Alternator not maintaing voltage

[STUART_T]

Hi Everyone,

I just want to ask a question, about a problem I have with my voltage output from the alternator.
When I have the fans, lights, heater fan, stereo and wipers on my voltage according to the gauge drops to 11v. On a recent outing the voltage dropped enough that when I went to start the car after stopping a service station, nothing, the car would not turn over. With a push start and all eccesories off the battery gained enough charge and it started fine at the end of the journey.
I have fitted a new alternator (100amp Delco universal) which is identical to my old unit. When I measure the ouput from the alt it is 13.6v with no accessories running, the same at the battery terminals. As soon as I turn headlights, fan the voltage drops. Should the voltage from the alt maintain a voltage higher than 13v even with acc's on. The battery is about three years old that is my next replacement item. I have checked my earth connections from the battery and relocated the position and checked continuity between the engine and chassis and it looks fine. But apart from replacing the battery I am lost. I have a volt guage and an idiot light which is also the excitor wire, the globe is only 2w and I believe I should have a 3w but I am going to add a resistor 15ohm 10w across the globe connections, as a safe guard if the lamp blows. Any help would appreciated before I take it to an auto electrician.
Thanks
Stuart

[spookypt]

Stu, probably not the answer but check alt belt tension...

Spookypt

[STUART_T]

Spookypt,

It doesn't sound like it is slipping and it feels like there is enough tension on the belt, but an easy thing to check, I will try it when I get home.

Thanks

[Bill E]

How big is the pulley on your alternator? Check to see at what rpm your alternator turns on . You may not be running it hard enough to keep it excited.

[Stokesy]

Does the alternator have an internal regulator or an external plug in type? If external then it might be at fault. Haveyou tested the current draw?

[sideshow]

is your alt light an led
fk it off and run a normal old school 6w globe just for a test
if it goes out means yr alternator is sort of working fine until further tests

how have u wired the wires on the alternator
u might have not wired the s terminal porperly
L is the light whihc goes to neg side of the globe in dash
S is the supply which means battery or ign
on most alternators we just piggy back this off the big pos terminal on back of alternator
if your alternator had dropped a phase it would charge at 12v
so since its at 13v then its charging but i recon its not getting a correct reference from the S wire therefore not charging at capacity when u turn lights on

so make sure the s wire is getting good accurate voltage

otherwise take it to auto elect

[Gav]

Reckon you're right Sideshow, sounds like it is not being exited properly.

[STUART_T]

Sideshow

On the back of the alt I have the pos+ lug and 2 other posts marked with a 1(R) and 2 (F)
The idiot light (old fashioned globe 2w) goes to the number 1 (R) the light comes on with the IGN is on and goes out when the car is started.
The other post the is splice back to the pos+ lug. I had a feeling the globe I have is not enough watts, you are saying 6w globe. As I suggested would the resistor 15ohm 10w help?

Thanks

[sideshow]

not sure on the resistor
i just get the small globes used in old school dashes
or the ones used in late model car blinkers
just goto wreckers and cut the wiring and small socket from a blinker in new car

when i have to wire a charge light and its an led i run a secondary globe in parallel
behind the dash to make it excite better

anyway i doubt thats yr problem
i just realised your alternaotr is so old school its got dinosour dna on it heheheheh

i think your alternator needs an external voltage reg does it run one??

this is a warning to anyone who reads this
ive wired afew customer bought alternators
they r fancy and chrome looking
but they are a pain to wire up as they dont come with ext regs
the shops selling them know fk all about alternators

when u buy a new chrome alternator make sure its internal reg
this means u have supply wire and light wire

old alternaotrs with r and f means u need external reg

here is a pic

Alternator Conversion - TriFive.com, 1955 Chevy 1956 chevy 1957 Chevy Forum , Talk about your 55 chevy 56 chevy 57 chevy - Belair , 210, 150 sedans , Nomads and Trucks, Research, Free Tech Advice

i went thru the summit racing catalogue awhile ago and found 4 or 5 types of alternators for old fords and holdens
some need an external reg and some dont
get the ones with internal reg as it gets rid of alot of wiring

if u need any more info just ask
or email me thru website tomorrow if i dont reply tonight as im off soon since kids just went to bed to play the ps3 hehehe

[STUART_T]

Thanks Sideshow that makes sense I will make sure I get an alt with an internal reg.

I thought that's what I had, this will save me a heap of time

[sideshow]

no probs
unfortunately the shops are buying em from usa bumping up the price by 3 times
and selling em as exact replacement for old ones
but these days most guys get rid of the ext reg cause they cannot handle hi output alternators and can also fail easily


ive run into this afew times and customer is upset as they cant take em back cause
they have been bolted on
then i tell them they are 100 bucks in usa rather than 400 bucks here heheheheeh
look on summit racing website

[STUART_T]

Just to follow up, I managed to fix the charging problem, it turns out that I did have an alternator that was internally regulated, (dismantled the old one and checked the parts). I ended up disconnecting the wire orginally fed to the alt bat+ terminal (painless wiring) and ran a new wire from the Alt to the fusible link. I also added a resistor across each leg of the warning light which will allow the alt to obtain a excitor even if the globe blows. Adjusted the fan belt to the correct tension just in case (it was a bit loose).

Started the car straight away 14.5v, lights and fan on drops to 13.5v and when the engine revs the voltage raises, all good.

But, when I went to turn the car off it kept running, (needed to disconnect the wire for the idiot light to stop, not a practical way to stop the engine) so I added a diode (from the alternator I dismantled) to the excitor wire and it now stops power being back fed to the ignition and the motor turns off no problem.

Thanks to everyone for your help and suggestions.

[tirod]

We see this in the US a lot.

Exactly - the reference voltage that feeds the voltage "load" to the regulator was routed back to +. That means it had nothing to turn it on and make it work. It can't sense what the electrical draw is on the wiring at the main load connection. That's usually at the first + connection where all those wires get bolted to one stud. There, the voltage drops due to load, and it's the best place to reference when to turn on the alternator.

"One wire" alternators references it's own output voltage. Most won't even start charging until they spin above a set rpm, 1700 to 2500. Idle around in normal driving all day and it drains the battery.

They were invented for farm tractors, not cars. Some people just carried the concept over for hot rods because they didn't want to mess up their work of art with actual wiring. What makes it worse is to add a underdrive pulley, then they don't spin up at all, and adding a gel cell high cap battery then disguises it's inability to charge up. Basically they cruise around on the battery, then put it back on a float charger until next weekend.

It's actually quite common now, all the "best" hot rod parts, and they don't work as a system well, if at all. And - if someone repeatedly has their battery warrantied out, most parts houses and vendors will finally just refund their money, to get out from under the bleeding costs. That leaves the owner going from store to store until they finally take off the wrong parts in disgust and install the proper alternator wired back to sense the load.

Just say no to one wire alternators - unless it's for your tractor.