why i call Li fussy

[pianotuna]

Hi all,

This doesn't cover all the concerns for me, but it does show at least some of them: https://youtu.be/_PgthByAYz4

[BFL13]

That CANBAT blurb from wegosolar is confusing about the BMS disconnecting at low temp, and how the heater works . The actual manual says:

" LiFePO4 batteries can safely charge
between 32°F to 113°F (0°C to 45°C). Canbat Low Temperature series (LT)
can be recharged between -31°F to 113°F (-35°C to 45°C). The LT series has a built-in heating system which activates when the temperature reaches the
freezing point. It works by warming up the lithium cells to above freezing
and only then the BMS would allow in the charging current."

The manual says the battery can be discharged down as low as -20C, so what is the state of play between -35C and -20C? No 12v to the rig? But it says the heater comes on (or did it say that? maybe means it activates charging when it gets up to freezing from a lower temp) at 0C, so where did the heater get its power doing that? (You are not charging at the time-- unless you are! 😞 )

It is a muddle with this brand's "info". Need another brand to check how it works.

[3_tons]

I will predict that upon the next LFP thread these detailed explanations will all have been in vain - Calling it a form of ‘thread Alzheimer’s’ (Groundhog day 9.0) eems to be appropriate…

3 tons

[time2roll]

Best to stay above 5C for charging. This value can be changed on some BMS to avoid any issues. The slow charge is about pointless IMO. Better to just avoid it.

[BFL13]

FWC, thanks for the detailed explanation.

BTW, I did not invent the 0-5C "issue", that came from the Trillium charging specs to use reduced charging below 5C. The Relion heater lets charging begin at 5C. Seems to indicate that there is something going on there.

Para 6.6 here:
https://www.trojanbattery.com/pdf/Trillium_UsersGuide.pdf

Also, wrt the other question, note this from the same para 6.6--

"If the charger will not run until it detects battery voltage, be sure that Group 24 or Group 27 batteries are turned
on. If the charger provides charge without detecting battery voltage, and the battery is shut off, the battery will
turn on automatically as soon as the charger starts."

The charger that needs to see battery voltage first, is not quite the same thing as an inverter/charger needing 12v to operate its charger, but it does make you wonder (unless you know the details, which I sure don't)

[FWC]

It certainly seems to me (and probably others) that there is a whole lot of picking going on. To paraphrase, the question is never 'how does this work?' but 'looks like it won't work between 0 - 5c', 'looks like it won't work with an inverter/charger'. Then there is the 'it would be impossible to heat the battery because I made up some numbers', 'let me come up with some sort of crazy scenario where that might not work' etc. The whole point of this thread seems to be to pick at something without any real understanding or experience with how it works.

As to the 'BMS disconnects the cells', as you suggest, the writer of that really does not understand how their solid state BMS works. The battery will continue to allow the battery to discharge below 0C so clearly it cannot have 'disconnected the cells'.

As I think I have explained several times before, the BMS acts like a programmable ideal diode. For most of the time, when the temperature/voltage/current is within spec it is in bidirectional mode and will let current flow in either direction (ie it looks like a wire). When it is in charge cut off mode, either because the temperature is too low, or the voltage is too high etc, it will only allow current to flow out of the battery. When it is in discharge cutoff mode, because the battery is depleted, it will only allow current to flow into the battery. It will never be in both charge and discharge cut off mode.

A heated battery at low temperature is in charge cut off mode - it won't allow current into the battery, but turns on a heater upstream of the BMS 'diode' so that current can flow to the heater. To the charger it looks like any other LiFePO4 battery.

I am happy to explain how this stuff works and clear up some of the many misconceptions, but it would be nice if this wasn't always an argument.

[3_tons]

Per FWC: “ 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.” …BINGO!!

Maybe the forum operator should charge per number of bit wasting keystrokes…

3 tons

[BFL13]

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.

[FWC]

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.

[BFL13]

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.

[FWC]

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!

[BFL13]

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!

[BFL13]

deleted-duplicate

[2oldman]

Youtube Battleborn battery heater

[time2roll]

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.

[pianotuna]

2oldman,

Got a link?