earl0101 avatar image
earl0101 asked

Why is the multiplus not utilizing a generator fully?

Recently I purchased a small Honda generator with Bluetooth (this allows one to monitor output) to support use of an air conditioner. The generator feeds into the multiplus which then feeds the circuit panel with one breaker dedicated to the air conditioner. The generator is rated to a steady state value of 15A*.

When the batteries are at 100% this works as expected and the generator consistently produces ~1600 VA. This appears to be close to what the air conditioner needs with both the fan and compressor on.

However, when the batteries are as some lower level, say 50%, this doesn't happen in steady state! Initially, yes, the generator produces ~1600 VA. but that doesn't not last too long. In one case it maintained ~1600VA for an initial 10 min or so but then it suddenly reduced to some lower level (~1400 VA) even though the air conditioner was running fully! With insufficient generator output the Multi pulled from the battery to meet the air conditioner demand which I learned after the fact. A very undesirable situation, particularly when the battery is already at a low SOC!!!

In the case where I caught this happening I used the Digital Multi Control Panel to turn the multi to "charge only" for a few seconds and then back to fully on. I found doing so caused the situation to somehow reset and the generator went back to producing ~1600VA temporarily.

Obviously, what is desired (and what the manual suggests) is that the multi itself keeps the generator at maximum output and any extra energy above the current usage is used to recharge the batteries (i.e. when the compressor cycles off).

What is going on here? How do I prevent this behavior going forward? I'd like to be able to trust that the generator is utilized to it's maximum and no power is unnecessarily taken from the battery.

* Note: I am using a Digital Multi Control Panel which is set to a current limit of 16A. After some experimenting I found this value prevents the generator from overloading and shutting off.

** To get around this issue I did consider using the Multi Auxiliary AC output. However, I hesitate to wire this directly to the air conditioner as that would bypass the distribution panel and the 20A breaker protecting the wire to the AC. I don't have space for another box to house a separate breaker.

2022.05.10 MultiPlus configuration.pdf

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Matthias Lange - DE avatar image Matthias Lange - DE ♦ commented ·
What batteries and capacity?
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earl0101 avatar image earl0101 commented ·

Hi Matthias,

Batteries are the Lion Safari UT 1300 -- four 105 Ah Lithium Phosphate Batteries in parallel so ~420Ah. According to the Lion technical person I talked to, they can be charged at 100A each. That is, 400A total but I've never tested that.

The generator is a Honda EU 2200i. I checked and the steady state power rating is 1800VA with 2000VA peak! With less than 100% batteries remaining the goal is to have the Multiplus running the generator at a constant 1800VA with any unused power going to charge the battery.

The battery bank is connected to the Multi using ~4' of 4/0 AWG cable (rated at 440 Amps). Within the bank, the batteries themselves are chained (positive at one end and negative at other end) in parallel with 2/0 cable.

Air conditioner is wired with a soft start box.

Note from the attached configurations file that UPS function is ON and dynamic current limit is OFF. However, I have not experienced any issues with the generator dropping out... it is just reducing power output.

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3 Answers
kevgermany avatar image
kevgermany answered ·

Have you configured the correct charging parameters in the multi? These need to come from the battery suppliers, if you're using the default preinstalled multiplus settings.

Another cause may be temperature. Multi will downrate to prevent overheating if necessary.

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earl0101 avatar image earl0101 commented ·

Thanks. There are so many variations but, yes, for my situation I believe so. I did contact both the battery supplier and my Victron rep to settle on the charging parameters. In particular, Float and Absorption at 14.2V since I have lithium was the consensus.

Two key Parameter decisions are UPS function ON and dynamic current limit OFF. Since my generator does not shut down I don't believe I need to turn UPS off. Dynamic current limit doesn't seem to be an issue in this situation because there is no sudden load increase. The air conditioner remains on throughout and I'm sitting outside so no other loads could have been added or subtracted.

Overheating could be a possibility but I have run the air conditioner completely off battery and it worked fine. This was before I got the generator ... tt just draws down the battery very fast!!

