Hey guys. I run a Detroit diesel generator at work for emergency power. Every Friday morning at 3am I get out my hearing protection and fire the beast up utilizing transfer switches to put her under a full load. This Detroit is a 16 cylinder, twin turbo charged, twin supercharged engine.
My question is, when I went to fire it up, it went into an "overcrank" situation. I tried to read up on this but didn't get much of an answer. Seems like it's programmed to do this every certain number of starts but I'm confused as to why and what happens in a real emergency situation when I need backup power? I'm kinda new to the generator thing.
We also have a brand new CAT generator but it's only hooked up to a new section of the plant. It's a 12 cylinder twin turbo. Beautiful piece of machinery and I feel almost honored to be in charge of it....

 

on auto back up genset the controler moniters start conditions, over crank is when start sequence is started but failes to start after a set time or number of cranking revolutions. this protecte the starter,batteries and engine. some controllers will auto reset and try again, some require operator overide.
Clark

 

Thanks for your response, but I'm still confused. I walked up to the ATS (automatic transfer switch), turned the key switch to test, and nothing happened. Normally the engine would fire up immediately. The generator hadn't ran since the prior week. Can you be more specific as to why this happened?

Thanks in advance...

 

i dont know much about them but thinkin about them makes my heart race

 

Overcrank alarm results from any of several conditons - low battery(s), oxidized connections, dragging starter, other crankshaft load - just means the cranking rpm is too low to start the engine, or starter is drawing excess cranking current, or not enuff current for a successful start sequence.

F'rinstance - the controller runs a load test on the battery(s) - the voltage is initially good at 12.63v or greater, but quickly drops to 10.7 under test - that won't crank the engine so you get the alarm

 

We have several large cat powered Gen sets at work, the generator at my station had a similar problem, it wound up being a 9v battery for the "keep alive memory", it was buried in the transfer switch control panel.

Good luck,

Tim

 

The way I have understood overcrank is that the computer has attempted to start the engine several times, and the engine did not start. The computer will be preset to number to failed start attempts before it will trip the alarm.

A number of problems can prevent the engine from starting.

We had a 125 kW Cummins/Onan genset at my last unit, in automatic service. One time we had an overcrank alarm, the starter was stuck.

 

Some of our generators in our unit also have electronic start feature. To start we would just push the start button it would crank over 4 times to start. If the engine did not start in those 4 times it would trip the overcrank light and would not continue to start until it was reset by an operator. There our many reasons for an engine not to start, but our generator had a pinhole in fuel line and would loose prime after it was stopped. Always took a couple cycles to start.

 

All are right - the more intelligent the controller, the more system variables are monitored - the purpose of the weekly test is to ensure it will crank up at any unexpected event - this failure should be noted and checked against any station event log, where procedures should indicate necessity for service

 

And it was duly noted in my log. This unit is about 35 years old. It has 168.5 hours of run time. I tried to start her manually but nothing happend. I quickly started troubleshooting small control fuses and the like to no end. There is definitely a problem. We are having a subcontractor come out to look at it. From what I've been told this has happened in the past, contractor comes out and says all is good. I've only been at this job for three months now. I feel an additional amount of stress because this is a hospital and patients lives are dependent on this back up power. We are supposed to tie in the rest of the facility to the new CAT later this year and we'll be selling the Detroit.

 

TRIK, What CAT gen set do you currently have.... I'm guessing for your power needs, its either a 3500 series CAT or the new C-175 CAT. Possibly having the the EMPC-3 panel on it?... either way, nice setup.
As others have said, theres alot that can cause an overcrank, depending on what type of control system you have. I'm assuming you are running electric starter motors. Could be something as simple as a loose or corroded cables, bad winding in the starter motor (causing a dead spot) Could be that if its older technology, there is a weak relay that isn't closing consistently so the initiate contact never happens. Unless you have some electrical savy, sounds like you're doing the right thing getting a qualified tech. out to look at it. Especially that its emergency power for a hospital.

 

I'll find out the model of the CAT when I go back to work Tuesday night. It's a 12 cylinder twin turbo inside a completely insulated trailer type housing. I believe it will handle 4000amps at 480v. Very quiet on the outside when running... on the inside, it's another story...
I know more about electricity than anything else, but, specializing in generators and control systems is something my chief wants contracted out to protect our behinds....

 

You should be able to find Detroit Diesel genset info on the 'net, as well as any other switchgear you're responsible for - be worth a search