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Old 05-21-2006, 04:28 PM
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Adding Fan Relays Didn't Help Maintain System Voltage

Well, I wired in two relays to run my electric fans and I can't tell any improvement in keeping my system voltage near 14 V when the fans cut on.

My alternator is wired:
- Bat (main output stud) to the Kwik Kit fuse panel
- #1 tab to fuse panel (from what I understand this is the field wire to a switched source that energizes the alternator)
- #2 tab jumpered to the Bat terminal on alternator (from what I understand this is the excitation/voltage sensing wire)

Relays power the fan from a junction box taking power from battery connection on starter solenoid through 4 ft length of 8 gauge wire.

My voltage readings with engine off:
- alternator Bat terminal, junction box, and battery all read 12.74 volts

My voltage readings with engine running:
- 1200 rpm, fans off: 14.2 at alternator, 14.0 at junction box
- 1200 rpm, fans on: 13.0 at alternator, 12.6 at junction box powering fans
- 600 rpm idle fans on, out of gear: 12.5-12.7 at alternator
- 500 rpm idle in gear, fans on, in gear: 12.3-12.5 V at alternator

The alternator doesn't seem to be responding to higher demands from the electrical system.

I might need to work some on improving my grounds, but this is no improvement over what was happening when the two fans were run directly from the fused connection in the fuse panel.

Do I possibly need to connect the #2 tab (which is now jumpered to the alternator output stud) to the junction box instead to sense the demand there?

Or is my alternator not working correctly (we just rebuilt it last month)?

John

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Old 05-21-2006, 05:23 PM
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Doc here,

Not knowing the nomenclature of the harness system you have, It's kinda hard to tell..

From what you wrote..

The Alternator output is going to the fuse panel..This is wrong..It should go directly to the Battery Stud on the solenoid, or to the Battery itself.

It sounds like you are charging the system first and the battery second..you want to reverse that..unless I'm reading that wrong (and I do that so well from time to time..it's that age thing...).

Also from what you wrote, The relays sound like you hooked them up properly, 8 gauge wire from a direct battery source to the Normally open contact, 8 gauge wire from the center-wiper to the fan motor(s), The coil power to a switch 12 volt source line, and ground to your sensing device or switch..

Your Alternator if putting out 14.4 under a "No Load " condition is correct..as you load the battery up, the more current consumed , the more voltage is dropped..(High Current=lower voltage, Low Current=high Voltage) 12.75 under load at low RPM is not unreasonable..and considered within the "Normal range" for A charging system..You are not going to see 14.4 under a full load going down the road with lights, fans, Ignition, ACC, all running..

If it goes below 12.5 , then I would suspect a problem, wire bonding or an under rated output alternator..But I'm not seeing it here..

You could improve it by better grounds, and switching the output to the battery source instead of the system first by a half a volt or so..but if it isn't dipping below 12.5 volts I'd call it good..

Doc
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Old 05-22-2006, 10:32 AM
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I guess the system improvement isn't evident by the voltage measurements, but the fans definitely are getting more voltage and run faster.

From what I read on the MadElectircal site, I expected the system voltage to stay closer to 14 V.
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Old 05-22-2006, 03:06 PM
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Quote:
Originally Posted by JohnTN
I guess the system improvement isn't evident by the voltage measurements, but the fans definitely are getting more voltage and run faster.

From what I read on the MadElectircal site, I expected the system voltage to stay closer to 14 V.

Doc here,

Naw, Under full load 12.5 is more like it..

14.4 is a no load condition, going down the freeway at high noon, with nothing on.

All the Vettes I have / tested run pretty close to the 12.5 figure while under a full load..but close to 14.4 sitting idling while taking readings at Idle..I always like to check voltage at certain points in the system.

Doc
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