WHAT IS HAPPENING HERE? Any electrical engineers here?

Okay, so I had this all written, and my browser crashed and lost it. So here is the "I'm frustrated with this" quick version.

I finished putting my fan shroud together last night. I've had these fans for a couple years, and they work fine. If I hook them up backward, they run backward. They are 1995 Mercedes C280 fans, hooked in parallel from the factory, with factory connections except where I cut the wires.


The wires end right at the edge of that picture.
I have a hot wire running from the battery cable on the starter, just for doing engine test runs, and test driving. I have a maintenance charger on the battery.

I put my fan shroud together last night, and tested the fans in reverse and forward, to see where and how the air moves, now that I have a proper shroud on it. It worked great. Water was running downhill, fire was hot, and the IRS still wants more than their share.

Rather than have a hot wire laying loose, I hooked the hot supply to the fan hot, and grounded the negative to run the fans. I used to have the ground wire under a screw on the fan shroud, and connect the hot wire to run them, but I accidentally shorted it to the frame once, and so that's why I switched the connection.

So I'm planning on wiring the fans with a relay and such, and from what I've seen on other fan systems, and one I have on my 59, the fans have constant power, and a switched ground to run. Right now, it's just hot to hot, and touch the wire to ground to run.

I walked out this morning to go to work, and heard my fans running. I went back behind the garage, and sure enough, my fans are running, with no ground! I took a quick video without touching it first.

http://youtu.be/GZDC21_oP48

I had to get to work, so I didn't have time to investigate.
What is going on here?

8literbeater said:

Okay, so I had this all written, and my browser crashed and lost it. So here is the "I'm frustrated with this" quick version.

I finished putting my fan shroud together last night. I've had these fans for a couple years, and they work fine. If I hook them up backward, they run backward. They are 1995 Mercedes C280 fans, hooked in parallel from the factory, with factory connections except where I cut the wires.


The wires end right at the edge of that picture.
I have a hot wire running from the battery cable on the starter, just for doing engine test runs, and test driving. I have a maintenance charger on the battery.

I put my fan shroud together last night, and tested the fans in reverse and forward, to see where and how the air moves, now that I have a proper shroud on it. It worked great. Water was running downhill, fire was hot, and the IRS still wants more than their share.

Rather than have a hot wire laying loose, I hooked the hot supply to the fan hot, and grounded the negative to run the fans. I used to have the ground wire under a screw on the fan shroud, and connect the hot wire to run them, but I accidentally shorted it to the frame once, and so that's why I switched the connection.

So I'm planning on wiring the fans with a relay and such, and from what I've seen on other fan systems, and one I have on my 59, the fans have constant power, and a switched ground to run. Right now, it's just hot to hot, and touch the wire to ground to run.

I walked out this morning to go to work, and heard my fans running. I went back behind the garage, and sure enough, my fans are running, with no ground! I took a quick video without touching it first.

http://youtu.be/GZDC21_oP48

I had to get to work, so I didn't have time to investigate.
What is going on here?

Click to expand...

I don't claim to be any kind of engineer but....
I'd say when you shorted the positive to the frame accidently some thing arced
and created a ground on a mounting bolt or something.
I would take the fans loose from the frame and isolate them and see if they still ran without the ground wire.

Good luck.

The ground wire has to be pinched, a screw ran through the insulation under the shroud somewhere or a bare spot in the insulation.

I assembled it on the bench when I took that first picture. The wires are tied up out of the way. I also ran it in reverse after screwing everything down, so that means I had power running straight to the ground wire, and if it was grounded, it would have shorted out. Then, it wasn't running when I left it. If the ground wire was grounded, it would've been running when I was watching it, right? I left it alone, and it just spontaneously started sometime in the night.
The only screws anyway, are 6 inches from the wires.
It's witchcraft.

Has to be getting a ground somewhere or it wouldn't run.

Toad

Something grounded it.

There is no way, unless it grounded inside the motor housing. The wires are double insulated, and you can see the full length of the wires in the picture above. I grabbed the ground wire while the fans were going, and moved it around to see if it was touching where it comes under the fan shroud, and it wasn't.
I checked it when I got home, hooked up power again, and it ran. I grounded the positive wire, and put power to the other, and they ran in reverse. Then I switched back and put the power to the forward wire, and nothing happened. I grounded the negative, and they ran again like normal.

It may be grounded inside the housing. Or, more exact, TO the housing. If the fans were designed to have the + side switched, putting the switch on the - might be the problem. It appears the fan is held in position by plastic, so there would be no way for ground to reach the housing except through the wiring? If that is the case, re-check all that wiring again.

Are these single or dual speed fans?

christcrusader13 said:

Are these single or dual speed fans?

Click to expand...

Mercedes might have had a variable speed controller on them.

