rkd@ccice5.UUCP (R. K. Downes) (11/09/84)
Question #1.)
I have (on order) a Eclipse-brand electric vest. Does anyone what these
vests draw, current-wise? I'm guessing 4-5 amps.
Question #2.)
Is there a convenient circuit to regulate the jacket temperature?
I'm thinking of using a National Semiconductor LM395 power transistor
(TO-3 type case, two devices in parallel)
in "two terminal current limiter" mode. If the device was placed so that
it would be cooled by the wind (when the bike was moving), I think it would
"regulate" the jacket temperature quite nicely.
--
Ray Downes
Computer Consoles Inc.
ccice5:rkd (CCI Central Engineering systems only)
{rochester!ritcv, ccivax, rayssd, rlgvax}!ccice5!rkd (UUCP)kpmartin@watmath.UUCP (Kevin Martin) (11/17/84)
>Question #1.) >I have (on order) a Eclipse-brand electric vest. Does anyone what these >vests draw, current-wise? I'm guessing 4-5 amps. Sounds like a reasonable guess, for the purposes of addressing your next question. >Question #2.) >Is there a convenient circuit to regulate the jacket temperature? > >If the device was placed so that it would be cooled by the wind >(when the bike was moving), I think it would >"regulate" the jacket temperature quite nicely. > Ray Downes Let's see... If the device you are regulating with is just running as a regular series variable resistor, it dissipates the most heat when its resistance is equal to that of the vest. At this point, the total resistance is twice that of the vest, the current is half of the maximum, and both the vest and the regulator are dissipating 1/4 of the top heating capacity of the vest. For a vest that draws 6 amps (72 watts, R=2 ohms), the total resistance at this point would be 4 ohms, the circuit would draw 3 amps, and both the vest and the regulator would be generating I**2*R = 3*3*2 = 18 watts. I guess with a good power transistor, lots of silicone grease, and a good solid piece of metal to attach it to, the idea would work. A somewhat less wasteful regulator would use some form of switching (alternating between full-on and full-off, with the transistor dissipating very little power during either state), but the problem lies in finding a transistor (or other semiconductor device) which: 1) Has a *LOW* "on" voltage drop (transistors usually have 1 or 2 volts, at 5 amps, that's 5-10 watts, or 8-16% of your heating capacity). 2) Switches rapidly (since power dissipation by the transistor is highest during a switching transition) 3) Switches both on and off (i.e. can't use an SCR easily) Making a continuously-variable duty-cycle oscillator with a 555 is the easy part. Finding a device which satisfies the above constraints is tough. I think I remember finding a Toshiba power RF FET which filled the bill, but it did so in two ways... I think it cost about $60 for some other manufacturer's replacement. I'm not sure what rate I would run the thing at. Maybe 10Hz? The bike may have instrumentation which goes fubar when there is noise on the DC supply, and a switching device like this would certainly generate noise! Kevin Martin, UofW Software Development Group