Selecting BMS

Riplash

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Headrc said:
I am following you ..way behind! :blush:

I have followed the BMS debate for a while now. I think a lot of the "Anti-BMS" people don't like the cheap BMS units because they cost money and time anddon't give you any feedback---You have to assume that they work, and when your battery quits working it may be because the BMS malfunctioned.

Alot of these people know their batteries very well, test them, have monitors on every cell with high voltage alarms, low voltage alarms, temp alarms. And they can balance charge or manually balance them. So these people are have basically turned themselves into a human BMS. If you know the batteries, or know what to do if you get an alarm this is fine.

However if someone else is using the battery system I would want a BMS that is automatic. For instance I have two younger brothers. If I had them use something that had a manual BMS and there was a problem, one brother would shut it down and/or check on the problem. The other brother would ignore the alarms and possibly set the batteries on fire or something.

I like the Batrium because it gives you feedback....Meaning it can tell you the cell voltages, temp, amp hours, error codes and all that stuff rather than being a green PCB that you just add on to your battery pack. I haven't decided if I am going to buy a Batrium, or Similiar system or design and build a BMS. But I guarantee you that what ever system I use will give me plenty of information, and be automatic.

-Cheers,
Ryan
 

daromer

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BMS VS NO BMS:... What to choose?


First of all we need to get some things straight her

WHAT is a BMS?
Its a management system. It can be very very complex and it can be utterly junk!

Why do you need stuff to Lithium batteries? Why didnt we need it to Lead Acid?

Lead acid does balance itself manually during high voltage you can say... And yes how many lead acid packs havent been killed on solar? There is actually BMS systems for Lead acid too :)

A BMS have a couple of main functions:
1. Over and under voltage protection
2. Over and under voltage cell protection
3. Temperature protection
4. Balancing

Those are the most common.
An inverter or normal charger without balancing functuon can do #1 and #3. They cannot do Balancing nor cell level protection.

Thing with lithium is that they can/should not go outside its limits and that is why you generally need something on cell level. Either balancing or just protection or both... You decide


So those Ebikers skipping BMS? Is it possible? Or even Powerwallbuilders?
Yes it is possible. You dont have any protection but doable.
A well matched pack will not drift much in terms of balance. And as long as they dont drift due to balance problems the top and bottom protection voltage on the inverter or charger works just fine. Is this recommended? I would say NO.
But for those running 1000A through you want as little as possible in the way between the battery and motor.

If you then charge the packs with an RC charger that does Balancing you will take care of the top voltage protection and also keep them balanced good enough. In such cases I never use BMS myself!!


But for static installations or places where you just plug in a dumb PSU to charge I highly recommend one even though it is the cheapest one you can find.


So once again. YES you can run system without BMS.. You can also run a system without fuses... Its up to you to decide.
 

Gregory Charles

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Lots of thread drift going on. :) I am making the assumption few here have built a system that has such a high current demand during operation. I suspect some fork trucks may hit the numbers but they have been designed to use lithium batteries form the beginning, not retrofitted from wet cells.

Some have suggested very expensive solutions but honestly, I could go with a lot of other options for that kind of money. I am trying to keep costs down and have something reliable, that other people can understand, use and recharge without my being there to supervise it all. No multi-plugs, checking this or that, etc. Plug it in and walk away is about as technical as my farm hands will get.

Oh, why electric instead of gas powered or even a four wheeler? Gas / Diesel make a lot of noise that can really upset the cattle when approached. The silent cart doesn't bother them at all and that's a very good thing during calving.
 

Korishan

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Having no BMS is like having sex without a condom. If you know your partner, you both operate within the safety of each other, and work around her cycle with a safety of margin of error, then no kids or other issues.
However, if one of them is out and about having fun on the side, and not reliably telling when the cycle is, then diseases and/or pregnancy could, most likely, occur.
Does it mean it will, no. Is it likely, yes. Is it safe and reliable, no.
You decide ;)


Gregory: Good point. silent moving up on the cattle is a good thing. They are easily spooked. We have a few small farms around here and just a car driving by while they are lined up on the fence is enough to make them scurry if the muffler is loud enough.

Gregory Charles said:
Some have suggested very expensive solutions but honestly, I could go with a lot of other options for that kind of money. I am trying to keep costs down and have something reliable, that other people can understand, use and recharge without my being there to supervise it all. No multi-plugs, checking this or that, etc. Plug it in and walk away is about as technical as my farm hands will get.

