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Old 02-06-2020, 02:25 PM   #1
SD-Slim
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Default TESLA batteries in golf cart

I purchased two "24" volt Tesla batteries on ebay. Removed the charger, 8x6volt batteries and battery box from my 2015 parcar p5 with DC motor.

I built a wooden box to accommodate 2 6s74p stacked battery modules connected in series. I used a fish bowl pump to pump cooling mixture through the batteries. I am using an EVPeak balance charger to asuure all cells are balanced.

By the way the 8-6 volt batteries weighed 560 pounds. The 2 Tesla weighed a total of 110 pounds!

I weather proofed the box installed the box and IT WORKS! Sort of. While the cells cn be charged to 4.2 volts/cell it is recommended that they be charged no greater than 4.15v. Still sounds right? Well they failed to say that the batteries quickly drop down to the 3.7v/ cell nominal voltage. So I have a bunce of amps but not much power because of the voltage drop.

Here is my question. Can I add another battery module in series, charge the pack to 3.9v/cell or 18x3.9=70.2 volts. Will this burn up the carts electronics? Is there a way to step the voltage down? If I can make this work the range will be awesome and so will the power.
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Old 02-06-2020, 03:17 PM   #2
S-N-R Customs
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Default Re: TESLA batteries in golf cart

When you say you have a “bunch of amps, but no power” do you mean you have plenty of torque but not much speed?

If you have the amps, you should have “power”

Voltage is what determines your speed.
Running your electronics at high voltage will decrease their life span. How much? That’s the question. If the voltage does drop fast, then MAYBE you could bump up the voltage and it’ll drop fast enough to not hurt your electronics much.... you can also waste a bunch of money experimenting also?

Are the Tesla batteries tested and proven good? Did someone sell you “bad” ones that drop voltage quickly?



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Old 02-09-2020, 02:06 PM   #3
SD-Slim
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Default Re: TESLA batteries in golf cart

The battery modules are 230Ahr each connected in series. The voltages are all charged to the same voltage but one of the cells does have more resistence than the other 11 and it charges at a much faster rate, initially.

I am only restoring 30-40 Ahr when I charge the battery. The Voltage controls the speed and the amps the distance. As the discharge goes down and through the Nominal voltage relatively quickly which leaves a lot of amps unused.

I wish I could reconfigure the cell connections to get a 7s63p configuration. 2 of those in series would be great.
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Old 02-10-2020, 01:58 PM   #4
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Default Re: TESLA batteries in golf cart

Quote:
Originally Posted by SD-Slim View Post
Here is my question. Can I add another battery module in series, charge the pack to 3.9v/cell or 18x3.9=70.2 volts. Will this burn up the carts electronics? Is there a way to step the voltage down? If I can make this work the range will be awesome and so will the power.
You do not want to partially charge the cells then attempt to regain the capacity by increasing the number of partially charged cells. The reason being is that the cells have a discharge curve where it provides a lot of capacity and the V only drops a little until it gets to around 3.5vpc (depending on the cell) and the vpc drops very quickly thereafter. So now you have much less difference between where you are charged to and where your knee is and then you'll cutoff your voltage.

But, I think you are seeing why I don't recommend a 12S pack for a 48v cart. Yes, it charges to 49.8V but it discharges to 42V... Your lead acid pack at 48V was basically dead and your cart showed it by going slower. The lithium has a much wider V range so if you go lithium I recommend increasing the max voltage. A 14S pack goes from 58v (57.6v is where I stop my charge at) gives a higher top speed and when discharged to 3.5vpc it's still 49V so it's still better than lead acid even though it's almost time to charge the pack.

But if the seller was correct and you have 230ah and you don't have any issues were some of your parallel strings are not connected, I'd think you would have several miles above the 48V threshold. I'd check the 74P part of your pack to make sure some of those strings are not disconnected.

If you do find disconnected strings be careful because the V on those cells may be much higher/lower than the V of the other cells and simply connecting them can create a massive current transfer...
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Old 02-10-2020, 02:01 PM   #5
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Default Re: TESLA batteries in golf cart

Quote:
Originally Posted by SD-Slim View Post
but one of the cells does have more resistence than the other 11 and it charges at a much faster rate, initially.
This cell may be bad... If it charges more quickly it will discharge more quickly. Indicating it may be much less capacity that it's peers.

The imbalance will likely cause issues with both charging and discharging.
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Old 02-18-2020, 11:38 AM   #6
SD-Slim
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Default Re: TESLA batteries in golf cart

Thanks for the replies and suggestions.

I do not know if there is a way I can bypass any of the cells in a module. If it were possible that would be great. I would get a third module and select 14 or 15 of the best cells and still have backups in the event one of the selected cells degraded.

If you want know what a module looks like go to: https://www.ebay.com/itm/Tesla-Batte...gAAOSw96ldr6Ll

You will have a better idea what I am dealing with.
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Old 11-04-2020, 07:10 PM   #7
Murby
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Default Re: TESLA batteries in golf cart

What you have is not a 48 volt lithium ion battery, its a 44 volt battery.

For proper use, lithium ion batteries should be configured for 7s (24v system) or 14s (48v systems).

I've been down this road and will never go back to a 12s system for a 48 volt load. There's just too much power left on the table.
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Old 11-05-2020, 07:26 AM   #8
SD-Slim
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Default Re: TESLA batteries in golf cart

I agree. It would be great if Tesla would reconfigure their modules to a 7s for golf carts and other 48v applications. I sent a 2 proposals to them with the justifications. No reply.
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Old 01-23-2021, 05:47 PM   #9
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Default Re: TESLA batteries in golf cart

@SD-Slim did you ever pickup a 3rd pack or replace the bad cells in this setup? I am quite curious about doing something similar in a cart I am restoring. However I'm not sure I'd use cylindrical cells like used in the tesla packs. I saw these on ebay that looked very promising, especially how easy they are reconfigure. I would buy 2 of those for a total of 42 cells, which could be configured for 14s3p at about 5.7kWh and 84lbs.
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Old 01-24-2021, 11:54 AM   #10
SD-Slim
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Default Re: TESLA batteries in golf cart

No I am still running the 2 module setup. This setup is 12s74p. Lots of amps (235 Ahr) but the voltage degrades to the nominal 45 volts rather quickly. I purchased and installed 48v/160 AHr Roypow battery pack (ebay) that included BMS & charger that I installed in another cart.
Voltage and Amp Hours are the keys. Additionally you need a special charger that is matched to a bms (battery management system. the RoyP{ow battery pack weighs 160 lbs.
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