35kw generac 8479-0 voltage problems

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New Member
New Member
Posts: 1
Joined: Mon Nov 21, 2022 2:49 pm

I have a problem with my generac PTO generator, model 8479-0 35kw
(Not sure of year made)
Used last year and no issues.
This year tried to use it and the output voltage is cycling.
Bringing PTO up to needed rpm and the generator will swing up and down from around 20 volts to 240 and back again.
Cycling up and down occurs within 1-2 seconds.
It is not a gauge problem, have confirmed with electric meter and incandescent light.

Have tried adding load to the unit, no difference.
Any help would be appreciated.
Thank you.
Generator Jedi Master
Generator Jedi Master
Posts: 3611
Joined: Mon Apr 20, 2020 5:59 pm

i honestly didnt even know Generac offered a PTO generator. i tried to look up the model number on Genserv, but i get no hits. i cant find any info on a diagnostic manual for this unit. i have to assume theres a voltage regulator in the electronics that is failing.
Birken Vogt
Generator Jedi Master
Generator Jedi Master
Posts: 1036
Joined: Sun Nov 11, 2018 12:02 am

I think in ages past, PTO and such was about all they made. They claim to have been in business since like 1959 but I have not seen anything like a normal standby genset older than about the mid 1980s.
Site Admin
Site Admin
Posts: 7002
Joined: Sat Aug 04, 2018 8:46 pm
Location: Clawson, MI

It could be that the DPE breaker is opening and shutting down the regulator, however 1-2 seconds is much faster than I would expect for an issue like this... Generac used a special voltage regulator for the PTO stuff, but I'm not sure what exactly is different about it...

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