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  1. #1
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    Electric fan load causing too much of a voltage drop

    I have an electrical issue that for the past few months I have just lived with, mostly because my car was apart doing the suspension. But now it's time to attack it.


    I have this alternator in the 180amp idle 1 wire version: https://www.qualitypowerauto.com/catalog.php?item=551

    I have this fan setup from C&R/SPAL: https://www.crracing.com/product/che...r-module-sb-bb

    I'm running 2 30amp fan relay kits w/fuses from Summit, I think the Perma-Cool kit.



    I have this electronic programmable duan fan controller: https://www.summitracing.com/parts/dak-pac-2750

    I'm running TEMco 4/0 welding wire for the alternator (w/500F heat shielding) and grounds. New Odyssey battery.

    My ground goes from my battery to the alternator bracket at the engine block, from the engine block to the front frame/radiator support, then from the rear of the body back to the battery (battery is in the trunk). All using 4/0 welding cable. On the way back from the battery, my positive wire goes to a giant 4 post 3/8" block on the firewall. Power goes straight from there to the fan relays via 8 gauge wire. The fan relays are grounded to the radiator support using sheet metal screws and as mentioned, the ground from the engine block is indeed grounded at the radiator support where it meets the front frame.

    Everything on my car works fantastic, but when these fans kick-on, the voltage on my DD gauge goes from just below 15 all the way down to 13, sometimes even 12.8/9 at a stoplight. Just 1 fan isn't that much of a problem, but when they are both on when the car is hot or with the Vintage A/C, the harness voltage just drops. I was thinking maybe the alternator wire was getting hot and adding resistance going along the valve cover/intake even in it's heat sheilding, but the fact of the matter is that it happens when on a cold start if I switch the A/C on to turn on both fans.

    Any idea where to start? Everything is new and I thought sized appropriately.

    Thanks!
    http://www.TheFOAT.com/92GTA
    1969 Pontiac Firebird
    w/BP 461ci stroker kit, 670 heads & XE274H cam. Primer black w/black interior.
    1992 Pontiac Trans Am GTA w/SLP Performance Package. Dark Jade Grey Metallic, grey leather, T-Tops.


  2. #2
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    I would start by measuring the voltage right at the output of the alternator with a multimeter. Put the ground lead of the meter right on the alternator and positive lead right at the output post of the alternator. This will help determine if the alternator is at fault or if it's a problem with the wiring. If the voltage stays around 14V while the DD gauge indicates something much lower then it's most likely a problem with the wiring. One of the disadvantages of a one wire alternator is that it can't compensate for voltage drop across the wire that goes from the alternator to the main distribution point. But if the meter and gauge both drop in voltage then you may need a bigger alternator.

  3. #3
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    Alright, I'll check that first.

    I put in a call to the alternator company and explained what I was seeing and they over and over again reassured me that because of how theirs is made that 1 wire or not wouldn't make a difference. I sure couldn't imagine needing a larger alternator, that beast is rated for 320amp max and 180amp at idle and cost me $518.

    I did make a measurement of the loss in the wire going from the alternator to the battery in the trunk (25ft) plus from the battery to the distribution point (22ft) and I was shocked that it was only 1/10 of a volt. Did that multiple times just to be sure. So the voltage loss from the alternator to the distribution block is so negligible I can't imagine that being it.
    http://www.TheFOAT.com/92GTA
    1969 Pontiac Firebird
    w/BP 461ci stroker kit, 670 heads & XE274H cam. Primer black w/black interior.
    1992 Pontiac Trans Am GTA w/SLP Performance Package. Dark Jade Grey Metallic, grey leather, T-Tops.

  4. #4
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    Does the reading on the volt meter drop momentarily when the fans come on or does it drop and stay low as long as the fans are running?
    Donny

    Support your local hot rod shop!

  5. #5
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    The wire gauges you listed does seem more than enough for those components. I guess I kind of misspoke as I don't think you need a bigger alternator to power all your accessories, I only meant that you might need a bigger alternator if the meter and gauge don't match which would indicate that the alternator is not keeping up with the power demands of the system as it currently sits.

    Bad grounds and bad terminal connections can also cause power loss. They might appear okay when there is no load but under heavy load even a few ohms of resistance can cause a significant voltage drop. There are tests you can do to find these hot spots but I would start with the meter voltage test first to determine we are going down the right road.

