# Older B&S standby generator



## Chrisj (Feb 4, 2016)

Hi all,

I'm working on an older Briggs and Stratton model 1938 10kw generator someone gave me. It's an NG\LPG Vtwin.

While I know electronics, and I can work on engines I've never worked on a unit like this so I'm hoping someone can help me with the basics.

From what I can tell, the circuit board starts\stops the unit and simply monitors voltage, frequency etc. The actual voltage regulation is done in the alternator and the frequency\rpm is done mechanically by the engine. So, in theory, the unit will work without if for testing purposes? I'm asking because I need to replace some caps on the board and so some other minor repairs. But, would like to fire the unit up and see how it runs while I'm waiting for parts.

Is this correct?

Also, how is this thing cooled? The service manual warns that removing panels will cause it to overheat. Does the engine's fan force air through the alternator?


Thank you for taking the time to read my post.


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## RedOctobyr (Aug 8, 2018)

Wow, when you said "older", you weren't kidding! 

Do you have any pictures of it? Engine shrouds often direct air from the flywheel fan, over the engine's fins. So removing the shrouds effectively reduces that airflow (the air goes elsewhere instead), and can cause the engine to overheat. 

This is less likely to be an issue when running briefly, of course, and with no real load on the engine. Less heat is being generated. 

On my generators, the shrouds have never covered the generator side, maybe there are fan blades inside of it? I've only seen setups where the shrouds help cool the engine, but not the generator itself. 

I don't want to try and guess about circuit board aspects. Hopefully someone can chime in. Is there maybe a fuse or something you can pull, to prevent a partially-functioning board from being powered? 

As I understand it, at least nowadays, generator heads are typically tightened onto a tapered crankshaft. Getting them off can be difficult, even after removing the bolt that attaches them, as the taper can be locked together. So removing the generator head, to allow testing just the engine by itself, might be difficult. 

I gave up trying to remove the generator head from my ~2000 10kW Briggs-powered Generac, as I was afraid I was going to break something.


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## Chrisj (Feb 4, 2016)

RedOctobyr said:


> Wow, when you said "older", you weren't kidding!
> 
> Do you have any pictures of it? Engine shrouds often direct air from the flywheel fan, over the engine's fins. So removing the shrouds effectively reduces that airflow (the air goes elsewhere instead), and can cause the engine to overheat.
> 
> ...



1938 is the model, not the year. It's from 2004. :tango_face_grin:

The service manual to the entire generator warns about it overheating if panels are removed, not the engine.
I was just looking at an exploded view of the alternator and it definitely has it's own fan, and it pulls air from outside and vents inside the enclosure.

So I'm completely baffled by their warning now.


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## RedOctobyr (Aug 8, 2018)

Oh, ok, that makes more sense  I was surprised/impressed by circuit boards on an 80 year old generator, but hey, who am I to say what they were using back then? 

My $0.02, I expect that warning applies to the engine, not the generator itself. Though I'm on my phone, and assuming this is a portable unit. 

If it's a permanently-installed house unit, then ignore me, and perhaps the shrouds do help the generator itself. The enclosure for the entire unit may play a role in managing airflow, and therefore cooling. 

But again, if you're just running it as a test for 2 minutes with no load, I'd be surprised if it could overheat itself that quickly, even if you messed with the cooling. Especially the generator head, with no current flowing through it.


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## tabora (Sep 6, 2018)

My Onan *2.8KV-FA/26100A* has essentially the same warnings about not running it without the enclosure and service access cover installed. It's designed to draw the air in at the generator end, flow it over the engine, and then the muffler, exiting below it.

"Operating the genset with the cover removed can cause equipment damage. Genset cooling air does not circulate properly with the access cover removed. Do not operate the gen-set with the access cover removed."


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## Chrisj (Feb 4, 2016)

Hi all,

This is an enclosed standby generator, similar to what tabora posted.

Looking at the schematic closer, I see all I need to do is supply the fuel cutoff solenoid with 12VDC and it should run. Best I can tell, the control board does very little meaningful. The alternator is 100% self contained as is the engine. In fact, there doesn't appear to be any wires to the engine at all except the starter connection.

I'm going to make up some wires tonight to make this happen. Once I prove that it runs good I can proceed with making a new cabinet and frame for it as well as ordering any other parts I think I'll need.


I think I always assumed these units were far more complicated than this. At least this one, is little more than a portable generator with a cheesy control board that does some simple monitoring and auto start\stop. I suppose that's a good thing.


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