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matthiasu avatar image
matthiasu asked

[Solved] Multi 24/500 doesn't want to charge with more than 100W

I have a test setup with a Multiplus 4/500 and a 20Ah LiFePo4 battery. ESS is active (mode 3).

Problem: when I tell the Multi to charge my battery, it maxes out at 100W. Why??

DVCC is on and doesn't set any limits. The BMS current limit is at 12A and the voltage limit is 28V, i.e. 2V above the current DC voltage. I couldn't see anything in VeConfigure that'd limit charging to anything less than 10A and >28V either. I scanned the DBus data

dbus -y | while read a ; do echo ""; echo $a; dbus -y $a / GetItems 2>/dev/null; \
  done | grep -iv history | less

but didn't see any limit <10A there either.

Anything I overlooked?

Is there some way to figure out why the censored this happens? If not, where do I ask Victron to pretty please implement a method to discover that?

Multiplus-II
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3 Answers
nickdb avatar image
nickdb answered ·

Is this the test setup with the DIY BMS and code for managing it?

If so, you'd need to expect a response about it being unsupported and to demonstrate the issue with a certified BMS.

The recent mantra in this community is special batteries create special problems.

I will shuffle this to modifications space where you're likely to get a better answer.

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matthiasu avatar image matthiasu commented ·
*Sigh* the BMS is setting a charge limit of 12A. I can demonstrate that with DBus logs if necessary.
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matthiasu avatar image matthiasu commented ·
Un-shuffled, since this proved to be a VeConfigure problem and completely unrelated to any mods.
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johanndo avatar image
johanndo answered ·

Maximum charge current is 10A for the 24V version and 6A for the 48V version, they are derated by temperature when the unit gets warm or when the input is unstable (wiring). Your BMS may use DVCC and limit the current itself or your absorption / float settings are way too low to drive a higher current. No voltage difference - no current. You may use too small too long wires to the battery that cause a voltage drop. There are many reason why the current is low. Most of them are easy to track down with a multimeter.

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matthiasu avatar image matthiasu commented ·

Well, the BMS does limit the current – to 12A. Float etc. settings are nowhere near 28V and don't explain why the charger runs at exactly 100W no matter what the voltage is – I started at 24.5V, the battery is now at 27.5, charger AC load is constant at 100W. The wires' total resistance is 0.065 Ohm, and a voltage difference 0f 0.2V doesn't matter when the same behavior is observed across 15 times that range.

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matthiasu avatar image matthiasu commented ·
Yes there are many reasons. This is exactly why I'm asking for the Victron system to simply tell us what the reason is instead of asking people to go hunting for possible causes.
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johanndo avatar image johanndo matthiasu commented ·

What are your hard limits set in the Multiplus and on the Cerbo DVCC? besides this, nothing from Victron. Current derating based on temperature is published too, and there is a app to look it up.


So it boils down to user error, misconfiguration, wrong communication from the bms or wiring issues. Turn of DVCC, set Absorption to 29.2V (8x 3.65V) and look what the current does.

Make sure your battery is not full yet when you test.

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matthiasu avatar image
matthiasu answered ·

Found it.

Turns out that you turn off the "charger" part in VeConfigure, because in my system the thing is externally controlled and shall not ever charge anything on its own, the current limit that's now greyed out and no longer editable is still observed.

Sigh.

I turned on the Charger checkbox, set the charge current limit to 10A, turned it off again, tapped Send, reconnected everything, and now see reasonable currents. Problem solved.

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