BMS for LiPo: yes or no? what is it?

I have read several threads in this forum regarding BMS for LiPo. I understand most LiFePO batteries have a BMS, unlike LiPos. But I still do not know what it all means. What I think I understand is:

1. With a BMS, one has a single charge point for LiPos, instead of having to connect many cables for every charge
2. Would one need a specific LiPo charger? Or one could use other, simpler chargers?
3. There is a LVC and a HVC. How much does this reduce the likelihood of a security incident regarding the usage of LiPos?
4. BMS limits amperage, but apparently, if the max amperage of the BMS is equal or higher than the amperage of the controller, everything is fine

I ask this because LiPo has some appeal to me, but the reported security events I have read in this forum regarding LiPo usage scare me. I would charge indoors. I was wondering if adding a BMS would reduce security concerns enough in order to make LiPo usage viable.

Thanks.

the BMS protects the battery pack from overcharging and from over discharging. it will balance the cells and provides short circuit protection on the output.

it is not used on these hobbyking RC lipo packs that are used on model planes and helicopters that have now been adapted to use on ebikes.

you can buy a balancing charger that has a BMS built into it so that the balancing charger will balance the pack as you charge it just as a pack with a BMS does.

but a balancing charger will not protect the pack from over discharging or from short circuits on the output.

for a long time there was no source for a useful lipo BMS until agnius found these guys at bestechpower.

http://www.bestekpower.com/

you can find all kinds of lipo BMSs there and we are now testing them to see how well they work. i have built 4 different lipo packs with their BMSs. 15S,20S, and 24S lipo

they also have BMSs for lifepo4 too. first rate stuff imo.

Where I can see prices? For example 12S pack and 35A discharge current

they are a manufacturer and don't list prices because they normally deal with distributors or battery makers but they will respond if you send the email to henry. i have been putting together orders big enuff to get them to offer me something close to jobber prices.

dnmun said:

the BMS protects the battery pack from overcharging and from over discharging. it will balance the cells and provides short circuit protection on the output.

it is not used on these hobbyking RC lipo packs that are used on model planes and helicopters that have now been adapted to use on ebikes.

you can buy a balancing charger that has a BMS built into it so that the balancing charger will balance the pack as you charge it just as a pack with a BMS does.

but a balancing charger will not protect the pack from over discharging or from short circuits on the output.

for a long time there was no source for a useful lipo BMS until agnius found these guys at bestechpower.

http://www.bestekpower.com/

you can find all kinds of lipo BMSs there and we are now testing them to see how well they work. i have built 4 different lipo packs with their BMSs. 15S,20S, and 24S lipo

they also have BMSs for lifepo4 too. first rate stuff imo.

Click to expand...

Thanks for the reply, it is helpful.

So, let me see if I have understood you correctly:

So far, most people using LiPos were using chargers (such as those in http://www.hobbyking.com/hobbyking/store/__216__408__Chargers_Accessories-Battery_Chargers.html), with BMS built into them, which were balancing the batteries when charging. But the problem is that at discharge (ie when using the batteries) there was no protection (obvious: the charger remains at home).

But now there are these BMS for LiPos from bestekpower which "protect at discharge". Questions:

1. Apart from puncture, could one say LiPos with BMS are "safe"?
2. What happens then for charging? Does one need to use the same system as before (chargers such as in http://www.hobbyking.com/hobbyking/store/__216__408__Chargers_Accessories-Battery_Chargers.html) or could one use a simpler system?

The cells need to stay balanced no matter how you do it. Plenty of opinions about what balanced means. Also, if a cell goes under 2.7v, replace it. Printed on all the LiPo I've ever used, it says to charge with flammables at least 10 feet away. That is pretty good advice. For me, I'd use a BMS but I don't have the time or self-discipline to monkey with disconnecting and balance charging. But again I'd heed the warning of the manufacturer regardless.

I couldn't recommend lipo personally, if something went wrong, it'll light on fire. If you are very clever, diligent, and understand the risks then I recommend (no matter what) having linked fire alarms and the appropriate fire extinguisher paired with a solid practiced plan in case of fire. This fire safety advice should be standard regardless. If you were able to keep the bike with lipo somewhere where it would never catch anything on fire that you couldn't stand to lose, then it wouldn't be as big of a deal. If you could build a small charging shack for your bike like a shed or something, then you'd probably be just fine with using any chemistry you saw fit assuming the shed wasn't a fire risk for other things like trees or other property and so on. Some seem to charge their lipo in odd places like fire places and ovens, that might be something you could consider.

