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Lithium cell charging properties questions

1531 Views 4 Replies 3 Participants Last post by  ElectriCar
Hi all, I'm almost ready to order but I need a teeny bit of info. Here's the deal.

I've got an Advanced FB1-4001A motor, Curtis 1231C-8601 500A controller rated at 180V max. Currently running lead pack at 144V, until you hit the throttle at which time it's a 120-130V pack! :( After the charger turns off, the pack voltage drops from about 186, over the controllers rating, down to about 160 or so in like 5 seconds, plenty quick enough so I can't crank it up and blow it before it gets to a safe voltage.

I've been wondering about LifePo4 batteries and how they behave. So if you're charging at 3.85 for example, how long before the voltage drops to about 3.4 or so after the charger stops? Seconds or minutes???

The reason I'm asking, I'm able to fit 50 200Ah cells in my truck comfortably and would like to do so for maximum range, minimal C draw and to maximize cell life.
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I really wouldn't go past 48 cells with a 144 volt controller. 50 may be O.K. but voltage at the bleeding upper limits are quite hard on the controller. 45 cells is most often billed as a 144 volt pack. With 50 cells you will be hitting the throttle many times at 3.35 volts per cell but that kind of voltage would only happen once at startup with 12 lead acid batteries. The ripple and the electrolytic caps -- seems like a way to early controller death (and even the Curtis is expensive.)
Thanks! I know a lot of people use a 156V pack on it with no problems. My 144V pack always starts up at about 160-162V after sitting over night, maybe slightly less. So I assume a 156 pack would be sitting about 172V or so.

However, I don't plan to charge fully the pack, only to about 90%, which is the CC charging mode where you can rapid charge if you like. Rickard says there's not much energy above the CC charge point AND it will stay in balance better this way. I plan to only monitor, not control individual cells.

This will extend the cell life I understand but I don't know what the voltage resting will be and how soon it drops after charging. 3.35*50 cells would be 167.5V but I don't know if that's resting voltage after 100% charge or what, I'm assuming it is.

I've got to call Bob at EVAmerica about the controller and I've already emailed Dave Mosher, a repair technician about it.
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how long before the voltage drops to about 3.4 or so after the charger stops? Seconds or minutes???
Minutes. For what it is worth, I have a Curtis 1231-7501 controller with 130V max. I use 36 CALB cells and typically charge to around 123-124V. HPEVS recently told me they are charging "all their cars" with this controller to 128-129V now. Myself, I wouldn't charge to over the charger max V, even though the pack "relaxes" down to a voltage lower than that minutes after charge. Just seems like it might stress components leading to problems over time, but sounds like you have been doing it for a while with no problems. Guess it depends on what safety factor Curtis has built in, and where the components in your controller are in the distribution around the mean on which they based the factor. You will only have the max voltage of 3.85V/cell if you top balance. If bottom balance, it will be lower as you lowest capacity cell limits the voltage the other cells are charged to (that's why I only get to 123-124V). So depends on that too. I would guess 46 would be fine with top balancing and charge to 3.85V/cell to 177V max V.
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Fresh off the phone with a guy I know who's factory authorized, did a warranty issue for my Curtis 1231C controller last year. Turned out not to be a control issue after all.

But I told him I wanted to go to 50-51 cells and at 3.85 charge would come out to 196V while charging. Said he would prefer I stay at 50 cells to keep it at about 192 or so IF I charged to 100%. I would like to only charge to 90%, 182.5V and discharge to 80% if find that acceptable range wise.

Also asked him if he could set the low voltage to keep it at 2V per cell. He said it's currently fixed at 60V but he could change it to whatever I wanted for $150. Said you have to open it up and seal it back up to do it.

He can also increase the max operating voltage. Said one guy wanted to run his at 250V so he changed the caps for 250V and upped his amps from 500 to 900. That is some control right there! I don't need that though, just want to drive wherever I need to go.

Now to talk to the motor people...
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