Voltage drop when the fan is on

SBSerpent · #1 (**permalink**) 07-17-2020, 11:09 PM

Without the fan on, the voltmeter is indicating around 14V. Fan kicks on and it drops to 12V or even lower when at idle or at a stop light. Amazing how much a drain the fan is on the charging system.

twobjshelbys · #2 (**permalink**) 07-18-2020, 05:06 AM

Yep. Mine did too. Power hungry fans and alternator right at the edge of capacity.. never had any issues.

Moritz55 · #3 (**permalink**) 07-18-2020, 06:58 AM

I agree .. Fans drop voltage and amperage quite a bit. I did find that my Alternator needed a GND cable added so that it performed better. I have a Powermaster 105amp (17294) alternator.. It's a 1 wire alternator which required 8gauge wire ground. The original install did not have a GND cable!

This made a huge difference under load... mine went from 14.2V at 900rpm down to 13.4V at my battery with Lights ON and Fans ON ... but still charging the battery!

May be wise to confirm you have a solid GND to chassis or block as insurance... just a thought.

cycleguy55 · #4 (**permalink**) 07-18-2020, 10:27 AM

Quote:

Originally Posted by SBSerpent

Without the fan on, the voltmeter is indicating around 14V. Fan kicks on and it drops to 12V or even lower when at idle or at a stop light. Amazing how much a drain the fan is on the charging system.

Running a 1G alternator? If you're not hung up on period correct look of 1G, switch it out for a Ford 3G alternator. Internal regulator and fans, higher capacity and widely available. Easy bolt-in swap with some minor re-wiring to eliminate the external regulator. Serpentine pulley is easily removed and replaced with V-belt pulley. Mine is a 130 amp rated unit that fits a 1995 Mustang V6 and can generate more amps at idle than my 1G alternator could generate at 2,000 RPM.

The only caution I would offer is the higher output at idle of the 3G may cause belt squeal if things aren't 100%. Some go to double pulleys, but I'm running a CVF Racing billet aluminum pulley - the aluminum seems to do a better job of grabbing the belt. I also run a turnbuckle type adjuster from CVF that allows for finer tuning of the belt tension than does the old slider and bolt style adjuster.

Alternator output curves:

Left to right: 1G, 2G and 3G alternators - avoid the 2G:

3G alternator - note V-belt pulley:

Wiring diagram - minor changes:

Check this out article out for all the details (and more photos): https://www.hotrod.com/articles/inst...r-older-fords/

SBSerpent · #5 (**permalink**) 07-18-2020, 02:38 PM

Quote:

Originally Posted by Moritz55

I agree .. Fans drop voltage and amperage quite a bit. I did find that my Alternator needed a GND cable added so that it performed better. I have a Powermaster 105amp (17294) alternator.. It's a 1 wire alternator which required 8gauge wire ground. The original install did not have a GND cable!

This made a huge difference under load... mine went from 14.2V at 900rpm down to 13.4V at my battery with Lights ON and Fans ON ... but still charging the battery!

May be wise to confirm you have a solid GND to chassis or block as insurance... just a thought.

Only two wires attached to my alternator - thick red one on the backside and a thinner red one with yellow stripe on a connector attached to the side. Doesn't appear to be any ground wire. How and where do I attach a ground wire?

Jerry Clayton · #6 (**permalink**) 07-19-2020, 07:47 AM

A short note of caution----------Fiberglass bodies, braided stainless steel hoses, painted engine/chassis parts----------they all creat possibilities of malfunctions---------no ground circuit thru painted, powercoated items or the fiberglass---------Stainless bolts and aluminum or iron parts will create an issue (don't remember what the term is but common in boats) and the stainless braided hoses turn into dangerous shorting circuits---

joyridin' · #7 (**permalink**) 07-19-2020, 08:09 AM

What size is the power wire you are using? Mine originally had a 10 or 12 gauge and I switched it to a 6 gauge. Made a world of difference. Now when the fan comes on, it doesn't drop like yours is doing now.

desgros@vtlink. · #8 (**permalink**) 07-19-2020, 08:14 AM

Great info! Wish I had known at least some of this when I owned a Lone Star years ago.

John
ERA #3010 Slabside 289 SB BRG

SBSerpent · #9 (**permalink**) 07-19-2020, 12:43 PM

Quote:

Originally Posted by joyridin'

What size is the power wire you are using? Mine originally had a 10 or 12 gauge and I switched it to a 6 gauge. Made a world of difference. Now when the fan comes on, it doesn't drop like yours is doing now.

Based on the wire diameter (with insulation) which is around 0.25", I'm guessing it is 6 guage.

avdcav · #10 (**permalink**) 07-19-2020, 02:34 PM

You should really spend some time re grounding everything with 4 gauge welding cable
All to the battery

Alt to batt
Alt to block
Engine to batt
Frame to batt

https://youtu.be/BQdQBesuJCs Watch this video
This is how it’s done .

I run fuel injection On relay
Moroso elec water pump On relay
Massive fan puller type On relay
Elec vacuum pump On relay
Elec fuel sump On relay

130 amp 3g alt
Never an issue and I idle at 850. Charges at 14:1 all day long

Moritz55 · #11 (**permalink**) 07-19-2020, 06:03 PM

Quote:

Originally Posted by SBSerpent

Only two wires attached to my alternator - thick red one on the backside and a thinner red one with yellow stripe on a connector attached to the side. Doesn't appear to be any ground wire. How and where do I attach a ground wire?

