RE: (ET) charger - extension cords

["Humphrey, Timothy" <HumphreyT neads ang af mil>]

My mother in law has a mobile dog grooming van. Sometimes she goes to local
campgrounds and sets-up for the weekend and grooms from the van. Overall 
she
does very good business this way.

In the van she has a doggie blow dryer. This thing has a full power
nameplate rating of 120v 17amps. Once upon a time when she was grooming, 
she
blew the campsite breaker. She asked me to check it out. 

I cold see nothing obviously wrong. But everytime we plugged the van in the
breaker tripped immediately. She had a 50ft 12-2wg extension cord wrapped 
on
a reel that she uses to get power from the outlet to the van. 50ft should 
be
enough to reach about any plug.

I determined that there was something wrong with the extension cord. So, I
proceeded to remove it from the reel. After about two wraps in it started 
to
get soft. Two more wraps deep and it was fused into one solid object made 
up
of paper,copper and plastic. This thing never smelled, never let out a wisp
of smoke. It just melted together giving no indication of anything wrong
until the lines burned through to each other.

Bottom line....Never use a coiled up extension cord when drawing multiple
amps. 1 or 2 amps I could see, but now I always uncoil all the way anyway.

Stay Charged!

Hump



> -----Original Message-----
> From: Ken Olum [mailto:kdo cosmos phy tufts edu]
> Sent: Thursday, May 01, 2003 12:36 PM
> To: rmurcek geisinger edu
> Cc: elec-trak cosmos phy tufts edu; pabendro gemair com
> Subject: Re: (ET) charger - extension cords
> 
> 
>    From: "Bob Murcek" <rmurcek geisinger edu>
>    Date: Wed, 30 Apr 2003 22:03:16 -0400
> 
>    By the way, cord coiling is a no-no when significant power, like
>    that required for EV charging, is involved.  A coiled cord is an
>    inductor, and that will increase voltage drop and heating.
> 
> I don't think so.  The current flows out through one wire in a cord
> and back through the other, so there is no net current in the cord as
> a whole.  Furthermore, induction would not cause heating.  In fact,
> since the charger is a capacitative load, I think having an inductor
> would improve the power factor and so reduce heating.
> 
> In my experience, the heating in the cord itself is trivial as
> compared to the heating at the point where it is plugged in.  I think
> the greatest value in having large wires is that they conduct heat
> away from the plug where it is generated.
> 
>                      Ken
>