question

mattyb avatar image
mattyb asked

Multiplus and MPPT combining currents

Hi all, I live in an off grid cottage and use a generator to charge my battery bank through a Multiplus 24/2000/50. I also fire up the generator to use high power appliances like power tools and washing machine etc.. I want to get started with solar but the question that really bugs me is this:

What if I start my generator while my batteries are already being charged by the solar array? Will the charge currents from the generator and the solar array add together and potentially overcharge the batteries?


Is this a stupid question because I can't find an answer anywhere? What is the ideal wiring setup for this system, keeping it as simple as possible?


Many thanks


MPPT ControllersMultiPlus Quattro Inverter ChargerGenerator
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3 Answers
JohnC avatar image
JohnC answered ยท

That'll work fine Matty. They won't overload your batts, they'll both continue to charge your batts to a target V. One will tend to 'override' the other depending on the target settings of each, but that can be fooled with. If you're not watching you wouldn't even know.

Just wire the solar input to exactly the same place your genny feeds the batts.

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Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ยท

Hi Matty,

Your thinking is correct. It is possible for the solar current and the generator current to combine.

This can lead to issues, such as overloading battery fuses, IF you batteries accept the combined currents.

What is likely happening instead (as John C mentioned in his answer) is that the additional current will also raise the voltage, and this will lead to both chargers backing off the current to keep the voltage to it's target.

It is possible to limit the combined charge current of the two devices, while having each still maintain its full potential individually. It is the Distributed Voltage and Charge Current (DVCC) feature, and it is an option when both the inverter/charger and the MPPT solar charge controller are connected to a GX Venus-device.

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mattyb avatar image
mattyb answered ยท

Hi guys, thanks so much for your quick responses that's brilliant.

I had guessed that the Venus or CCGX would have some way of addressing this, but I wanted to avoid these, partly on account of cost, but mainly because I'm trying to keep it simple and the venus doesn't look like it will help in that respect!

I was planning on using the bluetooth dongle and smartsolar for monitoring everything, I suppose if i'm worried about overcharging I could just flip an isolator switch from the panels while the genny is running? That sound reasonable and safe?

Thanks again for your help, can't tell you how much I appreciate it!

5 comments
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Yes, that is a common and simple solution, to turn off the solar panels. Though, regularly disconnecting DC supply under current will eventually burn out the isolator contacts.

Another option is to turn off the MPPT charger with the software switch inside VictronConnect.

If it's possible, leave some space for the possible future addition of a CCGX. Once you are most of the way into Victron with an MPPT and Multiplus, it is a great addition.

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mattyb avatar image mattyb Guy Stewart (Victron Community Manager) โ™ฆโ™ฆ commented ยท

Awesome, thanks Guy

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tylera avatar image tylera Guy Stewart (Victron Community Manager) โ™ฆโ™ฆ commented ยท

@Guy Stewart (Victron Community Manager), When I turn off the MPPT via the software switch, there is a warning about "This is intended for maintenance purposes". Is there anything bad about using this switch? Is that the best way (vs a shut-off switch on the PV side).

[My boat builder installed a BlueSea switch to shut off the panels, I hadn't realized using this would be problematic.]

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Hi @TylerA,

Using the switch that was installed by your boat builder may not be problematic, it would depend on the design, rating and loading on the switch. Could be totally fine and outlast the rest of the components.

It is also fine to use the software switch. I don't know of anything bad about using it. Except forgetting to turn it off/on again.

It is hard to say definitively what is the best for any particular installation. It is best to understand the behaviour, limitations and requirements of the equipment and the operator.

The best for me personally is maximum information, and minimal necessary interaction/effort, so the GX device control using DVCC is best.

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tylera avatar image tylera Guy Stewart (Victron Community Manager) โ™ฆโ™ฆ commented ยท

Thanks @Guy Stewart (Victron Community Manager) ,

My actual use case is going to be even more complicated than the boat builder intended. I have a 48V bank and 24V bank of batteries, and one solar bank. I'm manually rewiring it between them and reconfiguring the MPPT (lots of room for error here), because based on certain conditions, I'd rather have it on the 24V or 48V batteries.

I think I'm going to buy a second MPPT and just have a switch that directs the PV input to one MPPT or the other based on where I feel it would be best. I was concerned that having such a switch would be a problem when I read your response initially. :/

The switch is a standard non-sparking switch rated at 300A (well above the 35A MPPT)

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