Generac 3500XL Field Flashing

[rfwilli]

I am new to this board and have found very good information here as I try to trouble shoot my Generac 3500XL. After "cleaning" my old crusty Generac MG set, I no longer have any electrical output. The engine runs very well and the electrical output was perfect up until now. I followed the instructions for flashing the field and this is what I found:

With a 12 volt battery attached to the brush leads, the 120V circuit puts out 95 Vac while the generator is running. Disconnecting the 12V battery produces 8.15 Vac. The idle control circuit functions normally when the 12V DC is supplied to the brush leads, but does not function at all otherwise.

Before I disassemble the generator to inspect the windings, I thought I would ask this forum if it is more likely a problem with the Power Regulator Board or System Control Board? There is also a part called a Battery Charge Rectifier.

Any help is deeply appreciated...

[EricWood]

Do you have the owners manual for this? I can send you a copy, if not.

When you were flashing, did you have + on the brush closest to the bearing, where a white (#4) wire comes in? Also, did you isolate these field leads coming to the brushes from the regulator during extended battery operation?

Flashing should always be done with a pair of diodes on your battery leads, if the voltage regulator is still in-circuit.

Not to be a wise guy, but how did you clean it? When faced with this kind of situation, the rule of "it worked before I fixed it" applies. Did you use compressed air in the controls? Have you looked closely for any loose/disconnected wires? Trace back through exactly how you cleaned it up and see if you can find anything.

Outwardly, I would say yes, sounds like your voltage reg. is shot. Ohm the DPE windings, wires #6 and #2 to the voltage regulator, should have a fairly low resistance value to it. You could also momentarily flash while running again, and see if you are getting voltage in on the DPE wires.

eric

[rfwilli]

Thanks for responding...
Yes I have the owners manual and have been looking at the schematics. When I was flashing, I had positive to the white lead but I did not isolate the regulator nor do I have a pair of diodes on my battery leads.

I will ohm the DPE windings. Below I included a post with what might be a similar unit. It has the same 84132 regulator module as my unit. The DPE should read about 1.56-1.91 unless a 7500 watt gen is much different than a 3500 watt. The field winding of these units could be the same right?

from a post on http://sci.tech-archive.net/Archive/.../msg00291.html I got the following info:

Some 7500 Watt Generac models had winding resistances in Ohms as
follows, per the Clymer volume 2 manual:

Rotor 7.6-9.1
Main AC Power .20-.25/.20-.25
Excitation(Dpe) 1.56-1.91
DC Battery Charger Winding .05-.09/.06-.11

The Excitation (Dpe) winding supplies AC voltage to the 84132 module,
which rectifies it and supplies current to the field via the brushes.


As far as my "cleaning" job, I was not too delicate. My MG set has been used in a horse stable for the past few years and has been running great for this purpose but the huge amount of caked on dust was concerning me so here I am. I did not use compressed air but shop towels to remove the caked on grime, trying to keep it from entering any of the vents on the generator. I did use a degreaser on the engine and hosed it off. I couldn't detect any sign of water entering the control panel or the generator in case of a splash as the light dust inside was not disturbed. Maybe soaking the oil pressure leads or low oil leads could have effected something on the system control board?

I will do a quick reflash on the #2 (blue) and #6 (red) DPE leads and see what the voltage is. Do I need to isolate the regulator by disconnecting the #1 (blk) and #4 (white) leads and just supply the 12 V to the brushes?

Thanks in advance

[EricWood]

Yes,

Isolate the excitor output leads at the regulator, and apply your battery power there. Measure the DPE for an AC output....I don't know exactly what value.

Your DPE should ohm out similar to the values you posted.

Also, I know its not on the schematics, but the larger Generacs (5kw and up) that used DPE excitation had thermal protection in-series. Make sure there isn't one of the little one-time use thermal protectors, life coffee makers have, or something similar hiding in there somewhere.

Let us know what you get.

eric

[K D Redd]

The 20 KW Generac I worked on Last summer had one of those fuses in the DPE winding. It also had a third wire connected behind the fuse so if the fuse blew you could gen the generter producing power again BUT without ANY overload protection.

Kent

[rfwilli]

OK. I disconnected the white and black leads at the brushes and measured 3.0 ohms between the blue and red dpe leads (which are both black)

I then attached a 12v supply to the brushes, with correct polarity, started the generator and measured 96 volts AC from one of the 120V AC outlets and 128 volts AC measured on the dpe leads.

Summary of the results:
128 AC volts measured on the DPE leads with 12V supplied to brushes, engine running.
3.0 ohms measured on the DPE leads with no 12V to brushes, engine stopped.
50 ohms measured at the brush leads, through the field and brushes, engine stopped.
2 Volts AC measured at an AC outlet with no 12V to brushes, engine running.

I hope this is enough info to determine if the regulator is bad or if it's one of the windings. Let me know if more measurements are needed.