  6. #6
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    Quote Originally Posted by dontlifttoshift View Post
    Does the reading on the volt meter drop momentarily when the fans come on or does it drop and stay low as long as the fans are running?
    It goes down and stays down until the fans go off.
    http://www.TheFOAT.com/92GTA
    1969 Pontiac Firebird
    w/BP 461ci stroker kit, 670 heads & XE274H cam. Primer black w/black interior.
    1992 Pontiac Trans Am GTA w/SLP Performance Package. Dark Jade Grey Metallic, grey leather, T-Tops.

  7. #7
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    Does the voltage come up after leaving a stop light and while driving down the road ?.

    I know the company said it puts out 180A at idle but is it spinning fast enough at the unknown idle speed ?

    Another thing I notice is hardly any alternator company includes a cold and/or hot output specification. An ice cold alternator will put out more power than one that is heated up to 200 degree's. Maybe they are rating theirs at a cold temperature ?. On some old Lestek alternators I used to put on customer's cars as well as my own, they specified the output ratings at a 200 degree alternator case temperature.

    After the car has been sitting a while with the engine off, what is the battery voltage ?.

    Jim

  8. #8
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    Quote Originally Posted by Jim Streib View Post
    Does the voltage come up after leaving a stop light and while driving down the road ?.

    I know the company said it puts out 180A at idle but is it spinning fast enough at the unknown idle speed ?

    Another thing I notice is hardly any alternator company includes a cold and/or hot output specification. An ice cold alternator will put out more power than one that is heated up to 200 degree's. Maybe they are rating theirs at a cold temperature ?. On some old Lestek alternators I used to put on customer's cars as well as my own, they specified the output ratings at a 200 degree alternator case temperature.

    After the car has been sitting a while with the engine off, what is the battery voltage ?.

    Jim
    No, voltage stays pretty steady. Maybe goes up 0.10v from a stop sometimes. My idle is about 900rpm because of my cam so it's not crazy low like 650rpm which helps I'm sure.

    Haven't measured the voltage at the battery in a while, I'll check that and post it when I check the voltage at the alternator with the fans on.

    As I mentioned, even when the car is on a cold start it does it if I turn both fans on. Same as if the engine is heat soaked.

    Thanks
    http://www.TheFOAT.com/92GTA
    1969 Pontiac Firebird
    w/BP 461ci stroker kit, 670 heads & XE274H cam. Primer black w/black interior.
    1992 Pontiac Trans Am GTA w/SLP Performance Package. Dark Jade Grey Metallic, grey leather, T-Tops.

  9. #9
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    Here are some test results. I just got back into town and have to leave tomorrow again for work so I can't do more until over the weekend.

    Taken before a drive:
    13.45v at the solenoid and ground in the trunk. 13.44 at the alternator.

    Taken after a drive, engine still running of course:
    14.3v at the alternator with the engine heat soaked after a 10-mile city drive and both fans on.

    Taken after the engine was shut off but battery cut-off switch still set to on:
    13.70v at the solenoid and ground in the trunk. 13.70v at the alternator.


    While taking that 14.3v reading at the alternator the Dakota Digital dash was clearly showing 13v spot on the money. So something is not right. Maybe the gauge cluster's ground is in question now since that seems to swing from like 14.8/9 to sometimes 12.8/9 depending if the fans are on. I didn't install the gauges, previous owner did, so I have no idea where they are grounded to but I was planning on replacing the cluster in the coming months anyway to ditch the silver face/blue lights for the black face/red lights. I'm sure it doesn't help that the DD cluster is getting power from the factory fuse block/harness and the alternator/fans are running off of brand new wiring. I guess the issue could be in the old harness too.

    That explains why my lights never dim or anything as if the alternator really was putting out a low voltage. Although my LED headlights do sometimes VERY quickly flicker for a nanosecond when the 2nd fan kicks on.

    It seems to me the next step is to get a reading at the positive terminal block on my firewall with the engine heat soaked and fans running to get a clear picture of the voltage the fans are seeing where they are drawing their power.

    Thoughts?
    http://www.TheFOAT.com/92GTA
    1969 Pontiac Firebird
    w/BP 461ci stroker kit, 670 heads & XE274H cam. Primer black w/black interior.
    1992 Pontiac Trans Am GTA w/SLP Performance Package. Dark Jade Grey Metallic, grey leather, T-Tops.

