Electric Fans drain battery

[Chevy1TonFun]

After installing my new 4000cfm electric fan kit, new my voltmeter show 11.5 volts at idle. When at 3000 RPMs I still do not have 14v. At idle if I turn off the fans the voltage jumps from 11.5 to 13 volts. Any ideas as to what the problem could be. I believe I have 100Amp alt.

[panhandler62]

A lot of things come to mind, all the way from wondering about the voltage regulator to pondering a change in the pulley diameter for the alternator. Newer vehicles will throttle up slightly off idle when more current is needed but a 71 is going to need to be able to run all of its eletrical load at idle since it doesn't have a pcm.

Can you post more details on the alternator/regulator?

[Longhorn Man]

I would start with getting an actual reading off the battery with a multimeter. Depending on how the guage is wired, it could be giving a reduced reading from reality.

[dwcsr]

Originally Posted by Chevy1TonFun

After installing my new 4000cfm electric fan kit, new my voltmeter show 11.5 volts at idle. When at 3000 RPMs I still do not have 14v. At idle if I turn off the fans the voltage jumps from 11.5 to 13 volts. Any ideas as to what the problem could be. I believe I have 100Amp alt.

What kind of fan is it and what amp draw does it pull? At 4000 cfm your most likely pulling a constant 40 amps and will need at least a 100 amp plus alt. Are you running aftermarket pulleys? under drives maybe?

13.4 to 14.4 is normal unless your under an extreme load. I would start with checking how many amp the alt puts out. Take it to auto zone or some other place that can test it for you.

[fixit-p]

It would be helpful to know what you have, how its wired, stock, modded 1,2 or 3 wire alt.

Besides having the right components, system design is just as important for getting the most out of your electrical system.

[Chevy1TonFun]

I charged the battery and picked up a bigger alt. today. After install the voltage was just over 14v with everything on for daytime. It never been that high. I deem this fixed. Thanks for the help everyone.

[Chevy1TonFun]

Nevermind, problem is back. I bought a 96Amp alt and after a few days the battery is dead. Watching my voltmeter when I turn off the fans the voltage is above 12 at idle. I looked up the fan kit, it has a 50 amp draw! HOLY S***! I was looking at 120+ Amp alternators and they are all one wire alt. How do I go from a 3 wire to a one wire system. Thanks

[fixit-p]

Originally Posted by Chevy1TonFun

How do I go from a 3 wire to a one wire system. Thanks

Don't, they are junk. As I stated earlier a properly designed system is important. Also what alt do you have 10 or 12 SI or CS series alt. The CS alts have a Delta wound stator which produces more power at lower RPM's than the SI alts which have a wye wound stator. Can you post a diagram of how you wired your system?

[Chevy1TonFun]

If I had to guess, its a 12SI. I have a "Painful" wiring kit install on the truck. I am running an Autometer voltmeter. Here is the diagram. Thanks

[VetteVet]

Are your fans constant on or do they cycle on and off like thy should?
I would convert to the CS style alternator using this link....http://temp.corvetteforum.net/c3/zma...ternator01.htm

[Chevy1TonFun]

Right now they are on anytime the truck is over 180*. I haven't dialed in the thermostat for the fans.

[dux406]

Any updates on your problem because i am having the exact same problem. I installed a 3-wire 140 amp alternator with no change. Thx

[Chevy1TonFun]

Originally Posted by dux406

Any updates on your problem because i am having the exact same problem. I installed a 3-wire 140 amp alternator with no change. Thx

You aren't giving me any hope. I will be installing my alt tomorrow. I'll let you know.

[panhandler62]

Some types of alternators produce more power at low RPM than others. The total output of the alternator might not be much help if it doesn't produce much power at idle.

Kind of like big cammed engines that produce tons of power but not until 3500 rpm.

[Chevy1TonFun]

ok I bought a CS type alt and still no change at idle. Any other ideas? I am going to run a ground strap from the core support to the frame and see if that helps.

[panhandler62]

I don't think you mentioned the battery in here (sorry if I am missing it.)

If you are going to support a 70+ amp load at idle you are going to need a pretty hefty battery. If you are going to run at idle/low RPM for a large percentage of the operating cycle then you may need to also go to a later model or after market alternator as well since the common alternators of the 70s era are not going to support that load.

If you spend a lot of time at idle and very low RPM you may need something heavy duty like a CS 144 series at 90/140a output.

Of course; good, well connected cables that support that sort of current are essential also.

[VetteVet]

You need to refer to the link I posted above and you need to show us exactly how you have the alternator wired. Your "L" terminal is for the resistance wire and the "S" terminal is the sensor wire that connects to the battery. IF you have wired a resistor into the resistance wire that is higher than 300 ohms then it will restrict the internal voltage regulator and lower the alternator's output.

