Another ammeter thread...sorry (1 Viewer)

Cruiser804

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I know this subject has be discussed at length. I have read the thread by LostMarbles but still not sure where to go next.

Like most my ammeter doesn't appear to work. (I know, who cares. But I would like it to work. I am OCD that way) . I have checked and replaced the fuses and the fusible link with a new one provided by Coolerman. The meter does not move at all either way, with an additional load, with the - battery cable disconnected, nothing stays right in the middle, not even a tiny amount.

So as a serial parts replacer I would normal just replace the gauge. Seems to me that the one two components that are left in the system are the wiring and gauge. I am thinking I should check the voltage at the gauge? Not sure what that should be but I guess something relative to the battery voltage?

If there is voltage at the gauge I assume it is bad.

Thanks
 

John Smith

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I know this subject has be discussed at length. I have read the thread by LostMarbles but still not sure where to go next.

Like most my ammeter doesn't appear to work. (I know, who cares. But I would like it to work. I am OCD that way) . I have checked and replaced the fuses and the fusible link with a new one provided by Coolerman. The meter does not move at all either way, with an additional load, with the - battery cable disconnected, nothing stays right in the middle, not even a tiny amount.

So as a serial parts replacer I would normal just replace the gauge. Seems to me that the one two components that are left in the system are the wiring and gauge. I am thinking I should check the voltage at the gauge? Not sure what that should be but I guess something relative to the battery voltage?

If there is voltage at the gauge I assume it is bad.

Thanks

Your gauge is probably shot. When I bought my 79, my ammeter actually moved some. Nothing like the 78 and earlier ammeter gauges, but I know it worked. A few years later it stopped working. I checked the fuses and everything was fine. I just installed a Auto Meter volt meter and forgot about it. I didn't know at the time you could buy replacement gauges for the cluster. Have you priced a new one from CDAN?
 

Cruiser804

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I have not priced one from CDAN yet. I usually deal with Onur (Beno) there. But one of the on line OEM sites showed it for around 85.00. I would expect American to be around 100.00.
 

Coolerman

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I agree the meter sounds like it's toast...

Can you post some feedback good or bad on the replacement fusible link?
Anything that I should change, or could improve on? Wires long enough, too long? Not having an actual model to base it on, I build then from a description and a picture. ;)
 
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If you've read my thread you'll see that I think the late-model ammeter (shunt-type) design is flawed Cruiser804.

I think people who like to keep their cruisers as close as possible to "ex-factory condition" (with good batteries that are never far off being fully-charged) and who haven't added things that promote increased needle movement (like high-output alternators or electric winches) can expect to see no needle movement from their shunt-type ammeter even when the ammeters themselves are PERFECT.

You can of course get movement by increasing the resistance of your shunt/fusible-link (by decreasing its gauge or increasing its length) ... but IMO this has the undersirable effect of reducing the reliability of your entire electrical system (by making the fusible link more likely to blow in the event of a HIGH current flow ... such as you would experience if your alternator were to be charging a dead-flat battery).

As you will have seen from my thread, I now run with an aftermarket voltmeter that tells me all I need to know about the condition/charge of my battery and how well my alternator in performing during day-to-day running.

For me, my ammeter is there mostly just for show.... but I expect it to "come to life" if I ever do something like:
  • run my cruiser with an old battery that won't hold its charge properly
  • fit an electric winch (or other heavy electrical load) that draws more than my alternator can supply
  • fit a higher-output alternator
  • run a fridge off my battery when I'm parked
  • etc
:beer:

PS. But if you do find a means of making your ammeter become really useful (without compromising reliability) then I might be keen to copy.....So good luck in your quest and I'll be following this thread with interest.
 
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First check the meter resistance by removing the fuses and putting an ohm meter on the side of the wires that run away from the fusible link. It should have about 10-100 ohms (I'm guessing) and it should not be open or have infinite resistance.

If the meter is good, then the reason you don't see it move is because your battery is charged and the charging system is working. It should deflect noticably to the left if you turn on everything in the truck without the engine running.
 

bj40green

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First check the meter resistance by removing the fuses and putting an ohm meter on the side of the wires that run away from the fusible link. It should have about 10-100 ohms (I'm guessing) and it should not be open or have infinite resistance.

If the meter is good, then the reason you don't see it move is because your battery is charged and the charging system is working. It should deflect noticably to the left if you turn on everything in the truck without the engine running.

The ammeter is a shunt type. In other words there is a metal strip with very low impedance (resistance) where the actual meter reads millivolts (induction) which are translated in amps on the scale.
So if the (resistor) strip is ok and the meter is broken, the charging sytem will work but the reading is zero.
The resistor strip is something close to 0 ohm. See pic below.
Image-30 detail.jpg

So; how to figure out if the ammeter is ok or not.
Meassure between ground and the + of the ammeter (key is in on position). There should be 12V.
The same for ground and - of the ammeter. there should be 12 V.
Now switch on your headlights and meassure between the + and the - of the ammmeter. You should meassure a voltage drop of less then 1 Volt. If this is so the circuit is OK but the meter itself is kaput.
If all you readings are 0 but the battery is charged, it means that the ammeter is bypassed somewhere.

