01-11-2022, 08:50 AM | #11 |
Gone Wild
Join Date: May 2012
Location: Rio Verde, Az
Posts: 7,183
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Re: DIY Lifepo4 Daly BMS cell voltage drop issue under load
With my Yamaha carts, I can limit my current to 300 amps without a major difference in performance. We don't have any real hills here though. Going 25 on level ground draws about 75 amps at speed with my cart. Full acceleration on level ground will draw over 300 amps at startup. My Leaf cells handle that without any significant voltage drop. I don't know what the "C" rating of my cells is but it's way more than 3C.
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01-11-2022, 09:04 AM | #12 | |
Not Yet Wild
Join Date: Apr 2020
Posts: 24
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Re: DIY Lifepo4 Daly BMS cell voltage drop issue under load
Quote:
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01-11-2022, 09:06 AM | #13 |
Not Yet Wild
Join Date: Apr 2020
Posts: 24
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Re: DIY Lifepo4 Daly BMS cell voltage drop issue under load
I'm using a 60amp BMS, but the BMS just cuts off a relay that cuts off the accelerator wire. The only thing running through the BMS is my 10amp charger and on the discharge side the 48v-12v reducer that powers a radio and lights. So may charge through BMS is 10 amps and max discharge is 3 amps. |
01-11-2022, 09:12 AM | #14 | |
Not Yet Wild
Join Date: Apr 2020
Posts: 24
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Re: DIY Lifepo4 Daly BMS cell voltage drop issue under load
Quote:
I guess I had it in my head that the aftermarket solutions all head Lifepo4 and that it would all be ok and that a 100AH battery was reasonably large enough to handle it. I'm going to rework all the BUS bars so they are uniform with the same exact washers, etc.. and all torqued the same and see if that helps but I'm not hopeful, will report back. Doubtful it helps. There also seems to one cell thats a little (.1V) worse than the others under load, maybe after a few charge/discharge cycles, I can tune that cell in better or replace it. If not, I may just go navitas and limit the amps, then I can upgrade cells down the road. |
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01-11-2022, 09:18 AM | #15 |
Gone Wild
Join Date: May 2012
Location: Rio Verde, Az
Posts: 7,183
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Re: DIY Lifepo4 Daly BMS cell voltage drop issue under load
Most of the available solutions are LiFePO4 now. Grade A new 200AH cells should be able to handle max currents in a cart without sagging much. One of my golfing buddies has a 105 AH box from RoyPow and he is loving it. The factory Lithium carts often come with only 60AH packs and they work fine also but my guess is that they are limiting the current somewhat. They are using very high quality cells in those.
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01-11-2022, 09:33 AM | #17 |
Gone Wild
Join Date: May 2012
Location: Rio Verde, Az
Posts: 7,183
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Re: DIY Lifepo4 Daly BMS cell voltage drop issue under load
That's a pretty big voltage drop. I would replace the lower ones with better cells. That might solve your immediate problem. You really need to know what current you were pulling under load to know if you can get away with reducing it. First thing I noticed when I switched to Lithium was how much less sag under load there was compared to my FLA batteries that I replaced.
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01-11-2022, 11:09 AM | #18 |
Not Yet Wild
Join Date: Apr 2020
Posts: 24
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Re: DIY Lifepo4 Daly BMS cell voltage drop issue under load
The more I have thought about it, the more I think it may be busbars. The cells where I doubled up busbars don't have significant voltage drops. Neither does cell 1.
I'm way out of my expertise but some quick googling of the existing busbars indicate they can handle 100amps. They are 14mmX1.2mm. I ordered some 1" x 0.25" Aluminum flat bar and will be making my own. These will be 10X the cross sectional area and have full coverage over the battery terminals. I will report back..... |
01-11-2022, 11:13 AM | #19 |
Gone Wild
Join Date: May 2012
Location: Rio Verde, Az
Posts: 7,183
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Re: DIY Lifepo4 Daly BMS cell voltage drop issue under load
If you can, make them out of copper. It's a better conductor than aluminum by a bunch. If you move your BMS wires from one side of a bus bar to the other and remeasure, you can test your theory. My Leaf cell battery has thick copper bus bars. Not sure how thick but my battery meter shows very little sag under load.
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01-11-2022, 11:24 AM | #20 | |
Not Yet Wild
Join Date: Apr 2020
Posts: 24
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Re: DIY Lifepo4 Daly BMS cell voltage drop issue under load
Quote:
I can re-arrange the doubled up bus bars to other parts of the pack on different cells. Is that similar to what you mean to test it? |
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