24s BMS for LiPo Battery

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pbrownhg

10 mW
Joined
Apr 7, 2013
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30
I am in the initial stages of building a battery pack for my Lynch LEM-200 motor. I would like to use a 24s LiPo pack. This topic is mainly to discuss a BMS for 24s LiPos and if someone has a lead about where to buy one. It is also to discuss a way to build a battery that is easy to charge, maintain, and is as light as possible. It is an aircraft application. I guess part of this is also to find a good bulk battery charger for this pack of 24 cells. It will be between 15-20 kWH pack.

I will start the topic here and am welcome to any leads and suggestions.

Thanks in advance....
 
i use the HCX-D131 24S lipo BMS from Bestechpower. it can balance a big pack because it has 4 of the 100 ohm resistors in parallel for 25 ohms equivalence, so it balances at 175mA which is pretty good for such a small BMS.

80A continuous and 120A surge so it can handle 8kW continuous 12kW surge. that is the spec but i think their spec is conservative and since it has 15 IRFB4115 mosfets on the output i think it could handle 180A surge and almost 100A continuous if it was not confined so it got hot.

also if you need more power you can either build two separate packs with their own BMS or you can build the packs so all the cells are in parallel, and then you can use 2 or more BMSs tied together through the B-,C-, and P- spots so that they can share the load equally.

but to combine them like that when all the cells in the pack are tied together at the cell level requires that you convert one of the BMSs into a slave BMS and then run wires from the master BMS over to the slave to control the charging and output mosfets.

they are really really cheap for such a high quality unit so i think they are the best deal around and i have about 5 of them.

lemme know if i can help, or if you need to contact them.
 
Thanks guys for the info. I am going to do a better search of the forum before I ask any more questions. I will take any comments in the meantime to shorten my searches. Below are the motor and controller I am targeting. The battery pack and system will need to be capable of 200 amp cont. 400 amp burst at 24s.

http://www.lmcltd.net/uploads/documents/LEM-200_Brochure.pdf
http://www.kruspan.ch/Products/MD95.htm

Thanks again...I would take any comments on the motor and controller if anyone has experience with them.
 
Sorry to make it sound like I did not even look...in fact I am incontact with them about a good plan for my application. The post was more to say thanks for replying and keep the discussion going.

I will premise my next comments with....I have not searched yet to see if there is info on this, but do you have a bulk charging method for your 24s pack?
 
Looking into the BMS and my application, there isn't anything that I have found for 24S Lipo that is rated for 200 amp and max 400 amp draw. It is a consideration to split up the banks and buy multiple BMS's. This gets ugly and bulky. Thinking out of the box.....
If I buy a 24s BMS from Best Tech Power and wire it into my charger for input protection, then have current limiters through my controller, and readouts for current, voltage, and maH draw through the cycle analyst, how critical is having a BMS to monitor my power take?

In other words, if I am checking the batteries each time I charge for low cells, and accurately putting in the energy, and I am careful not over tax the batteries during discharge, how much am I risking not using a BMS on the draw?
 
The plan was to use Turnigy nanotech 6s x 4 in series 5000 mAh 65C-130C x 4 rows in parallel giving me a total of 20 AH. Please correct my math/logic...

65C x 5000 mAh = 325 A draw x 4 rows = 1300 amp capability. I almost resist writing this in fear of showing that I only know enough about this stuff to be dangerous. Please be gentle with me.... :oops:
 
pbrownhg said:
.. how much am I risking not using a BMS on the draw?
Click to expand...
depends on your lvc settings of the controller. if you set it conservatively to 3.6v per cell and your controller turns off then, all cells are in good condition, and sag is not that much than you're safe.
 
My plan was to pay close attention to the fact that I have 20 AH of energy available, then reset the cycle analyst at the time of battery hookup and never go over 20 AH of draw before a recharge. Is this a good strategy?
 
pbrownhg said:
The plan was to use Turnigy nanotech 6s x 4 in series 5000 mAh 65C-130C x 4 rows in parallel giving me a total of 20 AH. Please correct my math/logic...

65C x 5000 mAh = 325 A draw x 4 rows = 1300 amp capability. I almost resist writing this in fear of showing that I only know enough about this stuff to be dangerous. Please be gentle with me.... :oops:
Click to expand...
sorry. but it's hard to be gentle now that you wrote that. NO WAY you're gonna draw 400amp out of a tiny 20Ah pack. you did a wrong calculation. you put them in series. so EVERY battery has to take the full load. even if they say 65c to 130c. your small 10awg wires will get super hot with 400a going through them.
if you put 4 of them in parallel. ok. this is doable. then every battery sees 100a, which is still a lot, as it's 20c, but the packs can deliver that.
edit: ok. re-read it. so it's 16 packs. in a 24s4p configuration. still a lot. but this should be doable. but still your wires won't do it.
 
I respect all the input and rely on you guys that know, but just to be clear, it would be 200 amp cont., but the odd time the current would go higher. The motor and controller is capable of 400 amp momentary (15-20 seconds or so), but I do not see drawing this much ever. Maybe 250-300 amp for very short times. That is only 50-75 amps on the battery wires. Is this taxing to the batteries and wires?
 
