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Old 01-03-2020, 10:25 AM   #1
fstop
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Default Lithium conversion - please help me understand some basics

I’m interested in going with a lithium pack in my Onward. I’ve tried to absorb some basics from numerous build threads but am still fuzzy on much of it. Appears Leaf cells are a common way to DIY, and probably within my capability if I knew enough…
So, a few questions regarding the following:

1) 7 (or 14) Leaf 8v cells
2) BMS (Chargery BMS16T, Zeva unit…)
3) Output fuse, Protection Contactor / Solenoid x2 (is there a difference?)
4) Charger
5) Mounting frame for cells, brackets for additional parts like solenoids, BMS
6) Sources for 1-5?

1 – eBay availability is primarily “70% + life remaining” – obviously used batteries, but does this mean 70% of AH delivery per charge available, or 70% of # original charge cycles remaining? Is there a source for new Leaf cells? Most listings indicate maximum discharge of 120a I think – is this sufficient for high performance GC motors? Obviously 14 cells provides more range and potentially better performance – I think I’d need 14 as my stock pack has limited range when using speeds above 19mph or so… I guess for that matter you could use 16 cells? I think the BMS16T can do that many? (My controller / motor is good to 72v…)

2 – Lot’s of variables here I take it… BMS ideally should monitor each cell or cell group for over or under voltage, and monitor (and control via simple solenoid disconnect) total pack current delivery and total pack charge current. So if charger goes rogue and tries to charge to voltages that are too high, the “charge side” solenoid disconnects. If there is a short on the output, or controller or motor fails in some way, the “load side” solenoid disconnects pack from the situation. Or the output fuse blows – do you need both?
Does the BMS balance the cells in some way by bleeding off power from cells that are higher into cells that are lower, or reducing charge to cells that don’t need it and directing to those that do during charge? What happens if a cell voltage is too high or too low – can the BMS do anything about it besides alert you via beeper or screen? Then what do you do about it?
What about Regenerative braking? (I’ve got a CC Onward with a Navitas AC drive system in it) Doesn’t the regen current come in to the “output” side of the battery pack? How does the pack / BMS deal with that?
What is the consensus on powering the BMS? Power with the total pack voltage or via a DC converter (the one on my cart for lights etc…)? Power it with its own dedicated battery? What is a “sleep switch” for?
I wonder what the EZGO and Club Car factory Lithium pack approach is regarding BMS / charging, etc…

3 – What is the coil voltage needed for these – is it total pack voltage or some setting within the BMS (since I presume it is what is controlling the coils of these solenoids…)

4 – What kind of charger is preferred on these installs? Is it connected via the BMS, or just to the “output” side of the battery? Does it communicate to the BMS or does the BMS just somehow stop current flow to cells that are too high during charging and allow others to continue?

5 and 6 – I don’t have a machine shop handy, and don’t want to re-invent the wheel on all of these things – is there a source / sources for all of the “stuff” needed to cobble all this together so it doesn’t look like a science project gone wrong under the seat? I’d like to make the whole unit fairly easy to remove with only a few wire disconnects if that’s possible.

Thanks for any links or other advice - obviously I've still got some reading to do on all this.
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Old 01-03-2020, 07:25 PM   #2
WalterM6
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Default Re: Lithium conversion - please help me understand some basics

You are never going to understand everything completely. Just jump in and do it. If a problem comes up then ask it here.
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Old 01-03-2020, 09:36 PM   #3
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Default Re: Lithium conversion - please help me understand some basics

Yep, as Walt said. And if you pick any of the build threads here you can see they walk you thru the process. In regards to BMS, you will get varying opinions. On several of the build threads they supply links to the items used.
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Old 01-03-2020, 09:40 PM   #4
fstop
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Default Re: Lithium conversion - please help me understand some basics

Thanks!

A number of good threads with some great input...

Will continue to absorb info before ordering parts, but since this same thing has been undertaken by so many on the forum, I'm hoping to pick up a few tips that I haven't read myself in the various threads.

Ready to ditch the FLAs
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Old 01-03-2020, 09:46 PM   #5
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Default Re: Lithium conversion - please help me understand some basics

And you may still get more, but there are soooo many different ways (Charger, BMS, Relays, Hall Sensor, etc.) that it comes down to personal choice or cost/availability.
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Old 01-04-2020, 03:38 PM   #6
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Default Re: Lithium conversion - please help me understand some basics

There is a lot to digest in your initial post, so I'll pick a few of the ones I can add my $0.02 to pretty easily.

