Replace alternator?

[efnfast]

this has been going on since day 1, but I've only start to question it now. I've got a 100amp Jegs 1-wire alternator.

When driving, volt gauge reads 14 (or maybe 14.1, I dunno, close enough). If my dual radiator fans come on (26amp max draw on start, about 15amp draw on each when running, so say 30amp) volt gauge drops to 13.4ish and remains at 13.4ish until they go off. If I turn my headlights on (which turns on headlights, rear lights, and dash lighting) battery drops to 13. If I drive around for 20minutes with my lighting on, battery drops down to 12ish. If I drive around with lights and radiators fans on, haha, it reads under 12 until I turn everything off. (so basically I just never use my lights)

Since I'm carb'd, the only other things drawing power are my ISIS unit and MSD ignition box (and gauges).

Should a 100amp alternator be able to support the above and keep the battery charged?? (ISIS, MSD box, gauges, lighting, 2 spaal radiator fans). Trying to figure out if my alternator is bad, or if it's just not enough amps to support that load.

[oldguy668]

I'm going to take a wild guess and say the wire you have going from the alternator to the battery is too small.

[skullandbones]

I'm not an electrical expert but have learned some valuble lessons. You should know the capacity of your device. You said the alt is a 100 amp unit. More importantly, the continuous duty cycle can give you an indication if the device will be adequate under the conditions you stated. It is common for a 100 amp alt to have a CDC of 60 amps. Even so called deep cycle or "STI" batteries may not supply long periods of negative charging service. A good example is a welder I was needing for welding 600 vertical peices in 14 8 ft panels. The one I looked at had a pretty low duty cycle. It would have worked but I would have had to reset it or "rest" it for periods. I ended up paying twice as much and got one that could cycle longer than I could. Had to take a break between panels. I find battery evaluation to be a black art. Even the marine batteries aren't usually as good as they are rated. I have read in several articles that 130 to 140 amp alternators are common now. My roadster has remote terminals and I am running a charger on it regularly. That should help support the service life but I also live in AZ which is hell on batteries. Good luck, WEK.

[efnfast]

I'm going to take a wild guess and say the wire you have going from the alternator to the battery is too small.

I have 8ga from alt to battery. Battery is 2ga power/ground. Should I go to 4ga?

I just keep thinking though, if there's no load on it the battery voltage is fine, load and it dips down and doesn't recover until the draw goes away .... that sounds like weak alt to me?

[michael everson]

Take it off and have it checked. Most parts stores can do that for you.
Mike

[efnfast]

Take it off and have it checked. Most parts stores can do that for you.
Mike

I did...they said it was leaking a bit. The weird thing is it spun up to 122amp on their machine, which makes no sense because it's only 100amp (although it would explain why it tripped my 110amp circuit breaker once...I could never explain that one).

Oh well, too much frustration with it so I bought another one. Also will upsize the wiring from 8ga to 4ga.

[rich grsc]

Did it ever fail to start the car? If not then there is nothing wrong! Under load it will naturally show a slight voltage drop, as amp load goes up, voltage will go down. Explain how an alternator leaks??????

[CHOTIS BILL]

Is there a mess after the alternator leeks? :confused:

Bill Lomenick

[Norm B]

If you have easy access to your battery, I would start the car, turn everything electrical on and test the voltage between the battery posts with a good multi meter. Have someone rev the engine above 2000 rpm (maybe a little higher if you're running under drive pulleys). Voltage should be about 13.7 volts. If it drops back to 12 at idle that's normal. Any less than 12 you are drawing off the battery. The readings you are getting with your voltage gauge may not be accurate depending on how it is wired into the system.
Good Luck
Norm

[Mustang Man]

Personally I think one-wire alternators should stay on farm tractors and not hot rods, but that's another post...

A typical alternator of say, 100 amps, usually has an idle rating, say 60 amps at idle, and a peak rating, possibly 120 or so, which is why you saw the number you did during testing.

I would upgrade to a 4ga wire and see what happens and double check all grounds.

I just installed a 3G alternator (Ford OE) 130 amp unit and it is 80 amps at idle and will hit 160 amps when fully loaded, so don't think the advertised rating is a max number.

HTH...
Mark

[CraigS]

I see similiar readings w/ my one wire. i didn't do the original build of the car so I sometimes wonder where my Voltmeter is getting it's reading from. I can even see the meter needle wiggle in time w/ the turnsignals. I used to be worried sometimes but the car has never had a weak battery problem so i quit worrying.

[efnfast]

Did it ever fail to start the car? If not then there is nothing wrong! Under load it will naturally show a slight voltage drop, as amp load goes up, voltage will go down. Explain how an alternator leaks??????

No, but I don't think I should turn on my headlights, dash lights, radiator fans, and go for a 5 minut drive (i.e., not just idling in the driveway) and not have the volt gauge showing under 12.

