Thread: 302 Stroker??

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Originally Posted by firebird77clone

Could be temperature related. If the temp switch cuts out, the relay opens, and the fan looses ground, free wheels , generating a floating voltage

With the loss of the ground the circuit is open, even if the fan could act as a generator the output would go no where the circuit is open.

Originally Posted by pepi

With the loss of the ground the circuit is open, even if the fan could act as a generator the output would go no where the circuit is open.

No, a stray voltage can still be induced and backfed up the positive side, essentially out of phase even tho' it's not AC current. The fans could potentially pulse feed but I don't fully believe it's happening, This same basic effect happens when you run spark plug wires parrallel to each other. It was so prominent that on ford v8's of the 50's, 60's and 70's one wire on each side of the motor was intentionally placed wrong in the wire seperator to break the voltage spike and false fire the plug!

I was searching if someone here had this experience as I have read about it on one of the forums I frequent.

I was reading thru this again and noticed that you said that you "controlled the ground" with the relay. Did you mean that you run constant voltage to the motor and use the relay to close a grounding circuit of the fan motor?


The reason I ask that specificly is because most use the relay to break/make the voltage to the fan motor

Geez, all this fancy electronics, and I still have a cable drive Moroso tach on the shelf!!!!!! (Saving it for just the right project, I guess)....

Yep Dave--I got one of them also plus an original iron fuel injected corvette distributor to drive it with----

Originally Posted by jerry clayton

I was reading thru this again and noticed that you said that you "controlled the ground" with the relay. Did you mean that you run constant voltage to the motor and use the relay to close a grounding circuit of the fan motor?

The reason I ask that specificly is because most use the relay to break/make the voltage to the fan motor

Yes, that is correct Jerry. For the fans and also the wiper motor. I copied a Chevrolet Corvette and control the ground circuit to make / break the circuit. A friend has a vette that was having some electrical gremlins, he asked if I could help sort through them, and I learned that for the wipers at least they were controling the ground circuit to run them. I don't remember the year but maybe 67 or 68?? This was the year the cowl had a door over the wipers which had to open first then the wipers would start.

ANyhow, I copied it and carried it a step further. And no.. I am not a "conventional" sort of person.. always testing and trying things "just because I can"

Originally Posted by Dave Severson

Geez, all this fancy electronics, and I still have a cable drive Moroso tach on the shelf!!!!!! (Saving it for just the right project, I guess)....

Oh Sure! NOW you tell me!!!

OK---on the corvette, and others , wipers ar a completely different sort of device, especially since they continue to run to the park position after you turn them off---------


On an electric fan set up, that is an incorrect method of wiring, and the reason is because of the fans being able to induce some current into there feed wires since they are actively still hooked up----

You really need to wire it so the relay opens and closes the contacts for the live feed wire to the fan and control the circuit in the relay that closes that contact.

I understand that lots of situations will control the ground side of an circuit because the ampereage is lower, however, generally speaking, maintain solid , constant grounds to the chassis for the complete return of the circuit---

Originally Posted by 34_40

No, a stray voltage can still be induced and backfed up the positive side, essentially out of phase even tho' it's not AC current. The fans could potentially pulse feed but I don't fully believe it's happening, This same basic effect happens when you run spark plug wires parrallel to each other. It was so prominent that on ford v8's of the 50's, 60's and 70's one wire on each side of the motor was intentionally placed wrong in the wire seperator to break the voltage spike and false fire the plug!

I was searching if someone here had this experience as I have read about it on one of the forums I frequent.

Well, not to nit pick, but first of all electrons need a path pos too neg. or neg. too pos, no path no go, feed back does not skip over open air. The interruption to ground of the coil that energizes the relay contact opens, no path. Second the spark plug example you bring forth is a totally different circumstance. The plug wire has a high voltage field external to the wire, it rises and collapses as the plug fires, that induces voltage into a wire close to it, this is known as counter EMF all high voltage has that capability.

As to this fan thing being a viable voltage generator ........ Unlikely, it is not going to spin fast enough from the get go. Other items are in play such as . Most circuits in your car are wired in parallel so even if the fan became a power source it would not add voltage. One more and I am all done with this, the fan generator will need to have a greater potential. Greater voltage then the circuit it is wired on, if not it will be ignored by the circuit, the most it could do if it were electrically in the circuit would be a load.

