Smart MPPT 100/30 seems to charge a little high

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cybermaus asked Feb 27, '24

Smart MPPT 100/30 seems to charge a little high

So I have a Smart MPPT 100/30 as well as a SmartShunt on a brand new 105Ah semi-deep-cycle FLA

I have been observing it for a while, and I find the voltages a little high. It is set to 14.4 and 13.8 absorb and float (copied the Victron deep cycle 2 profile) , but I seem to observe ~14.6 and ~14.0 fairly consistently.

Is not much higher, but it is consistent, and also the SmartShunt agrees with the voltages (see screen shots.

Is this deviation normal? Should I expect to read ~14.0V when I set 13.8 float?

Thanks for your suggestions

MPPT SmartSolar mppt overvoltage

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Answer 1 · 2024-02-27T14:26:27Z

kocki answered · Feb 27 at 02:26 PM

Do you have installed a battery sense / battery monitor and configured a local network with a battery sense / battery monitor and zhe MPPT? Otherwise the voltage may be not the voltage of the battery that you measure directly at the battery. You shouls check the battery voltage directrly at the battery.

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cybermaus commented · Feb 27 at 02:34 PM

Well, that's why I mentioned the SmartShunt is reporting the exact same voltage. It is measuring it with a sense wire directly to the poles. Also, you would be right during bulk, but during absorb and especially during float, there is not a whole lot of current anymore, so there would not be any significant voltage drop.

Also of course, the SmartMPPT does not have any sense input. Victron makes nice stuff, but they do not seem to be very big fans of extra sense wires. The Orion series also famously lacks them.

But most importantly: Would any voltage drop deviation be in the other direction? Correct voltage at the Victron, but too low a voltage at the battery?

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Answer 2 · 2024-02-27T18:15:00Z

Alexandra answered · Feb 27 at 06:15 PM

@cybermaus

If you have temperature compensated charging configured, then the voltage cannot be higher depending on the conditions.

You should also check if the temp compensation amount is correct for your particular battery.

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Answer 3 · 2024-02-27T19:16:33Z

cybermaus answered · Feb 27 at 07:16 PM

So @Alexandra the shunt is indeed feeding in the temperature, so that is a reasonable suggestion. I t would have been about 10~11 C this afternoon, and the compensation was never touched by me and is set to -16.20mV/C

Is it true that 25C is the anchor for the temperature compensation? So this would be:
-15 * -0.016 = +0.24V
Which indeed does get us to the correct value

So that explains the compensation itself. Now the question whether compensation value is correct. I have no data, not even after writing the manufacturer and vendor twice about the charge voltages, but given it is a FLA, I am just going with 14.4 and 13.8.

Which is why I duplicated the Victron deep cycle no 2, as it also had 14.4 and 13.8, and I assume that is where the -16.20mV/C came from

So now that the 0.2V is explained and I feel a little more happy, if anyone could comment on whether they think the -16.20mV/C is indeed a reasonable value for a generic semi-deep-cycle FLA, please do let me know.

Ps: the actual brand is Q-batteries SEM105, which is a German brand, but no idea if they make stuff themselves or relabel, and if they relabel, whether it is another German brand or something Chinese. Yes, I cheaped out on the battery. It is a stop-gap till I can install LFP this autumn, as I need to reshuffle a lot of guts on this very tiny, space challenged mini camper. At least I made sure all the other investments were LFP ready.

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Alexandra ♦ commented · Feb 28 at 01:34 PM

Yes the 25°C is the anchor point. Usually batteries (and most electronics too) are rated there.

Couldn't find anything specific on temp compensation for the Qbattery. Or anything really related to charging at all.

Some batteries use -32 some -16.

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