3800W 120/240V Homelite Textron generator goes full throttle till overload trips

Warwagon

Member
It's just that I have owned and used it hard for 25 years so it's special to me. It's also 30 years old being a 1989 model per the S/N best I can tell. I repaired it from a scrap pile in 1994 as it was badly damaged (crushed) by yellow iron on a construction site. It had served us well ever since. The engine went through the back of the control/plug board and broke a wire thus the two red wire nuts and new wire you see as a old repair in the pics.


This winter it snowed on us hard, rare for the Phoenix dessert heat area I live in. The fan grate on my heat pump froze up so I figured to burn some older gas and power a hair dryer to melt the ice off the grille. Burning through gas to keep it fresh is a thing for equipment you need in an emergency.


30 weight oil is not correct for 32 degrees on the starter rope. I got about 60 seconds of power on the hair dryer before the genset went full throttle and shortly tripped the field overload breaker. (Was still making AC power.) Unplugged everything and reset the breaker - instant full load and trips the thermal breaker again after a delay. Then back to full speed no load with thermal breaker tripped. Something is shorted somewhere?

I have checked everything I can with a voltmeter. Separated the windings from the control board - no shorts to ground. Don't have the tools to get a good resistance check other than voltmeter. No shorts on the plugs that the voltmeter can see.

What else can I do to test? Visually it doesn't look good in the generator.

Attached Electric Schematic SC 00065 Homelite PN 49570

Homelite Textron 176R142-A
UT: 03631A
3800W 120/240V
 

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Warwagon

Member
Just a couple more pictures of the gen end windings if it will help.

Fan was off center: maybe a factory defect. It's cracked in 4 places and was rubbing the end cover and a support.
 

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Andrew Mackey

Moderator
With SAE 30, was the engine at ambient (outside) temp when it was started? If so. the engine probably starved for lubrication and the governor has probably eaten its teeth. SAE 30 does not splash well when it is that cold! :eek: I believe it (the governor) is plastic in that engine. You probably can get parts from Wisconson. The engine is a Wisconson Robin engine. Personally, I do not think it's a generator problem, rather an internal engine problem, due to the heavy oil. You probably are lucky the engine didn't throw a rod!
 

Warwagon

Member
With SAE 30, was the engine at ambient (outside) temp when it was started? If so. the engine probably starved for lubrication and the governor has probably eaten its teeth. SAE 30 does not splash well when it is that cold! :eek: I believe it (the governor) is plastic in that engine. You probably can get parts from Wisconson. The engine is a Wisconson Robin engine. Personally, I do not think it's a generator problem, rather an internal engine problem, due to the heavy oil. You probably are lucky the engine didn't throw a rod!
Thanks for the reply.

We usually don't get that cold here, ever, and I will be ready next time in reference to engine oil grade. I changed the oil to a winter grade in other equipment after this event. Normally we get the extreme other end of the heat scale ruining engine oil. (I have some trouble with oil samples due to oil overheating now and then and have to take corrective action.) It's 81F out today after not even a full month ago: snowing in February.

I may not have clearly said above: the engine governor is still working properly. It's not running away. Rather it's seeing a load when the generator field breaker isn't tripped.

When I reset the generator overload breaker the engine goes near wide open to maintain RPM and returns to normal throttle and RPM after the field thermal breaker trips.

Older Homelite service manual that I could find calls for a no-load 3750 RPM and to hold 3600 RPM under full-load.

The Loadamatic idle control never worked. I only recently found a manual online that described how it should work. It had some magnetic field on the electromagnet, but, never pulled the engine speed down to 2400-2600 RPM like it should. I wasn't getting any magnetic field when I looked at it last fall. Just wanted to see it work once. But didn't have time to open it up and look at it then.
 

Joe Romas

Subscriber
For some quick troubleshooting I would first mark then remove the wires from the voltage select switch and meter it.
 

Thaumaturge

In Memory Of
I would concur on this being a govenor problem. Most smaller gens have NO feedback mechanisms between voltage output and engine RPM. Rather most all of them rely on mechanical govenor to control engine RPM. Exceptions being Inverterter type generators, which typically use a stepper motor throttle control.
Doc
 

Vanman

Subscriber
To me, if the engine goes from no load to heavy load when the field breaker is closed, and then the field breaker trips, it is a generator problem. In this instance, the governor is just doing what it's supposed to.

Either the regulator has failed and is going "full field", or something is shorted somewhere, causing the generator to be overloaded. Either condition would produce the observed results.

The first one will result in high output voltage. The second one will result in low output voltage. My money is on the AVR (first problem).

I'd put a meter across both lines (240 volt output), start it up, and record the reading you get when the field breaker is closed. This will tell you how to proceed.

