why i call Li fussy

Not trying to pick it apart, just not clear on the sequence. The inverter/charger has its 12v and starts charging when it gets the 120v and charger enabled. Ok. Charging amps are shunted to the heater, ok.

But now it says (when the shunting happens, same signal?) the BMS is disconnected from the cells. Or does it disconnect from seeing a certain cold temperature? Badly written blurb.

So no battery 12v to run the inverter/charger or the rig. Doug posted about that when I thought (wrongly) it worked like a converter, and could supply 12v with no battery. Nope, it needs 12v from somewhere --the battery usually--to operate before it can can supply 12v to the battery

That blurb is badly written, so maybe the BMS does not disconnect?

If that is how it works, then those with inverter/chargers would choose the heating pad method instead of getting these LFPs with built-in heaters, but those with converters would be able to use this type of heating.

BFL13 wrote:
Not clear how an inverter/charger, which needs 12v to operate, can supply 12v to the rig while the BMS has disconnected from the cells. The "charger" can't charge to run the heater or anything else unless the inverter/ charger has 12v already.

A converter could supply 12v to the rig with no battery.

This is not an issue - the cells are not disconnected from the charger. Before you attempt to charge it is in its 'normal cold configuration' where it will provide 12V but not allow charging. The inverter/charger will see it as a 12V battery and start charging. Once the charging starts, the battery shunts that current to the heater until the battery is warm enough to charge. The charger doesn't see any of this.

For some reason there seems to be a great effort to pick this apart without really understanding how it works. The funny thing is, the sky is not falling and there are people actually out there using these.

If you are actually interested in how LiFePO4 batteries work, buy one and play around with it. Or even better, build your own.

Not clear how an inverter/charger, which needs 12v to operate, can supply 12v to the rig while the BMS has disconnected from the cells. The "charger" can't charge to run the heater or anything else unless the inverter/ charger has 12v already.

A converter could supply 12v to the rig with no battery.

You don't need to be able to draw power from the battery while heating as they only heat when being charged (ie power is flowing into the battery). When the BMS detects the temperature is below a certain value, and current is flowing into the battery, it shunts that current to the heater until the temperature is above the set point, then it switches off the heater and charges as normal.

In practice, you turn on the charger (or the sun rises on your solar) and for the first minutes to a couple of hours (depending on the temperature) the charge power is actually going to the heater. Once the battery is up to temperature, the heater turns off and the battery charges like normal. This is superior to the BB scheme of just always heating the battery to maintain temperature. There is no need to heat the battery if it is not being charged.

BFL13 wrote:
Don't know who makes this brand, but the CANBAT with heater blurb says:

"In cold temperatures, the BMS ( battery management system) disconnects from the cells to protect your battery. Prior to charging, the built-in heating systems draw power from the charger in order to heat up the battery."

I have not watched that BB video yet, but does that mean you lose your 12v to the rig during the heating phase of the recharge?

Or do you still get 12v from the converter since the charger must be getting 120v and you don't need the battery when the converter is working? Unless it is an inverter/charger--where do you get the 12v to run that?

http://www.wegosolar.com/products.php?product=12V-100Ah-Cold-Weather-Lithium-Battery-%28LiFePO4%29

I see their spec balancing voltage is only 13.6v. Relion spec is higher. They claim it works down to -35C but very muddled as to what it really does for when you can draw from it as opposed to when you can charge it--badly written blurb!

Don't know who makes this brand, but the CANBAT with heater blurb says:

"In cold temperatures, the BMS ( battery management system) disconnects from the cells to protect your battery. Prior to charging, the built-in heating systems draw power from the charger in order to heat up the battery."

I have not watched that BB video yet, but does that mean you lose your 12v to the rig during the heating phase of the recharge?

Or do you still get 12v from the converter since the charger must be getting 120v and you don't need the battery when the converter is working? Unless it is an inverter/charger--where do you get the 12v to run that?

http://www.wegosolar.com/products.php?product=12V-100Ah-Cold-Weather-Lithium-Battery-%28LiFePO4%29

I see their spec balancing voltage is only 13.6v. Relion spec is higher. They claim it works down to -35C but very muddled as to what it really does for when you can draw from it as opposed to when you can charge it--badly written blurb!

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pianotuna wrote:
It would require a generator to be run--and a battery management system that would run the heater--but not allow charging.

Simple heater and thermostat can be independently controlled.
BMS would allow charging when the set point is reached. And yes people are doing this and it works well.

2oldman,

Got a link?

Have you guys watched the YouTube video on how these batteries are heated? This isn't like some electric blanket.