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JohnC avatar image
JohnC answered ·

Hi @Earl0101

This is possibly a Power Factor thing. You could test to see what happens if you tick Weak AC Input (a known PF fiddler). Your aircon possibly guilty, and that may change too depending on what 'mode' it's in.

In the washup, your genset is too small to do what you expect. All you can do is experiment with settings to get the most from it. I'd tick DCL and untick UPS functions, which will soften load changes and help keep the genset from tripping.

The aircon will still need a certain W (real power) to function, the VA ends up wherever. This is mine right now with a tv, pc and maybe fridge.. (207VA).. 1670817350731.png

1670817350731.png (6.1 KiB)
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earl0101 avatar image earl0101 commented ·

Interesting thought about Power Factor. I'm not sure what this means for the Multi in practice though. What/where is the "Weak AC Input" item in the settings? Is this related to Dynamic Current Limit?

I can't agree with the conclusion that the genset is too small. It works perfectly fine and and as expected when the battery is 100%. Moreover, the air conditioning load is not too great for the generator (particularly as I have a soft start) as I can bypass the multi completely and it will work in steady state; this was tested with no other loads present.

Even when the battery is at 50% the problem is under-utilizing the generator. This all suggest it's not too small. After all, one of the best things about the Multi with a battery bank is precisely that one does not need to size the generator for the largest load expected (as explained in the FAQ and other website locations). Keep in mind, with the current limited via the multi control panel, the problem is not a generator overload. That simply is not happening here.

In the end I suspect I'll have to live with what I get. It's very frustrating though for someone like me who has a Ph.D. in engineering (UCLA) and over 40 years of experience. I'd really like to understand why this is happening. My biggest complaint about Victron has been the lack of comprehensive public technical manuals explaining full functionality as well as the various setting options in detail. The few videos and the available documentation I've found have helped a little but are completely inadequate for something as complicated as a Multi. I appreciate this community and it's wisdom when available but I'd hate to think the only way to really learn about the multi is by others with experience and experimentation. There must be more, if only for Victron to train regional representatives! I'd sure love to get my hands on that.

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JohnC avatar image JohnC ♦ earl0101 commented ·


The Weak AC Input is actually shown in the link you provided. Not directly related to DCL, which I recommend for all genset users. DCL just winds up the load on the input a little more slowly to give the genset time to open it's throttle. (The mechanical weakness amongst the electronics). This only takes seconds, and Power Assist covers the applied loads while it's winding up.

There's some basic info on genset issues here..

While there take a look at the recommended genset sizes. I'm not entering into an argument about that, but the reason you've posted this question is seemingly that you're bouncing between the limitations of an undersized genset. Of course it will still work, and hopefully serves you well. But you perhaps expect too much, and a poor PF load can make it hard to decide on settings when limitations arise in all directions.

Re technical info, the Victron website has masses of it. This article is pretty old, and predates modern consumer inverter-regulated gensets. But it might open your eyes when you see the sinewave shapes generated by even expensive gensets. The downstream Victron kit has to deal with that..

For training, head to Victron Professional. Signin needed, but they won't say no.

Experience helps too. I'm still learning from mine. :)

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earl0101 avatar image earl0101 JohnC ♦ commented ·


Thank you. I do now see the Week AC input selector under the Charger menu. I'll need to repurchase the VE.Bus to USB to fiddle with that setting.

Indeed, I've spent many many hours and days scouring the web and Victron's website and have found good bits and pieces as well as great nuggets of information. The multiplus FAQ link you provide is one that I did read (noting with care the qualification text that explains the sizing table). I appreciate the link to the marine generator test report. It looks very interesting and I'll certainly read that. I'll also try finding and signing into Victron Professional ... that could be great as I have other lingering questions that my Rep couldn't answer (i.e. the issue with the Lithium battery selector and fusing for AC out 2).

Again, thank you for providing your viewpoint.

In the end, the multi is an extraordinarily powerful machine with so many options that I suspect there really are a very limited number of folks who really understand it completely. For most folks it suffices to use it as a black box... it's just in my nature to want to know more. In engineering there are always trade-offs and knowing these helps one to extract the most from a design. :)

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Michelle Konzack avatar image
Michelle Konzack answered ·

I have the same issue with a MultiPlus-II 24/5000/120-50 recently bought, when I connected a professional KOHLER Generator which produce constant 4800W (NOT VA).

