Lipo BMS

[dozentrio]

I've finally decided it's time for a proper BMS. I'm tired of using my battery medic to try to balance my pack (which is only 9Ah). It takes too long. I want a worry free battery I can ride until the lowest cell reaches cutoff.

So my question is, what are the options for lipo bms systems out there? my pack is 20s, but I can split it into two 10s packs. Are there working bms boards out there?

[heathyoung]

There is the fletcher/goodrum BMS, or you can roll your own. Cell-logs are a good HVC/LVC but no balancing. Battery medics are a good balancer (if you use the booster circuit) but the voltage measurement is sus.

There are a few different commercial ones out there for Lipo. I've been meaning to sort out something that works well, using LTC chips but the eyes are a bit ordinary these days to be using very small IC's. If anyone with better eyes is interested, check out LTC4070 - its a shunt charger IC that is perfect for Lipo. Ignore the comments about low power charging, you can hit the cells as hard as you like, as long as you drop off the power when you hit HVC so that the shunts can do their work and not be swamped.

[shawn_1976]

dozentrio

Where and when do you ride. Me and a bunch of buddies have e-bikes and board in Oshawa. I am also looking for a BMS

[auraslip]

Send smartec on alibaba a message asking for the bms you need. They'll build it to your specs.
No comment on quality, but it's fairly cheap. ($50 shipped)

Other than that, all I can say is that there are good reasons why people DON'T go this route here. Namely, how comfortable are you trusting a $50 BMS with your $1000 battery pack?
By far the better option is to just get 2x the capacity you'll ever need. This is the "correct" route to go for long term happiness with your battery pack.

WRT to balancing; if you have to balance your pack every time you use it, something is wrong. I have 90 cycles on my BMS-less ping, and the cells are still fairly in balance. Well, not REALLY balanced, but honestly I have enough capacity to where it doesn't matter. Balancing is only an issue if you run your pack to LVC each time, and that's something that should be avoided in the first place.
Also, I the chinese BMS aren't going to balance any quicker than the battery medic.

[dozentrio]

dozentrio

Where and when do you ride. Me and a bunch of buddies have e-bikes and board in Oshawa. I am also looking for a BMS

Every day! I may have met one of your group at Bay Cycle the other day. PM me and we can meet up

[dozentrio]

Send smartec on alibaba a message asking for the bms you need. They'll build it to your specs.
No comment on quality, but it's fairly cheap. ($50 shipped)

Other than that, all I can say is that there are good reasons why people DON'T go this route here. Namely, how comfortable are you trusting a $50 BMS with your $1000 battery pack?
By far the better option is to just get 2x the capacity you'll ever need. This is the "correct" route to go for long term happiness with your battery pack.

WRT to balancing; if you have to balance your pack every time you use it, something is wrong. I have 90 cycles on my BMS-less ping, and the cells are still fairly in balance. Well, not REALLY balanced, but honestly I have enough capacity to where it doesn't matter. Balancing is only an issue if you run your pack to LVC each time, and that's something that should be avoided in the first place.
Also, I the chinese BMS aren't going to balance any quicker than the battery medic.

Thanks auraslip. I will check this out. I don't think balancing speed will be a problem if I can comfortably leave it to do its thing overnight. The battery medic is only a pain because I'm trying to balance four sets of 5s separately, on my 20s pack so I have to keep switching it. I will guineapig the chinese bms on my 440 wh pack and if it is problem free, I will trust it with more.

[eva-michael]

LiPO cells are easier to balance. It will be easy to find out a BMS which will suit.
Generally Single cell over charge protection will be about 4.28V and 20Sx4.18V for battery pack over charge.
For Single cell over discharge protection, many supplier can provide 2.5V 2.8V 3.0V for your options.
If you just want to discharge till it cut off. I will suggest you to make it 2.8V or 3.0V.
If you make them 10S, then you can not charge them together. seems a bit unconvenient.




EV ASSEMBLE also have customized LiPO BMS.

[Gow864]

LiPO cells are easier to balance. It will be easy to find out a BMS which will suit.
Generally Single cell over charge protection will be about 4.28V and 20Sx4.18V for battery pack over charge.
For Single cell over discharge protection, many supplier can provide 2.5V 2.8V 3.0V for your options.
If you just want to discharge till it cut off. I will suggest you to make it 2.8V or 3.0V.
If you make them 10S, then you can not charge them together. seems a bit unconvenient.




