Re: (ET) dynamic braking

["Max Hall" <maxo iname com>]

>In my homegrown ET, my power take off is a 1500 watt 120
>volt ac modified sine wave inverter. I plan on powering a mower deck
>with whatever castaway drill or circular saw motor I can find.  BTW,
>does anyone have an idea on wattage draw for a 36 to 48" mower deck?


1500 W is pretty good for an inverter: it's enough to run, say, a hairdryer
which is a PIG. But I think it is insufficient. As for motors, you will
certainly need something more like a circular saw motor than a drill to run
a mower blade, but I'll wager that even the circ saw is up to the task.

See: say a circular saw draws 5 to 15 A at 120v, then EI is 600 to 1800 W.
If a saw is up to it, then your inverter is up to it. But I am sketpical
about the saw still.

Another tack: note that even a light-duty gas-powered mower employs 
anywhere
from 3 hp to 5 hp. I hp is about 750 W, so your maxed-out 1500 W mower 
would
offer about 2hp. That's on the light end of the spectrum for a 30" mower,
let alone 36" or 48" blades.

Why convert at all? Scrounge a 24vdc motor! or go with 36v (too late? this
thing is done?) because there's all kinds of 36v golfcart etc. etc.
components out there. You'll drive yourself nuts trying to run things off 
an
inverter. Nuts, I say.

>Another question, beside the inverter, I have a 5 amp dc-dc converter
>for my radio and cigarette light power plug. The one thing I haven't
>figured out how to do is jump start a car. Before you say battery tap,
>my battery is a 24 volt system made of 8 volt trojans. Two nominal  8
>volt batteries with a full charge will be more than 17 volts. I have
>visions of radios, computers and lord knows what else in the car going
>sizzel-pop-smoke. I know I can plug a 120 v ac to 12 volt dc charger
>into the inverter, but I'm looking for something a little quicker and
>straightforward.


One answer: the 5A dc-dc converter itself. At five amps, you will be a
charger not a "jump" and you'll be pissing away some energy in conversion
and it won't be fast, but heck. Also, make sure it has a current cut-off.
Even a low battery, let alone dead, will draw 5A, so you have to think 
about
protecting the converter.

If you are daring, another answer: just tap at 16v (nominal, 17v maybe) and
go for a guerrilla charge. (On the jump-ee: shut EVERYTHING OFF, and don't
try to start the jump-ee while the 16v pack is connected because that's a
risk to the jump-ee's electrical system and starter. I don't think it's a
big risk, but shit, even ONE BULB isn't worth it when you could just call
AAA. Oooh, imagine the rectrimination if you popped a headlight, or the
instrument cluster, ohmigawd!) You can put 17v across the jump-ee's batt
though, to charge it up, though you can't jump in the sense of adding
current to a weak (in the sense of curretn delivery) but fully charged
jump-ee's battery.

Be careful.

-Max Hall
- http://www.maxmatic.com