The MultiPlus was charging my 24V 2940Ah batteries (I am Off-the-Grid in Estonia) with 149A (I expected only 120A) and the load on the Generator was 3800W approximately.

The MultiPlus-II was setup to draw only 20,9A from the Generator but when I switched on some devices, I nearly killed the Generator (it made an overload noise and the speed went down)


The MultiPlus-II switched from Charging into Inverter modus and tried after a minute to go hack into Charging, but again it failed.

Since the Power of the Generator was not fully used, I tried a LEAB ABC2430 on AC2 output of the MultiPlus-II which should work but again, when the charging current of the LEAB increased, the MultiPlus-II switched to Inverter mode.

My conclusion is, that the MultiPlus-II if in charging modus suck 3,8kW out of the KOHLER, but more then 4400VA.

When I used the LEABit suck around 770W, but more then 1100VA!

The 4570W would have been no problem, but the 5500VA.

Is there a solution for this issue?

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JohnC avatar image JohnC ♦ commented ·

Hi @Michelle Konzack

Maybe not a 'solution', but gensets need to be 'understood' to get the most from them. They don't produce power like the grid does, as grid has a massive backup buffer.

So you say your genset is rated 4800W. That's likely the engine power rating (true power). So you've set the Input Current Limit to 20.9A to match that. Absolutely full-throttle rating in laboratory conditions - and then you might feed it some old fuel and hit it with full load while it's still warming up. Back off on the 20.9A setting until you see what it can actually produce in your real world.

Broadly speaking, gensets are rated in VA because the actual generator head is sized larger to accommodate poor Power Factor loads (no grid to buffer them). So VA rating is often a good deal higher. Yours should be stated somewhere.

And the real quality of a genset may well boil down to it's Voltage regulator. Some just don't cut it. Voltage sag, etc, that the Multi may reject.

Look also at Dynamic Current Limiter, among other things here..

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Michelle Konzack avatar image Michelle Konzack JohnC ♦ commented ·

The KOHLER genset is rated 4800W and 5500VA, BUT the engine is a 8,2kW Type. It is not one of the small consumer gensets, but a high performance professional one. The fuel is Bensin 98 just freshly bought from the Alexela petrol station and rated for -26C.

Since I have the KOHLER genset a second time, because my Battery Bank is to low and the MultiPlus-II does not deliver enough power, I see that the KOHLER genset deliver 250V and not only 240V or even 230V.

The MultiPlus-II deliver 239,2V if in Inverter Mode

I have now set the current to 19A and get

250V x 19A = 4750W

It seems, because it is a PRO genset, the Output Voltage is higher the usual (230-240V) because in most worksites you have long extension cables hence forced losses. My cable is a H07RN-F 3G6 with 10m lenght and 32A CEE connectors where I will have virtually no losses even at 32A.

It seems, the high Output Voltage of the KOHLE genset is the real reason.

Appropos warming up:

I put on the ACin Socket a Delay-On Relais which support the 32A Input current and it starts, when the ACin Socket get power and wait around 3min before feedin the power to the MultiPlus-II, which mean, I have not to program the relais in the Multiplus for it.

Thanks for your Help


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JohnC avatar image JohnC ♦ Michelle Konzack commented ·

@Michelle Konzack

My little examples with the 'fuel' and such was just me indicating what might happen in the real world. Good you have those under control.. :)

You mention this.. "250V x 19A = 4750W". If those figures come from the Multi itself then they'll be real W. If from somewhere else then they may be VA. Just something to keep in mind.

Not sure what you mean by the high V being a problem. If it's so that you'd need the 19A to keep under the rated 4800W then, ahh, just maybe. Gensets aren't usually that picky and often have short-term higher allowances. Always good practice though to start low and creep up with your settings to find that practical limit.

Your next challenge is to throw onto the Multi (while charging) a nasty load like an electric motor and see what happens. Especially between W and VA.

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