Load Testing 120VAC

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rg92051
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Load Testing 120VAC

Post by rg92051 » Thu Jun 12, 2008 2:53 pm

I'm working on a 50 Amp RV circuit tester from a set of plans I found online. Essentiallly it plugs into the service panel at the campground where you park your motorhome and it verifies that you have a true 50 service. You can also plug in a 1500 Watt hair dryer to load test the circuit by observing the voltage drop under load. Mine will be slightly more sophisticated than the original, using LED's instead of plug in circuit testers and using meters that are mounted rather than plug-in voltmeters. My problem is the load test part of the whole thing. I want to build it into the assembly rather than installing an electical outlet and using a hairdryer. Can someone help me build somehting that would place a load of 1500 Watts on a standard 120 VAC circuit? A big ass resistor is not going to be very practical, even if it would work!
Thanks
Rich

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haklesup
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Post by haklesup » Thu Jun 12, 2008 3:20 pm

A hairdryer IS a big ass resistor with a fan built in. Any 1500W is going to generate the same amount of heat. I can recommend some big heatsinks, fans and to-220 package resistors but it will cost a heck of a lot more than a hairdryer.

Your next best alternative is five 300W lightbulbs or 15x 100W if you want. It won't be as compact as the hairdryer and probably cost the same all told. Maybe a big halogen lamp but don't use anything with a ballast, I think you want a pure resistive load. Lamps of any kind are not ideal because they are non linear (this may be a deal breaker). I expect the hairdryer to be linear or close to it.

Does your RV have electric hot water heater, that would do but most have propane so thats probably not an option either. A burner element from an electric range might work, not sure of the resistance but the wattage is possible, probably more than 1500W but there must be small burners for someone. A space heater is just about the same thing as a hairdryer only lower speed fan.

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dacflyer
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Post by dacflyer » Thu Jun 12, 2008 4:03 pm

haklesup has the right idea as far as water heating elements,
i am guessing that you will probable only be doing this test for a few min at a time. perhaps you can use some of the water heater elements mounted in pipes filled with water water heater elements range from 1,500 watt up to 5,500 watt. and they are compact sized.
or if you like do what i did.. i am using the heat racks from old electric furnaces to load test generators, i have them built into a box, that looks like a suit case, and each element has a toggle switch so i can use a little or a lot, and it was all for free..even the switches..

hope it all works out for ya..

rg92051
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Post by rg92051 » Fri Jun 13, 2008 4:00 pm

Thanks for the replies. I guess I'll stick with the Hairdryer for now. I'm trying to keep the whole thing as compact as possible. The load would actually only be for 1 or 2 seconds but I'm sure it will still make lots of heat. I would have a (ON)OFF(ON) switch to control the load but without a timer of some kind it could be bad if someone unfamiliar with the device tried to use it.
Again, thanks for the replies.

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MrAl
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Post by MrAl » Fri Jun 13, 2008 6:39 pm

Hi there,


Hot plates are a little more stable than hair dryers, so maybe that
would help. If the wattage isnt up to exactly 1500 watts you can
compensate by adjusting the reading accordingly.
LEDs vs Bulbs, LEDs are winning.

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