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Alistair Warburton avatar image
Alistair Warburton asked

Bat temp OK, charge still limmited...?

Hi folks,

I cant get my battery to charge at more than about 2kW and I cant see why... Obviously missing something?

Small genny, circa 5kW on AC1. AC current limit set to hold that at 19A, circa 4kW, and working. Gen is a recent upgrade, previous unit was smaller.

Putting a 2kW load on results in circa 1.5kW charge whilst running the load, genny a tad over 4kW.

Dynamic limit is off, Weak AC is on - hence the losses I assume.

Bat will not charge above 2kW and typically hovers at 2kW+/- 80W, which looks suspissiously like a limit of some sort.

Easy solar so Multypluss 48/5000/70.

BYD 13,8kW (Temp mainined at 15C min)

Clearly I am missing something and would apriciate somone pointing out what Iam doing wrong or failing to apriciate.

Cheers,

Al

Lithium Batterychargercharge current limit
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7 Answers
JohnC avatar image
JohnC answered ·

Hi @Alistair Warburton

Try turning off 'Weak AC' if you can get away with it.

See also this thread and my answer there: https://community.victronenergy.com/questions/67792/generator-not-charging-batteries.html?childToView=67797#answer-67797

This fellow doesn't say re Weak AC, but you'll likely see similarities with your issue (and mine).


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Alistair Warburton avatar image
Alistair Warburton answered ·

I tried 'Weak AC' Off but it then has issues maintaining sync, or even recognising AC for that matter. When it connects, usually after a couple of attempts, it will drop out again when the passthrough load alters.

Its a little better with Wide VF on but to be honest I have mucked about with several combinations of settings and nothing seems to give a charge above kW

Wide and UPS are currently OFF, Weak is ON

Theoretically

Al

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Justin Cook avatar image Justin Cook ♦♦ commented ·

@Alistair Warburton, I'm in the US so I'm not familiar with these units in particular, but I know that they do ship with the default charge rate set to 100% (in this case 70A)... is there any chance that the charge rate was dialed down at some point during installation? With your reported AC draw for charging, it looks like the charge rate is roughly 50% of max, so I wonder if that was just -inadvertently or otherwise- dialed down from the default setting.

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Alistair Warburton avatar image Alistair Warburton Justin Cook ♦♦ commented ·

Odd you should say that... I noticed a post from somone else asking about VRM data reporting but the example shown had a charge rate almost exactly at 2kW...

The example was a 24V system, same multi bar the voltage, so circa 70A and I cant help thinking that perhaps the limit is in some way 2kW as opposed to 70A @ 50 odd V on my system

I cant find a setting that expresses that mind you.

The BMS, in the BYD enclosure, is supposed to be driving the two chargers, Multi and solar, using their external control option via the CCGX. This is definatly a current limit but probably also influences voltage. Not sure about the working inner speciffics, cant find info on it. Setup suggests setting limits, as a backstop, for the BMS which is acyually managing things.

2kW +/- 80W seems too humanly rational to be a coincedence. especially as it is, as you say, circ 50% of the theoretical maximum for a typical 48V pack in bulk with 70A charge limit...

Its all a bit odd and costing me LPG right now, no sun... I need the genny at 80%-85% not 50%

Cheers,

Al

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JohnC avatar image JohnC ♦ Alistair Warburton commented ·

@Alistair Warburton

Just for fun, I went back to a stable spot on my VRM graphs to do a 'power balance' on my Multi. The results (AC expressed in VA):

AC Input (generator, not limited by input/charge settings): 2853 VA

AC Loads: 90 VA

So, net available for charge: 2763 VA

DC Charge Current (in Bulk mode, trying hard): 1748 W

To keep it simple, let's ignore possible sampling time/accuracy discrepancies, efficiency losses, etc.

That's a 63% yield, only explainable by Power Factor. And we know that 'Weak AC' fools with that do do whatever it does.

I know too that I have used a inverter generator with no Weak AC selected, and that de-facto charge limit doesn't apply.

My conclusion is that the Multi's charger can't deal with that much doctored power. It's just enough for me, so I'm not complaining. Just sayin'.


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Alistair Warburton avatar image
Alistair Warburton answered ·

I would like to clarify what is actually going on...