Thanks, --Bob--

[rfwilli]

I don't think I have a fused circuit. My generator is 3500 watts and the wiring diagram and schematic shows circuit breakers etc for the control panel assembly and no fuses in the dpe circuit.

For what it's worth my generator is a Generac model 9441-5 and here is a link to the owners manual with the schematics.

Thanks for your help.

--Bob--

[rfwilli]

Hmmm... Here is the link!

http://www.generac-portables.com/doc...1_5EN4W_LO.pdf

Sorry...

[EricWood]

Bob,

50 ohms sounds way off the mark. Try measuring directly at the slip rings. Also, measure between the slip rings and the rotor shaft (should be nothing,there.)

Do you get the same result if you turn the idle control switch off (defeat auto-idle)?

You may need to dig deeper into the rotor, and look for a burnt/broke winding.

eric

[rfwilli]

Thanks for all of your help on this Eric. I removed the brushes (which looked clean and OK) and measure 12.8 Ohms through the field. There was nothing there when I measured the resistance between the slip rings and the shaft.

Is 12.8 Ohms more reasonable for the field?

--Bob--

[EricWood]

Bob,

12 ohms don't sound too far off. The specs you had in an earlier post shows 9.1, but its not the exact same model, either.

Given that you had said the auto-idle circuit seems to work when applying battery power, (presuming its idling down once it saw voltage, and no load) I would try sourcing the regulator and replacing it. Only other thing I can see are the snubber feed back and shield gate signal, and after doing some searching, I cannot find any info on their exact purpose. I don't know if they send a signal to the regulator to back off excitation when there is no load, and the engine is idling down. I don't know if flashing again, and monitoring these two wires with your voltmeter would show any kind of status change when voltage goes up, then changes again when the engine idles back or not.

Try sourcing a regulator to see how much it cost, and make your decision from there.

eric

[rfwilli]

Thanks again for your help on this. I am going to check the resistance through the brushes and field one more time to make sure I don't see a high resistance again. Do you think denatured alcohol is good for cleaning brushes and slip rings?

--Bob--

[rfwilli]

After checking on-line for info on cleaning slip rings and brushes, I found the following document which seams to have a wealth of info on trouble shooting Generac MG sets:

http://www.scribd.com/doc/3682862/Ge...Service-Manual

400 grit or finer non-metallic wet-dry sandpaper seems to be the recommended cleaning material for the slip rings and brushes.

I hope this helps anyone else trying to trouble-shoot their Generac portable generators...

--Bob--

[rfwilli]

After retesting the resistance of the field through the brushes, I am getting 13 to 14 ohms which seems normal.

When running the generator, with the leads disconnected from the brushes, and no 12V power connected to the brushes I measure 12VDC on the white and black wires from the voltage regulator.

Repeating this measurement WITH 12V battery connected to the brushes results in 240VDC, 130VAC on the white and black wires from the voltage regulator.

--Bob--

[EricWood]

Are you sure on the 240 DC? Where is that measured? Are you getting 240AC out of the machine, and 130DC to the excitor? Or did you make both (AC and DC) measurements on the same wires?

Since the regulator is measuring 12 VDC on the excitor leads, open circuit, try connecting it to the brushes and take a reading. There could be a voltage signal there, but no power behind it if an SCR driver is bad inside the regulator, and connecting it to the rotor will suck it down pretty close to zero. Plug an electric drill into one of the outlets and try running it to see what it will do. Leave the idle control switch off.

If nothing has shown up by now; ie-wiring, bad ohm values, etc..., might want to replace the regulator and see what you get.

eric

[Fred M.]

Bob-

My Sears generator is nearly identical to the older Generac 3500XL. When I checked on trying a new System Control Board, I was shocked at the price! Fortunately mine turned out to be OK.

The System Control Board apparently controls the Power Regulator Board (the 84132) which controls current to the field. Check the connector on the 84132, to see if your cleaning might have loosened it.

The System Control Board is located inside the AC Power connector housing, on the left side as you face the connectors. There is a rubber plug on the left side of the housing, that covers a small trim-pot on the System Control Board. This trim-pot is used to adjust voltage. Could it have been disturbed by your cleaning?

I don't think anyone mentioned engine speed. It should be 3600 RPM for 60 Hz. Mine is adjusted for 62 Hz no-load, with the voltage set to 126 VAC. When the idle control is operating on mine, frequency is around 40 Hz and voltage is around 90 VAC.

Fred

[rfwilli]

I am finally back from a two week trip so I can finish trouble shooting my generator. I am going to check the system control board connectors and recheck the voltages. I can't get to it for a few days but I appreciate your comments on checking the control board. Also, thanks to Eric for helping me diagnose voltage issues. It could be the regulator after all. A few more measurements might prove this. At least the regulator is less than $100. I checked inside the control panel and couldn't see any indication that water entered there. Maybe water on an external connector could have caused trouble with the system board or voltage regulator. Who knows...
Thanks, --Bob--