Connecting 36V li-ion packs in series to 72V - 180V

[iljak]

Dear battery gurus! I would like to get help on following; I would like to connect several 36V li-ion packs together to generate high voltage for a speedrecord project.
Would like to start off with two 36V li-ion packs (36V10Ah 20A), and eventually use up to 5 36V packs.
I played around before with putting whole packs in series but they tended to shut off (probably) because of over voltage proction.
Any tips, tricks and advice are highly appreciated.
Greetings from Amsterdam.

 

[Htfan]

Sounds like you are starting a great project!

There was no mention in your post of the controller or motor you are planning to use. If you try to put 72v through a 36v controller, it will absolutely shut off unless it is configured for that voltage.

 

[dnmun]

i have wired up multiple BMS controlled packs through their BMSs but i only built it up to 22 using the ping signalab.

but i know how to wire up multiple 24S BMS boards to build anything up to 72S or 96S or any number in that range.

i also have a technique of rewiring the Bestechpower D131 lifepo4 BMS power boards on my 24S 87Ah lifepo4 ping recycled pouch pack so i can use the power boards i separate from the balance boards on the D131 line from bestech.

on the balance boards you can carry the HVC and LVC lines from one balance board to the next down to the bottom BMS in the stack and let that BMS be the master control for all of the power boards rebuilt to 200A from each of the original BMS.

you can build a 96S lipo pack from 4x24S lipo D131 BMSs. total cost on our last group order was $260. you can even add more balance boards if you wanna have more than 175 mA of shunt current. i have some of those too.

so you would have 750A of output power spit between the 4 power boards. at 96S lipo. for $265 and people say using protection is too expensive and eats up too much power.

do the math. you have 75 IRFB 4115 mosfets in parallel. each mosfet with 3mR of channel resistance.

all of this for $265 and included you have as much balancing current as your charger can provide. so you can jam the charger at full charge right up to the last milivolt without pushing any cell over the HVC and have almost every other one within a few millivolts.

this is just my experience. when i charge my 24S pack to 88.2V i have no anxiety that it will explode or that the cells will suddenly spontaneously explode like roman candles. i do worry about the chargers blowing sparks out when the output caps blow up. i have learned from experience where the risk is and how to deal with risk. i can remove the chargers from the car to reduce that risk.

but i do not worry about the battery blowing up when i charge to full charge just like the LEAF or Tesla or other performance directed charging status. when i am not using my car, i leave it at a low state of charge. i do sometimes plug in the Elcon SLA pack charger after a trip where i know i have had to force the SLA pack on when i drain a lot of power out of my main lipo and lifepo4 packs, and the voltage drops down to the level of the SLA pack, and then that also puts some juice back into my lipo/lifepo4 packs through the diode when i recharge because the Elcon has a charge profile that pushes it up to 84V for my 100Ah Deka gel SLA packs.

so then with the Elcon charger cycling, my lithium pack is always carried up to about 80V and left there above the SLA pack, isolated by the diodes as the Elcon charger shuts off and goes into surveillance mode on the SLA pack. the SLA pack drops down to 76-78V then and leaves my lithium at 80-81V.

anyway lotta yakking over what i consider to be the cheapest most reliable way to building a decent voltage pack and maintain balance and control safely. $265 for 96S 403.2V lipo. you can drive on it. $265. 750A. why would someone pay $3k for a BMS? if the motor is just a simple Curtis controlled AC-30.

that would be the ideal compromise. AC-30 and 48S. spend the money on the motor and controller and not some unneeded excess canbus. just cheap and reliable. no failed state. just always on.

 

[leffex]

5 packs in series will then be 180v 10AH and 20A means = 3600w Or about 5 horsepower that the batteries can output before the batteries turn of (battery fuse protection over amps or single battery low voltage cutoff because of high drain) ifyour controller and motor for example is higher power than above fuses, and internal battery protection will cut power at hi drain after a few seconds.

Controllers have generally maximum voltages at 63v effective voltage and 100v. More expensive controllers can take more voltage and cost more as well.
Maximum power for a 100v limit controller can be 100v * 100A 10.000w that one cost 100-200 dollar.
200-400 dollars can get you 100-150v Controller and 100-400a.

At higher power and effeciency goes down fast and motor becomes an oven, a fireplace you name it.

Good luck!

 

[iljak]

Thank you so much for the quick and thorough answers!!

From the sounds of it, i think it will be necessary to use all them 36V packs without bms or fuse, by bypassing the bms' (maybe hook a low voltage buzzer? and a single 50A fuse?)
https://bmsbattery.com/ebike-battery/664-high-c-rate-polymer-li-ion-battery-heat-shrink-battery-pack-battery.html

I am using a custom 200V controller;
http://www.aliexpress.com/store/product/60V-200V-12000W-super-power-bldc-motor-controller-can-be-made-to-order-e-scooter-controller/937734_1857656652.html

And a 3kW gearless hubmotor:
http://www.theebikemotor.com/productshow.asp?ArticleID=1319&title=3000W%20electric%20motorcycle%20bike%20conversion%20kit,%20e%20bike%20kit%20with%20LCD%20display&bigclassname=Products&smallclassname=BLDC%20Motors%20&%20Conversion%20Kits

Any tips and tricks are very welcome!

(BTW: I ran a 100V 75kmh setup setup a few years back, 60V lifepo in series with 3 12V nimh batteries, Crystalyte 408, 72v1000W controller, i need to break this record..)

 

[dnmun]

that would be a really poor decision imo. buying unknown small packs with small number of and high Rsd mosfets and then stringing them into a series. worst of all worlds.

you need to learn how to build your own packs so that when they break down in use in competition or in a remote region, you need to be able to know enuff to fix it on the spot and know how to make it reliable and low resistance in discharge as well as preventing one pack in the middle failing and shutting down the entire multiple packs series.