Alternators and Ammeters (1 Viewer)

Helipilot

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If I update my 12/79 '77 FJ-40 alternator to a Mean Green higher output alternator I know the higher amperage will damage the stock ammeter. I want to keep the 40 instrument cluster stock if possible. On another thread a member manufactures replacement clusters with new gauges, pricey but maybe a possibility.

What is the recommendation of the gurus on this forum?
 

Helipilot

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Feb 23, 2013
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If I update my 12/79 '77 FJ-40 alternator to a Mean Green higher output alternator I know the higher amperage will damage the stock ammeter. I want to keep the 40 instrument cluster stock if possible. On another thread a member manufactures replacement clusters with new gauges, pricey but maybe a possibility.

What is the recommendation of the gurus on this forum?

Edit: I am planning to install the Warn 8274 winch and an extra battery in the engine compartment.
 
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You can simply bypass the stock ammeter. The cluster you mentioned simply adapts modern gauges into the stock guage panel. You would opt for a volt meter rather than an ammeter. You would also want to upgrade your battery cables. There is a lot of info on this topic.
 
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If you are like me, I grew up with amp gauges and understand them better than volt meters, although I do believe that voltmeters do have an important function also.

I recently came across pre-made shunts for ammeters. Go to: westach(dot)com then click on gauges, on that page click on accessories, then on that page click on shunts. A shunt will allow an amp meter to function without having the higher voltage inside the vehicle, under the dash, and going through the gauge. They have shunts all the way from 15 amp to 600 amp,

You will want to change out the stock amp gauge for one that has the correct amp range showing on the face of the gauge.

Don
 
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@handcannon Don - have you installed one of these shunts? I don't quite understand all of the ins and outs yet. So a shunt creates a path of least resistance so the ammeter doesn't get fried? Does it somehow step down the Amps so you still get a relative reading (higher or lower) on a stock gauge? The numbers on the gauge face wouldn't be right but one could tell the amp draw on the system. I don't know squat about electrical systems which is probably obvious to anyone reading this. Thanks.
 
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No, I have not. For a long time I've wanted to change out my amp gauge for one that will show what my replacement alt is capable of producing, but, I have not done so since I'm not knowledgeable about shunts. I just know that using a shunt will allow you to use a larger amp alt, with the appropriate gauge, than what was stock on the cruiser.

Using a shunt allows you to keep the high amps under the hood and not under the dash. As I under stand it the shunt is a circuit parallel to the wire under the hood that carries the high amperage. Here's a you tube video of basic amp gauge operation:
It hasn't been a priority for me as my cruiser has been inoperable with a cracked head for several years now, and funds for repair have not been available yet.

Don
 
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Great video. Thanks Don! So I have a mystery on my hands now:

PO had upgraded to a 130a Alt. Very simple one-wire Pestolite Alt. Two connections: direct to Batt + terminal and a ground to the engine. But here is where it is interesting. The ammeter works (at least it moves around according to load). It's the stock 30A gauge. Guess I'm going to be pulling the gauge cluster and tracing some wires to figure out what he did.

Quick and easy I guess is just replace my bad alt with a new one-wire of similar amperage, but I'd like to understand it all first. My education continues....
 
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When I installed a 120 Amp alternator (along with a SBC) I simply wired the battery directly to the alternator (bypassing the ammeter). The ammeter now only shows the draw and not the balancing output from the alternator. I'm halfway through installing a voltmeter into a different cluster to swap in.

More recently, I've learned about Shunts... My other rig has an ammeter on a 215 amp continuous duty Alternator. I regularly see it putting out 100-175 amps. This is possible because there is a shunt running in parallel to the ammeter. The actual ammeter is likely only handling 10% of the flow... More like 10-17 amps while the 90-168 amps is running through the shunt. With a stock setup & the right shunt, you could simply know to multiply it's reading x10.
 
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On a simple 1-wire alternator (ie CS130), where you go directly from Alt + to the battery, there is no problem retaining the stock Ammeter. All it will be telling you is how much current all your electrical loads that go through the stock harness are pulling from the battery. Not useful information, particularly, but not unsafe.
 
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Ah! :idea: I get it now. Explains why I never saw the needle move into positive territory on the gauge . Probably going for the CS130 quick and easy. Off to research getting the right one. Thanks guys!
 
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Basic electronics tells you , a true ammeter must be in series with the circuit being measured. It has to for a real amperage reading. Now, a SHUNT is placed in series with the current being measured that has a resistance. The resistance has nill effect on the current flow. NOW, VERY IMPORTANT , THE AMMETER SHOWN IS ACTUALLY A VOLTMETER, NOT AN AMMETER. The amount of voltage to full deflection is 75millivolts. SO, a ratio has been calculated to show a REPRESENTATION of current, not actual current. It is an easy way to represent what is there.
 
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Actually, all the meters (amp, volt, power) are power meters that measure the product of volts and amps to make the needle deflect. indeed, amps and volts are related by Ohms law. Increasing either the volts or amps increases the needle deflection. Since the voltage is regulated (more or less) in automobiles, the main cause of deflection when the meter is in series with the load is a change in amperage. When the meter is parallel to the load, it reads mainly the voltage, because the current flowing doesn't change much.
 

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