Temperature compensation in Victron manuals

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arminf asked Jul 4, '23

Temperature compensation in Victron manuals

Hi,

isn't there a contradiction between the 2 official sources?

https://www.victronenergy.com/media/pg/SmartSolar_MPPT_RS/en/troubleshooting-guide---mppt.html says:

5.4.7. Wrong temperature compensation setting

To find out the correct temperature compensation coefficient setting for your battery, refer to the battery documentation. When in doubt use the default value of -64.80mV/°C for lead acid batteries and disable the temperature compensation setting for lithium batteries.

https://www.victronenergy.com/media/pg/Manual_BlueSolar_MPPT_75-10_up_to_100-20/en/configuration-and-settings.html says:

The graph displays the temperature compensation for a 12V system and uses a -16mV/°C temperature compensation coefficient. For a 24V system multiply the voltages by 2 and for a 48V system multiply by 4.

I have a 24V, Lead Carbon, (2x 200Ah) with MPPT 100/30, Off-grid.

Using both mentioned sources, I can't figure out if -32 mV/°C (2x 16 according to the 2nd source) or -64 mV/°C (according to the first source) is the correct setting.

What I measured: Battery1=12,84V, Battery2=12,87V, B1+B2=Inverter=25,71V. MPPT Battery=26,1V

Victron App shows 26,1V.

Now, it is mid-day (hot, sunny, after charging for 5h) and the MPPT is in a warmer space (closet with inverter producing heat) than the batteries (under the bed). And I measured under load and while charging. That's probably the biggest mistake.

Thanks!

Armin

Edited: https://www.bluesunpv.com/bluesun-12v-200ah-lead-carbon-battery-with-certification-made-in-china_p514.html are my batteries. The data sheet does not

MPPT SmartSolar temperature compensation

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Answer 1 · 2023-07-04T10:47:26Z

klim8skeptic answered · Jul 04, 2023 at 10:47 AM

@ArminF Using both mentioned sources, I can't figure out if -32 mV/°C (2x 16 according to the 2nd source) or -64 mV/°C (according to the first source) is the correct setting.

The RS 450-100 mppt is a 48v battery charger, therefore the -64mV / C for this charger is correct.

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kevgermany ♦♦ commented · Jul 04, 2023 at 11:46 AM

I asked this some time ago, got no answer. Settled on -4mV/C per cell. I.e. -24mV/C at 12V. This extrapolates to -96mV/C at 48V.

I did quite a bit of searching. Most sources gave -4mV/C per cell. No difference for lead carbon. For safety I'm running at the lower end of charge voltage for lead carbon.

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arminf commented · Jul 04, 2023 at 12:55 PM

Ah, great, thanks. I overlooked that this was talking about a specific equipment.

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