ammeter vs voltmeter?????

[swedishsteel]

Recently got my '36 5 window roadworthy--36 LB, but had a fellow in Ohio build an alternator (6 volt, positive ground) on the stock generator mount. I have the original ammeter. Running in the daytime, it reads a small (normal) charge, greater initially after start up. When I turn the headlights on at road speed it reads discharge. This evening I checked the voltage--engine off, 6.34 volts at battery; engine running with lights on (revved up by wife!) 8.5+ volts at battery but still showing discharge on ammeter. Is that how an ammeter should read with an alternator. Any insight appreciated. Rod

[ford3]

ammeters are for generators, volt meters are for altenators, i think your amp meter is bad

[mralternator]

An amp gauge does not measure alternator output it measures the amount of current going into or coming out of the battery.

The advantage of the alternator is the ability to provide an output at idle and low rpms (something the generator could not do) to keep the lights bright and the battery fully charged. The total electrical load of the vehicle remains the same as it was before.

the average 6-volt car has an electrical load of about 36 amps with everything turned on.

The total amount of amperage passing thru your dash gauge will be the same or less with the alternator because the alternator is keeping up with the electrical load at all times. With the battery always fully charged at all times no large amounts of current will be flowing into or out of the battery as before.

[mralternator]

8.5 is VERY high , concerned by that alone, , alternators I produce should never get much over 7.4 and it goes as a teeter totter affect , higher amperage low volts and lower amperage higher voltage. the voltage is the pressure and the amperage is the flow

[Bluebell]

Swedish steel, I think you have a wiring problem.
In as much as the alternator is feeding the battery directly instead of feeding it via your amp meter.
The end result is that your battery is being charged, but the charge is not being registered through the amp meter.

Essentially a volt meter even though hard wired, is measuring the voltage of the battery.(all the time) the same as if you put a test volt meter directly onto the battery. (a volt meter is used in parallel)

The amp meter needs to be connected in series, or be part of the circuit. in your case it has been bypassed by the big wire between the battery and the alternator.
The ammeter shows a charge or a discharge depending on which way the current flows at the guage.
Contrary to what ford3 says you can run either gauge with either type (alternator or generator) in fact Henry Ford used both types of gauge as factory fitted,(in the forties) long before alternators were introduced to Ford cars.

[51 MERC-CT]

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Originally Posted by ford3

ammeters are for generators, volt meters are for altenators, i think your amp meter is bad

My original induction ammeter with the feed wire from the alternator to the battery threaded thru the meter reads charge and discharge as it should. So why are ammeters for generators?

[36rgtop]

Originally Posted by Bluebell

The amp meter needs to be connected in series, or be part of the circuit. in your case it has been bypassed by the big wire between the battery and the alternator.
The ammeter shows a charge or a discharge depending on which way the current flows at the guage.
Contrary to what ford3 says you can run either gauge with either type (alternator or generator) in fact Henry Ford used both types of gauge as factory fitted,(in the forties) long before alternators were introduced to Ford cars.

'36 as well as many other year ammeters are induction meters and are not part of the circuit.

[Bluebell]

51 Merc, Ford3, has it wrong.
36rgtop, the fact that they are an induction ammeter is just a technicality of the construction. It makes no difference at all, to what I have said ( other than to add confusion.
Yes, the Ford ammeter works like a Fluke (clamp) meter nothing has to touch any wiring, it just senses the current flow, in the wire passing through the loops.

The point I am trying to make is that the charging current is bypassing the ammeter, because of the way the wiring modifications have been carried out (or at least that's my gut feeling based on the information that Rod has provided.

[britman]

I fitted a homemade "shunt" (jumper wire) on the 30amp ammeter of my XK150 Jag after putting a 60amp one wire alternator on it a few years ago. I was a little nervous about it at first but it appears to have worked out ok. The ammeter is not accurate but it does indicate whether the system is being charged (must "do some math" to calculate the theoretical dimensions--size and length- of the shunt). I did my homework online about "shunts". Good luck with you project.
britman

[Teich]

Bluebell is 100% right amp meter, either loop on back or studs work the same, as the Fluke clamp they don't know volts either, just witch way current is going and roughly how much the wiring is also as Bluebell says, and 8.5V is too much should be close to what the generator would do. Laurie

[mralternator]

Alternators and Amp Gauges…
If you had a generator type of charging system you were used to seeing the amp gauge needle go over to the charge side quite a ways when going down the highway. When you replace a generator type charging system with an alternator type charging system you seldom see the needle on the amp gauge move much past zero…how come?

Remember – An amp gauge tells you which directi...on the current is flowing between the battery and the charging system…It DOES NOT tell you if the charging system itself is working. A discharge reading means current is flowing out of the battery…a positive charge means current is flowing to the battery and current is being replaced into the battery. A neutral (+) reading (needle is just barely on the plus side of the needle) means the battery is fully charged.

You can make the assumption that the charging system is working if the amp needle is over on the positive side and the battery is being recharged. After all the current going to the battery has to come from somewhere. Just remember that the amp gauge measures current flow and direction not charging system output directly.

You also have to remember that a generator does not produce any output below 20 miles an hour, (or 1200 rpm engine speed) so when you get up to highway speeds it has the job of replacing the current you are using now… plus the current you have already used. That is why the charge rate is always high with a generator charging system...it is always behind, trying to catch up.

By contrast an alternator type charging system is able to provide a strong current output at all engine rpms so the battery is always fully charged. In addition an alternator will provide increased output as needed for any accessories…so the battery just stores the current used for starting and the alternator provides the rest of the current needed for everything else. Because the battery is always fully charged the vehicle starts much better and the battery itself will last much longer in a vehicle with an alternator type charging system.

[swedishsteel]

The complete wiring system is stock with the exception of the alternator, which is one wire hook up, just as the original generator. The wiring harness is new. The wire runs through the back of the ammeter. The alternator I have was originally a GM 3 wire. Last night I discovered that the original, and I presume 12v, regulator was still in it. How does that work with, again I presume, a 6 volt rectifier? Would that be the cause of the high voltage? And, after reading and looking at several websites, it doesn't appear there are any diodes, at least where a you-tube video showed them in demonstrating how to check and change them.?!?! Talk slow, cuz I get confused really quick with this stuff! Thanks to all for helping. Rod

[mralternator]

Swedishsteel. if the regulator is a 12 volt , then it is a 12 volt and not a 6 volt, The diodes have nothing to do with what Volt it is, THEY do have something to do with what ground it is, as in positive or negative ground, and if it doesn't have diodes, your in trouble LOL as they are what changes the AC to DC for your vehicle to use, I would say that if you take the alternator to a local AUTO Electric shop and tell them that it is a 6 volt positive ground , they should be able to check it, if they don't , RUN , LOL either that or they just don't want to do it lol obviously most, if not all parts stores will have no charts and no idea how to test it , so your best chance is a auto electric , rebuilder shop, you could contact me and I could possibly answer any questions you might have about your problem 419-577 2341