  10. #10
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    Using that fan controller, do both come on with a soft start or are they both on/off? I had a similar issue with my old C5 style 145 amp alternator and a size 8 feed wire. Voltage would start off at 14.0 and drop down to 12.5 with both fans on (entropy fans are big power hogs) and everything else on. I switched to a 170 amp Holley alternator (along with a new drive setup on my LS) and added a 4 AWG feed wire. Now I am 14.5v at startup and 14.0v with everything going. It sounds like you wiring is good enough, I would be suspect of the alternator. Have you thought about swapping in another one/type? I really like the newer Holley alternator, it is 170 amps but puts out around 100 amps at idle. Between those and the Mechman style that Vintage Air uses on their front runner kit I think they are pretty nice pieces.

    The DD series gauges gets the voltage reading from the ignition power feed wire on the control panel. I would start there and find out what source is supplying that power.
    Chris
    1968 Chevy Camaro SS
    LS3/T56 Ridetech suspension


  11. #11
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    I also was seeing my DD volt meter jump a little and did a few basic tests. I was fearful the alternator wasn't charging the battery.

    I Put everything on, Lights, ac, hot engine to trigger the fans, blinkers, radio, wipers then put a multimeter at the alternator stud it should support all that with no hiccups in my case it was a 13.6v with no fluctuation . Also with everything on i checked the battery and was seeing 13.06v again with no fluctuation. I'm still not sure why the gauge shows one value and the alternator and battery are functioning normally. I don't have high spikes i'm using a DCC fan controller and a vaporworx pump controller.

    Nick
    ________________
    Nick S.
    Gold/Gray 1967 Camaro

  12. #12
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    Quote Originally Posted by 130fe View Post
    Using that fan controller, do both come on with a soft start or are they both on/off? I had a similar issue with my old C5 style 145 amp alternator and a size 8 feed wire. Voltage would start off at 14.0 and drop down to 12.5 with both fans on (entropy fans are big power hogs) and everything else on. I switched to a 170 amp Holley alternator (along with a new drive setup on my LS) and added a 4 AWG feed wire. Now I am 14.5v at startup and 14.0v with everything going. It sounds like you wiring is good enough, I would be suspect of the alternator. Have you thought about swapping in another one/type? I really like the newer Holley alternator, it is 170 amps but puts out around 100 amps at idle. Between those and the Mechman style that Vintage Air uses on their front runner kit I think they are pretty nice pieces.

    The DD series gauges gets the voltage reading from the ignition power feed wire on the control panel. I would start there and find out what source is supplying that power.
    The DD fan controller hard starts one at a certain temp, then hard starts the 2nd at yet another temp. I don't beleive it can do soft starts of the fans.

    After spending $580 on this billet mega amp alternator I'm not really interested in switching. Thank tho.

    - - - Updated - - -

    Quote Originally Posted by nicks67camaro View Post
    I also was seeing my DD volt meter jump a little and did a few basic tests. I was fearful the alternator wasn't charging the battery.

    I Put everything on, Lights, ac, hot engine to trigger the fans, blinkers, radio, wipers then put a multimeter at the alternator stud it should support all that with no hiccups in my case it was a 13.6v with no fluctuation . Also with everything on i checked the battery and was seeing 13.06v again with no fluctuation. I'm still not sure why the gauge shows one value and the alternator and battery are functioning normally. I don't have high spikes i'm using a DCC fan controller and a vaporworx pump controller.

    Nick
    As mentioned by 130fe above, it looks like I need to check the ignition power source says that's where the cluster gets it's power from. Could also be the power to the VHX box too maybe.
    http://www.TheFOAT.com/92GTA
    1969 Pontiac Firebird
    w/BP 461ci stroker kit, 670 heads & XE274H cam. Primer black w/black interior.
    1992 Pontiac Trans Am GTA w/SLP Performance Package. Dark Jade Grey Metallic, grey leather, T-Tops.

  13. #13
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    Quote Originally Posted by anguilla1980 View Post
    The DD fan controller hard starts one at a certain temp, then hard starts the 2nd at yet another temp. I don't beleive it can do soft starts of the fans.

    After spending $580 on this billet mega amp alternator I'm not really interested in switching. Thank tho.

    - - - Updated - - -



    As mentioned by 130fe above, it looks like I need to check the ignition power source says that's where the cluster gets it's power from. Could also be the power to the VHX box too maybe.
    You can’t get a soft start using relays.

