Generator Question

[Bad Wolf]

Here’s a question for an Electrician or Electrical Engineer.
After riding out hurricane Irene, we’re dealing with the power outages.
I have a big generator that runs the whole house nicely and then I have a small 900 watt two stroke to run the fridge when the big one isn’t running. I don’t need all that wattage most of the time.

Anyway the two stroke is a cheap china made unit, but it was billed as a “digital inverter†generator. Now it seems to run the fridge OK and anything else that I’ve tried to run.

But here is the mystery. I plugged a Kill-o-watt meter into it to see what it was putting out and what things draw. It showed the generator putting out 118 volts but when I tried to read the frequency it gave me a dC display. Alarmed I plugged it into the big generator and it said 60.1 Hz. When I plug it into the 700 watt camping inverter it says dC, and the pure sine wave inverter says 59.9 Hz.

What is going on? I’m only a poor Mechanical Engineer and this is beyond me.

Greg H

 

[maverick06]

might be that there is too much noise in the signal for the kill-a-watt meter to get a good reading. Obviously its putting out a sine wave, just a noisy one. Its certainly NOT an inverter if it is cheap... try putting the generator under a load and measure it then, loading the generator will change the poweroutput, sometimes improving the quality, at least "changing" the power quality

cheap inverters put out a step wave, or maybe a modified sign wave (a few steps). physical generators put out sign wave, but its usually pretty noisy, true sign inverters put out the cleanest power possible. how much all this matters, depends on what you plug into it....

A inverter generator (at least the honda and honeywell) make a power curve like this:

but a regular generator (this one was from costco)

The bottom one is good enough for a lot of things, but I would be careful with using it and electronics.

 

[Bad Wolf]

Thanks Maverick.
I defiantly would NOT use the cheapy generator for electronics. That's why I bought the Xantrex Prowatt "true sine wave inverter" http://www.xantrex.com/power-products/power-inverters/prowatt-sw.aspx because of your earlier posts. How would I know if there is a problem with the generator output? I started out using the Prowatt for the TV (its an older projection TV) DISH box, and DVD player. Later I switched them over to the big generator (it's a Troybilt 7,500 watt 11,000 watt surge) and they seem to run just fine. How would "dirty" power manifest itself?

I got the cheap generator because I didn't want to run the big one for 8 hours at a stretch. I figured I would use it for the fridge in the summer or the furnace in the winter if I needed to run overnight and didn't want to burn five gallons of gas doing it. What effect would a poor quality inverter have on the fridge or furnace?

I posted the manufacturers site in a later post. I'm just going by whats on the box. I didn't expect to get top quality unit for $75.

Thanks

Greg H

 

[Highbeam]

Good question, you hear all the time about how you should be "careful" with electronics and generator power. Well, what is that supposed to mean? You either run it or you don't. Maybe on a television you would get waves or something. Maybe the devices buzz, maybe they smoke a little.

I run a champion genset, the very common 3500 watt model. It has a very good sine wave for a portable genset. It is not a pure sinewave like a Honda inverter might put out. So I use it and everything seems to work great. I guess I'm being careful.

 

[maverick06]

I really dont know what they mean either. I do know when i hook my cheap inverter (modified sine wave) to the insert blower I have it humms and buzzes a lot. The other big concern I have is if the generator cant hold the voltage. I plugged my microwave into the honeywell I have (pure sine) and it definitely sounded like it was running slower and the light inside wasnt as bright, so i stopped. The microwave is just at the limit of the generator anyway, its a huge microwave. Likewise your concern is when something kicks on and the voltage drops as the generator comes up to load.

oversimplified: V=IR (voltage = current * resistance of appliance)

The resistance of the appliance is the same, so if the voltage drops the current goes up. The increase in current draw might go over the capabilities of the electronics and burn them out.

I think that is the genesis of the concern.

Also you have the extra abuse of the powere rapidly going up and down as the sine wave chatters.

but i am only a lowly mechanical engineer as well

 

[Bad Wolf]

Here's the company that imports them. www.giobikes.com It's the GIO-950w-Mini-Generator. I can't get on the site from work because they consider it an auction site.

Here's an outfit that carries them. Seems to be big in Canada

http://franksmotorsports.com/Generators.php The 1000w one, far left.

They claim clean power but without an Oscilloscope to check I guess I'll never know.

What do you want for $15 on E-bay? (plus $60 shipping)

I just want to know if I'm going to smoke a motor or something.

Greg H

 

[maverick06]

If thats an inverter i will buy one.

Who wants to buy a osciliscope.

donations to me and I will buy one and test whatever you want. $50 and I will pull the trigger paypal [email protected] hahaha well... seriously,

 

[Bad Wolf]

Maverick, I watched the kill-o-watt meter when the fridge kicked on and it did show 59.9 Hz for a while. After start-up it when back to reading dC. I put my ear up to the side of the fridge and it doesn't sound any different than normal i.e. no buzzing or odd noises.
I'll ask around and see if I can find someone with an O scope. Would be interesting to see.

Meanwhile I'm still out of power and alternating between the big genny twice a day and the small one overnight and in the morning until it runs out around 1:00 pm.

The novelty has worn off and its just a PTA. Kind of weird driving through the neighborhood and seeing all the houses dark. People are starting to get grouchy.

Greg H

 

[BrotherBart]

Here people are starting to get their generators stolen. Three that I know of have been stolen.

 

[maverick06]

Goodluck, we were on generator for 2 hours saturday night (running the sump pump, from the time my water alarm went off until i had the generator running we got an inch in the basement, spent hte next 4 hours fighting).

Then we were on generator for 7 hours on sunday (running fridge, chest freezer, sump pump, and a few misc items)

I am now thinking about buying a backup generator (this one is fine for me, but my wife wouldnt be able to move it or start it easily), so a backup for the backup. And another sump pump. because htis one is probably a decade old... and right now the only way to know it is dead, is when water comes in... I dont like that method.

 

[Bad Wolf]

When not running I roll mine back into the garage and lock the door. I have visions of sitting in the driveway next to the generator with a shotgun.

The little generator starts right up, but you do have to hald it down with one hand.

The big generator is electric start, and I have written standard work instructions for the wife to start it up and transfer power. (you can tell I'm an Engineer)

Greg H

 

[Badfish740]

Here people are starting to get their generators stolen. Three that I know of have been stolen.

Yet another reason why built in is the way to go. Pretty tough to steal a 14kW generator connected to propane and bolted to a concrete slab :lol:

 

[fbelec]

here is a idea for the generator that is to heavy for anyone to move around bolt it down to a piece of plywood. bolt the plywood to two 2 by 4's on the flat. when it's time to move the generator grab a two wheeler and move the generator much easier than with the wheel kits. i'm talking over grass or humps even steps, any uneven spot.

 

[begreen]

Damn, I a am really sorry to hear about generators being stolen. I have never heard of that locally in spite of being without power for a long period of time. If someone was in bad need I would lend them the genny for a few hours if they had gas. Bad news when you are stealing just for a bit of power.