Such as it is, you are or were looking for an intermittent ground. If the car was up on jacks, just sitting the motor out less weight the frame and body sit differently. Maybe it opened up a space,, that caught a little rust, now that you have taken the car out and spun it up a few times, everything in place it has fixed itself. That would not be the first time an electrical circuit got quirky in a machine or car that has sat unused, airplane systems are much worse when the are not flown regularly.

Originally Posted by jerry clayton

OK---
You really need to wire it so the relay opens and closes the contacts for the live feed wire to the fan and control the circuit in the relay that closes that contact.

I understand that lots of situations will control the ground side of an circuit because the ampereage is lower, however, generally speaking, maintain solid , constant grounds to the chassis for the complete return of the circuit---

The purpose of a relay is to control the big amps, it takes that load off the switch or sensor. I do not ever remember seeing relays wired after the load/motor whatever. The wiper parking can be controlled with a timed circuit, consisting of a cap and resistor, keeping the relay energized after turned off @ the switch.

I was going to write a dissertation of sorts but that will defeat what I wanted to achieve. The wiper connection on the corvette was to show that even the big 3 sometimes do things we may not usually see. They used electric/mechanical switches in line to control the wiper motor and this was all done on the ground circuit was all I was trying to say.

As I also said earlier, while I know it is possible to induce a stray voltage (and I never said it had to be 12 volts!) it could be induced and "act" out of phase! This would cause the gauges to go flukey! So as I said, I do not believe this to be the reality, I was searching for someone who had experienced this.

The example of the plug wire was only to show that it can happen even at a voltage high enough to jump a spark plug gap!

As far as my fan wires being "in-correct....?" Hmmm.. I'll agree it's unconventional... for a car!

And I'll say thanks to all for participating! I loved all the ideas and directions, if it happens again - I'll update the thread and see if anyone cares! ROFL..

Dakota Digital seems to think switch on the ground side is ok, too!!!!



The relay coil is what is activated to perform the “switching” action. The coil is
located between pins 85 and 86. When the relay coil is energized, pins 87 and 30 will be
connected. When the coil is off there will be a connection between pins 87a and 30.
There are two ways to energize the coil, switching power to the coil or switching ground
to the coil.
Most of Dakota Digitals products that require an external relay are ground
switching, meaning that the relay control goes to ground when activated. So for these
types of outputs one side of the relay coil needs to be connected to +12V power, and the
other side to the grounding output of the controller. Figure 2 shows how to connect a
single relay pack in this fashion. The relays in Figures 2-7 will supply +12V power to
the solenoid, or load, as long as the control output is grounded. This would be a good
application for fans, fuel pumps, and other motors.
The green fused +12V power wire should connect direct to the battery to provide
a good power source for the desired load. An appropriate gauge wire should also be used
for the +12V supply. The black “switched power” wire should also use an appropriate
sized wire to supply power to the load. The red and white coil connection of the relay
can be smaller gauge wires, around 22 AWG,since there is relatively low current draw.

Not meaning to confuse anyone anymore than they already are.

A switch is a switch, which side of the device it is attached to does not determine the amount of the load (amperage). The load (current draw) on the switch is the same regardless the side of the device it is attached to.

In house type wiring switches are attached before the devise as this arrangement will allow the switch to operate as a disconnect of the main power to the device, which is safer for the consumer. But remember older homes (pre- 50’s) did not have earth ground and the wiring was not polarized as it is today, thus switches in these older homes can be on either side of the devise, which presented a shock hazard that was later corrected by building codes.

Car voltage is much lower and normally does not present a shock hazard, consequently switches are often on either side of the device they are intended to control with no determent. When the switch is in the off position there is no load on the device regardless the side of the devise the switch is on, a circuit must be completed to establish a load.

This is not to say a switched devise can not make electrical noise in the off position, it can in the case of the DC fans being spun by other means (generator effect), regardless the side of the devise the switch is attached to, as noise can travel through ground as well as power. However, this type of noise normally has no ill effect on most analog circuits used in our older cars other than a little whining noise in our music. Digital devices are different and they require other means of protection, which in most cases is built in by the manufacturer.

I thought I'd share with you my birthday present to myself! I couldn't afford anything like this when I was a kid so I figured it's a bit of a luxury but what the hell!

Yes, Charlie! I'll be having ice cream right after supper!! (cake too!)

Happy Birthday, nice cake!