OT- Onan 20 kw generator- short in electrical...possible reasons ? (wiring diagram)
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    Default OT- Onan 20 kw generator- short in electrical...possible reasons ? (wiring diagram)

    1993 year Onan MDL4 marine generator has developed a short such that if I press the rocker switch (S11 or no. 7 in parts book) either to "start" or "heat" positions, it immediately trips the main DC on/off breaker. (CB 11 in schematic, part 16)

    From what I gather on marine forums a common cause of this is either a short in one of the glow plugs or one of the gauges...but apparently not the case here...disconnected wire to glow plugs, no difference, disconnected gauges, no difference.

    Also substituted K11/part 23 relay from good generator to bad (I have two), no difference.

    All overload switches and other switches check out with proper continuity.

    Have examined the electrical control box and the engine itself carefully for chafed wires...all seems good. The short extends to the wires that connect to the fuel injector to open it's internal solenoid. I disconnected a wire in the electrical box once (months ago, can't remember which one now) that allowed the (Cummins) engine to turn over normally without tripping CB11, but engine wouldn't start as no voltage was going to the fuel injector solenoid....thus no fuel allowed past it.

    Any ideas what else to check ?

    fullsizerender-74.jpg fullsizerender-75.jpg

    (as yes the print quality and size of the schematic suck but it's all I have)

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    Have you checked the injection pump solenoid for a dead short?

    The solenoid is actually a bypass solenoid which means that when not energized, fuel is routed back to the fuel tank. When energized, the solenoid valve closes and allows low pressure to build in the injection pump and allow the injection pump to function.

    There is usually a knurled screw that sticks out the end of the solenoid. Screwing in the screw closes the valve and allows the engine to operate without electrical power to energize the solenoid.

    I would try starting the generator without the fuel shutoff solenoid connected.

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    Quote Originally Posted by Ziggy2 View Post
    I would try starting the generator without the fuel shutoff solenoid connected.
    I'm pretty sure I tried that already and it still tripped the breaker (months ago, can't remember) but will do it again to be sure.

    If the "months ago" part sounds odd it's because it's winter, not using the boat, connected to dock power, don't need the generator and the other generator works fine, so keep putting off delving into fixing this one....but now got a couple of buyers nibbling at the hook so figure I'd better fix it before it goes to survey.

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    You might have to resort to divide and conquer.

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    Onan Generators - SmokStak

    These guys are all about Onans... I've got an Onan 7.5kw gas engine generator.. got lots of info off there.

    You can also locate and print off nice, easy to read spec sheets, service manuals and parts lists on most every Onan ever made on there. They've got a link to the treasure trove of Old Onan manuals.. and newer ones, too.

    All they ask is when you post a question about your machine that you include the word Onan and the exact model number in the thread title, complete with all letters and numbers, so that everyone can tell what machine you're asking about.

    It's also a good idea to take a closeup picture of the machines' badge plate as well. There are a variety of things they can tell by the info on that plate... like this one off another 20 kw machine.

    That very top line is the important information.... "20DGAB 39553F" .. especially the "F"... that's key to lots of info.


    0.jpg

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    Quote Originally Posted by Milacron View Post
    I'm pretty sure I tried that already and it still tripped the breaker (months ago, can't remember) but will do it again to be sure.

    If the "months ago" part sounds odd it's because it's winter, not using the boat, connected to dock power, don't need the generator and the other generator works fine, so keep putting off delving into fixing this one....but now got a couple of buyers nibbling at the hook so figure I'd better fix it before it goes to survey.
    Different rig - Fermont assembled MEP803A, Onan-branded Lister-Petter, 10-12KVA, 8000 ft / sea level.

    Very nearly the same symptom. Not "glow" plugs. Intake manifold heater, and that part worked OK.

    What at first appeared to be a short at actual startup - Injectors not being enabled, was first addressed with a bit of wood holding it open.

    Among other players, it was also being given a false low-oil-pressure alarm shut down command. Other weirdness was fuel level gauge reading backwards, showing negative on a visually full tank.