EV ASSEMBLE also have customized LiPO BMS.

So, Michael can you supply a BMS for a 20s lipo pack that will let them charge to 4.15V, and a discharge cutoff of 3.5V?

[Gregory]

LiPO cells are easier to balance. It will be easy to find out a BMS which will suit.
Generally Single cell over charge protection will be about 4.28V and 20Sx4.18V for battery pack over charge.
For Single cell over discharge protection, many supplier can provide 2.5V 2.8V 3.0V for your options.
If you just want to discharge till it cut off. I will suggest you to make it 2.8V or 3.0V.
If you make them 10S, then you can not charge them together. seems a bit unconvenient.




EV ASSEMBLE also have customized LiPO BMS.

So, Michael can you supply a BMS for a 20s lipo pack that will let them charge to 4.15V, and a discharge cutoff of 3.5V?

And what is the max continuous discharge rate and charge rates?

[eva-michael]

LiPO cells are easier to balance. It will be easy to find out a BMS
.

So, Michael can you supply a BMS for a 20s lipo pack that will let them charge to 4.15V, and a discharge cutoff of 3.5V?

And what is the max continuous discharge rate and charge rates?

This will according to requirement of customers.
Options for discharge: 15A 30A 45A 60A 75A 90A 100A 150A 200A 250A
Options for charge: 15A 30A 45A 60A 75A 90A 100A 150A 200A 250A
Options for brake regen: Yes or No

Normal BMS can balance battery pack from 5Ah-40Ah efficiently. If your cells are higher than this, generally the will need more efficient setting of balance function.
for example, the capacitor BMS will have double or even more capacitors to handle the balance functions of power transfer.

[Gow864]

This will according to requirement of customers.
Options for discharge: 15A 30A 45A 60A 75A 90A 100A 150A 200A 250A
Options for charge: 15A 30A 45A 60A 75A 90A 100A 150A 200A 250A
Options for brake regen: Yes or No

Normal BMS can balance battery pack from 5Ah-40Ah efficiently. If your cells are higher than this, generally the will need more efficient setting of balance function.
for example, the capacitor BMS will have double or even more capacitors to handle the balance functions of power transfer.

Michael. Can you supply me a BMS for lithium polymer cells? charging the cells to 4.15V, with a discharge cutoff of 3.5V with 50Amp continuous. if you can, how much would it cost?

Gow.

[eva-michael]

Michael. Can you supply me a BMS for lithium polymer cells? charging the cells to 4.15V, with a discharge cutoff of 3.5V with 50Amp continuous. if you can, how much would it cost?

Gow.

Hello Gow,
Lithium polymer cells is nominal 3.7V. 3.5V is under the stage when cell discharge most of power on the cells. So you should not set it 3.5V cut off.
You can set it 3.0V

The capacitor-20S-50A-BMS for Lithium polymer(5Ah-40Ah batteries pack) is 119USD.
Normal resistor bleeding BMS version is 69usd.

You can contact me or irene via email and we will open a paypal proforma invoice to proceed it.
Customed BMS will take 10-14days to proceed.
Shipping a BMS via DHL is around 19-23usd.

[Spacey]

Lithium polymer cells is nominal 3.7V. 3.5V is under the stage when cell discharge most of power on the cells. So you should not set it 3.5V cut off.
You can set it 3.0V

Coming from a guy who is supposed to understand the chemistry? Bit like all those chargers you sold with your lifepo4 kits that did not trickle charge at the end of charge allowing the BMS to actually balance the pack.

3V is ground zero! if you set an lvc to this you will kill your pack very quickly. I charge to 4.15V max and discharge to 3.8V usually using 9Ah from a 17Ah 66V 16cell Turnigy pack.

There is a reason why I have not used a cheap BMS...not just from these guys...but from anyone to look after my pack. Especially as the BMS can and does go wrong spectacularly. Do you really trust a big fire to be stopped by such a cheap and badly made device, Lifepo4 sure it's worth the risk but Lipo!

If you just want to discharge till it cut off. I will suggest you to make it 2.8V or 3.0V.

