remagnetize a generator?

[spokewrench]

I read here that an emergency generator can lose its magnetism. I googled. One source said time will demagnetize, but it takes decades. You can do it quickly with an AC field, heat, or hammering.

When it comes to generators, one source said you must run an emergency generator every two weeks to maintain magnetism. Another said 15 minutes once a month. Another said running without a load, or shutting down with a load, will demagnetize a generator. That last one might make sense. If the engine slows while current flows, maybe you lose the phase relationship and it will be like demagnetizing with an AC field.

Another source mentioned three methods. Stroking the rotor with a magnet could do the trick. (I'd have to get to the rotor.) Current from a battery can get it going. (That sounds like flirting with disaster.) The third method is to plug in an AC drill and, with the dead generator running, spin the drill backwards. One youtuber said it had worked for him on two generators. A long list of commenters thanked him and verified that it had worked. It sounds dangerous, but it seems that if it works, it takes time for the generator to produce enough power to spin the drill fast.

Maybe rotors aren't made of the kind of iron that holds magnetism long, and maybe they're laminated. I wonder if heat accelerates the demagnetization. If I wanted to switch off a generator that had been pulling a big load, maybe I should let it idle a minute after switching off the load.

Any advice?

 

[RunForTheHills]

My Onan home standby generator has a maintenance cycle where it runs itself once a month for about an hour. I have an auto-transfer switch and it does run for a few minutes after switching back to city power. It will be 25 years old next year and still works. Knock on wood. I get it serviced once a year and have had the valves adjusted twice. If the generator died tomorrow, I would have gotten my money's worth out of it and it owes me nothing.

 

[Roamers]

I bought a generator for an outage used it for 2 days then put it in the garage. I needed it again 6 or 7 years later. Started 1st pull after throwing some fresh gas on the old. I now try to remember to start it once a year and run it until it's warmed up; same gas (treated with Sea Foam) in the tank for the last 5 years. Good thing I bought the cheapest Toro? They had at Lowes.

 

[RunForTheHills]

I bought a generator for an outage used it for 2 days then put it in the garage. I needed it again 6 or 7 years later. Started 1st pull after throwing some fresh gas on the old. I now try to remember to start it once a year and run it until it's warmed up; same gas (treated with Sea Foam) in the tank for the last 5 years. Good thing I bought the cheapest Toro? They had at Lowes.

6 or 7 years between power outages? I can't remember going 6 or 7 months. So Cal Edison really sucks that last few years.

 

[Roamers]

6 or 7 years between power outages?

We have a pretty good idea how long an outage will be in under an hour. I'll pull the generator out at 2+ hours

 

[indianajo]

Indiana must be paradise. My city AC power (Duke Energy) hasn't gone off more than 10 seconds except when a semi truck trailer knocked down an electric pole across from the shopping center 2 blocks away, 12 years ago. 10 hours to replace that pole.
I keep a 12 VDC light in the kitchen that will run off a car battery if a reoccurance of the outage during the flood 30 years ago happens. My kitchen stove is gas, my room heat is gas without a blower. I have a battery FM radio for weather info and entertainment if the 120 VAC is off for a week again. My basement leakage pump is 12 VDC.
If the electric bike still worked charging that would be a problem without AC power. Unfortunately the motors that will propel 160 lb me and 60 lb groceries up 12% hills out near the summer house are banned in 41 states. Nobody will sell 1300 w geared hubs anymore. Plenty of 2000 w DD racers for sale everywhere, but hill grinders are illegal. My Mac12t motor topped out at 23 mph on the flat in 26" wheel. I've burned up three 750 w geared hubs on the first trip. Mid-drives? I don't want to spend 6 hours on the seat grinding up the hills at 1 mph with the 52 tooth rear sprocket. The ebikeling & Mac12t motors would average 8 mph over 77 hills. Scandalously dangerous!

 

[PCeBiker]

One source said time will demagnetize, but it takes decades.

With my cassette deck, it was the opposite.

Time will magnetize the heads from the magnetic tapes running across them.

Then the magnetized heads will start to erase the tapes as they play.

You can do it quickly with an AC field, heat, or hammering.

I used to manually clean my cassette decks capstan and pinch roller with isopropyl alcohol, and demagnetize the heads with this manually operated demagnetizer,..

It simply used a coil and the 60 Hz 120VAC field to demagnetize the heads.

The instructions said to touch the probe directly to the heads, then Very Slowly lift the probe away from the heads.

