System voltage is low - Battery not charging

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This is the current wiring at the back of my alternor:

-One field wire is grounded to the block
-The other field wire is a part of the original harness
-Three wires on the battery post:
Original harness, under hood bypass, under dash bypass.

 

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I am at a loss. I clearly didn’t understand the jumper wire advice. When I reconnected the battery all I got was smoke and melted connector. I will go back to my FSM and try and figure it out. Hope I didn’t fry my system.

 

[Big_John]

I am at a loss. I clearly didn’t understand the jumper wire advice. When I reconnected the battery all I got was smoke and melted connector. I will go back to my FSM and try and figure it out. Hope I didn’t fry my system.

What did you connect the jumper wire to?

It should go to the field connection on the alternator to the output post. It can also go to the +post on the battery, just be aware that a discharged battery gives off explosive hydrogen gas and sparks aren't good.

I notice that you have a later alternator with 2 field connections. One is grounded, as you need to do with a later alternator to duplicate the internally grounded early (1969 and earlier) alternator. For the test, you don't touch that wire or connection. If I'd seen you were running that, I would have noted it.

The wire you disconnect is the one running to the voltage regulator. In the stock, OEM wiring, this is a green wire. Once you disconnect that, the jumper goes on the alternator terminal to the output terminal.

What this does is duplicate how the system works, bypassing the VR. The headlights are on to have a heavy draw on the system. The FSM uses a carbon pile to create a heavy draw, but it's not something most people have.

 

[SPF Required]

I truly appreciate your advice @Big_John

The only labels on the alternator are ‘field’ (2 of those ) and ‘battery’

I left the ground attached to the upper field terminal
I disconnected the dark green wire from the other field terminal (looks black in the pic above)
I jumped from that 2nd field terminal to the battery post on the back of the alternator. (I had a pic, but in frustration/embarrassment with myself I deleted it)

When I reconnected the battery the jumper connected at the field terminal on the back of the alternator melted down. I pulled the battery cable off as quick as I could.

I reassembled everything back to normal. Had 12.5v at the battery, 12.5 v on the ignition side of the voltage regular with key on. Started the car and the voltage at the battery dropped to 11.8v. Ran it for a bit to get the temp up (to checking my radiator project). All ran fan, but still no charge coming at the battery.

My frustration got the best of me so I packed it in for the day. I will probably pull this alternator and return it back to Napa and start over next weekend.

 

[rags]

When I reconnected the battery

the test is supposed to be done with the engine running and the battery connected. the jumper would only be connected momentarily under the above conditions. at least now you know the field windings have (had) continuity. hope that they are not plain shorted...

 

[SPF Required]

I am beginning to think I got a bad alternator from Napa. While I figure out that return process, is there a way to bench test the voltage regulator? The old school one and new solid state one??

I did some continuity testing on the wires and those seem to check out.

Last question. What Amps were the original alternators (1968 300 with 440 non TNT)

Learning new stuff everyday!

 

[rags]

I am beginning to think I got a bad alternator from Napa.

i rate napa's electronics as at the level of diseased meat. they may have a test bench at the store. i know that the other large chains do. whether anyone there knows how to use them? upside is that, at least at my local napa, they don't question the warranty return. if the alternator is still in the car you try the test again. if done correctly it is conclusive and takes all of two minutes.

 

[SPF Required]

Have a new 78 amp alternator coming tomorrow. Turns out this is what my engine was upgraded to when I had it rebuilt a while back with EFI, etc., etc. I also have a new voltage regulator and I have confirmed the field wire between the 2 is intact. I have also confirmed I do have battery voltage at the ignition side of the voltage regulator when the key is on.

Sooooo…. IF the alternator I receive is good, and IF the regulator functions as normal, and I have 12v on the ignition side, and the field wire going back to the alternator is good….. where would be the next place to look if I am not getting 13-14 volts at the battery when it is running?

I realize there are a lot of assumptions and ‘ifs’ in that scenario above, I am just try to forecast my next steps tomorrow in the event I am still at battery voltage when I fire it back up.

 

[rags]

where would be the next place to look if I am not getting 13-14 volts at the battery when it is running?

to a place other than napa for electrical parts. just kidding. fingers crossed it's going work! the only thing i would question overall are the ten gauge wires coming off the battery post of the alternator. they don't seem adequate to charge the battery through. won't keep the system from working though.








1

 

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I’ll provide an update tomorrow.

 

[SPF Required]

I am looking into swapping out that 10 gauge wire as recommended. Before I get too deep in though, I am of the understanding each of the bypass wires (under hood and under dash) are meant to help with the load from the alternator, not necessarily carry the whole thing (unless of course there is a melt down in the other circuits).

When I look at recommended wire sizes for a 78 Amp alternator the interwebs indicate I should use 6 gauge wire. Not a problem, easy to find all over town. But if I follow the same logic as before, would I then also include a 8 gauche fusible link wire? This size fusible link does not appear to be as easy to find.

