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Old 06-19-2007, 12:32 PM   #1
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Volt - amp meter?

The air-conditioner works! I was able to stop at the local State Park--Catalina State Park and plug into 30 amps and test the unit.

Now what I need is advice on a voltmeter/ampere meter......are they one and the same? I think the RV Park I stayed in where the air-conditioner....actually the heat pump quit working had low whatever--volts or amps???? Any way low.

What do you suggest for testing in RV parks?
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Old 06-19-2007, 01:15 PM   #2
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Smile Hi,

What you need is a good VOM. Volt, Ohm , Amp, meter with the ability to check AC as well as DC voltage. Simpson is a good brand or go to Radio Shak and get a digital VOM.Price around 25 to 125 dollars.
Regards from Russell in sunny and hot Tucson Az.
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Old 06-19-2007, 01:26 PM   #3
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Thank you, Russell.

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Old 06-19-2007, 02:27 PM   #4
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Kistler, what you need to detect is low voltage from a campground supply. If several trailers in the campground are running A/C, microwaves, etc, the voltage at your trailer can drop. Why is this important? Well, many electrical devices will insist on drawing a certain power from the supply. Power, in watts, is calculated by multiplying amperes (like gallons per minute of water in a pipe) by voltage (like water pressure.) Lets suppose one of your devices, perhaps the A/C, insists on working at 2 kilowatts (2000 watts). If the campground supply is at 120 volts, it will draw 2000 divided by 120, = 16.7 amps. If the campground supply drops to a pressure of 90 volts, it will draw 2000 divided by 90, = 22.2 amps . Thus, as the voltage drops by 25 per cent, the current draw, in amps, increases by 33 per cent. Heat produced in a current carrying conductor is proportional to the square of the current, which in this example means 77 per cent more heat. Your A/C has just either blown the breaker, or melted! That's a simplified and approximate analysis, but I hope it explains the point. You need to monitor campground supply voltage. Constantly. From most RV supply stores you can purchase a suitable voltmeter to plug into a 120 volt receptacle. Camping World has one for ten dollars:
AC Voltage Meter - Camping World
I have one of these permanently plugged into the receptacle by the kitchen work surface in our trailer, where it is easily monitored. A range of 105 to 135 volts is recommended as safe by one authority I've read.
This is also the reason that using long power cords can be a problem. The voltage supplied will be lower at the end of a long power cord, because of the resistance in the long wire. The device being used may draw a higher current than usual, and it may burn out. A few years ago I burnt out a brand new nine inch angle grinder the first time I used it by using a long extension lead. That's an expensive way to learn that lesson. I hope this helps.
Nick.
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Old 06-19-2007, 02:42 PM   #5
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Nick, I just pulled up and was going to post that link too! Monitoring this helps prevent undervoltage brownout situations. I also can assure myself from across the room that I'm plugged in to an effective campground power source. Examples from real life have been pillar circuit breaker not switched from 'off,' during a lightning induced campground outage, forgot to switch on master switch by the door, etc. This is more than just an issue of using LP to run the fridge (doesn't use much anyway). I would otherwise run my interior lights not realizing I was running off battery alone.
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Old 06-19-2007, 03:03 PM   #6
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Thank you all; I saw the one at Camping World (on-line) and wondered if it was enough for my purposes.

No longer being in The President's Club, I have to pay the $11 +/- and the shipping is almost $9 but what can I say. Our Camping World is almost in Nogales and I am in East Phoenix.......

Actually, I am in a suburb northwest of Tucson and Camping World is about 25 miles south across Tucson.

I guess I'll order it. The keeping plugged-in all the time sounds good to me.
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Old 06-19-2007, 03:10 PM   #7
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Quote:
Originally Posted by RUSSELL
What you need is a good VOM. Volt, Ohm , Amp, meter with the ability to check AC as well as DC voltage. Simpson is a good brand or go to Radio Shak and get a digital VOM.Price around 25 to 125 dollars.
Regards from Russell in sunny and hot Tucson Az.
It's been a few years since I bought a VOM, but most of them measure Amps only at a VERY low current. Unless this has changed, if you want to measure amps, buy an ammeter.
Someone current on this stuff chime in - I just don't want him to buy a VOM with false expectations.
Dave
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Old 06-19-2007, 03:38 PM   #8
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Like I wrote, thank you all. I think the one from CW will do it.

I was up at Priest Gulch--it's outa Cortez, CO-- and had to run the heat pump because it was cold. We leave the electric on for the hot water heater and I suspect that the electric source was a bit weak and then with the hot water getting cold and us getting cold.....you get the drift.

Until my next problem, be good!

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Old 06-19-2007, 04:58 PM   #9
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Originally Posted by Fyrzowt
It's been a few years since I bought a VOM, but most of them measure Amps only at a VERY low current. Dave
Dave, that's an important point. If you want to maintain and fault-find your trailer brakes, you need to measure currents in the order of 12 amps at the 7 pin, (3 amps per wheel, and 4 wheels on my trailer), so a digital voltmeter of 20 amp capacity fits the bill. The one I use is excellent, and cost $40 a few years ago. It is Metex brand #M3800, JAMECO part# 27115, from JAMECO, 1355 Shoreway Rd., Belmont, CA 94002 (800) 831-4242. (www.jameco.com). Many of the cheaper meters will only measure half an amp.
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Old 06-19-2007, 05:11 PM   #10
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Originally Posted by CanoeStream
Examples from real life have been pillar circuit breaker not switched from 'off,' during a lightning induced campground outage, forgot to switch on master switch by the door, etc. This is more than just an issue of using LP to run the fridge (doesn't use much anyway). I would otherwise run my interior lights not realizing I was running off battery alone.
Bob, I had exactly that issue one stormy night last winter. In my trailer, the 120v line to the Intellipower charger also powers the bathroom receptacle and, crucially, the exterior 120v receptacle under a flap on the kerbside. In the driving rain,dampness must have affected the exterior receptacle, and the GFI tripped, leaving us quite unaware. However, this meant that while we were using the lights, refer, etc on 12 volts, the batteries were running down. I only discovered this late at night when I noticed that the lights were dim, and I then had to do some detective work. A better wiring system would have the Intellipower on a circuit not subject to the GFI, which, IIRC, is legally required on outlets subject to water ingress. Does anyone know why the charger is on the GFI circuit? One year, I might have nothing better to do than to re-wire the trailer. On the other hand.....
Nick.
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