Alternator Voltage (1 Viewer)

[cb97angler]

I roasted a battery with very little usage over a year and a half of use and it sat on a trickle charger while not in use. I figured I'd look for issue. Turns out I was getting inconsistent current from 13 to 15.8 volts at alternator and battery. I figured VR, replaced and same issue. I saw someone say if VR is wired with switched wires it would not work at all. This got me thinking that when I did power steering and moved alternator to passenger side of engine, maybe I swapped wires. After swapping wires yesterday I get a constant 12.7V at alternator and at battery. Does this seem correct? 1974 F.5 engine with 1977 45 amp alternator. Seems low but being an old vehicle I am thinking maybe stock alternator only puts out 12.7V not higher 13 or 14 like modern alternators. Thanks for any replies.

 

[Steamer]

12.7 is not enough. Do you also get 12.7 when not running? In other words, not charging at all.
If you can read this diagram, you'll see how it works and where the wires go.
Take note alt components are within the red square. Regulator parts are within the green square.
EDIT: added in the 3 wire color id's.

 

[cb97angler]

OK thanks for the schematic. I will have to trace my wires from alternator to vr and confirm they are correct as well as the wire running from positive Battery to under dash and make sure it goes to ammeter, then ignition, I don't think it does, I think it only feeds the radio etc, and the only other wire coming off positive side goes to starter. So possibly the VR is not seeing the battery and its need to be charged, although that doesn't make sense because when I turn key the ammeter registers the amps from battery while not running. When not running the battery voltage creeps back up to a 13.4 resting voltage. That's kind of what tipped me off that voltage was low.

 

[Steamer]

Post deleted after editing the diagram above.

 

[JohnnyC]

Are you checking it’s output at idle only?

What’s the voltage when at higher rpm’s?

 

[cb97angler]

Good point. I will check at higher rpms in a bit and report back. Thanks again for taking the time to help me with this.

 

[cb97angler]

Yep just got home and tested... Even at high rpm voltage at alternator is 12.7v. As side note. Alternator is brand new yesterday.

 

[cb97angler]

OK now I am lost.... I switched VR wires back, everything is how it was when it was pushing 15v but now still sitting at 12.7v. At higher rpm it goes up to 12.83v. What the heck is going on here...

 

[sodafeld1]

maybe try take your alternator, even though it is new (quality , one would hope), and get your local sparky to bench test it. It is the quickest fail safe way to know if alt works. If they are good they don't charge you, but do it in their own time. Bench testers are exy.
Simple yes/no.

Second guess from here is your reg. I did have problems in the long past on a 'b' engine finding a suitable reg. Alternators are often quite regulator specific, you need the right one. The trouble is, every aftermarket alt has a different aftermarket reg, a sparky's nightmare, all made at differing levels of quality.

If your reg or alternator dies, it quickly kills your battery, which gets expensive. If driving at night and lights went bright then slowly get dimmer driving on, your alternator just died.

12.7v is the minimum a new battery should hold on the shop shelf. It needs to charge above 13v to put something at all into the battery, preferably over 14v. Over 15-16v you are cooking your battery. The job of the reg.

Smart charges are the best, they do a flood and float charge to maintain your battery without cooking it.

check your alt, then make sure your reg works and it is the correct one whilst the engine is running at different revs. Too low, it does nothing, too high it fries your battery. Installing a cheap ebay cig lighter volt meter is handy.

Needless to say all connections and earths need to be clean, non corroded and tight.
(Makes me grimly smile a bit that the world is heading to all electric, there shall be big calamities!)

 

[middlecalf]

I roasted a battery with very little usage over a year and a half of use and it sat on a trickle charger while not in use.

Based on your first sentence I doubt you roasted your battery from the specified very little use even if at only 12.7 charging volts during its specified very little usage. I’d check that trickle charger, I’ve had them kill batteries, esp. cheap trickle chargers.

 

[cb97angler]

Ha, well that's why reading past first sentence helps.... I was pushing almost 16v consistently.... Not 12.7. I am at 12.7 now....

 

[cb97angler]

But also yes, I got rid of my trickle Charger and got a new one as well. Just in case...

