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Ambient temp of MPPT and lead acid battery charging


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Am wondering, @plonkster, Victron MPPT's can, I quote: "In case there is no external source for battery temperature; charger uses its internal temperature for battery temperature compensation. The temperature reading is taken in the morning; when the charger has been idle for at least one hour, i.e. when the charger is not actively charging a battery or supplying a load."

So I put the controller and batts together to be in the same ambient temperature. But, I need to make a change ... again. (facepalm)

If I want to move the MPPT away from the batts, having a battery temp sensor on the Multigrid and on the VenusGX, does the MPPT use either of those temp sensors to compensate charging, or must one get a Smart Battery Sense to make sure the temp compensation is done properly, if the MPPT is not in the same room?

Question stems from the fact that the batts are not always near 25deg, working harder than before, even though very seldom going below 80% SOC.

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1 hour ago, The Terrible Triplett said:

If I want to move the MPPT away from the batts, having a battery temp sensor on the Multigrid and on the VenusGX, does the MPPT use either of those temp sensors to compensate charging, or must one get a Smart Battery Sense to make sure the temp compensation is done properly, if the MPPT is not in the same room?

Smart Battery Sense is not to be used with a system that has an inverter, so you can put that idea out of your head so long :-)

If you tie a temperature sensor to the Multi, it will be used. But not directly. Let me explain. In an ESS system the solar charger doesn't use its own voltage anyway. The Multi tells it what voltage to charge to. So the temperature sensor in the MPPT is moot anyway, it is not used.

If you connect a temperature sensor to the Multi, then the Multi will adjust the charge voltage according to temperature, and since that voltage is copied across to the MPPTs, the effect is that they too are compensated correctly.

The one in the Venus-GX is not used. But in theory it could be. There is something called Shared Temperature Sense, which allows a remote temperature reading to be communicated to the Multi. Presently it only works with batteries that support temperature, eg canbus batteries and a BMV702 with a temperature probe attached.

Edited by plonkster
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1 hour ago, plonkster said:

Smart Battery Sense is not to be used with a system that has an inverter, so you can put that idea out of your head so long :-

I quote, after translating: "The temp sense helps when the batteries are loaded via solar, then the MPPT gets feedback on the bat temp and adjusts charging. If there is no MPPT, no benefit."

"Die temp sense sal help wanneer daar van die son af gelaai word want dan kry die MPPT terugvoer oor die bat temp en hy kan laai daarby aanpas."

So you are right, if I use the MG to charge, no benefit. But I don't use the MG to charge the batts ever - all done by the MPPT all the time. :-) 

At R600 odd, I'm not sure it will benefit me though.

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1 minute ago, The Terrible Triplett said:

I quote, after translating: "The temp sense helps when the batteries are loaded via solar, then the MPPT gets feedback on the bat temp and adjusts charging. If there is no MPPT, no benefit."

It's meant for DC systems where you have only an MPPT and a battery, no inverter, no Venus device.

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2 minutes ago, plonkster said:

It's meant for DC systems where you have only an MPPT and a battery, no inverter, no Venus device.

Now who's side do I take? Plonkster's or the decades long Victron dealer ... :-) 

Truth be told, I did not ask the question, leading with I'm using ESS.

FWIW. I'm moving the MPPT (AGAIN!) out of the heat, next to the MG and I'm going to keep it connected to the 2nd battery poles inside the inverter.

Therein the question about where the MPPT gets the temp from, to adjust charging, if the batts are hottish, as the temp difference between the two will be substantial.

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1 minute ago, plonkster said:

Stop worrying so much. Install the temperature sensor that came with the Multi and the right thing will happen.

Done and dusted day one. :-)

Boet, that MPPT is getting beyond hot where it is ... not a worry, a freaking bother I tell you. ;)

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