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**To**:**aquatic-plants at actwin_com****Subject**:**[APD] Re: 24 volt transformer for BIY substrate heater****From**:**Bill Wichers <billw at waveform_net>**- Date: Fri, 21 Nov 2003 18:36:55 -0500
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To those DIY gurus out there. I have an Azoo 300 watt substrate cable heater and would like to use a 24 volt transformer to heat it. I

found that the local electrical outlet have a 24 volt transformer that puts

out 40 amps (used in furnaces). So that will give out 960 watts, right ?

Will that be suitable for my 300 watt cable ? I also plan to use a 500 watt

azoo heater controller for the cable. OTOH, I have not found out if both

the primary and secondary coils are physically separated in this

transformer. If it is and if you think that it is suitable, I think this

will be a viable project. Thanks for your time and any inputs will be

greatly appreciated.

Electrical systems don't operate in a way that would allow you to do that. Electrical loads consume power based on their resistance (I'm going to simplify a bit to make the math easier and neglect power factor and some other things). For example, your 300 watt cable uses 300 watts when operated on 120 volts. Volts multiplied by amps gives us watts, so from your 300 watt cable we get 300/120 = 2.5 amps. Ohm's law gives us the resistance by volts/amps, so 120/2.5 = 48 ohms. This is a convenient number for the next step, which is to determine the wattage the cable will be when fed with a 24 volt power supply. At 24 volts, we get a current (in amps) of 24 volts / 48 ohms (again from ohm's law) of 0.5 amps. To find the wattage you multiply the current by the voltage, which is 0.5 * 24, which gives 12 watts. That's not a very potent heating cable.

***************************** Waveform Technology UNIX Systems Administrator

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