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Generac Frequently asked Questions (FAQ's)


Staff member
Last Subscription Date
Folks, when asking our Resident Smart Guys, questions on Generac Gensets, PLEASE give us as COMPLETE Model Number and Serial Number as possible. Generac built, and builds, MANY different Models, Versions, and Spec'd Gensets over MANY Years. Just telling us you have a Generac Genset doesn't tell us anything that would help to solve your issues. Pictures are a good way to help identify just what you have. ALSO Please describe your problems as best you possibly can, and give our guys the most information to work with. We have folks with many YEARS of small Generator Maintenance and Repair experience on many different Brands and models, here, that volunteer their time to help the Stak's Users, so PLEASE help us, HELP You.....

Onan Dan

Last Subscription Date
This is an old thread on Generac Generators out my area where I live I see more and more folks getting Standby Generac Generators at their homes I have talked to some and they have no problems with them so hopefully they are improving to what they were . Me I talk up the old Vintage onan Generators but to each his own Far as the new modern day version of the Cummins /onan I would not want one of those either I guess I am old school ;) peace and good health to all


Hi I am Steve I just joined and I am looking for some help. I have a 1999 Generac 5500XL generator. Everything works but only getting half voltage on all outlets. 220 equals 132.20 ac volts and 110 outlet is 70.1 ac volts. and 12 volts dc is 6.50. Engine idle circuit works for rpm. Have done all the checking I can think of have tried 2 AVRs with the same results. I suspect stator windings. Any ideas? Thanks! Steve


if it is a brushless gen check the rotating diodes some may be out. check with the wires that run down the shaft disconnected.

if it is a brushed gen check that the slip rings are smooth if they are not sand them with 5000 grit sand paper till smooth & check the the brushes for resistance should be 1 to 2 ohms depending on how acerat your meter is.



A little late on the question, but that vintage had stationary diodes (rectifier) and if it goes bad you may only get half voltage to the VR. (and half output) The rectifier is about 1.5 inches square, has cooling fins on one end and 3 terminals on the other. Usually mounted inside the gen end cover on the left with a single screw. Center terminal is the input (AC from winding) and the outside ones are the output. You can check it with an ohm meter and it should flow only in one direction. The part is fairly cheap, still available from Generac, and likely from other sources. (Amazon?)

BTW, since most of these had a 12v charging plug on the panel you can do a quick check to see if there's 12v there. Same circuit.


I have 4 Generac 99A-01101S , SG015-A151.5V 18CDNLC units that I am trying to find out what they are and what they are worth used.
about 400 hours on each. Generator #A7641, Conrtol Panel#A5226, Engine#A7642, Fuel Sys#A7066. Can anyone decifer these #s and give me a clue what I have? Thank you


Birken Vogt

It is easier for us to tell what you have with some pictures of the whole unit with engine, control panel, etc. than decipher that number.


SG015-A151.5V 18CDNLC

G=Gaseous fuel (Natural gas or LP)
015=15 KW
A=120/240 single phase
A15=engine type
1.5=1.5 liter engine
18=1800 RPM
C=C Panel type control
D=Brush type generator end
N=No Enclosure
L=Shipped with loose muffler
C=emissions type (probably not much emissions controls at all)