DIY Lithium Packs, Proposal and Discussion

Midwestdrifter

Engineer In Residence
A few notes as I wind down the testing.

The Orion BMS requires some cell taps to be attached to a specific cell when not in use. Failing to do so can cause the ASIC which reads cell voltages to pick up noise, creating a random fault code, which made me think the BMS was failing.

The Jr 2 also uses the current convention where positive current is discharge, and negative current is charge. I got them backwards, and it caused me an hour of fiddling.

For SOC calibration, I have decided to use only upwards drifts. Specifically at around 3.5Vpc it resets to full. Though I may add a down drift at the lower knee if I find myself spending a lot of time there.

I am only seeing about 30mv drift at 200A discharge, so the cells seem well matched. I will do a full discharge capacity test tomorrow, and log it all for a nice graph.
 

VanGoSki

Well-known member
How's the software for configuring the Orion BMS? I'm a bit underwhelmed with the REC-BMS tool. And I had to pay extra to get it. 🤨
 

Midwestdrifter

Engineer In Residence
How's the software for configuring the Orion BMS? I'm a bit underwhelmed with the REC-BMS tool. And I had to pay extra to get it. 🤨
Its got a bit of a learning curve, as you need to understand the logic used for some inputs. There is a pretty good manual with flowcharts though. The tool has decent graphs which show you the inputs for some features, which is nice. It has a live graph and data logging as well.

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I got a weak cell fault when testing, so I checked the BMS internal resistance measurements for the first time. They were pretty varied, with one cell over 1mohm, and others near 0.5mohm. I should be seeing around 0.2 max (at mid range SOC, discharge), and about 0.12 nominal. Though it will vary with SOC and temperature.

I bit the bullet and opened the cover. Nothing seemed out of place. So I took all the busbars off, and polished them with 1,000 grit paper. Easiest method was to oil my belt sander with a 1000 grit belt. I should have paid closer attention, but the 200 grit I used before was not up to the task, and I saw the scratches when I got a few passes in.

Reassembled and torqued to 35 in-lb. Results shown below at nearly full charge. Much better. The values do fluctuate a bit, but should be fine for my application.

1599854843500.png

I will hopefully be (finally) able to do a full discharge/charge cycle tomorrow.
 

VanGoSki

Well-known member
Nice. My 100AH cells are rated at 1 mohm. They have a high state of charge because I top balanced them at full charge, minus some testing. My BMS hasn't calibrated it's SOC indicator yet, so it's hard to know exactly. Here's what my display looks like. It's showing around .4-.5 mohm resistance. I had a bit of cell voltage variation even after top balancing. But the BMS seems to have improved it. Here's what my monitor looks like. I actually have 8 cells so each BMS cell is actually two physical cells in parallel.

 

Midwestdrifter

Engineer In Residence
Did a full discharge test. Called it done at 520AH. Looks like all 560AH are available, but I going a bit conservative. I will post up a graph when I have a chance.

Tested the alternator charging and control. For the naysayers about "alternator meltdowns", I had my alternator pegged at ~100-120A for an hour in 85F temps low idle only. The main case never got over 150, and the outer windings maxed out around 180F. This was measured with my IR thermometer, which is plus/minus 10F accuracy at those temps. With the pack at around 20% SOC actual, the alternator was outputting 13.46V, and the pack was at 13.17V. With no charging source the pack was at about 13.1V. My pack is around 0.5-1mohm at this SOC/temp.
 

RVBarry

Well-known member
Hi, what size is your alternator, and are you using a resistive (smaller gauge) wire like you were thinking of?

Also, the batteries appear to be about $2500 now... does that seem right?

Thanks!
 

Midwestdrifter

Engineer In Residence
My charging circuit is unchanged. Mostly 2/0 cable. Alternator is 200A version. I don't see any reason to change it based on my most recent test.

The only difference with a smaller alternator, is that the current would be lower, and depending on wiring, the voltage at the alternator could be closer to the battery terminal voltage.
 

rollerbearing

Well-known member
With your data upload - I am curious about your per cell voltages at the bottom SOC reached and their spread.

And - is the 40 ah "reserve" based on the weakest cell or the overall pack voltage?
 

Midwestdrifter

Engineer In Residence
With your data upload - I am curious about your per cell voltages at the bottom SOC reached and their spread.

And - is the 40 ah "reserve" based on the weakest cell or the overall pack voltage?

Voltage spread between cells was about 20mv when I terminated the discharge at 12.1V or so.

The discharge limit is based on pack voltage (for my inverter). All other loads will continue to function until the BMS drops them out. The BMS drop out is based on cell voltages. I haven't decided on the BMS low voltage limit. Its 2.8V now, but I am thinking 2.95V. At 2.8V the BMS will shut down, but it still consumes a few mA, so for long term storage I need to pull its fuse.
 