1) 70% is generally thought of as remaining capacity. As a battery is used the capacity slowly diminishes. If the battery is abused the capacity quickly diminishes. BUT... Ebay people say 70% life because that isn't a clearly defined term and you can't go back on them for it if you didn't clarify with them before hand. It might (and should) refer to capacity, but they intentionally chose to list "70% life" instead. Also be careful of the cells that are measured, some people measure from 4.2vpc to 2.5vpc others measure from 4.17vpc to 3.0vpc. Obviously the second seller is more honest in their approach than the first. So if you get cells with a measured capacity check out what the start/end V was when they measured the cells.

2) There are many options on the BMS. Some use CANBUS communication to the charger and remote displays and foot massagers (I made that last part up) others are low powered nonadjustable and pretty useless. You want a BMS that will handle the number of cells you are putting together. You want one you can adjust the max V and the min V. Any decent BMS will open the contactor if the pack V gets too high or low (even when regen braking). Some BMS units can supposedly shift the charge so cells that are fully charged then don't get further charged and wait for the rest. Other BMS (the one I just bought does this) put a small resistive load on cells that are high and then when any single cell gets beyond the parameters (say above 4.17v) it shuts the entire charge process down. Still other BMS without balancing function don't use the resistive load and just shut it down when outside the params. Yes, use the fuse in addition to the contactor. The contactor is there to save the pack according to the BMS. The fuse is there in case the cable rubs raw against the frame.

3) the voltage should match your pack max V in theory. I am using a 48V solenoid on my 57.6v pack. It may help that I have a 300 amp controller though.

4) The charger I have is an aftermarket one that I can set the output V to a specific value. Some people use chargers with CANBUS communication so the BMS tells the charger directly that it's time to stop. Most use a dumb charger that they can specify the final V and the BMS will will act as a backup and disconnect the charge when the V gets too high on any single cell.

5) Lithium Pouch Cells (like the Leaf and others) need to be under compression. So you'll need threaded rod and nuts to tighten them down, but how you attach it in the cart and how you make it look is entirely up to you as this is a relatively niche product there are not a great many parts out there to dress up DIY lithium installs. Getting it to be quickly removable but also entirely secured in case of a rollover may be difficult. My pack is secured and it'd take me 45 minutes or more to remove. There are many really pretty installs here. Mine isn't one of those... :)



Then again....... You have a 72V controller/motor/solenoid. If you went with an 20S pack the max V at 4.17vpc would be just under 84V. What is the Max V your controller is good for? Your current lead acid pack is 72.6V at 50% when it's time to charge. If you get your lithium settup going with a max V at where your current pack is basically dead you may not like how it runs... A 20S leaf pack (10 leaf modules since they are double) is between the cost of your proposed 7 module and 14 module packs.

Also on the regen braking front, your cart will weigh a lot less so it will take a lot less regen to slow the cart down. You won't need 250 amps of regen anymore, 130 will probably suit you fine. My cart is set to 86 amps for max regen here in Flat Florida and it feels like I put the brakes on. I have a 94ah pack and I know I can charge at greater than 1C I still like to keep the max at 1C for charging, just my preference.
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Old 01-05-2020, 05:14 PM   #7
fstop
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Default Re: Lithium conversion - please help me understand some basics

Quote:
Originally Posted by bronsonj View Post
There is a lot to digest in your initial post, so I'll pick a few of the ones I can add my $0.02 to pretty easily.

1) 70% is generally thought of as remaining capacity. As a battery is used the capacity slowly diminishes. If the battery is abused the capacity quickly diminishes. BUT... Ebay people say 70% life because that isn't a clearly defined term and you can't go back on them for it if you didn't clarify with them before hand. It might (and should) refer to capacity, but they intentionally chose to list "70% life" instead. Also be careful of the cells that are measured, some people measure from 4.2vpc to 2.5vpc others measure from 4.17vpc to 3.0vpc. Obviously the second seller is more honest in their approach than the first. So if you get cells with a measured capacity check out what the start/end V was when they measured the cells.

