Well this is one of those things, I wouldn't mind just purchasing the volt meter from Camping World but that requires a membership fee higher than the cost of the meter itself. after spending a few hours calling RV dealers, Radio Shack, various electronics and industrial supplies outlets I'm amazed such a simple straight forward device is so hard to find.
I plan on using the meter to monitor voltage on a 4000 watt emergency generator. for now I'll use my DMM but I like this simple volt meter cause I don't think it requires a battery. the reason being, apparently under certain loads the automatic voltage regulator (AVR) on the generator can be damaged causing the output voltage to rise to levels that will damage your appliances as well as the generator. very expensive !
The following are posts from RV.net and help to explain things.
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N9WOS
Nashville Indiana USA
That headroom on a AVR unit is what allows the voltage to go to 170~190V and beyond when the AVR fails and pushes the unit to saturation. That voltage you see on the output when it fails in the high output condition is the output you would see if the generator head was operated as a capacitive feedback unit with those stator windings.
Another warning to people on this board. AVR units have another little quark to watch out for. Watch what type of loads you connect to your generator. An AVR generator head can jump into capacitive feedback operation if the right type of load is connected to it. There is nothing special about the winding the capacitor is connected to on a capacitive feedback generator head. Any winding on the generator head can act as a capacitive feedback winding. And the AVR unit can not stop the generator head from jumping into direct capacitive feedback regeneration. The only thing that maters is the type of loads that is connected to the windings.
If you connect a load with a large capacitive (leading) current then it can push an AVR generator into a capacitive feedback (self excited) loop. When that happens, the AVR looses control and the voltage jumps up to the saturated output level. That can cause connected loads, and even the AVR to be damaged if it isn’t designed to take that level of input on the metered side.
You can illicit that mode of operation by connecting an AC capacitor to the output terminals of an AVR generator with no other load. Usually 12 to 24uF should be enough. 40uf should definitely be enough. It will jump right up to the saturated output level.
You will find out that a purely resistive load, even up to the rated output of the generator will not effect the capacitance needed for capacitive feedback to take over. The feedback happens when the output voltage crosses zero which means resistive loads have no current and do not affect the feedback loop. The thing that cancels out the capacitive feedback is inductive loads.
Most loads are inductive. Just make sure that your inductive loads always outnumber the capacitive loads by a large margin.
Some loads can shift from inductive to capacitive to inductive depending on operating load. Like capacitor start motors and capacitor run motors. Or motors with capacitors in parallel for PF correction. If you are running a capacitor run motor off of a generator and see the output voltage of the generator start to climb as the motor load increases then shut it down because the current the motor is pulling is starting to shift capacitive with an increase in load. If it gets far enough then the generator will go ballistic. If you run a capacitor start motor off of a generator, you may see the voltage spike when the motor starts. With the start capacitor in line, the motor current is almost always heavily capacitive. That will cause the generator to operate in capacitive feedback mode until the motor comes up to speed and the start capacitor disconnects. That can damage an AVR unit, and the other stuff connected to the generator.
If a large inductive load (motor) has a PF correction capacitor across it, is often a good idea to remove the PF correction capacitor. Because when the PF of the motor it’s self goes from lagging to unity when the load increases, the PF correction capacitor can push the total PF into the leading range.
Capacitive feedback generators do no suffer that problem because that is the normal mode they operate in. The only damage that can happen to them because of a capacitive load is if a large capacitive load is left on for a long time. It will cause the armature to overheat and burn out. It basically causes an extreme over excitation of the armature winding if the capacitive load is big enough.
If you ever pull apart a capacitive feedback head and the stator is fried, it is usually because of someone running a heavily capacitive load.
To sum it all up. Do not run loads with a leading (capacitive) power factor on a generator, especially a generator with an AVR.
So..
Watch out for capacitor start motors.
Watch out for equipment with PF correction capacitors in it.
Watch out for HID lighting and some florescent lighting. It often can run with a leading PF.
Watch out for anything that generates a capacitive load.
Capacitor start motors are in some refrigerators, larger AC’s, some well pumps, air compressors, and large power tools. I think the refrigerators (capacitor start refrigeration compressor motors) I had running off my original generator is what killed the AVR on it. That is what occurred to me after doing the post mortem on everything after the meltdown. I always noticed the volt gauge jumping when the refrigerators kicked in but never though about it until it was too late.
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MrWizard
Van Nuys, Ca
The key element to this is 'IF you see the voltage going up, disconnect the load" , shut down the genny, start over and observe what is going on, above all do NOT allow the voltage to go to high, shut things down when you see votage going up under load instead of down, I consisder anything above 130 as TOO HIGH
but would be watching very carefully if I saw it going up instead of down or stable, when a low is applied