Battery Preheating

[Jonndeka]

I want to use preheat for battery and when the battery wants to charge subzero it should be triggered. Bu I don't know what's the threshed for disconnecting the circuit.
I mean if temperature is lower that 5C the circuit shall be active until the temperature reaches a certain temperature. What's the maximum temperature?

 

[calab]

You want to charge your battery below 5*celcius?
Whats the battery chemistry?
Who sold the battery to you?
You making your own circuit or is it already a feature in whatever you bought?

 

[Jonndeka]

You want to charge your battery below 5*celcius?

Yes. I mean if the temperature is lower 5C, for charging first we need to do preheating and then charge the battery.

Whats the battery chemistry?

NMC

Who sold the battery to you?

A supplier.

 

[Jonndeka]

You making your own circuit or is it already a feature in whatever you bought?

I need to make my own circuit. I just want to know the threshold for lower and upper limit for enabling the preheating circuit.

 

[harrisonpatm]

If I were in your situation, i would set the low temp to 7-8 degrees Celsius, and the high temp heater cutoff to 13-15 degrees. NMC can charge/discharge up to 40-50 degrees C, but theres no reason to heat it that much, waste of energy, you just need it to be a bit warmer to charge. I say your circuit should start heating at 7-8 degrees so that you have a margin of error, in case your thermocouple readings are a bit off from the actual battery temp.

 

[dominik h]

I preheat my 21S5P 77V 100Ah nmc scooter battery to 15C and when it is really cold outside I set 10C for preheating. My battery is fully isolated with 15-30mm armaflex.
I have no real need to preheat my battery for charging, because it can be charged with 100A above 5C and with 20A above 0C, i just do it to have less voltage sag during driving.
My daily driving distances are to short to keep the battery over 10C. If I do not heat during normal Winter days the battery stays around 3-6C.

 

[Jonndeka]

If I were in your situation, i would set the low temp to 7-8 degrees Celsius, and the high temp heater cutoff to 13-15 degrees. NMC can charge/discharge up to 40-50 degrees C, but theres no reason to heat it that much, waste of energy, you just need it to be a bit warmer to charge. I say your circuit should start heating at 7-8 degrees so that you have a margin of error, in case your thermocouple readings are a bit off from the actual battery temp.

Thanks!

 

[Jonndeka]

I preheat my 21S5P 77V 100Ah nmc scooter battery to 15C and when it is really cold outside I set 10C for preheating. My battery is fully isolated with 15-30mm armaflex.
I have no real need to preheat my battery for charging, because it can be charged with 100A above 5C and with 20A above 0C, i just do it to have less voltage sag during driving.
My daily driving distances are to short to keep the battery over 10C. If I do not heat during normal Winter days the battery stays around 3-6C.

You mean if your battery temperature is lower 10C, preheating is activated and when the temperature reaches 15C, preheating circuit is deactivate. Right?

 

[dominik h]

I messure the battery temps , and normaly my heating is set to 15C. The tolerance is plus minus 1.5C. On very cold days I reduce to 10C. My heating system is supplied by the battery , so it is always turned on and kicks in when needed.
I have a 70kg 77V 7.7kwh power pouch battery installed in my scooter. On a very cold day it takes 10Ah to heat to keep the battery warm.

 

[From-A-To-B]

I messure the battery temps , and normaly my heating is set to 15C. The tolerance is plus minus 1.5C. On very cold days I reduce to 10C. My heating system is supplied by the battery , so it is always turned on and kicks in when needed.
I have a 70kg 77V 7.7kwh power pouch battery installed in my scooter. On a very cold day it takes 10Ah to heat to keep the battery warm.

Wonderful work on this front, dominik h, thanks for sharing about your build. I've toyed with putting a battery heater in some of my larger packs. My tinkering abilities do not extend to Arduino boards or programming -- I was thinking about having a simple click button and a relay to trigger the heating circuit. Can you share more about what your heating setup looks like? Or about the circuit you're using to automatically maintain battery temp?

 

[dominik h]

I have a switch to turn on a temperature controller. I bought the controller. I have installed a temperature sensor in the middle of the battery . The heating is done with two 250W 230V silicone heating mats underneath the battery housing, like you can by them for 3D printers.
On the sides is a floor heating mat installed. All is powered with the 21S Lithium Scooter battery.

 

[dominik h]

Pictures.
The temperature controller is mounten in the little piece of wood.
After the first winter the internal relay died. So I soldered in a new one and now the relay switches only a bigger external 12V relais which easily can be changed.
The controller is from Wachendorff type UR3274U5

Changed a lot of things over the last three years. Startet with an ANT 150/350A BMS and a Sabvoton SVMC72260 but killed it with weakening field on the main stand.
Changed to SVMC72150, killed it again in the exact same way. Installed a new SVMC72150, drove 10000km with up to 175Adc . Now changed to a Fardriver ND72680 which really has double the power compared to the SVMC72150.

 

[Jonndeka]

So for battery preheating, do we need to use main battery as power source or we need external battery to warm up them?

 

[Jonndeka]

I have a switch to turn on a temperature controller. I bought the controller. I have installed a temperature sensor in the middle of the battery . The heating is done with two 250W 230V silicone heating mats underneath the battery housing, like you can by them for 3D printers.
On the sides is a floor heating mat installed. All is powered with the 21S Lithium Scooter battery.

When you use main battery as a power source to heat the silicone heating mats, it means you are discharge the battery at low temperature, even subzero temperature. This way is not correct!

 

[dominik h]

You can use your main battery, or you can use an AC-outlet in your garage or you can use an external battery.
Discharging my battery is allowed up to -20C. Only charging is not allowed below zero.
My battery is big enough to heat the battery for more than one week in the coldes winter days, and I drive nearly every day.

 

[From-A-To-B]

When you use main battery as a power source to heat the silicone heating mats, it means you are discharge the battery at low temperature, even subzero temperature. This way is not correct!

I agree with Dominik H — discharging a cold battery is not dangerous or damaging to the battery. Cold batteries perform poorly, which is why it’s clever to use a cold battery’s energy to warm itself. There are legions of EVs on the roads that use their own battery energy to modulate (warm or cool) battery temp.

Generally speaking, dont CHARGE frozen or near-frozen batteries.