Generator Question

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Lenp
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Generator Question

Post by Lenp » Sat Sep 17, 2011 3:15 pm

I have a 5KW Coleman generator with a B&S engine. In all the years I've used it there was no problem with the connected loads.
This year during hurricane Irene, it would not start the submersible well pump without assistance.
Unassisted the pump would cut out on overload since the voltage drooped so low. If I manually advanced the engine throttle the pump would start and run the cycle. I tried tweaking the throttle/governor adjustments and if I got it running with the pump load the unloaded voltage was way too high (270V). If I set the low end, (240V) the voltage would droop (160V) at the higher pump load.

Now I'm a bit confused!
The generator 'seems' capable of producing the required power if the engine speed is increased.
The engine 'seems' to have the horsepower to run the generator under a full load.
The 'governor' is a simple spring vs air vane affair but I cannot find a sweet spot that satisfies both the low and high load demands.

Any suggestions anyone?

Len
Len

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Bob Scott
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Re: Generator Question

Post by Bob Scott » Sat Sep 17, 2011 5:09 pm

B&S engines cover a large range of quality. B&S engines are all still flat heads, right? 1920's technology. There are those good ones with steel cylinder liners and those cheap models with pistons running directly on the aluminum casting. The latter kind, sometimes seen in really cheap lawn mowers, don't hold compression longer than a few months of use.

I think that the engine is showing its age and the compression isn't what it used to be, or the carburetion might be too lean. Yer'll have to tinker and maybe replace piston rings, valves, etc. Otherwise, might gear reduction (or belt-pulley ratio change) be a possibility?
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dacflyer
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Re: Generator Question

Post by dacflyer » Sat Sep 17, 2011 5:36 pm

actually most modern B&S engines are overhead valve now. the flat heads ( L-heads ) have not been made in a really long time.

but it does sound like it could be possibly running lean if the engine dies down or bogs down.
and almost every generator i have worked on being 8hp and up, have cast iron sleeved cylinders.
only one i worked on that was just aluminum bored was 5hp and less.
try this.. have the choke slightly on. but not so much that it makes the engine start flooding.
then try the pump.. if it starts ok, then it means carb is running lean.
i have news that unleaded fuel ( regular grade ) is not good to use in small engines any more. because the Ethanol blend fuel, they recommend that you use higher octane fuel (plus or super grade)
also you have to beware that the Ethanol eats up carburetors also. it reacts with the aluminum and many MFG's will void warranty if they detect Ethanol in fuel. and ya they have test to prove that.

maybe with more info i can help you out..i have worked on a lot of generators, even a few basket cases.

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Re: Generator Question

Post by Dean Huster » Sat Sep 17, 2011 7:37 pm

The "IC" B&S engines all have sleeved cylinders.

I don't know why it is that on decent generators, they don't have throttle control based on a 60 Hz feedback loop and voltage output adjusted by field current on the generator. It's always been a project I've wanted to pull off if I had a decent generator system to work with ..... e.g., a rebuilt VW Golf diesel engine turning a 20 to 40 KW generator. That'd be good for powering a full house even if it was all-electric.
Dean Huster, Electronics Curmudgeon
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Lenp
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Re: Generator Question

Post by Lenp » Sun Sep 18, 2011 7:37 am

So the opinions point to a possible engine problem! It has a pull start and it does seem to start quite easily so I'll do a compression test. What typical compression peak should I expect?

I think I'll dig out my stash of high wattage stage lighting lamps and build a load bank. While it's not exactly the inductive pump load, I think it's safer to use for tests than possibly damaging the well pump by the under voltage conditions.

If it ever stops raining I'll get on this project (I hope before I need it again!)
Len

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Re: Generator Question

Post by jimmy101 » Sun Sep 18, 2011 8:56 am

For any small engine I would assume that the general replaceables need to be replaced. (Always go with the simplest and cheapest fixes first.)

New plug(s), new air filter, and in particular, a new fuel filter. If the fuel filter is starting to plug up the engine will run lean but may still seem to operate normally.

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Lenp
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Re: Generator Question

Post by Lenp » Sun Sep 18, 2011 11:28 am

Jimmy,
It was tuned up last year, but it wouldn't hurt to look into those items, given the cost of another generator!
Thanks,

Len
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MicroRem
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Re: Generator Question

Post by MicroRem » Mon Sep 19, 2011 7:45 am

Just a thought, could it be that the water table is lower right now than in the past, requiring more amperage to get the water to the surface? I would also check the motor capacitor.

best

Tom

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Externet
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Re: Generator Question

Post by Externet » Mon Sep 19, 2011 8:15 am

Len :
What is the rated current for the pump ; what is the current measured during the troublesome run ?

