That is a great way of wiring your fans! Thanks for posting that!
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That trick would work on the remote sense wire of the alternator but I don't think it will work on the excite/trigger wire. Regardless it's not going to work on a one wire alternator that self excites and has no remote sense.
One way to help determine why the DD gauge does not match the real voltage is to put your meter probe on the ground terminal of DD controller and put the other lead on a known good body ground (preferably away from the controller). If you're seeing anything other than 0V then you now know that there is a grounding issue somewhere in the harness. It's best to do this test while under heavy load conditions when the gauge is misreading.
I think there are (2) problems. First is them spal fans have to spin 30,000 RPM to achieve their “advertised” CFM-blade/motor design is weak compared to OEM fans, so there’s one reason why the inferior motor design has to pull crazy amperage to compensate-but hey, Spal does a good job with advertising so they must be great fans.
Second is imo whoever wired your DD volt gauge should have put the sensing wire ahead of all power drawing components-not just tap into a fuse panel IGN bussbar or whatever. You really need to have 1 central junction from which all of your devices pull power from and land that sense wire there too. This way, the gauge will read as fast as the alternators’ regulator reacts to changes in voltage fluctuations. As for soft start fan control harnesses using relays, they exist because I build them but a good DC Controls unit should be able to handle those Spal fans...even your DD controller should too...oftentimes the reliability of a fan controller is directly related to how well thought the installer made the process.
That's true but I would treat the constant power terminal of the DD gauge as if it was the voltage sense terminal and use a dedicated wire from the fuse block otherwise you do risk measuring the voltage drop of a wire that may be powering a high current device like the blower fan.
My reply might be a little late, but I had the exact same thing happen with my setup. I'm using a SPAL fan setup with a relay. I'd be running 14 volts and the minute I turn on the fan, it would drop down to 12 volts or a little below.
I found out my ground wire was way to small. I ran a 1/O awg wire from my - on my battery in my trunk, up to a grounding terminal which holds all my ground points for my components and then used the same size cable and grounded my motor to the chassis.
Now I have a solid 14 volts at all times.
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I am going to be buying this serpentine setup soon and I don't think they offer a smaller alternator pulley anyway: https://www.cvfracing.com/stealth-bl...ic-water-pump/
I would suggest you look elsewhere.....Yea nice folks to talk to.
Lets see.....I broke a engine block due to their instructions being backwards. The stuff just doesn't line up well either.