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Battery Box Build

lance said:
Looks great! I've not followed all the details but, are you heating from the bottom or the sides?
Click to expand...
Bottom only, each box has it's own heating pad. I added a HDPE spacer between the pads and the bottom of the cells.
I'm thinking I'm going to keep the bus bars for the pairs of cells, but add flexible pairs of 2awg jumpers to connect the pairs instead of the small bus bars.
 
willo said:
Bottom only, each box has it's own heating pad. I added a HDPE spacer between the pads and the bottom of the cells.
Click to expand...
How thick is the HDPE? I thought I saw you considering aluminum plate at one point. Bottom makes sense to me.

I saw on another battery box thread the idea of a thicker VHB tape vertical run where the cells meet that I really liked as to me it accomplished 3 things: allowing heat to flow up and around the cells, allowing the cells a fractional amount of room in which to expand (on that thread it was discussed that a tiny amount of allowed expansion is good.), and securing the cells in the group firmly which for a vehicle application appeals to me in protecting the terminals.
 
The manufacturer specs said not to mount to metal - likely to prevent shorting. The hdpe is .187 thick.
12x24 pieces were about $15 each from amazon.
 
willo said:
The manufacturer specs said not to mount to metal - likely to prevent shorting. The hdpe is .187 thick.
12x24 pieces were about $15 each from amazon.
Click to expand...
Did you put anything between cells too or is the blue film is enough?
 
Any reason you went the long way instead of a wider box for side by side? Also, has anyone lokked at using marine double battery boxes?
 
Sanwizard said:
Any reason you went the long way instead of a wider box for side by side? Also, has anyone lokked at using marine double battery boxes?
Click to expand...
Ayup.
1) I wanted an even weight distribution across my camper. I chose the layout to optimize for that. I have a bay up front where this will work nicely.
2) Limiting the length of jumpers between cells is important - anything over 15cm has too much inductance and will cause issues with balancing. Between the two boxes and two layers of insulation, that's 4.5 inches (11.43cm) before you add in the distance to the terminals. To use a side to side layout, I'd have to modify the box design.
 
Following, fellow 5th wheel traveler here too. Currently have 8 Xuba 280Ah 4s2p 12v config looking to do something like this. I might have missed it in another thread but how are you connecting to your 5th wheel electrical?
 
Tball said:
Following, fellow 5th wheel traveler here too. Currently have 8 Xuba 280Ah 4s2p 12v config looking to do something like this. I might have missed it in another thread but how are you connecting to your 5th wheel electrical?
Click to expand...
This should be useful for you: https://diysolarforum.com/threads/changes-to-my-build-after-this-summer-fall-of-usage.16962/
24v battery, using a 24/12 70a converter now. Old 12v FLA is gone, I added a breakaway SLA and charger to run the breakaway brakes.
 
willo said:
This should be useful for you: https://diysolarforum.com/threads/changes-to-my-build-after-this-summer-fall-of-usage.16962/
24v battery, using a 24/12 70a converter now. Old 12v FLA is gone, I added a breakaway SLA and charger to run the breakaway brakes.
Click to expand...

That brings up an issue I've been thinking about for the past few days. RV trailer owners that eliminate the SLA battery and add a DC-DC charger between the 7-pin and the LiFePO4 battery bank are going to have a problem with the breakaway system. If the 7-pin cable becomes disconnected, there is nothing there to provide power to the breakaway system. The DC-DC charger functions in one direction, towards the LiFePO4 battery bank.

To work around that, a new wire from the LiFePO4 battery bank has to be run back to the breakaway system.

7-pin -> DC-DC Charger -> LiFePO4 -> Breakaway System

It's something that I'll be on the lookout for when reviewing proposed systems.
 
HRTKD said:
That brings up an issue I've been thinking about for the past few days. RV trailer owners that eliminate the SLA battery and add a DC-DC charger between the 7-pin and the LiFePO4 battery bank are going to have a problem with the breakaway system. If the 7-pin cable becomes disconnected, there is nothing there to provide power to the breakaway system. The DC-DC charger functions in one direction, towards the LiFePO4 battery bank.

To work around that, a new wire from the LiFePO4 battery bank has to be run back to the breakaway system.

7-pin -> DC-DC Charger -> LiFePO4 -> Breakaway System

It's something that I'll be on the lookout for when reviewing proposed systems.
Click to expand...
Adding a $20 SLA and a $5 charge controller solved this for me. My victron battery monitor has an aux battery voltage monitor that keeps an eye on it.
 
willo said:
Adding a $20 SLA and a $5 charge controller solved this for me. My victron battery monitor has an aux battery voltage monitor that keeps an eye on it.
Click to expand...

