Temperature Compensation Settings

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solgato asked Mar 30, '19

Temperature Compensation Settings

Can someone please confirm what value I should set my 75/15’s Temperature Compensation settings for if my battery manufacture specs are to increase by .028V per cell for every 10 degrees below 80F and decrease by .028V per cell for every 10 degrees above 80F?

How does that translate to Victrons setting range as I see only the ability to set a + or - value?

I’m in the tropics and more concerned with heat than the cold.

My battery bank is 2X12V series for 24V, so 12 cells x .028. = .336V. Thanks as far as I’ve gotten, now how does that translate to choosing a value in the settings?

Thanks!

Temperature Sensor

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Answer 1 · 2019-03-30T07:23:10Z

JohnC answered · Mar 30, 2019 at 07:23 AM

Hi Sol. Your 0.336V is for 10 deg F, so divide by 10 = 0.0336V /1F

Multiply by 1.8 to convert to C = 0.060V /1C = 60mV /1C

The + or - is just to tell it which way to correct. Ie. If the temp rises, a -ve would tell it to reduce V on a temp rise (what you want).

The default on your 75/15 seems to be -32mV /1C for a 24V bank. So just change it to -60.

Hope this helps..

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Answer 2 · 2019-03-30T07:45:37Z

solgato answered · Mar 30, 2019 at 07:45 AM

Awesome, thanks JohnC!

I woke up sick today and my brain didn’t want to work so I was second guessing the math.

On another note, now that my bank is floating at 26.4V after installing the optional temp sensor (before it would only get to 25.5V or so even though it was set for 26.4V), I found that the voltage may be too high for my brushless electric motors. I have an email in to the manufacturer, but I suspect the motor controllers are going into a high voltage protection mode as they do not maintain RPM. I know the manufacture has a low V protection/limp mode built in that reduces max Amp draw so as not damage PWM controller. Hoping they also have a high limit and that perhaps I’m reaching it causing the behavior. When the bank was at 25.5V the motors worked fine. Will wait to hear from manufacturer before I start playing with my Float value settings, but if it turns out the controllers are that sensitive I may have to create two different presets for my chargers -one for running and one for charging at rest.

Ahh.. the old one step forward, two steps back.

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JohnC ♦ commented · Mar 30, 2019 at 08:17 AM

Yeh, I know the feeling. If you can't find satisfaction with your dc motors, a Victron Orion 24/24 dc/dc converter could fix it though if W matches. I hate suggesting spends though, so just thrown that in so you won't despair. More $$ hey, but you Americans taught us all about that universal fix.. :)

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