The pump may have gone bad, partially seized, shorted windings... Have you tried the generator with known good loads ?
Miguel
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Lenp
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Re: Generator Question

Post by Lenp » Mon Sep 19, 2011 4:45 pm

Hi Guys,
The pump is not an issue, The run current is within the published numbers, on the generator once it overcomes the start up and the pump runs without fail on the normal power. As for a low water table, I am on the East Coast Hurricane, weeks of rain.... More water than ever!
Len
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“To invent, you need a good imagination and a big pile of junk.” (T. Edison)
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dacflyer
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Re: Generator Question

Post by dacflyer » Mon Sep 19, 2011 6:10 pm

just curious, how does the pump act on normal AC power ? do you have a amp meter ?

how does the generator do on other electric motor loads that have a start / run phase ?

Ken1
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Re: Generator Question

Post by Ken1 » Mon Sep 19, 2011 7:09 pm

Does the generator's engine lose speed when the pump is trying to start? Do you know if the generator has an electronic voltage regulator? The vast majority of generators are electronically regulated nowadays. I would be suspicious of the regulator if it's electronic. I have a generator and it's electronically regulated and it holds the engine's RPM very constant regardless of load and load fluctuations right up to the generator's maximum output. If I overload the generator then the motor slows down and it also lugs hard as it tries to gain speed.

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Lenp
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Re: Generator Question

Post by Lenp » Mon Sep 19, 2011 8:13 pm

The generator runs a full size refrigerator, an under counter refrigerator and and a mid size upright freezer. Beside these loads all the circuits on the first floor, including entertainment loads, security and telephone system are powered. When a compressor starts, the generator lugs for a second, recovers and runs, even with all other loads. With the pump alone, the generator lugs down and will not recover unless I manually move the throttle and speed up the engine. From what I can see, there is no voltage regulation other than the throttle/governor arrangement.

The pump is a Goulds 1/2Hp submersible and the run current is about 7.5A which is close to the pump rating.
I can't find a start or a LRA rating but I can measure the it with a peak and hold meter as soon as I find time

The odd thing, as I said before, the generator seems it is capable of the required output and the engine seems to be able to produce the horsepower but they cannot do it without external intervention.

Here's a band aid :idea: ...A low voltage sense circuit that kicks a solenoid that pushes the throttle up! :roll:

Thanks!
Len
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Bob Scott
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Re: Generator Question

Post by Bob Scott » Fri Sep 23, 2011 3:35 pm

Dean Huster wrote:I don't know why it is that on decent generators, they don't have throttle control based on a 60 Hz feedback loop and voltage output adjusted by field current on the generator. It's always been a project I've wanted to pull off if I had a decent generator system to work with ..... e.g., a rebuilt VW Golf diesel engine turning a 20 to 40 KW generator. That'd be good for powering a full house even if it was all-electric.
I have dreams like that too. Your comments got me thinking deep thoughts.
I think a good RPM to choose would be 1800 RPM. At 60 Hz, it would have to produce 2 Hz per revolution. I guess that makes a difference in which alternator to choose.
1HP =746 Watts, so 40Kw would need an engine with 53 HP minimum at 1,800 RPM. I would want to oversize the engine a bit, so I'd choose a motor with a hundred horses at 1,800 RPM. That, or use the VW engine and downsize my dream maximum KW rating to compensate.

I worked out an equation for calculating torque necessary at 1,800 RPM for any engine HP output. It works out to 2.9178 foot-lbs of torque necessary for each HP at 1,800RPM. (If you want, I can post my calculations. Basically, it allows you to use a constant equal to 5252. Divide 5252 by the RPM and you get torque needed for each developed horsepower.)
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Smoke_Maker
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Re: Generator Question

Post by Smoke_Maker » Fri Sep 23, 2011 4:30 pm

Lenp, The sweet spot is 60 Hz, don't pay any attention to the voltage. Just set the RPM to 60 Hz and your pump will be smiling, A/C motors don't care about voltage as much as frequency thats why the power company guarantee 60Hz and not voltage setting.
Richard Furniss
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