Technical Electrical Question

[PbFut]

I have a set of spal fans connected per the manufacturer’s recommendation at the +block near the battery. When the fans are running the Amp meter on the dash shows a fairly strong draw to the charge side of the meter as though the battery is heavily charging. Turn on the AC or headlights and the meter moves closer to center. That seems incorrect to me. After some research it seems that the power connection for the fans to the electrical system should be at the bus near the voltage regulator at the same point the headlights are connected. Would this not be a more correct point of connection for indicating electrical component draw rather than a phantom battery charging? Does moving the fan connection to the bus close to the voltage regulator put too much draw on the 10 gauge wire feeding the bus? Am I totally overthinking this?

[68 C10 Driver]

On every vintage vehicle I have ever worked on, I have always added accessories that were never available to that specific vehicle on a new circuit that goes to a new fuse block that is hidden so you don't see it in car shows. The system was only designed for so much draw, and it is easily over-tasked with modern gadgets and accessories. For example, on a MGB, there are only 4 fuses protecting the wiring harness from catching fire or blowing fuses. The system was designed to operate a radio, wipers, headlamps, and brake lights and turn signals.

So having said that, i would set-up a new fuse block and wiring (preferably with relays) for high draw items.

This way you will never have to "butcher" the OEM wiring harness which usually opens the electrical system to other problems. I then wrap all of my harnesses, OEM and what I build, with black cloth harness tape for that finished vintage look. I have found that the vinyl electrical tape usually looks cheap (although it is correct for our trucks) and often does not hold-up over time and heat cycles.

[68 C10 Driver]

Here are a few photos showing how I installed an additional fuse block and wrapped my wiring. First photo shows the panel I installed behind the seat (relocating the fuel tank), under the dash wiring at the OEM fuse block, and wiring going to the speakers.

[PbFut]

The kit I have is from Champion and works very well and is protected by a inline 40a fuse at the positive connector block next to the batter. It all works fine. No hot wires or other issues. The question has to do with the amp meter. Connecting is this manner, confuses the amp meter into thinking there is a draw at the battery falsely indicating a heavy batter charge condition. I would like to avoid this meter error but concern that attaching fan relay at the location I believe would correct the meter might overwhelm the 10 guage curcuit at the voltage regulator harness bus. Wondering is anyone else is bothered by the incorrect amp meter reading on the dash and if they have done anything to correct?

[PbFut]

I really need some input on this. The bus connection in question is in the harness. I am not keen on opening this harness up unless no other option given it is original in extremely good condition.
This rather informative site provided some good info but I am not confident in my assumption that moving the fan connection to the bus will fix the amp meter reading. http://www.madelectrical.com/electrical-tech.shtml

[pjmoreland]

Originally Posted by PbFut

I have a set of spal fans connected per the manufacturer’s recommendation at the +block near the battery. When the fans are running the Amp meter on the dash shows a fairly strong draw to the charge side of the meter as though the battery is heavily charging. Turn on the AC or headlights and the meter moves closer to center. That seems incorrect to me. After some research it seems that the power connection for the fans to the electrical system should be at the bus near the voltage regulator at the same point the headlights are connected. Would this not be a more correct point of connection for indicating electrical component draw rather than a phantom battery charging? Does moving the fan connection to the bus close to the voltage regulator put too much draw on the 10 gauge wire feeding the bus? Am I totally overthinking this?

When the engine is running, the electrical system is powered by the alternator. Current is flowing down the 10 gauge wire from the alternator to the +block near the battery to power your fans. In my opinion, the thing to do is to increase the gauge of that wire. HO455 has a good write-up on this in his build thread, starting on post #467.
http://67-72chevytrucks.com/vboard/s...698377&page=19
Tying your fans into the electrical system closer to the alternator would make your battery gauge reading more accurate, although the gauge won't work right with heavier gauge wire installed. It is a challenge to get the stock ammeter "Battery" gauge to work right on electrical systems that have been modified to handle higher loads. Converting to a voltmeter is a common remedy.

[54blackhornet]

I have experience with amp gauges burning up vehicles built during the 50/60’s. Always wondered why GM continued with them for so long ?

[54blackhornet]

Can you tell me what the device is to the right of fuse box ?

[CanadianNascar]

Originally Posted by 54blackhornet

Can you tell me what the device is to the right of fuse box ?

The horn relay has a red, green, and black wire.
Red is 12vdc
Green goes to the horn
Black is the horn button

[kwmech]

No mention of which alternator you are running or what the output is.

[Steeveedee]

Originally Posted by 54blackhornet

I have experience with amp gauges burning up vehicles built during the 50/60’s. Always wondered why GM continued with them for so long ?