    Problems started to go away as it warmed up. Took some hours of testing and fiddling, but two culprits eventually confirmed:

    1) Batteries (2 X 12V) looked fully charged per each of two 12V charger "green lights", were actually not even close. Total load of starter and various solenoids were too much for them to sustain during start cycle, FI pump control oscillated until wood was applied.

    2) Moisture had gotten into the control panel, MIL-SPEC or no, slime grew on that, confused the lowest power sensitive bits, they then passed their confusion downstream to the heavier players.

    Fuel level gage eventually died outright, but is 'don't care' as one can get visual on the "set" tank it reads, and the Aux tanks all have their own gages.

    2CW, but battery condition, "for real" as-in charged maybe, but high resistance possibly, is worth testing whilst stressed.

    Moisture and fungoides bit, you'd see always whilst on the water, surprised me on a dry-air-mostly area and covered carport above the already "MIL SPEC weatherproof" + tactically quiet uber-enclosure.

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    Quote Originally Posted by JoeE. View Post
    Onan Generators - SmokStak

    These guys are all about Onans... I've got an Onan 7.5kw gas engine generator.. got lots of info off there.

    You can also locate and print off nice, easy to read spec sheets, service manuals and parts lists on most every Onan ever made on there. They've got a link to the treasure trove of Old Onan manuals.. and newer ones, too.

    All they ask is when you post a question about your machine that you include the word Onan and the exact model number in the thread title, complete with all letters and numbers, so that everyone can tell what machine you're asking about.

    It's also a good idea to take a closeup picture of the machines' badge plate as well. There are a variety of things they can tell by the info on that plate... like this one off another 20 kw machine.

    That very top line is the important information.... "20DGAB 39553F" .. especially the "F"... that's key to lots of info.


    0.jpg
    Thanks....
    below is photo of my data plate and the control box.

    fullsizerender-76.jpg img_1118-2.jpg

    To start the generator the red rocker must be in "on" position, then if cold push the black rocker switch down to pre heat for a few seconds, then push it up to start. Currently if I move the black rocker to preheat or start position the red rocker immediately trips to off position.

    (the reason you see oil pressure, etc in the photo is the picture is of the (identical model) working generator in "on" mode)

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    Quote Originally Posted by Milacron View Post
    1993 year Onan MDL4 marine generator has developed a short such that if I press the rocker switch (S11 or no. 7 in parts book) either to "start" or "heat" positions, it immediately trips the main DC on/off breaker. (CB 11 in schematic, part 16)

    From what I gather on marine forums a common cause of this is either a short in one of the glow plugs or one of the gauges...but apparently not the case here...disconnected wire to glow plugs, no difference, disconnected gauges, no difference.

    Also substituted K11/part 23 relay from good generator to bad (I have two), no difference.

    All overload switches and other switches check out with proper continuity.

    Have examined the electrical control box and the engine itself carefully for chafed wires...all seems good. The short extends to the wires that connect to the fuel injector to open it's internal solenoid. I disconnected a wire in the electrical box once (months ago, can't remember which one now) that allowed the (Cummins) engine to turn over normally without tripping CB11, but engine wouldn't start as no voltage was going to the fuel injector solenoid....thus no fuel allowed past it.

    Any ideas what else to check ?

    fullsizerender-74.jpg fullsizerender-75.jpg

    (as yes the print quality and size of the schematic suck but it's all I have)
    Hard to read the print with phone so switching gears to NFM mode... (No ######/ Manual).

    Ou likely already have done this but look for anything any where that plugs into anything any where.

    Does not matter at all.

    One thing at a time unplug and test.

    When the problem changes it is related to that connector.

    It is not elegant by any means but effective.

    Next is wires that require work...

    Let's assume the engine has protection for low oil pressure or other bad thing.

    When one is starting it these conditions usually cannot be met until running so they are bypassed during starting.

    Depending on how the protection works it could be applying power to a bad selenoid maybe.

    Again one can look for things to disconnect like oil pressure sending unit or water level sensor.

    Sent from my SAMSUNG-SGH-I337Z using Tapatalk

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    Most likely you have chafe on a wire somewhere and a short to ground.

