----- Original Message -----
From: <M35products@aol.com>
To: "Military Vehicles Mailing List" <mil-veh@mil-veh.org>
Sent: Saturday, July 14, 2001 2:12 PM
Subject: Re: [MV] Multifuel lift pump
> In a message dated 7/14/01 3:35:03 AM Eastern Daylight Time,
> Recovry4x4@aol.com writes:
>
> << was to mount 2 12 volt
> pumps tee'd together on the frame rail. Wiring them in series compensates
> for
> the voltage difference >>
>
> Au Contraire, mon frere: (that's French for it ain't gonna happen,
buddy).
> You can put two (similar) light bulbs in series, and they will split the
> voltage evenly. If, however, you put two motors in series, even if
perfectly
> matched in terms of current draw and general condition, one will
invariably
> start before the other, and what is known as a "chase" condition will
occur.
> One pump will run very fast, possibly to the point of burning out, and the
> other will just sit there and pass current to the other.
>
Indeed so, back EMF at work.
Running motors are also generators and generate a reverse voltage opposing
the supply and therefore the current taken, when slowed fractionally the
back EMF drops and so more power is supplied - up to the point of winding
resistance losses.
Big motors, with exceedingly low winding resistance, smoke when overloaded,
hence the usual starter and thermal trip.
Richard
Southampton - England
This archive was generated by hypermail 2b29 : Tue Aug 07 2001 - 09:34:12 PDT