I anyone knows what limitations the charger has please feel free to let us know or point to a spec. Anticipate conversion loss and and limits based on power quality woud be nice as a start...

It cant just be an efficiancy thing or I would be seeing just shy of 4kW on the DC whilst the genny was loaded up well beyond that.

Interestingly I do see 500W-600W of 'losses', when looking at reported power which I attributed to power factor. Although now i think about it I dont actually know if that figure is W or VA in actualiy.

I suppose what I am getting at is that I dont know much and feel that I need to...

Any and all help would be apriciated, I am struggling to believe that I/We are the only two folk seeing this or even that it isnt documented somwhere!

Cheers,

Al

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Alistair Warburton avatar image
Alistair Warburton answered ·

Just a quick update... I have been fiddling.

'Weak AC' is defiantly introducing a hard limit at about 2kW into the battery.

Turning it off introduces loads of noise into the control loops for both battery and generator current and the oscillation eventually upsets the 'system' enough to cause the charger to drop out.

I managed to get several minutes of charge at 2.5-3kW by carefully tweaking both AC and DC current limits and setting the systems target AC voltage to a value closer to the genny output.

The dynamic current limiter seems to help rather than hinder as I thought it might but honestly the entire thing is unstable when weak AC is off.

I suspect that the issue is harmonic distortion messing with the instrumentation which then destabilises the PID loops but that is just a guess. If it was a PLC doing something in the world that was behaving like this I would be looking at filtering the PV, process Variable not solar :-), or getting rid of the noise on the item being measured/controlled.

I happen to have some big ferrite cores kicking about so I may try a common mode choke and a couple of reactors with a cap between them on the AC to see if I can decouple whatever nonsense is messing with the charger input and or the AVR.

Of course I have no idea how many turns will work if the plan has any merit in the first place so I will likely go with 'some - whatever I can get on there' turns as opposed to trying to be any cleverer.

The cores are about 80mm Dia with a 20X20 cross section, just in case anyone can shed light on an actual design.

Please feel free to tell me if I am missing something or just talking rubbish... I will learn eventually with a bit of a leg up.

Cheers

Al

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Alistair Warburton avatar image
Alistair Warburton answered ·

Update.... The bodge sort of works, not perfect by any means but far better.

I tried several configurations, classic filter with wo chokes and a cap between them was my first attempt and it didnt help much at all.

In fact a cap anywhere seeemed to generally upset things, audably, although a couple of configurations stabilised both AC and DC current whils it was connected.

I have ended up with a choke in both L and N, not coupled, and that is making a big difference, all be it far from perfect.

Weak AC is off as is dynamic A limit. AC limit is set to limit th genny to about 4kW give or take and the battery is now taking its full 70A when the base load allows.

I think the chokes are around 12mH each but as the cores were scrounged up I cant be sure of the permiability so that could be an over estimation.

I have just wound a common mode choke on a core half the section which I will try on the inverter side of the two units I have in now...

If anyone can suggest some actual values / arrangement that will be optimal I would be very interested... Electrical design by tinkering is seldom a good plan I know, but I seem to be moving in the right diredtion.

I just cooked tea... 2kW induction hob and the fan oven cycling between 750W & 1;5kW... Another 600W or so elsewhere and it went in and out of assist and bulk without much of an issue.

Feel free to tell me how to do this properly if I am missing a point somwhere. I am not saying this is the right aproach or even a good one. It is however the only one I could think of without aditional kit.

Any and all comments welcome as always.

Al

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Alistair Warburton avatar image Alistair Warburton commented ·

It didnt like the common mode choke at all, although it my just be too big...

Whatever is going on is an interaction between the generator, or at least its AVR, and charger.

The chokes help all round and I noticed that the frequency meter on the genny is aproximatly right with them in-line. Usually it reads utter rubbish with the charger connected.

Progress, but I am still not there and dont know what to do next ?

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Alistair Warburton avatar image
Alistair Warburton answered ·

Started a new more targeted thread...

Power quality, from generator, limiting charge... Solutions?

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Alistair Warburton avatar image
Alistair Warburton answered ·

Started a naw thread...

Power quality, from generator, limiting charge... Solutions?

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