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Thursday, August 20, 2009

36V Test Ride

Again, couldn't get to sleep at all, so worked on the bike till way past dawn, then was finally worn out enough to sleep about 4 hours before having to get up for work, so I rode the bike to work as a test.

First, I fixed the "quirk" mentioned in the last post. It was indeed just a zener; I had stacked 36V worth of zeners for my 24V version of the controller, and forgotten that when I hooked up 36V to it. Since that's more like 41V fully charged, it meant that parts of the controller might be at 41V, but the rest of it at 36V (because of the zener protection shunting away the rest of that), so likely the comparator's reference is one of those things that was affected, causing the motor power to be partly turned on even at 0V throttle. I just stacked up 48V worth of zeners instead, and it works fine now. I added an Anderson connector for power while I was at it.

I finished up working out some temporary mounts for these lighter batteries, and moved wires around in the Anderson connectors (they can be slipped out using a flatblade screwdriver if you're careful, without damaging or uncrimping/cutting/etc, to just reconfigure the wiring). This gave me a harness that hooks 3 12V batteries in series for 36V, to give the greater motor speed necessary for the ratios I setup a few hours before.

The mounts are actually from a discarded "power panel" retail display, meant to hold some sort of spray cleaners for a display at the side of an aisle endcap. They looked like decent steel wire frames that I might someday hang on pegboard or something, to use for trays, so I saved them. Now they are battery trays. :) I did not know how well they would work, so I only zip-tied them in place, rather than welding, for now. I still would rather make lockable batteryboxes (once I find some good cabinet locks with keys, or keys for the ones I already have a pile of).

These trays hold one battery each (could hold two 12V/12Ah or smaller, I think), so the third went on my slanted rear cargo rack, zip tied down under the spring-loaded backpack-hold-down. Cabling with the Anderson connectors runs to each one, with each having it's own bolted to it's terminal tabs. The bad part is that nothing is fused yet, with no circuit breaker either, because I did not want to cut the cables at all, and don't yet have a terminal block mounted on the bike where I could safely connect the motor and pack to where I could put fuses and/or breakers.

There's also no charge connector, because I don't have a 36V charger. I'd have to use my 24V charger to do a pair of them at a time. Probably by charging one pair halfway up, then swapping to one of those plus the 3rd battery for another half-charge time, then the other plus the third battery for the rest. It is not a perfect solution, but is the best I can easily do. I can also automate this process by using some of those relays from the UPS, and a comparator circuit to check the voltages across each battery, and automatically flip things around in a "circle" until charged up to whatever set point I find works.

As a temporary option for slow charging, I can also simply hook it up to my Sorenson current-limited bench supply, set it to the final pack voltage, limit it to say, 1.5 amps (it's max continuous rating), and just let it charge all three overnight. Since it's current limited, and voltage regulated, in theory this should charge them fully but not overcharge them; in reality I'd need to do this to each battery individually to balance them correctly. Maybe I should build myself some "Volt Blochers"-style current shunts for each cell during charge (switched in and out of circuit by those relays so only connected during charge).

Anyhow, I had already charged all the batteries up as far as the 24V charger I have will go, since it has a light that comes on when it thinks they're done. Once it finished them (while I was working on the controller and the wiring harness), I just picked three out of the set of 7 (since one only goes up to 9V and is definitely bad). I hooked them up to the bike physically, then tied them and the controlller down, and took it for a spin around the block.

Wow, it works pretty well. Other than the derailers needing serious adjustments (I've switched around a lot of stuff including sprockets and haven't got that far yet), it works very well. I don't even have to pedal at all to get started from a stop, which is the main thing I really really wanted to work. Even if I have it in the highest gear it still easily pulls away from a stop (it might actually be working *better* in higher gears than lower ones). No tire-smoking, but maybe if I had a lighter bike and batteries. ;-) I think it'd probably throw gravel and/or sand on an unpaved canal path.

No video of it working on the road, since again I don't have someone to use the camera while I ride or vice-versa. I did not do any speed testing, as I had forgotten to charge the batteries in the PDA since I last had the whole thing working, before summer. Ooops.

After I made sure it all worked, I put the PDA batteries on the charger and went to bed. After getting up, I put them in the PDA and sync'd it up to put VeloAce back on, reset it to Miles and 192cm for my 24" tires, then set the odometer back to the last place it was plus the standard-distance trips I have put on it since then: 412.9 miles. (some places I go to exactly the same way and I have notes with their distances via trip odometer, so it's reasonably easy to just add in that times how many times I went there). I'm going to guess that half that mileage is entirely under human power, without the motor and batteries on it at all, both before I got the motor on it and during the time I had it all taken off during the long dark repair time of the controller.

I got ready for work, left, and rode around a mile before suddenly it acted like there was a bad connection somewhere, and I could get no torque at all. The motor was spinning, but not pushing the bike. I stopped and checked them all, but it all seemed ok. I had no DMM with me (stupid, since it is a test ride), so I couldn't check a lot of things. I just disengaged the motor clutch and pedalled the rest of the way to work. I had not gotten to the parts of the trip where I don't have to start and stop a lot, so I had not yet shifted into higher gears or used higher throttle speeds, so the max speed it had reached at that point was 13.5MPH (just before the failure).

Later during lunch at work I found it was caused by one of the batteries. I just disengaged the clutch so the motor can run without moving the bike, and run it at minimal speed so I could hear it change if I found a loose connection as I went thru it all again. It would barely run at all; maybe a third of full speed, if even that. Probably a lot less.

Probing around with my fingers, I found that the negative terminal of the righthand underseat battery was VERY warm, almost hot. Nowhere else on the bike was anything remotely warm (except the motor a little bit, after a while). Connection was good, and I took it off and scraped the metal post and tab and cable connector clean in case there was something invisible causing excessive resistance, but no change. Eventually I had to just take the Anderson connector off that battery and bolt the cable's pos and neg wires together so I could at least use the bike at 24V.

After doing that, it seemed ok, but wouldnt' know for sure till I tried to ride home. Worked alright during that ride, and still had decent startup power, though top speed was only about 12MPH. Made it home safely, and am now typing up this post.

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