View Full Version : Low Voltage
10-14-2007, 03:02 PM
Is there any sort of upgrade I can do to my current alternator for some more power?
When sitting at lights with the blower and lights on the voltage drops quite a bit.
Is there an upgrade aletnator if mine cannot be 'upgraded'?
I don't want to spend a lot, as this one is less than 2years old.
10-14-2007, 04:07 PM
What makes you think you need it?
If you don't have a winch, alot of lights, ect, then there's really no reason for it. The best upgrade you can do is get a good reliable battery.
There is an "upgrade," but the problem is that every alternator gives noticeably lower voltage at idle. As long as it's higher than engine-off, it works. It should be normal (at least 13.5V) at 2000 RPM.
If it isn't higher than engine-off, or is low at 2000 RPM, or has significant readings on AC V, then it's broken.
Note that it's also possible your brown-out is due to corroded wiring. This can be checked for with a voltage drop test, or by repeating the test above with connections at the alternator, then at the battery. You may have nothing at all wrong with the alternator.
Honestly, your charging system worked at the factory. Why do you think you need an "upgrade?" It certainly came with headlights and a blower motor.
10-15-2007, 12:09 AM
Well obviously it did have a set of headlights and a blower motor when it left the factory 18 years ago.
However, the OEM alternator I took off when it went bad did not have the problem that this current one does. In fact, I took the first "replacement" off and took it back thinking it was bad, and the second one is the same way.
I heard it once mentioned that it was common for rebuilt alternators to have this problem. Maybe I am wrong.
The only extra load I have on the truck other than the OEM stuff is a set of Hella 500 lights. With those on, the blower on high, the headlights, aftermarket stereo, I get rather nervous to even think about hitting the rear window defrost button.
The reason I think I need it is because the lights dim considerably when at idle with the above mentioned load.
10-15-2007, 03:04 PM
my trucks voltmeter shows a drop at idle also with the napa alternator in it.the aftermarket alternator that was in it before diden't do this and neither did the factory alternator.i have a winch so i've been wondering if powermaster or another company makes something that can be adapted.if you don't have one already you can get a power window spec. alternator with more amps.
10-17-2007, 09:12 AM
do you wounder why the lights dim when you have all thouse loads on the alternator? Its cuz your idleing,. and the alt' isnt putting out its max amperage. If you think there is an issue with the charging system, diagnose the system, dont just condem the alternator because of a story you heard. In some cases, re built alternators are better then mass produced oem units
10-17-2007, 11:43 AM
do you wounder why the lights dim when you have all thouse loads on the alternator? Its cuz your idleing,. and the alt' isnt putting out its max amperage. If you think there is an issue with the charging system, diagnose the system, dont just condem the alternator because of a story you heard. In some cases, re built alternators are better then mass produced oem unitsi don't know about spafford but i don't need anything on for the gauge to fall at idle and there is no voltage drop all the way to the battery.a LOT of aftermarket electronics are garbage,its more than likely its not turning on as soon and or doesn't have the same output.
10-17-2007, 12:36 PM
Yeah, just the lights and the blower are enough to run mine down.
But with the extra loads it goes to hell.
I think a vehicles electrical system should be able to handle at least a little aftermarket load. My F-250 has all the above and it doesn't even breath heavy when it is all run at the same time.
10-17-2007, 02:47 PM
is your F250 a diesel? does it run two Batterys?
rickcdewitt- There is NO voltage drops, at all? When the alternators at Max charging output? theres NO Vd? thats interesting, actualy, a first. How did you perform your Charging system tests??? There needs to be a controled load on the system to get proper readings, and no max output test is done at idle, cuz no alternator puts out max amps @ idle.
10-17-2007, 03:03 PM
Charging system tests:
No load idle output test-
Conect the red lead of your DMM to the B+ on the alternator, conect the black lead to the battery negative.Now conected an amp clamp to the wire/s coming from the B+ on the alternator. Start the engine, with all electrical acessorys turned off. Charging voltage should be aroung 13 more or less. To see how your regulator reacts, get somone to quickly rev the engine, while still watching the DMM and ammeter. The voltage output should jump quickly and leval off at 14.6v more of less.
