Measuring Watts on 24HP Electric Generator

[dlgoff]

The electricity supply to your house will be fused to limit the power supplied to your house (maybe 20kW), That doesn't mean that you are using (or paying for) 20kW all the time.

I like this. Simple and elegant.

 

[256bits]

I didn't realize people ever rated electrical outputs in horsepower -- I thought that was used solely for mechanical outputs, i.e. motors.

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The power company transformer on the power pole used to be, and maybe still is, rated in HP. A typical step down transformer for a 60A 120v fuse box in a dwelling would have been 10HP.

 

[Jimmy Snyder]

The ad for the Kill A Watt says you can use it to measure the efficiency of household appliances. Perhaps it was my own fault, I took that to mean that the Kill A Watt was not what I needed. I no longer think that.

Here is how I understand it:
1. Plug the Kill A Watt into the output of the generator.
2. Plug the male end of an extension cord with 3 female receptacles into the Kill A Watt.
3. Plug a lamp with a 100 W bulb into one of the female receptacles.
4. Turn on the lamp, the generator, and the driver of the generator input shaft.
5. Read off the watts from the Kill A Watt. If the value is less than 100 W, then that is what the generator is putting out and the amount of power coming into the generator is some multiple of that, presumably greater than 18/13.
6. If the value is just 100 W, then plug a second lamp with a 100 W bulb into the extension cord, turn it on, and remeasure. If less than 200 W, then finished, otherwise, try a third lamp. I seriously doubt that there is 300 W going into the generator, let alone coming out of it, so 3 should suffice. But if not, I can buy a second extension cord and plug it into one of the receptacles of the other cord and so test up to 5 lamps & etc.

The reason for all these questions is that I have an inventor friend who has a gizmo that drives the input shaft of the generator. I saw the generator itself today and turned the input shaft with my hand. It requires a lot of force to get it started turning, and impossible to keep it turning for more than a second or two and the rpms were about 20 or 30 at best. In order to run it at capacity it requires something like 3000 rpm, but he has a transmission attachment that allows him to run the transmission's drive shaft at 500 rpm and the transmission converts it to 3000 rpm at the generator's drive shaft. Since I was turning the transmission shaft, the speed provided was roughly 1/20th of what was needed. I asked him if he had a crank so I could spin it faster, but he did not. There was no load on the output. His invention that delivers power to the input shaft was not set up. He told me that he intended to have it set up 'real soon now' and when he does, I can see his gizmo in action. He said that he is going to make a more expensive version ($2000) of his invention and I suggested the $35 Kill A Watt to him so that he could measure the output of the generator with his contraption in place before sinking that much money into it. He said that he would and that I could see that running too.

I think he has an unrealistic view of how much power his 'invention' is able to provide to the drive shaft. He thinks it will deliver 5 kW. My suggestion to him was that 750 W (~1HP) at the output was a good cutoff point. In other words, if the Kill A Watt measures 750 W coming out of the generator, then he could sink the extra $2000 into an improved version, but if less, then he should work on design improvements rather than construction improvements. The 750 W figure was arrived at by considering a different way of getting electrical current that was cheaper than his method and could provide roughly 1500 W. He knows that he must reach the 1500 W mark and surpass it and that if he can't even get 750 W then it was unlikely his invention would work no matter how it was tweaked. I didn't tell him so, but in my opinion, he won't give 300 W to the input of the generator and that the output of course will be even less.

I actually watched his setup running an air conditioner a few years ago. However, in addition to the generator, he also had a UPS attached so I couldn't tell how much he was getting from the generator and how much from the UPS, and I had no clue how many watts were being consumed.

 

[Averagesupernova]

I'm not clear on exactly what you are saying. The link you provided specs the input shaft requires 540 RPM to get 60 Hertz out of the generator. Most likely the actual generator spins at 3600 RPM geared up with a ratio of 6 2/3 from the PTO shaft RPM of 540. So what is it that your friend is trying to do? If a generator specs an output of X watts, the required mechanical power so spin that genator will need to be X + inefficiencies no matter what. This is starting to smell like a free energy scheme, which of course will not work.

 

[berkeman]

It sounds like the friend just has some type of motor, and wants to measure the output power of the motor. Using a generator with a measured load is a reasonable way to do that. (As long as the electrical output is not being fed back somehow to the "motor", in which case I agress with ASN that the friend may have some free energy goal in mind...)