Radio silence....what are the thoughts if I increase my pack to 24s5p? That is 40 amp cont. -60 amp momentary draw. Or tell me what is a sustainable draw for the HK technology? I don't know if it matters, but the run at this current level is 5-10 min max. for my application.
 
Now I am just firing posts without replies....if I go with the 24s5p, can I go to a lesser "C" rating maybe 25-50C, to save some $$$? It sounds like the wiring is going to be the weak link??? If HK is selling under false pretenses, what is the truth?
 
just to be clear: i didn't want to say that it can't be done, but it depends on your needs and expectations.
if you take helicopter rc flying: that's why those high c-rated batteries are built initially. so sure, they can handle what you want. but these are single packs, and the 10awg wires will see those 100A, and not 400A. those packs get really hot and the helicopter is meant to fly for minutes.
so if you need those batteries for some high power drag racing and can accept that you won't get many cycles then you're ready to go. just don't expect 500 cylces from them - something that ebikers normally want as the bike is used to commute.
 
pbrownhg said:
Now I am just firing posts without replies....if I go with the 24s5p, can I go to a lesser "C" rating maybe 25-50C, to save some $$$? It sounds like the wiring is going to be the weak link??? If HK is selling under false pretenses, what is the truth?
Click to expand...
no. you WILL need to go nanotech. those 65c cells are ok and they are able to deliver what you want. the 20c cells are highly overrated. they will sag massively. my bike needs 40A cont and i have a 4p setup. so every battery sees 10A, which is a 2c discharge from a 20c pack, and i'm fine with that :)
 
they do have the nanotech in 25 constant-50C burst...is the technology the driving factor or the C rating. I do want 500 cycles or more. It is an airplane application, because of this I do not think there will be spikes. I can see needing more current to get the sailplane rolling, but once moving dialing it back to a max of 200 amp. I may even just set the controller to a max of 200 amp and my ground roll will get a little longer. Is 50 amps/battery for 5-10 min. to get me to 2000 ft going to degrade the battery life to less than 500 cycles?

25C would be 250 amp/ row of batteries rated and 50 amps draw on the wires...if HK is over stating these batteries, what would be realistic for current draw per battery to get the 500 cycles?
 
If you want to pull 200A from a 4p battery pack, then each P should have 10awg wiring hooked to #1awg or equivalent wiring buss. Each P will supply 50A, which 10awg is more than capable of. i'm not sure what you're trying to do, but 20ah at 200A will be drained in about 6 minutes.
 
afaiu he wants to power a sailplane. you need the motor to take off and gain height and then you turn it off and sail.
another hint to calculate how long your battery will last: 1c is 1h discharge time. 2c is 30min. 10c is 6min. so 25c is 2min+.
if you need 200a for 10min, and you need 24s the battery would need 200a*90v/6=3000wh=3kwh. this is 90v*35ah=4*7=28x 6s 5000 mah packs.
i hope i calculated right. it's almost midnight and i'm tired.
good thing is, this is a 24s7p pack and 7 batteries in parallel will have no problem to provide 200a.
 
well he has to use more batteries. there is a way to use a BMS like the D131 and have one master BMS and use slaves on the other sections of the battery.

i did that with the 44Ah lipo pack i used in the battery in my little ZENN electric car.

they have 120A surge i think, but since they have 15 mosfets i would guess it can do more.

on mine, i have two different 21S lipo packs. one is a 24Ah 21S and the other is a 20Ah21S and they are both tied together to each other in the 3P or 4P but also between the two batteries, so they then have one set of sense wires to the one master control BMS. it makes the commands for all the other power mosfets on the individual BMSs. i can show you how to do that if you wanna use the D131. also you can use the balancing shunts with the slave BMS too and you increase the effective balancing current, and spread the heat out more. i like doing it that way rather than using one big BMS or contactor.

i do not make nearly that big of a demand on my battery so i only get about 50-65A peaks on each one. the power is actually split between the two identical BMS mosfets according to their capacity too. it is so interesting to confirm scientific curiosity.
 
First I would like to stop and say thanks for everyone and their help...it is all good.

I am not discounting the master/slave bms configuration. Actually, I think it is a good way to get around my problem. The issue that we are running against is that it is an ultralight sailplane and weight and space are an issue. I can see with previous discussion that any available space and weight room will be taken by getting as many batteries on board as possible. We will be pushing these limits.

Safety is a concern. Given this, can I be relatively safe by monitoring the bulk charging with the BesTech BMS board (what is the difference between BMS and PCM) and then closely monitoring max current draw, my minimum voltage of the pack, and expecially my Amp*Hour draw from the pack while in the air only by use of the cycle analyst? I have read somewhere that if you do not over current the batteries or bring them below 3.2 V/cell that Lipos stay fairly balanced. If I am confirming balance everytime I charge and paying close attention to how much I draw and how fast, can I do my individual cell monitoring only on charge and not discharge?
 
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