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  #1  
Old 12-27-2006, 11:23 AM
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aerocorey aerocorey is offline
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Ammeter vs Voltmeter

I'm comfortable with the differences between what an ammeter shows and what a voltmeter shows and interpreting the readings, but what would be involved in upgrading from an ammeter to a voltmeter? I found a reference that says there's a big difference in the way each meter samples current to make its reading. Can I unplug my ammeter and replace it with a voltmeter with no other modifications and have it work?
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76 J20 project "Ox"
90 GW parts rig "Velma"
77 J10 parts rig "NoMo" (as in "no more Jeeps, Corey!")
94 YJ "Coop"

Past
88 GW "Hercules" (had to sell in '08, curious who has it now)
83 Wag parts rig "Shaggy" (used to build Herc, then scrapped)
73 J4000 (had to sell due to PCS in '07)
75 Cherokee "Jerry Lee" (sold in '13 because I'm an idiot)
74 Cherokee "Dino" (used to build Jerry Lee, then scrapped)
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  #2  
Old 12-27-2006, 11:36 AM
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Quote:
Originally Posted by aerocorey
I'm comfortable with the differences between what an ammeter shows and what a voltmeter shows and interpreting the readings, but what would be involved in upgrading from an ammeter to a voltmeter? I found a reference that says there's a big difference in the way each meter samples current to make its reading. Can I unplug my ammeter and replace it with a voltmeter with no other modifications and have it work?

No you can't just replace it. You would have to splice the wires that went to the ammeter together to keep the charging circuit in tact. The voltmeter can be installed anywhere in the vehicle that there is a hot wire and a good body ground.

There are tons of articles on this... I am sure you have read a few. Not sure how many made it through the BB upgrade. I think there are some articles in the tech archives under "electrical" too.

Too bad JYG can't chime in on this one...
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"Brutus" '74 J10 360/T18/D20/Front D60 Pro Rock & ARB/2" shave, ARB, 15 bolt FF Rear/ 4.56 Gears/38.5 x 16 TSL
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Last edited by BRUTUS : 12-27-2006 at 11:39 AM.
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  #3  
Old 12-27-2006, 11:38 AM
johnwaynejeep2
 
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I'm not sure that a voltmeter can be put in place of an ammeter because of the way the reading has to be taken. to get a good amperage reading the ammeter has be placed in series with the signal being measured (In between 2 components). A voltmeter can get a reading in parallel (externally from the circuit), I'm not sure if a voltmeter can get a reading in series. With this being said you may have to do some rewiring to get the voltmeter to work properly.

I plan on eventually installing a voltmeter in the distant future so I'll be in the same boat at some point in time.
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  #4  
Old 12-27-2006, 11:42 AM
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aerocorey aerocorey is offline
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Sounds simple enough. I'm looking for a voltmeter that will sit in the same place as the stock ammeter and look similar. I had a parts rig with one a few months back, wish I'd have kept the cluster.
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87 GW "Big Bear"
76 J20 project "Ox"
90 GW parts rig "Velma"
77 J10 parts rig "NoMo" (as in "no more Jeeps, Corey!")
94 YJ "Coop"

Past
88 GW "Hercules" (had to sell in '08, curious who has it now)
83 Wag parts rig "Shaggy" (used to build Herc, then scrapped)
73 J4000 (had to sell due to PCS in '07)
75 Cherokee "Jerry Lee" (sold in '13 because I'm an idiot)
74 Cherokee "Dino" (used to build Jerry Lee, then scrapped)
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  #5  
Old 12-27-2006, 11:45 AM
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Quote:
Originally Posted by aerocorey
Sounds simple enough. I'm looking for a voltmeter that will sit in the same place as the stock ammeter and look similar. I had a parts rig with one a few months back, wish I'd have kept the cluster.

here you go:

http://www.ifsja.org/forums/vb/showthread.php?p=418438
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  #6  
Old 12-27-2006, 11:54 AM
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aerocorey aerocorey is offline
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Man, I looked for a thread like that and couldn't find it. I need to get better at searching for stuff. Thanks, Brutus.
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Corey

