[ausev] Cold weather and lead acid batteries

[Ken Thomas]

I am calculating Watts per foot.
Adding more feet does increase the total disipated Watts, however, the 
goal is to keep the Watts per foot the same.

Yes, Watts = E squared / R or Volts squared / Resistance.

120 VAC / 25' = 4.8 Volts per foot.
4.8 Volts squared / 2.5 Ohms = 9.216 Watts

Or, 120 VAC squared / (2.5 Ohms * 25 feet) = 230.4 Watts.
230.4 Watts / 25 feet = 9.216 Watts per foot.

At 240 VAC and 50 feet:

240 VAC / 50' = 4.8 Volts per foot.
4.8 Volts squared  / 2.5 Ohms = 9.216 Watts

Or, 240VAC squared / (2.5 Ohms * 50 feet) = 460.8 Watts.
460.8 Watts / 50 feet = 9.216 Watts per foot.

Ken




-----Original Message-----
From: Gil Dawson <Gil at Gil.Dawson.name>
To: AustinEV News Announcements and General Discussion 
<ausev at austinev.org>
Sent: Thu, 18 Dec 2008 11:23 am
Subject: Re: [ausev] Cold weather and lead acid batteries



On Dec 18, 2008, at 7:06 A, Ken Thomas wrote:
> PS. IMPORTANT: If you are using a charger that runs off of a 240 VAC
> input, the heater wire will need to be 50' long. 25 feet at 120 VAC is
> about 9 Watts per foot, which will warm the wire to the touch. 25' at
> 240 VAC would be about 18 Watts per foot, which would be hot enough to
> melt plastics and burn you if you touched it. 50' at 240 VAC will
> maintain the 9 watts per foot.

Isn't E squared?  Wouldn't that be 36 watts and 100 feet?

> one heater wire connects
> to the black wire and the other heater wire connects to the white wire


When you touch the warm wire put your other hand in your pocket.  And
don't lean on the car.
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