Replacing SLA with lifepo4

[Draggin]

     Considering replacing my now defunct SLA's for 36v 18Ah lifepo4's.  I have the standard controller 26" wheel with 2000km on the unit.  The charger that comes with the battery says that any charger will do as long as it puts out 46v.  It seems to me that I measured my charger output and it is 42v.  Not that it matters the new unit comes with a charger, but does the controller need to be modified to accept the additional voltage.  Does the low voltage cutout need to be changed as well?  From previous posts lifepo4 cutout per cell is 2.51.  I'm guessing here 2.51x12 cells is 30.12v.  That is close to the 32.5v cutout that is currently built into the controller.  Or maybe not.  Maybe 25% of the charge if nominal value is used.  Does anybody know how to do all this.  Or if it's possible.  I want to be able to go into town 18km and back without charging up. 

[OneEye]

Nice upgrade, Draggin.  You should be pretty happy with the results. 

From the charging spec it sounds like you have a 12 cell pack.  If it is a 12 cell pack I wouldn't worry about adjusting your low-voltage cutoff, the cells you are using have a pretty steep voltage curve at the end of their cycle, so you shouldn't miss out on much capacity from the higher cutoff value.  For a 10 cell pack the Low Voltage Cutoff of a 36V controller sits near the middle of the discharge curve, so you miss out on almost 1/2 of the available power if you don't change it.

You won't need to play with the controller to accept the highest voltage from the pack, even a 12 cell pack will only put out 43.2V at the high end anyway, and will almost instantly settle down to 39.6V when any sort of load is applied.  It shouldn't be enough to overheat the 15V linear regulator that was giving pdonahue some trouble in his 48V mod.

[Draggin]

     Thanks oneeye.  I think LiFePo4 is going to give electric bikes the autonamy they need to do some really outragious commutes.  I can hardley wait for spring!

[Draggin]

    I got out bid on the 36v 18Ah LiFePo4 battery and ended up with 36v 15Ah battery.  It took 6 emails to find out that the new battery will not fit in the old box because it is bigger.  So far the battery size is 100mmWx200mmHx300mmL.  Although length width and height mean something completely different in Chinese.  The old SLA's fit in a box 100Wx150Hx300L.  That's three 12v 13Ah batteries.  I guess these are the new flat cells that we saw being made on "how it's made" or You Tube "LiFePo4".  The ebay ad refered to Cheer Ocean and there website has a little info on their cells. It will be interesting to see what shows up at the door.  I hope thay don't glue the cells together. Draggin.           

[Draggin]

     So the nearest I can figure is that each cell is 275mmx160mmx8.3mm.x 12 cells actually will fit in the box on there side.  I think the cell equalizer battery maintenence thingy is better on the charger than on the battery from what I have read elswhere in this forum. Draggin

[johnbear]

Hi, have you recieved these batteries, I have ordered the same batteries - cheer ocean from ebay, and I have been getting a runaround from the seller. So far they were not sent when promised. He said that EMS got the address wrong and they were returned to him. It has been one delay after another.

[Draggin]

   I have not.  I have just gotten in agreement about what size to make. I thought that we might document this experience, good or bad, so that others might know what to expect.  I think allot of people will want to do this upgrade.  The first thing I notice is that the 15Ah cell is not smaller than the 13Ah cell that it is replacing.  I think!@?  And according to the website the 36v 15Ah pack is the same size as the 36v 20Ah pack.  Communication is very difficult at best.  I.m hoping that the border agent in Vancouver is a litttle cheaper than the one in Windsor.  It could be as much as 100 bucks extra just to get it into the country.  Even still these cells are cheap.  I have read acouple of US ebike shops offering 10Ah packs for 650.00USD and I still have to import it.  So 250.00US plus 80 for shipping plus 18.00 or so for GST still aint to bad.  But it still remains to be seen what will show up at the door.  I would expect delivery to be a couple of months.  Even though they say otherwise.  Maybe these cells are diffrent but sla's are not allowed on airplanes.  Draggin   

[Draggin]

     So I got the notice in the mail that a parcel had arrived.  Its been so long that the listing expired in my ebay and I had a hard time finding the seller to leave feedback.  I picked up the battery from the local post office. And was ammased that there wasn't any brokerage fee, no GST, and no delivery charge from the point of entry to my house.  I was delighted to find that the cells were about 10% smaller than the guy was talking about.  in order to fit my box I had to split the battery in half.  Sixteen cells on the left and 16 cells on the right.  if I had to do it again I would unsolder the tabs instead of snipping as the one closest is very short and will not stay attatched.  these two batteries fit nicely in the spot where the 12v13Ah lead acid bateries had been.  The BMS battery management system ended up in the spot where the third cell went.  I filled the empty void with expanding foam.  I had to hack the end of my old charger and solder it in the new charger that came with it.  The voltage on the battery when I got it was 40 and didn't change during the surgery.  I must have checked the polarity 50 times on the battery and the charger before I plugged it in.  The light went green red then dark.  This was not good.  I remember in here somewhere somebody had a BMS that cut them out on too big of a load.  I waited a minute and plugged it back in and it charged for the next 4 hrs or so.  When it was done the nominal voltage on the battery was 44v  thats 5v higher than the SLA's ever went.  I spun the front wheel and the speedo went to 45kph.  Thats 3kmph faster than it ever went before.  So me and my bike have both lost about 15 pounds since last fall.  Maybe I should buy some spandex         

