BMS wiring mistake?

[MDLNB]

2004 Yamaha G22E

Over a year ago, I purchased some (7) Nissan Leaf lithium battery mods for my wife's 48volt golf cart. Since the Trojans were still working, I left them in until they finally got too weak to make a decent run. I set up the lithium pack on my work bench to charge and test it. I purchased a cheap Chinese BMS and installed it so I could charge it. I also purchased a Chinese charger made to charge lithium batteries to 58+ vdc. After doing a lot of research (and finally getting expert advice on here) I had the BMS hooked up and the battery charged perfectly, with the charger cutting off after it achieved it's proper charge. I left the charged battery pack on my bench for a year without charging and the battery charge stayed pretty stable at a full charge.
Yesterday, I finally removed my Trojan batteries and put the lithium pack in the cart to test it before making the permanent change. I first connected the positive cart cable, along with the positive wire from the 48v to 12v converter to the battery pack. Then, I attempted to connect the negative cable from the cart to the battery pack, along with the negative wire to the 12v converter and INSTANTLY the BMS started a "clicking" sound and it (BMS) heated up. I disconnected the BMS and connected the cart wires to the negative connection on the battery pack, and everything was OK. I drove the cart around the block a few times and the battery pack did not change in temp. The cart responded instantly upon apply the power pedal and quickly accelerated to the point where the regen kept it from going any faster. Or the governor or whatever it is that keeps it from going faster than 19mph.
I have attached photos of the temp hook up in the cart. As you can see(photo 1), the negative connection to the BMS is not connected to the battery terminal. That would be the wire marked "B" on the BMS that was originally connected to the negative terminal for charging. The "C" connection on the BMS is connected to the charger NEGATIVE connection (photo 2). The ribbon cable connects to the individual cells on the battery pack. Sorry about the quality of the photos taken with my cell phone. I took them in my garage with limited light.
Question: Why is it that it charged fine the way it was connected, but when I attempted to connect it to the cart, when the negative cart cable was connected while the BMS was connected, it started to malfunction and heat up, even smoked before I disconnected it? Where did I connect the wires wrong? I made no other changes to the cart, just changed the old lead cell batteries for the lithium pack. The cart works fine without the BMS connected, but without it, I won't be able to charge the battery. I have a feeling that it is something simple that I am missing-not understanding. I am just seeking a simple system, not an elaborate modification.

[augiedoggy]

I have to be missing something but that looks to be a tiny 20amp bms? do you somehow have it wired to a relay to control the load? typicall if installed as designed, the negative lead power is controlled by the bms and that would be the b- to the battery and -c (negative current lead to load but the tiny 12awg wire and bms cannot handle hundreds of amps which unless you have some sort of modified system with an external relay wont work. It would work to keep the cells charged for long term storage but thats it

I use a similiar bms in my RV pack I made and thats how it works.
for my golfcart I have something a bit more stout rated for 300a cont and 600a peak. https://batteryhookup.com/products/7...ithium-ion-bms

the bms I linked above not only works with bluetooth but also one of these screens if you buy the model with the uart and rs485
https://www.aliexpress.us/item/32568...d=vfP8YFNY9U4A

the red positive power wire coming off your pack looks to be just 6wg wire.. you really need at least 4wg minimum.

[MDLNB]

Originally Posted by augiedoggy

I have to be missing something but that looks to be a tiny 20amp bms? do you somehow have it wired to a relay to control the load? typicall if installed as designed, the negative lead power is controlled by the bms and that would be the b- to the battery and -c (negative current lead to load but the tiny 12awg wire and bms cannot handle hundreds of amps which unless you have some sort of modified system with an external relay wont work. It would work to keep the cells charged for long term storage but thats it

I use a similiar bms in my RV pack I made and thats how it works.
for my golfcart I have something a bit more stout rated for 300a cont and 600a peak. https://batteryhookup.com/products/7...ithium-ion-bms

the bms I linked above not only works with bluetooth but also one of these screens if you buy the model with the uart and rs485
https://www.aliexpress.us/item/32568...d=vfP8YFNY9U4A

the red positive power wire coming off your pack looks to be just 6wg wire.. you really need at least 4wg minimum.

Thank you.
Question: Why would I need more than a 20amp BMS? Wouldn't the only going through the BMS be from the charger? And the charger doesn't have anywhere near the amps surge of what you are suggesting. Am I wrong? The way I see it (right or wrong?) is that the positive of the charger is going directly to the battery. The negative of the charger was going to the BMS. A negative from the BMS was connected to the negative terminal of the battery pack. It worked fine until I connected the golf cart cables. Then, it only worked if the BMS negative lead was not connected to the battery. The BMS advertised that it would work with a golf cart. I guess you get what you pay for, and it WAS cheap.. I just don't understand why the BMS acted up when I connected the negative golf cart cable? Could it be that I have it wired wrong? It worked OK with just the charger.
I'm just trying to get this right in my head, and I am a senior and a bit slower than I was a few years ago. I think my charger is only rated at 15amps unless I am mistaken. I have no problem with changing to a more expensive BMS, but I don't really need all the bells and whistles. I will purchase a replacement, if I can get it right in my head as to how this is working. If I have it wired wrong, I do not want to replicate my error on a new BMS.
Thanks again for responding. Sorry, if I do not quite get it right away.