Current
87 GW "Big Bear"
76 J20 project "Ox"
90 GW parts rig "Velma"
77 J10 parts rig "NoMo" (as in "no more Jeeps, Corey!")
94 YJ "Coop"

Past
88 GW "Hercules" (had to sell in '08, curious who has it now)
83 Wag parts rig "Shaggy" (used to build Herc, then scrapped)
73 J4000 (had to sell due to PCS in '07)
75 Cherokee "Jerry Lee" (sold in '13 because I'm an idiot)
74 Cherokee "Dino" (used to build Jerry Lee, then scrapped)
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  #7  
Old 12-27-2006, 12:03 PM
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Great Pharoah Great Pharoah is offline
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You can't just unplug your ammeter. All the current going from the battery to the rest of the electrical system, except for the starter, flows through the ammeter. You have to bypass the ammeter. I didn't see what year model you have, but the quick and dirty way is to look at the back of your instrument cluster. The ammeter has two wires going to it, one on each post. Just connect both wires to the same post, and your ammeter is bypassed. It's a good idea to do that, especially if you put a higher output alternator in your Jeep. The ammeter gauge has been known to cause dashboard fires. That's not good.

That being said, you don't have to do anything with the ammeter to also have a voltmeter. You can have both. All you have to do to install a voltmeter is to connect the negative side of the voltmeter to a good ground, and the positive side to a 12 volt side. Use a 12 volt accesory (ACCY) so as to read voltage with the ignition key in RUN or ACCY. Do not connect it to a BATT source, you could drain your battery that way.
But switching from an ammeter to a voltmeter isn't an upgrade, it's just a different way of monitoring the electrical system, measuring different values. The ammeter monitors the total amount of current, in amps, the electrical system is drawing from the alternator and battery, while a voltmeter is measuring the amount of electrical force, in volts, the alternator and battery are outputting to the electrical system.

A lot of the group favors bypassing the stock ammeter, because some of us tend to install larger output alternators the have far more output than the 60 or so amps the stock gauge can handle, mine is a Delco CS130 rated for 105. That makes the stock ammeter a fire hazard. So we use voltmeters to indicate the output of our alternators, since installing a voltmeter is a lot easier than going out and replacing our 60 amp ammeters with 200 amp ammeters. But you can install a much higher rated ammeter, that's not impossible, it's just not worth the cost and the hassle involved in finding an industrial grade ammeter and adapting it to automotive use.
GP
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Last edited by Great Pharoah : 12-27-2006 at 12:07 PM.
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  #8  
Old 12-27-2006, 12:19 PM
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I prefer a voltmeter over an ammeter any day. If the voltmeter is connected from the ignition bus (ign) to ground then one can monitor how much the battery "squats" under cranking load. Might not be a bad idea to install a 3A 1000PIV diode across the meter terminals--banded end of diode connected to the + terminal and the other end of the diode to the - terminal. This will shunt any kickback from the starter and protect the meter.
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  #9  
Old 12-27-2006, 01:04 PM
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Quote:
Originally Posted by drlocke
I prefer a voltmeter over an ammeter any day. If the voltmeter is connected from the ignition bus (ign) to ground then one can monitor how much the battery "squats" under cranking load. Might not be a bad idea to install a 3A 1000PIV diode across the meter terminals--banded end of diode connected to the + terminal and the other end of the diode to the - terminal. This will shunt any kickback from the starter and protect the meter.

That is the problem with having JUST the voltmeter, you can only use it at startup and it tells you what you already should know, that you have a voltage drop. The battery could be dead and it will still show 12V.

The ammeter tells you much more than a voltmeter ever could because it is a live diagnostic of your charging system.

It would be like having an "oil volume guage" instead of "oil pressure guage". It is accurate DATA... but how pertinant is it?
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  #10  
Old 12-27-2006, 01:11 PM
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Quote:
Originally Posted by BRUTUS
That is the problem with having JUST the voltmeter, you can only use it at startup and it tells you what you already should know, that you have a voltage drop. The battery could be dead and it will still show 12V.

