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electric radiator fan question

Old 05-08-2018, 12:13 AM
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ronarndt
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Default electric radiator fan question

I just finished fixing a problem with my ammeter on my 68 convert. I thought everything was fine. Today after the car was driven about 5 minutes the ammeter showed a constant 10-15 amp discharge. I initially thought I had another bad wire, but realized the current draw happened when my electric radiator fan kicked in. I have the fan supplied with power from the terminal on the horn relay, which also is where the ammeter senses current draw, so I am getting a faulty reading on the ammeter. For those who have added an electric fan, where do you have the power wire connected? I'm running out of places on my fuse block- fuel pump, electric choke already connected on the spare terminals.
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Old 05-08-2018, 07:55 AM
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Keeping in mind that the fans do draw a lot of current, and it's possible your alt. isn't able to keep up with the demand, especially if it's the original one and you've added other electrical ...

But back to your question, mine were wired to a set of relays fed through an external fuse block to the starter lug. The relays were powered off the horn relay and controlled by the temp sensor.

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Old 05-08-2018, 08:18 AM
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The starter lug is the equivalent of the pos post of the battery. The horn relay is in between alternator and batt. You tap power there you are between the alt and the ammeter. At low engine rpm's, the alternator puts out less amps, so that ammeter can be all over the place.
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Old 05-08-2018, 08:46 AM
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Your ammeter is more than likely reading correctly. Do you have a stock 1968, or close to stock, low ~63 amp alternator?
I used to have my Mark-8 fan wired off a tap in a parallel loop from the alternator output to the starter lug. I had a capable alternator, but that 8-gauge loop in parallel with the stock 10-gauge lead from the horn relay to the starter lug would make the voltage at the starter lug seem higher than the voltage at the horn relay (hence the ammeter would indicate discharge) even though the voltage at the starter lug was actually satisfactory and actually positively maintaining the battery.

I ended up wiring the fan power supply from the starter lug so that the ammeter would properly indicate loading.

What alternator do you have?

If you have a stock alternator, then it's probably not maintaining adequate voltage to support running electric fans. Pretty big load and it'll eventually draw down your battery.

Last edited by carriljc; 05-08-2018 at 08:48 AM.
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Old 05-08-2018, 09:07 AM
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Starter lug for my fans also.
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Old 05-08-2018, 09:32 AM
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Both 68s that I've worked on had external regulated 42 amp alternators when stock, neither had A/C. One BBC and one SBC, one early one late 68. Definitely not capable of maintaining battery voltage with electric fan. T
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Old 05-08-2018, 10:42 AM
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Originally Posted by ronarndt View Post
I just finished fixing a problem with my ammeter on my 68 convert. I thought everything was fine. Today after the car was driven about 5 minutes the ammeter showed a constant 10-15 amp discharge. I initially thought I had another bad wire, but realized the current draw happened when my electric radiator fan kicked in. I have the fan supplied with power from the terminal on the horn relay, which also is where the ammeter senses current draw, so I am getting a faulty reading on the ammeter. For those who have added an electric fan, where do you have the power wire connected? I'm running out of places on my fuse block- fuel pump, electric choke already connected on the spare terminals.
As mentioned above, Fans do draw a lot of power. I ran a separate distribution block under the hood directly from my battery to power the fan. No issues there. My fan controller will vary the speed and ramp up the amp draw so it's not an all at once hit.
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Old 05-08-2018, 12:27 PM
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Thanks to all for the advice. The electric fan was installed when I got the car about three years ago and the stock alternator and voltage regulator keep the battery charged OK. The PO had the fan wired to the fuse block without any kind of sensor or relay, so it ran all the time whenever the ignition key was on. I added a temperature sensor in the intake manifold that turned on the fan when coolant temp reached 180 degrees. I ran the power from the horn relay thru a circuit breaker and on-off relay that received signal from the temp sensor. Until a week ago my ammeter was not working. When I got it working is when I noticed the current draw. I believe I will also run a line to the starter lug so the current draw from the fan is not sensed as total current draw for the entire car by the ammeter.
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Old 05-08-2018, 01:15 PM
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You will still see the draw at the starter lug. I do with a 100 amp alternator in my 68 when the fan kicks. Mines a little wonky as it goes more positive probably because it's on wrong side of the meter but it does deflect. I wouldn't run it off the horn relay because you're pulling all the amps through the fusible links

