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solar batts for EV conversion


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Hi gents I am in prosses of converting Mini Cooper in to EV. .Result  of my research broth me to $5000 96v 180Ahbatteries which is to high for me. I came to idea of using solar batteries ( pylontech  type ). Would it be possible?

Any respond will be highly appreciate 

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You generally want a 3C battery for an EV. The BMS should also be capable of handling the higher voltage, so the US5000/3000/2000 is out of the question. Then there is the temperature sensitivity - but that depends on where you live mostly. If it gets really cold you would need heating. If it gets much hotter than 25°C, the battery cycle life will be affected.

I would rather suggest you get the same cells others successfully have used for an EV conversions from a reputable supplier on alibaba. In the numbers you would need, it most likely would end up being cheaper as well.

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  • 1 month later...

Popular Lifepo4 brands for EVs are EVE and CATL.

Usually EV manufacturers will get "Grade A" / EV certified grade cells, while for solar many are using "Grade B" / ESS (energy storage) Grade.

On Alibaba and Aliexpress it's one bug mess... They advertise Grade B cells as being Grade A.

For you DIY project it might not be significant.

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It is important to look at both kW and kWh. Solar storage usually only worries about kWh.

For the numbers you gave - 96V, 180Ah = ~17kWh.

Solar batteries are generally rated at 0.5C continuous discharge with 1C bursts. Which means you could run your motor continuously at 8kW or intermittently at 17kW - neither of which is going to give you particularly impressive performance.

So, either you need more packs in parallel, or you need high C rating cells (which you won't typically find in solar batteries).

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That is why most industry EVs have a high pack voltage e.g. the old Nissan Leaf has nominal pack voltage of 360V. Higher voltage means less current draw from cells; thinner wires to the controller and the motor etc.

What is the rating of the motor you are planning to use ? The very popular ME1003 (up to 72V) is used in many a conversion where a DC motor was the option chosen. The motor is rated at 20kW peak so that means (with 72V pack) the current draw is approx 277A !  The controller correspondingly needs to be rather beefy.

I almost converted a beetle to electric using the above motor and a Kelly motor controller - 180A continuous and 1min current 400A. See KDH14401E - KDH - Opto-Isolated PM DC Controller - KellyControllers.eu

My conclusions on a BMS were that to get one to handle that level of current was impractical and my plan was to use a BMS purely as a battery/cell monitor and thus as a warning system. This so that when there was an instance of low pack or cell voltage then the BMS output would drop and sound a buzzer/beeper. Over current is typically handled by the motor controller and failing that..... the fuses.

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On 2022/09/21 at 9:47 AM, GreenMan said:

That is why most industry EVs have a high pack voltage e.g. the old Nissan Leaf has nominal pack voltage of 360V. Higher voltage means less current draw from cells; thinner wires to the controller and the motor etc.

What is the rating of the motor you are planning to use ? The very popular ME1003 (up to 72V) is used in many a conversion where a DC motor was the option chosen. The motor is rated at 20kW peak so that means (with 72V pack) the current draw is approx 277A !  The controller correspondingly needs to be rather beefy.

I almost converted a beetle to electric using the above motor and a Kelly motor controller - 180A continuous and 1min current 400A. See KDH14401E - KDH - Opto-Isolated PM DC Controller - KellyControllers.eu

My conclusions on a BMS were that to get one to handle that level of current was impractical and my plan was to use a BMS purely as a battery/cell monitor and thus as a warning system. This so that when there was an instance of low pack or cell voltage then the BMS output would drop and sound a buzzer/beeper. Over current is typically handled by the motor controller and failing that..... the fuses.

I bought a 96V 15 KW AC motor

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5 hours ago, JustinSchoeman said:

With such a small motor, you could probably get away with solar batteries.

Your issues would be:

1) make sure they are rated for 1C discharge.

2) find/build a balancer/bms system to manage 2 batteries in series.

1. Yes 1C rated solar batteries (ie LiFePo4) would work. Assuming the motor is 15kW peak then max current draw will be approx 156A. 

2. For 96V yes a BMS to manage/monitor/protect the pack.  For 96v you would be looking at 32S pack configuration (with sufficient cell capacity to give you the full load current). Something like the following would work. 

image.png.90b3a9662e5ba2aae86dcddb5399107a.png

One option is that the BMS would be used for afore-mentioned monitoring and pack/cell protection, - and also for charging protection. However, power to the motor would be direct from the battery pack via a contactor. This so that the large current does not have to go through the BMS. The contactor's coil is is energized via BMS 96V output with suitable DC to DC converter to match the contactor's coil. Drawback of this option is that if the BMS drops the output then the contactor will drop out as well and there will be zero current to the speed controller/motor. 

Second option is to use the output of the BMS (negative logic) to activate suitable warning device such as siren and/or waring lights to indicate an out of line condition that has been detected by the BMS. This way there is no sudden loss of power to the motor. Some motor controllers may put the motor into limp mode if it gets an alert signal. 

 

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32 minutes ago, JustinSchoeman said:

Each battery has its own BMS already. No need to replace it.  It is a fairly simple job to hook them up in series and build a simple system to manage/balance them as individual 48V packs.

That depends on the battery supplier. e.g. The FreedomWon eTower does not allow series connection. From Freedom-Won-Spec-sheet_LiTE_eTower_.pdf (freedomwon.co.za)

image.thumb.png.d2e1b07f1487564869a55e23da0294e9.png

The EG4 (as used by Will Prowse) 48V LiFePo4 batteries also do not allow series connection. 

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1 minute ago, GreenMan said:

That depends on the battery supplier. e.g. The FreedomWon eTower does not allow series connection. From Freedom-Won-Spec-sheet_LiTE_eTower_.pdf (freedomwon.co.za)

image.thumb.png.d2e1b07f1487564869a55e23da0294e9.png

The EG4 (as used by Will Prowse) 48V LiFePo4 batteries also do not allow series connection. 

I am not aware of any solar batteries that allow series connection.  But they should work in series. You just need to build your own management system to sit outside of the batteries and manage the series string.  Should not be out of the capabilities of a serious DIYer.

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