lifepo4 controller shorted out overnight damaged mms?

[robb]

Hi I recieved a cammy-cc 20 amp hour 24volt lifepo4 battery about 2 months ago http://cgi.ebay.co.uk/LiFePO4-24V-20AH-Electric-Scooter-E-Bike-Battery-power_W0QQitemZ170326000698QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item27a838843a&_trksid=p3286.c0.m14&_trkparms=72%3A1688%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318%7C301%3A0%7C293%3A1%7C294%3A50 . Seemed fine taking me about 20 miles before cutting out. I realise now I should have not let it drop charge enough to cut out but too late now A few weeks ago something must have shorted in the controller while I was not using it, I must have forgotten to switch of the isolator switch, and when I tried to use it a day or two later found that the 25 amp fuse had blown, the battery was completely discharged and the brushed dc motor had burnt out. Luckily I had been given the motor off an ancient e bike a neighbour was throwing in a a skip. The battery seemed to charge ok and yesterday I fitted a a new 360 watt cyclone.But a few seconds after I twisted the throttle the bms cuts out. It even cuts out with just a tiny bit of throttle but does not cut out with no load and the back wheel off the ground.Tried it without the bms for about 3 miles of hilly road and it worked fine though the voltage dropped from 27 to 25 volts. Is it ok to use it without the bms whilst discharging and use the bms to charge? If so can I use the voltage of the battery as a guide to when to stop using it and what voltage should that be? It seems to charge to just over 28 volts , that seems to drop on todays experience to about 25 volts after probably 4 or 5 miles. I read the post about testing individual cells but there are only 7 wires as far as I can see in the wiring "ribbon strip" connecting the bms to the battery , should there not be 8? I want to work out wether the fault is the bms or the battery, presumably caused by the short and wether it is worth doing anything about it, eg buy a new bms?
Rob

 

[dnmun]

your 8th wire is the positive battery wire and no sense wire is needed. i still haven't figured out what you did and i just read it twice.

measure the cells and go from there. make sure it is charged and balanced.

 

[swbluto]

If you plan on discharging anywhere near the capacity of your pack(I.e., > 7 Ah on a 10 Ah pack), you'll definitely want the BMS to use during discharge. If you don't, I can guarantee some cells will flatline and you won't notice until at least 2 to 3 cells have flatlined and you would have essentially killed them. Of course, if you don't mind risking repairs and replacements, then go right ahead.

 

[dogman dan]

Dang, that sounds like a lot of damage for a bike just sitting there. Any possibility it snuck off for a drink on it's own, taking a freind of yours with it? A short in the motor can fry a brushed motor controller I found out the hard way. Mabye it also damaged your bms? I wouldn't ride the bike at all without a bms. I've been saved several times when I "thought" I had a full charge and didn't.

 

[robb]

measured the cells they are all 3.5 except for 2 which were 3.6 so they seem well balanced. This is about 5 hours after fully charging but no use.
Actual measurements wer 3.5 7.1 10.6 14.1 17.7 21.2 24.8 28.3 The BMS looks perfect no burns or signs of damage. The cyclone 360 watt motor should not be drawing too much current should it ?
Rob

 

[dnmun]

you need to see how much current the cyclone is using and if that is why it shuts down. time for a wattsup or CA. if it charges up ok, and balances that is your biggest worry with the BMS, but it may be shutting you down when the current gets over 35A on the cyclone. you are only running 24V so overcurrent shutdown seems most likely.

 

[robb]

I have pasted the specs of the motor I am using and the 24v 20amp/hr battery below. According to them the combination should be fine or am I not taking something into account. If the battery is not capable of running the cyclone 360 motor without cutting out ,would it help to have a different bms, or wire another battery in parallel with it, preferably two sla batteries I still have. Thanks for help so far
Rob


360 Watt Motor with 9.55:1 Planetary Gearbox and Internal Controller

Size: Length: 6.183"L x 3.50"H x 3.50"W
Weight: 6.45 lbs (2.92 Kgr)
Gearbox: Integral, Planetary - 9.55:1 Ratio
Rotation: CCW
Sprocket: Not Included
Motor Controller: Internal, PWM 40Amp Max.
Peak Current: 32Amps
Continuous Current: 16.5Amps
Maximum Motor RPM: 2800
Performance chart http://www.cyclone-usa.com/360w_chart.htm?PHPSESSID=44670b8e13d407b075923f7d0820f37f


Cammy-cc 24v 20amp/hour battery specs
Fit 24V Motor Wattage: 200 Watt to 550 Watt, 400 Watt Suggested
Voltage: 24 Volts
Capacity: 20 Amp Hours
Dimension: 70 x 345 x 140 mm
（If need other sizes, possible to make order, please provide the size）
Weight: 8 kg ( 17.7 lbs)
Charging Voltage: 31 Volts
Charging Current: <5 Amps
Standard Charging Current: 1.5 Amps, 10 Hours
Quick Charging Current: 5 Amps, 5 Hours
Rated Discharging Current: ≤ 20 Amps
Max Discharging Current: 40 Amps
Max Discharging Current (Peak): 60 Amps
Lifecycle of the whole pack: >1000 times, >85% capacity.
Lifecycle of single cell: >85% capacity after 1500 cycles, >70% capacity after 3000 cycles. (<1C discharge rate and <1C charge rate)