 

[Big_John]

I am looking into swapping out that 10 gauge wire as recommended. Before I get too deep in though, I am of the understanding each of the bypass wires (under hood and under dash) are meant to help with the lid from the alternator, not necessarily carry the whole thing (unless of course there is a melt down in the other circuits).

When I look at recommended wire sizes for a 78 Amp alternator the interwebs indicate I should use 6 gauge wire. Not a problem, easy to find all over town. But if I follow the same logic as before, would I then also include a 8 gauche fusible link wire? This size fusible link does not appear to be as easy to find.

You could run another #10 wire in parallel with fusible link etc.

Two #10 wires in parallel is the equivalent of one #7 wire. (Yea, I know, nobody sells a #7 wire... But that gauge does exist.)

 

[rags]

out of curiosity, i took a look at the wiring in my '69. single 10ga wire on the battery post and what appears to be a 8ga link at the battery itself. it's all been there since the late '80s with no problems.

take it as you will.

 

[Big_John]

I am looking into swapping out that 10 gauge wire as recommended. Before I get too deep in though, I am of the understanding each of the bypass wires (under hood and under dash) are meant to help with the lid from the alternator, not necessarily carry the whole thing (unless of course there is a melt down in the other circuits).

When I look at recommended wire sizes for a 78 Amp alternator the interwebs indicate I should use 6 gauge wire. Not a problem, easy to find all over town. But if I follow the same logic as before, would I then also include a 8 gauche fusible link wire? This size fusible link does not appear to be as easy to find.

You could run another #10 wire in parallel with fusible link etc.

Two #10 wires in parallel is the equivalent of one #7 wire. (Yea, I know, nobody sells a #7 wire... But that gauge does exist.)

Taking this one step farther, when you think about it, your #10 wire is now in parallel with the existing #12 wire that goes through your ammeter etc.. That gives the equivalent of one #8 wire in current capability (in theory anyway). You might be losing something in connections on the #12 wire, but if you added another #10 wire, you are now at the equivalent of one #6 wire.

Here's an easy web page for figuring that out. Wire Combination Calculator

 

[SPF Required]

Taking this one step farther, when you think about it, your #10 wire is now in parallel with the existing #12 wire that goes through your ammeter etc.. That gives the equivalent of one #8 wire in current capability (in theory anyway). You might be losing something in connections on the #12 wire, but if you added another #10 wire, you are now at the equivalent of one #6 wire.

Here's an easy web page for figuring that out. Wire Combination Calculator

Love the idea of running some parallel lines. Mainly because I a cheap and don’t want to buy new wires! I have lots of 10 gauge and small fusible links lying around.

 

[SPF Required]

Got the new alternator in. I also did continuity test on all the wire coming off the alternator. All seemed to check out ok. Finally figured out the jumper wire you described earlier.

Started the car, turned on the lights, and jumped the field wire to the negative post on the battery. Volts went from an idle at around 11.9 down to about 9.0 (I thought it would go up). only ran it like that for like 4 seconds and pulled the jumper wire off the battery and shut ‘er down.
Also, does it matter which field wire is grounded on the back of the alternator? In my case, the field terminal point towards 2 o’clock is the one grounded to the block.

 

[Big_John]

Got the new alternator in. I also did continuity test on all the wire coming off the alternator. All seemed to check out ok. Finally figured out the jumper wire you described earlier.

Started the car, turned on the lights, and jumped the field wire to the negative post on the battery. Volts went from an idle at around 11.9 down to about 9.0 (I thought it would go up). only ran it like that for like 4 seconds and pulled the jumper wire off the battery and shut ‘er down.
Also, does it matter which field wire is grounded on the back of the alternator? In my case, the field terminal point towards 2 o’clock is the one grounded to the block.

View attachment 620280

It doesn't matter which field is grounded.

But you need to jumper the other field connection to positive not negative for the test.

 

[SPF Required]

Gotcha. Back to the garage I go!

 

[SPF Required]

But you need to jumper the other field connection to positive not negative for the test.

Well baby steps in the right direction…. I did see the voltage head in the right direction, but not much. From an idle voltage at around 11.8 up to 12.3, but then dropped back down a little when I gave it some throttle…. nowhere near the 13.5-14.5 I am reading it should be to charge the battery.

May need to get this over to a pro if I plan on enjoying it at all this fall.

 

[rags]

I did see the voltage head in the right direction, but not much.

and that was while the jumper was connected.

but then dropped back down a little when I gave it some throttle…

and all the while the jumper was connected? the jumper replicates what the voltage regulator would do up to doing exactly what the jumper is doing: full fielding the alternator. the voltage regulator on it's own really should have been able to produce the exact results that the jumper did. the thing that i would do now is to check the voltage across the field terminals with the engine running and no jumper. it should be about the same as battery voltage if the battery voltage is below twelve. it sounds as if it's another bad alternator. when it was my '65, i got the cheapest $35 reman from autozone and it's still in the car today.