Battery/amp gauge

[72lb4x4]

Originally Posted by VetteVet

Here's the definition of an external shunt ammeter which is what we have in our trucks.

An external shunt is basically a very low value resistor that is in series just as the ammeter was in the previous example, and then the ammeter is in parallel to the shunt. Basically MOST of the current goes through the shunt and only a small percentage goes through the ammeter. By knowing the resistance of the shunt and the meter, the meter is able to calculate the total current by measuring only the small current that goes through the meter. This kind of setup allows small wires to be run to the ammeter in the cockpit, and the high current to remain in the engine compartment. The danger in these setups on some old cars is there isn't a fuse on that small ammeter wire, So if the shunt is damaged or a connector breaks, it would try to flow all the current through the remaining path which is the small ammeter wire and that would melt that wire (along with whatever else it is next to).

This is the reason there are 2 small fuses in the wiring circuit on our trucks that have battery gauges. They are actually amp meters since they measure amperage differential and not volt meters because there is no connection to the negative side of the circuit.

Sorry, but you just don't understand what you're talking about. Your last sentence, among others, proves this.

The meter that reads in amps in a shunt ammeter is still a voltmeter measuring the voltage across the shunt resistor.

Look at the battery gauge and you'll see that it will fry before anything else in the circuit.

You might want to try using a web search to learn what an actual ammeter is and how it works.

The OP may want to look into the differences in the two underhood harnesses to see if they are missing the wires needed to make the gauge work.
Look

[VetteVet]

Originally Posted by 72lb4x4

Sorry, but you just don't understand what you're talking about. Your last sentence, among others, proves this.

The meter that reads in amps in a shunt ammeter is still a voltmeter measuring the voltage across the shunt resistor.

Look at the battery gauge and you'll see that it will fry before anything else in the circuit.

You might want to try using a web search to learn what an actual ammeter is and how it works.

The OP may want to look into the differences in the two underhood harnesses to see if they are missing the wires needed to make the gauge work.
Look

After going back and re-reading my post I discovered that I mistakenly said the shunt ammeter measures amperage differential. I meant to say voltage differential so I concede that mistake. I also maintain that the external shunt ammeter is neither a volt meter or an amp meter in the exact definition of either. It would be nice if you would point out errors instead of just saying that I don't understand what I'm talking about. It would also be helpful if you would actually contribute to the OP's problem instead of criticizing my post.

While I'll admit I'm not an electrical engineer I do know how to do a web search and I do know how an amp meter works. Your comments are merely semantics .
This web site defines both amp meters and external shunt ammeters.
http://home.cogeco.ca/~rpaisley4/Ammeter.html
There is a voltage drop (differential :edit) across the resistor on the shunt ammeter and while you may call it a volt meter I do not see it referred to as a voltmeter in any of the definitive web sites that I have researched.
Perhaps you can show me where any of the wiring to the battery gauge is connected to the negative side of the circuit. My reference to the lack of fuses in the circuit is correct and if the resistor on the shunt doesn't burn into then the small gauge wire will.

[neba]

i have to agree with stepside that nothing i try will make this guage work.dont think both of our guages would be bad. hookup makes no sense to me.taking a voltage reading on the same wire a few feet apart gives the same reading. my truck also has no fusable link. maybe there is enough resistance in the link to make a difference?
as far as hooking up the brown wire that used to go to #8 to #5 on the new panel, it works. the system needs a light bulb.instead of the old gen light your using the temp light in the new guage. if the bulb burns out your system wont charge, just like it would with the old panel.

[VetteVet]

Originally Posted by neba

i have to agree with stepside that nothing i try will make this guage work.dont think both of our guages would be bad. hookup makes no sense to me.taking a voltage reading on the same wire a few feet apart gives the same reading. my truck also has no fusable link. maybe there is enough resistance in the link to make a difference?
as far as hooking up the brown wire that used to go to #8 to #5 on the new panel, it works. the system needs a light bulb.instead of the old gen light your using the temp light in the new guage. if the bulb burns out your system wont charge, just like it would with the old panel.

And there you have it. So why can you not run a resister in place of the light from the brown wire to the external voltage regulator as has been indicated?

BTW I re-read the thread and noticed you mentioned the terminal 5 on the gauge dash was for the temp light in your first post and I missed it. I should have included that in my post where I said terminal 5 dead ends. Sorry about that and hope I didn't cause confusion.

