Voltage Drop – Lights and Electric Fan – Need Help

5211 Views 22 Replies 7 Participants Last post by sevenzeronova, Aug 22, 2012

nutcase

Discussion Starter · Aug 21, 2012 (Edited)

3

I have a 70 Nova with a 3 Wire 100 Amp PowerMaster Alternator. I have trunk mounted Moroso kit with an Optima Red Top Battery. The battery looks like 2 guage wire and it runs to a firewall mounted distribution block where the starter ties into. I am running MSD 6 with an HEI ignition, electric black magic electric fan (Draws about 15-20A). I put a fresh braided engine Grounding strap on as well. I am kinda of a noob when it comes to electrical on these cars and not sure how this car was wired, as I wasn’t the original owner.

At idle, my voltage is 14.2V. When I turn my lights on my voltage drops to 13.1V and when my electric fan turns on I drop to 12V. These are all gauge readings
I took so measurements at three different locations to try and figure out where the drop is taking place.
Before performing these measurements , I fully charged my battery with a Ctek 7002 charger. I charged battery on the recommend settings (snowflake) as Optimas are supposed to be charged at a slightly higher voltage then normal batteries.

It should also be noted that the voltages below did not change when reving the engine to a higher RPM. The car idles @ 1050 RPM's.

I also assume the pully on the car is of stock size and its a 3:1 Ratio but I am not 100% sure how big the crank Pulley should be. Based off my readings it looks like the alternator is doing just fine at idle.

Voltage Measure @ Battery:
14.4V Idle
13.77V lights + Idle
13.4V Electric Fan + lights + Idle

Voltage Measure @ Alternator:
14.67V Idle
14.67V lights + Idle
14.67V Electric Fan + lights + Idle

Voltage Measure @ Gauge:
14.2V Idle
13.1V lights + Idle
12V Electric Fan + lights + Idle

Voltage Measure @ Horn Relay:
14.36V Idle
13V lights + Idle
12.4V Electric Fan + lights + Idle

Someone please correct me if I am wrong but these readings are indicating my battery and Alternator are working within spec?
The drop is somewhere in between the horn relay and the gauge? Should I be concerned? If the battery is reading 13.4V @ idle with the lights and the fan on, does it really matter if the gauge is reading 12v?

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Burke

· #2 · Aug 21, 2012

It sounds like your problem is due to undersize wire. What size is your charge lead off the alternator, how long is it, and what does it connect to?

Yes your battery and alternator seem to be working fine.

Ashman101

· #3 · Aug 21, 2012

I have the same issue.
But it's never left me hanging with a dead battery.
I'm thinking the old school fuse box, can't handle the extra draw from all the new electronics.

642doorhardtop

· #4 · Aug 21, 2012

Burke sounds like hes onto something.

I dont even know if this is possible without looking at a schematic, or knowing your setup, but have you tried to test the resistance of the wires in question to see if an abnormally high ammount of resistance somewhere could be causing this? Circuits by nature have a certain amount of voltage drop it induces on current that increases with factors such as length, amount of connectors etc. Some resistance is normal, but 5ohms for exp example, in a 4' section of wire with 2 butt connectors is not acceptable.

nutcase

Discussion Starter · #5 · Aug 21, 2012

Burke said:
It sounds like your problem is due to undersize wire. What size is your charge lead off the alternator, how long is it, and what does it connect to?

Yes your battery and alternator seem to be working fine.

I am not sure the gauge or the length. Can you tell the guage of the wire from the pictures I provided? I assume your when you say charge wire you are reffering to the big red wire on the back of the alternator where I read the volatge?

If the Battery is getting 13.5 V all the time then is it really a problem? I was thinking the drop is happening at the gauge inside the car and its not going to effect the charge of the battery.

nutcase

Discussion Starter · #6 · Aug 21, 2012

642doorhardtop said:
Burke sounds like hes onto something.

I dont even know if this is possible without looking at a schematic, or knowing your setup, but have you tried to test the resistance of the wires in question to see if an abnormally high ammount of resistance somewhere could be causing this? Circuits by nature have a certain amount of voltage drop it induces on current that increases with factors such as length, amount of connectors etc. Some resistance is normal, but 5ohms for exp example, in a 4' section of wire with 2 butt connectors is not acceptable.

Which wire should i test?

642doorhardtop

· #7 · Aug 21, 2012

nutcase said:
Which wire should i test?