The ammeter tells you much more than a voltmeter ever could because it is a live diagnostic of your charging system.

It would be like having an "oil volume guage" instead of "oil pressure guage". It is accurate DATA... but how pertinant is it?

A "dead" battery can read 12 volts--until you put a load on it. If the battery is a little tired it's "Thevenin" or internal resistance is apt to increase, manifesting itself as an even greater "stoop" in voltage during cranking under controlled conditions. A "dead" battery reading 12 volts will read close to zero when the starter is engaged.

The voltmeter shows how the charging system is operating by dint of the fact that the voltage reading will be higher than 12 volts--on the order of IIRC 13.5-14.5 volts or so. Much higher or lower than that range would indicate problems with the system--undercharging or overcharging.

While oil flow rate granted as you say is not perhaps as useful an information as oil pressure, the ammeter is a good analogy to the oil flow meter, as it measures the flow of electrons. The voltmeter is more analogous to the oil pressure gauge, as "voltage" in volts is the measure of the electromotive force--or "pressure" to push electrons at a certain rate through a resistive circuit.

Last edited by drlocke : 12-27-2006 at 01:15 PM.
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  #11  
Old 12-27-2006, 01:35 PM
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Quote:
Originally Posted by drlocke
A "dead" battery can read 12 volts--until you put a load on it. If the battery is a little tired it's "Thevenin" or internal resistance is apt to increase, manifesting itself as an even greater "stoop" in voltage during cranking under controlled conditions. A "dead" battery reading 12 volts will read close to zero when the starter is engaged.

The voltmeter shows how the charging system is operating by dint of the fact that the voltage reading will be higher than 12 volts--on the order of IIRC 13.5-14.5 volts or so. Much higher or lower than that range would indicate problems with the system--undercharging or overcharging.

While oil flow rate granted as you say is not perhaps as useful an information as oil pressure, the ammeter is a good analogy to the oil flow meter, as it measures the flow of electrons. The voltmeter is more analogous to the oil pressure gauge, as "voltage" in volts is the measure of the electromotive force--or "pressure" to push electrons at a certain rate through a resistive circuit.

Good Analogy Dr, Locke,

Relating "Amps to Flow" and "Volts to Pressure" Makes it easier to understand. Like it was said above in the discussion on bypassing vs. removing the ameter...you want to do a bypass in order to maintain your flow of electrons.
My 2 cents.
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  #12  
Old 12-27-2006, 01:38 PM
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I agree with you but what I was getting at is that under normal operating conditions, the engine runs off the alternator by itself. The battery is only used for the radio, CB, lights, fans, etc (once it is started and running)

Ironically enough, that is how I came up with the analogy in the first place...
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  #13  
Old 12-27-2006, 01:44 PM
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DieselSJ DieselSJ is offline
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Quote:
Originally Posted by BRUTUS
I agree with you but what I was getting at is that under normal operating conditions, the engine runs off the alternator by itself. The battery is only used for the radio, CB, lights, fans, etc (once it is started and running)

Not exactly. The alternator powers everything while the engine is running. The battery powers everything while the engine is not running.
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  #14  
Old 12-27-2006, 01:45 PM
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aerocorey aerocorey is offline
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Quote:
Originally Posted by BRUTUS
That is the problem with having JUST the voltmeter, you can only use it at startup and it tells you what you already should know, that you have a voltage drop. The battery could be dead and it will still show 12V.

The ammeter tells you much more than a voltmeter ever could because it is a live diagnostic of your charging system.

It would be like having an "oil volume guage" instead of "oil pressure guage". It is accurate DATA... but how pertinant is it?