Yes a professional BMS seller saying that it is ok to discharge Lipo regularly to 2.8V lol

Generally Single cell over charge protection will be about 4.28V

pulled off the figures from the net maybe? No actual knowledge based from experience?

How many cycles do you think the Lipo pack will last being charged to 4.28V and discharged to 2.8V? 200 cycles?....100 cycles? How out of balance would a pack be after it had discharged the lowest cell to 2.8V

Great advice, and some of you guys wonder why I don't like this guy.

[auraslip]

And thats also why I chose not to use a bms.

Most sellers either dont know or dont care how to take care of a pack. All of the ones ive seen have the lvc and hvc way to liberal for my tastes. they set them to deliver the max amount of capicity with no thought to long term cell health. With the lvc set so low it might not even have enough time to protect tge pack from overdisharge im some cases.

If you can find a compang willimg to build one to our specs, awesome! Im waiting for that day to come....

[eva-michael]

I think Spacey may have better setting solution and even have a BMS to provide.
You can provide a better BMS to Gow....
Please try to speak with your data. Data will always the best support of your word.
We also use the KP-Charger to work with EVA battery pack.
We leave the battery pack few days and right now all of them are 3.32-3.33V. We have many battery packs charge and discharge everyday here. And I can just take some photo as a prove.
Most of the LiFePo4 chargers are quite similar. Difference is only quality from different sellers. KP-Charger is a one of the big brand which use in wild range.
I think this is a fantastic performance. Gorde have a post about his testing of our BMS. He is a expert user.
Install of evassemble 100Amp BMS in a Scooter
viewtopic.php?f=10&t=28783&p=418902&hilit=evassemble#p418902

No EV sellers or users want their batteries are limited by BMS. Cruisingability should not been limited. That's why 3.0V LVC is most popolar for no matter EV or cell phone.
Even a good cell phone user know that charge his cell phone when power is low(80% DOD). This is a way to keep cell phone battery work longer life in his/her phone. Nokia or I phone will not take the responsibility to keep your batteries longer cycle. But ourselves, USERS! A good use habit are requested. As a batteries user, we should know this.
Keep it 80% DOD in most of your application and then charge again. Not always high C rate working.

[Spacey]

I think Spacey may have better setting solution and even have a BMS to provide.
You can provide a better BMS to Gow....

Yep can do, it's called a Cell 8 Log from Hobby king, and a Lipo pack large enough that you only use 60% of it to get where you need to go. Occasional balancing using an icharger 1010B+ when the cells get out of balance once a week.

Buy a normal KP style charge that will totally shut off with no trickle charge set for 4.13V per cell i.e 16 cells = end voltage of 66.4V with no trickle charge so that the charger shuts off when pack voltage is reached.

We leave the battery pack few days and right now all of them are 3.32-3.33V. We have many battery packs charge and discharge everyday here. And I can just take some photo as a prove.

Well with those figures it could be anywhere from 20% depleted to 60% depleted or didn't you know that Lifepo4 has a flat discharge curve....and you are supposed to be an expert?

That's why 3.0V LVC is most popolar for no matter EV or cell phone.
Even a good cell phone user know that charge his cell phone when power is low(80% DOD)

That is not 80% DOD more like OMG we have gone past the point of no return on Lipo.....expert indeed! Know your product before you try to sell to people new to this!

[heathyoung]

Charge termination at a specified voltage will not ensure complete charging.

Charge termination should occur at the specified voltage AND C/20 (ie. 5AH cell should stop at 5000/20 = 250mA).

Cell Log 8's are a great lipoly BMS. You can set them to whatever you want your LVC and HVC to be, and use the alarm output to drop the throttle - if you use a 5V reed relay, you can use the throttle power as an 'ignition' signal to turn on your cell-log when the controller is on, and use a 24V reed relay to isolate the alarm outputs to pull the throttle down to ground.

If you but the cheap 6S balancing extension wires, and servo (3 lead twisted) wires you don't even need to faff around with a PCB if you dont want to.

[dozentrio]

I could be wrong but didn't eva-michael say that they would build it to your spec? So if you want a 3.8V LVC, they will make a 3.8V LVC.

I think we shouldn't jump the gun here. Judge the product by its performance rather than anything else.