Good luck.
Rudi
Image-30 detail.jpg
 
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The ammeter is a shunt type where the actual meter reads millivolts (induction) which are translated in amps on the scale. .......................................................Good luck.
Rudi

I think your pictures refer to the earlier-type ammeter Rudi.

The later type that we're discussing here uses the main fusible link as its shunt as shown in this image:

ChargingCircuit.jpg

:beer:
ChargingCircuit.jpg
 

bj40green

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Thanks Tom for the education. Another lesson learned.
Mine is a '78 and Cruiser804 is a '79 so I thought "we" have the same cluster, but not.

Anyway, the method for checking the working of the ammeter is the same.

Rudi
 
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Thanks Tom for the education. Another lesson learned.
Mine is a '78 and Cruiser804 is a '79 so I thought "we" have the same cluster, but not.

Anyway, the method for checking the working of the ammeter is the same.

Rudi

I gained a lot from your post anyway Rudi.

Up until reading it, I hadn't absorbed the fact that the old and new-type ammeters are BOTH "shunt-ammeters".

So I should really be describing the later ammeters as "EXTERNAL-shunt" (as opposed to "INTERNAL-shunt").

And because they are both operating from exactly the same principals, I guess in theory we should be able to get our latter versions to work just as well as your earlier version.


:beer:
 

bj40green

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I gained a lot from your post anyway Rudi.

Up until reading it, I hadn't absorbed the fact that the old and new-type ammeters are BOTH "shunt-ammeters".

So I should really be describing the later ammeters as "EXTERNAL-shunt" (as opposed to "INTERNAL-shunt").

And because they are both operating from exactly the same principals, I guess in theory we should be able to get our latter versions to work just as well as your earlier version.


:beer:


To put the last dot on the I and to cross the T, the one I described in post #9 reads the magnetic field in the shunt resistor and the one you showed in post #10 is actually a millivoltmeter which reads the voltage drop over the shunt resistor. As Tom said before, the principal is the same.

Saludos :cheers:

Rudi
 
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I have an '82 FJ40 that I have never seen the ammeter move. Upon replacing the speedometer cable I accidently grounded out the ammeter for a millisecond and the ammeter needle flipped upside down. (Note to self:Disconnect battery cable when working on cluster). I figured it was toast at this point. So, I took the cluster apart and seeing the needle counterweighted upside down I just reset it. Well, I have no idea why, but now it works. I dunno, but maybe it needed to be woke up.
 

DSRTRDR

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@ Claudia
It may be wired backwards because it should swing right when the battery is charging.

my earlier post wasn't clear: it swings right when everything is on and the truck is driving - I have to test what it does when the truck is standing (I typically avoid putting drains on the battery without the alternator running :doh:)
 
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Cruiser804

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Can you post some feedback good or bad on the replacement fusible link?
Anything that I should change, or could improve on? Wires long enough, too long? Not having an actual model to base it on, I build then from a description and a picture. ;)

Nothing major. I have the original if you want it for a template. Seems well made and fits fine.
 

Cruiser804

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So; how to figure out if the ammeter is ok or not.
Meassure between ground and the + of the ammeter (key is in on position). There should be 12V.
The same for ground and - of the ammeter. there should be 12 V.
Now switch on your headlights and meassure between the + and the - of the ammmeter. You should meassure a voltage drop of less then 1 Volt. If this is so the circuit is OK but the meter itself is kaput.
If all you readings are 0 but the battery is charged, it means that the ammeter is bypassed somewhere.

Good luck.
Rudi

I will pull the gauge and try this.Or can i do this at the fuses?

If the meter doesn't move with the battery disconnected doesn't that tell me the same thing? It just sits in the middle.
 

bj40green

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I will pull the gauge and try this.Or can i do this at the fuses?

If the meter doesn't move with the battery disconnected doesn't that tell me the same thing? It just sits in the middle.

If you disconnect the battery you open the circuit and nothing will work (charge or discharge) so the meter won't move at all.

Yes you can do it at the fuses but, ............. if you do it at the meter you include the wiring from the fuses to the meter.
Maybe one of the wires to the meter is broken, or a bad contact on the back of the meter. If you meassure on the meter you include these possibilities.

Good luck :wrench:

Saludos :cheers:

Rudi
 
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Is the calibration between the two ammeters the same? In other words, will a pre-79 ammeter work on the millivoltmeter style wiring of the post '79s? The reason I ask is that I have an '82, but the gauge cluster has been replaced with a pre-79 cluster (i think, the scale on the ammeter reads +/- 30a vs the +/- 50a for the later ammeters). The ammeter was disconnected when I bought it, I guess this might explain why?

Thanks, Taro
 
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Yes, the later meters are higher current: 50A vs 30A. This is part of the problem as with a good battery and charging system, the meter rarely sees swings of more than a few amps after starting. A less sensitive meter deflects even less, making it hard to notice.

If you want to do a quick and cheap test of the meter, drain your battery by cranking the engine for a few minutes with the coil wire disconnected and then start it. Then it should deflect strongly right if it is working.
 

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