Military Vehicles, May 1997,: Re: [MV] Re: Voltage reduction
Re: [MV] Re: Voltage reduction
bdk (bdk@geocities.com)
Thu, 01 May 1997 11:03:32 -0700
Torfinn Sørnes wrote:
>
> Postage paid by: [Image]
>
> ---------------------------------------------------------------
>
> A voltage reduction from 24 to 12 volts can be obtained in two ways:
>
> First you can use a resistor in series with the load. What size resitor is
> needed: There are two equation you need to use: Ohm's law (U=R*I)and the
> power equation ( P=U*I). (*) states multiply. If the fan use 5Ampere on 12
> Volts then the internal Resistance is 2.4 ohm (12 over 5). Since the
> voltage on which you are going to use the fan is 24 volts, you need a
> resistor that is 2.4 ohm. When this resistor is connected in series with
> the fan, it uses an equal amount of energy as the fan. This energy has to
> be removed. The Power is 5A multiplied by 12Volts equals 60Watts. That is
> you need a resistor 2.4ohm and at 60Watts or more.
>
> An other way is to use a voltage converter 24 to 12V. The converter must be
> bigger in watts than the load. These converters use a switching technique:
> It connects 24 volts to the fan for a very short period of time
> (microseconds) and then it shuts off the 24 volts for an equal amount of
> time. The converter does this repeatedly. Then the average voltage to the
> load is 12 volts.
>
> >From an energy point of view, the second method is the best. The efficiency
> is about 80-90 percent. The first method is the cheapest, but it vastes
> energy, and the generator has to produce more power.
>
> Torfinn Sornes
> 42 Ford GPW
> tsornes@online.no
>
J.C.Whitney sells 24 to 12 volt regulated power converters (Part No.
38NR1492U) for $87.99. It features a 10 amp capacity, low ripple output,
and internal heat protection.
It can be ordered by calling 1-312/431-6102.
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