Also, you can see it's drawign down - the longer my headlights are on the weaker they become, so it's not a case of a bad reading on the gauge.

i think leak was the wrong word to use .... basically drawing power from the battery when it shouldn't be (which would also explain why I can leave my car parked and 2weeks later the battery is dead unless I turn my battery kill switch ..... I traced everything in my I2 unit and found no problems, but I never checked the alternator)

[David Hodgkins]

Alex, I have the same issue as you with my I-Squared unit in that it saps energy from my battery over time. I think this is an inherent bug in their system. Have you talked to them about that?

:)

[Benji]

Yep so there is something else causing a drain on the system all the time... need to track that down.

[efnfast]

Alex, I have the same issue as you with my I-Squared unit in that it saps energy from my battery over time. I think this is an inherent bug in their system. Have you talked to them about that?

:)

I spoke to Chris years ago about it and checked everything he had me check - no issues, and yes, it does draw power from the battery, but it's very little. Shouldn't be able to kill a battery in a week or two.

[efnfast]

Turns out it was a variety I love issues (I love when that happens, like when both my radiator and a hose was leaking at the same time and sent me around in circles).

I replaced the alternator and my drawn down battery issues were solved, plus volt gauge seems to show it charging a bit more than before. When I turned on the rad fans volts came down, but not as much as before.

For giggles I replaced my 8ga wiring with 4ga and bam, now when I turn on my headlights or rad fans volts come down slightly then pop right back up to 14.2.

So it was a case of bad alternator and undersized wire.

Makes me wonder though - on the old forum I'd asked whether or not to use 8ga or 4ga for alternator, and the majority said 8ga was fine. But I clearly can't run basic basic carb (ignition + rad fans + lights) on 8ga, so WTF at people telling me that would be okay?

[rapistanxxx]

I'm seeing this same issue, and I have the million system. I looked up and the wire size on the diagram, on the Isis website, shows an 8 gauge wire. Maybe that should be changed. I'm going to change mine to a larger wire tomorrow. Thanks for posting this as I've been fighting this for a while now.
Ron



Turns out it was a variety I love issues (I love when that happens, like when both my radiator and a hose was leaking at the same time and sent me around in circles).

I replaced the alternator and my drawn down battery issues were solved, plus volt gauge seems to show it charging a bit more than before. When I turned on the rad fans volts came down, but not as much as before.

For giggles I replaced my 8ga wiring with 4ga and bam, now when I turn on my headlights or rad fans volts come down slightly then pop right back up to 14.2.

So it was a case of bad alternator and undersized wire.

Makes me wonder though - on the old forum I'd asked whether or not to use 8ga or 4ga for alternator, and the majority said 8ga was fine. But I clearly can't run basic basic carb (ignition + rad fans + lights) on 8ga, so WTF at people telling me that would be okay?

[tirod]

A one wire system doesn't use the specified 3 wire gauge, it's a different animal.

Mustangman alluded to why, when you wade thru this link, it explains the difference in wiring: http://www.madelectrical.com/electricaltech/onewire-threewire.shtml

It's complicated, is what it is.

[CraigS]

Tirod, that is a fantastic link. I had to create a new folder to save it bit I have it now. My car came w/ a one wire and some kind of output wire w/ a fusable wire section in it that ran to the firewall solenoid. I had some problems finally traced to the fusable portion that was opening sometimes due to not be secured correctly and flexing. I also got better performance, in spite of the smaller 51 series battery, when I moved the batt to the Breeze forward location. Shorter wires I think helped. Never had a dead battery but I watch it carefully. The link convinced me that any future upgrade will be a three wire alt. Thanks for great info.

[Scott Zackowski]

A one wire system doesn't use the specified 3 wire gauge, it's a different animal.

Mustangman alluded to why, when you wade thru this link, it explains the difference in wiring: http://www.madelectrical.com/electricaltech/onewire-threewire.shtml

It's complicated, is what it is.


Awesome link - very helpful!


Mk IV, Complete kit, FFR 7304

[tirod]

Thanks, a different link I stumbled on. The previous one I used was from a Chevy forum IIRC.

There is a mythology that "race car" tips and tricks should be superior and preferred in building a kit or modifying a car. If they are mostly cosmetic, no harm no foul - like wings and such. Some engine mods are much more than that, they are actually counterproductive to a daily driver. The guy who figured it out and used it on his track only car didn't care - he was after a few more hp at high rpm for just a few hours, 24 at the most. If it lasts thru a race, ok, he can tear it down and replace the damage in time for the next race. Cost of business and competition.

Watching your rig blow up with less than 25k on the odometer, not so much. Yet, we see reports of high dollar crate race motors getting installed in weekend cruise machines and self destructing constantly. It's not legions of incompetent builders. It's buyers not understanding they got exactly what they paid for - high hp high rpm motors that cannot last for 100's of thousands of miles. More like 40,000, tops. Push a stock block 5.0 over 450 hp and the life is measured in hours.

We need to be careful what we ask for.