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Voltage drop between dash and engine

Aerohokie

SM 2020
PM 2017
Full Member
Joined
Apr 16, 2006
Messages
249
Location
Pensacola, FL
I have a 2004 Z71 1500. Recently I put in electric fans off of an 05 with a painless wiring controller. I also added a Carquest 145 amp alternator. The voltage readings on my obd2 port read 12.5V with fans on 100% in the cab and the voltage needle is at 12V. Using a multi-meter the battery is at 13.4V and the alternator outpu voltage is 13.6V. With headlights off, all numbers go up about 0.6V so 14.2 at alternator, 14 on battery, and 13.5 in the cab.

Unfortunately, my multimeter can only read 10 amps, so I don't have a measurement on amperage. The fans are grounded to the hood ground strap. I have disassembled, cleaned, and regrounded the battery ground on the radiator support, the 3 grounds under the driver door, and the engine block and hood grounds.

Does this sound like the alternator can't put out enough current? Or are there more grounds to check? The voltage needle sways a bit despite constant load, but the alternator passed both a bench test and installed test at advance auto. Any help and advice is appreciated.
 
The alternator will handle the fans..

You say they are grounded to the "hood ground strap".. If that's the case then you need to connect the fan ground directly to battery. The positive should go directly to the battery also or the J-Box where the alternator charge wire connects.
 
I can look at moving the ground. I followed painless wiring' instruction video installing on a 2004 Silverado. The power comes from the power cable under the fuse block trim on the driver side of the engine. I have an optima, so I should be able to get a clamp to go on the post and not mess with the battery cable. The ground is currently an eyelet and is the only thing grounded to the bolt. I have a fiberglass hood, so there is no hood ground strap.
 
Here's some data that I've copied and pasted from another web site on the 05 fans current draw: 

Both Fans on High Start up: 87A 
FLA (Running Amp): 38A

Both Fans Low Start up: 29A     
FLA (Running Amp): 9A

One Fan on Hi Start up: 55A   
FLA (Running Amp): 20A
 
Good info, moving up from 105 to 145 covers the 38 amp draw. I can see it dipping in voltage for the 87A start up. I am looking for someone with a good multimeter to read the amperage the alternator is putting out. The fans come on at 100% when the AC is turned on, so I am assuming the initial load is 87 amps, then drawing 38 from there.

I also need to load test some stuff. The issue mainly is headlights and fans. Any idea how much amperage all lights on draws?
 
I'm pretty sure all lights on should draw no more than 10-15 amps max! Interior Lights draw around 1 amp and headlights and fog lights together draw anywhere from 8-10 amps.  I'm not 100% sure if these are the exact numbers but they should be pretty close.
 
I'd say you're looking at close to 20 amps draw for headlights, taillights, fog lights, etc. combined.

OEM headlight bulbs are 65W each, I believe the fogs are 35.  For a pair of each operating that's 200W, or about 17 amps just in those lights.
 
I would strongly suggest running right to the battery as already been suggested.

Problem is that if you are grounding to the fire wall you are depending on the ground straps from the fire wall to the engine block and from the engine block to the battery. I suspect you are way over the capacity of the ground straps currently and the best way to fix that is to get your power and ground directly from the battery.

You MAY be in the process of burning up the wiring currently running from the firewall to the block and from the block to the battery....

Unless you are running 1/0 gauge wire or bigger from the battery to the block and from the block to the battery...

Rodney
 
It's been so long (probably nearly 10 years since I installed e-fans) I can't remember how I've run the ground side of my fans.  I ought to take a look.
 
I inspected all the grounds today. After removing the ground strap from the firewall to block, I found a lot of corrosion in it. It's the steel braided cable. I have some spare 4 gauge wire laying around, that should be ok right? I could loom it or use a reflective tape to wrap it. Or should I just order a new one?

*edit* I grounded the fans to the battery. Voltage is much more stable now. The voltage at the alternator varies between 13.75 and 14.0, the battery voltage 13.5 to 13.75. Obd2 voltage was 13.2 to 13.5. This was loaded, at idle, fans on full and all lights. The interior lights still flicker and the voltage needle is very dynamic. Where are the interior grounds that I should check? Could this also be because of the corrosion in the braided cable?
 
I hope you don't mind a suggestion, I've had a few issues with grounding Hi amp circuits so.

I would ground it straight to the frame or radiator support depending on where you mounted the controller. Keep the wire as short as you can. I have found grounding it to the body or engine can be an issue.
 
Yes the corrosion could be a problem... You can get similar ground straps at most auto parts stores...

Also if you hooked the positive for the fans to the cable that feeds the main fuse box from the battery like they did in the Painless video then IMO you should remove it from there and connect it to the red junction box where the alternator charge wire is connected to, I bet it will reach... Move it and I bet your you'll see less fluctuation in the voltage.

That's where I have mine hooked up to with zero voltage fluctuations on the voltage gauge... It drops a little when the fans come on but it doesn't jump around and my lights do not flicker.

I don't know why they did it that way but I would not put any more load on that positive feed from the battery to the main fuse box...

There's also a ground under the drivers door on the frame to body, and one toward the rear.. Just crawl around and look between the frame and body and you will see them..
 
Ok I tried 2 things, first I put the power for the fans on the power destroy box instead of the fuse block. No change.

Second I took some spare 4 gauge cable to go from the engine block strap to the battery. Once I got it on, the headlights seemed steady, but instrument back lighting and overhead lights still had a fluctuation. More interestingly, as I was disconnecting the ground strap to attach the cable, it sparked. Vehicle was off, battery connected. There must have been current going through it, but I don't have a problem with the battery dying. The longest it has sat is probably 4 days and it cranks right up.

I am at a real loss.
 
Which painless wiring kit did you use.
 
I've always had a bit of a flicker in my instrument panel when the fans come on, and see the voltage gauge needle push to the left as well.  Hasn't seemed to be a problem after about 10 years of running that way.

For what it's worth I'm also running fans out of an 05 truck but using a Nelson Performance harness controlled by the PCM for temp and tapped into the AC clutch control line for AC indication which affects fan operation with that harness.

In the past I've toyed with putting chokes (inductors) in the fan power lines - would also need to put power diodes in parallel with them.  I never got around to doing that - the electrical engineer in me never saw it as that much of an issue.  I'd surmised that I could probably get some toroid cores at Radio Shack along with some good-sized transformer wire and make some chokes for pretty cheap.
 
Where did you attach the brown wire 14
 

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The brown wire is tapped to the thick pink wire that comes down the steering column. So today it behaved much better. With the extra 4 ga ground on the firewall, voltage stayed closer to 13.8 with the fans on and 14.2 off. Headlights are still the big current draw. The fluctuations in cluster and dome lights are constant still.

Where are the interior grounds and where do the headlights ground?
 
I'm not sure what the big pink wire is, but as long as it is a switched ignition circuit that should be fine.

They are not very many of them.
 
Another question do you have a stock radio.
 
Aerohokie said:
and where do the headlights ground?

Starting in 03 they started switching the ground side of things instead of the positive side so your headlights are grounded through the relay that controls them.
 
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