Electric Fan, Now Truck Wont Charge - The 1947 - Present Chevrolet & GMC Truck Message Board Network

jays68yak · 07-08-2003, 12:20 PM

I installed one of those taraus fans in my suburban. The past two weeks Ive had to jump the truck when I go to start it. It sits as of now cuz I dont drive it much, so its not a problem yet. I noticed that with the fan off I get a reading of 14 volts at the battery (its charging). Once I turn the fan on it goes to 12 volts. What is the amp rating on a stock alternator? Would a 100 amp alt fix this problem? If not what would?

Thanks

tom hand · 07-08-2003, 12:32 PM

I ran into this when I nstalled vintage air in my truck. I had installed enough goodies that with all of them on I was drawing more amps than the alt. could put out even tho it was still charging. I went to a bigger alternator and it solved the problem. If you go to a 100 amp you need to replace the wire between the alt and the battery because the stock wire won't handle that many amps.

JimKshortstep4x4 · 07-08-2003, 12:56 PM

I believe that the optional alternator for AC vehicles was 63 amps.

Before you change the alternator, I would check the alternator drive belt. If it is even slightly loose, you can get this problem.

Just a thought.

Jim

jays68yak · 07-08-2003, 01:08 PM

it should be tight cuz it was making noise and I also had to take it off when i replaced the water pump.

Does anyone know what an alt from an 85 454 with ac would be? Or would it be the same 63 amps?

71GMC_3/4T · 07-08-2003, 01:26 PM

I wouldn't think a car fan would draw enough current to pull down your alternator, at least not completely. A heater motor draws about 25 to 30 amps on high. Don't know about an electric fan though.
You say the battery drops to 12V when you turn on the fan. Check the output at the alternator when the fan is on. If it's higher than 12V there, your problem may be in the wiring between the alt and the batt. You may have a weak connection or a fusible link that's gone resistive. To find the bad spot, measure voltage drop on the wire. I use those little pointed Xacto knife blades to poke a small hole in the insulation. You are measuring voltage, so you don't need to worry about current carrying capability of the blade.
If you have 12V at the back of the alternator when the fan is on, maybe you have a bad alternator that is dying under load.
Hope this helps...

jays68yak · 07-08-2003, 01:33 PM

well i know this fan sucks some juice so it wouldnt surprise me if thats is the problem.

The dieing alternator thing sounds like whats going on with my other truck. Charges fine until you turn the ac on full blast, then it goes down to about 12v and the truck wont start after wards.

Im glad I dont have an electric car cuz it would never work, it seems like all of my cars dont want to start or charge and some point in time. Maybe its just me.

Blue68 · 07-08-2003, 03:05 PM

May I recommend some 'light' readin on the subject. I saw it mentioned on the board before, and I found the site a couple of weeks ago myself, but check out http://www.madelectrical.com/electrical-tech.shtml and view some of their technical documents. You may need to look at the 'remote sensing' article in particular followed by the "chevy main power" and the "one wire three wire" articles.

I highly recommend reading these articles. I've read them since I'm in the middle of re-wiring my truck and find the information helps me to understand why GM did what they did and also to understand the schematics a little better, at least for the charging system.

BTW, I'm running the engine and setup out of a '98 with the serpentine and the CS130D alternator. Supposed to do 115 amps. It's on the passenger side so I really needed to understand how the buss bar connection, distribution block and ammeter guage all interacted. These articles helped.

jays68yak · 07-31-2003, 04:33 PM

ummmm seems like it was a dead battery

. Charged my optima over night sunday , dropped it in last night and it started like 5 times.

Time to go

, well if it had the power.

07-08-2003, 12:20 PM	#1
jays68yak Registered User Join Date: Oct 2002 Location: Gilroy, CA Posts: 1,454	Electric Fan, Now Truck Wont Charge I installed one of those taraus fans in my suburban. The past two weeks Ive had to jump the truck when I go to start it. It sits as of now cuz I dont drive it much, so its not a problem yet. I noticed that with the fan off I get a reading of 14 volts at the battery (its charging). Once I turn the fan on it goes to 12 volts. What is the amp rating on a stock alternator? Would a 100 amp alt fix this problem? If not what would? Thanks __________________ 1969 Chevy Project SWB Fleet, 20s, 5.3, t56, in the weeds. 1970 Chevy Truck cab on a 1979 Jimmy frame-8.1 liter 496 bbc/sm465/np203-jeds doubler-np205/d60/14bff Welded/42 tsls on recentered H1s 1998 Chevy Crew Cab K3500 SAS'd with hpd60, links and swayaway coilovers. 8.1l vortec DD/towrig "I like long walks, especially when they are taken by people who annoy me. "

07-08-2003, 12:32 PM	#2
tom hand CCRider Join Date: Feb 2000 Location: Olive Branch,MS,USA Posts: 2,232	I ran into this when I nstalled vintage air in my truck. I had installed enough goodies that with all of them on I was drawing more amps than the alt. could put out even tho it was still charging. I went to a bigger alternator and it solved the problem. If you go to a 100 amp you need to replace the wire between the alt and the battery because the stock wire won't handle that many amps. __________________ 72 GMC Sierra SWB almost finished---- 84 Softail Olive Branch MS