Well, Im not sure how you are wired up, but looking at a diagram for my 64, a hot lead goes from the battery directly to the horn relay. If you are measuring THAT wire at the horn relay, and it reads the 1V drop, I would suspect your wire. Check resistance of that wire (NO CURRENT...disconnect the wire from the car or you could hurt your meter on OHM setting) and see how much resistance the wire has. I believe you could use OHMS law to figure out the voltage drop if you plug the numbers in.

"Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points. Introducing the constant of proportionality, the resistance,[1] one arrives at the usual mathematical equation that describes this relationship:[2]"
.....from wikipedia

I=V/R (I (Amps) is equal to Volts divided by resistance)

You could test the resistance with OHMS in a dead circuit (no power) or probe with your lead (meter on volt setting), tracing from where you know you have good voltage, back down the circuit to where there is the low voltage.

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642doorhardtop

· #8 · Aug 21, 2012

Found this. If you have access to dial calipers you could get a good idea....

http://www.chromausa.com/blog/from-the-bench/how-to-determine-wire-gauge/

sevenzeronova

· #9 · Aug 21, 2012

The aftermarket connectors are color coded for most part,Ex..
yellow,blue,red,etc. Which will tell the min to max wire size it will hold. Looks like from the pictures to be 10 AWG.

nutcase

Discussion Starter · #10 · Aug 21, 2012

IS there a wiring diagram for 70 Nova? I am not sure how things are wired. Also, no one answered my question. IF the Alternator and battery are getting good voltage, does it matter if the horn relay and the gauge inside the car are getting voltage drops?

sevenzeronova

· #11 · Aug 21, 2012

Here ya go.

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642doorhardtop

· #12 · Aug 21, 2012

nutcase said:
IS there a wiring diagram for 70 Nova? I am not sure how things are wired. Also, no one answered my question. IF the Alternator and battery are getting good voltage, does it matter if the horn relay and the gauge inside the car are getting voltage drops?

Well like I said, it depends on how it was wired. I dont know why your horn relay are not getting full juice, especially if your testing from the lead straight to the battery. A whole volt in a wire that short seems funny. Are you sure you are testing the wire that comes off of the battery? Maybe it is your relay?

I guess, it depends on you. As long as nothing is shorting, or overheating, like a small gauge wire carrying too much current, then you should be fine. Maybe its just a dirty connection, or old corroded wire. In that case you should be ok. But I am hesitant to say its ok because I dont want you to write off a potentially dangerous situation. I say this because I had a short to ground in my bug once, under the dash...It took 10sec for smoke to start billowing out from under my dash, and a few more and the car would have caught fire. I have never run so fast to my garage to grab that 13mm wrench and rip the battery terminal off the positive!

And on that note, maybe you could put a battery cut off switch in there, just in case you ever had to kill the power quick...Its just a switch....

I hope I didnt confuse you with more info than you needed..Just want to make sure your on top of it:yes:

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nutcase

Discussion Starter · #13 · Aug 21, 2012 (Edited)

2

If you look at the trunk picture you will see the safety cut off switch so no worries there. But I don’t know how the wiring goes to that Horn relay. I know the wiring from the alternator and starter goes to that distribution block that I took a picture off. ITs mounted on the passage side bottom firewall. The horn relay is on the driver’s side next to the head light.

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642doorhardtop

· #14 · Aug 21, 2012

Well the distribution block, if its what Im thinking your talking about, looks like a starter solenoid, but not a factory one. Factory starter solenoids were mounted on the starter itself if I am not mistaken. That looks like a ford unit. I dont know how much of your wiring is stock, but looking at my diagram, the battery hot lead goes directly to the starter solenoid. Another lead comes from the positive of the battery, and terminates at the horn relay. Its a black wire. There is a thinner gauge wire (red one) that goes from that terminal that the battery powers, and into one of the plugs on the bulkhead that connect to the back of your fuse block. From there, the wire goes into a splice. From the splice it takes 4 different paths. One to the light switch, one to your ignition switch, one to the cigar lighter, and one back into the fuse block.

But your battery is in the trunk..not stock. DO you have a good idea of where everything routes? Or could you find it with a meter?

To find where wires lead, disconnect the battery to protect your meter, use a long jumper lead, and connect the lead to where you want to test.

Example if you were testing your wire from the turn signal switch to the rear turn signal at the bulb, I would connect a jumper wire to the rear light and a meter to the other end of the jumper. Then Id go and probe the switch with the other lead from the meter on continuity setting until you have a complete circuit, or something other than infinite resistance, which is an open circuit.

Does this make sense?

