Ok then. You have done your research.
Sorry for wasting your time here.
Carry on.
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Really? What do the manufacturers know?
Bms is protecting them now by shutting down when a cell is pulled into the danger zone. Below 2.5v. It can not protect battery if bypassed, doh!
Go to 2p16s which will double the rating. Or buy ev rated high c cells. Your battery supplier and buddy “engineer” Doesn’t know this?
If you don’t want to know, don’t ask. I’m sure there are plenty of sites who will tell you what you want to hear.
I think the BMS still protects for under and over voltages. But, as I understand, the BMS cannot pass the current through. I see that you’ve taken offense at my believing that a BMS with MOSFETs is the only way to protect lithium cells, and maybe you are correct, but the more I read it may be the easiest way, but I’m not convinced it is the only way. I do not think that EVs current runs through the BMS. I have a friend who is a retired electrical engineer and part time genius. I may pose it to him, though I doubt golf carts are in his bailiwick. Maybe he knows about them and has some general information. But I won’t bother you with it as I can see that you don’t take disagreement well. I appreciate your input. It is helping me get closer to the truth.
Not offended. I’m just looking for a better way to explain. It doesn’t matter if the disconnect means is mosfets or contact relay. Only that when battery is in a bad state, output can be disconnected. Using the existing main contactor is a viable method, but it does not open the complete circuit. During long storage battery can continue to drain through auxiliary circuits. Dc converter etc.
To overcome this you could use a second output relay. But why? That is doing the same function as mosfets. Switching battery output off.
If I understand your thoughts, you believe mosfets can’t carry the load or limit current in some way. This is not true. Mosfets are just a switch. Changing to relay control will not fix the underlying problem of voltage sag or over current, and cart will still shut down.
We haven’t discussed the shunt. If you bypass shunt then you lose overcurrent protection.
You can’t have it both ways. If you take away the bms ability to shut down battery output, you lose protection. The fact that bms is shutting down is the very reason for using a bms. If you had high c batteries that did not lead to bms tripping, then you would have an argument for not needing bms protection.
Look at it like fuse protection. If there is no problem causing fuse to blow, the wiring is safe, and jumping fuse may be safe. A fuse blowing is a poor time to bypass it
I believe I understand both and each has it’s advantages. Currently, getting my BMS to work is the best solution bc I have it built and paid for it all. I really do not want to start over, nor can I afford to. Now when I get into my 2002 GEM, I’ll take another look at it. I did talk to a friend of mine who is a computer engineer and EE, and he said the same thing “Get a Bigger BMS,” which is the easy answer and logical, but if I didn’t know this set up works, that’s what I’d do. My friend also said it sounded like a software issue, the program settings. And. I believe that is the case as well.
A bigger bms will only help if it’s a bms issue. At this point it seems to be a battery issue. I doubt that a 100 amp battery can trip a 350a bms. Monitor current in the bms app to see. No sense guessing.
My experience and understanding is that you can get more than 100A from this setup. Why do you say that I have only 100 amps? Bc they are 100Ah cells? That’s what the BMS guy says, but I know I easily get more than 100 amps now. The guy that shows me how to build this gets more than 100 amps. My Lead acid batteries were 100Ah batteries and I got more than 100 amps out of them. At 100 amps my cart won’t go very fast or make it to the top of the hills. I don’t know what the correlation to Ah and current are, but I do not think it’s this. I just remembered that I have a shunt and volt/amp meter on this setup up. Maybe that will give me some answers. I’ll let you know what I find out. Joe
No, only the 1C = 100 amps the safe continuous draw. As per manufacturer from googling your part number.
I am suggesting that you may not be able to draw 450 amp peak. That is what it takes to hit fixed scp setting. Or 350 for over “Time” setting. If battery can not supply that, then it is not tripping on OC.
It may be, but you need to check if we are to find a safe solution.
If battery is anemic, it may be tripping on balance or a sagging cell, to protect itself. Again, not a bms problem. Set uvp as low as you can to see if it helps. I don’t do many lfp and do not know the lowest setting it will accept. Close to 2v maybe? Also set balance delta to a high level to take that off the table, for now. Tbh, I’m not sure that high delta will trip. Some of these settings are rarely changed from defaults.
I am trying my best to determine what is tripping, but need some cooperation. Such as monitoring amps while driving. And reading log after a trip.
Cells are new, fully charged and I know for a fact that I can get more than 100A. My old lead acid batteries were the same 100Ah and I easily got over 100 amps out of them. I’m going to hook up a volt/amp meter to a shunt. That may give me the information I need.