[Draggin]

I finally got out the other day for a spin with the new Lifepo4 battery.  I only went about 5k.  The performance seems to be almost identical to the performance of the old SLA batteries.  It was pretty hilly and windy and very cold' but it was nice to get out.  I rode up the steep hill at the end of the street and there was no loss of power.  I rode it right down to a crawl expecting the BMS battery management system to cut out the motor. It never did. so so far It seems great.  can't wait to see how far she'll go an a charge. 

[Draggin]

     I finally got out for a spin with my new 36v15ah LiFePo4 battery.  I thought I might just go for a quick one before dark.  But before I knew it I went all the way into town.  I stopped in at the local bike shop so the guy could have a laugh at my contraption.  He thought It was cool.  They used to sell Bionx but stopped because the service wasn't freindly.  I went 28km round trip.  I was on the bike for 50 minutes.  My average speed 32.5km/hr.  Not bad considering I stopped for 4 stoplights.  My battery guage wasn't dimming at all so I'm guessing there is still lots left.  Yea Hoo Biking Season started. 

[Draggin]

     I ride into town again today travelling 30.64Km round trip.  It was windy! But sunny.  I think I hit every stop light red.  About 12 of them. My avarage speed was 29k/hr.  Pretty respectible.  It took me just an hour.  At that distance I did feel that I had had a good workout.  But mostly a feeling of accomplishment.  The other day I rode home from work 16k then I dropped my daughter off using the Trail-a-bike and picked her up 10k each.  I must have forgot to charge because the battery died on the way in the driveway.  Strangely it was the EMS that kicked out.  It started again after a minute.  I was home by then.  36km isnt to bad for range.  Not bad for a 36v15Ah LiFePo4 cell.  Plus at 1.19 for gas I wont need any for a while     

[andre]

Draggin,
I reach 55 km yesterday with the same batery  as you, (36v 15ah li po) however I'm impressed by your average speed! what is your top speed? mine is about 33km/h with a regen controller. that give on my 26 km round trip approx 26 km/h average.

[Draggin]

Andre 55k that's amazing.  26km/hr that sucks.  Thats how fast I go when I unplug the motor.  Are you sure the motor is plugged in.  Have you tried the pedals at all?  Just messin with ya.  I don't have regen and I go 30 unassisted.  if I pedal eventually I will get to 35 or so 38 with a tail wind.  Going to work is 16.5 Km and I get there in 30-32 min averaging 30-35km/hr.  Wind won't change my arrival time at all.  I do put 60 lbs on my tires as anything less slows me down.  I think I might have made a mistake on the distance from before.  I wasn't on my way home from my daughters school when the BMS kicked out the power.  I was on my way home from a Lions club meeting so It was actually 46km total.  Andre

[andre]

Draggin, there is something surprising in your reply...

I go also 30 unassisted... with my regen controller... so yes it is ebike and with motor plugged in!!!...If I pedal on top, I go also to 33-35 without pushing a lot! for info, I go to my work (13 km +13km round trip) and nobody see/feel any difference on me independantly if I came by car or by ebike!
Now with motor unplug,on the same trip, I reached with difficulties 26-km/h and my average fall at 16-18km/h.... The trip is really a downtown trip and even if we don't have a lot of stop lights, there is pretty a lot of roundabout or crossing roads! Honestly, if you said your cruise speed is at around 30 (like me) then your average could be 30 max (except if you push a lot on the pedals or if the wind is always in the tail... which would surprise me a lot), and without any stops on the trip.... which is not my case...
Perhaps there is some differences btween regen and standard controler on the top speed, but it seems less obvious now, compared to what is written on other posts...
For the battery, I recognized also if fall promply from 2 lights to red and nothing. I think this is typical of Lifepo battery.

[Draggin]

     Ive been spoiled by only having one stoplight and it is pressure activated, so It is usually green.  The trip I made yesterday into town was really slow due to lots of lights. And yes it was hard to get your average over 30 in town.  Tell me about the regen controller.  Do you like it.  Is it a seamless transition between power and regen?  I drove a bionx once.  I rode about a mile and used 10 percent of the power I kicked it into regen when I turned around and when I returned the bike the battery was at 100.  To go to regen you select it on the controller and touching the brake engages it.  I don't remember how it is turned off.  I could hardly tell it was engaged unless you really pushed it.  I think I read that the drop off at the end was pretty steep for LiFePo4.  That explains the sudden stop instead of pulsing like the SLA's did.  If you can go 55Kms before recharge and LifePo4 have negligible losses, could you make your battery last longer by not charging every ride?  You could effectively charge every other day and cut the cycles by 4.