Unknown Generator to Engine interface

[Tuzi]

Dear Technical Wizards.I hope there is a simple explanation to what looks like black magic to me. I have a 20kva Northern lights gen and a pair of C9 cats. On two occasions in the past 10years I’ve gone to start the gen while happily motoring along only to have the engines stop and the gen not start.I found a flat gen start battery on both occasions. Jumped the battery and all is well. But why does it kill the engines? I have a engine room fire extinguisher system. Could this be the connection? Thanks in advance for any help. Baz

 

[Lepke]

You may need an electrician or a lot of wiring tracing. My guess the dead battery is somehow switched to supply the power to the mains fuel stop solenoids while you are trying to start the generator. The solenoids lose power and stop the fuel to the mains.

 

[STB]

Will the engine restart after it stops and before recharging the battery? Or does the battery need to charge 1st?

The engine disconnect relays normally require /both. power and the pressure switch being closed to /enable/ the engine. If they lose power, the really is normally open and the engine stops. They are normally powered off of whatever powers the ignition circuit, usually the start battery, not an unrelated battery such as house or genset.

Electric fuel lift pumps are also a possibility, if someone installed them. I think the C9 has mechanical one's natively. But, people do like to install electric ones when they fail. If there are electric fuel pumps, they could be a problem if they are wired to the wrong battery.

Lastly, there is, almost literally, everything else. By (fallible) memory, the C9 is a modern engine with a billion electrical sensors, solenoids, and an ECM. It isn't like an old school Perkins, or Lehman, or Detroit. It is more like a gasoline engine -- no power, no run. It is hard to imagine how it would end up miswired, but anything is possible. (Don't hold me to this, it is just what I remember).

I'd start by disconnecting the genset battery (red wire is fine) and seeing if the engines start and run. If they don't, then I'd see what has lost power, e.g. the fireboy or the lift pumps, or, ... And, then go from there to get any engine-related systems moved over to the right battery.

If the engines do start and run without the genset battery, then I've got a million more questions, some of which may not have apparent answers.

 

[Tuzi]

Thanks Gurus for the quick response and putting me on track. The engines won’t start with the gen battery disconnected. I found the fireboy control box is powered from the gen battery and heard the relays in that box click when disconnecting the gen batts. The fire boy relays are in the engine ignition circuit.
So Iam thinking when I went to start the gen with a failing gen battery it dragged the power supply from the fireboy control and opened the engine ignition relays.
It also explains why the gen batt is a 4D. I always thought that was an overkill to start a 2.2 Lt diesel.

 

[STB]

Good work! You know what to do now...

 

[twistedtree]

The fireboy relay box is meant to be powered from multiple sources for just this reason. So you might want to run a wire from your main engine start battery (assuming there is a separate one), and perhaps from your house bank as well.

 

[STB]

The fireboy relay box is meant to be powered from multiple sources for just this reason. So you might want to run a wire from your main engine start battery (assuming there is a separate one), and perhaps from your house bank as well.

Good point!

My memory is that the battery is intended to be supplied from each of the engine's ignition/run circuits after the key switch or run switch such that either power input is only live when the "ignition is on". This prevents a parasitic drain from the unit when the engines are off.

From there my memory is that, internal to the unit each ignition circuit passes through a diode "one way valve" before coming together to power the unit.

The diodes ensure that the unit will be powered as long as either has power while also preventing one battery from charging or discharging the other through the unit.

As a last thought, as should be the case anyway for a million reasons, the batteries need to have a common ground for this to work.

I can imagine some units are designed without specific support for twins and would need external wiring to combine multiple batteries (although I don't remember ever seeing such a beast)

So, I guess my high level thought is to wire it, or have it wired, according to the diagram because problems are possible otherwise. And, problems are often more easily moved than fixed (and can become worse).

 

[twistedtree]

Good point!

My memory is that the battery is intended to be supplied from each of the engine's ignition/run circuits after the key switch or run switch such that either power input is only live when the "ignition is on". This prevents a parasitic drain from the unit when the engines are off.

From there my memory is that, internal to the unit each ignition circuit passes through a diode "one way valve" before coming together to power the unit.

The diodes ensure that the unit will be powered as long as either has power while also preventing one battery from charging or discharging the other through the unit.

As a last thought, as should be the case anyway for a million reasons, the batteries need to have a common ground for this to work.

I can imagine some units are designed without specific support for twins and would need external wiring to combine multiple batteries (although I don't remember ever seeing such a beast)

So, I guess my high level thought is to wire it, or have it wired, according to the diagram because problems are possible otherwise. And, problems are often more easily moved than fixed (and can become worse).

That’s it exactly. Ideally each protected device provides switched power to active the FireBoy when you run the device. When all protected devices are turned off, the FireBoy turns off. But it’s also pretty common the just wire two or more power sources and leave the FireBoy on all the time. The down side it that you don’t cycle the relays, and verify that the system is working.

 

[Tuzi]

Thanks again for your input. There are independent start batteries . 24/7 power to the fireboy from the gen battery. I’ll check if the fireboy gets additional input power when engine ignition is turned on but I doubt it as the engines wouldn’t have been shut off when gen batt power dropped. Unfortunately I don’t have a ships circuit diagram for the fireboy.

 

[KnotYet]

Thanks again for your input. There are independent start batteries . 24/7 power to the fireboy from the gen battery. I’ll check if the fireboy gets additional input power when engine ignition is turned on but I doubt it as the engines wouldn’t have been shut off when gen batt power dropped. Unfortunately I don’t have a ships circuit diagram for the fireboy.

Spring project!