Some Battery Capacity Measurements (BL36)

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slomove
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Some Battery Capacity Measurements (BL36)

I finished my BL36 conversion project and it came out quite nicely. Took it to work 12 miles round trip a few times (300 feet altitude difference) with no problems. However on my first day the juice ran out with full throttle (20-28 mph) all the time. With a more moderate speed no problem.

To find out more about the reach I did some current measurements vs. GPS speed and calculated theoretical operating distance (see attached chart). May not be super accurate because the current fluctuates quite a bit and I don't know the exact Peukert Number of my SLA Gel batteries but I thought it may be interesting for other e-bikers.

Cheers, GB

slomove
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Re: Some Battery Capacity Measurements (BL36)

Hmm, image upload did not work....BTW, these are 12Ah batteries. To eliminate wind and slope influence I rode a rather flat piece of road in both directions and averaged.

BatteryDistance.jpg

dogman
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Re: Some Battery Capacity Measurements (BL36)

Nice, 12 miles with sla's is pretty impressive. What distance did you get full throttle? 8 miles, or more? With the less efficient bd motor I never got more than 6 miles full throttle. Edit, oh, now I see you run 48v, that makes a difference, with one more sla in capacity.

On one of my bikes, I am experimenting with sla batteries paralell connected with a nicad pack. It is working suprisingly well, with a 12 ah sla and an 8 ah nicad turning out to be very well matched in capacity. It has added a lot of range without near as much weight as more sla's, and the cost is much less than a lifepo4 setup. The usual voltage sag is just about gone, so I get better top speed, better acceleration, and the sla's get used a lot more gently. The sla's should last a lot more cycles used like this.

Be the pack leader.
36 volt sla schwinn beach cruiser
36 volt lifepo4 mongoose mtb
24 volt sla + nicad EV Global

reikiman
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Re: Some Battery Capacity Measurements (BL36)

I like the Cycle Analyst dashboard unit because it shows you directly amp-hours being used and other useful measures. Yes impressive you're getting that range with SLA.

slomove
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Re: Some Battery Capacity Measurements (BL36)

Not sure if I was really clear about the distance. It is 12 miles *round trip*, that is 6 miles each way. I thought that was pretty normal? On the other hand, my batteries are new.

As for Dogman's question: That first day I did under mostly full throttle I still made it home but had to help with the pedals uphill the last mile and the voltage under load dropped to 36V (or 9V per battery). As far as I understand that does not do the battery much good to be so deeply discharged. Maybe that Cycle Analyst gadget is one of the next things on my improvement list. My current measurement was a bit jury rigged, measuring actually the voltage drop over one of the lead wires.

Here some pics of my project:

BatteryRack1.jpgBatteryRack2.jpgBatteriesLoaded.jpgRearLightHorn.jpgPanniers.jpgFrontComplete.jpgFrontWheelMotor.jpgGangCharger.jpg

reikiman
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Re: Some Battery Capacity Measurements (BL36)

Wow, that looks like the rack I made for the bike I'm building right now. Square aluminum tubes bolted to the frame. I didn't think anybody else was crazy enough to do that. It sure lacks some in esthetics but it appears it will be strong and able to carry lots of stuff.

I like how you camouflaged the rack. I painted mine to match the bicycle color and I have a motorcycle trunk mounted on the top.

slomove
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Re: Some Battery Capacity Measurements (BL36)

Well, seems like madness is universal ;-)

But, honestly I do not think it is really crazy. With the rear wheel suspension I had to do something different. I wanted it really sturdy and the center of gravity low. Having tons of batteries dangle from the saddle stem just is not right.

It looks admittedly utilitarian when naked which why I wrapped the pannier around it. They are Avenir Metro III panniers for something like $35 on Amazon. I cut the back side of the bags open with cutouts for the metal rods and used heavy string to sew it back together behind the batteries. I still can use the top bag and the secondary side bags.

GB

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