I got everything wired up and ran the batteries through a charge cycle until some cells started getting to max 3.5V+, and now I'm letting it balance. I don't know what the best method is to top-balance such a pack, but, for now I'm going to just let them balance through the BMS while I work on getting other stuff in place.
A123, Battery EVO, Big Battery, Tech Direct, etc.
- Thread starter shot428
- Start date
TheHappyNomads
New Member
- Joined
- Dec 19, 2022
- Messages
- 139
Just got back into town after being away for a couple of days and my batteries arrived! Can't wait to pull them out and wire up a series!
TheHappyNomads
New Member
- Joined
- Dec 19, 2022
- Messages
- 139
I finally got around to unloading the modules from the pallet and stacked in the garage. Out of the 12 total packs I ordered I'm pretty sure 1/2 are negative polarity and 1/2 are positive polarity based on the labels on top of each unit.
Pretty sure I won't have to reorient my packs like you had to when connecting a BMS to them. However, once each set is wired up to a BMS I'm wondering what kind of complication I'll run into when I need to connect all 4 sets together to create the actual, final bank
TheHappyNomads
New Member
- Joined
- Dec 19, 2022
- Messages
- 139
Since these aren't separate cells but clusters of pouches did you end up still using 16 leads from the BMS?
Sorry, I didn't see your latest post.
Yes. I did use16 leads from the BMS. I cut off the BMS connector on each battery and spliced on a 7-pin JST-SH connector.
I bought these and cut them in half: https://www.amazon.com/gp/product/B07ZJJQ4XB
I put the female side on the battery and the male side on the BMS. That's the standard connector used for standard LiPo batteries, so it means you can charge these batteries with a standard LiPo/LiFe charger if you really want to.
I connected the first 7 wires from the BMS to the first battery, skipped the first balance connection on the second battery, since that's connected to the last balance lead on the first battery, skipped the first lead on the third battery, and connected the last three BMS leads to pins 2-5 on the third battery.
BTW, I finished top-balancing my first set today and did a capacity test. I charged my EV at around 70-80A (from the battery), and got 230 Ah out of the it. There's still some capacity remaining, but I'm very happy with that.
Yes. I did use16 leads from the BMS. I cut off the BMS connector on each battery and spliced on a 7-pin JST-SH connector.
I bought these and cut them in half: https://www.amazon.com/gp/product/B07ZJJQ4XB
I put the female side on the battery and the male side on the BMS. That's the standard connector used for standard LiPo batteries, so it means you can charge these batteries with a standard LiPo/LiFe charger if you really want to.
I connected the first 7 wires from the BMS to the first battery, skipped the first balance connection on the second battery, since that's connected to the last balance lead on the first battery, skipped the first lead on the third battery, and connected the last three BMS leads to pins 2-5 on the third battery.
BTW, I finished top-balancing my first set today and did a capacity test. I charged my EV at around 70-80A (from the battery), and got 230 Ah out of the it. There's still some capacity remaining, but I'm very happy with that.
TheHappyNomads
New Member
- Joined
- Dec 19, 2022
- Messages
- 139
No worries. And great idea! I was trying to think through how to connect all the leads but this makes a ton of sense and very creative.
I think my second battery is pretty well top-balanced now, and I just connected the two together, following Off-Grid Andy's suggestion that it's no problem connecting LiFePo4 together without worrying about voltage difference, since the voltage difference is so small.
Well... I went fine. No circuit beakers popped, no BMS current overruns. Current went up to 40A or so at first, which tapered off pretty fast.
The only odd thing is that the two BMSs read a full 1V difference at 0A current. I measured the voltages every where I could outside of the BMSs, and they both measure the exact same voltage, which it around 1/2 between the two.
I could see there being some error if they, for example showed the total battery voltage as the sum of all the cells, which could accumulate errors, and may be what they do, but, considering that they're already reading 20 voltages (for a 20S BMS), it seems like they could have added one more A2D to calculate the total battery voltage correctly.
Maybe that is the case, and could explain one reason why BMS tend to have a bad rep when it comes to calculating battery SOC.
I'll let the second battery top-balance a bit more and do a full capacity test this weekend. I expect it's should take a good part of a day to drain the whole thing at 80A, which is the max I can do currently.
Well... I went fine. No circuit beakers popped, no BMS current overruns. Current went up to 40A or so at first, which tapered off pretty fast.
The only odd thing is that the two BMSs read a full 1V difference at 0A current. I measured the voltages every where I could outside of the BMSs, and they both measure the exact same voltage, which it around 1/2 between the two.
I could see there being some error if they, for example showed the total battery voltage as the sum of all the cells, which could accumulate errors, and may be what they do, but, considering that they're already reading 20 voltages (for a 20S BMS), it seems like they could have added one more A2D to calculate the total battery voltage correctly.
Maybe that is the case, and could explain one reason why BMS tend to have a bad rep when it comes to calculating battery SOC.
I'll let the second battery top-balance a bit more and do a full capacity test this weekend. I expect it's should take a good part of a day to drain the whole thing at 80A, which is the max I can do currently.
Similar threads
