Re: DIY Substrate Heating

["Steven Pituch" <spituch at ev1_net>]

Gordon,

I'm not sure how the transformer is hooked up or how you are determining
Voltage.

30 gauge copper wire has a resistance of about 113 Ohms per 1000 feet.  Your
12 feet probably has a resistance of about 1.4 Ohms.  Since Volts = Amps x
Resistance, in theory at least, at 9 Volts you would be getting about 6.4
Amps of current which would give you about 57 Watts (6.4 x 6.4 x 1.4) of
heat.  However, the 50 Watt 12 Volt transformer probably can only take 4
Amps of current before (50/12) dropping its Voltage.  Hence perhaps this is
the reason for you using only 9 Volts out from the transformer.

You probably need 3 Ohms of resistance (12V/4A) to keep the current under 4
Amps and permit the full use of the 12 Volts available from the transformer.
If you used about 27 feet of wire you would have 3 Ohms.  The power out
would be P=IxIxR=4A x 4A x 3 Ohms = 48 Watts of heat which is what the
transformer is rated.

I can't vouch for the safety of your experiment.  You should at least have a
fuse on the AC (120 V) side of the transformer (I'd try .5 Amp first) and a
GFCI.  I get very nervous when I hear of electricity being put in water.
You can still get electrocuted when using a GFCI.

For  reference, per the Innes Book, 2 Watts is required to raise 1 gallon of
water 5 degrees F above ambient temperature.

Hope this helps.

Regards,

Steve