Engine control schematic brainteaser (warning - longish)

[bobofthenorth]

My brain is stuck - I need some out of the box thinking.  I have become thoroughly disgusted with the needless complexity that is incorporated into my Kubota G6500 genset.  I wish I had thrown it in the bush 2 years ago and bought a new one from Dick Wright - at least then I'd have something.  As it is I have an engine rebuild into it 2 years ago now plus a new head this winter so I'm at least halfway to a new generator and instead I still have my noisy, high revving, needlessly complex contractor's set.  But I digress.

This winter some of the control harness started acting up - after I had ponied up for the new head of course - and I decided that enough is enough.  I'm not buying any more $500 bits of plastic in the hope of making it run.  Instead I have taken the time to figure out how it runs and have built some workarounds using cube relays.  Its a 16 HP diesel engine with a mechanical governor - there's no way it needs 4 separate computer-like boxes with 20 or 30 wires coming out of each one.  And I've got it running just fine.  Now we can start it and be sure that it will run long enough to cook supper or recharge the batteries.  Believe me, that's progress. 

The next step is to re-implement the Murphy switches but WITHOUT THE COMPUTER.  I had it running reasonably reliably but the computer would decide it needed to shut down despite having good oil pressure and cool temperatures.  I did all the connection cleaning, checking for continuity, replacing sender and eventually talked to someone at Wrico who agreed that everything points to me needing another expensive bit of Japanese plastic which as I have already said ain't gonna happen.  So I have the high temp shutdown implemented as shown below:


So what's the problem?  My current shutdown depends on power being supplied to the relay coil all the time.  If that wire falls off, gets corroded, whatever, the system fails.  I'd like to make that failsafe but I can't wrap my brain around a way to do that with the existing components.  I can see how to do it if I could find a NC temp switch but I'm kind of in "don't spend any more money mode" so I'd like to do it with current components. 

Any suggestions?

[Sean]

Bob,

What I would do (and did on mine) is to get a N/C temperature switch that opens above whatever shutdown temp you want (typically 220 or so).  I bought my switch from Dick Wright.  It's a two-lead switch; simply wire it in series with the power to the run solenoid.

FWIW, our oil pressure shutdown is the same -- a two-lead switch, this time N/O.  It closes above a fixed pressure, somewhere around 7-10psi.  Here again, we bought the switch from Dick.  This is also wired in series to the run solenoid.  Holding the start switch down bypasses the oil safety; by the time you release the switch, the oil pressure is high enough to keep it closed.

HTH,

-Sean
http://OurOdyssey.BlogSpot.com

[Sean]

FWIW, here is the schematic of the control system I made for our genny.  It is WRICO-compatible, right down to the color scheme, so it can use his remote switch panel:



If your run solenoid has only a single lead (rather than separate leads for "pull" and "hold" like mine), then you need to connect the dark red lead coming off relay 1 (marked "to start solenoid") through an appropriately rated diode to the yellow lead heading to the run solenoid.  This implements the bypass during cranking.

-Sean
http://OurOdyssey.BlogSpot.com

[James77MCI8]

Did the same thing to my Kohler 7.5. Got rid of the black box and went to mechanical relays, Wiring is similar to Seans. I have schematics if you need them.

[bobofthenorth]

Thank you guys.  You cheated but thank you anyway.  The rules of the game were that I had to use my existing components and only my existing components.  However the knowledge that NC temp & pressure switches with 2 contacts are available is pretty tempting.  I think I'll put up with my current setup until next winter and then make a detour in Oregon.  I had been working on a complicated system to handle the oil pressure shutdown involving a delayed relay to give the oil pressure time to come up after starting.  If a simple bypass will suffice I'll use the money I'll save on the fancy relay to buy some of Dick Wright's switches. 

Thank you again Sean for your as usual excellent explanation complete with schematics. 

[Sean]

...  You cheated ...  The rules of the game were that I had to use my existing components and only my existing components.

Bob, I went back through your OP several times and I just never found these "rules," sorry.  Next time I will wait for you to post all the contest rules before I send in my entry

Since you say it that way, though, I can suggest two things.

First would be to feed the positive voltage to the relay coil in your diagram from the incoming positive signal to the relay, from the "run" switch.  Then jumper from that relay coil terminal to the contact terminal.  Now if the coil voltage drops out, the input signal also drops out and the run solenoid will close.  You would only be at risk for a failure in the short jumper between the coil terminal and the input contact terminal.

If even that is too much of a risk, you could instead install a low-amp fuse or circuit breaker between the run switch and the run solenoid.  Then wire the run lead to the terminal of the N/O temperature switch, downstream of the fuse/breaker.  Now if the switch closes, the run signal will be directly shorted to ground, blowing the fuse or tripping the breaker and thus interrupting the current to the run solenoid.  Sort of a poor-man's crowbar circuit.  If you choose this as the only method, you can wire directly, but every over-temp will require a new fuse, or else use a push-to-reset circuit breaker.

You could also use this method as a backup to the cube relay.  In this case, use a slow-blow fuse or breaker, and a pair of diodes to separate the relay-grounding pathway from the fuse-blowing pathway.  If the relay opens, then the fuse/breaker will not have time to blow/trip, and the current will be safely interrupted with no further issues.  If the relay does not open quickly, say because it is stuck or there is no power to the coil, then the fuse/breaker will blow/trip, saving the engine.

