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Old 07-01-2021, 08:23 AM   #31
bronsonj
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Default Re: Lithium Pack Build Questions

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Originally Posted by Booshy68 View Post
I purchased a built pack from a local company and the BMS cuts off as soon as a hit the throttle on my cart with a Alltrax controller. (I assume I am pulling to many amps and the BMS is protecting the battery's)
The company said the BMS in the pack was rated to 130 amps. But no matter how slow I pushed the peddle it would reset the BMS. I turned the amp draw down on the alltrax but then the cart would barley move.
Can you describe the mods on your cart? If it's the one in your avatar then I see you have larger wheels/tires but can't tell the size. I know you have an aftermarket controller because you said it was an Alltrax. What diameter are your tires? Do you have high speed gears in the rear diff? Did you put in an aftermarket motor?

I know that people using the RoyPow pack with the 130 amp BMS are doing "fine" with amp draws as high as 200. When you turned your max amps down what did you turn it down to? My cart will pull 75 amps continuous just to maintain cruising speed and pulls a lot more getting up to speed. If you set your max amps to 130 then I can see why it barely accelerates.
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Old 07-01-2021, 10:32 AM   #32
Booshy68
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Smile Re: Lithium Pack Build Questions

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Originally Posted by Pat911 View Post
Hi Booshy68,

Everything you need to know is in the thread I linked to but simply, the BMS is only used to disconnect the key switch on low voltage conditions. The main high current cables from the controller are connected directly to the battery pack, bypassing the BMS so there’s no high current protection.

Reusing the cells in your existing pack is a possibility but you’ll need to ensure that they are capable of supplying the currents that your motor/controller will be drawing.

The Eve cells you linked to on Alibaba may or may not be adequate. They are very good cells but their maximum continuous current is only 1C (105A) with a 30 second peak of 3C (315A). You’ll need to decide if they are up to the task in your application.

Cheers
Pat.

Thanks Pat. I am a rookie at BMS stuff so I am kinda going off what I have picked up just trying to trouble shot my two carts. I am going to crack open one of the packs this weekend and see what brand the BMS is and see what the battery's look like. Is there a way to test and determine the AH rating of a pack??

I have already been in the pack as I bypassed the negative lead per the battery maker when the pack kept shutting off and I was headed to the river. The negative lead from the battery's runs thru the BMS and then to the Anderson connector. The BMS was cutting this connection when I pushed the throttle just a tiny bit. So I cut it off the BMS and connected it directly. Now the carts works but travels maybe 5 miles. Maybe different BMS work differently? Sounds like what your talking about bypasses the BMS altogether? I was under the impression BMS's over saw charging of the cells evenly as well as watched to make sure you didnt overdraw the batterys?

I would like to see if I can use the cells in some configuration and possibly get a new BMS. I hate to waste them.

I also have a 4 seat EZGO my daughters drive. I was big tires but the motor and controller are stock from what I know.

Who would have thought battery's and golf carts would be so difficult..
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Old 07-01-2021, 10:47 AM   #33
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Default Re: Lithium Pack Build Questions

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Originally Posted by bronsonj View Post
Can you describe the mods on your cart? If it's the one in your avatar then I see you have larger wheels/tires but can't tell the size. I know you have an aftermarket controller because you said it was an Alltrax. What diameter are your tires? Do you have high speed gears in the rear diff? Did you put in an aftermarket motor?

I know that people using the RoyPow pack with the 130 amp BMS are doing "fine" with amp draws as high as 200. When you turned your max amps down what did you turn it down to? My cart will pull 75 amps continuous just to maintain cruising speed and pulls a lot more getting up to speed. If you set your max amps to 130 then I can see why it barely accelerates.

Hi Bronson,


One of the carts I am referring to yes is in the avatar. I had it built 5 years ago so some of the items are a bit vague to me. Here is some info.

Tires are 23"
Controller is one of the larger Alltrax SPM models. 48volt.
Motor is a Spicer motor 012AJ3951 don't know about gear changes.

I really would like to find a pack that allows me to pull as many amps as possible. I have a pretty steep hill I have to go up at the river. Normally we load the cart up coming back off the water and I would hate to have an issue every time we try and come up the hill..

The RoyPow packs might be a challenge even if they can pull 200amps? I can set my controller to 200amps and see how she drives. But after setting it to 400 amps and then back to 200amps I know I will not be happy..
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Old 07-01-2021, 01:33 PM   #34
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Default Re: Lithium Pack Build Questions

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Originally Posted by Booshy68 View Post

Who would have thought battery's and golf carts would be so difficult..
They're not hard. They are really easy.....until the are not!
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Old 07-01-2021, 01:40 PM   #35
Bama Brad
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Default Re: Lithium Pack Build Questions

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Originally Posted by Booshy68 View Post
Hi Bronson,


One of the carts I am referring to yes is in the avatar. I had it built 5 years ago so some of the items are a bit vague to me. Here is some info.

