Running your engine off a converter - anyone out there?

[Fuss]

Does anyone run their engine off a converter. 24-12 or 12-12v. Not engine starting of course.

I'm interested to know if anyone does this

There would be no spikes through the instruments. (yes, there is other ways to achieve this... but just for this argument)

engine instrument battery voltage would be incorrect, this is important to some but these days many have other monitoring systems.


anyone, anyone out there?

[SailingHarmonie]

On many engines it would be a bit of work to separate the instrumentation system from the starting system. It can be done, but what's the point?

The only "spikes" to be concerned with come from the starting motor, and if you have a separate starting battery, that's already fixed, and if you do NOT have a separate starting battery you have not accomplished anything useful--I can see.

It also GREATLY depends on the kind of engine you are talking about. My engine is all mechanical and runs happily without any battery power at all. You don't get any instrument data for temperature and such, but it runs. A modern common rail engine... not so much. It needs electrons like it needs diesel fuel.

[rslifkin]

I see no reason to do it. I'd just keep the engine on its own battery that nothing else runs from. The engine electronics shouldn't have any issues with the voltage dip during start and things like that, as they were designed to operate in that environment.

[Calif.Ted]

Mine will run just fine with NO electrical once started, most will I believe. I've had both a Perkins and yanmar that had the fuse in main wiring harness come loose while the engine was running. Both engines have a 20 or 30 amp fuse in the main harness on top of engine which is the interface between boat and engine wiring. When disconnected the engine continues running and all gauges are dead, engine will not restart if stopped. Power needed to start but mechanical fuel pump takes over from there. Not sure what you are trying to do, but boat diesels usually only need power for the starter and instruments.

[rslifkin]

Originally Posted by Calif.Ted

Mine will run just fine with NO electrical once started, most will I believe. I've had both a Perkins and yanmar that had the fuse in main wiring harness come loose while the engine was running. Both engines have a 20 or 30 amp fuse in the main harness on top of engine which is the interface between boat and engine wiring. When disconnected the engine continues running and all gauges are dead, engine will not restart if stopped. Power needed to start but mechanical fuel pump takes over from there. Not sure what you are trying to do, but boat diesels usually only need power for the starter and instruments.

For mechanically injected diesels that's often true, although some do need power to hold the stop solenoid in the "run" position (others default to "run" and power it to "stop"). Electronic diesels and any gas engine need power to run, however. But it's usually not too hard to keep a good power supply to an engine, at least to the extent of "by the time this fails, I've got bigger problems to worry about".

[Fuss]

Originally Posted by rslifkin

I see no reason to do it. I'd just keep the engine on its own battery that nothing else runs from. The engine electronics shouldn't have any issues with the voltage dip during start and things like that, as they were designed to operate in that environment.

Yes they were but then additional instruments are added to this convenient 12v system and the spike problem begins.

The starter has its own direct cable to the battery. Solenoid activation , instrument power etc happens through the motor wiring, so, separated from the big starter cables.

There are some good reasons for doing this, I don’t want to get too much into this part right now as I’m interested to see if others have considered or done this.
However I know that I need to give a reason , so , one reason is that you may wish to run your engine wiring, instruments, stop solenoid etc off the house bank.. this then would give you a truly dedicated start battery that is only used for starting and absolutely nothing else, not even running the motor instruments.
However this is not my main reason for considering this.

Anyone out there doing or considered this?

[skipperpete]

Originally Posted by Fuss

Does anyone run their engine off a converter. 24-12 or 12-12v. Not engine starting of course.

I'm interested to know if anyone does this

There would be no spikes through the instruments. (yes, there is other ways to achieve this... but just for this argument)

engine instrument battery voltage would be incorrect, this is important to some but these days many have other monitoring systems.


anyone, anyone out there?

Good question, I’ll give you an answer when I get this done. I’m re powering my boat and the instrument panel (12V) for the replacement engine is pretty much toast…. BUT I happen to have 2 x 24volt panels with full instrumentation, harness and senders bought 8 years ago for another project and I figure if I can find a 12-24v step up converter I can use one of those panels. If there is no such converter, I’ll probably make the engine 24volt and run a 24-12 converter for the domestic supply instead, my DC loads are relatively light with the biggest draw being refrigeration….. but that does well on solar panels alone anyway.

[HankOnthewater]

The best system .... in my opinion..... is something like the original post suggested.
I had that in my off-road RV for the last 12 years:
- starter battery is only used to operate starter
- all other loads ie dash instruments, lights, radio, winch and what have you, are connected to a 2nd battery ('house')
- the single alternator is connected to starter battery with VSR that connects to the house battery when starter battery if voltage exceeds 13.8 volts (adjustable)
- current start battery is now 13 years old and still going strong, house batteries lasted 8-12 years (Odyssey P2150)

I more or less copied this on my boat, and as said above, the only electrical equipment on engine (shutoff solenoid) is powered by ships batteries
- one small alternator is connected to starter battery
- all other alternators and other charging devices go direct to ship's batteries
- That way no need to use any converter, when both voltages (starter and ship's) are the same.
This was good for 8 years, although ships batteries did not last that long.

Now with lithium being introduced, some minor changes are planned, but the same principle applied: no other loads on starter battery than starter motor.
And guess what, just purchased a P2150 as starter battery on the boat.

And yes, you can have 2 different voltages for starter motor and ships voltage, no need for converter.... if the dash has the correct voltage.
And I cant see any reason why you can't use an converter to match the dash voltage if ships voltage if it is different to that.

[rslifkin]

Originally Posted by Fuss

Yes they were but then additional instruments are added to this convenient 12v system and the spike problem begins.