SBSerpent, the back half of the Alternator requires Grounding. There should be a threaded hole for a GND Screw... ~5/16" dia size...
If you can get a 1inch long machine screw, Washer, GND cable , Star Washer you are all set. Note put the Star Washer between the GND Cable and Back case of the Alternator. Then the Washer and Screw Head complete the sandwich.
The Front of the Alternator with the Belt/Pulley assembly is insulated from the back since Alternator cases are made of 2pieces.

Then run your cable (if 0.25" dia cable, it may be actually 8gauge which is good up to 6ft of length) to the chassis GND or the GND on the Solenoid. Also use a Star Washer between your Cable, Solenoid post/cable you are attaching it to...

Keep us posted on the results....
Good luck...

Gaz64 · #12 (**permalink**) 07-19-2020, 06:31 PM

Quote:

Originally Posted by Moritz55

SBSerpent, the back half of the Alternator requires Grounding. There should be a threaded hole for a GND Screw... ~5/16" dia size...
If you can get a 1inch long machine screw, Washer, GND cable , Star Washer you are all set. Note put the Star Washer between the GND Cable and Back case of the Alternator. Then the Washer and Screw Head complete the sandwich.
The Front of the Alternator with the Belt/Pulley assembly is insulated from the back since Alternator cases are made of 2pieces.

Then run your cable (if 0.25" dia cable, it may be actually 8gauge which is good up to 6ft of length) to the chassis GND or the GND on the Solenoid. Also use a Star Washer between your Cable, Solenoid post/cable you are attaching it to...

Keep us posted on the results....
Good luck...

Please explain, since the two case halves are bolted together when assembled. The rear case is grounded through the assembled through bolts.
Gary

SBSerpent · #13 (**permalink**) 07-19-2020, 07:14 PM

Quote:

Originally Posted by Moritz55

SBSerpent, the back half of the Alternator requires Grounding. There should be a threaded hole for a GND Screw... ~5/16" dia size...
If you can get a 1inch long machine screw, Washer, GND cable , Star Washer you are all set. Note put the Star Washer between the GND Cable and Back case of the Alternator. Then the Washer and Screw Head complete the sandwich.
The Front of the Alternator with the Belt/Pulley assembly is insulated from the back since Alternator cases are made of 2pieces.

Then run your cable (if 0.25" dia cable, it may be actually 8gauge which is good up to 6ft of length) to the chassis GND or the GND on the Solenoid. Also use a Star Washer between your Cable, Solenoid post/cable you are attaching it to...

Keep us posted on the results....
Good luck...

Can I ground to the engine block?

Gaz64 · #14 (**permalink**) 07-20-2020, 12:42 AM

Quote:

Originally Posted by SBSerpent

Can I ground to the engine block?

Both halves of the alternator case are already grounded to the engine block.
The large negative lead is already a good enough path to the battery, if it is good enough for starter motor current.

Moritz55 · #15 (**permalink**) 07-20-2020, 09:30 AM

Quote:

Originally Posted by SBSerpent

Can I ground to the engine block?

Yes... you can Ground to the engine block...
It must be clean(no oil/gaskets etc...) so it's a solid connection....

Just as a side note... My Chromed Powermaster Alternator was NOT grounded to the block...with my Roush engine there were Plastic Bushings between the Front mounting Case of the Alternator and engine block. So having a reliable solid ground is very worthwhile.

Ozzie Goat · #16 (**permalink**) 07-20-2020, 10:00 AM

I had the same drop in voltage with the fans, my heater switches too.

Grounding from the battery to the front chassis solved all my of irregularities
I'll add a G3 alternator to the to-do list.

bkozlow · #17 (**permalink**) 07-20-2020, 10:59 AM

Checkout mechman.comthey manufacture for a lot of the private label companies, call them and talk to them, tell them what you need and they tend to deliver just that. If you need a V-belt pulley let them know and it will come with that from them. Just make sure it is a G-3, You will need a larger main fuse for your system as these are HIGH output systems, at 1800 engine RPM mine puts out 174 amps, NO they are not cheap but I can run 2 16" fans with no trouble or major drop off of voltage.

Bill K

SBSerpent · #18 (**permalink**) 07-23-2020, 08:42 AM

My Powermaster alternator is also chromed. Do I need to file off the chromed finish around the area of the hole where the GND bolt screws into in order to ensure metal to metal continuity between alternator housing and the wire lug??
Or, will continuity exist through the lug/bolt head and the fact that the bolt is threaded into the alternator housing?

Do I need to use star washers or are regular washers ok?

Gaz64 · #19 (**permalink**) 07-23-2020, 06:29 PM

Quote:

Originally Posted by Ozzie Goat

I had the same drop in voltage with the fans, my heater switches too.

Grounding from the battery to the front chassis solved all my of irregularities
I'll add a G3 alternator to the to-do list.

This is where the largest amount of electrical issues exists, especially in fibreglass cars.

Gary

Moritz55 · #20 (**permalink**) 07-28-2020, 05:11 AM

Quote:

Originally Posted by SBSerpent

My Powermaster alternator is also chromed. Do I need to file off the chromed finish around the area of the hole where the GND bolt screws into in order to ensure metal to metal continuity between alternator housing and the wire lug??
Or, will continuity exist through the lug/bolt head and the fact that the bolt is threaded into the alternator housing?

Do I need to use star washers or are regular washers ok?

You always should use Star Washers between the GND cable and Alternator .. The Star Washer will help "Dig" into the case of the Alternator and the same holds true on the Block or Chassis attach side.
You use the Washer on the other side between the Bolt Head and GND cable. So sequence....
Bolt Head->Washer->Cable->StarWasher->Alternator

Good luck.....