question

Niko Järvinen avatar image

Multiplus 12/1600/70 not charging at full rate

I just finished installing my multi and 280Ah of lifepo4 batteries with REC BMS. Everything else seems to work fine but I can't get multi to actually charge at 70A. It claims it's charging at 60-62A but when measuring with Fluke clamp meter it shows only ~50A flowing. Additionally my BMS shunt shows the exact same reading as fluke does so I'm betting that the Multiplus current measurement is nowhere near accurate...

How do I get the missing 20 amps of charging out of multi? That's quite a big drop from the expected value and increases significantly the charging time for a 280Ah bank..

I have the weak AC off, 70A set as the limit in the settings. Environmental temp is around 27-29C where batteries and multi are. Batteries were at around 70% when I started charging so they should be easily able to take the full 70A.

And to be clear the REC BMS is not communicating with Victron yet so that can't be the issue either.


Edit1:

Additional info as requested. Screenshots of the settings at the end of the message. During the screenshot I had set the device not to charge so I can make sure it's cooled and not doing anything for a while so when I flip the charging switch there can not be any issues with heat in the beginning at least. The environment is around 25C right now so even if it was slightly derating due to temp it should not be too many amps as per this doc https://www.victronenergy.gr/upload/documents/Output-rating-operating-temperature-and-efficiency.pdf

Multiplus firmware version 481 which should be the latest as no updates are available.

AC is grid AC right now so no limitations on that side.

Did a new test with no AC loads on at all and multiplus in charge only mode. Discharched the lithium battery to 30% so it's nowhere near full.

Voltage at victron end:13.5V

Voltage at battery terminals: 13.3V

Still Victron showing about 62A in victron connect but real amps about 52A. And victron is in bulk charge mode.


Additionally I'm able to easily pull 130amps from the batteries and with solar + multiplus able to charge at 80A. Smart solar MPTT has the same voltage levels as Multiplus as well. So definately seems that there's a problem with the multiplus...



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MultiPlus Quattro Inverter Chargerbattery chargingLithium Battery
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Bumping this up if anyone has any ideas...
also bump, experiencing the same issue. not more than 50a, doenst matter what battery state, also rec bms (12v 400ah)

Hi Tuxie

what is the DC voltage output at the time at the Battery and also at the Inverter

what is the mutliplus absolution voltage settings

some screen shots of your settings would help as well

also what firmware is in the multiplus

whats is supplying the power to the multiplus ie mains or generator and its voltage and amps incoming

whats is the AC load output at the time

have you got a GX device connected and if so has the DVCC option been turned on and had a max charge current set as this also limits output DC current


Your Environmental Temperatures might be too high or your ventilation is poor. The MultiPlus is rated for 70A output at 25°C.

Check the Voltage at the Battery + and - cables of the MultiPlus when it is charging. Maybe you set the end of charge voltage too low and you have too much voltage drop over the cables to the Battery.

If you have a GX device, you can connect the REC-BMS to VE.Can or BMS-Can on the Cerbo GX. Then you can switch DVCC on and the MultiPlus gets the accurate readings for current, voltage and temperature from the BMS.
Manual for REC Q BMS_Victron compatible.pdf

Ok I added all the info requested to the original message and also redid the test.. No joy. Still absolutely the same issue.
2 Answers
Alexandra avatar image
Alexandra answered ·

Unlike on the AC input, the multi does not have a way of measuring the DC current or charge current to the batteries. It is more of a 'calculated' amount. That is why most people add a bmv or shunt or have smart batteries.

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That's fine if we're talking about the "stats" that multi is showing. As I said I already have a BMS that's showing the actual amps... However the issue here is actual performance of multi which is 30% lower than advertised... The datasheet does specify 70A charging which should be achievable and the reason I got this multi is because the advertised 70A charging so I can charge in about 3 hours instead of 5 hours...

If your cables are longer and small then you may be getting drop over them? Or some high resistance connections like on lug crimping? I think the issue is more setup specific.

Ours is charging this morning at around 65A this morning, but I do know my cables in my system are a bit long, so for that reason we have the provided cables to a bus bar and ran 95mm to the battery bank..

We measured with both the shunt and meter.


1623652603743.pngimg-20210614-082448.jpg

I'm using the standard cables that came with the device so assuming those should be fine. It's 35mm2 for 1.5 meters to the busbar and then 30cm from busbar to the battery in 50mm2. I think I'll cut the cables today and get rid of the slack so I can shorten the cables by ~1 meter to see if that does anything but if that's the problem I seriously wonder why they would sell the device with that cable then.

I've been touching and feeling all my connections and they don't get warm so I don't think that would be the issue. AFAIK the connections should get warm if that's the issue.

It's good to know your setup works so there's hope at least.

What are your voltages inside the victron vs at battery terminals?

Please advise the Battery voltage at the battery and the voltage at the inverter terminals. when its charging at the maximum amount that can be seen.

for interest and testing only increase absorption voltage to 16 volts, JUST testing to see if the amps go to 70 amps, then after the test put the setting back to 14.2 volts


Edited

Also enable the multiplus internal battery monitor and set the correct settings. No harm here as its just for the multiplus anyway


FOR testing Also adjust the float voltage to the same as absorption, as you have the repeat absorption set to 20 days. it maybe in float mode, after testing change it back to its correct figure

These are the voltages when charging is happening: Voltage at victron end:13.5V Voltage at battery terminals: 13.3V. I wonder why Victron is not charging at 14.2V...

I'll try the 16V trick later today when I get to the boat.

At least Victron status was not speaking anything about float mode so I doubt that would change anything but I'll try that as well...

I suspect as you have the repeat absorption set to 20 days and thus the inverter charger is in float mode, change this setting to 1 day or a more suitable time span
No change when playing with repeated absorption or setting the voltage to 16V. For whatever reason multiplus is just charging with the 13.5-13.6V but not going up to the 14.2 or even 16V..

You never quantified the AC voltage that the multi has reported??

Li batteries can absorp huge currents before their voltage rises to near full Soc.




It's 229V here now. It's the grid power in Greece so have no doubt that should be fine...
Alexandra avatar image
Alexandra answered ·
@Niko Järvinen

So after a few days of experimentation, we have worked out that the ac input also has a bearing on the charging amps.

Have used longer and shorter extension cables. Thinner and fatter gauge wiring, even changing to a cheaper plug on the all changing the charging amps coming in. Got it as low as 55A from the normal 65A.

We used the same settings the whole time.

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Interesting. When you had the issue of 55A only, did you see if you can run AC loads at the same time? In my case I was able to run 1.2kW water heater at the same time as charging the battery at 55A.. So the AC side was not limited for sure... And when turning off the water heater the system still only charged at 55A...
No we didn't run full loads and test. We first wanted to see about the charge issue as an isolated problem.


All we can say is that you are running into ohms law in your system somewhere. The current voltage resistance relationship is an inescapable demon.

Other possible culprits are inter bank connections or in one battery we had (chinesium all the way) the links between cells caused high resistance points. Changing those made a huge difference to the bank especially charge and discharge efficiency.

In other high amp systems it is often lug crimps and cables or corrosion.