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Old 05-09-2018, 12:46 AM
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Originally Posted by Rescue Rogers View Post
You will still see the draw at the starter lug. I do with a 100 amp alternator in my 68 when the fan kicks. Mines a little wonky as it goes more positive probably because it's on wrong side of the meter but it does deflect. I wouldn't run it off the horn relay because you're pulling all the amps through the fusible links




That may have contributed to the wiring melting the link in the first place.
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Old 05-09-2018, 12:12 PM
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It would seem to me that your ammeter is indicating properly. After all it is measuring the voltage drop from (essentially)the horn relay node and the starter node ---- therefore- with your fans connected to the starter lug, then the ammeter would see this as a load on that side of the ammeter....same as it would indicate if your battery was low....more amps being supplied "thataway"....


Originally Posted by Rescue Rogers View Post
You will still see the draw at the starter lug. I do with a 100 amp alternator in my 68 when the fan kicks. Mines a little wonky as it goes more positive probably because it's on wrong side of the meter but it does deflect. I wouldn't run it off the horn relay because you're pulling all the amps through the fusible links
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Old 05-09-2018, 12:55 PM
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Originally Posted by carriljc View Post
It would seem to me that your ammeter is indicating properly. After all it is measuring the voltage drop from (essentially)the horn relay node and the starter node ---- therefore- with your fans connected to the starter lug, then the ammeter would see this as a load on that side of the ammeter....same as it would indicate if your battery was low....more amps being supplied "thataway"....
Thanks
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Old 05-10-2018, 12:33 AM
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Well, I ran the power wire for the electric radiator fan relay directly to the positive terminal on the battery. I added a six circuit fuse block and used one circuit to connect from the battery to the relay. The ammeter still acts funny. I have my electric fuel pump wired to one of the extra connectors on the stock fuse block, so tomorrow I will also run the fuel pump power directly to the battery thru the new fuse block and see what happens. I may end up just ignoring the gauge, since the battery stays charged.
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Old 05-10-2018, 04:31 AM
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Put a volt meter in place of the amp gauge. T
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Old 05-10-2018, 07:45 AM
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The ONLY correct way to run the main power for the fans is through the relay control to the alt output stud on back of the alt....I use a heavy 8 ga wire, run directly over top to the front of engine where the fan control relay is setting, right on top of the fan shroud.....the fans are grounded to the frame on the main cross support, with heavy star washer and then with RTV to insulate against rust/corrosion, same with negative bat terminal to frame under the batt compartment....

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Old 05-10-2018, 06:13 PM
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Originally Posted by mrvette View Post
The ONLY correct way to run the main power for the fans is through the relay control to the alt output stud on back of the alt....I use a heavy 8 ga wire, run directly over top to the front of engine where the fan control relay is setting, right on top of the fan shroud.....the fans are grounded to the frame on the main cross support, with heavy star washer and then with RTV to insulate against rust/corrosion, same with negative bat terminal to frame under the batt compartment....


My 68 convert has the one-wire alternator with separate regulator. If I understand your suggestion, it would work on the newer alternators. However, I will check grounding to see if the fan is properly grounded to metal that is also grounded to the alternator.
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Old 05-10-2018, 06:17 PM
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Originally Posted by ronarndt View Post
Well, I ran the power wire for the electric radiator fan relay directly to the positive terminal on the battery. I added a six circuit fuse block and used one circuit to connect from the battery to the relay. The ammeter still acts funny. I have my electric fuel pump wired to one of the extra connectors on the stock fuse block, so tomorrow I will also run the fuel pump power directly to the battery thru the new fuse block and see what happens. I may end up just ignoring the gauge, since the battery stays charged.

Well, I re-wired the electric fuel pump, but not directly to the battery or it would run all the time. I used a spare terminal on the fuse block that is on only when the ignition is on. It did not change the ammeter reading much, but I got to use another space on my new fuse block.
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Old 05-10-2018, 07:08 PM
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As previously mentioned...you need an alternator that can produce more AMPS. Simple as that.

I do not care if it has an ammeter in it or a voltmeter. I guess that can be a matter of preference.

