Battery/amp gauge

[PbFut]

I have installed a set of spal fans to 1972 GMC C25/2500 Per the instructions from Champion, they say to connect to the power source at the Positive terminal close to the battery. I have everything working relative to the fans and relay triggers to my satisfaction. Connecting in this manner confuses the loads read by the Battery/Amp meter giving a erroneous heavy charge condition when the fans are on. I moved the connection on a very temporary (what if) test, to alternator post. Without the alternator turning I did as brief as I could trigger to run the fans. It pinned the meter to correctly show a discharge, but obviously way too much. I disconnected and verified I had not popped any links or fuses. So it is clear I need to wire this circuit differently to correctly use of the Battery/Amp meter with the fans. I am just not sure of the correct procedure. Do I need to connect the fan power close to the Alternator with a shunt to the terminal by the battery??? If so, suggestion for best location to connect and how to shunt?
If I sound like I know what I am saying, I don't. If not its again because I really don't fully understand the mechanics of the wiring.
Thank you for the assistance

[ray_mcavoy]

Originally Posted by PbFut

I have installed a set of spal fans to 1972 GMC C25/2500 Per the instructions from Champion, they say to connect to the power source at the Positive terminal close to the battery. I have everything working relative to the fans and relay triggers to my satisfaction. Connecting in this manner confuses the loads read by the Battery/Amp meter giving a erroneous heavy charge condition when the fans are on. I moved the connection on a very temporary (what if) test, to alternator post. Without the alternator turning I did as brief as I could trigger to run the fans. It pinned the meter to correctly show a discharge, but obviously way too much. I disconnected and verified I had not popped any links or fuses. So it is clear I need to wire this circuit differently to correctly use of the Battery/Amp meter with the fans. I am just not sure of the correct procedure. Do I need to connect the fan power close to the Alternator with a shunt to the terminal by the battery??? If so, suggestion for best location to connect and how to shunt?
If I sound like I know what I am saying, I don't. If not its again because I really don't fully understand the mechanics of the wiring.
Thank you for the assistance

Yes, as you have discovered, any additional loads that are connected to the battery will cause the gauge to read incorrectly, showing a higher than normal charging condition.

The "ideal" place to connect additional loads would be the truck's main power distribution point. For 67-72, that's a factory multi-wire splice located within the wiring harness near the voltage regulator. Unfortunately, that factory splice doesn't lend itself to easily connecting additional loads. So connecting to the alternator output terminal like you did is the next best thing. The other alternative would be to replace that factory splice with a junction block or bus bar that would make additional connections easier. And if doing that, it would also be a good idea to run a heavier gauge wire from the alternator output stud to that junction to handle the increased load.

The fact that the meter pegged to the discharge side when you triggered the fans with the engine off can be considered normal. These gauges were designed to register current levels drawn by the stock electrical loads in these trucks ... those fans likely draw a lot more current than that.

However, with the engine running, power for the fans will be coming from the alternator (rather than the battery) so it shouldn't even register on the gauge (normal). Running the fans with the engine off (or an alternator failure) would be the only time they would be running off the battery and registering heavy discharge on the gauge. So unless you have the fans wired so they continue running after the engine is shut off, that shouldn't be an issue.

[dmjlambert]

Except in the case of front wheel drive cars, where the engine sits sideways in the engine compartment, I don't understand the benefit to convert the kinetic energy of the engine rotation to electric energy using an alternator, and then convert the electric energy back into rotation with an electric fan motor that sits pretty much right there in the same physical position where the fan blade would normally connect to the water pump shaft and thermal fan clutch. It seems inefficient, since there is energy loss with each type of energy conversion, and overly complicated, well, because it is.

[PbFut]

Originally Posted by dmjlambert

Except in the case of front wheel drive cars, where the engine sits sideways in the engine compartment, I don't understand the benefit to convert the kinetic energy of the engine rotation to electric energy using an alternator, and then convert the electric energy back into rotation with an electric fan motor that sits pretty much right there in the same physical position where the fan blade would normally connect to the water pump shaft and thermal fan clutch. It seems inefficient, since there is energy loss with each type of energy conversion, and overly complicated, well, because it is.

Because the fans turn off most of the time on my setup and use. A decoupled mechanical fan still pulls a load. A correctly set up a spal fan with shroud will pull a very sizable volume of air only when needed.

[PbFut]

Originally Posted by ray_mcavoy

Yes, as you have discovered, any additional loads that are connected to the battery will cause the gauge to read incorrectly, showing a higher than normal charging condition.

The "ideal" place to connect additional loads would be the truck's main power distribution point. For 67-72, that's a factory multi-wire splice located within the wiring harness near the voltage regulator. Unfortunately, that factory splice doesn't lend itself to easily connecting additional loads. So connecting to the alternator output terminal like you did is the next best thing. The other alternative would be to replace that factory splice with a junction block or bus bar that would make additional connections easier. And if doing that, it would also be a good idea to run a heavier gauge wire from the alternator output stud to that junction to handle the increased load.

The fact that the meter pegged to the discharge side when you triggered the fans with the engine off can be considered normal. These gauges were designed to register current levels drawn by the stock electrical loads in these trucks ... those fans likely draw a lot more current than that.

However, with the engine running, power for the fans will be coming from the alternator (rather than the battery) so it shouldn't even register on the gauge (normal). Running the fans with the engine off (or an alternator failure) would be the only time they would be running off the battery and registering heavy discharge on the gauge. So unless you have the fans wired so they continue running after the engine is shut off, that shouldn't be an issue.

Thank for detailed reply.
Given your reply, my thought would be to add a bus bar fed by the factory splice and increase the gauge for the jump between the factory splice and alternator. Protect the jump from splice to battery with a fuse at splice and leave fusible link at battery. The only way to protect battery meter is to turn off fans with a RPM switch. That's a lot if complicated wiring for a 50 year old truck. Maybe best to ignore the battery meter and use a volt meter at the battery and leave the fan power leads at the battery block to confirm a charge state. Rats, I really wanted to retain a factory appearance.
Any one know of a volt guage that replaces the amp for a 72?

[ray_mcavoy]

Originally Posted by PbFut

Thank for detailed reply.
Given your reply, my thought would be to add a bus bar fed by the factory splice and increase the gauge for the jump between the factory splice and alternator. Protect the jump from splice to battery with a fuse at splice and leave fusible link at battery. The only way to protect battery meter is to turn off fans with a RPM switch. That's a lot if complicated wiring for a 50 year old truck. Maybe best to ignore the battery meter and use a volt meter at the battery and leave the fan power leads at the battery block to confirm a charge state. Rats, I really wanted to retain a factory appearance.
Any one know of a volt guage that replaces the amp for a 72?

You're welcome.

Check with fellow member T-Bone ... I don't know if he's still doing it or not, but he used to convert 76-87 truck voltmeters to work in 67-72 clusters. I believe he was using the 67-72 face plate to maintain a fairly original appearance.