OCP? I’m not sure that I agree that bypassing the BMS in the fashion that I’m proposing will hurt the cells. The more I look at it the more sense it makes. The cells are still protected and the bursts of higher amps won’t hurt them. Do Teslas shut down went they go up a hill? The guy ghat I added the link too builds EVs and his video shows the by pass and says a good BMS that can handle 500A and more would be an expensive piece of equipment. It may be worth a peek at his video. I was impressed, obviously.
Ok then. You have done your research.
Sorry for wasting your time here.
Carry on.
Really? What do the manufacturers know?
Bms is protecting them now buy 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 battery 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