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Wiring Tesla Modules with a Curtis AC50 and 1238

1354 Views 10 Replies 6 Participants Last post by  Goldin Crazy, 
A
Hi, I'm looking for some basic confirmation and get my head around on how it's best to wire 4 Tesla Model S modules (22.8 Volt, 5.3 kWh each) together in a VW conversion. I've been using the EV West information as a starting point (attached pdf), and they recommend a 1p5s configuration with 5 batteries at 26kWh. I don't need a ton of range for my application and am looking to maximize budget, so I'm trying to use 4 batteries instead of 5. From the attached diagram, it looks like the front-rear are connected in series. But then to get the extra kWh, I assume the modules need to be connected in parallel to each other?

Front group: two modules wired in parallel to each other (22.8v, 10.6 kWh combined)
<front and rear connected in series>
Rear group: two modules wired in parallel to each other (22.8v, 10.6 kWh combined)

I think this comes out to a combined total of 45.6v and 21.2 kWh, but I am not sure and was hoping someone could confirm. If that is the correct way to wire it, would there be any issues, apart from reduced range, from using 4 batteries instead of 5?

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1. Is your controller going to work with 45v? (There are multiple versions of the Curtis 1238)
2. Are you using a BMS? (I think you should) Each Tesla module is a string of six cells. When you connect two modules in parallel, you have two parallel strings. When you then repeat that at the other end of the car, you have two parallel strings in series with two more parallel strings. That will present a challenge for selecting a BMS.

If you are trying to reduce costs/weight/space by omitting one tesla module, and if your controller can operate at ~91v, then you should consider wiring the four tesla modules in series. If you plan to drive on the highway, then I think you should consider designing for five modules (or more) and a nominal battery voltage of 112v (or higher).
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Ken S said:
1. Is your controller going to work with 45v? (There are multiple versions of the Curtis 1238)
2. Are you using a BMS? (I think you should) Each Tesla module is a string of six cells. When you connect two modules in parallel, you have two parallel strings. When you then repeat that at the other end of the car, you have two parallel strings in series with two more parallel strings. That will present a challenge for selecting a BMS.

If you are trying to reduce costs/weight/space by omitting one tesla module, and if your controller can operate at ~91v, then you should consider wiring the four tesla modules in series. If you plan to drive on the highway, then I think you should consider designing for five modules (or more) and a nominal battery voltage of 112v (or higher).
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Thanks for the response. Yes, the plan was to use a BMS. The use case for the car is mostly an around-town beach cruiser - I don't anticipate it ever going on the highway. I'll check and see what version the Curtis controller is.
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Yes, you can connect the 4 modules in series. The kWh adds no matter if series or parallel or any combo, so your energy storage is n times the modules - in your case 4*5.6 = 22.4 kWh. connect 2 modules in series in each box and connect the boxes in series. No idea why you would want to parallel the modules in a box other than your misconception of how kWh adds - you don't need to.

4 modules in series gives you a nominal 4*22.8V. No, you don't need 5 modules if your motor and controller are happy at a nominal 91V that 4 modules will give you. Even on the highway.

Get yourself matched modules from the same car and you don't have to have a BMS. You will need to monitor the 4 modules' voltages to make sure they stay matched before, during, and after charging. You might need to charge each module separately to rematch them every few months, but just keep an eye on them (you only have 4 voltages to monitor) and you should be fine.
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reiderM
remy_martian said:
Yes, you can connect the 4 modules in series. The kWh adds no matter if series or parallel or any combo, so your energy storage is n times the modules - in your case 4*5.6 = 22.4 kWh. connect 2 modules in series in each box and connect the boxes in series. No idea why you would want to parallel the modules in a box other than your misconception of how kWh adds - you don't need to.

4 modules in series gives you a nominal 4*22.8V. No, you don't need 5 modules if your motor and controller are happy at a nominal 91V that 4 modules will give you. Even on the highway.