The reason being...the car was built with basically no major electrical components drawing current from the system. Basically the blower motor, wipers and possible power windows command the most on your car other than the actual starter when you go to start it....which is why those to components go dead when cranking the car..

When GM started adding more electrical stuff on the cars...the alternator got to where they can produce more amps so if these components are all on the alternator can keep up.

Running your fuel pump on the IGN terminal in your fuse block....may not be wise. You are aware that the IGN terminal in your fuse block is getting its power from the fuse beside it. SO...that means that the IGN terminal is already protected by a fuse...and the amount of draw on your fuel pump is begin shared with whatever is beside that terminal in the fuse panel.

When wiring in an electric fuel pump...depending on what teh manufacturer of that pump requires....making sure you are using the CORRECT GAUGE of wire that supplies power to that pump is critical for it to work effectively. When voltage drops occur in a wire or circuit...especially if it going to a motor...such as your fuel pump. Its efficiency is greatly reduced. One again..t all depends on the pump.

I know that all of the fuel pumps that are aftermarket that I have installed...I verified from the manufacturer that if they want a 10 gauge wire going to the motor for the power and ground...I do it. Regardless if it only draws 15 amps of power.

And as many may know how many of us change the ground wire that goes to the blower motor and increase its size due to is was actually smaller in gauge than the power wire going to it from the factory to help it out.

Just saying.

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Old 05-11-2018, 04:01 PM
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fuel pump and radiator fan connected to the two center lugs. IGN and ACCY

Originally Posted by DUB View Post
As previously mentioned...you need an alternator that can produce more AMPS. Simple as that.

When GM started adding more electrical stuff on the cars...the alternator got to where they can produce more amps so if these components are all on the alternator can keep up.

Running your fuel pump on the IGN terminal in your fuse block....may not be wise. You are aware that the IGN terminal in your fuse block is getting its power from the fuse beside it. SO...that means that the IGN terminal is already protected by a fuse...and the amount of draw on your fuel pump is begin shared with whatever is beside that terminal in the fuse panel.

When wiring in an electric fuel pump...depending on what teh manufacturer of that pump requires....making sure you are using the CORRECT GAUGE of wire.

DUB

DUB- thanks for your advice. I am using the ACC lug on the fuse block to supply power to the relay for the electric fan (not the fan motor) thru a 16 ga wire. Power to the fan motor is from the battery + terminal thru a 14 ga wire, as recommended by the fan mfgr. A temperature sensor activates the relay and closes the 14 ga wire circuit when coolant reaches 180 degrees. I have the 14 ga power wire protected with an in-line 30 amp fuse on my fuse block. The motor draws 18 amps, according to my multi-meter.
I am using the IGN lug on the fuse block to supply power thru a mfg recommended 16 ga wire to my electric fuel pump. The advertised draw for the fuel pump is 4 amps. My multimeter shows 3.5 amps. I have an in-line 15 amp fuse on the 16 ga wire.


Both of these circuits needed to be on only when the key is in the on position and the extra lugs on the fuse block allowed easy connection without cutting wires.


I'm not certain just adding a larger capacity alternator will solve my problem. With the car running, with the fuel pump, electric fan and all of the other equipment running, the net current draw at the + terminal on the battery is always charging, running 1-3 amps. It is discharging momentarily, of course, when the starter motor runs. The electric fan was installed when I got the car in 2015 and there has never been a problem with a dead battery. I merely added a relay so the fan did not run all the time. I also added the electric fuel pump and an 18 ga wire for the electric choke on the carb. Somehow the location where these add-on electrical devices tie into the stock wiring is tricking the ammeter and showing a discharge. I may just note where the normal reading is on the meter and not worry about it.
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Old 05-11-2018, 07:52 PM
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I understand now once more detailed information was given. We are good...or rather you are good as you know.

I test the system by turning everything that can possibly be turned on and used at once. The worst case scenario.

I guess you have a handle on it and know what to expect.

I can say it kinda does not make sense that IF the electric fan is coming on and your ammeter is showing a discharge...and it is drawing the amps like you wrote...that the gauge should not be doing that IF that is the only thing running other than power for the ignition.

What does the fan blower motor do to the ammeter when it comes on at high speed and the electric cooling fan is off? I am sure the amp draw for this motor is less that the cooling fan motor...but something to check and see for the heck of it.

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