# Oops! (Transformer voltages)

```Should have done a little proofreading on my own message...  please ignore
the numbers and use THESE instead (250 watt heater, not 200 watt heater).
What I said yesterday was completely true and consistent for a 200 watt heater.
The version I'm posting today is for a 250 watt heater. :)

(I retrofit my post from yesterday)
> If it was a local distributor, ir was probably a 250 Watt, 24 volt cable.
> You should be able to verify it though an ohm meter.  Because P = V^2/R,
> a 42 volt, 250 watt cable should have a resistance of 7.1 ohms, while a 24
> volt, 250 watt cable will have a resistance of 2.3 ohms.
>
> > I have searched far and wide, and not yet come up with a 42 volt/200 watt
> > transformer.  So, I turn to the collective knowledge of the list:

Ah, this is why I was confused.  Frank was confused too!  He said 200
watts here!

...
> You can use a LOWER voltage transformer on the same wire, but not a higher
> one (unless you know for sure the wire can take the higher current).
> Without knowing if you have a 7.1 or 2.3 ohm wire, here are the three
> possibilities you might have:

| 42 volt transformer  	| 24 volt transformer
--------------+------------------------+----------------------------
7.1 ohm cable |  Need 6-10 amp xformer	| =81 watts, needs 4-5 amp xformer
--------------+------------------------+----------------------------
2.3 ohm cable |   (DO NOT USE) 	| Need 11-15 amp transformer

> Note though the dramatic difference in output power you get from operating
> the 42-volt 250 watt cable at 24 volts.  1/3 the power!
>
>    - Erik

---
Erik Olson
eriko at wrq.com

```