$25 Chinese Generator

I was at a local consignment auction last Saturday and wound up buying a Yokohuma 4400/3500 watt generator for $25.  After bringing it home and cleaning the carb, draining out all the old nasty fuel, and replacing the fuel line and filter, it fired on the first pull and runs great.  When I first tried it, no electricity was being produced.  After doing some research on line, I found out that if a generator sits for an extended period of time the diodes become discharged so there is nothing to induce the magnetic field needed to produce electricity.  The website I was reading suggested plugging an electric drill into the generator, start the generator, hold the trigger open on the drill and spin the chuck backwards to excite the windings.  I tried it and it worked great, the generator now starts on the first pull and generates 240v.

I haven't had the opportunity to try it on my 30a 5Th wheel yet, but hopefully it will run the trailer ac.  For a Chinese knock off generator, I must say that this thing is quiet.  Can easily have a conversation standing right over the generator with out having to raise your voice.  We have a Honda 3500Ex generator at work that is twice as loud as this one is. 

So far I have $26.74 into this generator and seems to work great, just see how long it holds up I guess.

Oh, it is a Chinese made generator. I thought it was a machine that generated Chinese people.

>>first pull and generates 240v.
I haven't had the opportunity to try it on my 30a 5Th wheel yet,<<

Be very careful to get the voltages correctly wired to your 5th wheel or the $25 cost can go to several hundred. Your 30A 5th wheeler is a 120V system.

judway said:

>>first pull and generates 240v.
I haven't had the opportunity to try it on my 30a 5Th wheel yet,<<

Be very careful to get the voltages correctly wired to your 5th wheel or the $25 cost can go to several hundred. Your 30A 5th wheeler is a 120V system.

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I already have the adapter from the L14-30 plug on the generator to the 30a cord on my trailer.  Have ran the camper off the Honda generator I metioned in the other post. 

I found out that if a generator sits for an extended period of time the diodes become discharged so there is nothing to induce the magnetic field needed to produce electricity.

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Hmmm... must be some sort of typo here. Diodes don't "charge" or "discharge," though capacitors attached to them might.

Larry N. said:

Hmmm... must be some sort of typo here. Diodes don't "charge" or "discharge," though capacitors attached to them might.

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That is what I thought also.  I just posted it on here the way it was written on the other website.  I'm not real familiar with electronics, but what was posted on the other website did work, so I figured whoever wrote that post knew more about it than me.  Apparently not.... :-\

Irocrcr said:

That is what I thought also.  I just posted it on here the way it was written on the other website.  I'm not real familiar with electronics, but what was posted on the other website did work, so I figured whoever wrote that post knew more about it than me.  Apparently not.... :-\

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Sounds like the old "flash the field" process we used to have to do when installing automobile voltage regulators.

unless there is a center tap on the 240v output, it's not going to do you much good. you need 110 volts.

mrschwarz said:

unless there is a center tap on the 240v output, it's not going to do you much good. you need 110 volts.

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It has the 4 prong twist lock L14-30 outlet that a lot of generators have.  It also has a 120/240v selector switch and a standard 20a outlet.  With my L14-30 to 30a rv adapter plugged in, it does measure 120v hot to neutral, and hot to ground with a volt meter.

It's not the diodes, it's the generator's iron core that's lost it's charge (residual magnetism).

What you're doing is flashing the field to put some magnetism back into the core.  For an automobile generator, you do this by momentarily connecting the generator's output to 12 volts by jumpering around the voltage regulator.

You can't do this to an AC generator, because when once the core is magenetized it sends 120 VAC into the battery.

The electric drill workaround is really quite clever and is something for me to remember.  Thanks!

Lou Schneider said:

It's not the diodes, it's the generator's iron core that's lost it's charge (residual magnetism).

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Is that why they recommend to start a generator monthly?

Lou Schneider said:

The electric drill workaround is really quite clever and is something for me to remember.  Thanks!

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Yes, very good tip.  Probably any AC motor that you can plug in and spin in reverse would work.  However the drill is probably the most common motor and safer to use.

Who has an electric-plug in drill anymore? All 5 of mine are battery powered.

Chet18013 said:

Who has an electric-plug in drill anymore? All 5 of mine are battery powered.

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I think you can get one in an antique shop.

Marc L said:

Is that why they recommend to start a generator monthly?

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Same idea, different part. Slip rings (the rings the brushes ride on) in generators get dirty and oxidized if not exercised. This is not only the electrical connection for output, but also is where the field flash voltage is introduced by the the circuit board. And just like the discussions in the previous posts, the generator has to receive this flash voltage to begin producing electricity. It "excites" the field windings.

Is that why they recommend to start a generator monthly?

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Not really - the recommendation to run the generator monthly is to drive out any condensation that may accumulate in the windings while the generator sits.  Plus it keeps the bearings lubricated and the slip rings clean.

The generator itself (not just the engine) has to get up to operating temperature to drive out moisture, so you have to put it under a load and let it run for a while.

Ok, so I understand that the reason to run it periodically is to dry it out and keeping parts moving.  But does running it periodically prevent the original poster's problem?

RV generators flash the field when you start them up, just in case the residual magnetism has bled off.  So unless there's something that prevents the voltage from getting to the windings you'll never have the OP's problem.

Inexpensive generators that don't have a battery or other voltage source may on rare occasions have that problem.  But it's pretty rare - even a minute amount of magnetism remaining will let the generator self-excite once it's turning.

In other words, I wouldn't worry about it unless you're trying to revive a generator that's been sitting for quite a while.

But if you do have to use a motor to flash the field, use a drill.  A variable speed drill actually has a DC motor inside since it's easier to vary the speed on a DC motor vs. an AC motor that syncs to the line frequency.  When you spin the drill backwards it generates DC voltage to feed back into the generator.  If you spin an AC motor you'll get AC voltage, and that won't work.  The rapid polarity reversals will scramble and erase any remaining core magnetism.  That's the principle behind bulk tape erasers.