Hope that's clear enough; if not, I will try to draw it up for you.

-Sean
http://OurOdyssey.BlogSpot.com

[mikelutestanski]

Bob;   Use Dick Wrights setup right down to the terminal strip.. Easy too figure out and troubleshoot.  The  2 sensors are about 75 dollars from DIck Wright.  I just lost the overtemp.   35 bucks and the oil sender is about 34. THey are sending the replacements in the mail. I decided to buy both and put the oil pressure switch in stock in the bus as a spare.  THe genny quit on our last trip downstate at a train place during lunch. SInce we were heading home I waited until we got home .Terminal 4 on Dicks strip shows voltage when running and mine did not.  Actually It would start and run until I took my finger off  the start switch then it died.  It turned out to be the overtemp switch.    It only lasted 10 years with about a 1000 hours on the 8 kw genny.
   Justin @ Dicks was very helpful so I really did not have to think very much..
   I first suspected it was algae in the fuel as the filter looked dark so I changed the oil filter, fuel filter, air filter, and oil.  It was time anyway ; but it still would not start..
    So life is grand, new sensors in the mail and we are getting ready for a Texas trip to see the grandkids..
      Hope you are doing fine and your better half as well.
       Regards and happy busssin   mike

[bobofthenorth]

I was leaning that way already Mike.  I just had to tease Sean about cheating on the brain test.  I talked to Justin a couple of times last week and was very impressed.  He helped me troubleshoot my generator with absolutely nothing in it for him.  I'm glad I bought my AGMs from them but that is 6 years ago now so they don't really owe me anything.  He also was the first guy I have talked to about this miserable gennie who didn't start out the conversation by saying "oh that's a really old generator - it's probably obsolete now."  The next time a partsman tells me that I'm going to let him have it.  Who do they think pays their wages if it isn't us fools who insist on running old rigging?

Justin is evidently pretty smart but the knowledge in the BCM brain trust is pretty impressive too.  I had no idea that anything like a 2 pole temperature or pressure switch even existed.  So there was no chance that I would go looking for one until Sean mentioned it here.

And Sean thanks again for the new ideas.  I had thought about something involving grounding the solenoid power through the sender but hadn't come up with the fuse or c/b idea so that idea wasn't going anywhere for me.  I think I'll just enable the oil pressure switch in the existing circuit and run it the way it is until next winter when we go through Oregon.  I won't mind the excuse to stop at Wrico.

(edit)
Its done - it works - next stop Wrico - next winter.  Thanks guys.

[Melbo]

Good Deal Bob

Glad it is working for you --- it's ok for you to cheat and add parts next year

Melbo

[luvrbus]

 OK  ? for you guys how do you control the overspeed on generator set with that setup I know the engine is governed but I lost a 13kw Wrico from overspeeding and it can happen to a Kubota. 
I really want one of the Murphy controllers but 600 bucks is a little pricey for me


good luck

[Sean]

Clifford,

If the engine is the electronically governed type, then the control box needs to be reading the speed and have a cut-out switch for the run solenoid.

My generator has no governor at all -- the RPM is controlled by a completely mechanical throttle set screw.  You adjust droop by first setting the throttle at no load till it reads around 63 Hz or so, then re-check at full load to make sure it is no lower than about 59.  There is no other speed adjustment.  So my unit has two speeds -- 0, and 1800 rpm.

Lots of older Kubota-powered sets use the exact same setup, especially the non-electronic, transformer-regulated units such as mine.  I love it, and after the nuclear strike, I will have one of the few generators still running

-Sean
http://OurOdyssey.BlogSpot.com

[muddog16]

Sean, that was hilarious........"after the nuclear strike", made my morning thanks!

[luvrbus]

Sean, how do maintain the 1800 rpm under load without a governor ? mine was mechanical also yours maybe different but every Kubota I tore down has a governor in the injection pump housing I am lost on this one



good luck

[bobofthenorth]

Mine has what I would call a governor on the fuel pump as well.  I assume the computer could theoretically have detected overspeed from the generator output frequency but I have no way of knowing whether it did or not.  I'm just happy to have the miserable beast running again - I'll take my chances on it blowing itself up with an overspeed.  At least if it blew up completely then I would know exactly what I had and it might not be a whole lot different than what I have right now.

[Sean]

Sean, how do maintain the 1800 rpm under load without a governor ? mine was mechanical also yours maybe different but every Kubota I tore down has a governor in the injection pump housing I am lost on this one

Sorry, Clifford, I should have been more clear.  I meant "external governor."  My Kubota, like yours, has a flyweight governor built in to the fuel system just after the injection pump.  The throttle lever actually moves the fork on this governor to set engine speed.  In a vehicle application such as the tractors in which these engines are commonly found, the throttle pedal is connected to this lever with a mechanical linkage.

On my unit, and many other generator sets, this lever is set with a mechanical set screw and jam nut.  On electronically governed sets, however, this lever would be connected to a solenoid linkage so the electronics can control the rpm.  The internal mechanical flyweight governor would still be present.

When you were talking about a runaway I did not understand you to be referring to the flyweight governor.  These things are incredibly simple and fool-proof; I'm having a hard time imagining how the flyweights would allow an overspeed to happen, as they respond almost instantly.  There is also a maximum fuel stop that can only be bypassed by operating the lever fully to the start position.

-Sean
http://OurOdyssey.BlogSpot.com