Thursday, December 3, 2015

Tidying and repairs evening

The mod I did on the 12V power switcher seems to be good, so that was secured up under the dash and everything buttoned up on that.

On the bicycle front, the road bike has been out of commission due to an incident a few weeks ago where a stray bit of paracord got wrapped around the rear derailleur and sucked it into the wheel, wrecking the derailleur, derailleur hanger and the chain.

I got a new derailleur hanger from Amazon today, a new derailleur (used) off eBay on Monday. I switched to a short cage derailleur because they're easy to find for $20 on eBay, while the standard medium cage ones are difficult to find and are $50 new. I adjusted the front derailleur to not drop into the little chainring (which I never use anyway) so I'm within the throw range for the short cage.

The hanger didn't quite fit right, after measuring it against the old one I determined that the frame was a bit big in one place, so I filed about a millimeter off that one place and it works fine now.  The chain I was able to straighten to what I think will be acceptable standards, and I had to take 3 links out to work with the new derailleur. A road test will tell if I need a new chain or not.

Cable and screw adjustments were done on the stand. I will road test it on Saturday if there's not snow or ice on the ground.

Having the rear wheel lock up while riding also dug down to the cords on the tire so that went in the trash as well.

Net damage was $20 for the hanger, $20 for the derailleur and $10 for the new tire (a Cheng Shin/Nashbar slick, which I still had a couple new ones here). Much cheaper than I had expected.

Wednesday, December 2, 2015

Switched 12V circuit adjustment

The circuit I built in the last post worked well in theory, but in practice with my car it wound up cycling power to the output quite often when the car was running. I put a voltmeter in the car to watch when driving.  It appears that when the car decides the battery is absolutely topped off, it completely removes alternator power from the line.

At these times, the bus voltage drops as low as 12.3 volts.  At other times it's as high as 15 volts. Typically it's in the 13.2 to 13.8 volt range.  The trigger point for my circuit is about 12.6 volts.

As built with a 2.2μF capacitor, it would shut off almost immediately, no more than a couple of seconds delay.

I modified the circuit by replacing that with a 680μF capacitor.  It does now take about 12 seconds to switch on while the capacitor charges, but it takes 3 minutes to shut off. I never observed a low voltage situation on the line that lasted more than about 20 seconds so this should be great. In fact I don't mind that the camera continues to run for a few more minutes after shutting the car off.  Bonus feature!