Your last generator Maintenance Run

[LouNY]

I've been watching YT gen repair videos and have a couple questions.
When you take off the end cap of the electric end, there is usually a large capacitor in there.
First, what does it do (help in startup?) and does it fail often enough that we ought to have a spare.
Like i do for my hvac compressor.
GRS, lots of capacitors get changed out in electrical equipment due to age, what about gens?
Did many break?

if someone could explain what flashing means in getting an electrical end to start producing voltage?
I saw one guy use an electric drill, then a heater, something about adding load. ??

I figure if I learn what breaks these gens, might help in prevention. Condon is excellent

Why do generators need to be flashed?


Residual magnetism in the generator exciter field allows the generator to build up voltage during start-up. This magnetism is sometimes lost due to shelf time or improper operation, among other reasons. Restoring this residual magnetism is possible and is sometimes referred to as "flashing the exciter field".

 

[daugen]

Thanks Lou. Seems to need a draw to expedite that.

 

[3930dave]

All preparations, testing and maintenance done on gas and PTO generators. Once in 30 year snow and ice storm last week, not even a flicker. Last time lost power for 8 days.

Well prepared

8 days will definitely get your attention !

Rgds, D.

 

[90cummins]

While we’re on this topic I need to ask why my nephews generator which ran flawlessly for 5 days failed to produce power on the next exercise cycle a couple days later.
It needed to be flashed then was fine
90cummins

 

[kirkawilson]

Residual magnetism can be lost naturally from not being used or from the load on your generator being connected when the generator is shut off. It can also happen from running a generator with no load for too long.

 

[90cummins]

I’d still like to know how/why that actually happens but knowing that (can) it would be a good idea for me & fellow gen heads to look at our generators to find out where and how to flash it if it does happen.
Poking around under pressure could dire consequences
90cummins

 

[grsthegreat]

Permanent standby generators produce a flashing current when they start up. Portable units do not, and usually don’t need them.

sometimes you can simply place a drill motor on a portable that is not producing power and manually turn drill head while pulling trigger switch on drill. This sometimes makes gen produce power.
very rarely have I replaced a capacitor on a generator, but mainly because only brushless generators use capacitor’s and I bet 99% of the units i work on have brushes.

 

[grsthegreat]

Heres a youtube video showing how to flash a gen

 

[Patrick Herd]

I've been watching YT gen repair videos and have a couple questions.
When you take off the end cap of the electric end, there is usually a large capacitor in there.
First, what does it do (help in startup?) and does it fail often enough that we ought to have a spare.
Like i do for my hvac compressor.
GRS, lots of capacitors get changed out in electrical equipment due to age, what about gens?
Did many break?

if someone could explain what flashing means in getting an electrical end to start producing voltage?
I saw one guy use an electric drill, then a heater, something about adding load. ??

I figure if I learn what breaks these gens, might help in prevention. Condon is excellent

So the cheaper generators (at least in my experience) run essentially an induction motor style alternator. The capacitor supplies the leading reactive power (the VArs) which magnetises the stator allowing the rotor to be magnetised.
In this case the voltage regulation is (entirely?) achieved by making the rotor saturate. If you put a scope on such a generator then the output is is going to look more like a square wave at light loads. This is due to the rotor acting non linearly funky at high magnetic flux.

Definitely worth having a spare if you're in a critical need situation: My ~5kW diesel generator had a capacitor decide to start wearing its insides on the outside.

 

[3930dave]

Very interesting discussion on magnetism.

When I got my first little Briggs portable in '98 (still have), I noted the Recommendation for 2 minutes of running with loads Unplugged, before shutdown. Mainly considered that wrt. Thermal, but it may have been in part a reminder to unplug the loads.....

Yep, turned in my Man-Card long ago, as I read manuals

Rgds, D.