I’m trying to cooperate, I just don’t have everything you need at hand. But, I’ll get it. Thanks
I’m not saying that you can’t force more amps. But you will be exceeding design limits. The most apparent effect, beside safety, is voltage drop.
I understand what you are saying, but I still believe that the bypass method still protects the cells for under voltage, just not in the same sense as a BMS with the MOSFETs. J believe that it’s protecting the BMS more than just the cells. Be that as it may, I have been talking to the Expert Power people, that’s where I purchased my cells, and here is part of their response. I think you may find it interesting.
“Thank you for your response. It actually comes from the manufacturing process and architecture of the cells, our 100Ah are designed for deep cycling, for which thick rolls of electrode are compressed to increase the energy density. Our 304Ah cells are designed with electric vehicles in mind, for which they use thinner and more conductive internal layers with improved current paths, which allows higher continuous and surge currents. The 100Ah cells prioritise energy density and long deep-cycle life, so their internal layers are thicker and optimised for efficiency rather than high power output, they therefore get hotter faster, which also increases resistance and reduces voltage, and cannot keep their voltage as high while simultaneously delivering high currents, when your BMS reads the voltage lower than the threshold you set, current is dropped which stops your vehicle.”
That was good info for me!
Joe
That’s what I’m trying to tell you. Your belief that cells can be protected without a means of disconnecting the load makes no sense.
Take away the bms ability to drop current by opening the circuit and cells are not protected. What kind of magic “protection” do you think a bms has? All a bms can do is monitor voltage, current, and temperature. Then open the circuit to protect the battery.
Keep talking to “experts” until someone agrees with you! The response from the expert power people is in agreement with me.
That was good info for me!
Is it opposite day?
Even the manufacturer is saying their 100Ah batteries are not designed for EV (high current) use.
I’m not sure what you are trying to justify here.
You have not proven this is tripping the Over Current Protect (OCP) yet. It is possible if it is set too low, but have you set it to the max yet?
I understand what you are saying, but I still believe that the bypass method still protects the cells for under voltage
It doesn’t appear so.
If bypassed in the way you propose, What exactly happens when a low cell condition appears:
- during run conditions
- when car is sitting for long periods of time (ex: while you are away on vacation).
You guys are aggressive! But, you are either denying or ignoring that my setup works and not just for a short while. You seem to be focused on proving yourselves right, but ignoring some realities. I’m not trying to convince you of anything. Do what you want to do. I’m just trying to learn from others. The Expert Power support guy didn’t say what you are saying. He did say that the 100Ah cells were more designed for a more gentle discharge and the 304Ah cells were more for an aggressive discharge, but they don’t say that in their marketing literature. None of them do that I looked at. Guys, I’m ok, but trying to convince me that you are absolutely correct is a waste of time. Telling me what I Should have done instead of giving practical advice about how to help, isn’t help.
I do appreciate your opinion and insight, but not so much of your judgement.
Anyway, I thought you might enjoy what the support guy said, not enrage you.
Take care, Joe
There are people who ask for help but don’t actually want to be helped.
“There’s a difference between it will work and it will work properly and consistently over time.”
To understand what’s really happening with your battery, go to the bottom of a hill where you know it will trip. Connect your phone and record your screen. Then smash the pedal going uphill until it trips. After that, you can analyze what’s happening with the cells under load and acceleration from that video.
I’ve personally been installing, designing, and building batteries for a couple of years, and C-rate is one of the most underrated aspects of battery systems. Look online “burst, peak, and continuous” load ratings.
Ideally, your system should operate under 1C (although some cells can handle more) once it reaches continuous load—which usually happens after about 10 seconds. If you exceed that, you’re stressing the cells, busbars, and the entire system. Also remember, the BMS must be properly programmed for the specific battery. Its main job is to protect it. If you push it too far or bypass it, you’ll end up melting busbars or wires—or just killing the cells altogether.
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I appreciate that, but I was asking for help and got more preaching than information. I do understand what you guys are saying, but at the same time, I cannot go back in time and start over. I can’t afford to either. I have to deal with what I have and figure out some things. I never disputed that “C” rating thing, but I never heard of it, and none of the places I’ve been looking in ever mentioned it, including the manufacturer of the cells I bought. They answered the question I asked, but still never mentioned the C-rating. Maybe, I asked the wrong questions before, but how do you learn if you do not ask questions? While I’ve been somewhat ridiculed for not knowing what a C rating was, no one ever answered why so many people are building battery packs for golf carts out of these and similar cells including the people that posted the instructional video I followed. I don’t need to be preached at; I need information. I have a situation and telling me I don’t know what I’m doing and that I “Should Have” done it definitely is not much help. If the C rating was that critical, then after looking at many manufacturer and distributors’ websites and a 100 YiouTube videos, I think it would have come up and it never did. If I hadn’t asked the manufaturer the question of what they recommend for golf carts I wouldn’t have known what I posted to you from them. And, I thought that someone would be pleased about what I found out, but instead I got a bunch of “I told you so’s.” That’s not what I came here to hear. I can get that at home from my wife.
