Another example of my auto electrics knowledge

[harmony]

I've built a run engine stand for my spare 251 flathead.  I had one of those plastic radiator fans kicking around, so I thought why not add more air flow, so I mounted it on the outside of the fan since it is a pusher fan.  But it's 12 volt and I'm running a 6 volt battery.  No big deal, it still operates, just turns a little slower.  

However, as you all know my engine is positive ground.  The fan is negative ground.  If I reverse the wires on the fan ( positive to ground) it runs in reverse and turns it into a puller fan.  Defeating the purpose.

 

Ok, so here's my stupid question of the day.  What will happen if I run the fan, negative to ground, while everything else is positive to ground?  Will there be an explosion or a melt down?  If so, is there a way around this?

Edited March 11, 2023 by harmony

[allbizz49]

Why not just wire it to a 12 volt negative ground battery on its own? Easy enough to do.

[Bryan G]

There shouldn't be any issue at all. I think the only way you'd run into a problem is if the fan used its case as a ground, and that case was then connected to the engine ground. I would imagine, though, that the motor has two wires, not just one, so it grounds through the wiring. No problem.

[harmony]

17 minutes ago, Bryan G said:

There shouldn't be any issue at all. I think the only way you'd run into a problem is if the fan used its case as a ground, and that case was then connected to the engine ground. I would imagine, though, that the motor has two wires, not just one, so it grounds through the wiring. No problem.

The case of the fan is all plastic.  I have it fastened to the radiator through the core with plastic zap-straps.  Yes two wires coming off the fan motor. 

[harmony]

40 minutes ago, allbizz49 said:

Why not just wire it to a 12 volt negative ground battery on its own? Easy enough to do.

Certainly easy, you're right.  I just don't have a spare 12 volt battery, and I built the mobile ( on wheels) engine stand to accommodate only one battery.  

[greg g]

There is a theory that ground is ground and the same ground can be used for seperate power sources regardless of voltage or polarity of loads.  Your engine is not 6v. The starter and ignition is 6v.

 

This has been discussed here before, but I don't remember  it clearly enough to explaine it properly.

 

The easiest way is to power the fan with jumper cables a jumper pac or a spare battery. The fan has a permanent magnet which is polarity sensitive starters, generators are temp magnets and are  polarity tolerant.  

 

Hopefully one of thebrighter ones on here can explaine the universal ground thing.

Edited March 11, 2023 by greg g

[Tired iron]

No problem with that! It'll work fine.

[Los_Control]

I know enough about automotive electrics to get into trouble.

I think you already got your answer.

I do not see any reason why you could not run the engine 6 volt negative ground. Take away any guess work.

Same time if you did have a spare 12 volt battery you could run the engine 12 volt negative ground.

 

Only advantage is when you do find a home for your spare engine ... you know you are shopping for another project

Your engine run stand will be more versatile for the next engine you set on it.

[OUTFXD]

I have a cigarette lighter housing in Jacquiline specifically for modern USB electronics.  I wired it backwards and It has powered my Offline GPS  for months without issue.

[Sniper]

As long as the supply side of the different voltage sources are isolated from one another they can share the same "ground" or more appropriately return.

 

remember you need a supply AND a return for electricity to work so as long as one side of the circuit (supply or return) is isolated there isn't a problem with the other side being in common. 

 

In this case you are looking at a 6v negative supply and a 12v positive supply sharing the return side.  That will work fine if the supply sides are isolated from each other. 

[harmony]

1 hour ago, Sniper said:

As long as the supply side of the different voltage sources are isolated from one another they can share the same "ground" or more appropriately return.

 

remember you need a supply AND a return for electricity to work so as long as one side of the circuit (supply or return) is isolated there isn't a problem with the other side being in common. 

 

In this case you are looking at a 6v negative supply and a 12v positive supply sharing the return side.  That will work fine if the supply sides are isolated from each other. 

How do you mean "isolated" Sniper?

[Sniper]

Isolated as in they do not share anything at all. 

 

 

[harmony]

9 hours ago, Los_Control said:

I know enough about automotive electrics to get into trouble.

I think you already got your answer.

I do not see any reason why you could not run the engine 6 volt negative ground. Take away any guess work.