The starter has its own direct cable to the battery. Solenoid activation , instrument power etc happens through the motor wiring, so, separated from the big starter cables.

There are some good reasons for doing this, I don’t want to get too much into this part right now as I’m interested to see if others have considered or done this.
However I know that I need to give a reason , so , one reason is that you may wish to run your engine wiring, instruments, stop solenoid etc off the house bank.. this then would give you a truly dedicated start battery that is only used for starting and absolutely nothing else, not even running the motor instruments.
However this is not my main reason for considering this.

Anyone out there doing or considered this?

Personally, I'd think adding a converter into the mix increases the risk of a problem, not decreases it. For my engines the gauges and engine ignition systems run off the start battery (as they're powered through the key switches), but that's it. And all of that stuff will handle some voltage fluctuation, etc. I don't see how feeding it a perfectly constant, regulated voltage will improve anything. If there are voltage spikes occurring beyond the drop in voltage during cranking, then something is wrong. FWIW, the tachs I have installed handle the cranking voltage drop well enough that they read accurate cranking RPM during engine start.

[Fuss]

Originally Posted by rslifkin

Personally, I'd think adding a converter into the mix increases the risk of a problem, not decreases it. For my engines the gauges and engine ignition systems run off the start battery (as they're powered through the key switches), but that's it. And all of that stuff will handle some voltage fluctuation, etc. I don't see how feeding it a perfectly constant, regulated voltage will improve anything. If there are voltage spikes occurring beyond the drop in voltage during cranking, then something is wrong. FWIW, the tachs I have installed handle the cranking voltage drop well enough that they read accurate cranking RPM during engine start.

Yes adding a converter adds complication but gives the advantage that I can run the instruments etc from some other source than the start battery which plays a large role in my installation…more on this on another thread later.
It’s not too much of a safety concern for me as my motor needs absolutely no electricity once it is running.
I think you will find that there is a flying diode somewhere on your panel that protects against spikes.its not a matter of something is wrong , spikes occur when your battery starts your engine and these spikes affect sensitive instruments if it reaches them.
These flying diodes are in themselves not totally reliable and can cause engine safety concerns when they malfunction.

[SailingHarmonie]

Originally Posted by Fuss

Yes adding a converter adds complication but gives the advantage that I can run the instruments etc from some other source than the start battery which plays a large role in my installation…more on this on another thread later.
It’s not too much of a safety concern for me as my motor needs absolutely no electricity once it is running.
I think you will find that there is a flying diode somewhere on your panel that protects against spikes.its not a matter of something is wrong , spikes occur when your battery starts your engine and these spikes affect sensitive instruments if it reaches them.
These flying diodes are in themselves not totally reliable and can cause engine safety concerns when they malfunction.

A “flying diode”??? Do you mean a fly back diode?

So your plan is to remove all the diodes in the engine control circuit in the interest of reliability? If you leave them there, they are still susceptible to failure, so you have not really fixed anything.

You realize there will be a lot of them, not just the fly back diodes, and failure of any of them can disable the engine control systems.

You can, and will, do what you want, but diesel engines accumulate 10s of thousands of hours on the standard electric designs. But if you know better, have at it.

[Fuss]

Originally Posted by SailingHarmonie

A “flying diode”??? Do you mean a fly back diode?

So your plan is to remove all the diodes in the engine control circuit in the interest of reliability? If you leave them there, they are still susceptible to failure, so you have not really fixed anything.

You realize there will be a lot of them, not just the fly back diodes, and failure of any of them can disable the engine control systems.

You can, and will, do what you want, but diesel engines accumulate 10s of thousands of hours on the standard electric designs. But if you know better, have at it.

I never said I was removing them, I just explained what they do and how they can also be an unreliable component.
I am mainly interested in others using a converter for running the engine wiring, instruments etc.
This is not you as your engine battery runs your engine instruments as most do and hopefully you connected no other instruments to it…oh dear, you did connect depth, wind speed to it… I knew it….well, maybe this thread is for you then..

[rslifkin]

Originally Posted by Fuss

Yes adding a converter adds complication but gives the advantage that I can run the instruments etc from some other source than the start battery which plays a large role in my installation…more on this on another thread later.
It’s not too much of a safety concern for me as my motor needs absolutely no electricity once it is running.
I think you will find that there is a flying diode somewhere on your panel that protects against spikes.its not a matter of something is wrong , spikes occur when your battery starts your engine and these spikes affect sensitive instruments if it reaches them.
These flying diodes are in themselves not totally reliable and can cause engine safety concerns when they malfunction.

My instrument panel isn't a pre-built setup from the engine manufacturer, the boat builder rolled their own (and some of the gauges have since been replaced). No external flyback diodes or anything in the harness, but the gauges are intended to survive the spikes, etc. related to engine start. Outside of a few gauges that were replaced for various reasons other than electrical failure, I have 38 year old gauges that still work fine after many start cycles. There's nothing in that system that would be sensitive.

In my mind, if anything isn't strictly related to engine operation and doesn't get the power cut when you turn the engine key off, it should never be powered from the engine start battery. Depth or any other instruments should be powered from the house bank, both for isolation from voltage dip during engine start and also to make it basically impossible to accidentally drain the engine start battery.

[tjr818]

As an aside, years ago I converted my 6 volt Jeep to 12 volts, the starter absolutely loved running on the higher voltage. The 6 volt wiring was sized for much higher amperage than the 12 volt wiring required so everything worked out great. I would not hesitate to run the 12 volt starter off of a 24 volt system.