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MEP 17a -2A042 -Onan 5KW- Resistor value in voltage controller


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  #1  
Old 01-22-2017, 01:43:52 PM
roelant roelant is offline
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Default MEP 17a -2A042 -Onan 5KW- Resistor value in voltage controller

Dear Folks,

I have recently bought a mep 17 a generator, which is a bit of a rarety here in europe, and i am in the process of reviving it. After a lot of carb-cleaning and a rusted through oil filter top, i have now managed to get the engine running reasonably smoothly. It still has a few smaller issues like a rocker that someone grinded down, probably not being aware that this engine has hydraulic tappets..

Anyway, the reason i am looking for some help is my problem with the voltage regulator. After finding the generator does not produce more than about 45 volts I removed the voltage regulator from the set and found out it has a resistor that has fried...

In the doc i found on the internet it is stated that this generator should have a solid state regulator that has two transformers and a transistor end stage. On my (apparently a bit older ) mep 17a there is a different type of regulator. It has two smaller transformers ( one is actually a coil not a transformer) and a round transformer in a black casing with 8 connections. I believe this is a magneciter like type of regulator. It uses a 'magnetic amplifier' to regulate the power that goes to the field coil of the genny head.

I have not found a schematic of this regulator. Does anyone have this for me?

The fried resitor is R4 and my problem is that i cannot read the proper value of it anymore.

Any help on this problem would be very much appreciated.

I will include a picture of this regulator ( onan 305D316)
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  #2  
Old 01-22-2017, 04:52:23 PM
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Jim McIntyre Jim McIntyre is offline
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Default Re: MEP 17a -2A042 -Onan 5KW- Resistor value in voltage controller

Yep - It's a mag amp. I have some of the 1.5 kW gensets in that family that use a similar regulator.

In fact, the tech manuals for the 1.5 kW gensets included the schematic for the mag amp AVR, but I just checked my 5 kW manual, and all it shows in the later electronic AVR.

You do know this can be replaced with an SX-460, right?

Oh, and Welcome to the forum!
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Old 01-22-2017, 04:58:26 PM
roelant roelant is offline
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Default Re: MEP 17a -2A042 -Onan 5KW- Resistor value in voltage controller

Ah an answer allready, thats nice! So i should find that manual of the 1,5 kw version.. It is probably on the smokestak site somewhere....I will go find it..

Good to hear it can be replaced by a SX-460. Not sure how easy that is to find in europe for an affordable amount of money.

Thanks again for the info.
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Old 01-22-2017, 08:13:33 PM
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Default Re: MEP 17a -2A042 -Onan 5KW- Resistor value in voltage controller

Well, I don't know how much help it will be. The 1.5 kW version, while similar, is a different item - designed for about 1/3 of the field drive power, I'd guess.

Chinese clones of the SX-460 are all over eBay for around 25 USD.
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Old 01-23-2017, 12:31:18 AM
Vanman Vanman is offline
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Default Re: MEP 17a -2A042 -Onan 5KW- Resistor value in voltage controller

I don't know- a mag amp is an elegantly simple device. I'd want to replace the bad resistor before installing a complicated electronic circuit made out of Chinese components in its place.
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Old 01-23-2017, 01:52:05 AM
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Default Re: MEP 17a -2A042 -Onan 5KW- Resistor value in voltage controller

I agree, but if the OP can't figure out the resistor value, and isn't able to reverse engineer it, the SX 460 is a viable option...
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Old 01-23-2017, 05:12:42 AM
roelant roelant is offline
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Default Re: MEP 17a -2A042 -Onan 5KW- Resistor value in voltage controller

I have meanwhile found the schematic that was menitioned by Jim. It is basically the same diagram but not 100% the same. Actually ( bad luck) the resistor that is smoked is not in this diagram. The resistor that has burned out is in series with the field coil and has a zener parallel to it. I am not sure of the meaning of this setup. It might have something to do with getting the generator going on remenent magnetism.

I have found and ordered a sx460 on 'aliexpress'. ( aliexpress is a chinese web site that offers all sort of stuff , a bit like amazon) So it is a chinese version... It is very cheap but will take at least 3 weeks or so to arrive from china to the netherlands.

I am planning to connect a universal 0-30 volt (adjustable) lab power supply on e.g. 5 volt to the field just to check the generator to be alive..

Then i will wait for the sx460. I think it is an elegant solution, even if not 'original' to this genny.

Thanks again for help and advice..
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Old 01-23-2017, 06:29:29 AM
Rich Mc Rich Mc is offline
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Default Re: MEP 17a -2A042 -Onan 5KW- Resistor value in voltage controller

You should try to determine what caused the resistor to fail. Is it a short in the field coil or over volt etc. The defect may damage the new AVR.
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Old 01-23-2017, 06:40:26 AM
roelant roelant is offline
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Default Re: MEP 17a -2A042 -Onan 5KW- Resistor value in voltage controller

Thats a good tip. I will try out the gen head without the new regulator just supplying the field with a separate power supply. The current limiter on this power supply will tell me about a possible short in the field windings. anyone familiar with 'normal voltage and current' in this field coil during operation of the gen head?