07-08-2003, 01:08 PM	#4
jays68yak Registered User Join Date: Oct 2002 Location: Gilroy, CA Posts: 1,454	it should be tight cuz it was making noise and I also had to take it off when i replaced the water pump. Does anyone know what an alt from an 85 454 with ac would be? Or would it be the same 63 amps? __________________ 1969 Chevy Project SWB Fleet, 20s, 5.3, t56, in the weeds. 1970 Chevy Truck cab on a 1979 Jimmy frame-8.1 liter 496 bbc/sm465/np203-jeds doubler-np205/d60/14bff Welded/42 tsls on recentered H1s 1998 Chevy Crew Cab K3500 SAS'd with hpd60, links and swayaway coilovers. 8.1l vortec DD/towrig "I like long walks, especially when they are taken by people who annoy me. "

07-08-2003, 01:26 PM	#5
71GMC_3/4T Weapons Of Construction Join Date: Apr 2000 Location: Colorado, USA Posts: 1,095	I wouldn't think a car fan would draw enough current to pull down your alternator, at least not completely. A heater motor draws about 25 to 30 amps on high. Don't know about an electric fan though. You say the battery drops to 12V when you turn on the fan. Check the output at the alternator when the fan is on. If it's higher than 12V there, your problem may be in the wiring between the alt and the batt. You may have a weak connection or a fusible link that's gone resistive. To find the bad spot, measure voltage drop on the wire. I use those little pointed Xacto knife blades to poke a small hole in the insulation. You are measuring voltage, so you don't need to worry about current carrying capability of the blade. If you have 12V at the back of the alternator when the fan is on, maybe you have a bad alternator that is dying under load. Hope this helps... __________________ 1971 GMC 2500, 402/TH400 4.10 Daily Driver Lafayette, CO

07-08-2003, 01:33 PM	#6
jays68yak Registered User Join Date: Oct 2002 Location: Gilroy, CA Posts: 1,454	well i know this fan sucks some juice so it wouldnt surprise me if thats is the problem. The dieing alternator thing sounds like whats going on with my other truck. Charges fine until you turn the ac on full blast, then it goes down to about 12v and the truck wont start after wards. Im glad I dont have an electric car cuz it would never work, it seems like all of my cars dont want to start or charge and some point in time. Maybe its just me. __________________ 1969 Chevy Project SWB Fleet, 20s, 5.3, t56, in the weeds. 1970 Chevy Truck cab on a 1979 Jimmy frame-8.1 liter 496 bbc/sm465/np203-jeds doubler-np205/d60/14bff Welded/42 tsls on recentered H1s 1998 Chevy Crew Cab K3500 SAS'd with hpd60, links and swayaway coilovers. 8.1l vortec DD/towrig "I like long walks, especially when they are taken by people who annoy me. "

07-08-2003, 12:56 PM	#3
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	I believe that the optional alternator for AC vehicles was 63 amps. Before you change the alternator, I would check the alternator drive belt. If it is even slightly loose, you can get this problem. Just a thought. Jim

07-08-2003, 03:05 PM	#7
Blue68 Registered User Join Date: Apr 2000 Location: Frisco, Tx, USA Posts: 606	May I recommend some 'light' readin on the subject. I saw it mentioned on the board before, and I found the site a couple of weeks ago myself, but check out http://www.madelectrical.com/electrical-tech.shtml and view some of their technical documents. You may need to look at the 'remote sensing' article in particular followed by the "chevy main power" and the "one wire three wire" articles. I highly recommend reading these articles. I've read them since I'm in the middle of re-wiring my truck and find the information helps me to understand why GM did what they did and also to understand the schematics a little better, at least for the charging system. BTW, I'm running the engine and setup out of a '98 with the serpentine and the CS130D alternator. Supposed to do 115 amps. It's on the passenger side so I really needed to understand how the buss bar connection, distribution block and ammeter guage all interacted. These articles helped. __________________ http://home.comcast.net/~r.landrum/w...tos.html-.html '68 C-10 LWB, '98 Z-71 350 w/accessories (Serpentine), Edelbrock Performer, Edelbrock 1405 (600cfm) carb, GM HEI, CompCam Extreme 4x4 roller cam, Thorley Headers, Carter Electric Fuel Pump, Vintage Air, 700r4, 3.73, disc brakes and power steering upgrades.

07-31-2003, 04:33 PM	#8
jays68yak Registered User Join Date: Oct 2002 Location: Gilroy, CA Posts: 1,454	ummmm seems like it was a dead battery . Charged my optima over night sunday , dropped it in last night and it started like 5 times. Time to go , well if it had the power. __________________ 1969 Chevy Project SWB Fleet, 20s, 5.3, t56, in the weeds. 1970 Chevy Truck cab on a 1979 Jimmy frame-8.1 liter 496 bbc/sm465/np203-jeds doubler-np205/d60/14bff Welded/42 tsls on recentered H1s 1998 Chevy Crew Cab K3500 SAS'd with hpd60, links and swayaway coilovers. 8.1l vortec DD/towrig "I like long walks, especially when they are taken by people who annoy me. "



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