Because they are shunt wound and each side is fused. The Mopars that had full charging system current run through them (unfused, IIRC, maybe a circuit breaker?) were the culprits. I've seen many of those with just nasty burnt wires at the gauge.

[HO455]

Originally Posted by 54blackhornet

I have experience with amp gauges systems burning up vehicles built during the 50/60’s. Always wondered why GM continued with them for so long ?

The fires associated with amp guages are a result of the design of the amp guage as a system. Early systems and most aftermarket amp guages have the vehicle's positive lead from the battery routed through the firewall to one post of the guage and then out through the other post of the guage. From there the wire got routed back through the firewall to the main power connection point for the vehicle's power distribution.

As the vehicle would require 25 to 35 amps for operation the amp guage and wiring was sized for that. There was no fuse or other form of overcurrent protection on this part of the wiring harness. When some component failed (like the guage itself) it resulted in a direct short to the chassis. With wires capable of handling 25 to 35 amps. This short was no different than welding and often resulted in a fire.

The system in our trucks is completely different than those early systems. GM very cleverly designed a system that measures the amp draw over a specific sized wire and the that is shown on a remote indicator in the dash. Both end of the wires to the guage in the dash are protected by 5 amp fuses to protect the vehicle from any problems in the system. So none of the components are capable of handling more than 10 amps at most. The system as designed has a very low probability of causing a fire unless modified.

So in reality GM didn't continue with the same problematic early style amp guages that were used in the 1950's Advanced Design and Task Force truck. Some other manufacturers were much later in going away from them as were aftermarket guage manufacturers.

And to the OP's original question. Yes, you are correct in your deductions about how the system should be wired. Going back to the factory wiring splice near the original voltage regulator provides the optimum voltage sensing for the charging system.

To get your ampmeter to read more appropriately hooking the fan load to the system near the voltage regulator is key. The factory did this on trucks with the larger 63 amp alternators buy use of an add on harness that basically doubled the wire from the alternator to a insulated terminal identical to the one on all trucks near the battery it also had an additional wire to the voltage regulator. These posts were provided for owners to have a place to hook their high amperage loads up. And back in the day they were mostly used for VHF radio systems.

You could duplicate this additional harness on your truck to maintain its factory look.

Disclaimer time. I have only seen two of the factory high amperage harnesses. (One of which I salvaged from a truck in a wrecking yard.) Neither one was complete or unaltered. In addition I have never seen any wiring diagrams that show these additional harnesses. Somewhere here on the board there is a discussion about these harnesses.

[RichardJ]

>>When the fans are running the Amp meter on the dash shows a fairly strong draw to the charge side of the meter as though the battery is heavily charging.<<

>>Turn on the AC or headlights and the meter moves closer to center.<<

The Amp meter is a charge indicator. The alternators job is to charge the battery. A high charge rate indicates, the battery has been drawn down and the alternator is trying to replenish the battery and get it back to full charge. that's its job.

When the Amp meter says zero (or near zero), that means all is GOOD. The alternator has charged the battery back up and is still able to supply current to accessories such as ign.

When you start the engine, the starter draws 250 Amps. Your fans may each draw 16 Amps at start-up and drop to about 9A at rated speed. It takes time for the alternator to put this back into the battery.
You mentioned a voltage regulator. If you are talking about a 37 Amp alternator, that's the output at about 2000 rpm. At idle, maybe about 20 Amps max.
It takes time to charge a battery back up. The lower the charge rate, the longer the time.
Some get impatient and have to get a 200 Amp Alt.

You turned on the AC or headlights right after start-up? This increases the time to get the battery back to full charge and zero on the amp meter. I'm assuming here that at this point you turn the AC off and the Amp meter stays at the same reading.

The fan guys tell you to connect @ the battery. Vintage air says to connect their 30Amp circuit breaker @ the battery. All the headlight relay kits have you connect @ the battery.
See what I'm getting at?

[68 C10 Driver]

Originally Posted by 54blackhornet

Can you tell me what the device is to the right of fuse box ?

That is the linkage to the hydraulic clutch master cylinder.

[PbFut]

Originally Posted by RichardJ

>>When the fans are running the Amp meter on the dash shows a fairly strong draw to the charge side of the meter as though the battery is heavily charging.<<

>>Turn on the AC or headlights and the meter moves closer to center.<<

The Amp meter is a charge indicator. The alternators job is to charge the battery. A high charge rate indicates, the battery has been drawn down and the alternator is trying to replenish the battery and get it back to full charge. that's its job.

When the Amp meter says zero (or near zero), that means all is GOOD. The alternator has charged the battery back up and is still able to supply current to accessories such as ign.

