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Old 05-12-2014, 01:21 PM   #11
kuntryboy
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Default Re: Anyone using lithium batteries?

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Originally Posted by sportcoupe View Post
Okay... I'm very curious to see how the Leaf batteries worked out for you Sportcoupe. What are you running (motor, bms, cart)? What are the results regarding weight savings, range, speed? Did those huge battery banks fit under the seat of the cart? I know your just digging in, but can't wait to see the results. Also, I would like to know exactly which package you bough from hybridautocenter.
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Old 05-12-2014, 01:31 PM   #12
caokgafamily
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Default Re: Anyone using lithium batteries?

Yes Sport,

Any updates on you lithium build? Pics, I'm sure your wide open in this build.

Steve
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Old 05-12-2014, 03:07 PM   #13
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Default Re: Anyone using lithium batteries?

Cart frame is at powder coaters. I am far from driving a lithium cart as of now. Drive system isn't determined but I think I'll go with PDS.

As for a "huge battery bank" under the seat, nothing could be further from the truth. The T105's that came out weigh roughly 400 lbs. My new pack only weighs 120 lbs.

I bought individual Leaf batteries from hybrid auto center.
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Old 05-12-2014, 07:58 PM   #14
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Default Re: Anyone using lithium batteries?

I'd be interested in hearing about the charging and battery management plan/hardware you have selected.
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Old 05-12-2014, 08:07 PM   #15
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Default Re: Anyone using lithium batteries?

Charging my 48v Leaf battery pack will be via a Quick Charge, on-board charger programmed with a lithium charge algorithm and custom 4.2v per cell constant voltage at the end till amps drop. The 4.2v is for the Leaf cells and not LiFePo4 cells, beware there is a major difference.

No BMS because I am bottom balancing the pack before first charge. Each battery will finish slightly different at the end of the charge cycle but none will pass 4.2v because of the charger settings. I can handle a few 4.1v cells. The most critical is discharge, since I am balancing them at the empty end no one cell will ever drop below minimum voltage and be damaged.

My battery pack getting bottom balanced.
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Old 05-13-2014, 07:43 AM   #16
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Wow. This looks like a great build. I can't wait to see the outcome. For ignorant souls like myself, could you please explain what bottom balancing is and procedure to "bottom balance".

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Old 05-13-2014, 08:04 AM   #17
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Default Re: Anyone using lithium batteries?

Bottom balancing is just discharging each cell to the exact same state of charge value, in my case 2.75v. After they are balanced, they will all charge up equal to my chargers maximum 4.2v. Some will charge to 4.2 before the others because of the slight difference in capacity and manufacturing variables of each cell. This is ok because once discharged they will all be equal so no one cell gets discharged more then another.

Top balancing is just the opposite. Each cell is monitored individually and charged to it's maximum value each and every charge. This is more complex in the vehicle. While the vehicle is driven each cell will reach a different lower state of charge, again due to cell capacity and manufacturing tolerance's so one call can actually be discharged more then the other and will be allowed to drop below the danger level. Top balancing is for people that want to squeeze each and every Ah out of a cell.

To summarize, you can either have the pack ragged at the top (bottom balance) or ragged at the bottom (top balance/BMS). I prefer to leave it ragged at the top.
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Old 05-14-2014, 03:53 PM   #18
interstate
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Default Re: Anyone using lithium batteries?

Been reading a little on top vs bottom charging, and also have hobby related battery experience where we top balance our lipo packs. It seems one must keep an accurate monitoring system on every cell in the battery bank. For top balancing this is done with bms bleeding or shunting devices, or this is done with a charger that can charge each cell individually.

How are the cell voltages monitored on your bottom balancing system?

Does the charger go through a discharge cycle to bring every cell down to a set voltage before it refills the cells with a complete charge?

In our hobby scenario, our speed controllers watch total pack voltage. We set a low end threshold that is high enough that even a weaker cell will not be damaged. The motor is shut down or at least reduced in output. We also then monitor the total battery bank capacity that is discharged. When we hit 80% consumption we recharge. The chargers will then top balance the packs, but we have balancing leads for every cell in the battery bank.
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Old 05-14-2014, 04:17 PM   #19
interstate
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Default Re: Anyone using lithium batteries?

Another thought on charging, again from other interests and experiences not related to EV.

We run our batteries in series to achieve our desired voltage. All cells have the same capacity. We then charge our batteries in parallel, which allows each cell to charge fully and then spill over the current from the charger into the slower charging cells. A balance monitoring wire is connected to each group of parallel cells to monitor those combined cells as a whole.

How does your charging system work?
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Old 05-14-2014, 05:17 PM   #20
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Default Re: Anyone using lithium batteries?

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How are the cell voltages monitored on your bottom balancing system?
My DVM has programmable outputs I use to control a solenoid that connects the cell to a power resister.

Quote:
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Does the charger go through a discharge cycle to bring every cell down to a set voltage before it refills the cells with a complete charge?
No, that would be a complete waste of energy and take FOREVER. You only have to bottom balance a pack once.
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