Go back and read all the posts and answer any questions that you have missed.

[Chevy1TonFun]

I have a CS 130 alt with no resistor, only a diode. I have it wired according to the the CS wiring diagram. Looped the bigger "S" wire to the battery post on the alt and "L" wire goes to the white 914 wire. Now what, do I really need the CS144? I have the biggest 12v battery Costco carries. Battery suggestions if that is even an issue.

[cableguy0]

How are the fans wired? Are they on relays? Where are they getting there voltage from? Also what temperature thermostat do you have? If the fans are running constantly thats a huge draw constantly. Most gm's came factory with a 195 thermostat. If your fans are coming on at 180 they will never shut off with a 195 thermostat.

[Chevy1TonFun]

Originally Posted by cableguy0

How are the fans wired? Are they on relays? Where are they getting there voltage from? Also what temperature thermostat do you have? If the fans are running constantly thats a huge draw constantly. Most gm's came factory with a 195 thermostat. If your fans are coming on at 180 they will never shut off with a 195 thermostat.

The fans are on a a relay system that came with the fan kit. The fans are on pretty much the whole time. My thought is the fans are going to be on regardless of the thermostat. The truck runs at 210*. A 195* thermostat is not going to change the fans operation. Please educate if I am missing something. I am going to be focusing on this issue this weekend. Gathering as much intel before the weekend. Thanks for everyone's input!

[panhandler62]

A CS 130 puts out about 52a at 2000 rpm (if I recall) which would be pretty marginal in supporting a constant 40a load from the fans and whatever else might be running. If you engine idles at 800rpm or so then the alternator is at 1600 and is banging out a whopping 36a.

If the fans need to run constantly then the CS 130 is not going to sustain operating current at idle and the battery will discharge.

Upgrading to a CS144140 (144 series, 140a) will provide sufficient current at idle (around 85 or so) and they can be pick-a-parted from junkyard Caddys if the $280 refurb price is too steep.

Upgrading to one of these larger case alternators will require some bracket engineering as they are physically much larger than the CS 130 and, as I mentioned above, you need to run good heavy cables and make sure all the connections are clean and solid since you will be more than doubling the current from the OE levels.

Before diving into that upgrade you may want to review your current system design and factor in planned electrical needs. Ask these questions:

• Do the fans need to run constantly to keep the temp in range?
• Am I going to be adding a large stereo amplifier?
• Do HO projecotr lights sound cool?
• Am I going to run a couple compressors (if it's a 4x4 probably not)

If you find that you are going to need to support 60a to 70a at idle for periods longer than the battery can sustain then you need to move up to a CS 144 (or other HO alternator) but if you can reduce the idle load (pot down the fans so they cycle on and off at idle, don't add lots of high current accessories, etc) then the CS 130 may be fine.

Here is a helpful resource to help choose an alternator appropriate to the needs of your truck:
http://oljeep.com/gw/alt/Alternator_...html#Section_3

[dwcsr]

Originally Posted by Chevy1TonFun

The fans are on a a relay system that came with the fan kit. The fans are on pretty much the whole time. My thought is the fans are going to be on regardless of the thermostat. The truck runs at 210*. A 195* thermostat is not going to change the fans operation. Please educate if I am missing something. I am going to be focusing on this issue this weekend. Gathering as much intel before the weekend. Thanks for everyone's input!

If your truck runs at 210 and your OK with that then get a corvette fan switch that comes on at 200 -210. It will fix your battery issue. If you want to run cooler then get a Mark VIII fan and install it with a 185 fan switch and a 170 stat.

[Longhorn Man]

I'm going to guess the switch for your fan is moun ted in the engine isn't it?
There is no reason for your fan to be on all the time if it is big enough to cool the coolant in the rad, esp if it is on when going down the road over 40-ish MPH.

[cableguy0]

If you run constantly at 210 you have a problem. Too small of a radiator comes to mind first. You should hover just above your thermostat opening temp. With a 195 thermostat I would expect the engine to run at 195-200. If it runs at 210 while driving down the road the fans wont bring the temp any lower. Having the fans come on at 180 is going to do nothing but smoke your electrical system. The fans cannot constantly run. I dont care what alternator you have or how much amperage it puts out. Nothing can handle that much constant load.

[Chevy1TonFun]

I just fixed a bad over heating issue. Its a HP 486 Stroker BBC, its going to run at 205 -210. Plus, later chevy motor blocks run hotter. My sliverado runs just under 210 everyday. If you have any ideas on how to lower my op temp even more, then please post it here: http://67-72chevytrucks.com/vboard/s...BC+overheating



I'll put my 195* thermostat back in this weekend. Install a CS144 and I also planned on having one fan stay on and and the other come on and off as needed per the fan thermostat control.