[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

**To**:**Aquatic-Plants at actwin_com****Subject**:**Re: Transformer for Dupla heating cables****From**:**Paul Nicholson <paul at eisusa_com>**- Date: Thu, 9 Oct 1997 09:29:30 -0700
- In-Reply-To: <199710090748.DAA11140 at acme_actwin.com>

At 3:48 AM -0400 10/9/97, Neil Schneider <pacneil at home_com> wrote: >Ohms law says: P(ower in watts)=E(volts) x I(current) so a 250W cable at >42 volts draws 5.95 amps of current. Driven by a 24 volt transformer the >same cable would draw 10.42 amps. I doubt the voltage is crititical for >something like a heating cable. You will need to supply a transformer >that >can supply sufficient current. I would recommend something capable of 15 >Amp >minimum, preferably 20 Amps for a safety margin. As always Your mileage >may >vary. > You are absolutely right that P=EI. The conclusion that the current will go up as the voltage decreases is like saying that as the water pressure goes down, you can get more water through the same size pipe. The resistance of the heating cable is constant. You first need to figure the resistance of the cable using the formula R = E^2/P where E and P are the rated voltage and power ratings of the cable. If it's rated for 250 watts at 42 volts, then the resistance is 7.056 ohms. WIth a resistance of 7.056 ohms at 24 volts, the cable will deliver P=E^2/R which is 81 watts at 24 volts. I suggest that you measure the resistance of the cable with an ohmmeter, and verify the rated voltage and power. Paul Paul Nicholson Electronic Imaging Systems, Inc. TEL 805 532 1068 5148 Commerce Avenue, Unit F FAX 805 532 1065 Moorpark, CA 93021 U.S.A. paul at eisusa_com http://www.eisusa.com

- Prev by Date:
**Plant Bleaching** - Next by Date:
**Dupla heating cables** - Prev by thread:
**Re: Transformer for Dupla heating cables** - Next by thread:
**Re: my tiny tank (again)** - Index(es):