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Discussion Starter #1
I just installed a black magic electric fan (Draws about 15-20A) and I had to upgrade my alternator. I got a powermaster 100A alternator. It puts out 75A at idle. My voltage readings are 14.2V when car is idling no headlights or electric fan. When the fan kicks in it drops to 13.4V. I need to add a vacuum pump because I have a very radical cam and need more vacuum to my brake booster. I am afraid I my not have enough to power it. It draws 10A initially to get pump going and shuts off once brake booster is full. (Can take 1-2 mins) I am running a brand new optima 34/78 1000cca battery, which I fully charged with a ctek 7002 AGM Multiphase battery charger, so I know everything is fully up to snuff.

Power Master makes a 140A alternator but it only puts out 10 extra Amps at idle and I would have to upgrade my wiring.

Can someone give me some guidance on what I should do?
 

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Where are you measuring your voltage at and what gauge wiring are you runing? Also, what guage charge wire are you running? 75 Amp should be enough. Also, what size crank and alt pulleys do you have? you may not be driving it fast enough. I'd look for other causes first.
 

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Where are you measuring your voltage at and what gauge wiring are you runing?

Measuring voltage at the autometer gauge. I think wire thickness is 10 gauge.

Also, what size crank and alt pulleys do you have?

Its a standard 3:1 pully.
Where is the guage connected? If you have a 100A altenator, an 8 gauge charge wire to your distribution block should be used. For really long runs, you should have a 6 guage. Undersized wiring will cause a voltage drop.

You need to measure your voltage at the altenator, then at the battery to see how much voltages are really dropping between the alt, battery and guage. Also, are you running a 1 wire altenator?

13.5 volts is still ok. Does it drop much lower when you turn on your head lights and heater?
 

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Discussion Starter #5
Where is the guage connected?
Not sure.

If you have a 100A altenator, an 8 gauge charge wire to your distribution block should be used. For really long runs, you should have a 6 guage. Undersized wiring will cause a voltage drop.

You need to measure your voltage at the alternator, then at the battery to see how much voltages are really dropping between the alt, battery and gauge. Also, are you running a 1 wire alternator?



I am running a 3 wire alt. I will take a picture of the solenoid and the alternator when I get a chance.
How do I measure voltage across the alt? I have a volt meter. I also am getting one of those equus timing lights that gives you a digital read out with battery and alternator voltage.

13.5 volts is still ok. Does it drop much lower when you turn on your head lights and heater?

You know, I havent taken it out at night with the new fan installed Next chance I get I will take it out and put lights on while fan is on.
I can tell you when I put my lights on without the fan going it drops to 13.5-13.75 normally.


I also want to mention battery is in the trunk. Moroso kit.
 

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It is hard to say how much voltage drop you have because of long runs unless your measure the length. With your voltmeter you can easily measure voltage at any location. Simply touch the red lead to the measuring location and touch the black to ground. You don't have to wait for nightfall to turn on your head lights. Since you have a 3 wire altenator (very good), measure your voltage at the heavy red wire at the voltage regulator as well. This is where your altenator is reading your voltage
 

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Also, Is your 100A altenator an internally regulated model? If so, did you wire the sense wire to the positive post of the altenator? Doing so defeats the remote sensing and will result in lower voltages at the end of your circuits.
 

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The pics look good. I see the sense wire going into the harness. Where does it connect?

You really need to measure the voltage at the altenator post as you turn things on. If it stays in the 14 volt range there, it is working fine. If it drops to 13.5 at idle and goes above 14 when you rev the engine, you are in good shape. This is considered normal operation for a 10si altenator. Let us know if this is not the case.

You will have voltage drops on every circuit. The higher the load, the greater the drop. The longer the runs, the greater the drop. The goal of remote sensing is to keep the overall system between 13.5 and 14.5 volts. There are things you can do to increase it. Strategic positioning of the sense wire and upping wire size will help.

IMO, your system is working correctly. The only thing I can see you need to do is upgrade your charge wire to 8 guage. You will need a 6 gauge if it is going back to the trunk.
 

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I think the sensing wire is going to the solinoid. What gauge is the sensing wire now?
Going to the Solenoid is usually good. Running it to the main distribution block is usually the best compromise location. I can't tell what what gauge your sense wire is. It looks like 12 or 14 guage which is good.
 