[fixit-p]

72lb4x4, you last post was a bit harsh I see alot of those statements in the general forums but in the specialized sections (suspension, engine & drivetrain, electrical, ect...ect.) there seems to be a level of mutual respect and when there is a difference of opinion it's more productive to further the discussion. This thread is a perfect example.

neba, 72stepside, The system does make sense if you go back to the basic fundamental that electricity will always take the path of least resistance. The best way to explain this is to imagine a large 6" diameter water pipe with 10 gpm (equivalent to volts) of water flowing through it. If you were to tap an 1/8" line into the 6" pipe not much water is going to flow through it because the 6" pipe offers little or no resistance. Now put a valve (shunt) on the 6" pipe and close it half way you now have a pressure drop on other side of valve which is the electrical equivalent to a voltage drop and the pressure drop (voltage drop) at the end of the 1/8" hose allows water to flow through the 1/8" line the amount of water flowing is equivalent to electrical current which is expressed in amps. Increasing the water supply also increases the pressure drop and more flow thought the 1/8" line or ammeter in our case. So the current flow through the ammeter will be proportional to the current flow through the shunt. The voltage drop at either end has no direct effect on the ammeter other than influencing the direction and amount of current flow which is expressed in amps, so yes it is an ammeter (only measures a small percentage of current flow) and not a volt meter.

Vette, Thanks for verifying the paths on the circuit boards are still there from terminal 5, I don't have spare parts to double check myself also the link you posted on the ammeter is the best I've seen so far and this is a highly debated topic in this and other forums.

72stepside, Have you double checked continuity through the circuit board to the ammeter. Sorry for the long post hope it adds more help than confusion.

[neba]

i would like to say thanks to all who have tried to help. i wasnt trying to argue, just trying to figure it out. i agree you could add a resister, just seemed easier to plug a wire into empty socket. anyway i dont think those old guages are very accurate and will add an aftermarket set under the dash. thanks again

[bluschek]

I'm installing all new wiring harness and 1-wire alternator. My attached diagram the correct way to wire up the battery gauge? Do you have the part number for shunt? Thanks in advance.

[ray_mcavoy]

Originally Posted by bluschek

I'm installing all new wiring harness and 1-wire alternator. My attached diagram the correct way to wire up the battery gauge? Do you have the part number for shunt? Thanks in advance.

The wiring diagram you posted may or may not give the desired reading on the meter. It all depends on where you'll be drawing power for the electrical loads in your truck.

For example, if you were planning on using the "BATT" stud on the starter solenoid as your main power distribution point, your meter will only show the output current of the alternator as a "charge". It will never show "discharge" current being drawn from the battery because it's not in the path to measure that current.

Now, if you were to make the right side of the shunt your main power distribution point, the meter will show both "charge" and "discharge" current flowing to or from the battery just like the stock configuration.

The shunt that fixit-p showed back in post #5 is for ChevyII/Nova SS applications and is available from sources such as --> http://www.modernperformanceclassics...s%20Shunt.aspx

However, I see you're showing 4 gauge wiring on your diagram so I assume you're planning on using a fairly high output alternator. I don't know the exact rating on those Nova SS shunts, but I doubt that they are designed to handle much over 60 amps (the largest available alternator on a '65 ChevyII/Nova was a 62 amp unit).

As fixit-p also said in post #5, the "shunt" in these trucks is simply the inherent resistance present in the charge wire ... not a separate component. So the stock "shunt" was a section of 12 gauge wire about 4 and a half, maybe 5 feet long that ran from the junction block on the passenger side fender near the battery, across the radiator support to the factory multi-wire splice that served as the main power distribution point. The current carrying capacity of this system can be increased by using a heavier gauge wire. But that has lower resistance per foot so the sensitivity of the battery gauge will be reduced.

In other words, it would be possible to make the stock battery gauge capable of reading 100 amps or more by using a suitably heavy gauge shunt wire. But it wouldn't be very useful because you wouldn't see much needle deflection at lower currents. For example, with the stock configuration, you can see the needle move to the discharge side if you turn the headlights on without the engine running. But with a larger gauge shunt you might not see any needle movement at all.

With that in mind, I would recommend changing to a voltmeter. That will simplify the wiring and work with most any charging system. I believe member T-Bone converts the '76-'87 style voltmeters to fit '67-'72 gauge clusters.

[Ronald29609]

The in dash battery gauge on my 67 pickup works but only on discharge.
Can't figure it out. I know its charging because I checked with a meter 14.7v.
The truck starts every day without a problem.
Any ideas?

[VetteVet]

Originally Posted by Ronald29609

The in dash battery gauge on my 67 pickup works but only on discharge.
Can't figure it out. I know its charging because I checked with a meter 14.7v.
The truck starts every day without a problem.
Any ideas?

