Input Current Limit MultiPlus-II

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jbakuwel asked Mar 15, '21

Input Current Limit MultiPlus-II

Hi all,

I am wondering if anyone knows what happens when I:

disable PowerAssist (it has to be disabled so the Input Current Limit can be lower than 3.9A for a Multi)
set the Input current limit of a MultiPlus to say 2A
switch on a 10A load on the AC-out

I'm looking into ways to dynamically adjust the power take from an external power source between "as low as possible (0A would be great, but 1A will do too)" to 20A.

Would the MultiPlus supply 8A from the batteries and 2A from it AC-in in my example above? Or would it trip with an overload?

Jan

Multiplus-II current limit input current

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Answer 1 · 2021-03-16T18:21:13Z

Alexandra answered · Mar 16, 2021 at 06:21 PM

@jbakuwel

The lower current limit is affected by the firmware loaded on it.

https://www.victronenergy.com/blog/2018/04/20/multiplus-quattro-inverter-chargers-improved-current-limits/ not sure if you read this article?

https://www.victronenergy.com/live/multiplus_faq#powerassist

If you disable power assist then it will pull sudden loads from the grid source not assist from the battery bank as power assist is designed to do. A small video demonstrating power assist https://www.youtube.com/watch?v=MEF7X1gPPzw

You will only overload if you exceed your battery or inverter capability.

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Answer 2 · 2021-03-16T20:50:42Z

jbakuwel answered · Mar 16, 2021 at 08:50 PM

Hi @Alexandra,

Thanks for getting back to me. I have read the article. The minimum current limit for the MultiPlus 5KW is 3.9A with PowerAssist enabled. You can go lower with PowerAssist disabled. My use case is a "reverse" PowerAssist: the Multi needs to provide the bulk of the power at all times. Depending on a number of factors, there's also a "bit" of power available from an external power source which I would like to dynamically regulate, if possible between 0 and 30A.

I don't know what happens when you disable PowerAssist, yet have a (limited) power source connected to AC-in. From what I've read and heard in various places the Multi will engage the relay, ie. connect AC-in with AC-out. In other words, the power source on AC-in will power the loads - to the maximum set by the limit. I hope that, despite the fact I have just told the Multi not to assist, it will provide power to AC-out as well to supplement what the limited energy source on AC-in cannot provide.

Jan

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Alexandra ♦ commented · Mar 17, 2021 at 04:03 AM

@jbakuwel

Are you using virtual switch or other programming? From what i understand from how you are explaining it you are wanting more of an island mode. To use the grid only under certain circumstances?

The purpose of power assist is to keep the inverter switching on the bigger loads instead of using the grid. That is what was demonstrated by the video i linked in the previous reply.

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jbakuwel Alexandra ♦ commented · Mar 17, 2021 at 06:50 AM

Hi @Alexandra,

Yes, I understand that. This is indeed an off grid system. If it would work, I could choose to connect the AC-in to an external power source that has variable capacity. With PowerAssist enabled, the minimum is 3.9A (almost 1KW), which is a bit much for that external power source. What I need to know is what happens when PowerAssist is disabled, there is a external power source connected to AC-in, the Input Current Limit is set to lower (or much lower) than the loads that will be on from time to time on the AC-out.

Best regards,
Jan

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Alexandra ♦ jbakuwel commented · Mar 17, 2021 at 03:38 PM

@jbakuwel

What will most likely happen is the power source you are using is perceived as week, the multi will disconnect itself from the source.

If the source you are using is able to provide a good sine wave under load then you should be fine.

What i have experienced when using a generator that is underpowered is exactly that.

Had tried it with power assist off and dynamic current limiter unchecked. No virtual switch, no other assistant set either. Had enabled high frequency range and voltage range acceptance, ups unchecked no grid code set. but always found the source would be disconnected when higher loads came on. Sometimes it would reconnect after but often i had to jimmy it back on repeatedly.

Even with the minimum of 4amps set.

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jbakuwel Alexandra ♦ commented · Mar 17, 2021 at 07:56 PM

Hi @Alexandra,

The external power source could deliver more power - but I have my reasons for not wanting it to. In other words, it will generate a nice sine wave also under load. So ... for the sake of argument assume that the grid is connected to the AC-in, PowerAssist is disabled and the Input current limit is set to 1A. Then a 10A load on the AC-out is switched on. Will the Multi happily take 9A worth from the batteries and limit itself to taking just 1A from the AC-in?

Note I want to go below the 3.9A limit that applies when PowerAssist is enabled, hence the need to disable it.

Jan

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Alexandra ♦ jbakuwel commented · Mar 17, 2021 at 08:19 PM

Hi @jbakuwel

I think you are going to have to experiment for yourself on this one. We could all take guesses all night and still may be wrong as every set up is unique.

What happens when a load switches on is determined by more than just those two settings. from what I have seen it still tries to do a form of power assist even with it disabled. But with it enabled works harder to keep the limit set.

This I have seen is affected by what load type switches on, for example a heating element and a pump have different effects. So does resistance in cabling and setup. And also if the battery is trying to charge off the source as well.

If it is easier for power to come in from one source it will pull from there first then work to the setting you want as you would have seen in that video linked in previous comments.

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jbakuwel Alexandra ♦ commented · Mar 17, 2021 at 08:26 PM

Hi @Alexandra,

Sure can do experiments :-)

However I was (am :-) ) hoping someone either knows (guess that's Victron staff) or someone has tried this already. I'm in the planning stage for this system and am reviewing various options.

Thanks for your time and help!

Jan

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Alexandra ♦ jbakuwel commented · Mar 17, 2021 at 08:30 PM

@jbakuwel

https://community.victronenergy.com/questions/66672/min-shore-current-limit-with-power-assist-off.html

There are quite few threads on this forum about switching off power assist, the answer from Guy Stewart you may find interesting

Limitations of the input limit are more about the way the Victron detects the current in and that really is what affects the way things work on ac in

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jbakuwel Alexandra ♦ commented · Mar 17, 2021 at 08:51 PM

Hi @Alexandra,

Thanks for that link - I hadn't seen that one yet.

It also answers the question: what I'm trying to achieve (a kind of reverse PowerAssist) is not possible. Back to the drawing board!

Best regards,
Jan

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jbakuwel jbakuwel commented · Mar 29, 2021 at 02:02 AM

Hi @Alexandra,

Just to share a thought with the community here as it might be interesting for others too.

I'll look into the feasibility of using ESS on the system that has the AC in. The external power source is reliable and always present, but as mentioned I need to regulate how much power can be drawn from that. Considering the external power source as "the grid" and using ESS might be the perfect solution in this case.

cheers,
Jan

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