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Charging is low when blower motor on...

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 89GMCSuburban, May 5, 2003.

  1. 89GMCSuburban

    89GMCSuburban 1/2 ton status

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    On my truck, I do have a large power amp with a 50 amp fuse and a fan from a Taurus that pulls 30 amps when on...although, even with both of these off, my blower motor in the dash for the A/C, when it's on, draws enough power to drop my gauge below 13. The alternator should be fine, battery is at least 1 1/2 years old. I know it sounds like the ground, but the ground coming off the blower motor to the firewall is down tight. Is there another ground I should look for? Has anyone else had this problem?
    And, as on off-topic, I'm going to drive to Estes Park, CO from here (San Antonio, TX) in 2 weeks with my 31's on so I turn 2,000 RPM at 65. My question is, would it be a good idea to install a tranny cooler, or is it not really necessary?
     
  2. 88Silverado

    88Silverado 1/2 ton status

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    Depending on where the meter is reading the voltage this can be true. Alternators voltage is set by the voltage regulator internal to the alternator. When the load gets high enough to pull the voltage down the alternator will switch the voltage up or down as needed. Most alts run 13-14V normally to keep a positive charge on the battery thus charging it. You cant drop below 12V cuz thats the battery's base voltage. Ty reading the voltage at the alternator's output when the fans are on and see what it says.

    I have the dual winstar fans and a 105amp alternator on my 71 Elky, when the fans are on, it reads 12V but the alternator is putting out about 12.5, still enough to keep it from loading the battery.
     
  3. TxK5Blazer

    TxK5Blazer 1/2 ton status

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    i am assuming that you have a 700r4 in ur burb and wouldn't be a bad idea for a tranny cooler the really help with the life of those trannys from my experiance anyway....Jason
     
  4. 89GMCSuburban

    89GMCSuburban 1/2 ton status

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    I just bought an Imperial tranny cooler rated for class "A" motorhomes towing an extra 10,000 lbs...that should be enough. /forums/images/graemlins/thumb.gif
    Maybe there's some confusion, my blower motor in the dash is what seems to draw too much. When I turn it on full-blast, it pushes the gage down to about 12. If I have the Taurus fan on with my A/C at full blast and the radio on, the gage is just above the red part at the low end when at idle. Driving, it moves up to about 10 or so. I will do the test on the output of the alternator, but how do I test it?
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    Red single wire from the back of the alternator, and the other lead to ground.

    You can also test voltage from battery terminal to battery terminal, if the battery is good, it will be very close to actual alternator output.

    Measuring from the fuse panel inside works as well, but when you are dealing with 12.5V vs. 12V, thats not the best place to be measuring, nor is the battery. It will at least let you know that the gauge is giving you a fairly accurate reading.

    To be honest, stock older alternators are pretty bad for idle output, mines an 87 amp unit that I rebuilt, and works fine, but no difference than before...low idle output voltage. Increasing RPM by about 300 bumps output into the 13V+ range, but increasing idle speed that much is pretty drastic. Also tried approx. 33% overdrive pulley with it (turned it faster), no dice. Thats with stock stereo, HD heater on high, headlights on, and nothing else.
     
  6. HarryH3

    HarryH3 1 ton status Author

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    [ QUOTE ]
    The alternator should be fine

    [/ QUOTE ]
    But it doesn't sound like this is the case. Any electrical repair shop can test the alternator for you, on the vehicle. They have a device that lets them vary the load and see how much current the alternator can supply at various RPM's. Yours sounds like it has some diodes that are fried, preventing it from putting out its full rated current.

    The stock alternator isn't up to the task of running all the stuff that you've added anyway. You really should upgrade to a more powerful unit. /forums/images/graemlins/frown.gif You've added a fan that draws 30 amps and a stereo that draws 25-40 amps. The fan on high can draw about 25 amps. Headlights, another 20-25 amps. Running lights, brake lights, etc. Figure 8-10 amps. Wipers, 15 amps? Your stock alternator, when in perfect condition, can put out about 105 amps, with the engine turning at least 1,800+ RPM. At idle, the output drops way below its max rated output. /forums/images/graemlins/frown.gif

    Running all the extra loads that you have is most likely what's killing your alternator. It's been forced to run at or near its max output current for long periods of time and the heat is cooking it. /forums/images/graemlins/shocked.gif
     
  7. 88Silverado

    88Silverado 1/2 ton status

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    OOps...Sorry, I was thinking about the other fan /forums/images/graemlins/blush.gif

    One of the other problems is the main wire coming from the alternator or distribution block to the vehicle's fuse block is probably around a #12 wire. With the length of that wire and the load of the electrical systems in your truck (blower fan) the resistance or loss increases a fair amount thus lowering the voltage. If your running an external fan on the radiator, and using a stock alternator, thats a pretty good load. As you noticed, when you increase the speed, the voltage comes up. This is common with most alternators, there are a few aftermarket type that have full output at very low RPMs or as it was mentioned, you can go to a smaller pully on the alternator to have it spin faster at idle keeping the voltage up.
     
  8. 89GMCSuburban

    89GMCSuburban 1/2 ton status

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    Hmmm, that could be the case. I'll take it to get tested, it's a lifetime warranty O-Reilly unit. What high output unit would you recommend? I did find a 140 amp conversion kit from Iceberg that gives me a new housing for keeping the alternator cooler than stock housing...
    88, it's cool man! It's still advice I can use... I'll check out some of the wires and grounds and make extra sure...that drive to Colorado is a long one from here, wanna make sure I'm in good shape. Who sells the smaller alternator pulley?
     
  9. dyeager535

    dyeager535 1 ton status Premium Member

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    http://tech.oldsgmail.com/echa_140a.html

    Don't know anyone thats done the swap to a Chev yet, but should be similar deal for sure, knowing GM interchangeability.

    All the aftermarket alternators aren't garbage, but this is one of those "I never hear people that buy Delco stuff complain" deals. There have been enough problems with the aftermarket alternators that I'd go GM when I could. There are plenty of people running aftermarket alts without problems I'm sure, but a 140amp stock alternator sounds pretty nice.
     
  10. 88Silverado

    88Silverado 1/2 ton status

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    You can check on the CS-144 alternator upgrade which was an option on the late model trucks and cars.
    Heres a example link for comparison.
    http://www.alternatorparts.com/cs130d_cs144_trk_suv_upgrade.htm

    You may need to run a larger wire from the alternator if you upgrade to a high output alternator or you wont get any additional benefit from it except a hot wire that can melt /forums/images/graemlins/eek.gif

    You could probably go to any junk yard or alternator rebuild shop and find a smaller pully for the one you have.
     
  11. 89GMCSuburban

    89GMCSuburban 1/2 ton status

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    Oh, that's perfect! I should do the alternator upgrade then add a dual-battery setup. /forums/images/graemlins/thumb.gif Thanks guys! This is the exact reason why this board rocks the net! /forums/images/graemlins/usaflag.gif /forums/images/graemlins/burb.gif /forums/images/graemlins/usaflag.gif
     

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