Quote:
Originally Posted by ShrimpBurrito
I don't know if I would buy it, but I'd certainly be interested in learning more. Like, what is the "auto-sensing heater", what would be the final weight, what would the coulomb counter look like, would there be a low-voltage shut-off (presumably with the BMS?), etc.
I'm personally just starting to explore LiFePO4 batteries a bit more for the TM. I already have a Battle Born 50 Ah 12v battery for a different application.
Dave
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Hi, Dave. I was thinking of BB as the USA standard (I've installed a few, in both TT and Class-B applications) and realized this morning that I could build an even better battery pack in only about 5 hours (mostly spent in constructing the compressing structure for the cells inside) - plus overnight component testing before building, and overnight testing afterwards.
Each of the cells weighs 5.4 Kg, so I've got about 48 lbs of cells within the battery box. Overall packed weight for my shipment does exceed 50 lbs (bummer), but my shipping insurance costs is also high (and knocks me out of "standard" USPS medium-large package shipping anyway). Probably about 60-70 lbs from me to you and other recipients. The auto-sensing heater diagram is from my post on 3/22 mostly wired as attached. Wiring and heater pads are hidden inside the Group-31 battery pack, only the thermostat reading display (with a few control buttons) and the switch for Boondock use in the AM are exposed on the outside- along with the BMS fan blower vent, and a couple of small air intake slots for that blower.
Inside the Group-31 box are the Coulomb-Counter shunt, the BMS, the heater circuit wiring, and the main terminal blocks. I think that I will send the battery out with DC "power distribution blocks" attached to the +12V terminal, and also to the Shunt "battery grounding" lug. That way, end users don't need to disturb the battery lugs, on which the torque values need to be very carefully respected. On the distribution blocks, you can just clamp in the larger wires "pretty darn tight" by hand, using Allen wrenches, without measuring your final torque at all.
For installation, the Group-31 case can be mounted either horizontal or vertical. If you prefer to have the temp display visible for an external view (e.g., on the vertical wall of an under-dinette storage spot), then I can simply provide 4 much longer wires through the side or top of the case, and let you attach it with a cut-out of your own. The same goes for the "Boondocking" manual heater switch (used to heat cold batteries before allowing Solar Charging to begin).
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I will try to obtain a BMS with a higher-than-normal "low voltage" shutdown, although I might be stuck with default parameters when ordering in only small quantities. Most "default" Lithium BMS devices don't execute discharge cut-off until less than 11 Volts, some even go less than 10. If you're discharging at 1C or less (which you certainly SHOULD be doing all the time), then you have already passed 90% discharged at about 12.0 Volts. I don't want to allow discharge past that point. Lots of people have been using separate battery cutoff devices to "make up" for the BMS defects, but thy're yet another gadget - and most them can't handle high current.
The first draft of the auto-heater is here:
https://www.trailmanorowners.com/for...1&d=1616594311