Alternator Max output test:
For this you will need the DMM and Amp clamp as well as a Battery load tester.
Hook up the amp clamp and the DMM in the same way as the no load test, but this time, conect the batt' load tester to the battery. Get somone to hop in the truck, start it, and rev it up to about 2000rpm. Get them to hold it there during the test. Useing the load tester, load the system down to 13.5 Volts, and read Again, record the reading from the DMM and the output amps. dont load it down for too long, or you will let the smoke out of the load tester, thats not good. So, now your done the Alternator output tests. Voltage drops are done useing the same idea, high idle, load the system down, and check the Vd on both the positive and negative sides of the circuit. Go from center of the batt post to the center of the conector, this way the resistance in the conections them selves will be measured as well. If you find that when you do the high idle test, and the amperage does not increase much, then you need to look at the regulator, if you find that nothing happens at all, you should find out of you are getting voltage to the I termanal on the alternator. You should get 12 volts at that wire with the key on, engine off.
10-17-2007, 03:04 PM
oh, btw, you NEED a controled load on the system during the max output test, if not, then its pointless
10-17-2007, 04:07 PM
Nope, 5.4L with one battery.
I wish it were a diesel, but that's another thread.
10-17-2007, 04:19 PM
hmm, another thought might be, when you replaced the alternator, did you replace it with one of the same output? Run through thouse tests, see what you come up with
10-18-2007, 11:14 AM
i diden't think about load testing the new alt.(tested the old one and threw on a new one) or voltage drop @ max load.good idea,there was no noticable drop at idle it makes sense to check it while carrying a big load.. i had trouble with the regulator on the last crap napa alternator,if the voltage drop at max load is good i'm guessing that the quality napa regulator is a little lazy turning on.
10-18-2007, 04:56 PM
um, voltage drops check the phsical conections of the battery cables, as well as the condition of the cables them selves, voltage drops dont tell you if the alternator is outting out or not. you tested the old alternator? how are you doing these tests? simply jaming leads hear or there when its idleing tells you next to nothing usefull. alternators arnt designed to produce max amp and voltage at idle, and they dont put out max amperage where there is no demand for it. Why would it be pumping out amps at idle, when nothing is turned on? it would cook the battery. amperage output increases as electrical system loads increase.
10-21-2007, 01:28 AM
is your F250 a diesel? does it run two Batterys?
rickcdewitt- There is NO voltage drops, at all? When the alternators at Max charging output? theres NO Vd? thats interesting, actualy, a first. How did you perform your Charging system tests??? There needs to be a controled load on the system to get proper readings, and no max output test is done at idle, cuz no alternator puts out max amps @ idle.you can probably tell i'm a bondo brain(bodyman) not an eletrician.i don't know a whole lot about electrical:icon_confused:.it makes sense that increased resistance would only show itself as voltage drop when there is more electricity flowing than at idle(at least i think thats what you are saying).to be more specific my truck registers only battery voltage at idle(12.5) and if i rev it 200-300rpm's above idle it goes up to where it always used to sit at idle.i should use a load tester while checking for drop first but i can't help wondering if the wire/s going to the regulator are corroded and make it lazy or the new regulator is bad.the last napa alt i got developed a big crack in the resin the regulator electronics are potted in and had similar symtoms that got worse until it quit and i had to put a 20 year old motorcraft regulator in it until i warrantied the alt. and got a new one and soldiered it in.the mechanics i work with(separate business same building) have had the napa alternators do turn on a little late on a few rigs also.
what would your plan of attack be?diden't you say what the procedure for checking the regulator is,and could you elaborate for a paint huffin' fool like me?:icon_hornsup:
maybe i should try swapping regulators?(i know-damn parts swappin')
10-21-2007, 12:59 PM
run through the tests I already mentioned, and then see what you come up with.
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