Same time if you did have a spare 12 volt battery you could run the engine 12 volt negative ground.

 

Only advantage is when you do find a home for your spare engine ... you know you are shopping for another project

Your engine run stand will be more versatile for the next engine you set on it.

Haha!  The next project is already waiting for me.   I have also built another run engine stand for my 1930 Hudson straight 8, patiently waiting for me, to see if I can get it running.  I just need a radiator for it. Plus do all the wiring.  Won't that be fun.  !! 

[harmony]

1 minute ago, Sniper said:

Isolated as in they do not share anything at all. 

 

 

Well in a sense they do, according to my electrically brain dead mind.  They share the battery.  Just reversed wiring so to say.

[Sniper]

I was responding to this

 

23 hours ago, greg g said:

There is a theory that ground is ground and the same ground can be used for separate power sources regardless of voltage or polarity of loads. 

 

Reversing your fan leads won't be an issue.  What may be an issue is the fan speed may be insufficient to cool the radiator.

[harmony]

16 minutes ago, Sniper said:

I was responding to this

 

 

Reversing your fan leads won't be an issue.  What may be an issue is the fan speed may be insufficient to cool the radiator.

My mistake for say "Just reversing wiring so to say"  I was just trying to emphasize that the wires on the fan were going to the opposite battery posts.  I'm not reversing the fan leads.  That would make the fan a puller, not a pusher.  

The load wire (positive)on the fan, is going to the ground post of the battery.  The ground wire on the fan is going to the load side of the battery where all the components of the electrical system are getting their power from.  

Will that confuse the fan motor?  As in start to smoke.  Or will it confuse one of the electrical components on the engine causing it to smoke?

The fan is plastic and it's attached to the radiator with plastic snap ties.  So it's not finding ground through the engine.  Only through the battery.  If that is any consolation. 

 

I was kind of surprised at how fast the fan actually goes when hooked up to a 6 volt battery.

 

Another alternative would be that the engine run stand likely to be within the length of a 100 ft. extension cord away from 110 AC volt outlet, whenever I'm running the engine.  Or I do have a relatively quiet Honda 2000 generator.  So I could set up a floor model 110 volt fan in front of the radiator.  

[Sniper]

You can wire your fan however it needs to be wired to spin the proper direction as it is electrically isolated from the rest of your electrical system.

 

However, and there is always a however, a 12v fan on 6v may draw excessive current.  I don't know as I never tried that experiment.  I do know that my 12v fan on high speed draws in excess of 25 amps at 12v.  On 6v, to maintain the same wattage, that would be 50A.  Not sure how the wiring would like that if it were to happen.  I think I would put a fuse in line rated at whatever amps the manufacturer specifies.  That should keep the smoke in the wires, lol.    

[harmony]

16 minutes ago, Sniper said:

You can wire your fan however it needs to be wired to spin the proper direction as it is electrically isolated from the rest of your electrical system.

 

However, and there is always a however, a 12v fan on 6v may draw excessive current.  I don't know as I never tried that experiment.  I do know that my 12v fan on high speed draws in excess of 25 amps at 12v.  On 6v, to maintain the same wattage, that would be 50A.  Not sure how the wiring would like that if it were to happen.  I think I would put a fuse in line rated at whatever amps the manufacturer specifies.  That should keep the smoke in the wires, lol.    

That's an interesting point that I never considered, about the draw.  There is actually an inline fuse on the load wire of the fan now with a 25 amp fuse in it.  It came that way when I stumbled across the fan a years ago  The information decal on the fan is not readable anymore so I'm not sure what it is rated at. 

With what you just said, maybe perhaps I should go with a 110V fan set up.  The plastic electric 12 volt fan sort of looks out of place attached to the radiator of a flathead engine anyways. 

[Sniper]

1 hour ago, harmony said:

That's an interesting point that I never considered, about the draw.  There is actually an inline fuse on the load wire of the fan now with a 25 amp fuse in it.  It came that way when I stumbled across the fan a years ago  The information decal on the fan is not readable anymore so I'm not sure what it is rated at. 

With what you just said, maybe perhaps I should go with a 110V fan set up.  The plastic electric 12 volt fan sort of looks out of place attached to the radiator of a flathead engine anyways. 

 

To be honest, I think the fan will just turn slower than normal.