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Burke

· #15 · Aug 21, 2012

With a 100 amp alternator I would be useing 8 or 6 guage wire (depending on the length) for the charge leg. With the drop you have I would expect the battery life to be shortened. The reason the voltage looks good at the battery now is that you just charged it. The battery voltage will creep down some at the battery as it discharges due to the voltage drop not allowing a full charge.

Jim383

· #16 · Aug 22, 2012

Is the battery grounded to the trunk floor? Not having a frame to ground to may be a problem. Maybe a battery ground all the way back to the engine block would help,not just to the body sheetmetal.

nutcase

Discussion Starter · #17 · Aug 22, 2012

6

Jim383 said:
Is the battery grounded to the trunk floor? Not having a frame to ground to may be a problem. Maybe a battery ground all the way back to the engine block would help,not just to the body sheetmetal.

The Battery Ground is screwed to the trunk panel via.

I don’t see a ground going back up to the engine block.

I also took a look at the positive terminal coming from the battery and there is a large cable with a bolt that goes through the trunk panel.
Picture 2 shows the cable coming from the battery to the trunk floor. Picture three shows another red wire that’s connected to the same bolt from underneath. I assume that red wire goes underneath the care to the center connection on the distribution block mounted on the firewall.

I sanded where the cable goes to the trunk and the connection from underneath to ensure a good connection. The connection wasn’t bad but I did it anyway.

I am not sure if that positive wires running underneath the car is the right size guage?

I also tried measuring resistance across the distribution block:

The only reading I could get is when I measured between the right and center connectors. The Right connector is the starter, the middle I think is the positive wire running from the battery in picture 3. The resistance across the right and middle first went from 5 ohms quickly down to 3 then 2 then 1.5. So I am not sure what to make of that. Also, I should note, when touching the red and black lead and setting the meter to the lowest ohm setting, the meter drops from 1 ohm down to .5 ohms in a few secs and stays at .5 ohms. So it doesn’t zero out. I assume .5 ohms s = 0 ohms as I cannot calibrate the meter?

I also tried to measure resistance across the Horn relay as that was the spot where I saw the most voltage drop and it gave me about .7 ohm reading.

In the pic below there is a derale fan relay that kicks on when the thermo sensor reaches 180 degrees'. Under that is the Fan Relay.

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642doorhardtop

· #18 · Aug 22, 2012

Alright the first picture looks like an inline manual reset breaker. If it blows the tab pops out the side and you have to push it back in to reset it. Our rigs used to have those installed for the lift gates and they used to blow all the time. I am not sure why that is on the ground side, if that is the ground wires I am seeing. I dont see how that would help you, but maybe I am missing something.

The fourth picture where the little red wire is bolted to the body on a ring terminal, and then routes through the hole in the sheet metal, Id toss a grommet in there for insurance if that is a hot lead.

That brown distribution block is actually your starter solenoid I believe. The left larger diameter terminal powers various electrical components, and right lead kicks the starter over. It is activated by the small red wire in the middle. At least thats how my fords always worked.

Do you want to keep your current set up as it is and fix the charging issue, or what is your overall goal for the car?

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nutcase

Discussion Starter · #19 · Aug 22, 2012

642doorhardtop said:
Alright the first picture looks like an inline manual reset breaker. If it blows the tab pops out the side and you have to push it back in to reset it. Our rigs used to have those installed for the lift gates and they used to blow all the time. I am not sure why that is on the ground side, if that is the ground wires I am seeing. I dont see how that would help you, but maybe I am missing something.

The fourth picture where the little red wire is bolted to the body on a ring terminal, and then routes through the hole in the sheet metal, Id toss a grommet in there for insurance if that is a hot lead.

That brown distribution block is actually your starter solenoid I believe. The left larger diameter terminal powers various electrical components, and right lead kicks the starter over. It is activated by the small red wire in the middle. At least thats how my fords always worked.

Do you want to keep your current set up as it is and fix the charging issue, or what is your overall goal for the car?

Everything is working ok. I just want to fix the issue and not have to redo everything.

Philip

· #20 · Aug 22, 2012

First where is the wire connected that the alternator uses to sense system voltage?

Here are you readings at the alternator
Voltage Measure @ Alternator:
14.67V Idle
14.67V lights + Idle
14.67V Electric Fan + lights + Idle

If you connected the voltage sensing wire to the battery terminal on the alternator then the alternator is not seeing the load on the system, only its own output.

Second you need to run fine strand welding cable from the battery to the front of the car. Heavy strand cable will not carry the same load as fine strand.

If it were me both positive and negative would be run to the front using fine strand 2/0 welding cable minimum, 4/0 would be better.

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