Posted: 11/2/2012 9:18:03 AM EDT
|
I've been scratching my head on this one. Couple of months ago I was testing my generator out with some household vacuum cleaners and my killawatt meter and was overloading my 3500/4000 watt generator at around 2800 watts. I put it aside for a while and came back to it today.
Today I used two hair dryers and metered them. Each one pulls in around 1680 watts each per the "killawatt" meter with 121 volts and 60hz. If I hook both of them together, theoretically, it should be 3360 watts, but the killawatt meter only shows about 2300 watts going out, with 57hz and 119 volts. Is my meter wrong? Or is there some scientific affect that I'm not taking into account? I'm using a 30 amp RV plug routed into a 3 way plug with about 3ft of cord, am I losing voltage across the plug? |
|
Inrush or surge current is higher. That is why you should not run your gen at capacity. Startup of devices will kill it. To accurately measure inrush current, you need a oscilloscope and a current probe. Power factor correction is another thing you may want to consider. |
|
Quoted:
Inrush or surge current is higher. That is why you should not run your gen at capacity. Startup of devices will kill it. To accurately measure inrush current, you need a oscilloscope and a current probe. Power factor correction is another thing you may want to consider. +1. A clamp on ammeter may give you a general idea, but not as accurate as the above. |
|
Quoted:
If it was surge voltage, it would be higher at first, the wattage listed was continously measured over 30 seconds or more. Kill-A-Watt only measures average. Not peak. My generator is a 4kw. When running, my water pump uses less than that, so it should run. But it won't. I hooked up an ammeter, and discovered that on startup, it can be double or triple the running wattage. It's less than a second, so the Kill-A-Watt won't catch it. Moot point, as that's not what you are encountering. Most Kill-a-watt devices are rated at 15 amps. At 120V, that is 1800 watts. If you were plugging two hair dryers into the Kill-A-Watt, you were overloading it. 
|
|
Quoted:
I'm using a 30 amp RV plug routed into a 3 way plug with about 3ft of cord, am I losing voltage across the plug? Could be. Make sure you plug in the Kill-A-Watt at the end of your cord, right before the load. That way, you'll measure the voltage actually being delivered to the load. The amount of power that most resistive loads (like hair dryers) draw drops off pretty quickly when the supply voltage drops - So, it's possible that your cord and plugs are introducing enough additional voltage drop to greatly reduce the amount of power being drawn by your hair dryers. Slightly OT, but electric space heaters make excellent test loads for generators. |