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Dreaded "low voltage/dim lights at idle"

Discussion in 'Repairs, Maintenance, Help' started by kzooman83, Oct 7, 2016.

  1. pt006

    pt006 Active Member

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    I've found Chrysler ammeters of the 70's to be dependable. However, the nuts on the back got loose with age or weren't torqued enough at the factory. This resulted in excessive heat which melted the plastic housing in some of the trucks. [and electrical problems.]

    Cars/trucks back then lasted 100,000 miles or so. There were a few exceptions. And, during those years, cars were shuffled thru auctions and the true mileage got 'modified'. The trend back then was to buy a new car every few years. Because cars looked different due to styling changes most every year, your friends would know you were driving an 'old car'.

    The old Acclaim didn't dim its lights much at a stop light. But it had a smaller alternator pulley [serpentine belt].
     
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  2. ImperialCrown

    Level III Supporter

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    Yes and it wasn't just a poor connection at the ammeter gauge nuts. The entire electrical load of the vehicle had to pass from the engine compartment, though the firewall (bulkhead connector), through the ammeter (and its parallel shunt) and then back to the engine compartment.
    There was a lot that could go wrong here in the way of something causing a high resistance, especially with age and oxidized terminals. It could also be intermittent.
    High resistance with a high load can cause intense heat. Ignition switch, headlamps, rear window defogger and heater motors pass a lot of current that can melt plastic connectors and wiring.
    The automakers couldn't get away with having such a fire hazard these days.
    The OP has apparently bypassed his ammeter (current flow meter) and is using a voltmeter as a charging indicator?
     
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  3. Rick Anderson

    Rick Anderson Well-Known Member

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    I think the OP said he added a voltmeter and kept the ammeter. Which means he has an additional tool to access the state of the electrical system, but didn't rectify the problem "IF" the problem is the ammeter.

    Hmmm, to further what IC said;
    An Ammeter has to be inline with the entire circuit to read the current flow, and all the current running through the circuit runs through it.
    A Voltmeter just has to tap anywhere on the circuit to ground to read the voltage at that point, the amount of current flowing through it is very low.

    So an Ammeter you have big main cable from the battery and alternator rerouted to run through a cheap plastic gauge in the dash (plus all the other connectors IC spoke of), hmmmmm, lots of things to go wrong there that effects everything in the electric system....
    But a Voltmeter, depending on what wires are already running under the dash, you can just tap one to go to the voltmeter, there will be more than one wire under the dash that will be the same voltage potential as the main cable from the alternator/battery. If something goes wrong, its only effecting that tiny tap that can be fused to prevent a short.

    Another way to look at it, the water flow through a pipe analogy.
    A voltmeter is just a pressure gauge, any of the pipes that are at the same pressure as the water main that are nearby, you can tap a tiny hole for a pressure gauge, and have a good idea the pressure of the water main, something goes wrong, you're only losing what can go out that tiny hole for the pressure gauge.
    An ammeter is a flow gauge, so its got to be inline in the entire water main itself, so to put it on the dash, you have to run the water main up under the dash and back, and if something goes wrong the entire water main is compromised.

    My guess, back then so few drivers understood electricity well enough, that an ammeter that could simply show if the battery was charging or draining, was a benefit, a voltmeter would be utter useless to most drivers.
    Might explain why since the technology became cheap enough in the 80's/90's, just about every vehicle went to digital processor that simply monitored and lit a Warning Lamp on the dash if there was something a voltmeter or ammeter would show as bad. Not to mention they monitor the field control of the alternator, and can warn of things even the most knowledgeable driver could miss with just a gauge.

    Personally, I think a Voltmeter is more valuable, "IF" you understand enough about electricity to understand what its telling you.
    I'm sure designers, when giving the challenge that the vehicles had to last longer and be more reliable, realized the way they were doing ammeters had to go. There are ways to do it more reliably, but they're not cheap, as well, for most drivers, the warning lamp that cost even less than the gauge was probably more valuable and reliable.
     
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  4. schelled

    schelled Well-Known Member

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    You don't need to run all the current through an ammeter to get a reading. An ammeter shunt is a strip of metal with a known resistance, where there are two leads connected to your gauge. The gauge is actually a voltmeter reading the voltage drop across the strip of metal, however the gauge is calibrated to read amps . You can make your own shunt with a piece of scrap metal provided your have an ammeter to calibrated it with.

    Datcon-Datcon - Shunts For Ammeters, 300 Amps - 07618-00-07618-00
     
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  5. Rick Anderson

    Rick Anderson Well-Known Member

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    Doh! Yes, you're right, and I'm pretty sure this is the way its done on cars and their ammeters.

    But, that doesn't change most of what's been said, because the cables providing the current to the shunt and ammeter, if something goes wrong, still can draw enough current off the system to create problems for the whole system.
     
  6. Dave Z

    Dave Z It's me, Dave
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    The ammeter held out for WAY too long, but it was very good at being perfectly clear about what was going on.

    I still havent' replaced mine but it's on the long list. In a Valiant, with a steel dash, it's a real pain to get to, though.
     
  7. AllanC

    AllanC Well-Known Member

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    I think it is interesting that Chrysler had equipped all vehicles produced starting in 1961 and later (probably through the 1970s) with ammeters but the labeling indicated the word ALTERNATOR. Ford and Chevrolet had been using an idiot light for generator charging for many years before and continued even after adopting alternators in 1965 and 1963 respectively. Chrysler advertising in 1961 touted the advantages of the only manufacturer using an alternator to keep a better charge on the battery. I wonder if using an ammeter named alternator was a marketing decision to exploit an engineering advantage?