If you removed the probe too quickly, it might leave a positive or negative pulse behind, and leave the head with a North or South magnetic charge.

You can do it quickly with an AC field, heat, or hammering.

We learned in physics class, that you can take an iron rod, aim it directly North then aim it down with the angle of inclination of your latitude, then hit it with a a bunch of times, and the earths magnetic field will magnetize the iron rod.

 

[sc00ter]

I always found it weird that one old Vespa, when pulled out of a barn or shed, had a weak coil and another that sat just as long of the same vintage was fine. It made no sense. We've messed with Honda Monkey bikes that sat since the late 70's and they'd fire right up with two or three kicks! I think there is a quality factor involved in the magnets but I'm not tech savvy enough to understand the details. I'll try to pull the Honda generator out one day and see if I can get it running. I'll post my findings. Costco had Generac hanging out with some good offers, along with Zevo bug control demos, that got our attention. The Zevo guy did a great old school carnival barker pitch!

The co-worker who mentioned the flywheel magnets was a old SEARS service tech in the 80's. I found it funny because I watched him get his butt kicked with some of the simplest problems at work. Then again I forget things after awhile as well so I can't really pick on him. I need to pick up a old 2-stroke to stay fresh with working on them, but ebikes are just easier! Plus I feel learning batteries and emotors will serve me better.

 

[6zfshdb]

I read here that an emergency generator can lose its magnetism. I googled. One source said time will demagnetize, but it takes decades. You can do it quickly with an AC field, heat, or hammering.

When it comes to generators, one source said you must run an emergency generator every two weeks to maintain magnetism. Another said 15 minutes once a month. Another said running without a load, or shutting down with a load, will demagnetize a generator. That last one might make sense. If the engine slows while current flows, maybe you lose the phase relationship and it will be like demagnetizing with an AC field.

Another source mentioned three methods. Stroking the rotor with a magnet could do the trick. (I'd have to get to the rotor.) Current from a battery can get it going. (That sounds like flirting with disaster.) The third method is to plug in an AC drill and, with the dead generator running, spin the drill backwards. One youtuber said it had worked for him on two generators. A long list of commenters thanked him and verified that it had worked. It sounds dangerous, but it seems that if it works, it takes time for the generator to produce enough power to spin the drill fast.

Maybe rotors aren't made of the kind of iron that holds magnetism long, and maybe they're laminated. I wonder if heat accelerates the demagnetization. If I wanted to switch off a generator that had been pulling a big load, maybe I should let it idle a minute after switching off the load.

Any advice?

This can be an issue for older generators that see long periods of disuse. Sometimes "flashing" is necessary to restore magnetism using the methods you describe.
Newer models are less prone to this, but it is always a good idea to follow the manufacturers recommendations.

I inherited a 45 year-old Honda generator from my father that hadn't been used for 10 years. Started on the second pull and it ran fine.
When you need a generator, you really want it to work. I don't take chances and do test runs on mine every couple of months.

 

[spokewrench]

In February I bought an EMF meter. It may show an electric field near an appliance that's plugged in or on a street with 9,000 volt power lines, but I haven't seen magnetic fields except near the motor of a running fan. Maybe storage in motor fields accounts for some cases of demagnetization.

 

[spokewrench]

With my cassette deck, it was the opposite.

Time will magnetize the heads from the magnetic tapes running across them.

Then the magnetized heads will start to erase the tapes as they play.



I used to manually clean my cassette decks capstan and pinch roller with isopropyl alcohol, and demagnetize the heads with this manually operated demagnetizer,..



It simply used a coil and the 60 Hz 120VAC field to demagnetize the heads.

The instructions said to touch the probe directly to the heads, then Very Slowly lift the probe away from the heads.

In my 20s I went to Alaska for several months. Traveling by motorcycle, I didn't take my cassette player, collection of 30 or 40 cassettes, or head demagnetizer. One tape was Nick Gravenites' "My Labors." When I got back, there wasn't much on it but hiss. The other cassettes in the box were fine. I think my nasty older sister went through my tapes, didn't like that one, and demagnetized it.

 

[RunForTheHills]

A direct drive bicycle motor can be used as a generator. That's how regen braking works. We don't spend much time worrying about our motors demagnetizing, but overheating your motor can demagnetize it.

https://www.emworks.com/blog/demagn...sm-rotors-understanding-and-mitigating-faults