MPPT 150|100 battery voltage reading high

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riclin asked Jul 29, '21

MPPT 150|100 battery voltage reading high

I have recently upgraded our existing off-grid installation to include the following:

1.5kW existing panels -> MPPT 100|20 48v -> 48v 400Ah battery bank

4.5kW new Jinko panels -> MPPT 150|100 -> same 48v 400Ah battery bank

Cabling is short and the voltage drop between the controllers and the battery bank is less than 0.01V. The two charge controllers are networked over bluetooth and each has the most recent firmware. However synchronizing the two controllers is a problem because the MPPT 150|100 is incorrectly reading a battery voltage 0.2V high, and hence moving from Bulk->Absorbtion->Float earlier than the smaller controller.

For example, the 100|20 status display may report a battery voltage of (say) 55.7V. This voltage can be confirmed via actual measurement at the 100|20 terminals, the 150|100 terminals, and also at the battery bank itself. However the 150|100 at this time instead reports 55.9V. As a result, the 100|150 switches up between charge modes prematurely (and presumably switches down late as the battery voltage falls), switching the larger panel array into Absorbtion while the small array continues to operate in Bulk. Accordingly, the larger solar array is effectively switched out before the batteries are fully charged leaving the small array to finish the task. Although this is unlikely to cause a problem in sunny days, the premature switching out of the larger array on overcast days does not permit full recharge of the batteries and to an extent defeats the intent of this upgrade. As a temporary workaround, I have set the 150|100 Absorbtion and Float voltages 0.2v high to compensate for the battery reading error which does seem to help, but I am unsure as to whether this may eventually contribute to cooking the batteries and do not see this as a permanent fix for this new device.

Has anyone else encountered this problem? Can the problematic 150|100 be recalibrated in the field? - or is this a matter that can only be fixed with a replacement controller?

Cheers, Richard

MPPT Controllers

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Answer 1 · 2021-07-30T04:50:05Z

JohnC answered · Jul 30, 2021 at 04:50 AM

Hi @riclin

I've seen it on my own system, where the Multiplus read ~0.3V too low, vs a 150/100 which was ok. They can't be recalibrated afaik.

You don't mention having a GX device, but your system warrants one. The fix then is to invoke DVCC and use the 'global' V sense, so all your kit sees the same reading.

I chose to use a Smartshunt for the V sense, and it's Current Sense is also passed through too to the mppt, so it can now use the true battery current for the mppt Tail function to end Absorb. This would be especially useful with multiple mppt's.

A bonus is the Temp (which I get from the Multi), which also can pass to the mppts, to give real-time temp compensation on pb batts.

I hate recommending to go spend on more kit, but adding that shunt completed my system, with DVCC bringing it all together.

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Answer 2 · 2021-07-30T08:57:24Z

riclin answered · Jul 30, 2021 at 08:57 AM

Thanks John - I'll investigate your suggestion. The Smarshunt looks to be a useful device - am I correct in understanding that it will communicate with the charge controllers using the VE.Smart network over bluetooth and can be configured from within VictronConnect?

Tx, r/

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JohnC ♦ commented · Jul 30, 2021 at 11:24 AM

@riclin

I'm unfamiliar with the bluetooth kit, but I know networking that way has limitations. And it's not DVCC in it's full form. I just use wires to a GX, which networks it all, then wifi to the home network.

I'm guessing you don't have a GX, so I'd suggest looking at that first. Even if you go the cheaper RaspberryPi route.

Else forget all I've offered so far.. :)

DVCC is described in this flagship CerboGX manual.. https://www.victronenergy.com/media/pg/Cerbo_GX/en/dvcc---distributed-voltage-and-current-control.html

But keep asking.

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wkirby ♦♦ commented · Jul 30, 2021 at 01:58 PM

If both of your MPPT units are the Smartsolar models then they have Bluetooth built in. In that case you can set up the two MPPTs and the Smartshunt in a VE.Smart Bluetooth network. If they are Bluesolar MPPTs then a Bluetooth dongle will be required.

The Smartshunt will become the primary Voltage measurement device and transfer its readings to the two MPPT's. Additionally, the Smartshunt can convey net battery current to the MPPTs so that they can use this for more accurate tail current decisions since this will be that actual battery current. Also battery temperature can be measured too if you have the temperature sensor for the Smartshunt.

Another option could be the less costly Smart Battery Sense. The will measure battery Voltage and temperature in one unit, no current measurement though. Again, set it up in a VE.Smart network with your MPPTs.

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Answer 3 · 2021-07-31T02:00:42Z

riclin answered · Jul 31, 2021 at 02:00 AM

Ahah - thank you both. This is exactly what I needed to know. Both controllers are Smartsolars, so I suspect that the Smart Battery Sense module will do exactly what I need and intend to pick one up shortly. Meantime, thank you again for the suggestions - it is clear that I need to spend some time perusing the Victron cattledogs to learn the range of accessories and options available. Cheers!

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Answer 4 · 2021-08-05T22:58:57Z

riclin answered · Aug 05, 2021 at 10:58 PM

Feedback to JohnC and wkirby: thanks again. The Smart Battery Sense unit is now installed and did exactly what was required with the two controllers now operating in sync. I happened to notice the 150|100 move from bulk to absorbtion, then watched as the 100|20 also switched 15 seconds later. Perfect!

Cheers both,

r/

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