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Old 03-14-2017, 10:35 AM
AEM AEM is offline
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Default Use of 6S and 12S Tesla Modules

I know at least one person is using Tesla Modules for their conversion. Could you use 6 modules modified to 12S and use them in series with 4 6S modules to use 10 Modules with 350vdc nominal, that would be about a 53 to 64 kWh pack using either an 85 or 100D pack. Would there be issues with the Modules having different voltages and capacities.
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Old 03-14-2017, 01:47 PM
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Default Re: Use of 6S and 12S Tesla Modules

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I know at least one person is using Tesla Modules for their conversion. Could you use 6 modules modified to 12S and use them in series with 4 6S modules to use 10 Modules with 350vdc nominal, that would be about a 53 to 64 kWh pack using either an 85 or 100D pack. Would there be issues with the Modules having different voltages and capacities.

Do not use the Tesla modules unless you use all the original electronics to run them.

See www.evtv.me for more information.

Roy
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Old 03-14-2017, 01:49 PM
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Default Re: Use of 6S and 12S Tesla Modules

Well yes I don't think it would be a good idea to run the Modules without the electronics to protect them.
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Old 03-15-2017, 07:48 AM
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Default Re: Use of 6S and 12S Tesla Modules

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Originally Posted by AEM View Post
I know at least one person is using Tesla Modules for their conversion. Could you use 6 modules modified to 12S and use them in series with 4 6S modules to use 10 Modules with 350vdc nominal, that would be about a 53 to 64 kWh pack using either an 85 or 100D pack. Would there be issues with the Modules having different voltages and capacities.
Mixing 6s and 12s modules in a series string would not be ideal. Since the 6s configuration has 74 cells in parallel and the 12s configuration has 37 cells in parallel, when the cells in the 12s modules are discharged to zero, the cells in the 6s modules would still have half their capacity remaining. You would be better off building your system to use either all 6s or 12s modules.

And yes, you should definitely use the appropriate BMS to monitor the modules, however most folks using these modules are not using the original Tesla slave BMS boards that are on each module. They are using the built-in cell taps on the modules that can be used to connect a separate BMS.
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Old 03-15-2017, 12:05 PM
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Default Re: Use of 6S and 12S Tesla Modules

EVTV likes to hear himself talk. Plenty of folks using Tesla Modules just fine without any Tesla Electronics. You do however still need to be smart about using any battery and any battery chemistry.
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Old 03-15-2017, 01:49 PM
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Default Re: Use of 6S and 12S Tesla Modules

So 10 12S Tesla Modules would probably work for a conversion, that would be about 120S 37-43P or 432vdc nominal or 504 at max charge, 120 to 148ah.
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Old 03-16-2017, 08:42 AM
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Default Re: Use of 6S and 12S Tesla Modules

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EVTV likes to hear himself talk. Plenty of folks using Tesla Modules just fine without any Tesla Electronics. You do however still need to be smart about using any battery and any battery chemistry.
Plenty of folks drive around just fine without wearing a seat belt. Plenty of folks drive a motorcycle without a helmet. Some of those people fly through the windshield or splash their brains across the pavement. That you can do something is not the same as you *should* do something. But, it's true, you can use different BMS hardware if you want. I think the relevant point is that it is crushingly stupid to use lithium cobalt cells without any sort of cell monitoring at all. Sure, use an orion or miniBMS or something different. But, use something. So, your last point is perfectly valid. Yes, you do just need to be smart when using any battery. Teslas have caught fire while using the built-in BMS. I would not want to be around a set of Tesla battery modules where no BMS is being used. It would probably work fine as long as you never over discharged or charged it. But, the module has a built-in BMS with cell monitoring and temperature sensors. Why wouldn't someone use it if it is there?
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Old 03-16-2017, 11:14 AM
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Default Re: Use of 6S and 12S Tesla Modules

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Plenty of folks drive around just fine without wearing a seat belt. Plenty of folks drive a motorcycle without a helmet. Some of those people fly through the windshield or splash their brains across the pavement. That you can do something is not the same as you *should* do something. But, it's true, you can use different BMS hardware if you want. I think the relevant point is that it is crushingly stupid to use lithium cobalt cells without any sort of cell monitoring at all. Sure, use an orion or miniBMS or something different. But, use something. So, your last point is perfectly valid. Yes, you do just need to be smart when using any battery. Teslas have caught fire while using the built-in BMS. I would not want to be around a set of Tesla battery modules where no BMS is being used. It would probably work fine as long as you never over discharged or charged it. But, the module has a built-in BMS with cell monitoring and temperature sensors. Why wouldn't someone use it if it is there?

Well usually its because the built in BMS is proprietary and rather out of reach of most DIY guys to deal with. So someting else is required. Even when Jack prattled on about his NO BMS montra he actually did use simple monitoring tecniques to help reduce the chance of any bad ju ju happening. Bottom balancing was the top deal. Then it was a smart charger that could cut off the charge at a predetermined voltage and amperage and then to reduce the top cut off voltage down to a safer place and then have his smart controller be able to prevent him from going below a specified voltage and amperage so never to destroy the batteries while in use. He however did not have thermal points in place and never would do active battery balancing. Bad Ju Ju there.

So with those things in play amost any battery chemestry could be safely used. I would venture to say one other thing needs to be in play. A way for the system to be shut down in case any of the others no longer work. So something that can monitor the charger/controller and a thermal switch. So if anyone goes out of play its OFF. One other thing is the battery bridge circuit from Lee Hart. It monitors a split pack and if one side goes out and its plugged in from charging then OFF goes the charger.

So a BMS in many parts. Not just a plain old BMS. I too have seen factory BMS systems fail because they did not monitor themselves. Ruined lots of batteries.

