If I build some LiFePO4 battery packs, would anyone buy them?

[rickst29]

This is only a preliminary query, and definitely not yet a "Part For Sale".

I see that I can buy parts for a "270/280 Ah battery, using EVE or LIFSHEN cells, along with decent 250A (continous power limit, peak is higher) BMS into a Group-31 box for roughly $820 each. This INCLUDES the low-temperature auto-sensing heater parts for plugged in campgrounds. The temperature display of the heating controller is built into the top cover, along with the coulomb-counter Meter and a small on/off "master switch" for enabling the heater circuit in Boondocking. (These three components could also be mounted separately, using relatively small cables.) During installation, it is possible to disable Solar Panel power when the battery temperature is too cold.

In a configuration where a separate "Charging" Wire can be pulled from the Power Converter, the Power Converter line can be connected directly as a "power input" for the heater circuit (which auto-switches to become the battery charging line, whenever the battery pack is warmed up to at least 45 degrees Fahrenheit).

But complications arise when a single wire is shared for both "charging" and output delivery to the TM +12v power distribution board. I recommend against using this configuration, because manual switching is required in Boondock situations, and wintertime battery maintenance becomes complicated. At a "plugged in" campground, you may simply turn on the "heat from the battery" switch and leave it set for the entire stay. When the heater needs to warm the battery, it draws power from the battery, and the battery draws power from the Converter. And when heat isn't needed, the warmer circuit is switched back to the battery itself (with zero power consumption and zero voltage). The battery stays warm all night.

Boondocking with the heater running through the whole night (from the battery) wastes energy. You turn the "master switch" of the heater OFF for the evening and night, making the thermostat ineffective. Then, if you want to charge with a Generator you must warm up the battery first (by turning the "master switch" back on and warming the battery), BEFORE connecting the generator.

Solar Charging (when boondocking) can be switched off automatically in low tmeperatures, so that the Charge Controller does not charge the battery before it is warm enough to accept the charge current. But in the morning, you must again turn on the "self-heating" switch for the battery to warm itself. When the Battery temperature has reached 45 degrees, Solar "PV power" is re-enabled.

Keep in mind that you probably need to spend another $220 on upgrading your old Converter. I will put most of the "cold weather heater"parts and wiring inside the box. Built into the Group 31 box cover two are the two switches and the heater controller's temp display, and the Coulomb-Counter Monitor Display. There is also a large heatsink for the BMS, on one long side of the box. The "Coulomb Counter meter, switches, and meter can be or left as a pair of terminated wire ends if you want to put the switch and temp display outside the battery box, on an interior storage compartment wall). Plus shipping, plus about $100 for my build-and-verify work.

At roughly $900 plus tax and shipping, they'd be expensive. But you would end up with 3x the capacity of a BattleBorn $1050 heated battery kit. (To match my box, you'd need to spend $3150 with BattleBorn, and you'd have to wrap the heater cables yourself, and you'd end up with 3 Group-24 battery boxes to wire together - instead of just one smaller one.)

Would anyone be SERIOUSLY interested in getting one of those from me? I know that it's way more battery than most TM Owners need. (It's possibly capable of running the Air Conditioner through a HUGE Inverter, for 1-3 hours). But I
'm not interested in building any battery pack smaller than 270Ah, or any simple battery pack which excludes my "auto-heating for charging" feature.

[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

[rickst29]

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

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).
- - -

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

[inghamm]

I would be interested. Sounds like you have thought things out well. We have our batteries on the tongue. Would this work there?

[rickst29]

Originally Posted by inghamm

I would be interested. Sounds like you have thought things out well. We have our batteries on the tongue. Would this work there?

I would recommend against putting such a battery on the tongue, for a bunch of related reasons:

1. In the 'normal' configuration, with the temp sensor and display built right into the battery box, it would definitely attract thieves.
2. In the normal configuration, you would need to go outside to switch the "heat directly from battery" switch.
3. In a custom configuration with a long cable between the battery box and the heater controller/display unit inside the TM, you have a new cable leading back to the display. It only two wires, but one is the temp control Sensor cable - a cable whose resistance must never be accidentally changed by crimping or bending with an insufficient bend radius. (They work by measuring resistance changes, and they're extremely sensitive to damage).
4. The 'outdoors' placement has a lot more temperature stress (reducing the lifespan of the battery), and also tends to leak away generated heat from the heater pads in the wind. The heater pads must be engaged more often, and more power is wasted while they keep running.
5. If I assume the acquisition to be related to typcial 120-VAC "jobs" in a Boondock (such as using a normal 120v microwave, or a hair dryer, or a coffee maker), through a big Inverter, then the wiring distance to the Inverter is greatly increased. Since those wires would need to be #1 or even #1/0 (huge) it would be extremely difficult to make the connections and wire back to a dry Inverter location within the TM. It would also create another exterior 'advertisement' that the battery is exceptional, and worth stealing.

The "under rear bed" and exterior battery compartment locations are both very good. Placing inside forward benches also works, that's where I have my batteries and Inverter. This can save weight on the tongue, while preserving interior under0the-benchstorage sapce - but the risk of theft is really too high IMO. (It maybe depends a lot on where you camp, of course).

[rickst29]

That allows me to do a "group buy" of 16 battery cells, reducing the proportion of expense spent in shipping (in comparison to buying only 4 cells at a time). It also allows me to turn my cell compression components and other stuff into more of a production line.

Cell compression, BMS, case, bus bar assembly, and terminals are the main reasons why battery "packs" cost more than individual cells. In some YouTube videos, you can see people "building batteries" by merely wrapping tape around the 4 cells and attaching the BMS -- that's not how it is done. These "prismatic" battery cells can last about 50% longer, if they are instead installed into a highly compressed, spring-loaded interior clamping structure. (The total pressure, sideways on these cells stacked next to each other, needs to be right around 240 lbs. It's spring-loaded because the cells expand and contract with heat and discharge current.)

[randomusername]

When I find a TM that works for my family, I'd be interested in this.

[rickst29]

Just keep in mind that this is only REALLY advantageous in boondocking, and with a massive Solar Installation on the roof. Withouth both of those things, a generator is cheaper and better.

[inghamm]

Battery locations make sense.

[randomusername]

I’m curious how these compare — 400Ah for about $1,600 https://maxxisenergy.com. They’re relatively local, so no shipping costs, too.

We’re going on our maiden voyage and will see how long we can dry camp hopefully this weekend. I’m unsure how much power we’ll need, but will report back when I know to confirm interest.