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gwindhurst
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# Posted: 3 Aug 2025 09:26am
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Just received a Humsienk 12v 314Ah Mini BT ($339 AMZ), and Form Industries 12v 30a charger. As far as I can tell, the battery and charger performed as they should. The battery reached 100% at 13.58v and peaked at 14.25v. Then settled in at 13.61v roughly 7 hours after charge completed. Is this normal? I'm new to this LifePo4 world and was wonder if this is normal and/or if anyone has any comment. Thank You.
The following are my results:
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Steve_S
Member
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# Posted: 3 Aug 2025 10:23am - Edited by: Steve_S
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Take the voltage and Divide by 4 to get average cell voltage.
LFP has 2 Voltage Ranges like all batteries. (see chart @ bottom)
Gross Range = 2.500 -> 3.650 Volts per cell.
Working Range = 2.800 -> 3.400 VPC.
NEVER EVER Exceed 3.650 VPC and NEVER go below 2.500 VPC as that WILL harm the cells.
* Working Range is the optimal working performance range where the cells chemistry is Optimal and delivers the Actual AMP HOUR rating as labelled on the cells.
** NB: LFP has a very flat Voltage Curve compared to other chemistries and they are Millivolt & Milliamp "sensitive" and so must be measured accordingly.
13.6 = 3.4V per cell. PERFECT as that IS 100% and the best "settled" voltage.
14.25 = 3.56 VPC is a Perfect Cutoff Voltage for charging and leaves the room to settle to 3.400 +/- 0.15 V
** All Lithium Based cells will settle slightly lower after charge, this is normal & expected, LFP is pretty consistent with the amount the cells settle.
YOUR Battery can take a MAX of 157A (0.5C-rate) for Charging and can handle up to 314A (1.0C-Rate) for Discharging. *NB: The internal BMS (Battery Management System) controls this and will limit that lower to 100A protect the battery. (Per your product info as posted on humsienk site spec data) BE AWARE that should a Full Short Fault occur, a 314AH Battery can DUMP @ 5C which is 1570A (a serious kick in the pants). There is a HEAP OF JUICE lurking in there and so RESPECT IT !
WARNING ! NEVER EVER Charge a Battery when it is below 2C/35F Temp ! THAT WILL DAMAGE the cells ! LFP will discharge fine down to -25C/-31F and will charge safely up till 50C/122F The BMS in that battery has Temp Protection for Hi & Lo Temps, so it is safe
Here is one of my charts that shows the voltages etc.
Hope it helps, Good Luck
Steve
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gwindhurst
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# Posted: 3 Aug 2025 10:51am
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Thank you very much for the very informative response. I will print this out for future reference... As, for the cold weather and Low-temp cut-off, that's been one of my contentions to NOT buying a LifePo4 however, with the newer built in safety features I felt more comfortable with this purchase. Also, I plan on building a well insulated box out of 3/4" plywood with 2" closed cell foam (Owens Corning Foamular 200) and adding a thermostatically controlled RV Tank Heater like this as a safety net:
https://www.amazon.com/gp/product/B0DNTGLPMQ/ref=ox_sc_saved_title_8?smid=A1U5K42UL16 JP0&th=1
Thoughts on that?
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Steve_S
Member
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# Posted: 3 Aug 2025 11:24am
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I know many people use battery heaters, usually the silicone ones with the element within and there are many versions with temp controllers. Depending on type (aluminium plate vs silicone embedded) you need to have some protection between the insulation material (foam with aluminium can carrey current) and even battery bottom pending on type of casing etc.
IF a Manufacturer sells you a battery with built-in heater (there are many) they are almost always the silicone embedded ones as they are the safest and most affordable from manufacturers perspective.
It's important that "whatever heater" have it's own temp sensors and that it will cut off all draw when not required and that it will not heat too much, but rather keep the batt at +5C/41F to +7C/44F so not to "cook" the batt or waste energy trying to bring it to a higher temp which is not needed.
I should point out, that during Carging, the chemical interaction generates heat, the warmer the cells, the more heat they will generate as they charge.
The Batt Specs say it has a BMS with BlueTooth and APP that let's you interact with the BMS and to monitor the internal state of affairs. That BMS does NOT have Internal Cell Balancing (not mentioned in description) so this means the batt is playing the "Averages" game meaning there can be a difference in cell voltage, ie: One high say at 3.500 while another maybe at 3.330. Now if ONE CELL drops to cutoff point, the BMS will shutoff the batt... Same if one cell reaches Overvolt setting (most often they set that to 3.650 as the default) the while thing will stop till that cell settles down & the BMS unlocks the charging.
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gwindhurst
Member
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# Posted: 3 Aug 2025 11:42am
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Got it. I think I will leave it as is in an insulated box this winter, and see how in performs on its own. And if necessary, I will add a silicone heating pad with a programable thermostat. Winter usage is minimal, weekend a month in central Vermont. It does get pretty cold at times... Thanks again.
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