Keith
 
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Warwagon

Member
Thanks for the ideas. I have tested the items I can including the bridge rectifier in the generator end bell.

Not looked at the AVR board as it is either working or going full field as suggested. The 250V cap on it deserves respect as it looks to have a 120v 4 turn winding for the AVR and idle control system on it.

I will isolate the idle control board in case it's the source of a short.

So I will put it back together and see what the voltages are this weekend. I will also check the engine RPM with an optical tach just to be sure.

Thanks for the suggestion for the 240V mode getting the best result. Looks like 120v only mode ties the two windings together by reversing one of them in the select switch in reference to ground etc.
 

Warwagon

Member
I don't have a year specific service manual. However the one I could find calls for: no-load 3750 RPM and to hold 3600 RPM under full-load. Linked below.

I measured 164-166VAC, identical, on each 120V winding. So 164/164 to 166/166. Looks like the regulator is full field till the thermal overload device trips off.

RPM via optical hand held tach:
No Load: 3920 RPM
Breaker in: 3620 RPM

Yes, running a little fast unloaded. Has throttle left so governor is still working.


https://www.yumpu.com/en/document/read/15323949/homelite-repair-manual-5th-editionpdf-parkinlube/113
 

Warwagon

Member
I can't find a fan available anywhere.
P/N: A53769 FAN NLA

P/N: A48999B VOLTAGE REGULATOR NLA

The Voltage regulator is available on eBay as a aftermarket part. But asking ($154.75 shipped) is more than this set is worth.

Fort Rock Improved Voltage Regulator
eBay item number:
181418183370

I can't imagine something that lasted 30 years is "unreliable" as the eBay listing goes on about. They appear to be selling very well so what do I know...

The part numbers are on everything on the VR including the big NPN power transistor: MJ16010 Motorola NPN Transistor.

Anything that commonly burns up on the VR's?
 

Vanman

Subscriber
His post #11 confirmed what I suspected and suggested all along. Faulty regulator stuck at full excitation. That modestly fast governor setting would not cause the observed results. I wonder if this would be a suitable application of the handily cheap SX-460 that everyone talks about?

Keith
 

Warwagon

Member
How risky is it to run with the cracks in the fan?
Sigh... OMB fan... "In Stock At Distributor: No"

No Load: 3920 RPM is 65.3 HZ
Thermal Breaker in: 3620 RPM is 60.3 HZ

I took a close look at the VR today. Not even coated so repair is as easy as it gets.

Couple things stand out:
MJ16010 Motorola NPN TO3 Transistor.
LM358N Low Power Dual Operational Amplifier. Got to be a similar design to the Generac reverse engineered VR around here.

The heavy lifting is done by the TO3 package NPN as in field brush to ground. Good place to start as any. Sure enough it's shorted out. C-E measures 18 Ohms both ways: The Transistor is toast! I removed it just to be 100% sure on measurements. Other transistors up the control path (on the base pin) of the TO3 appear ok. (That would be the two big ones held down by the white stuff.)

So spent an hour looking up spec sheets... Nothing in my TO3 junk box is rated to take the punishment of 20A and the extreme 450V the MJ16010 can. A higher rated MJ16010A appears to be more available today. My junk box does have a heat sink to "improve" the design. :D

So the repair looks like it can be done for $20 for a transistor off of eBay (pair for sale for this amount, maybe they sell just one?) or $20 for a SX-460...
 

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Vanman

Subscriber
That's pretty cool! While I'm not normally much of a fan of electronics, I do appreciate the nice, old designs that can still be serviced by those that know how. Nice!
 

Warwagon

Member
I took another look at this board to confirm an answer I got in the SX-460 thread.

It has patent number on it.

https://patents.google.com/patent/US4697135A/en

The patent has a description of how it actually works in extreme detail.

I found the following info from it very interesting:

Commercial generators produced utilizing a power transformer to regulate the output voltage typically have regulated output voltage to about ±4%, and motor starting ability is about 0.35 hp/kw. These values are less than desired.

... electronic voltage regulator ... it is possible to regulate the output voltage of the generator so that it is about ±0.8%, and to provide a motor starting ability of about 0.75 hp/kw.
 

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Kevin K

Subscriber
If you can find some time, it would be interesting to compare the circuit diagram in the patent to the actual circuit board, and add some component values.
 

Warwagon

Member
IT'S ALIVE! :D

I found severe "rust" on the wire connectors going to the thermal overload breaker. I suspect this didn't help.

I cleaned the rust up and replaced the big power transistor. Also added overkill of a heatsink I had around. Some insulation between the heatsink and MOV surge to make sure it doesn't get any ideas of shorting to the heatsink.

Fired up and got 121v on each leg. Ran a 1500W heater for 45 min and voltage still checked out.
 

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