    Does the unit have a remote panel? If so, disconnect the harness to the remote at the generator, jumper the appropriate wires (there's usually a removable link between two terminals) and see if the problem persists.

    Once you have eliminated the remote panel & harness, you'll basically have to step through each section of the control circuitry to look for the short. Usually I start off by disconnecting the safety devices (i.e. oil pressure, coolant overheat, exhaust elbow temp) to see if any of those are shorted to ground when they shouldn't be.

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    This brings up a question.

    Does a boat get mice infestations ?

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    Quote Originally Posted by digger doug View Post
    This brings up a question.

    Does a boat get mice infestations ?
    Rats, rather, but to eat, nest, and breed, not bring their own rations from afar, watch TV, or admire sunsets.

    Bet this is not a watercraft with grains or other food carried as hold cargo, left by crews, nor probably stored at all. They'd do a periodic recce and hie off to better meals. Shelter is secondary to food and water for that clan's metabolic rates.

    And.. rodents are opportunistic defecators as well as feeders, so there is usually an evidence trail before there is damage from new litters of little critters teething on anything in reach. Adults are more selective as to chomping.

    Meanwhile - there is enough old corrosion on housing edges, gauges, and panel of the "good twin" pictured, that I'd reinforce a need for a cleanup of possibly grown conductive fungoidal, microbial, and airborne salt and debris trails.

    Could be as temporarily simple as exhausting a decent shop-vac warm-and-dry through the innards for an hour or three, sprays and brushes applied later.

    And may have already been done. Hull owner ain't ignorant. Just prone to double and triple checking many sources.

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    Thoes DC breakers do get weak and nuisance trip, if you have a matching generator, may be worth swapping the breaker, would not be the first time i have seen that especially after most the common causes have been ruled out.

    Low voltage DC is very uninclined to break down insulation, so a meter should easily detect any shorts.

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    Quote Originally Posted by adama View Post
    Low voltage DC is very uninclined to break down insulation, so a meter should easily detect any shorts.
    It is, OTOH, inclined to support the growth of nastiness. The extreme case the "fuzz" that can grow around battery terminals.

    A less obvious one the electro-biological sustaining of the growth of what become progressively more conductive leakage paths through the accumulation of a film of airborne debris, live and dead microbes, fungi, their own byproducts of life and death, and the atmospheric water vapor absorbed and held. Salt air? Spare us!

    Didn't get much notice when all electricals were BFBI, relatively high voltage and/or high current, and widely spaced, physically.

    Became a problem as closer-packed transistors, IC's and such - all progressively seeking to operate more efficiently on lower voltages and lesser and lesser rations of power - took over sensing, health and alarm monitoring, display, and control functions that were then "leveraged" back up to control the higher powered goods.

    And then.. there exist major atmospheric static charge effects, even those far short of a "near miss" lightning strike easily capable of damaging electronics good.

    Systems reliant on even modest levels of sophistication, partial automation, electronically assisted simplification for operators - all also selling points - became more vulnerable than the older, simpler, "BFBI" goods were.

    War One submarine diesels an example. Air-start. Mechanical pumps and injectors. Mechanical governor. Mechanical tachometer. Mechanical temp and pressure gauges.

    No 'lectricity anywhere atall until the output shaft meets the generator head and its whole separate universe.

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    Quote Originally Posted by digger doug View Post
    This brings up a question.

    Does a boat get mice infestations ?
    No hint of such on this one.

    although I did have a sailboat once with mice....amazing the little suckers crawled down a 250 foot pier, metal ramp to dock float, and up the lines into the boat, where they proceeded to breed and have lots of fun. Conventional snap traps worked at first, but then stopped working.....as if the dead mice could communicate with the live ones to warm them....and yes they were new traps so no "dead comrade smell" to warn either...maybe the live mice see their dead relative in a trap before I get to it, and remember that thing must be dangerous...if so, smart little guys aren't they ? ....only poison pellets finally got them all.

