Multiplus / Axpert playing together


We have a Multiplus 3-24 working powering an off-grid home with 1800W of PV (6 panels), a 150/60 MPPT and a Freedom Lite 5/4 battery.

I also have a redundant Axpert MKS Plus 3/24 with 4 Trojan T105s and 3x250W panels that was only used as backup in another home

Sometimes at the off-grid home we need to use a generator to charge the batteries a bit if solar output is down or if we want to run a large load. I was wondering if I could hook up the Axpert and feed the Multiplus with that full-time on the AC-in? If I added 3 more panels to the Axpert it would increase the total PV power substantially. Would the Multiplus be able to assist and power loads in excess of 3kW if it can pull eg 10A from the Axpert?

Hi there Kari (my ex-colleage :slight_smile: ),

I would not use power assist or ESS with an Axpert upstream. The Victron inverter feeds energy backwards into the AC source in these cases, and if you feed power back into the Axpert (even for a second or so) it will either raise an error because the High voltage DC bus went too high… or blow its IGBTs.

What you can do is connect the solar panels and the battery of the Axpert (but leave the inverter off). As far as I know (I am no expert on the axpert… hehe), the solar charger still works in this case, so that will allow you to use the MPPT in the Axpert to charge the batteries or for the Quattro to power loads.

Of course VRM and the GX device will not see the PV produced by this arrangement, but the FreedomWon battery does its own current measurements and SOC, so you shouldn’t see any SOC drift. If you turn on the DC loads option on the GX device, it should even show the DC power coming in from the Axpert.

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As @plonkster has said. I would add the Axpert to the battery bank and use it when you have appliances you want to run… I think the Axpert will charge with solar while the switch is off…
You could get extra techy and add a automation between the relay on the Victron and the switch on the Axpert to switch the inverter on automatically… but that’s another discussion.

So are you suggesting I connect the Lead Acids to the DC Bus in parallel with the Lithium? Would the charge voltages not be too different? Or would you not use them at all?

Can a generator handle power being fed back to it?

@karischoonbee No sorry. Definitely not… !

Ignore the Lead Acids and just add the Axpert to your lithium bank. I assume you have a DC Disconnect? The Axpert then comes off the same side of the disconnect as the Victron. Your cables size would need to be checked as well as the fuse size in the DC disconnect. You also don’t want to try and draw to much from the battery.

Hope this helps.

PS: Any chance you have a photo or 2 of the setup and also the cable sizes, etc

Yes and no. Put both of them on the 24V lithium bank. Forget the Lead acids. Leave the PV modules connected to the Axpert (for extra charge power), but leave the inverter off and the AC side disconnected.

Set them to be the same. Of course there are always subtle calibration differences which means that as the battery approaches the set voltage, one of the chargers will tend to stop first. That should not really matter… if one charger can keep the voltage up on its own, chances are the loads are not using that power and the battery is close to full anyway.

Curious, you still with the same company or moved on in the mean time? :slight_smile:

Oh no, moved on about 2 years ago. :slight_smile: Thanks.

I think it may be better to rather use the Axpert on it’s own and move some of the loads to it.

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Hi Kari

Hope I didn’t scare you off the Axpert addition. I think it will work well and having the extra power when the batteries are well charged and the sun it out would be great. The extra MPPT would also be a bonus to get your batteries charge faster. Izak can maybe back me up (or not :wink:)

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I suppose it depends what’s the bigger need. She said sometimes there are loads that exceed the 3kVA of the Multi, and it would be nice if one doesn’t have to start a generator for that (or at least, that is my take on it). Adding an extra MPPT with some PV (even if that MPPT is packaged inside an Axpert case :slight_smile: ) doesn’t really help with that problem.

The trouble is simply that the Axpert doesn’t expect a “generator” to be on its output. I’ve got a Multi on a Multi in my home (by accident, the house is backed up, and the test bench happens to be on the backup side) and that kinda works even during load shedding, but 1) I’ve heard it make some interesting noises at times, 2) I’ve seen it give up because the upstream Multi doesn’t make a clean enough signal, 3) the Multi is an old-school low-frequency design with a big old transformer buffering things from each other, while the Axpert is a more modern HF design with a high voltage DC bus and little in the way of a cushion…

I’m not suggesting a Series inverter setup. Just adding the Axpert in Parallel off the same bank.

You then switch on and run the extra load off the Axpert when needed. Gain the extra PV and leave the Genny on the Multi when you need the loads during low battery periods… the exception hopefully.

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