Not knowing the actual functionallety of the fried resistor and zener pair makes it harder to trouble shoot the situation. I will check the zener to be alive. If not it is easy to understand the resistor blowing up....
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Old 01-23-2017, 01:20:26 PM
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Default Re: MEP 17a -2A042 -Onan 5KW- Resistor value in voltage controller

Quote:
Originally Posted by roelant View Post
...I am planning to connect a universal 0-30 volt (adjustable) lab power supply on e.g. 5 volt to the field just to check the generator to be alive..
Good idea. I don't know for sure, but the field drive is pretty low power - 5 or 10V at under an amp, I think. Are you going for 50Hz ? Might take a tad more drive. If so, that might be a hint as to the cause of the original magamp failure. There have been reports of sub-60Hz frequency burning up Onan's magneciter. The SX460 will be fine in this regard.

Quote:
Then i will wait for the sx460. I think it is an elegant solution, even if not 'original' to this genny....
They're decent. Keep in mind that you might need to add some series resistance to your field winding, due to the SX460's minimum field resistance spec. Also, add a fuse somewhere, so if the SX460 fails, it's less likely to take your field winding with it...
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Old 01-26-2017, 09:03:00 AM
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Default Re: MEP 17a -2A042 -Onan 5KW- Resistor value in voltage controller

I am now pleased to report to you my progress on gettinge the mep 17a running and delivering power..

While waiting for the sx460 to arrive i went back to the defective mag amp regulator. After removing the fried resistor from its place i found out that the rear side was not completely black and i even managed to read the value! It turned out to be a 1000 ohm resistor.

Then i checked out the zener that is parallel to the resistor ( both together are in series with the field of the generator). It turned out to be bad. It is a 10 watt stud mount 5.6 volt zener. I found a replacement at Farnell and ordered one.

It arrived today. I replaced the resistor ( i happened to have several around of the proper value and wattage since one of my other hobby's is tube guitar amps and they use that value for G3 on a endtube pentode). Then i fixed the zener and installed the regulator.

After startup of the engine of the mep 17 still no power but field flashing solved that last problem!

I adjusted the engine speed to 60 Hz and loaded the genny with a flood light of 150 watt. The voltage seems fairly stable.

I will run the unit on a bit more load later, but feel confident it will be ok.

Oh boy that engine makes a fair bit of noise when running at 3600 rpm.. It would be no fun to have that running all day...It needs a somewhat isolated shed not to close to the house...

Thanks again for supporting remarks and good tips.
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Old 01-27-2017, 06:40:53 PM
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Default Re: MEP 17a -2A042 -Onan 5KW- Resistor value in voltage controller

Yes, they are loud. Maybe at 3000 rpm a little better. Aren't you 50 Hz in the Netherlands?
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Old 01-28-2017, 05:08:15 AM
roelant roelant is offline
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Default Re: MEP 17a -2A042 -Onan 5KW- Resistor value in voltage controller

Yes we are... But so far I am only test running this genny. I am not sure how well the avr will work if i lower the RPM's to 3000. Will the increased field current needed for getting the same output voltage at 3000 RPM not overload the voltage regulator or field coil?

This has been a fun project so far. I am not so sure how practical it will be to keep this noisy bugger around. In the netherlands we seldom have power outs and they generally don' last more then an hour or so at max.

Of course if we would have a serious power out it would be great to have this thing around. I could imagine all my nabours running long extention cords to my place just to keep their central heating, freezers etc going...

We could then all stand around 'our' genny and smoke sigars (with ear protection on...)

Actually a more practical use would be if i need to welding on my boat on a remote location..

Another plan i originally had with this generator is to use the generator head as a power brake for power testing small 1 cylinder engines that my son is working with. We have a project going where we have installed an electronic fuel injection on a honda 50 cc engine for a small motorcycle. I want to be able to do bench testing with engines like this and was planning to use the generator head for that.

Of course i now know that this gen head has only one bearing..
I might end up selling it again now that it is running ok and spend the money on an other gen head with two bearings..Or take the spark plugs out and spin the whole engine and gen head driving the crankshaft from the non flywheel side.
I need to figure a way to connect the output shaft of the little honda engine to the crankshaft of the genny in a safe way...

Some more thinking to do , i don't want to spend a lot of money , it all has to be done with old parts or stuff that is allready around.
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Old 01-28-2017, 01:03:18 PM
25Eagle34 25Eagle34 is offline
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Default Re: MEP 17a -2A042 -Onan 5KW- Resistor value in voltage controller

They really like Gas also, so better have a good supply ready
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