[Volt_Ampere]

I agree - that BMS does not look like it's designed to handle hundreds of amps during cart operation. You need a relay to interrupt the main power or get a BMS designed to handle the cart current.

[MDLNB]

Originally Posted by Volt_Ampere

I agree - that BMS does not look like it's designed to handle hundreds of amps during cart operation. You need a relay to interrupt the main power or get a BMS designed to handle the cart current.

I apologize for my ignorance. I just don't understand how the cart could be operating with "hundreds of amps" without blowing ten or fifteen amp fuses. My charger only works with about 15amps. Where are we getting "hundreds of amps" of current? Like I said before, please excuse my ignorance. This a learning experience for me, and I welcome any and all critique and criticism. I am not an electrician but I have done DIY home wiring, with 20amp breakers. Never woud have imagined "hundreds of amps" being utilized in a golf cart.
Thank you again for your patience.

[DaveTM]

AugieD is spot on. Your BMS is woefully inadequate to handle the current required by a cart.

Unless you can configure your current BMS to have the LV and HV cutoffs run through relay's (Guy's much smarter than me know how to do this) then you would be good.

But if you don't want to do that, and have the current "run through" a BMS, you will need one (as AugieD has linked) that can handle the current.

[augiedoggy]

I apologize but I have not read your entire post yet. However both the incoming and outgoing current Should go through the battery Management. System. This prevents Safety concerns from cells overheating or an overcurrent situation. Basically the BMS Can disable the battery current to protect the pack. This is also the only way the BMS can Accurately monitor state of charge and battery condition I don't know if you have a Regen cart. But that would make the situation even more Dangerous if you bypass the BMS.

[DaveTM]

MDLMB.....You are not asking "dumb" questions.

It takes a lot of amps to get a cart into motion....depending upon where the cart is going, how much weight it has, and what incline it's on.

Here's a printout from my Alltrax controller of the amps being pulled from my lithium pack under the steepest hill that is near me. As you can see at one point, the amp output was 392amps. That's a lot of "juice".

I have since dialed back the amps that can pass through to the motor (via the Alltrax controller) no matter what the motor is asking for.

If your BMS is setup to "run" the current that the heavy cables carry, then your BMS should also have some pretty hefty wires\cables to carry the current.

My BMS is setup so should a HV or LV occur, it shuts down the charge or discharge via relays. No "heavy" current runs through my BMS. My BMS also monitors current draw via a shunt.....it's just a different setup that gets the same results.

And FWIW, my chargers maximum output (like yours) is only 15amps.

[MDLNB]

Thanks DaveTM,

IF/IF I want to utilize the BMS for charging ONLY, how would I attach the BMS to the battery? If I have the positive from the charger to the positive battery terminal and the negative lead from charger to the BMS (C), would that work? I would not have the (B) connected to the negative battery terminal. Just guessing, but would that keep the cart from pulling amps through the BMS? I would not have the (B) wire connected at all. Not sure if the route of the current used would still go through the BMS if the (B) did not complete the circuit to the battery negative terminal. Am I totally wrong on that?
Seems I remember someone once describing how to connect the BMS for charging only.
BTW: I am currently shopping for a new BMS. I believe the one currently connected was fried when I was handling the battery pack into the cart. Probably a good thing anyway.

[jasonojordan]

To keep this simple, Lithium batteries need to have a correctly sized BMS used at all times not just during charging.

If one is not present you could over draw from the batteries and create a bad reaction. AKA Fire/Death/Destruction

Originally Posted by MDLNB

Thanks DaveTM,

IF/IF I want to utilize the BMS for charging ONLY, how would I attach the BMS to the battery? If I have the positive from the charger to the positive battery terminal and the negative lead from charger to the BMS (C), would that work? I would not have the (B) connected to the negative battery terminal. Just guessing, but would that keep the cart from pulling amps through the BMS? I would not have the (B) wire connected at all. Not sure if the route of the current used would still go through the BMS if the (B) did not complete the circuit to the battery negative terminal. Am I totally wrong on that?
Seems I remember someone once describing how to connect the BMS for charging only.
BTW: I am currently shopping for a new BMS. I believe the one currently connected was fried when I was handling the battery pack into the cart. Probably a good thing anyway.