What watt?

[jadney@vwtype3.org (Melissa & Jim)]

>
>According to my '65 T-3 owner's manual, the circuit requires a 16 amp
>fuse.  There is nothing else on the wiper's circuit, so I would feel
>safe that it needs just under 16 amps to opperate.

>Also if you were to put a variable resistor into this circuit you would
>have Fully adjustable, variable speed wipers just like the T-3 Ghia! 

I guess I didn't make the physics of this clear.  If your WW motor needs, 
say, 12 Amps at 7 Volts and you only have a 14 V (known as a 12 V) system, 
then you need to run the whole 12 Amps through something that will drop the 
other 7 Volts.  This means that whatever is doing your voltage dropping must 
dissipate that power=12v x 7A=84 Watts.  Now that means that your device 
needs to be a 100 watt device because that's the next available size.  
Before you say this is trivial, try to buy one and note that variable 100 W 
resistors are even MORE expensive.

Add to this the fact that you will now be using twice the power to drive 
your motor and you start to run into your own energy crunch.

Yes, I know that devices that claim to do this are sold.  I admit that I 
have no experience with any of them, but there is no free lunch, energywise 
or otherwise.  This might be a reasonable way to fly temporarily, but in the 
end I think you will want to find a 12 V wiper set.

BTW, I doubt if any of the original variable speed setups used rheostaats 
for the main motor currrent.  I think they pass only a small amount of 
current for the field winding through the variable resistor.

Jim
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       Melissa Kepner                                    Jim Adney
       jadney@vwtype3.org              jadney@vwtype3.org
                             Laura Kepner-Adney
                             Madison, Wisconsin
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