Midwestdrifter

Engineer In Residence
Here is the voltage, I tried to smooth out some of the noise, but this about as good as its going to get. Discharge was at about 140A. Charge was at 110A.

1599952916842.png

Here is the tail end of the charge cycle. The discontinuity in the middle is when my laptop went to sleep for a bit.

1599953183710.png
 

johnplyler

Active member
How's the software for configuring the Orion BMS? I'm a bit underwhelmed with the REC-BMS tool. And I had to pay extra to get it. 🤨
Hi there again. Well, guess what, you don't just go to amazon (or anywhere else) for a REC-BMS. I wondered if you could pray-tell where you got yours? I haven't even started to install the alternator. By the looks of your dining room table, I am betting you don't have a wife telling you what comes FIRST! Anyway, once I got the #9 wire figured out, the rest looked rather straight forward. I was wondering what you ran into?
 

johnplyler

Active member
I forgot to say, I am John Plyler here in Raleigh, NC. I would be glad to talk anytime if you should want to call 919-821-4784, but be forewarned, if I am thinking you are a telemarketer calling, I might say some things that would make the Devil blush!
 

VanGoSki

Well-known member
@johnplyler I got the REC-BMS direct from Wakespeed. They are a dealer for REC. They'll send you a price list if you ask.

I'll message you privately. The reason you get all those telemarketers is because you post your number publicly. :laughing:

PS: I just realized were in MWD's thread. We should probably take any future discussion to my thread or offline. Thanks.
 

johnplyler

Active member
Well, you are so kind! I can only see a few more Franklin's saying Bye!
When I was going over the options list picking out the aux. alternator, I never dreamed the money I would be spenting! Back then, I just figured I would run down to Advance and lay down a $100, or $200 since it is a Sprinter.
When Will P. was showing the BMS, I was saying anyone can do that!!! Heck, I had to have the wife help me with the TV the other night watching the Presidential debate I hadn't turned it on in so long...........
I will get up with WakeSpeed and see what I can do.
Thank you so much.
 

Vicobaba

New member
Hi - thanks for continuing to update this thread. It's been super helpful and interesting to future LFP-DIYers like myself :)



Does this mean you'll be wiring the Orion Jr output to control a small relay, then wiring that small relay to control the main ~300A (or whatever size you chose) contactor?

Are you going to have one main +ve busbar where everything (battery pack, solar controller, inverter etc) will connect? If so, have you thought about having separate "charge" and "load" +ve busbars (each with their own contactor)? Leafing through the Orion manual, it looks like it has separate output signals for overcharge and undercharge events. With separate busbars, you could, in theory, disconnect just your charging source(s) on a high-voltage/high-SOC event while leaving your loads connected. Or, say, use the temperature control/monitoring to disconnect just the charging sources at low temps, while leaving the loads connected.
Whereas with one combined charge/load busbar, if the BMS disconnects the main contactor on a high-voltage/high-SOC event, how will you discharge the batteries? (or vice versa, how to charge the batteries on a low-voltage/low-SOC disconnect event)
Hi, I am new here. Can you please show a schematic on how to connect the obd to work with the Orion jr? Also can I use a standard serial wire to connect the bms to my laptop? Finally what kind of relay can I use to turn on larger relays thanks
 

Vicobaba

New member
With the vibration this pack may experience, and the ~2mm expansion/contraction of a 4 cell stack, I think a more flexible approach may be called for. The typical bus bars with a slight arc are fine I think.

As a plus the ground strap material will let me mount my fuse inside the battery box without adding another inch of width. Its a very tight radius, but it fits.
Hi, I am new here. Can you please show a schematic on how to connect the obd to work with the Orion jr? Also can I use a standard serial wire to connect the bms to my laptop? Finally what kind of relay can I use to turn on larger relays thanks
 

Midwestdrifter

Engineer In Residence
The orion manual shows how to wire a FET to control a larger relay.

Wiring obd2 is simple. Connect the CAN +/- wires and power to an obd2 Bluetooth adapter. Then follow the instructions to setup torque for orion.

This should all be available with a few Google searches and reading the manual.
 

Vicobaba

New member
The orion manual shows how to wire a FET to control a larger relay.

Wiring obd2 is simple. Connect the CAN +/- wires and power to an obd2 Bluetooth adapter. Then follow the instructions to setup torque for orion.

This should all be available with a few Google searches and reading the manual.
Thanks. I am still not able to connect the bms to my laptop. I am sure it has to do with the rs232 serial cable. According to Orion website the serial cable has to be straight through kind and can’t seem to find it online, do you have a link where I can get one?
 

Midwestdrifter

Engineer In Residence
Many cables are null modem type which won't work. You want a cable with all pins populated/connected. I don't have time to hunt for you, but I found one in a few minutes on Amazon.

As a note the bms must be powered for the serial to work.
 

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