1. If you know what you're doing, you can make a single point connector for a lipo pack without a bms too. It's not rocket science.
2. An RC charger is normal, but there's ways to balance charge a lipo pack without one using separate balance board(s).
3. Well, you don't want to over discharge or over charge. Over charging is handled by an rc charger, or separate balance board(s). Over discharge is handle by controller LVC and/or the user.
4. Yes.

I don't use a bms, and haven't for 2.5 years without a problem. All the ones I've seen can't set LVC higher than 3.0V per cell. I don't want to run lower than loaded 3.5V per cell, so for me they are basically useless except for ease of charging, and there's other ways for safe single point charging that doesn't require you to use a bms.

wesnewell said:

1. If you know what you're doing, you can make a single point connector for a lipo pack without a bms too. It's not rocket science.

Click to expand...

Since I do not know what I am doing with precision yet, would you mind to describe how could one get a single point connector for a lipo pack without a bms?

Here's one way. If you pack is more than 14s, you'd need to use an appropriate balance board.
http://endless-sphere.com/forums/viewtopic.php?f=14&t=23362&p=374866&hilit=hyperion#p374820

battery murdering system

Every single BMS I have had the displeasure to use has been an issue, I only use BMS in the charger when charging, under discharge nothing on a day to day basis and cell log alarm monitor on long rides when the pack may go low, everything is disconnected at the end of the ride so the cells sit there with nothing on them, pack is removed from the bike and stored where it can do no harm, battery is charged on a fireproof blanket, away from the house, under a smoke alarm and monitored with a baby monitor.

Most of my battery problems and breakdowns out on the road were with BMS issues, starting way back 8 years or so now when I first started using them, keep it simple.

this is a picture of a 24S lipo pack i just built from hobbykinglipo packs using a BMS from those guys. i can only test it to 45A with the heaters i have for a load but i think it will handle about 100A. the reason they are not popular is because the sense wires from the BMS to the hobby king packs have to go through the JST plugs which is the weak link because bad connections can make it turn off the BMS. so this pack is waiting for authorization to solder the sense wires onto the wires from the cells to the JST plug.

if the wires are soldered together that will remove the connection problem.

I dont like that bestekpower BMS LVC cannot be 3.5V (Overdischarge can be 2.3V--3.0V)
That is a deal breaker for me, no need to send email for prices - I want 4.1...4.15V HVC and 3.5V LVC, and power 30A+
So I keep using low-voltage alarms and balance charger.

Meelis

I will not get into the bms argument, except to say only a fool blindly trusts a bms. With or without bms, check on your battery from time to time, as though there was no bms.

As for Lipo (lico chemistry) being safe. Well, it's a chemistry that has a track record for catching fire when it gets abused. So it's never really safe.

However, like Wes, I have used it safely for many years. It's a matter of doing some of your own quality control, and then avoiding breaking the "lipo rules".

Learn a lot about lipo before deciding to use it on a bike to be ridden every day. Other chemistries will be safer and more convenient. But if you will be building a hot rod bike, or need light weight for better off road handling, or wish to carry only enough battery for a very short ride, then lico will pack the most amps per pound of all the choices out there.

Hi
Just read this post looking for info on weather to use a bms for charging but not for discharging as all my bikes pull more amps than the bms boards I have found.
Knoxie summed my problem up very nicely and I will probably put his ideas to use.

Another point was rasied the only LVC boards that there are about are for a fixed voltage of 3v for lipos LVC side and 4.2 or higher for the HVC side. a few years ago I made some LVC boards to Fechters designs using smd components they worked well and I sold quite a lot, I was going to have a go at a board with LVC HVC and WLV(warning low voltage) the WLV would be chosen by popular demand, devices for the units to trigger would have to be made, also a simple Storage Voltage Cutoff might be useful for storing the bikes over winter if that is your choice, I can prototype such a system to check it works then design an SMD circuit board with all the items on it that are required, if enough show interest then I will do some costing and if those interested like the price I will go ahead and get it made.
Geoff