need a generator thats of higher capacity than your inverter/charger pack (10kVA).

It’s nicely explained here:

https://www.victronenergy.com/blog/2016/08/29/multiplus-magic-small-generator-big-power/

Considerations to that I can think of that define the generator size are:

- minimum input current limit (generator must be able to supply at least that)

- time to charge: take generator capacity, substract average load by consumers, and then you’ll have the available power to use to charge the batteries. Take ~15% out in losses in the charger, and now you’ll have the power that can go into the battery. Now, find out how much energy needs to go in, divide that by the power, and you’ll have the charge time. If too long, take a larger generator (or add solar instead of investing in a new generator).

- perhaps there are more considerations; I’m sure someone else here doing these calculations daily can chip in.

Success!

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Hi Peter. I too have a single 48/5000/70 (not 2x, so I don't quite know how to deal with that). But I have a CCGX, which has a setting to tell the Multi to limit genny input. If you don't have a GX box then perhaps you should?? Yeh, of course it works.. :)

An ongoing issue I have is that my Multi is very picky about accepting dirty power. Not blaming Victron for that, I just had to go through the VEConfigure settings to fix it. Right to the ultimate point of telling it to "Accept Dirty Power". That seemed to come with a downgrading of amps, below the GX setting, but still ok for me so I left it. Not sure if it's meant to do that.. Older Yamaha 6600 (AVR).

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Thanks John will check this out. Appreciate any help that anyone can give me.

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