When you start the engine, the starter draws 250 Amps. Your fans may each draw 16 Amps at start-up and drop to about 9A at rated speed. It takes time for the alternator to put this back into the battery.
You mentioned a voltage regulator. If you are talking about a 37 Amp alternator, that's the output at about 2000 rpm. At idle, maybe about 20 Amps max.
It takes time to charge a battery back up. The lower the charge rate, the longer the time.
Some get impatient and have to get a 200 Amp Alt.

You turned on the AC or headlights right after start-up? This increases the time to get the battery back to full charge and zero on the amp meter. I'm assuming here that at this point you turn the AC off and the Amp meter stays at the same reading.

The fan guys tell you to connect @ the battery. Vintage air says to connect their 30Amp circuit breaker @ the battery. All the headlight relay kits have you connect @ the battery.
See what I'm getting at?

Telling customers to connect at the Battery is convenient and safe for them relative to liability but it does not mean it is correct relative to the function of the Battery/Amp meter.
Understand that the Battery/Amp meter in our truck is not really an amp meter. It is a voltage difference meter. The meter is connected at two points in the harness on the positive side and 1 ground. The meter reads the voltage at the primary system splice in the harness very close to the voltage regulator. The second point the battery gauge is connected at the bus block next to the battery. The meter on or truck looks at those two points and indicates if there is a difference. Heavy draw at the splice lowers voltage at that point in the harness and the meter tips towards the D for discharge. If the Battery is charging and drawing more current than the rest of the truck at the splice, the gauge tips to the C side of center. That is why the meter on a unmodified system tips to C after startup while the battery recharges. As the battery completes its charge the amps needed reduce and the gauge moves to center as the two points the gauge is comparing balance. So any load you place at the Bus next to the battery completely F's up the intended function of the Battery meter. You want to measure only battery draw on system. Adding a device at the battery bus tricks the Battery Gauge to reading charge.
The biggest problem I find is that if you connect a high load device such as Spal Radiator fans to the harness splice next to the voltage regulator, the Battery guage will peg if the fans turn on without the alternator supplying energy to the splice. The fans literally pull more power than the entire rest of the truck.
Adding a RPM switch to the relay trigger circuit would protect the gauge by not letting the fans run unless the engine is running, but that is more expense and more complication just to keep the Battery meter working correctly.

[HO455]

Basically at this point you have exceeded the load capacity of the factory 37 amp charging system. Your ampmeter is doing what it was designed to.

You are currently at risk of having the system discharging more than it is charging. The end result of that is a dead battery. It good that you are aware of this condition and you understand why it's happening. Unfortunately the fix is going to require more expense and complexity. An alternator upgrade or having to remove the electric fans and return to a mechanical fan are the best options in my opinion. That is being said with a limited amount of information on your truck and how it is operated.

One low dollar to keep the fans (Or just one fan) off at idle is to have the the fan power controlled by a throttle pedal operated switch. (Like a T400 transmission kick down switch.) It was a pretty common method to control fans for drag racers back in the day.

[PbFut]

I got a Power Master 10DN alternator today. Fully aware it is a moderately powerfull alternater by moderen standards, it is an absolute Moose compared to original. For a very inexpensive price ~140 bucks all in, it came with a Individually tested card indicating 81 amps at idle, 98 at cruise and 110 at high end. Now I am fully aware pully size makes a difference as well. Already installed, I am getting a full 13v at the battery with fans, AC and lights on at idle with a very stable .02 volts fluctuation.
I've decided to add a second lead wire from the alternator through a fuse link to a new junction Block on the drivers side Rad support. My relays are in this location. I'll reroute the power lead from the battery port to the new block.
There are RPM switchs for pretty reasonable price. I can add one under the dash splicing into the tach signal lead. The relays coils are powered by a lead from the accessory pin on the fuse box. This turned off the fans while cranking the starter to preserve starter power. I can interrupt the lead with the RPM switch for anything under 400 RPM. That way the fans will not run if the morter is warm calling for fan and I am stopped with engine off listening to the radio or something. It will also protect the Battery meter from pinning in this state. Since I have everything needed except the RPM switch, I think this will be my best solution.
I can tell you I have learned a great deal the past two days researching the system design and why the battery meter acts the way it does. Thanks for all the replies.

[HO455]

Sounds good. How about some photos of the installation?

[HO455]

Originally Posted by 68 C10 Driver

Here are a few photos showing how I installed an additional fuse block and wrapped my wiring. First photo shows the panel I installed behind the seat (relocating the fuel tank), under the dash wiring at the OEM fuse block, and wiring going to the speakers.

Man! That is one clean truck.

[54blackhornet]

Thanks for the reply about the hydraulic clutch..