I’m having trouble with my BMS cutting out bc of high current draw collating and going up hills. I read some where that there is a way to bypass the BMS for the main current but use the BMS for balancing and charging. I actually ran across a video that the guy did it. It uses relays turned on by the BMS to activate a the main current to the controller, like the Lead Battery set up. Best of both worlds! But, I need a diagram of how to wire it. I’m not an electrical engineer, so hopefully it isn’t written in engineering lingo. I have a MOSFETs style BMS and I’m not sure what to do with the B- and P- cables. Maybe I should get a cheap non-MOSFETs style BMS, but I still need a diagram as to wiring it. Any thoughts?
That is not recommended. Put in a big enough bms. Without a bms it’s just a matter of time until you let battery go dead.
I recommend 350a jk bms or a larger ant bms. A gem will not trip either on if things are working normally.
How much are you actually pulling?
How big is your BMS?
What cells are in this pack? (what are they rated for?)
I agree with Inwo-
If you are going to buy something else, just put in a bigger BMS.
My BMS has 200A Continuous and 350A Peak. That should be enough. On the Buggies Gone Wild website, I found a guy, Sergio, who was an Electrical Engineer and he used a cheap 30A Chinese BMS and ran his CC Regen with no problems. Maybe I don’t know how to set it up, but 200A continuous should be enough. Though I don’t know how many amps I’m drawing it cuts off before I can read the Alltrax app. I think it is ideal if I can just bypass get BMS for the the main current. The BMS I’d to protect the cells and balance them. It never shut down with the old lead-acid batteries
I have a 200A continuous and 350A peak active BMS. 16s 3.2v 100AH cells. Alltrax SR4850 controller and a D&D motor.
Are you sure it is shutting down on high current. We have 100s of 200a jk bms with no reports of high current issues. Monitor you current in jk app.
Is this a 72v gem? If you are running 48v, 350a is not enough.
I see it now. 16s lfp. I recommend a larger bms. Battery is not protected if bms is bypassed.
It’s not if, but when, you let battery go dead.
Monitor amps in jk-bms app.
You can try turning up delay time.
This does not sound like a Gem.
Unless it has been gutted and converted down to lower voltage (which is taking a huge step backwards).
If you have app. Verify exactly what is happening. Are you really tripping over current? Or are you sucking the poor batteries inside out like a 6y/o on a juice box? You are probably going undervolt.
Is there anything in the logs?
Where did this battery come from?
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It’s a 48v 100Ah system in a 1994 Club Car 6-seater. It’s a 200/350A JK BMS.
I do have the JK app, but I don’t know how to read the log. It’s hard to watch the app while I’m driving. I did get that error 6 I think, that says cell short circuit, but it turns out the primary reason for it was Over current. An actual short circuit would have the same error, but probably would stay in the app. It now only pops up for a second and goes away.
I corresponded with the JK support people. He looked at my settings and said that since the cells were 100Ah that I can only have 100A discharge, which I know is wrong. I don’t know much, but I know that battery can and does exceed 100A output at least for a short time. He looked at screenshots of the app and was able to read the log and said that it was set up correctly. But I couldn’t have a Max Discharge set over 100A. It has a 350A peak. He emphatically said a larger BMS would not matter, it’s the cell specs that rule. They were of no real help.
I have my Controller connected to my laptop and it will show the voltage and current discharge as I’m driving, but again I can’t drive the cart and look at the screen at the same time and it goes away as soon as it cuts out. I cannot figure out how to read the logs. I guess I could put it up on stands so the wheels are off the ground ABC try that, but would free wheeling pull that much current, to make the BMS shut down?
As one of you mentioned the Delay Setting may help since it the bursts of current that triggers the shut down not normal discharge. But I have a lot of hills which will cause higher discharge. It’s probably a setting, bug I don’t know which one. 99% of the YouTube videos are for solar storage ghat have different discharge patterns. I’ve tried several of theirs with no luck.
There was this guy, Sergio, on Buggies Gone Wild website, who apparently was an Electrical Engineer and he built a similar lithium setup but only used a 30A BMS. How did he run his 48v cart in hilly terrain on a 30A BMS and a 100Ah battery pack? He bypassed the BMS for the main current just like it was on lead acid batteries, and used the BMS to manage the batteries. It was connected to the charger to look for over voltage and connected to the controller for the same anc connected to the main solenoid to close when you needed current same as it did before when you engaged the Pot with the accelerator pedal. The BMS protects the cells from over or undercharging, and balances the cells, but doesn’t shut the current flow off. Basically, he was saying that the BMS is to manage the battery cells, but not the discharge itself. That makes sense to me. My BMS has those MOSFET transistors in it where all if the current flows through the BMS. That’s where the problem lies. They can’t handle the current. That’s why those BMS cost so much bc the cheap ones only monitor the battery cells.
