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Sunday, August 30, 2009

Rigged for Testing

Well, the quick road test day before yesterday with the panel meter was half success, half failure, in that I found it only drew around 7 or 8 amps most of the time for cruising (at around 17-18MPH no pedalling), and pegged at 30+ at startup from complete stop for just about half a second before dropping quickly down to that steady rate.

However, after I parked the bike outside a store while I got some groceries, something must have happened to the meter, possibly because of direct sunlight heating it up (though I can't see why; there is no visible sign of a problem). When I came out it was stuck at around 6 amps, and I panicked at first as I thought something had shorted in the controller and was powering the motor even at a dead stop.

But after quickly yanking the main controller's Anderson connector (I haven't installed the battery cutoff yet), it stayed at 6 amps. I could tap the face and it wiggles, so it's not stuck, but it doesn't go to zero (it *was* at zero when I went inside, after turning it off and taking the key with me).

I hooked the power back up, turned it on and tested, and the system
itself still works fine, but the meter does not respond at all.

I unscrewed the casing and verified the movement coil is not burned open, but it doesn't respond to a controlled tiny voltage input either, not even from my multimeter on Diode Test. So something must be mechanically wrong; I suspect they must have used some adhesive to
secure the needle movement to the actual coil, which may have come loose from the heat of sunlight. I have to take the movement out of it to check that. There is nothing obvious wrong with it other than cheap physical construction.

Well, it looks like the movement coil itself has no continuity, so either one of the fine wires connecting it to the external red & black wires is broken, or it's burned open (which makes no sense since it still worked at shutoff, and had not yet had power thru it again).

Only a few hours and I already broke a new toy. :-(

In the meantime, I decided to ride the bike a longer distance (5 miles) on main streets on the way to a friend's to then carpool to a meeting all the way across the valley. I wanted to run it without pedalling at max speeds wherever possible, to test out the batteries and the controller heatsink, etc.

To that end, I wired up and zip-tied on a current meter (in the motor loop), a pack voltmeter, and a temperature-capable meter (with it's sensor down at the base of the heatsink). It looks awful, but I can glance down and read pack voltage and motor current draw at any moment, as well as controller heatsink temperature.

I thought about placing the thermal sensor on the MOSFETs themselves, inside the case, but decided not to, partly because I would have to dismount the controller, open the case, etc., and then do that again when I wanted to take it off after the test. Since I already verified that the MOSFETs don't get enough different temperature from the heatsink even at stall current for me to feel the difference with my fingers, then they should not be more than a few degrees different from it at most even though they're inside the case while the heatsink protrudes out of it.

If my theory is wrong, Murphy will notify me sooner rather than later, I'm sure. ;-)

I've also had a problem with the PDA and our intense midday sunlight, in that when it shines directly on the LCD, it darkens it and makes it difficult at best to read. Probably also damages it.

So I put this smoke-transparent plastic paper-guide-support from the back of some Epson inkjet in my junkpile onto the bars above it, in a way that shades it from most light above and at least a little to the sides, to see how well that might work but still allow some light thru for me to see it by, and not block my view of it.

I tried to get better pics of it, but it's just hard to see. Maybe it will show up better when I take the bike out on the driveway for some overall pics later.

It works pretty well, and unexpectedly it also helps keep certain road dust and whatnot out of my face, without blocking airflow to me. I'm not sure why that works, but it does.

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