If you have an affordable way for folks to utilize the built in BMS then by all means make it available. Many here though will not go purchase from EVTV.

Im supprised that you guys are still monitoring this site.


Im still bottom balancing and low top charging and checking them from time to time. Still going well.

Still using LiFePO4 chemistry as well. Leaf Modules are being bottom balanced and checked before being put into service.
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Old 03-16-2017, 01:00 PM
CKidder CKidder is offline
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Default Re: Use of 6S and 12S Tesla Modules

Well, I don't specifically speak for EVTV though you know my work happens to feature there. I'm involved in lots of projects both with EVTV and without so, yeah, I still look at DIYElectricCar.

Most everything is available open source. The ability to use the Tesla modules is no exception.

https://github.com/collin80/TeslaBMS

But, yes, EVTV will undoubtedly sell kits too. Some people will buy them, some won't.

It is true that some number of Teslas have burned up even with these BMS boards on the modules. Your guess is as good as mine but I think there are some issues with the Tesla BMS. For one, the fault loop can easily fail open and then will never go active. The fault chain logic should have been inverted. But, it transmits faults over the serial link too so the Tesla main board should know if faults happen even if the fault line doesn't trigger.

A second issue is that there are two temperature sensors per module but they're on the positive and negative terminals of the module. This groups every temperature sensor in the whole pack into a strip 3" wide in the middle of the pack. The whole rest of the pack has no actual temperature monitoring at all. I suppose a hotspot in the rest of the pack will eventually warm up the sensors that exist but it will happen perhaps too slowly. They really should have taken the time to put either more sensors in there or put the two sensors at the 33% and 66% point through each module so that they're more centrally located and pick up temperature abnormalities more quickly.

My best guess for the failure mode that burns up a Tesla module is that one cell somewhere will go south and heat up but the voltage doesn't change enough to trip a limit. It's hot but doesn't get close enough to the coolant loop and is in fact too small of a thermal mass to really change the whole coolant temperature. This causes the temperature sensors at + and - to never really see that much temperature rise. In the meanwhile the cell gets hotter and hotter and starts to affect its neighbors. This doesn't trip any temperature sensors until well after the first bad cell is past the point of no return. The cell chemistry is not very friendly. If a single cell goes thermonuclear it'll very easy cause a cascade failure that rapidly gets out of control and voila you've got a fire. The temperature sensors in the module are really only meant to check the whole pack temperature. That's fine for hard driving or charging normally. You'd expect the whole pack to warm up because of these things. A single or few cell failure seems likely to run away long before the temperature sensors could ever find out. The only hope would be for the voltage on those cells to also go crazy. Likely 99% of the time the voltage does go stupid and the BMS catches it. But, what about that 1% of the time where a cell gets angry but the voltage doesn't go over the limit? Still, this entire paragraph is idle speculation and should be given the proper grains of salt.
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Old 03-16-2017, 05:14 PM
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Default Re: Use of 6S and 12S Tesla Modules

Quote:
Originally Posted by CKidder View Post
Well, I don't specifically speak for EVTV though you know my work happens to feature there. I'm involved in lots of projects both with EVTV and without so, yeah, I still look at DIYElectricCar.

Most everything is available open source. The ability to use the Tesla modules is no exception.

https://github.com/collin80/TeslaBMS

But, yes, EVTV will undoubtedly sell kits too. Some people will buy them, some won't.

It is true that some number of Teslas have burned up even with these BMS boards on the modules. Your guess is as good as mine but I think there are some issues with the Tesla BMS. For one, the fault loop can easily fail open and then will never go active. The fault chain logic should have been inverted. But, it transmits faults over the serial link too so the Tesla main board should know if faults happen even if the fault line doesn't trigger.

A second issue is that there are two temperature sensors per module but they're on the positive and negative terminals of the module. This groups every temperature sensor in the whole pack into a strip 3" wide in the middle of the pack. The whole rest of the pack has no actual temperature monitoring at all. I suppose a hotspot in the rest of the pack will eventually warm up the sensors that exist but it will happen perhaps too slowly. They really should have taken the time to put either more sensors in there or put the two sensors at the 33% and 66% point through each module so that they're more centrally located and pick up temperature abnormalities more quickly.

My best guess for the failure mode that burns up a Tesla module is that one cell somewhere will go south and heat up but the voltage doesn't change enough to trip a limit. It's hot but doesn't get close enough to the coolant loop and is in fact too small of a thermal mass to really change the whole coolant temperature. This causes the temperature sensors at + and - to never really see that much temperature rise. In the meanwhile the cell gets hotter and hotter and starts to affect its neighbors. This doesn't trip any temperature sensors until well after the first bad cell is past the point of no return. The cell chemistry is not very friendly. If a single cell goes thermonuclear it'll very easy cause a cascade failure that rapidly gets out of control and voila you've got a fire. The temperature sensors in the module are really only meant to check the whole pack temperature. That's fine for hard driving or charging normally. You'd expect the whole pack to warm up because of these things. A single or few cell failure seems likely to run away long before the temperature sensors could ever find out. The only hope would be for the voltage on those cells to also go crazy. Likely 99% of the time the voltage does go stupid and the BMS catches it. But, what about that 1% of the time where a cell gets angry but the voltage doesn't go over the limit? Still, this entire paragraph is idle speculation and should be given the proper grains of salt.

I was not aware that you were doing both work away from and some with EVTV. Good to know. I'll check out that link. One other thing that crossed my brain awhile back was even if a cell goes over current and pops its fuse does not mean it still can't go thermal because of an internal short. It can happen and that sort of thing is pretty much something you can't control once it starts no matter what sort of system you have in play.


Thanks for the information.

Im going with Leaf Modules myself as well as the CALB cells.


Pete
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