2) There are many options on the BMS. Some use CANBUS communication to the charger and remote displays and foot massagers (I made that last part up) others are low powered nonadjustable and pretty useless. You want a BMS that will handle the number of cells you are putting together. You want one you can adjust the max V and the min V. Any decent BMS will open the contactor if the pack V gets too high or low (even when regen braking). Some BMS units can supposedly shift the charge so cells that are fully charged then don't get further charged and wait for the rest. Other BMS (the one I just bought does this) put a small resistive load on cells that are high and then when any single cell gets beyond the parameters (say above 4.17v) it shuts the entire charge process down. Still other BMS without balancing function don't use the resistive load and just shut it down when outside the params. Yes, use the fuse in addition to the contactor. The contactor is there to save the pack according to the BMS. The fuse is there in case the cable rubs raw against the frame.

3) the voltage should match your pack max V in theory. I am using a 48V solenoid on my 57.6v pack. It may help that I have a 300 amp controller though.

4) The charger I have is an aftermarket one that I can set the output V to a specific value. Some people use chargers with CANBUS communication so the BMS tells the charger directly that it's time to stop. Most use a dumb charger that they can specify the final V and the BMS will will act as a backup and disconnect the charge when the V gets too high on any single cell.

5) Lithium Pouch Cells (like the Leaf and others) need to be under compression. So you'll need threaded rod and nuts to tighten them down, but how you attach it in the cart and how you make it look is entirely up to you as this is a relatively niche product there are not a great many parts out there to dress up DIY lithium installs. Getting it to be quickly removable but also entirely secured in case of a rollover may be difficult. My pack is secured and it'd take me 45 minutes or more to remove. There are many really pretty installs here. Mine isn't one of those... :)



Then again....... You have a 72V controller/motor/solenoid. If you went with an 20S pack the max V at 4.17vpc would be just under 84V. What is the Max V your controller is good for? Your current lead acid pack is 72.6V at 50% when it's time to charge. If you get your lithium settup going with a max V at where your current pack is basically dead you may not like how it runs... A 20S leaf pack (10 leaf modules since they are double) is between the cost of your proposed 7 module and 14 module packs.

Also on the regen braking front, your cart will weigh a lot less so it will take a lot less regen to slow the cart down. You won't need 250 amps of regen anymore, 130 will probably suit you fine. My cart is set to 86 amps for max regen here in Flat Florida and it feels like I put the brakes on. I have a 94ah pack and I know I can charge at greater than 1C I still like to keep the max at 1C for charging, just my preference.
Thanks for taking the time to post this info - very much appreciated!
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Old 01-06-2020, 10:21 AM   #8
bronsonj
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Default Re: Lithium conversion - please help me understand some basics

If you go lithium then keep an eye towards redundant safety features.

Like having the BMS kill the power to the cart at 3.25vpc (on a 14S pack that's 45.5v) but also set the controller to have a low voltage cutoff of 45.5v. Set the max V in the controller to be the equivalent of 4.17 or 4.18vpc so that as the V rises the controller will reduce the regen current. Use the big fuse for battery out, put a much smaller fuse on the smaller charge cable, fuses won't help with V issues but are still necessary.
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Old 01-06-2020, 12:31 PM   #9
fstop
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Default Re: Lithium conversion - please help me understand some basics

Quote:
Originally Posted by bronsonj View Post
If you go lithium then keep an eye towards redundant safety features.

Like having the BMS kill the power to the cart at 3.25vpc (on a 14S pack that's 45.5v) but also set the controller to have a low voltage cutoff of 45.5v. Set the max V in the controller to be the equivalent of 4.17 or 4.18vpc so that as the V rises the controller will reduce the regen current. Use the big fuse for battery out, put a much smaller fuse on the smaller charge cable, fuses won't help with V issues but are still necessary.
Thanks - good info for sure.

I'm not sure I can set a low voltage cutoff in the controller (Navitas AC 600a), I think there is just a nominal voltage setting (which I have set at 48, and I don't think you can input any figure in there IIRC, just preset voltages...) and the controller begins to limit current at some arbitrary point related to that. I don't think there is a max v. setting in the controller app either (I have the dealer app).

I'll need to shoot Navitas a tech email concerning this.
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