So in absence of a way to get my current BMS to function properly, I’m looking at the bypass method. The man whose video I followed to build my pack uses the same cells and BMS for his carts and lives in a hilly terrain and rents carts out, and it works for him. Everyone is smarter and more skilled in this than me, but I need to figure this out. Either make my current setup work or figure out how to wire the bypass. I’ve exhausted my ability and need some help on either. The local golf cart shops don’t want to work on it bc it’s a DIY battery, and having don’t 30 years in commercial liability insurance, I understand.
I was hoping someone had done this before and had a wiring diagram that I could read. These parts are common and not expensive. So, I’ll try some more settings in the mean time and keep looking for a diagram to bypass the BMS.
I appreciate all of your input. Thanks
Bypassing bms is trivial, but not safe. Monitoring discharge current and low level cutoff are critical functions.
What is the C rating of your cells? It may only be one or two. If you are exceeding safe battery discharge, bypassing protection is not the answer. I certainly won’t help bypass protection.
The BMS is still active and monitoring the cells. And it does monitor the effects of the discharge current on the cells, but not the current to the load. That said, I do not know what the C-Rating means, and have never heard anyone else mention it. I’m trying to upload the Expert Power cell specs, but I cannot tell if it is attached or not. They are MODEL: LC32100, Expert Power. Maybe you can see what it is, but if that were my problem, I think with all of the videos and people that I’ve talked to, I would have heard it before. But who knows? I’m not that smart with these things, obviously. I think that these BMSs are more for solar applications than electric cars. Check out this video if you like: BMS for 500+ Current draw. The JK Support people may be correct that I cannot draw more than 100A with that BMS, even though it’s rated for 200/350A, bc my cells are 100Ah. I don’t think that’s true, but they are the experts, but plenty of people are using these for golf carts and getting away with it.
Hopefully, the Cell specs are attached. I cannot tell. And, here is the one diagram I’ve run into.
Thanks, Joe
There is much misunderstanding of info going on here.
- I cannot find you battery from the info provided, so I’m not going to guess how well they would work in your car.
- If a JK support made some suggestions, why are you so eager to brush it off? Know that they are not concerned about the BMS not being able to handle the power, (Yes, it is well able to handle 350a surges).
- It seems you are confusing 100Ah with 100a. They are not the same. One is more/less an estimated capacity, the other is a unit of current.
When someone talks about C rating, it is how much current can safely flow from a cell based on capacity. Roughly, a 100Ah battery with a 2C rating will flow 200a. It is totally possible the JK tech saw your cells are 1C rated. This means you are nly good for 100a current without stressing your cells.
The JK tech support probably took a look at your cell specs and decided the rate will not support more than 100a and suggested throttling it back with the BMS settings. - Bypassing the BMS discharge FETs is about like increasing the settings. Sure, It may work OK for a while, but don’t expect your batteries to last very long.
How does your car run with the OCP (Over Current Protect) at max?Does it still trip when pulling hills?
Checking the logs
When JK App is connected to a BMS, go to the top right of your screen and tap on the three dots. The first line down is System Logs. Scroll to the bottom and see if it has been capturing the latest faults. Match the time stamp with what your system clock reads to see if last log is current.
My system is very old and has a bug in the log routines. The buffer is full and no way to clear it. I think the latest versions are fixed.
Poor man’s data logging
For lack of correct syslogs, I have the app open on the Status page when I am doing a test run. When I am doing something I need info on (such as hard accel and pulling hills) I do a series of screen shots as the event is happening. I don’t even need to look at the screen. I can pull over and review when safe. Sure, it won’t tell me if something shut the system down, but t might give you an idea if you capture it right before shut down.
Look at the freeze frame while at rest, then again under load.
- A very high amp load will be up over 350a and the BMS is getting ready to trip OCP.
- But also look at how low your cellV drops. You may be tripping UVP (Under Volt Protect).
What is your goal?
You need to understand why everyone is going high voltage in the cart world. I don’t know who your boy Sergio is, but either he is behind the times or you are reading outdated info. (My limited search finds some stuff dated 2016. Is what you are reading recent?)
Sticking with a 48v system is kinda old school. Most everyone has figured out that If you double the voltage, the amps required to do the same work are cut in half. Cables can get smaller, resistance goes down, controllers and motors run cooler, everything is happier.
Why do you think Tesla is playing around up around 400v? Sure, the rules are way different up there and I don’t recommend going that high, but it is worth noting. (That voltage can kill you if you get something wrong)
I looked up your cells. They are for solar and other low current application. You are way abusing them. Most likely bms is saving you buy shutting down on voltage sag. Specs are only 1c or 100 amps max. It is not a bms problem. @LithiumGods reports discharge over 450a without tripping. His mighty max batteries use high quality ev rated cells. If he doesn’t jump in, I’ll try to search C rating.
C rating is maximum current that can be drawn without damage or risk. C x capacity = amps. There is a reason the cheap Chinese cells, are well, cheap. Use any ev rated cells for safety and performance. Sdi cells are a common pick for high current ev use and work over a wide range of temperatures, using nmc chemistry.
