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Hot generator

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Theurkauf
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Hot generator

Post by Theurkauf » Thu Jul 09, 2015 5:52 pm

I recently installed a rebuilt 6V generator on my model B engine. It's been working fine, but gets VERY hot. After a longish run, you can touch it, but not for long. It's much hotter than the cylinder head, for example I must admit that I never really checked the temp on my old generator. Is this norma, or an indication of a problem with the rebuild?

Thanks,
Bill

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evansjw44
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Re: Hot generator

Post by evansjw44 » Mon Jul 13, 2015 8:43 am

What does your ammeter read. For prolonged running I would think it should stay under 10 amps. I assume your is a "third brush" and has a cut-out, not a regulator. You might want to measure its temp with an infrared thermometer.
Jim Evans

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Re: Hot generator

Post by Theurkauf » Mon Jul 13, 2015 5:39 pm

The generator runs between 8 and 9 amps. Cuts in/out as expected. As I said, it seems to be functioning fine, just seems a on the hot side. I don't have an IR thermometer. If I can track one down, what would be normal vs hot??? Since it's working, perhaps best to just keep an eye on it and go boating...

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evansjw44
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Re: Hot generator

Post by evansjw44 » Mon Jul 13, 2015 7:48 pm

I agree. Let's go boating. Time enough to worry.
Jim Evans

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Jim Godlewski
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Re: Hot generator

Post by Jim Godlewski » Sun Jul 19, 2015 7:11 am

Just last week my generator just about went up in flames. Do not let it go, get it checked out. My cutout switch shorted out while the boat was at the dock after a 27 mile run (maybe during, I don't know) When I lifted the cover to sniff prior to start I got a face full of smoke and nasty electrical smell. The generator was so hot I could not imagine.
That was not a nice experience. Get her fixed.....
1956 17 Sportsman CC-17-2310
1930 Model 100 7152

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Jim Godlewski
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Re: Hot generator

Post by Jim Godlewski » Sun Jul 19, 2015 8:25 am

Jim Godlewski wrote:Just last week my generator just about went up in flames. Do not let it go, get it checked out. My cutout switch shorted out while the boat was at the dock after a 27 mile run (maybe during, I don't know) When I lifted the cover to sniff prior to start I got a face full of smoke and nasty electrical smell. The generator was so hot I could not imagine.
That was not a nice experience. Get her fixed.....
On an additional note, I did notice the amp gauge was way to the high side while under power and back to normal at idle. I should have took heed to the gauge telling me something was not right and could have diverted the scramble to the fire extinguisher. Next time I will...
1956 17 Sportsman CC-17-2310
1930 Model 100 7152

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Kerry Price
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Re: Hot generator

Post by Kerry Price » Tue Jul 21, 2015 9:26 am

After reading this thread I went boating and noticed that my ammeter reads at +10 amps pretty much continually when running on plane or at around 2400 RPM. After an hour or so of run time at various speeds I checked the generator and found it to be very hot but so was the (MBL) engine. Both generator and engine were way to hot to hold my hand to. I converted to 12 volt. That said, it was in the mid 90’s outside. I am not experiencing any performance issues. The engine is running smoothly and not overheating as far as I can tell. Temp gague needle barely moved from the bottom. I just am curious about what is being discussed in this post and questioning whether a hot generator is necessarily a bad sign. Also, I don’t know what a “cut-out” is and wondering if one of you would explain this and how to determine if it is working or not.
Thanks,
Kerry
1946 20' Custom Runabout: R-20-092
1938 19' Sportsman: 19501
http://www.chris-craft.org/registry/vie ... oat_id=532

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evansjw44
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Re: Hot generator

Post by evansjw44 » Tue Jul 21, 2015 10:42 am

The cut-out keeps the generator from becoming a motor when its internal voltage drops below that of the battery. If it sticks closed the generator will try to turn the engine. It will over heat and could cause a fire. The clue the cut-out is stuck is the ammeter showing discharge with the engine stopped and the key off.

That said, these generators are sealed and have no way to cool except through the case. You expect them to get hot.
Jim Evans

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Jim Godlewski
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Re: Hot generator

Post by Jim Godlewski » Tue Jul 21, 2015 10:57 am

evansjw44 wrote:The cut-out keeps the generator from becoming a motor when its internal voltage drops below that of the battery. If it sticks closed the generator will try to turn the engine. It will over heat and could cause a fire. The clue the cut-out is stuck is the ammeter showing discharge with the engine stopped and the key off.

That said, these generators are sealed and have no way to cool except through the case. You expect them to get hot.
Jim,
In my case my clue was the amp gauge was way to the high side while underway but normal at idle. Does that make sense for a bad cutout?
1956 17 Sportsman CC-17-2310
1930 Model 100 7152

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evansjw44
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Re: Hot generator

Post by evansjw44 » Wed Jul 22, 2015 9:46 am

That would not be a symptom of a bad cut-out. The cut-out connects the generator (armature) to the battery when it is producing enough voltage to charge the battery. That is, the generator voltage is higher than the battery voltage and current flown from the generator to the battery and whatever load is connected to it. When it output is not sufficient and the current reverses and flows from the battery into the generator (making it a motor) the cut-out disconnects the generator from the battery. That,s all it does.

If you have a "third brush" generator the charge rate is determined by the position of a third armature brush that picks up current from the armature and delivers it to the generator field. The more field current the higher the output. So, you high charging rate is the result of the third brush setting being too high. If you have a voltage regulator instead of just a cut-out, you have a cut-out in the regulator and a regulator device. Excessive charge rate in this case points at the regulator device being set too high. There is no third brush in the generator if it uses a regulator and the generator field windings are connected to the regualtor

The brushes are under the strap cover that goes around the generator body at the non driven end. One brush is connected directly to the body (ground), one is connected to the output (Armature, ARM) terminal and the third brush is connected to the field windings. I haven't adjusted one in years so I don't remember which way to move it to increase or decrease output.

A little Physics of Generators:

The voltage output of a generator, as measured at the armature terminal, is directly related to 1) the rotation speed of the armature; 2) the strength of the generator magnetic field as controlled the current passed through the field windings. If the generator armature is connected to a constant voltage load (i.e. battery) the armature voltage will remain constant but its current output will be directly proportional to the armature rotational speed and the field current
Jim Evans

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Kerry Price
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Re: Hot generator

Post by Kerry Price » Wed Jul 22, 2015 4:19 pm

Jim,
Thank you for such a thorough explaination on this. Much appreciated!
1946 20' Custom Runabout: R-20-092
1938 19' Sportsman: 19501
http://www.chris-craft.org/registry/vie ... oat_id=532

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Jim Godlewski
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Re: Hot generator

Post by Jim Godlewski » Sat Jul 25, 2015 4:43 am

I took out my freshly rebuilt generator for a test run. Mike Murley in Fair Haven MI, rebuilt it. (nice guy and quick turnaround)
At idle the gauge was just slightly below 0, under way it read +10. After running, the generator was warm but not hot. I hope this sounds normal and now have this issue resolved.
1956 17 Sportsman CC-17-2310
1930 Model 100 7152

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drrot
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Re: Hot generator

Post by drrot » Sat Jul 25, 2015 6:41 am

Warm is normal. If you look they are not vented.
Jim Staib
www.finewoodboats.com


1947 Penn Yan 12' Cartopper WXH474611
1950 Chris-Craft 22' Sportsman U-22-1532
1957 Chris-Craft 26' Sea Skiff SK-26-515
1968 Century 17' Resorter FG-68-174

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