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    Quote Originally Posted by Milacron View Post
    No hint of such on this one.

    although I did have a sailboat once with mice....amazing the little suckers crawled down a 250 foot pier, metal ramp to dock float, and up the lines into the boat, where they proceeded to breed and have lots of fun. Conventional snap traps worked at first, but then stopped working.....as if the dead mice could communicate with the live ones to warm them. (and yes they were new traps so no "dead comrade smell" to warn either)....only poison pellets finally got them all.
    "Crawl", Hell! Buggers can move so fast the human eye has trouble tracking them.

    Just went through a bout of that. Ultimately resolved with new garage door and door sill weatherproofing.

    Meanwhile - every trap or bait on store shelves tried. Every one got at least one mouse. Some got two. Few "mechanicals" ever got a third one.

    And then... Most reliable, as it got even the newbies too small to even trigger a latch?

    Glue trap. But mostly when "baited" with but fraction of an ounce of ignorant bottled water in its own inverted bottle-cap, centered.

    They need water as well as food.

    Especially when just off the teat 'coz Momma was nailed a day earlier, they are low on energy, high on ignorance, haven't learned fear, and they've not yet graduated to the complex trek to the outdoors to find their own beverages.

    House can be bone-dry, everywhere. Bone-dry bilge on a watercraft is rare. Ordinary hull condensation - fresh water, of course - is all even a whole tribe of rodents need.

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    Since I know you tend to be frugal I will not suggest buying the newer model which is over $400 but instead suggest buying one of these used.

    Fluke Y8100 DC/AC Current Probe

    fluke dc current probe | eBay

    This is not the first time you have had electrical problems with machinery and vehicles and these (used with a good multimeter) make troubleshooting of shorts and overloads much easier. I've had one for years (bought used) and it saves a lot of time and frustration. They are especially useful when used with a meter that can record peak values. With one of these it's easy to tell if the problem is excess current or a weak breaker.

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    Quote Originally Posted by Milacron View Post
    No hint of such on this one.

    although I did have a sailboat once with mice....amazing the little suckers crawled down a 250 foot pier, metal ramp to dock float, and up the lines into the boat, where they proceeded to breed and have lots of fun. Conventional snap traps worked at first, but then stopped working.....as if the dead mice could communicate with the live ones to warm them....and yes they were new traps so no "dead comrade smell" to warn either...maybe the live mice see their dead relative in a trap before I get to it, and remember that thing must be dangerous...if so, smart little guys aren't they ? ....only poison pellets finally got them all.
    I had a trapped (dead) mouse that I didn't get to within a week or so....some
    other small critter had chewed the brains out of the one in the trap....
    Attached Thumbnails Attached Thumbnails garylarson-mousetrap.jpg  

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    Quote Originally Posted by digger doug View Post
    I had a trapped (dead) mouse that I didn't get to within a week or so....some
    other small critter had chewed the brains out of the one in the trap....
    Cheese.. BTW.. is not a natural food for mice.

    My "bait" is a mixture of Wheat Germ, shards of wotever nuts are handy (cashew, pecan, walnut, pistach), bound up in a smear of Hazelnut Nutella.

    Now with the meese mostly messed, momentarily?

    Thot there was a truant DIESEL in here somewhere?



    Izzat running, yet?

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    Quote Originally Posted by digger doug View Post
    This brings up a question.

    Does a boat get mice infestations ?
    Pretty rare unless it's on a trailer up on dry land.
    I did once find a raccoon sleeping aboard a boat at a slip...

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    Quote Originally Posted by thermite View Post
    Cheese.. BTW.. is not a natural food for mice.

    My "bait" is a mixture of Wheat Germ, shards of wotever nuts are handy (cashew, pecan, walnut, pistach), bound up in a smear of Hazelnut Nutella.

    Now with the meese mostly messed, momentarily?

    Thot there was a truant DIESEL in here somewhere?



    Izzat running, yet?
    I don't use anything for bait.

    I buy the Victor traps with the large paddle of "fake cheese".

    And I always put them along a wall. The paddle being large, seems
    to make it work better.

    I have a few traps, so beat up and half chewed apart (blood & fur splattered as well) they still work fine, the mice run along the wall, and just run into them.


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