Get yourself matched modules from the same car and you don't have to have a BMS. You will need to monitor the 4 modules' voltages to make sure they stay matched before, during, and after charging. You might need to charge each module separately to rematch them every few months, but just keep an eye on them (you only have 4 voltages to monitor) and you should be fine.
Click to expand...
BMS is still good to have to control charging etc. And keep cells balanced long term. Plus having an easy SoC readout and module temps. Just checking module voltage won't necessarily confirm that the cell groups in each module are also at equal voltage.

Also keep in mind voltage sag under load. With 10 modules in my hyper 9 conversion 5s2p I'm seeing about a 12v sag under full throttle. 5 modules may be worth it.
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You just added $3000 to his VeeDub build with the extra module and BMS, Mr Moneybags 😛

"I don't need a ton of range for my application and am looking to maximize budget"
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Goldin Crazy
remy_martian said:
Yes, you can connect the 4 modules in series. The kWh adds no matter if series or parallel or any combo, so your energy storage is n times the modules - in your case 4*5.6 = 22.4 kWh. connect 2 modules in series in each box and connect the boxes in series. No idea why you would want to parallel the modules in a box other than your misconception of how kWh adds - you don't need to. 4 modules in series gives you a nominal 4*22.8V. No, you don't need 5 modules if your motor and controller are happy at a nominal 91V that 4 modules will give you. Even on the highway. Get yourself matched modules from the same car and you don't have to have a BMS. You will need to monitor the 4 modules' voltages to make sure they stay matched before, during, and after charging. You might need to charge each module separately to rematch them every few months, but just keep an eye on them (you only have 4 voltages to monitor) and you should be fine.
Click to expand...
I have been confused by assertions made " kWh adds no matter if series or parallel or any combo" so I refreshed my understanding of Ohm's Law.
Voltage increases in Series only. Capacity increases in Parallel only. Connecting two 24VDC Tesla 5.3KWH in series will result in 48VDC and 5.3 KWHs. Connecting two 24VDC Tesla 5.3KWH in Parallel will result in 24VDC and 10.6 KWHs. hope this helps
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No.

You have a bucket of water.

You add a second bucket of water to your collection.

Doesn't matter if you pour the water from both buckets into a bathtub or into a tall beer glass, you still have two buckets of water. The water level is irrelevant.

Series or parallel you are adding two units of energy (kWh) to the system.
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Goldin Crazy said:
Voltage increases in Series only. Capacity increases in Parallel only. Connecting two 24VDC Tesla 5.3KWH in series will result in 48VDC and 5.3 KWHs. Connecting two 24VDC Tesla 5.3KWH in Parallel will result in 24VDC and 10.6 KWHs. hope this helps
Click to expand...
The model S modules are 22.8V nominal
Actually the capacity is Ah x nominal Voltage in series 45.6V X 232.45 AH= 10.599 kWh , in parallel 22.8 x 464.9 AH= 10.599kWh
series increases the voltage, parallel increases the Ah
Later floyd
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Goldin Crazy
floydr said:
The model S modules are 22.8V nominal Actually the capacity is Ah x nominal Voltage in series 45.6V X 232.45 AH= 10.599 kWh , in parallel 22.8 x 464.9 AH= 10.599kWh series increases the voltage, parallel increases the Ah Later floyd
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Thank you Floyd. Yes I misspoke. I meant to show capacity as Amp Hours not kWh. Watts will always be the same as it is a function of volts times amps. Whether series or parallel, you’re either doubling the volts or doubling the amps.
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Goldin Crazy
Goldin Crazy said:
I have been confused by assertions made " kWh adds no matter if series or parallel or any combo" so I refreshed my understanding of Ohm's Law.
Voltage increases in Series only. Capacity increases in Parallel only. Connecting two 24VDC Tesla 5.3KWH in series will result in 48VDC and 5.3 KWHs. Connecting two 24VDC Tesla 5.3KWH in Parallel will result in 24VDC and 10.6 KWHs. hope this helps
Click to expand...
Amp hours. Not kWh
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