 

[mrboatman]

I use a 12V Deluxe Battery Maintainer and Float Charger and have had no problem for several years now.

 

[Steamer]

Was your new VR aftermarket? I ask because years ago, I got one from Cool Cruisers and right off, it was charging excessively high. I had to adjust it down and then it worked fine. A year or so later when I had the hood off and a tarp over the engine bay, the VR got exposed to rain & rusted up inside. Forgetting the over charging incident, I bought another VR from Cool Cruisers. I remembered the incident when the second VR was also over charging and required adjusting.

Also keep in mind, the VR isn’t a variable regulator but more like a three-position switch with the three positions being “High”, “Medium” and “Off” so jumps in charging voltage is normal.

HIGH = full vehicle voltage is delivered to alternator field.

MED = resisted vehicle voltage is delivered to alternator field.

OFF = resisted vehicle voltage gets grounded so zero is delivered to alternator field.

Rudy did a very nice write up on this “HERE”

 

[Grayscale]

When you read Rudy's write up, he says that when the F terminal is grounded, in the voltage regulator, the charging stops.

I was just looking thru my museum of harness parts, and noticed that the ground wire on a used voltage regulator subharness was really green/oxidized copper. If the firewall gets wet, this would be a wire to inspect. Could a bad ground here cause an overcharge?

 

[Steamer]

Could a bad ground here cause an overcharge?

Yes. With no ground, it would still deliver resisted voltage to the alternator field (F terminal) and would charge as in middle position.
I'm just thinking I may have better described the three positions as "Full", "Reduced" and "Off".

 

[Malleus]

Was your new VR aftermarket? I ask because years ago, I got one from Cool Cruisers and right off, it was charging excessively high. I had to adjust it down and then it worked fine. A year or so later when I had the hood off and a tarp over the engine bay, the VR got exposed to rain & rusted up inside. Forgetting the over charging incident, I bought another VR from Cool Cruisers. I remembered the incident when the second VR was also over charging and required adjusting.

Also keep in mind, the VR isn’t a variable regulator but more like a three-position switch with the three positions being “High”, “Medium” and “Off” so jumps in charging voltage is normal.

HIGH = full vehicle voltage is delivered to alternator field.

MED = resisted vehicle voltage is delivered to alternator field.

OFF = resisted vehicle voltage gets grounded so zero is delivered to alternator field.

Rudy did a very nice write up on this “HERE”

Rudy's post is my new favorite electrical thread. This needs to be in the FAQ.

 

[peesalot]

battery shows 13.4 at rest ? Possible the system is at or above voltage therefore the regulator is not exciting the alt. ? 2 things to look at - is alt. putting out juice ? is reg functioning correctly, thats where the bench test of alt comes in handy. Once thats determined you can check to see if the reg is actually regulating the output you have confirmed from the alt.

 

[Steamer]

Another quick test without removing components would be to physically move the VR through it’s three positions. Take the VR cover off and with something non-conductive, (toothpick works) move the arm that holds the center contact to engage the full charge contact, the grounded contact, or keep it in between for the reduced charge. Watch a connected voltmeter.

 

[cb97angler]

Update on this, after having the old alternator and the new alternator bench tested, both failed. So I went from putting out almost 16v at battery to alternators dying on me after replacing voltage reg. I was going to get another alternator and another voltage reg from dealer, re-wire from F and E and confirm ground in between was good, but the wires being 48 years old got me thinking about going a different route. I got a 10si 1 wire. Had to do some grinding on the alternator and on the existing alternator bracket, but it's in and after doing separate ground to block from alternator, cleaning up my battery ground and running wiring to battery, I am getting 14.2 volts at the battery at idle. I am happy. I did the research concerning the 10si and decided it was the right decision for my needs and usage. May not be for everyone. downstream if I feel I need to go beyond the self excite, the 10si has the 2 wire setup under a cover, so I can access that and wire it to ignition system. When I get some time I will add a write up of installing the 10si onto the passenger side alternator bracket. Side note, thank you all for the input and helping me try to get this solved. Much appreciated.