Having a good BMS in this situation with one you can trust is definitely a must. Plug the pack in and just forget about it. Only worry about the red flashing lights on the dash when/if they occur. And if the bms is good enough and does what it's supposed to do, then only red light you'll get is battery low warning.
 

Headrc

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Again for me ....it was really a question of needing a BMS on a mobile operation ....which usually dictates it is a much smaller battery build then something like a powerwall. For my application, I have not found a problem with being the human BMS. But that is me. If I were building for somebody else who does not make it their addiction :pto understand Lithium batteries and how they should be managed .... a BMS is a must. Which is why every manufacturer building for the public puts one in ...even if they are junk. They would rather kill the battery than be liable. But we are in the DIY market here on this forum and I guess my human BMS approach was decided after my studying and watching what others have done. So far it has worked for me with just a voltage monitor and I balance charge when needed. I also bottom balance for my application which did not prove to be any harder then top balancing. With that said, all the input here isas usual,helpful and I will continue to examine what I am doing. Maybe a BMS in the next build I do and see if it really is worth the time, expense and effort compared to what I have been doing currently.

Gregory ..I hear you on the farm! We have 120 acres inEast Tennessee ....withlots of hills and my applications currently are all to make my life easier by RC controlled electric means.
 

Gregory Charles

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Having a good BMS in this situation with one you can trust is definitely a must. Plug the pack in and just forget about it. Only worry about the red flashing lights on the dash when/if they occur. And if the bms is good enough and does what it's supposed to do, then only red light you'll get is battery low warning.


Yeah, I'm just hard pressed to spend that kind of money on this project. I can replace all the wet cell batteries for about $1,000 and be good to go for two or three years. I don't mind the cost of the lithium batteries as I can tell myself I will see a return because they last so much longer but, it's all the other expense (BNS, Charger, Connections, etc.) that's starting to tell me it's a losing proposition.
 

Korishan

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You'll get that cost back, too. All the equipment involved will have ROI. It just will take longer, that's all.
 

Headrc

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I looked through this whole thread but I don't see a capacity you are trying to achieve Gregory. What are your wet cells rated in AH at this time?
 

Gregory Charles

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Headrc said:
I looked through this whole thread but I don't see a capacity you are trying to achieve Gregory. What are your wet cells rated in AH at this time?

Here are the current wet cell batteries specs. https://www.trojanbattery.com/product/t-1275/

I am not trying to replicate the exact AH because, well its really hard to compare apples to oranges in this. If I have things figured even close I'm shedding several hundred lbs. of weight. Of course AH on a wet cell really depends on the soc withvoltage drop (less power and speed) that is more or less linear where LI-ION should keep voltage until nearly discharged.

I've chatted with a couple of guys that have done this and they built battery packs with 1kWH each and they tell me they get more mileage from them than they ever did with wet cell deep cycle and far more "launch" and acceleration power.
 

daromer

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If you build 10x1kwh packs or 1*10kwh pack doesnt matter. You still have the same amount of stored energy ;)
 

Gregory Charles

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daromer said:
If you build 10x1kwh packs or 1*10kwh pack doesnt matter. You still have the same amount of stored energy ;)

Yes but, I can find and buy 10 BMS that will handlethe amp load. (Spread the amps across all 10) I do not seem to find one that can handle it all in a single unit. That is the issue I am wrestling with. This speed controller and motor can pull 400 amps of in-rush current. On top of that, I'm told to under-rater the BMS ( They all seem to come from china) by half. That means one rated at 800 amps!!! WOW.
 

Korishan

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Use a shunt instead of trying to get the BMS to handle the load. No PCB will be able to handle those load currents. Not cheaply, anyways.

I think you are making things a whole lot more complicated than they need to be.

The under-rating for the china based bms's isn't so you can "handle" 800A, it's so that you will be actually "able" to do 400A without issues. That's the reason. The cheap china knockoffs happen to put parts in that are peak rated for what they are standard rating. If the FET is rated for 100A "surge" for 10seconds, then the china knockoffs will rate the device at 100A and not tell you that's only for 10s and that the actual max sustained current is only 50A. This is why it's derated.
 

Headrc

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I think you will be much happier with new battery technology as opposed to the old technology. Longer lasting, more power ....there is a reason small power tools have all moved to the newer technology.
 
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