"Connect your phone and record your screen . . . " I’m old. How do I record on my phone? I have logs, but as I’ve mentioned before, I don’t know how to read them, and the BMS support is of no real use. That is information I could use, but haven’t gotten.
“Also remember, the BMS must be properly programmed for the specific battery . . .” That’s another question, actually, the one I’ve been asking, but not getting any help with. But, I do know what a C rating is now. That an $1 will get me a cup of coffee at QT. The whole bypass deal came into play when I ran into so many people running golf carts on 30A Chep Chinese BMSs. I wasn’t looking for that, just a solution to my problem.
So, guys, I’m ok, and I’ll leave you alone unless you need a punching bag to make you feel better.
Joe
And, BTW, are you from the South? I only hear “Smash” of push in the South. Just curious.
Let me try and help you out. The bms only shuts down when one of the parameters are exceeded. If that happens it will disconnect and tell you why. I doubt you are exceeding the out put of the 200a/350a bms. I have run it and its little brother peaking over 450a and never had a trip.Now
I dont know your cart so it is possible, but again the bms will tell you. if it is tripping it is more than likely seeing a voltage drop. This usually happens with a bad connection between 2 cells. it has tricked us many times. The other major reason it is the batteries are split into multiple modules and a battery cable connects them. Dont know if yours are all one or multiple modules. This is an easy fix but you have to be able to look at the bms and read the history, it tells you why and and where it is happening.
I know you mentioned not being able to figure it out but some how to read the errors but you will need to figure it out, . Then the fix will become evident. One of the other reasons to trip is a bad cell, just had this happen on a clients Gem. looked good idle and low load but under heavy load it tripped.
As far as the cells go if they are rated to 100a max load and you pull more than that it will stress them and lead to premature failure, If you except that then run then hard and dont worry.
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Not trying to slap you or anything, but I get the impression that you want an answer I can’t really give you—at least not from my end.
Unless your car, your driving habits, and your terrain are the same, you really can’t compare your setup to another YouTuber’s. Their cart may simply have different power consumption.
All cellphones have a screen recording function. Start recording, then do your test. When you’re done, the replay of your screen will be saved in your gallery.
Start there. Look at all the cells. The lowest one will usually be marked in red, and the highest in blue. Check the sag, or voltage drop, from when the cart is stationary versus when it is under full load, that will tell you what’s going on. Also the 3 dots in the top right will get you some logs in yellow, if you see Cell # under voltage protection will get you an idea. It might say short circuit protection that happened once to me while testing a 15kW motor cranked up and bursted over 600A during acceleration.
And yes, I’m from the South — about 5,000 miles south of the southernmost point of the USA (Argentina) 
To properly come up with a solution- One must fully understand the problem.
@Joe - You keep saying you would like a solution to this issue, and you are convinced there is one because there are others that are doing it.
I cannot find the link you tried to offer up to those other builds.
Are you sure you followed their build exactly and bought the very same components?
How long have these carts been running, and are they still running today?
===
For those that are just joining the chat, here are a couple of the tech pages I found on a more detailed search path.
@Joe - Is this the battery/cell you based your battery on?
Note that this battery is rated using 0.5C
Yes, it does have a Max Continuous Discharge of 100a, but I bet at a substantial drop in the rating when actually pulled on it that hard. It looks like a bit of creative marketing.
Even the Expert Power Tech gave the hint when he mentioned "the 100Ah cells were more designed for a more gentle discharge "
Your BMS is cutting out because the current draw is exceeding its limit, especially under load like hills, so the issue is more about capacity than a fault. The relay method you mentioned can work, where the main discharge current bypasses the BMS and the BMS is only used for balancing and charging, but it does reduce protection on the discharge side. In a MOSFET BMS setup, B- is connected directly to the battery negative, while P- is used for both charge and load, so a common approach is to run the controller negative directly to B- and keep the BMS connected for balance leads and charging through P-. The relay or contactor is then controlled by the BMS output to cut power if needed, similar to a lead battery style setup. Just be careful because incorrect wiring can damage the battery or create safety risks. A safer option could be upgrading to a higher current-rated BMS instead of bypassing, unless you follow a clear and tested wiring diagram.