Tires are 23"
Controller is one of the larger Alltrax SPM models. 48volt.
Motor is a Spicer motor 012AJ3951 don't know about gear changes.

I really would like to find a pack that allows me to pull as many amps as possible. I have a pretty steep hill I have to go up at the river. Normally we load the cart up coming back off the water and I would hate to have an issue every time we try and come up the hill..

The RoyPow packs might be a challenge even if they can pull 200amps? I can set my controller to 200amps and see how she drives. But after setting it to 400 amps and then back to 200amps I know I will not be happy..
Mine is 500 amp controller and I have had no problems. Climbs hills with no problem.
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Old 07-01-2021, 02:40 PM   #36
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Default Re: Lithium Pack Build Questions

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Originally Posted by Booshy68 View Post

The RoyPow packs might be a challenge even if they can pull 200amps? I can set my controller to 200amps and see how she drives. But after setting it to 400 amps and then back to 200amps I know I will not be happy..
I can't speak to the RoyPow packs as I know nothing about them except for what I read here.

I know that I've hooked up a laptop to my Alltrax controller and found out that my cart demands (and got) 345 amps on the steepest hill I climb. My controller is a 650 amp so I adjusted the controller to "send" or "let thru" a maximum of 300amps even when the motor demands more.

I've not experienced any degradation in performance and with that adjustment I believe I am squeezing out a little more run time.

FWIW
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Old 07-01-2021, 05:35 PM   #37
Pat911
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Default Re: Lithium Pack Build Questions

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Originally Posted by Booshy68 View Post
Sounds like what your talking about bypasses the BMS altogether? I was under the impression BMS's over saw charging of the cells evenly as well as watched to make sure you didnt overdraw the batterys?
The BMS is not bypassed. Charging current still goes through the BMS and it has the ability to cease charging if either the pack voltage or cell voltage get too high. It can also cease charging if charge current is too high, but this is a function of your charger and you should size your charger appropriately. Cell balancing works as it should.

The key switch line is also controlled by the BMS. On a low pack voltage or low cell voltage the BMS will disconnect the key switch, effectively shutting down the cart.

The only thing that is being bypassed is the high discharge current cutoff but if your cells can supply the required demand, and you have an appropriately sized fuse or breaker, you’ll be ok.

Cheers
Pat.
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Old 07-02-2021, 03:04 PM   #38
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Default Re: Lithium Pack Build Questions

Quote:
Originally Posted by Booshy68 View Post
I have already been in the pack as I bypassed the negative lead per the battery maker when the pack kept shutting off and I was headed to the river. The negative lead from the battery's runs thru the BMS and then to the Anderson connector. The BMS was cutting this connection when I pushed the throttle just a tiny bit. So I cut it off the BMS and connected it directly. Now the carts works but travels maybe 5 miles.
OK, so the high current circuit has been separated from the BMS. Next, what is the V when the cart stops?

If it is using lithium Ion and I assume is a 12S then I'd suspect the pack goes from 49.8V (4.15vpc) down to 39v (3.25vpc). I'm wondering if your low voltage cutoff on the Alltrax is set to 45V or 46V. If it is you can plug into it with your laptop and set it to 40V to see if you double your range.
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Old 07-02-2021, 05:36 PM   #39
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Default Re: Lithium Pack Build Questions

Booshy68,

Quote:
I have already been in the pack as I bypassed the negative lead per the battery maker when the pack kept shutting off and I was headed to the river. The negative lead from the battery's runs thru the BMS and then to the Anderson connector. The BMS was cutting this connection when I pushed the throttle just a tiny bit. So I cut it off the BMS and connected it directly. Now the carts works but travels maybe 5 miles.
What you have done is bypass the BMS and it now cannot do it’s main task, protect the cells. You have no high voltage overcharge protection and the only over discharge protection you have is via the Alltrax controller low voltage cutoff. You have no individual cell low voltage protection. Controller low voltage cut off is fine for lead acid batteries but is useless for Lithium. Low voltage cutoff should (read must) be done by the BMS.

How long have you been running without the BMS connected? How many charge/discharge cycles? Your cells are probably unbalanced and your pack is only as good as it’s weakest cell, hence the 5 mile range. Hopefully you haven’t damaged cells.

You can’t bypass the BMS without implementing the other measures that are described in the thread I linked to in post number 5 on page 1. That thread describes how the high current pass through is removed from the BMS but all protection functions are kept.

Cheers
Pat.
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