    Don
    1969 Camaro - LSA 6L90E AME sub/IRS
    1957 Buick Caballero - huge project
    1959 El Camino - Ironworks frame
    1969 Mustang Sportsroof
    1956 Cameo - full C5 suspension/drivetrain

  14. #14
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    Quote Originally Posted by dhutton View Post
    You can’t get a soft start using relays.

    Don
    That explains it then lol. Even without relays tho and doing something else, I don't think the DD fan controller support it. Perhaps when I switch over to Holley EFI early next year. I'm pretty sure the fans are the right type for it.
    http://www.TheFOAT.com/92GTA
    1969 Pontiac Firebird
    w/BP 461ci stroker kit, 670 heads & XE274H cam. Primer black w/black interior.
    1992 Pontiac Trans Am GTA w/SLP Performance Package. Dark Jade Grey Metallic, grey leather, T-Tops.

  15. #15
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    I would consider installing a smaller diameter alternator pulley to spin the alternator a little faster. I had a voltage drop issue at idle and a smaller pulley corrected that. The fan current draw just exaggerates the problem.
    Steve Hayes
    "Dust Off"
    68 Camaro

    Speed has never killed anyone. Suddenly becoming stationary, that's what gets you!
    "Jeremy Clarkson"

  16. #16
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    That's a thought but I had one on my previous alternator and it did the same thing. Like I said, my engine idles at 900rpm and when RPM goes up, the voltage doesn't change but like 0.10v.

    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/
    http://www.TheFOAT.com/92GTA
    1969 Pontiac Firebird
    w/BP 461ci stroker kit, 670 heads & XE274H cam. Primer black w/black interior.
    1992 Pontiac Trans Am GTA w/SLP Performance Package. Dark Jade Grey Metallic, grey leather, T-Tops.

  17. #17
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    Quote Originally Posted by dhutton View Post
    You canít get a soft start using relays.

    Don
    What if he wired in a 3rd one like gm did on the 4th gens? Then low kicks both fans on at 6v and high both get 12? Would that lower that initial hit?

    Or scrap it and get a DCC controller. Name:  fan_schematic_1995_BOTTOM.jpeg
Views: 155
Size:  34.9 KB
    Scott from NJ.

    Vent Windows Forever! ... My junk, featuring the Red Dragon ... NastyZ28 ... NJ Camaros & Firebirds

    Feather-light suspension, Konis just couldn't hold
    I'm so glad I took a look inside your showroom doors

  18. #18
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    Here's an old trick for your alternator.


    Put a diode in series at the alternator on the excite/trigger wire. What the diode does is drops the voltage by about .6v. The alternator is tricked into working harder to compensate for the ~1/2V difference it is seeing. Might help you a lot with the voltages your are seeing.

    We use to do it all the time back in the car stereo days....

    Richard

  19. #19
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    Quote Originally Posted by Richard454 View Post
    Here's an old trick for your alternator.


    Put a diode in series at the alternator on the excite/trigger wire. What the diode does is drops the voltage by about .6v. The alternator is tricked into working harder to compensate for the ~1/2V difference it is seeing. Might help you a lot with the voltages your are seeing.

    We use to do it all the time back in the car stereo days....

    Richard

    Hmmm, that sounds pretty clever.

    I need to sort out why the gauge is showing different from the alt output and once I do, maybe that's something to consider. Thanks!
    http://www.TheFOAT.com/92GTA
    1969 Pontiac Firebird
    w/BP 461ci stroker kit, 670 heads & XE274H cam. Primer black w/black interior.
    1992 Pontiac Trans Am GTA w/SLP Performance Package. Dark Jade Grey Metallic, grey leather, T-Tops.

  20. #20
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    Quote Originally Posted by BonzoHansen View Post
    What if he wired in a 3rd one like gm did on the 4th gens? Then low kicks both fans on at 6v and high both get 12? Would that lower that initial hit?

    Or scrap it and get a DCC controller. Name:  fan_schematic_1995_BOTTOM.jpeg
Views: 155
Size:  34.9 KB
    Either would work but the first method really isn’t a true soft start. Much better than the Dakota Digital two speed implementation. I have used DCC with good results.

    OP’s issue really isnt a start current surge issue though. His gauge reads lower than the alternator and battery. Sounds like he has a voltage drop in his dash wiring.

    don
    1969 Camaro - LSA 6L90E AME sub/IRS
    1957 Buick Caballero - huge project
    1959 El Camino - Ironworks frame
    1969 Mustang Sportsroof
    1956 Cameo - full C5 suspension/drivetrain

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