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Old 05-14-2021, 04:25 PM   #1
bobmc
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Default Amp guage not working, battery not charging

This is for all the electrical guru's out there. Sorry this is going to be long. I have read all the threads about the junk amp meters being sold by the venders, and i agree they are of poor quality. But that is not exactly what this post is about. Yes my amp meter quit working yesterday, but something else happened. The car battery was no longer being charged. I barely made it home on the battery power. Now when the meter stopped working it went from 8-10 positive amps to 0. The use of power (lights /horn/etc.) would show a negative movement of the meter and return to 0. It wasn't until i got home and was able to test the system with the multi-meter. The 6 volt generator was showing a 7.4 volt output. According to a chart i acquired somewhere that is equal to 10 amps? I continued to check the terminal box and it showed the same output 7.4. on the passenger side (+)
but only 6.3 on the drivers side (-). Now moving to the battery the fluke meter only showed 6.3 volts Not having a nos meter and it was i nice day for a drive it went to the local parts supplier and purchashed a China made unit. This is where it get interesting. I installed the new meter in the dash just like the old one was. Started the car and the meter remained on 0. It did not mater what the engine speed was the needle never move, except to indicate discharge. But checking with the fluke meter i was getting the same reading on both sides of the terminal box when the car was running. Just another note i attempted to start the car when the meter was disconnected and it only crank, no start. So the bad meter needed to be in line but was serving no purpose. At a loss what to do now?
Thanks
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Old 05-14-2021, 04:49 PM   #2
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Default Re: Amp guage not working, battery not charging

It sounds like your original ammeter was good. The problem is earlier in the system. First thing I would do is to short the output directly from the generator to ground before the cutout and see if you get sparks to determine the generator is working. You must have the engine running to check this, so you may have to put the old ammeter back in or just jumper the two ammeter connections. If the generator is working, it may be the cutout is not working. If it is a diode cutout, it may have burned out. If it is a original type, the contacts may be bad.
After trying this, get back to us and we will advise further.

Last edited by midgetracer; 05-14-2021 at 04:51 PM. Reason: clarify shorting generator
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Old 05-14-2021, 05:05 PM   #3
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Default Re: Amp guage not working, battery not charging

The generator was rebuilt two weeks ago. I was thinking along the same lines so i replaced my gen with my spare. Same results with either gen.
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Old 05-14-2021, 05:06 PM   #4
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Default Re: Amp guage not working, battery not charging

Also i was showing voltage (7.4) at the gen and the terminal box
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Old 05-14-2021, 06:13 PM   #5
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Default Re: Amp guage not working, battery not charging

We have to assume that you have a model A type generator of one type or the other. Does it have an original type cut out or is it a diode that looks like a cut out? There is also the Fun Projects voltage regulator that looks like a cut out so it's important to know what you have.

The original form of the 3-brush generator system does not have a voltage regulator. The battery is the regulator for the system. All the generator does is put out current depending on the adjustment of the 3rd brush with the same basic voltage as the battery and just enough added voltage to overpower the potential of the battery. The battery condition and circuit connections have to be good for everything to function properly.

Even a 3-brush generator needs to be polarized so that the residual magnetism in the field pole shoes will generate enough current to close the cut out and bring the generator on line or at least push through a diode if that's what it has. If it has a fun projects voltage regulator that looks like a cut out then it may have problems. The voltage regulator gives a different reading on the amp meter when it functions properly. It only puts out enough amps to charge the battery back up and then it goes back toward zero on the meter. The amp meter only measures flow of current. If there is little or no current draw then the amp meter won't show much charge or discharge if things are working properly.

Last edited by rotorwrench; 05-14-2021 at 06:19 PM.
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Old 05-14-2021, 08:08 PM   #6
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Default Re: Amp guage not working, battery not charging

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Sorry, Both the rebuilt and spare gens are original with nurex cut outs. I have had this car for going on 10 years now. As long as i have had it the amp meter always showed 8 to 10 amps charge. I never witnessed the meter dropping because the battery was charged. Even on a long tour i would turn on my lights to reduce gen output,

Without going into detail of the wiring the yellow wire from the starter connects to the amp meter thru the terminal box. the black with yellow returns from the other side of the amp meter to the other side of the terminal box where it connects with the black wire to the coil. So how does the battery get recharged? Does the current reverse?

Also as indicated earlier the reading at the cut out and terminal box was 7.4 volts which is 8-10 amps
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Old 05-14-2021, 08:58 PM   #7
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Default Re: Amp guage not working, battery not charging

The black and yellow goes from the terminal box to the cut out.
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File Type: jpg wiring-diagramcolor2sm.jpg (82.1 KB, 38 views)
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Old 05-15-2021, 04:52 AM   #8
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Default Re: Amp guage not working, battery not charging

Bob That is true. But there is also a yellow and black wire that comes from the amp meter to the same connection in the terminal box, and the black wire for the coil all connect together. I have check several times and the wiring is exactly how the enclosed diagram indicates.

As sensitive as the model A is to poor ground issues is there any way a bad ground could effect the amp meter?
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Old 05-15-2021, 05:56 AM   #9
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Default Re: Amp guage not working, battery not charging

[QUOTE=bobmc;2016745]Bob That is true. But there is also a yellow and black wire that comes from the amp meter to the same connection in the terminal box, and the black wire for the coil all connect together. I have check several times and the wiring is exactly how the enclosed diagram indicates.




Thats not the way they are wired.
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Old 05-15-2021, 06:38 AM   #10
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Default Amp guage not working, battery not charging

The ammeter is a “straight through” connection, correct? It doesn’t depend on a chassis ground.