Most likely you've lost the connection on one of the wires to the gauge. There are two wires that go to the gauge and they are both positive. I stress this because some guys think that one wire is positive and one is negative or ground.
Each wire has a small four amp fuse inline to protect the ammeter in case of a short or a high voltage surge. The first place to look is at the fuses and the easiest one to find is on the junction bolt on the right fender. The other one is usually near and below the left headlight in the harness. This is probably discussed in the thread above. Both wires run directly to the dash cluster to terminals 1 and 12 and there are copper strips to the gauge from there. It is common for these connections at the cluster to corrode and lose connectivity. so it may be a case of just cleaning the connections.

[67 Burb]

Does any aftermarket supplier sell a volt meter to fit the 67 - 72 instrument panel in place of the crappy battery gauge?

[ray_mcavoy]

Originally Posted by 67 Burb

Does any aftermarket supplier sell a volt meter to fit the 67 - 72 instrument panel in place of the crappy battery gauge?

I wouldn't consider the factory battery gauge crappy ... when wired correctly, they actually do a good job of letting the driver know if the battery is charging or being discharged. However, as I described earlier in post #33, they will become less sensitive (and not as useful) if the shunt wire is up-sized to handle a larger current load than stock. And as I mentioned there, member T-Bone converts the '76-'87 style voltmeters to fit '67-'72 gauge clusters.

Originally Posted by Ronald29609

The in dash battery gauge on my 67 pickup works but only on discharge.
Can't figure it out. I know its charging because I checked with a meter 14.7v.
The truck starts every day without a problem.
Any ideas?

In addition to what VetteVet wrote, also check to see how your alternator output is wired into the system. For the battery gauge to function correctly, the alternator output has to be routed to the stock location, which is the multi-wire spliced junction in the harness on the driver side of the radiator support. If the alternator output is re-routed directly to the battery, the battery gauge will only show discharge even when the charging system is working okay.

[67 Burb]

Originally Posted by ray_mcavoy

I wouldn't consider the factory battery gauge crappy ... when wired correctly, they actually do a good job of letting the driver know if the battery is charging or being discharged. However, as I described earlier in post #33, they will become less sensitive (and not as useful) if the shunt wire is up-sized to handle a larger current load than stock. And as I mentioned there, member T-Bone converts the '76-'87 style voltmeters to fit '67-'72 gauge clusters.

Yes, you are correct. The factory battery gauge worked fine in the original electrical system, but when we (and in this case, I mean me) "improve" things with larger gauge wire connected from the alternator to the battery terminal on the starter, then that factory system no longer works like it should.

[IlludiumQ36]

This thread has been inactive for a while but there is some information that I would have liked to have that I found missing. So here goes:

Yes, it is an external shunt ammeter circuit. Looking at a samle size of one, so keep that in mind. The meter itself looks to require about 800mA of current to move 1/2 scale in either direction. The response looked pretty linear, I'd expect double that for full scale deflections. I did not dare run 1.5A through that 50 year old fine wire.




The 12AWG red wire from the junction block to the voltage regulator connector measured 30mOhms using a 4 wire meter. I did not want to unravel to expose the splice, the regulator connection should be close enough.



You end up with a low resistance ammeter path in parallel with a lower resistance wire path. A lot of current would need to run through that 30mOhm wire to deflect the needle. I will take a reading from the junction block to the voltage regulator connector with the red wire disconnected from the junction block to get the installed ammeter path resistance once I put it all back together. Cleaning up the instrument cluster now.


From a practical point of view, you have to make sure that ALL of the connections from the junction block, through the ammeter, through the fuses and to the splice are solid. Any added resistance in the ammeter path will cause a lower deflection than desired or expected.

[pjmoreland]

Very interesting. Thanks for sharing your results. I have never seen the stock ammeter needle deflect as far as it did in your test in the three 67-72 trucks I've owned that had an ammeter. I've seen it deflect maybe half that far, max, and that was after doing something like performing a compression test where I was cranking the engine over a bunch, or after forgetting to turn off the headlights while inside a store for half an hour. I've always wondered how much the needle would have deflected in a new truck that had perfect wiring.

[IlludiumQ36]

OK, I went back & put the instrument custer back in and took some more measurements.

I thought that the wire masurement was a bit high. 5ft of 12AWG wire should be about 8mOhms per the tables. I pulled the contact out of the regulator harness side connector, cleaned it up and remeasured to 13mOhms. That included crimped connections, so a reasonable number.

The meaurement of the in-place ammeter circuit path was ~0.875 Ohms.
From the junction block to the same regulator contact as above.

the circuit simplified looks like:

That drawing should say alternator out, not voltage regulator out, I think that is the equivalent of VR in sense.

Putting a low value resistor in series with the battery charging cable will slightly increase the voltage drop on across that segment & move the needle more significantly. The other way to look at it is, for a fixed current to/from the battery, increasing the resistance slightly in the 12AWG red charging wire path diverts a larger portion of that total fixed current through the parallel gauge path. Restrict flow in one of two paths of a river and what is needed simply goes to the other branch. The total flow won't decrease.

