Can I run my LiFePO4 Battery with no BMS?
Hello,
I am a newbie who just purchased my first e-bike conversion kit. I picked up the Phoenix 5304 hub motor with a 40 amp controller. The battery been used is a duct tape 48v 20ah pack. I converted my bike and everything worked fine my first time out........until I started to smell smoke :(. I looked over the battery pack it was fine, not even warm. I then inspected the BMS which basically melted. The solder was dripping off the BMS like water!
I did some testing, and believe it or not the BMS still works. After my testing I decided to do the following.
I created harness for the BMS. I am only using the BMS during the charging process. After a complete charge I remove the charger and the BMS via the harness. i then ride the bike with just the battery and an in-line 50 amp fuse. The bike seems to run great. Is this is a safe configuration? Am I in danger of damaging the battery? I assume that the BMS is only used for charging purposes, but I could be WAY off. Thanks for helping the new guy :).
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Re: Can I run my LiFePO4 Battery with no BMS?
Hi there,
By using the pack without a bms on discharge you could destory any weak cells that arn't charged to full capacity by overdischarging them. lithium cells have a max and minimum voltage, on charge the bms protects from overcharging and on discharge overdischarging. . See here for a general guide to lithium batts http://www.axeonpower.com/lithiumS.htm
In theory if you keep checking the cell voltages and make sure you have no weak cells you would be ok.
Was it a Ping pack?, he normally pretty helpful and should send you another bms, let you know what happened. You could a also buy a low voltage cutoff board from http://www.tppacks.com/products.asp?cat=26 which wires striaght to the controller to cut the power if any cell falls to low.
Re: Can I run my LiFePO4 Battery with no BMS?
Yeah, who's lifepo4 are you using? Over at the endless sphere there are some threads about other than ping sellers and thier packs you need to read. Notably the battery section thread about East Music and Jimmywu being the same seller.
In any case, you have too much motor for the battery, and will need to baby the heck out of it, like starting and hills, or get a cycleanalyst to limit the amps you can draw out of the pack. The big chrystalite motors need more than 20 ah to keep the c rate low enough for the battery to last. At least 24 ah, or even 30 seems to be the sise needed for the big motors. The smaller sise will run, but it just hammers the cells, and after much less than the 1000 cycles you will start losing cells. The symptoms you describe are very similar to those who had bogus bms from a seller who changes names frequently.
Long run, you need to start saving up for better c rate batteries, such as lifebatt, PSI, A123 etc. Those ones can handle the high amps your motor needs. In the short run, maybe get a smaller motor since a new motor is 4 times cheaper than a new battery. A 408 will be more suitable for the sise of lifepo4 you have.
Be the pack leader.
36 volt sla schwinn beach cruiser
36 volt lifepo4 mongoose mtb
24 volt sla + nicad EV Global
Re: Can I run my LiFePO4 Battery with no BMS?
Hello,
Thanks for the great information guys! I'm a little angry i didn't join this forum before spending my life savings on batteries. I hate being compulsive :). So here is the scoop on my batteries. I purchased two. The first I got for $600, its a no name duct tape brand from China. Here is the description from the page:
Specifications
Fit 48V Motor Wattage: 500 Watt to 1200 Watt, 800 Watt suggested
Voltage: 48 Volts
Capacity: 20 Amp Hours
Dimension: 160x150x270 mm ( 6 1/3x6x 10 2/3 inches )
Weight: 10.00 kg ( 22.00 lbs)
Charging Voltage: 61 Volts
Charging Current: <5 Amps
Rated Discharging Amperage: 20 Amps
Max Continuous Discharging Amperage: 40 Amps
Maximum Discharging Current: 60 Amps
Discharging Cut-off Protection: 40 Amps
Lifecycle of the whole pack: >85% capacity after 1000 cycles.
Lifecycle of single cell: >85% capacity after 1500 cycles, >70% capacity after 3000 cycles.
I have only been able to fully discharge the pack once. The first time I tried, the BMS melted. The second attempt with no BMS worked, but I am only getting 13.6ah according to my cycle analyst. I am hoping for better ah with the new BMS......but who knows. I also may be using the cycle analyst wrong......I haven't read the manual yet.....I was simply using it to measure amp hours.
The second battery also had a BMS problem.....one of the resistors was running very hot.....they are sending me another one. I am still waiting to test it. This battery was $950 when i bought it......it has since come down in price. Check out the lifepo4.hk website for details on this battery, it is also 48v 20ah.
I tried getting a new BMS from tppacks, but they have been out of stock for weeks. That guy ping on ebay is selling me one for $40....its worth a try I guess.
I have 2 Phoenix hub motors, the Cruiser, and the Racer. I also have a RoadRunner, but its just not giving me any speed compared to the Phoenix.
I noticed that several cycle shops in the US sell Yesa brand batteries for $1800. Are these any good? I contacted them directly and they will sell direct for $1200
Thanks again for helping me out! :)
Re: Can I run my LiFePO4 Battery with no BMS?
I use 2x 12v 20AH yesa packs on my emax (in series with a 48v thundersky pack).
i discharge at 100A on acceleration and 50A continuous.
The yesa batteries are pretty good (about the same C rating as thundersky, with same sag under load).
i get 3vpc under 1C load.
the BMS that came with the batteries were no good being in series with the thundersky pack, or in parrallel with each other.
especialy at the discharge rates i was subjecting them to. i bypassed the BMS on discharge 8000km ago.
the batteries are holding up fine.
Matt
Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah in July 2010. Done 194'000km
Re: Can I run my LiFePO4 Battery with no BMS?
Just for the record, which vendors sold you the batteries, and are they cylindrical cells inside, or foil pouches? A lot of folks are having problems with the packs made of hundreds of round cells. Let us know who not to buy from. Only Ping is known to use the foil pouch cells that are much more reliable than the small round cells.
Be the pack leader.
36 volt sla schwinn beach cruiser
36 volt lifepo4 mongoose mtb
24 volt sla + nicad EV Global
Re: Can I run my LiFePO4 Battery with no BMS?
Hello,
The cheaper of the two batteries is from user asale626 on eBay. This is the battery where the BMS melted. I peeled back over 40 layers of duct tape on the pack to find a mess of small peach cylinders with no markings, all glued together with enough hot glue to last you a lifetime. I mean seriously, I cant find a single wire or solder point......ALL GLUE. For the record....the charger also arrived damaged, and Im still waiting for a replacement. This guy really screwed me good.
The second battery hasn't been tested yet. I will peel the tape back later today and let you know what i find inside.
Thanks!
Re: Can I run my LiFePO4 Battery with no BMS?
Personally I have used batteries without the BMS. I prefer it. u can get away with more on a lifepo4 than u can with Lipoly
Im not sure who many amps the pheonix 5304 pulls, but with a 20Ahr battery ur really ok up to 60
No one has had a Lifepo4 long enough yet to really know if u do loose a few cycles of the life
Ive even got one of my bikes without a controller. (just an On / Off press button) - but u should feel the jolt when that beast goes lol!