Hot Rods One wire Alternator question

My battery is not charging, battery is one month old and a good one. Alternator(one wire) is 3 weeks old. All new batt cables, alt belt. As a test, I disconnected the positive battery cable and engine kept on running. Does this always mean that alternator is good? Is there an issue with wiring under dash then? One guy said to connect alternator wire to positive battery cable. Engine is a 1987 Ford 351W.(pre computer) Thanks for any help here!!

 

What voltage are you showing at the battery when the engine is running above idle say at 1500 rpms?

 

I do not have a volt meter, sorry. Probably need one. I drove 60 miles yesterday with battery 100 per cent charged (per my charger). When I got home, charger said the battery was at 45 per cent charge.

 

When disconnected the alt and the engine kept running, there was enough juice in the battery to keep the ignition working.
Do as said above, (connected) you should have 14/14.2 volts charging the battery. If not, assuming good connections, the alternator is not out putting proper voltage.

 

Just saw you last post, but an inexpensive meter for this, 10-15 bucks should get you something for testing. HF, Amazon, etc.

 

most parts store will check your battery charging voltage. Just remember most one wires need higher rpm's to begin charging.

 

Thanks!!

 

Disconnecting the battery cable while the engine is running is a good way to blow the diodes in an alternator.

The fact that it continued to run says it was charging enough for the ignition to operate, but as said before, you need about 14 volts to charge a 12 volt battery.

 

quick dumb question--have you rev'd it way up on idle, like 3500 or so? If not, try a few blips almost to redline and see if it starts to charge. I've had two that did not charge unless you did this first. They got better after the car was warm, just a slight rev and all was good.

 

Thanks!

 

Thanks for all your help, guys. You were right, that new alt is only charging 12 volts at the battery.

 

A good idea to have a voltmeter in the car instead of the traditional amp gage....

 

Get yourself a cheapy voltmeter, test the battery with the key off, key on, then with the engine running around 1500-2000 rpm. The alternator has an exciter built in (more than likely) so at idle, it won't give the best reading. Compare said readings. In a perfect world, you'll get a 12-ish volt reading with the key off, slightly less with the key on (depending upon accessories), and +14 volts when the alt is charging. Anything less, something is bad, but I would suspect the alternator. When you go to swap it out, I would look at your alternator cables. They're probably too small, see this chart from Powermaster and compare to your alternator.



Depending how the car is wired, I would reconnect what's at the alternator post now (you might have a wire that goes to the fuse panel) and run a new correctly-sized wire to either the same post on the starter as the battery cable or directly to the battery and a similarly-sized cable from the alternator's housing to a good chassis or engine ground. Wouldn't be a bad idea to install a 100-amp Mega-Fuse inline on the +12v alternator cable either, but this isn't always a simple job due to space constraints, etc. If the rest of the wiring system is good, that should be a huge step in the right direction.

 

Thanks, I bought one. Cheers.

 

The one-wire alternators usually need to be "excited" to a preset rpm (1800 - 2000) to begin charging upon each start. Also the one-wire (aka charging wire) should be of sufficient gauge according to the manufacturer (6 or 8ga.). As mentioned the voltmeter ga. is a necessary tool to chase electrical issues.

 

Thanks for your help. No worries if I hooked the alternator directly to positive terminal, wouldn't overcharge? I feel the problem in under dash wiring. At 73 years old, it's a XXXchore to get under there anymore for more than a few minutes. I took it for a drive at highway speeds and still only 12 Volt charge at battery, that's why I think the problem is in the rat's nest under dash. Thanks.

 

Got a meter, still chasing. I would rather swap motors than do this, as this is endless. Plus, no friend to help. They have all left the building by one door or another.

 

Rick, I have a one wire alternator on my 1950 Buick. Simply ran an 8GA wire from the alternator to the same post on the starter as the Pos Battery cable is hooked to. Effectively, to the battery. Left all other wires in place. Installed a volt meter/gauge hooked to a " key on" post , don't remember just where. It has been this way since 2012. Others are correct, a little throttle "blip" is needed to excite and start charging, but bet most of us do that blip anyway. Running direct will not cause nor allow an overcharge as the "regulator" is built into the alternator.
My 1992 daily driver has 4ga cable from the alternator. Bigger is better?!

Ben

 

Thanks, Ben. I believe I'll try that. Not looking for a perfect solution at my age. Only need to get there (and back HOME of course). Cheers

 

Why I just use the standard old GM alt. When all is said and done it has only two wire. Don’t have to rev it to charge just start and it works.At least for the last 25 years. Not chrome either.

 

My old heap came with a one wire, has worked fine until last week, it's a Ford and they are different as I'm finding out. Cheers.

 

I came here to say that. I really wish that people would stop leading other people to ruining alternators.

 

I have seen too many one-wire alternators disengage charging at low RPMs.

This is exactly the engine speeds that vehicles are driven in most often. That is why I refuse to install them.

You can have one that is "functioning as designed" and have it leave you stranded.

Having an alternator that can charge the instant both the switch is in the IGN position, and the alternator is turning is a much better idea.

 

" functioning perfectly fine & leave you stranded " applies to virtually everything .

 

That nonsense of disconnecting the battery to see if an alternator is charging has been around ever since Chrysler engineers took the battery out of a new car and drove 328 miles from Detroit to Chicago, ever since every back street grease monkey has thought that is how you test an alternator.
The one wire is feeding the electrical system with the key on and that is why it still runs unlike the exciter wire backfeeding to the ignition after the key is shut off.
1 wire alternators that were originally designed for farm tractors with magnetos and then picked up by hot rodders who liked the idea of less wires around the engine. That is really the only viable reason to use one, you want less wires showing or to hide.
If you don't gun the engine a bit to excite the alternator it might not charge every time . That's a non issue with most hot rodders as we tend to give it a couple of raps no matter what we have to charge the battery with.

Still you have to find out why it isn't keeping the battery up.
The alternator should put out right at 14.2 volts if it is working right. On a rod with no extra accessories to drag down the system 13.
Check the voltage output with a volt meter or take it to someone who has a tester that can test alternator output and battery condition. The local tire chain here has a tester that can do it all in about 2 minutes and tell you exactly what you have going on.

 

What is the voltage at the battery when not running?
What is the voltage at battery when running?
What is the voltage at the alternator when running (after revving engine to exite the alternator)?

 

I been using one wire alternators for years, I don't blip the throttle anymore. Start it up and head down the road, first gear is low enough that the rpm goes high enough to excite the alternator.

 

Pretty simple , you either have a junk alternator ,a junk battery or junk wiring , that's on!y three things to investigate , BTW the way ,is the fan belt tight ?

 

I forgot to mention. The alternator case needs to be grounded. Not through the brackets and bolts attaching it to the engine. There should be a screw/bolt on the case where you can run a minimun 12ga. ground wire to the frame of the vehicle.

 

All new battery, battery cables, new alternator. Belt new and tight. Thanks. And you are right, it should be simple...