[pjmoreland]

I'm interested to see how adding a shunt resistor works out. It would be nice to have the gauge move a little more.

[IlludiumQ36]

I just ordered up a 50mOhm 50W wire-wound resistor, it would be a little cleaner install than a shunt. 1/2 gauge should end up being about 11A.

I was torn between that & a 75mOhm wire-wound. Simple enough to swap if I don't like. I don't want it to get too far past half because I'm a chicken.

Will tell you how it goes.

[IlludiumQ36]

OK, here is how it worked out for my truck with my ammeter.

I placed a 50mOhm resistor in series with the 12AWG red wire to the terminal block. Keep in mind that this is a prototype, the final installation will be well hidden under and look original.



With the headlights on and the fan on, no motor running, the ammeter reads like:



That is probably too aggressive. My final will be 25mOhms I think. I bought two of those 50's and I will place them in parallel with each other.

I also do not like the 4A fuses, I am going to add a similarly hidden 1A fuse in series to better protect that meter. A 4A fuse won't blow until 6A.

In the end, I think my implementation will look like:



and for those interested, here is why I don't like the 4A fuses. The chart uses logarithmic axes, X axes is impotant in particular:

[pjmoreland]

I wonder how the gauge would hold up to increased current long-term. Adding a shunt could possibly be a good way to restore factory gauge movement for people who have replaced the original main power wire in their front harness with a heavier-gauge wire.

[IlludiumQ36]

An added shunt would work counter to a wire gauge decrease( larger diameter wire... don't ask me). You'd be adding back in the resistance you had been trying to remove with the wire change. The main difference would be that the heat generation would be at a point & could be easily disipated into a hunk-o-metal. It would be a trade. Me, I'd do it. Then again, I did this so I could get a needle to move.

Rethinking that, Yes. I forgot that this path was only for charging the battery & discharging when alternator nor running/working. I think that would be a viable solution, I'd expect that folks really did not need the increased diameter wire here in the first place but in the alternator out to the loads direction.

I don't expect that prolonged < 1A would be a real heat generator so I don't think it would be an issue, that said, I did decide to cut my added resistance in half just for that reason.

[IlludiumQ36]

At some point I'd choose to decouple from playing with the harness resistance, throw in a known low impedance shunt, measure across that shunt with an instrumentation amplifier circuit to feed an active gauge drive circuit. The trick is to keep it all compact enough to hide.

For now, for my configuration, the added wire-wound resistor will work. R

[dmjlambert]

50 watt resistor is not near enough for realistic loads. The best resistor to add would be a length of more 12 gauge wire. Add another 6 feet and fold it inside the wire holder that runs across the radiator top, and the needle will move about twice as far. I suggest don't worry too much about the 4 amp fuses. Their only function is to blow if the 12 gauge wire actually gets chopped in half or completely disconnected, and then you would be trying to run stuff in the cab or charge the battery through the ammeter, which would be the only remaining circuit to go through. Normally the ammeter circuit carries no significant current, it just gives you a voltage difference reading.

[IlludiumQ36]

Doubling back the wire is certainly a viable solution. Using resistors of known values allows me to trim the results as I'd see fit. I've already decided that I'd parallel two of those resistors... that would be 100W. I don't think it was really needed but I did not want too much current running through the gauge.

This gauge really is for charging/discharging the battery, not to measure the total load on the system. In the charging direction, all the current through this pair would be feeding the battery. Discharging kind of assumes no or poor alternator/voltage regulator or motor not running. To the rest of world, were everything be operating properly (regulator output voltage higher than the battery voltage), would be from regulator to the splice & out.

30A through would ask the 2 parallel resistors to dissipate ~25W (P=I*I*R), @ 60A -> 90W. I doubt my alternator can produce that anyway. I know that the 12AWG wire should not be carrying much that either. Plus, the fusible link would be less than that.

As for the fuse, I tend to agree. I really did not think through the case where my 12AWG separates, I blow the fuse & then nothing works to the battery. That said, I still don't like the idea of running that much current through that 50 year old magnet wire & the gauge internal connections. Good chance that it becomes the fuse instead. Maybe you've influenced me to go to 2A. I like my gauge.

[IlludiumQ36]

Here is a prototype of the 25mOhm load plate addition, I just made it out of 1/4" plywood. I still need to add the fuse holder to the installation.



Looks like it will all fit fairly well & I will still have access to all of the bolt heads.
You will never see it unless you are searching for it.

I think I will need to 3D print out some covers to go over the terminal blocks to avoid anyone unaware that there is a hot wire under there from inadvertently throwing lightning bolts.