[neptronix]

3.0v/cell would be way too low for RC lipo such as the hobbyking stuff.

That's just cutting it way too close. Even with a BMS i would not discharge past about 3.3v/cell just to extend the life of the packs by limiting that last ~1% of the charge.

At 3.55v/cell, lipos have got maybe 3% energy left.

[eva-michael]

The infomation from neptronix is good for everyone. Thanks.
My point seems to be misunderstood.....
We are not taking about BMS for a pcs of cell in a cell phone. Here is forum for EV cool guys who uses battery pack but not just a pcs of cell.
Single cell over discvharge protection is 3.0V. But there is also battery pack over discahrge protection which is 3.3V/cell. i.e. For a 7S Li ion pack. It will cut off when drop into 23.1V.

[eva-michael]

[quote="Spacey"][quote]
Buy a normal KP style charge that will totally shut off with no trickle charge set for 4.13V per cell i.e 16 cells = end voltage of 66.4V with no trickle charge so that the charger shuts off when pack voltage is reached.
[quote]
I dont know where you get this Li ion KP charger from as we have ever sent few pcs lifepo4 versions to you only. The settting should match BMS. As the data I provide earlier in the thread. 4.13V per cell is a bit low to make the BMS to balance cells if your BMS setting is similar. That's why max voltage are generally set to be number of cell in seriesx4.2V.

[Spacey]

I had to take the transistor off the chargers you sent me as they did not trickle charge any power through to let the BMS do its job. If the charger just turns off when pack voltage reached and never turns back on again then how can the BMS do its job.

The result was a pack going further and further out of balance even with a BMS fitted, it wasn't until someone on this forum told me about the thread where the Ping battery guy found the same problem. He said that the chargers were set up for Lipo and not Lifepo4.

I told you about the problem in a very long email and showed you how to test and fix them, you never replied back with even a thank you? Once you take the transistor off the daughter board guess what...... the BMS can do its job and the pack very slowly gets balances.

So you probably have a lot of customers thinking that they can just leave their battery on charge and the BMS will do its job, what they don't know is that the BMS will not be balancing their pack....but hey....what do I know, it's not like I haven't built over 30 Headway packs with a huge amount of real world testing. The amount of time I spent having to fix your battery pack from the terrible and dangerous wiring was bad enough.... having complaints from customers about their range getting less and less due to the wrong chargers being sent out wasn't funny wither.

With ebikes probably going to be band in lots of China cities you might want to read up on customer service and how to do business with the West because I think you are going to need it.

[eva-michael]

We also have Ebay shop as a promotion. Till now no bad comment.

Re: Need Help with wiring BMS! Doh!!
viewtopic.php?f=7&t=21070&p=307524#p307524

Is this normal? Headway cells
viewtopic.php?f=14&t=21475&p=313004#p313004.

Cheers Michael,
Have not received the email yet but have sent you an email with the details of the bms needed.

Basically I have one of your 16 cell 48v 12ah Headway packs and will be using an Infineon 40 amp controller, so pop one of those in the package and let me know what I owe you before I damage my headways lol.

Many thanks

Spacey

We dont worry about EVA battery pack as we are very confident of them. Right now we also provide BMS instructions with long details to make sure a good understanding of everyone.
Back to this thread, just hope my lipo data can help anyone here. If anyone have query, I will try to help. Anyways ES has a lot of kind people who is willing to help. This is just a good place.

[GGoodrum]

What Spacey appears to be missing here is that a cell level LVC of 3.0V is under load, which is quite different than a resting voltage. I don't care how high the C rating is on these packs, there can and will be a significant voltage drop, under even moderate loads, especially when the pack nears the end of capacity. Once the load is removed, however, the voltage will always pop back up, usually close to nominal. If you wait until the resting voltage is down below 3.5V, those cells are right at the "cliff" and much closer to dying than if you set the "under load" LVC at 3.0V. From what I've seen, it is probably closer to about 2.5V, but I've only seen this happen once and then the cell died. This was a pack that had a faulty LVC circuit.

-- Gary

[Emoto]

It's called a Cell 8 Log from Hobby king,

Hey Spacey

Do you mean Hobbyking Cell Meter 8 Lipoly Battery Checker http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=15516
How accurate is it anyone tested it with something accurate.