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Alain Ross avatar image
Alain Ross asked

MPPT 150/100 temperature compensation maximum value

Hello Victron User, I will like to know if it's normal that my temperature compensation maximum value on my MPPT 150/100 is -30mV...I cannot enter a higher data, For the moment it's cause me problem of undercharging my battery bank in winter season. My absorption charging voltage of 14,5V cannot reach more than 15,2V at -15 Celsius the same charging voltage that I got at +2 Celsius..?? Seem to be a kind of protection on the MPPT to prevent overcharging ??? (N.B. MPPT v3.08, I'm using it with the BMV-712 v4.08 & the CCGX v2.71) Thanks to help me figure it out !!!

temperature compensation
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2 Answers
JohnC avatar image
JohnC answered ·

Hi @Alain Ross

Indeed it's not possible to enter more than -30mV, and I've never seen a batt maker spec more than 5mV/cell (degC). So Victron have limited it.

Your 15.2V barrier may be down to where temp comp is no longer considered relevant. This is a rather 'mushy' science anyway, and down that cold, who knows what happens. Maybe too they have a max correction value or even don't correct below a certain temp. I can't find this stated definitively, but no doubt there's limits to prevent issues arising from careless settings or sensor failure.

This won't stop you raising set Abs V, up to the limit of 16.5V. Your 14.5V and -30mV are already quite aggressive, so take care going further. You may well find your batts will charge adequately at a lower V, and you don't need to push so hard anyway.

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Alain Ross avatar image Alain Ross commented ·

Thanks for your knowledge @JohnC, I will play with the absorption charging value, I know my parameter may look agressive, but after stats data recording since the installation of my new battery bank last fall, I now read a specific gravity of 1,225 on each cell after an (15,2V) absorption time of 6 hour 30 min at 2 Celsius under acceptable sun condition . My 100% charged spec gravity must be 1,265 or higher....so my conclusion is they need more kick during the harsh winter condition down here !!!....any common sense idea welcome

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JohnC avatar image JohnC ♦ Alain Ross commented ·
@Alain Ross

Ha, when it comes to discussing pb batts it's more opinion than knowledge in most cases. We all differ. I abandoned SG readings long ago and use Tail Current to terminate Abs. And rarely longer than 1.5 hrs there too. But I never see extreme cold either.

I just get wary when something out of Victron's range limits is sought. It means it's unusual, possibly even not advised. Your choice in the end, and I wish you and your batts a long and happy life. :)

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Alain Ross avatar image Alain Ross JohnC ♦ commented ·
Hey @JohnC , just wanna say thank you for your tips on Absorption voltage value, I played with it to reach my Crown manufacturer battery spec in harsh winter condition up north & find the perfect set-up, also doing more equalization for this season is recommend... like you say more opinion than knowledge on battery maintenance but i'm old school & will stick on my SG for Lead-Acid one,, If your interest on this subject a good sunday reading blogs is HandyBob's solar,, lot of common sense solar experience there..hope breaking record on battery life :)
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ako avatar image
ako answered ·

Sounds like the same problem i have , i cant enter 5mv per cell x 12 = 0.60 for the batterie bank . I adjusted the Temperature compensation from the default of -2.7 per cell to the maximum which is -35 per cell which only equates to 42 mv for the Bank , almost 30% less that both Rolls and Trojan say i should set my compensation to . I cant understand why a unit would be limited to a figure much lower than major Battery manufacture's require . The batteries are far more expensive than a controller so looks like i will have to stick with Morningstar TS60 which can be set to the desired voltage .

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