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Discussion Starter #12
Ok after further investigation my car at idle is 14.3V, When electric fan comes on it drops to 13.5V and once you put headlights on while fan is going it drops to 12.2V


Doesnt matter if you rev the engine voltage doesnt go up until lights or fan goes off.
 

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Ok after further investigation my car at idle is 14.3V, When electric fan comes on it drops to 13.5V and once you put headlights on while fan is going it drops to 12.2V


Doesnt matter if you rev the engine voltage doesnt go up until lights or fan goes off.
If you are measuring at the altenator post, I would say the altenator is having a hard time keeping up. Are you measuring at the altenator? If not, you'll have to factor voltage drop for the length and size of wiring you are using. A 100 amp altenator should keep up with your load. I'm running a 105 amp on mine with a Taurus fan and it keeps up just fine. It has plenty left over for the lights, stereo and A/C.

You should be measuring at the big red wire in this pic.

 

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Discussion Starter #14 (Edited)
Ok

I measured voltage at the alternator. Its 14.2V with Fan and lights both on at idle!

I measured the voltage at the battery and it was like 13.2v same as the volatage gauge in car.

I did notice the grounding wire from the engine block to the frame was a braded wire. I am going to replace that with a new one and sand block and frame and see what happends. (powder coated frame).

If the grounding wire doesnt work, what else should I do now that I know alternator is good?
 

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Ok

I measured voltage at the alternator. Its 14.2V with Fan and lights both on at idle!

I measured the voltage at the battery and it was like 13.2v same as the volatage gauge in car.

I did notice the grounding wire from the engine block to the frame was a braded wire. I am going to replace that with a new one and sand block and frame and see what happends. (powder coated frame).

If the grounding wire doesnt work, what else should I do now that I know alternator is good?
Were these voltages taken at idle? If so, they are good. They should stay at 14.2 volts at 2000 RPM engine speed.

Checking your grounds is a good first step. You can rule the gound out by running a temporary ground from the device to the battery.

Voltage drop is normal. It is driven by load, wire size and wire distance. You will need to take three measurements: Voltage at the altenator, battery and the end of circuit. Measure the voltage at the fan, battery, and altenator. Your altenator and battery should be the same or very close. The voltage at the fan will always be lower. What size wire are you running to the fan and how long is it. Make sure you include all the wire including the runs from the power source, through the relay and on to the fan.
 

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Discussion Starter #16
Were these voltages taken at idle? If so, they are good. They should stay at 14.2 volts at 2000 RPM engine speed.

Checking your grounds is a good first step. You can rule the gound out by running a temporary ground from the device to the battery.

Voltage drop is normal. It is driven by load, wire size and wire distance. You will need to take three measurements: Voltage at the altenator, battery and the end of circuit. Measure the voltage at the fan, battery, and altenator. Your altenator and battery should be the same or very close. The voltage at the fan will always be lower. What size wire are you running to the fan and how long is it. Make sure you include all the wire including the runs from the power source, through the relay and on to the fan.

Yes it was at idle.

Also I forgot to mention. Even with the fan off, If I just put my lights on the voltage dropped to 13.4V.
 

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I looked at your pics again and I'm guessing the battery is in the trunk. Not a problem, but it will impact the voltage readings at the battery. I looked at your soleniod again and I'm trying to deterim what the two red wires are. Do you know?

What size is the charge wire comming off the Altenator? It should be 8 guage if you have a 100 Amp altenator. You may need to open the wire loom and see where they go. I'm wondering if that is the factory charge wire and sense wire that go into the main harness and run to the left side of the core support. A pic of the horn relay area may help.

It looks like you have a 10 SI altenator. If so, 13.4 volts at idle is normal. Check it with the engine is at 2000 RPM. I'll bet it will be 14 Volts.

You have three cables on one the Solenoid. One should go to the battery, one to the starter, but were does the other one go?

Once we know the wire size, we can do a little more trouble shooting.
 

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I was just on the phone last week with Mark at MAD Electrical and spoke about his very same topic. It may be worth a call to him for some alternate wiring options that may help with your voltage problems.
 
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