In my case, before my LiFePO4 upgrade, I had solar to charge the SLA bank on the tongue, so I retained that. The tongue SLA is also responsible for starting the generator. I need to reconnect the old AC-DC converter so that it charges the SLA battery while the generator is running. One more task to complete once the weather warms up.
 
Any reason why you wouldn’t simply connect your breakaway to your main battery bank? Accessibility?
 
I cut some lids, and decided to make up flexible 'bus bars' - really just 2awg jumpers. I used up my stock of crimp ends and need more.
I'm going to keep using the factory bus bars for pairing up the cells, but will have flexible ones to jumper the pairs in series.
I've been putting together an order of parts for my heater/control integration and have had the additional parts waiting to go into that order.

I have a couple of tasks to do on the boxes themselves:
I'm going to add 1/4 inch T-nuts to the outer shells - I'll use them to bolt the lids down, bolt the boxes to the metal flooring in my camper bay and to fasten some joining panels between the front and back of the shells.
I'm also trying to decide if I want to drill and tap my bus bars to secure my BMS wires or if I want to use ring terminals on the main terminals.

Here's how I see this wrapping up once I've crimped the pile of cabling.
1) I have to shuck both battery packs of their shell. not a huge deal, just annoying.
2) Throw some finish on the boxes to prevent moisture - I have some spar varnish that should do.
3) Install my various T-nuts, carpet coverings, etc.
4) Take the assembled shell (sans batteries) down to my camper, mark and drill my mounting holes and test mount the entire shell.
5) Re-assemble the pack and shell.
6) Install the final pack assembly (and curse at the bolt holes when they don't quite line up.)
7) Do up the final wiring.
 
Last edited:
it was more this that i was wondering about (Power: 20 ± 5W Thermostat: 70 Celsius) i don't understand the power consumption, is it only 5 watts 70c seems high for 5w.
 
70° C is high for a battery. I don't think my butt would like it either. Considering that a "good" temperature for LiFePO4 cells is 25° C (77° F), 70° C (158° F) is way up there. It looks like the power range in 15 watts to 25 watts, not 5 watts.

There is no need for the battery to be at 25° C if it is in storage. Actively in use, yet.
 
 
jonp, consider starting your own thread or posting in a thread about warming pads. Here are some suggested threads:

diysolarforum.com

LiFePO4 heating pad for cold temperatures

If you are trying to use a lifepo4 battery in freezing cold temperatures, battle born just released a 12v heat pad for keeping the batteries warm without melting the case. This pad should work for any standard lifepo4 battery. Just slap it under your batteries and connect it to 12v and you are...
diysolarforum.com diysolarforum.com
diysolarforum.com

Winter Heat For Battery Bank

Going to be putting 8 280ah cells at 4S2P in my semi so I can run my Espar bunk heater and Espar engine/fuel heater and will run my 7500btu a/c in the summer. I'm getting regular empty battery case to put the cells in. I've been think of ways to heat the cells for winter charging. Thought about...
diysolarforum.com diysolarforum.com
 
HRTKD said:
jonp, consider starting your own thread or posting in a thread about warming pads. Here are some suggested threads:

diysolarforum.com

LiFePO4 heating pad for cold temperatures

If you are trying to use a lifepo4 battery in freezing cold temperatures, battle born just released a 12v heat pad for keeping the batteries warm without melting the case. This pad should work for any standard lifepo4 battery. Just slap it under your batteries and connect it to 12v and you are...
diysolarforum.com diysolarforum.com
diysolarforum.com

Winter Heat For Battery Bank

Going to be putting 8 280ah cells at 4S2P in my semi so I can run my Espar bunk heater and Espar engine/fuel heater and will run my 7500btu a/c in the summer. I'm getting regular empty battery case to put the cells in. I've been think of ways to heat the cells for winter charging. Thought about...
diysolarforum.com diysolarforum.com
Click to expand...
i ordered the plant warmer maybe when i try it out i will start a thread. thanks... gosh $220 for the battle-born heat pad!!
 
Holy moly I am sore now.
Pardon the wire mess, I keep messing around.
Insulated the bottom of the bay, then tossed my original mounting plan.
Opted for brackets with 5/16 carriage bolts.

IMG_20210424_181643.jpg

Made up doubled 2awg jumpers a while back. Kept the bus bars for parallel cells.
IMG_20210424_181614.jpg
Finally, I designed and printed up a mount for my new sbms0.
IMG_20210424_174951.jpg
 
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