DIY Lithium Packs, Proposal and Discussion

Ducstrom

Active member
Drop-ins already have an inaccessible BMS internal.

Really quite a different topic from this (IMO much better) more DIY "bare cells + containment + BMS" approach, posts on each type should really be kept in segregated threads.
I realize they have their own BMS. I was pondering building my own system using the cells and BMS approach rather than the drop ins.
 

luthj

Engineer In Residence
Submitted an order for battery box parts. $175 cut and delivered in clean 16 gauge steel. Should have them in 2 weeks. I am going to cut through a floor support beam. I am not particularly worried about floor integrity. Given my load and how the box attaches. If necessary I will rivet or weld a section of tubing for additional support.
 

Verkstad

Raggarkung
Plan is to sandwich the copper braid between two pieces of 1" square copper
I did similar thing at my job. Seismic upgrades had me reconfigure batteries spacing in our datacenter, a few bussbars ended up too short.
I used rings of copper waterpipe squashed flat onto the braid. Being squashed on, needed no clamping to interfere with heat transfer. Soldering from the end, could easily watch the flow to prevent wicking too much.

Technically, that expedient would not be permitted. But the Auditor was willing to turn a blind eye considering the urgency situation and minimise downtime.
 

luthj

Engineer In Residence
Decided on Orion Jr 2 with canbus. I will install a CAN to bluetooth adapter for monitoring. I think i will also use a Hall effect current sensor instead of tapping into my existing 500A shunt. The wire run to the shunt is ~6ft, and there is interference risk.

1594065462193.png

I also ordered a heating pad. This model. Its a bit big, but should fit on the bottom of the box. It has a built in thermostat that is 45F on and 68F off, which should do a good job.


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bgflyguy

Member
I have two sets of batteries inbound. I don't know which will end up in the ambulance, but I'm hoping for the lifepo4's since they have considerable more wattage.

I placed an order with batteryhookup for 8 lg chem n2.1 120ah cells ( https://batteryhookup.com/products/new-lg-chem-n2-1-3-7v-120ah-cell-module ) and then placed an order with Dongguan Lightning Energy Technology Co., Ltd (https://www.alibaba.com/product-detail/Free-Shipping-8pcs-3-2V-280Ah_1600059397971.html ) for 8 lifepo4 EVE 280ah cells. I'm still looking for the BMS, but i'll probably end up with DALY. I will need a few, so I might order a couple of different ones. I figure it's worth it to test a few things and get the right solution for something like this. Even if I over buy on this, I'm still going to come out way better than Renogy etc. in terms of material cost.

lifepo4-280ah.jpg

I'll probably build a simple pack with all-thread and whatever backing material I can find. That box looks awesome though.
 
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luthj

Engineer In Residence
Cool, keep us posted on your results. If I was mounting inside I would use a simple enclosure method. But these are going exterior. The last piece of equipment mounted in that area got filled with Australian dirt and mud packed solid. So I need a bit of protection. :ROFLMAO:
 

hour

Observer
I'm still looking for the BMS, but i'll probably end up with DALY.
Shoo, I have 3 Dalys sitting around now that I swapped out in favor of chinese smart bms units. No problems now for almost a year on my 200+ah lifepo4 job running a 60a bms in negative and 110*F+ temps. Low/high cell/pack cutoff works great as does low temp disconnect. Tracks capacity just fine, only reason I still run a BMV712 is because I had it and it was already installed, and it's a redundancy for low temp cutoff mated to a Victron MPPT. Any reason you're not eying those?

edit: like luthj posted here. Not sure that pic is accurate though on Amazon, mine came without wires and is the size of an ipad.
 
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luthj

Engineer In Residence
I also dropped the old lead pack this week. Anyone near northern AR want some free batteries? ~70% of new capacity, no damage.

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luthj

Engineer In Residence
Making progress on the box. Everything is fitting so far.





I am working through the BMS specs, and making a wiring diagram. Since the Orion Jrs outputs are limited to 175mA, I need amplification/relay control. Something in the 5A range should work. Anybody got a solid state relay suggestion? I need low power consumption (<1mA is ideal) and 10-15V input.


I am starting to fill out a profile in the Orion software. I wasn't able to find detailed specs for the Eve 280AH cells. So I had to extropolate the temperature/performance data from the few points available, and some references from similar cells.


1595806678143.png

The BMS documentation on the charge/discharge inputs, safeties, and the various min/max voltage fields is a bit vague in places. I am figuring it out with the flow charts, but most of it will get turned off, as my chargers don't support current limiting via external input. Besides, I shouldn't ever exceed 0.5C worst case.
 

luthj

Engineer In Residence
Yeah, I have a few spares from the 4x4 display panel lying around to play with. After reviewing the specs, it looks like the relay pins are good to 60V and 175mA, so I don't need isolation, just a sufficient resistor to limit current under max transients.

Buried in the BMS manual is this example, though I would just swap the relay to the V+ side, as I am using a blue sea one with internal logic.

1595896203527.png

I am also considering if I need a relay to drop the PV input for safeties sake. Since it would be on all the time, I need something with very low power consumption that can handle up to 60V and 20A. Not much in the mouser catalog at reasonable price. The Victron battery protect 65A would be perfect, but its limited to 32V. They have a 48V version, but its 100A and 140$. I guess I could pick some FETs with low RDS and make my own solid state relay. Given the output is safe to 60V, I wouldn't need isolation for PV output control. I just need to keep the voltage drop under 1% at 20A, so a few in parallel would be required. That and a beefy heatsink,
 
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