    The driver would have to know how to interpret the ammeter gauge. You start the engine and for a short time of a few minutes the needle would be significantly moved to the right indicating a high charge rate. This was necessary to quickly replenish the battery after engine starting. After a few minutes and when the battery reached full charge the regulator would diminish the charge and the needle would hover around the midpoint indicating no charge or very little. If the driver did not know that his was normal, some could say the needle moving to center was indicating a problem.
     
  8. Dave Z

    Dave Z It's me, Dave
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    I don’t think there’s a lot of knowledge to gain — you pretty much described it. And I think you are on to something with the reason for using ammeters. We even called it “the alternator gauge” though in fairness we didn’t call the coolant temperature gauge a coolant temperature gauge... it was just a temperature gauge. The alternator gauge told you about what the alternator was doing.

    The use of an ammeter really hurt efficiency...
     
  9. Rick Anderson

    Rick Anderson Well-Known Member

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    I think your line of thinking, which I agree with, just proves my point. Chrysler tried to make the gauge the most useable for the typical owner, which they probably correctly assumed didn't have the first idea about how electricity worked. And most still don't today.

    And you probably know, Generators (technically Dynamo's, Generators are actually the whole group and Dynamo's and Alternators different subsets of Generators, but we just call Dynamo's generators today) have the their current producing windings rotating inside the magnetic field, Alternators have the magnetic field spinning within the stationary windings producing the current. When you're dealing with an consumer level device that has to be spun by a car engine, at its range of RPM, you can produce a much more reliable and powerful alternator by spinning the less complicated magnetic field within the stationary windings that carry the current. It wasn't until they came up with much better solid state diodes to rectify the current, could they start putting alternators in cars. That is why they were DC generators in the past (A DC generators brushes and commutator rectifies the current without diodes).

    Yes, the fact the magnetic field is created with windings and NOT permanent magnetics, can confuse the layman that hasn't read up on it, which is producing magnetic fields and which is producing current. I think some of the old 50's and early cars had permanent magnetics in their DC generators.
     
  10. schelled

    schelled Well-Known Member

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    I replaced the spade connection at the bulkhead connector with two eyelet terminals and a buss bar, I just ran the wire from the dash through the hole in the bulk head connector and made the connection on the fire wall My spade terminal connection was quite burnt. That solved all my problems so far.
     
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  11. schelled

    schelled Well-Known Member

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    One of the reasons they used the ammeter with a generator was that you could monitor if and when the cutout coil in the regulator would open up. After you shut a vehicle with a generator off, the generator will briefly pull current from the battery which triggers the cutout coil to open up and disconnect the two devices from each other. If you don't have an ammeter it would be difficult to see that.
     
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  12. Dave Z

    Dave Z It's me, Dave
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    Pics?
     
  13. AllanC

    AllanC Well-Known Member

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    Generators rotate the armature or electricity conductor within a stationary magnetic field. To produce more electricity you had to add more wire in the windings of the armature. This added mass and the higher current through the brushes that rubbed on the commutator caused arcing and heat buildup. The extra mass in the armature also could cause problems on high reving engines.

    It was not uncommon for hot rodders to blow up a generator when they would install performance enhancements to V8 engines from the 1950s. Generators were in common use in the 1950s. Add some performance enhancements that let an engine approach 6000 rpm and the generator would explode due to the forces placed on the rotating mass.


    I think Ford Model T cars used permanent magnets for the field poles. There was an adjustable 3rd brush that allowed a fixed charging rate. Those vehicles had a cutout on the generator which would disconnect the battery when the engine stopped running. Cut outs tended to allow battery overcharging and shorten battery life.
     
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  14. Dave Z

    Dave Z It's me, Dave
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    ... in pretty much every car until 1959, except police cars and some other fleets ... and it took a while even after 1960 for everyone to change to alternators.
     
  15. page2171

    Level 2 Supporter

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    True...my 1962 Buick Electra has a generator. If I remember right, Buick switched to alternators in 1963.
     
  16. schelled

    schelled Well-Known Member

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    Sorry I put it away for winter, won't have access to it until spring
     
  17. Dave Z

    Dave Z It's me, Dave
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    [sigh] I will wait ;)
     
  18. pt006

    pt006 Active Member

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    Mine may have been different, but by lowering the steering column [a couple of screws and 2 or 3 nuts], and tilting the top of the panel rearward gave easy access to remove the ammeter nuts. The hardest part is disconnecting the speedometer cable. ALWAYS disconnect a battery cable before you start.
     
  19. Dave Z

    Dave Z It's me, Dave
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    Wasn’t aware you could tilt the panel out since it’s all fastened to the dash. That would be a lot easier than lying on my back and working upside down.
     
  20. pt006

    pt006 Active Member

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    The original bulkhead [firewall] connector is adequate for the standard alternators. The prongs and connectors must be corrosion free. And tight. A careful squeeze of the female connector can help.

    If updating to a high amp. alternator, a hole and grommet can be drilled thru the firewall. Then replace the wire from the alt. to the ammeter and the wire from the ammeter to the starter relay stud with a heavier wire [# 8?]. Dodge did this on some of their trucks in the 70's.

    Post # 39. If my memory is right, there are 4 horizontal screws at the bottom of the panel and 4 vertical screws at the top of the panel.
     

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