 

[robb]

I was also wondering if I ran the bike without a bms until the voltage was about 24 voltsthen measured each cell if that would give a clue as to wether there is a problem with the bms or battery. Is that likely to damage anything? Alternatively I could leave the lights on which draw about 6 watts I think for 24 hours or more through the bms and then recheck the individual cells.
Rob

 

[dnmun]

there is nothing wrong with the BMS. you need diodes to run the SLA and lifepo4 in parallel. you can run them in series if your SLA is about 30% wider than the lifepo4.

 

[robb]

there is nothing wrong with the BMS. you need diodes to run the SLA and lifepo4 in parallel. you can run them in series if your SLA is about 30% wider than the lifepo4.

#
I think running them in paralell seems to be the best option for me. Iam going to get a Schottky-Diode . Would this one do? Vishay Schottky Diode VF40150C ITO-220AC 40A/150V http://cgi.ebay.co.uk/Vishay-Schottky-Diode-VF40150C-ITO-220AC-40A-150V_W0QQitemZ250276218169QQcmdZViewItemQQptZUK_BOI_Electrical_Components_Supplies_ET?hash=item3a45a00539&_trksid=p3286.c0.m14&_trkparms=72%3A1683%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318%7C301%3A0%7C293%3A1%7C294%3A50
I would epoxy it it to a heat sink presumably. Do you mean by "if your SLA is about 30% wider than the lifepo4" that if it has 30 % more capacity? The sla are 17ah each , the lifepo4 20 ah. Would not connecting them in series give 48v, ie 24v20ah lifepo4+ 12v17a/h sla+ 12v17ah sla.
Rob

 

[dnmun]

you can get a 60V 25A paired schottky in a 220 package from allelectronics.com for $1.35.

your first purchase should be adequate power measuring equipment. wattsup or CA from justin or tenergy had one on ebay for $50 i think. go find that thread, i think the first one anybody got was dead. haven't seen any more about it. but you need to know, not guess.

 

[swbluto]

I got a dual common cathode Fairchild shottkey 100v 60A for $4 from mouser.com. I think it needs a heat-sink and, luckily, I have a few hanging around. I plan on implementing my "booster on demand" with this diode. This booster on demand is meant more for my bike than my scooter, as it's a longer-distance type of machine.

 

[robb]

I now have a schottky diode http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWNX:IT&item=250276218169 connecting the 2x12x20amp/hr slabatteries to to the 24v 20 amp/hr cammy-cc battery and it all seems to be working very well. I have done a few longish rides with about a 30 mile ride today some of it up a quite steep one mile incline, The motor cut off towards the end of the incline and am not sure whether it was the controller within the 350 watt cyclone or something else. The schottky diode heat heat sink was very hot though. I was wondering wether it would reduce the load on the diode and hopefully the energy and heat lost if I connected another one in parallel.
After a walking for a few minutes it switched back on again ( presumably the controller in the motor though perhaps it could have been the cammy cc bms, I had no multi meter with me) to and worked fine for the rest of the journey about another 15 miles.

 

[dnmun]

the reason it broke down is because you forgot to bring the tools. it is the inverse murphy's law, whenever you bring your tools, it never breaks, but not bring your tools and it breaks as soon as you get far enuff away to regret it. forget the voltmeter and its electrical, forget the tube, and its a flat.

how hot is hot? 40A through 1/2V is 20W.

 

[robb]

the reason it broke down is because you forgot to bring the tools. it is the inverse murphy's law, whenever you bring your tools, it never breaks, but not bring your tools and it breaks as soon as you get far enuff away to regret it. forget the voltmeter and its electrical, forget the tube, and its a flat.

how hot is hot? 40A through 1/2V is 20W.

Didn't mention that I forgot a tube as well and had a puncture 5 miles from home
The heatsink on the diode was to hot to hold but not hot enough to burn so I guess around 70 to 80 degrees C . I could make the heat sink bigger on the schottky but wondered if having 2 diodes would cut current through each and decrease the energy lost through resistance of the diode. But it was up a long incline and probably I was in too high a gear. I suspect it was the controller that cut out with too high a current. Perhaps it is worth wiring in an ammeter to warn me to change down if the current is too high. I do have a 25 amp fuse and that has never blown. I am an electronic ignoramous so am guessing all this.
Seems that the 24v 20 amp cammy-cc battery on its own, does not provide quite enough current to power the 350w cyclone motor.
Rob