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Old 05-15-2021, 06:54 AM   #11
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Default Re: Amp guage not working, battery not charging

Patrick if you look at the diagram in Bob C post that is how the car is wired. I do not understand your post. Do you wire it differently?

Shew01 I am under the belief that your are correct. That is why this is so puzzling. How can the amp meter effect the charging of the battery? And if is indicates negative draw why does it not show positive charge?
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Old 05-15-2021, 07:01 AM   #12
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Default Re: Amp guage not working, battery not charging

With the engine off use the ohm setting on the Fluke to measure the resistance between the two terminals on the junction box on the firewall. It should be very low resistance, only a few ohms. Then measure the resistance at other places along the path from the generator to the battery following the wiring diagram. You will find an open circuit somewhere. It may be a connection, in which case take the connection apart and clean it up and then use an electrical grease, available at hardware stores, when you re assemble the connection.

A common problem is the grounding of the battery. It should be grounded to the frame and a ground run to the engine.
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Old 05-15-2021, 08:07 AM   #13
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Default Amp guage not working, battery not charging

Quote:
Originally Posted by bobmc View Post
Patrick if you look at the diagram in Bob C post that is how the car is wired. I do not understand your post. Do you wire it differently?

Shew01 I am under the belief that your are correct. That is why this is so puzzling. How can the amp meter effect the charging of the battery? And if is indicates negative draw why does it not show positive charge?

I did have an ammeter go bad a while back, and the car would crank but have a hard time starting (which does not appear to be your current issue). You can connect a temporary jumper wire between the two posts on the junction box to take the ammeter out of the equation. That’s how I identified the bad ammeter on my car.

I’d also recommend removing any accessory connections (like a tachometer) at least temporarily from the car. It’s easier to debug with stock connections. If anything else is in the circuit, the folks on the forum will not know or expect it, and that tends to slow down the debug process.

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Old 05-15-2021, 08:20 AM   #14
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Default Re: Amp guage not working, battery not charging

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Originally Posted by bobmc View Post
So how does the battery get recharged? Does the current reverse?
Yes it does. When generator voltage rises above battery voltage, current, like water, flows downhill.

Your problem could well be the battery ground connection at the frame. Clean up the frame connection and see if it improves. You can also run a #12 copper wire between the generator case and the battery ground post to eliminate all the incidental mechanical connections between them.
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Old 05-15-2021, 08:42 AM   #15
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Default Re: Amp guage not working, battery not charging

Quote:
Originally Posted by bobmc View Post
Patrick if you look at the diagram in Bob C post that is how the car is wired. I do not understand your post. Do you wire it differently?

Shew01 I am under the belief that your are correct. That is why this is so puzzling. How can the amp meter effect the charging of the battery? And if is indicates negative draw why does it not show positive charge?



One wire from starter to one connection in terminal box.
One wire from cut-out to other connection in terminal box.
The ammeter is connected across the terminal box. The starter wire to one ammeter terminal and the cut-out wire to the other ammeter terminal.

One terminal wire to coil - primary connection.
Coil + primary terminal to key switch, [ if battery is + grd]

Depending the year depends on which wire goes where is the terminal box, but, it doesn't really make any difference, it'll work either way.

If the ammeter ends up working backwards just reverse the 2 ammeter wires. That'll depend on battery grd.


It sounded from your post that you don't have it wired that way. Maybe I misunderstood you, but, it seemed you're using 2 wires from the same connection.

Last edited by Patrick L.; 05-15-2021 at 10:18 AM.
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Old 05-15-2021, 09:17 AM   #16
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Default Re: Amp guage not working, battery not charging

Folks really shouldn't worry about voltage in this system. It's all about amperage output. The amp meter just shunts a sample while the current passes through it so that it can tell what the difference between the draw of the load and the output of the generator. The voltage should increase enough to overpower the potential of the battery but that'a all it can do. The generator can not put out more amperage than what it is adjusted for.

Folks that mention checking grounds are giving good advice. The battery should be as well connected to the car as possible and all ground paths should be clean and tight. A loose connection makes resistance and resistance is a load on the system. Resistance makes heat that can damage things. Check your battery voltage. A good battery should be just a bit over 6-volts. If it won't maintain that or it runs out of capacity too quickly, it may need to be replaced. The battery is what maintains the system voltage within acceptable levels so it's condition is very important.

It's too bad that no company manufactures a decent replica of the original amp meter. Now and then, good originals and original replacements come up on flea-pay and other sources. I'd be looking for one of those myself.
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Old 05-15-2021, 10:15 AM   #17
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Default Re: Amp guage not working, battery not charging

The generator provides a charging current back thru the ammeter wiring to the battery. Yes it looks like the current is reversing. The current laws will allow current flow to LEAST resistance. Hence ammeter reading either charge or discharge depending on current flow thru the ammeter. Ain’t that just plain baffling?
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Old 05-15-2021, 10:20 AM   #18
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Default Re: Amp guage not working, battery not charging

Model A wiring.jpg



There is another wiring diagram that more clearly shows the connections, but, for some reason I can't get it post


Model A wiring.jpg

Last edited by Patrick L.; 05-15-2021 at 01:42 PM.
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Old 05-15-2021, 04:13 PM   #19
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Default Re: Amp guage not working, battery not charging

Thanks for all the great suggestions. Family matters are taking over the weekend so the car will have to wait until Monday. I will go over the connections and grounds and report back the the verdict.

Thanks for all the help

Have a safe and happy weekend!@
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Old 05-16-2021, 09:08 AM   #20
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Default Re: Amp guage not working, battery not charging

Check the screws/posts/bolts holding the terminal box
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