Okay I just did some looking. Apparently, they went from 2-speed to variable speed, some time before '98, according to this thread.

http://www.peachparts.com/shopforum/tech-help/10142-1998-c280-temperature-running-higher.html

Ok...don't see any module or relays in the pics...

Only see the wires running from each motor to that connector...so going back to basics....Hot to each motor....ground to each motor they run......if both motors are running then it has to have a ground somewhere....that is feeding and or back feeding ground to the motors....
either internally in the motor to the shroud or somewhere in the wiring....something somewhere is grounded ....can't be anything else....if you didn't have this problem before you shorted that hot wire to ground...I'd be looking first for an internal grounding of the motor somewhere....not much else you can have.....

Ok i'll say this without showing the big picture a gazillion times [ddd

I think you might got your wires crossed all not righty

positive from one motor connected to the other motor's negative?

Another possibility is if you have 2 hots and there is a voltage dofference between them there will be a current flow from the high voltage hot to the low voltage hot
Say for example... your battery has 11 volts and your battery charger is putting out 13 volts... ther MIGHT be a current from 13 to 11. water runs downhill so speaking also does electricity

In case you didn't know... since electrons have a negative charge...
Electrictrons flow from negative to positive even though the schematics read from positive to negative

when you have a negative ground the entire body of the car becomes a capacitor with a buildup of 12 volts worth of electrons.
The electrons flow from your engine block through the starter up the red wire to the positive terminal of the battery.
Really they do.

When you hook batteries in parallell the battery with a slightly lesser charge...
the weak battery will over time always "siphon" juice from the better battery from negative to negative.

Diesel batteries are hooked in parallell but they also get routinely charged so the leakage is not an issue until the diesel gets parked for a length of time.

When I was wiring my garage my neighbor thought it would be adequate to attatch the ground plug to the common ground
I got into an arguement with him
The problem there is that while yes the white wire in your house IS ultimately grounded ...
When something is using electricity its from hot to common. there is a voltage drop accross the circuit...the voltage doesn"t dissappear. it drops by the amount the appliance is using, the rest goes down the common to ground.
so if your ground plug is wired to your common and somethign is running in another part of the house and you get wet while using a power tool... the residual electricity travelling from the other appliance through the common to ground is now going to try to ground through you from the ground plug before it gets to that water pipe
Only ground your outlets to the green wire and wire the green wire to a seperate ground other than the one the common is grounded to... preferably some distance from it

Killy_Killerton said:

I think you might got your wires crossed all not righty

Click to expand...

Thought the same thing when I saw the picture!

Beercan

In agreement with everything that's been said.

I am one of the few people that knows that current goes from positive to negative. The wiring of the two fans together is the factory plug, and I've never disconnected it. Both fans always turn together, the same direction. It is in engine test configuration, so there are no relays, no switches, no controllers, and just chassis ground.

I'm as puzzled as you all are. I've been doing DC wiring and projects since I was about 6 years old. One of my favorite Christmas presents when I was a kid was this 200 in 1 electronic project kit. http://www.educationaltoysplanet.co...90xH4FzL4EGyfWIha3NiSWboMe6srqJH1caAs-M8P8HAQ
I wired as many projects from that thing as I could find the time to do. Actually, I'd like to have another kit like that.
Another of my favorite gifts was a battery charger when I was about 8. (I still have it.) I was wiring everything I could find in a DC circuit. My mom caught me sticking wires in a outlet once, after that she "grounded" me from AC.
I made a crystal radio, even wound my own DC motor for a project when I was little.

I've worked for low-voltage wiring companies doing phone, security, and home automation. I did some time with a company doing stereos, power door lock, and alarm systems in cars. All of this is DC wiring, 12 to 24 volt.

I just don't see how it can be stationary when I walk away, and when I come back, it's grounded itself, and is running.
When I tried reversing polarity, it didn't short to ground, it just took off and ran backward, the way it should. I thought maybe someone would tell me about some kind of back-feeding what's-it effect that I've never heard of, and solve the mystery.

The only thing left, is that it somehow temporarily grounded itself inside one of the motor housings, and when I tried to reverse it, it burned that ground point of contact off, and stopped grounding. Now the world is back the way it should be.

Has it happened again?

Ok Sam.....

Sam_Fear said:

Has it happened again?

Click to expand...

since you're up........NO....it happened before...but when he disconnected the positive, electrons flowed and made a bridge between the capacitor and the motor winding and cause the motors to run in opposite directions....WITH NO WIRES CONNECTED.... we think it might be static electricity from the plastic fluid lines....so he drained the fluid, changed the oil and rotated the tires and BOB'S your uncle..... ....sorry....again...couldn't resist being a not so smart a$$...(by the way....Sorry BobW)...

just spewed coffee....

Hey Sarge, lay off the eggnog! You're getting light headed!

Wwwat yu's talkin bout...

Bamamav said:

Hey Sarge, lay off the eggnog! You're getting light headed!

Click to expand...

a widdle eggnok is gud for wht ails y a....