On 03/09/2012 09:01 AM, Anne Pearse Hocker wrote:
> Hi Rick,
>
> I have the Dometic CoolFreeze 35, and reading from the spec sheet:
>
> 12v = 6.0A 24v = 3.0A 120v=1.3 to 0.7A
>
> There is an integrated multi-voltage power supply with a priority
> circuit for 120v. The integrated fuse is a 4A 250V.
>
> I used it on the standard 12v outlets this fall and didn't notice any
> problems (well, I didn't burn down the coach anyway) but I'd
> appreciate any hints for wire gauge and sockets. At least if I hire
> an electrician I'll have the right parts and not rely upon what he
> can scrounge in his truck.
>
> Anne in VA On Mar 9, 2012, at 8:24 AM, Rick Kunath wrote:
Someone was mentioning 15 to 20 amps, and while you can get away with
current like this for short periods of time using a lighter jack, the
resistance in the design causes the jack/plug combination to heat up.
This causes a failure eventually. And wiring is generally not sized for
pure lighter use to be large enough to keep the voltage drop and wiring
heating where it should be. When you are designing for a 10 second usage
of power to hear a lighter, you can cut a lot of corners.
Even at 6 amps I would recommend using some other connector than a
lighter jack and plug. You want something that is low loss and will stay
connected so that you don't have food spoilage because the plug fell out
or the spring in the lighter plug or jack weakened because it got hot.
As to wire size, this is dependent on the length of the wire. And that
is the length of the wire times 2 because you have the positive and
negative wire losses due to resistance to factor in. Resistance is a
much larger factor at 12 volts as a percentage of loss because of the
lower voltage. So you will want to make sure that the wire resistance is
low enough (i.e. wire gage sized right) to keep this voltage loss as low
as it needs to be. This will be easier on any device plugged in as the
voltage won't sag as it draws more current. This cycle causes it to have
to draw even more current to keep operating, and in anything with a
motor, this causes more heat in the motor.
Wire should be stranded, and a fairly fine very flexible stranding, with
a good protective and flexible high temperature jacket (insulation)
material, to prevent stress breakage from vibration as the coach moves
down the road. And appropriate crimp-on lugs should be used, never
soldered connections (these cause solid flex points and will fracture
eventually.) All transitions as the wire passes through any bulkheads
should be grommeted to prevent wire movement and chafing.
If we know more about the design, we can offer real concrete advice.
Rick Kunath
WBCCI #3060
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