Re: [MV] 24 Volt System

jonathon (jemery@execpc.com)
Thu, 8 Jul 1999 20:05:01 -0500

>OK Folks, I just saw an item that isn't true and can't stay silent on this
>one! There is a very good reason that 24 volt systems are used. Totally
>forget the notion that the Gov't used it because it was "odd".

I agree, it's a matter of simple engineering.

>..... If you use Ohm's Law, you will find that when
>voltage goes up-current (Amps) goes down proportionally. (Also a principle
>used in high voltage power lines going through cities) Simple! OK, Now
>when you use 24 Volts, current is half that of a similiar 12 Volt system,
>and respectively will have twice the stamina. If you had a similiar system
>using 6 Volts, you would have FOUR TIMES THE AMOUNT OF CURRENT TO DO THE
>SAME JOB RESULTING IN VERY HEAVY WIRING, CONTACTS AND CONNECTORS NOT TO
>MENTION OF A VERY SHORT DUTY CRANKING CYCLE.

There is an additional situation with starter motors, that being the voltage
drop in the brushes which is a function of current. Thus the percentage of
voltage (or energy) lost in the brushes in a 6v starter is signifigantly
higher than the percentage lost in a 24v starter. The more voltage
available to the windings themselves the more torque the motor will produce.
This is why a 24v motor will roll over a cold engine better than a 6v motor.

My appologies to any fellow EE's out there as my description is lacking but
I'm just trying to illustrate this without getting bogged down in to many
details.

je

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