We sold 100s of 22s sdi batteries with many supplying over 350 amps, safely.
“Samsung SDI 94Ah NMC prismatic cells (3.68V-3.7V nominal) are high-performance cells often used in electric vehicles and ESS, supporting up to 4C discharge rates. Recommended operation is 0.33C-1C (approx. 31A-94A), with a maximum continuous charge of 72A or 1C and high-performance cycle life up to 4,600 cycles at 25°C, say PushEVs”
4c is about 400amps peak.
The might might 100ah ev batteries have sold out.
Here is similar a123 chemistry lfp batteries, showing you the lacking of your choice.
Module Specifications
| Make | BAE Systems |
|---|---|
| Model | 235C9387G1 |
| Dimensions (WxLxH) | 31″ X 6.5″ X 3″ |
| Weight | 19.55 lbs |
| Voltage | 40V |
| Configuration | 12S8P, 12*3.2v = 38.4v |
| Current | 400A contiuous, 960A Peak |
| Watt Hours | 736 wH |
| Battery | 26650 LiFePO4 |
| Voltage Miniumum | 2V * 12 = 24V |
| Voltage Nominal | 3.3V * 12 = 39.6V |
| Voltage Maximum | 3.6V * 12 = 43.2V |
20ah cells and 960a peak output. If @LithiumGods jumps in I’m sure he would explain it better. There is much more to building an ev battery than most realize. These far exceed even our beloved Samsung Korea sdi batteries.
Thanks, Guys. I understand most of what you said, and I wasn’t getting Ah and A confused. The JK support guy said that. I did look on this site before I started my build but really never found the instructions I was looking for. The guy I used builds these for his own rental carts, and if they worked for him, I figured they should work for me. He has built dozens of the same battery for his rental fleet, and according to him, it works. And, it may work for me if I can get it set right. Sergio was an electrical engineer, so I believe he knew what he was doing. I don’t doubt what any of you are saying, but as much as I have read and looked at, that C rating was never mentioned by anyone. None of the major cell manufacturers, like EVE and Expert Power, said anything about the C rating. No one that I looked at even sold cells by C rating class. I don’t doubt you, but no one else has brought that up before. I see that some are selling used cells of all sorts, but if I’m struggling with a simple build, trying to figure out using some of those used EV cells will be harder, though I started this project using Leaf modules which seemed popular with DIY builds, but in the interim time LiFeP04 cells have come way down in price. I need to know what to do to fix this and not what all I may have done wrong. Maybe when I get to that 2002 GEM I have, I’ll try some of this stuff.
My goal, as I stated before, is to get the cart working. Either get the BMS set properly, which would be the best solution, or figure out how to bypass the BMS for the main current flow. I saw virtually no 48v batteries on the market that had more than a 200A BMS. I appreciate your manual dexterity, but taking screenshots while driving is out of my range of skills. I’m old, and it happens in a split second. I see the logs on the BMS, but I cannot decipher them. The JK Support guy saw them and had little to say.
I guess it boils down to the fact that other people have built this exact system and others nearly the same, and they worked for them. It should work for me. I just have to figure out how. Thank you for all of your comments. I’ll report back as I figure this out.
P.S. It won’t let me attach a PDF file, so I cannot attach the Specs on the Expert Power cells that I used.
(Attachment Expert Power LiFeP04 cells. Specs..pdf is missing)
Have you gone back to thsi guy who built you this pack? What did he say about what was going on?
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No one that I looked at even sold cells by C rating class
Probably they are selling to people that do not need to know or care about such things (like Solar guys). Car guys have totally different requirements.
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I appreciate your manual dexterity, but taking screenshots while driving is out of my range of skills.
What phone do you have? On the iPhone it is two buttons, one on each side, squeezed both at the same time. I don’t even need to look at the screen other than make sure it is on the BMS page I want to monitor.
Or have someone ride with you. They can be the nut behind the wheel, or the guy taking screen shots.
Yes, I’ve talked some with the guy that did the video. He gave me some things to look at, but due to illness in the house I haven’t been able to implement them yet. Hopefully tomorrow. He’s busy and hard to get a hold of. I understand about how to take a screenshot, but I have a hard time taking them when I’m just sitting still. I have arthritis in my hands and that is a more difficult task for me than one might think. But I hadn’t thought of that, so I’ll give it a try. But when it would cut out I would get one error message that stayed on the screen for like 2 seconds. My wife won’t drive it and my kids are really busy, but I have thought about that. When I have the controller hooked up to my laptop same thing it happens so fast that I cannot get a clear ready, but I don’t think the amperage ever got much above 125 to 150A. Still within the specs of the BMS. It has great acceleration, just for a short time.
Is your BMS OCP still set to 100A? As per JK suggestion?
Dial it up! It won’t hurt the BMS.
What we are saying is that it will probably be damaging your pack. What you are proposing (bypassing the BMS) will be doing the same thing, so what is there to lose?