That's a good point. Maybe I'm just used to the voltmeter and need to think about what the ammeter is telling me and how it's useful. It might be that the best scenario would be to have an ammeter and a voltmeter, but without some explanation the average consumer (like myself until today) wouldn't find it useful. Perhaps I'll be leaving the ammeter in place after all.
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Current
87 GW "Big Bear"
76 J20 project "Ox"
90 GW parts rig "Velma"
77 J10 parts rig "NoMo" (as in "no more Jeeps, Corey!")
94 YJ "Coop"

Past
88 GW "Hercules" (had to sell in '08, curious who has it now)
83 Wag parts rig "Shaggy" (used to build Herc, then scrapped)
73 J4000 (had to sell due to PCS in '07)
75 Cherokee "Jerry Lee" (sold in '13 because I'm an idiot)
74 Cherokee "Dino" (used to build Jerry Lee, then scrapped)
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  #15  
Old 12-27-2006, 02:10 PM
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Great Pharoah Great Pharoah is offline
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Quote:
Originally Posted by aerocorey
That's a good point. Maybe I'm just used to the voltmeter and need to think about what the ammeter is telling me and how it's useful. It might be that the best scenario would be to have an ammeter and a voltmeter, but without some explanation the average consumer (like myself until today) wouldn't find it useful. Perhaps I'll be leaving the ammeter in place after all.

NO, bypass the stock ammeter, it can cause you lots of problems if you install high current draw accessories or a higher output alternator, including a dash board fire. Anything that can draw more than 60 amps can burn you up (think big stereos, subwoofers, amplifiers, and large lights here). If you have a high output stereo, night time with headlights on, A/C on, and all the goodies you can draw more than 60 amps. Safer to do without it and use a voltmeter.
GP
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American Jobs should be for Americans.
Some Cheros run at 75, and some do 69,
But if I can get mine to start and run at all, I think I'm doing fine.

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"Whoopi" 80 Cherokee Golden Hawk. 360/727/208
Horseshoe Bay, Texas
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  #16  
Old 12-27-2006, 02:20 PM
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The only non-stock items this truck will ever see is an MSD 6A and a Howell TBI. I might change the alternator, but it will be to a stock newer style with an integrated regulator, and I may not do that. My goal with this truck is to keep it close to stock, restore it, and possibly show it. Should I still bypass the ammeter? Is this something I should be concerned about bursting into flames in the garage one night? I'm not oppsed to any modification, and I'm thinking about going to a Painless harness, but I don't want to modify just for the sake of needless modification on this particular rig.
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Corey

Current
87 GW "Big Bear"
76 J20 project "Ox"
90 GW parts rig "Velma"
77 J10 parts rig "NoMo" (as in "no more Jeeps, Corey!")
94 YJ "Coop"

Past
88 GW "Hercules" (had to sell in '08, curious who has it now)
83 Wag parts rig "Shaggy" (used to build Herc, then scrapped)
73 J4000 (had to sell due to PCS in '07)
75 Cherokee "Jerry Lee" (sold in '13 because I'm an idiot)
74 Cherokee "Dino" (used to build Jerry Lee, then scrapped)
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  #17  
Old 12-27-2006, 02:46 PM
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Quote:
Originally Posted by Great Pharoah
NO, bypass the stock ammeter, it can cause you lots of problems if you install high current draw accessories or a higher output alternator, including a dash board fire. Anything that can draw more than 60 amps can burn you up (think big stereos, subwoofers, amplifiers, and large lights here). If you have a high output stereo, night time with headlights on, A/C on, and all the goodies you can draw more than 60 amps. Safer to do without it and use a voltmeter.
GP

Ok... so maybe it is safer to bypass the ammeter but count me in the "living dangerously" category. I am keeping my ammeter!

Facts: I have a 110amp alternator and a functioning ammeter, I also have a 17amp electric fan (puller) and a 14amp electric fan (pusher) and my dash is very much in tact so far as a 33 year old dash should be. Has been for the last two or so years that I have had 31amps worth of fan installed.

I do however disagree with the "reasons" stated above...
Lights on at night... 55W (low beam) and 65W (high beam) = 5amps
High output stereo... 300W (rough guess for typical FSJ'er) = 25amps
Aux lighting... 400W = 33amps

AC uses gasoline to compress refrigerant through the belt run off the crank pully. AC only uses electric power to engage the clutch to turn it on or off. Once it is holding the clutch engaged... it doesn't use any current (think of the flow analogy above - pressure [voltage] holds the clutch engaged) The only thing electric when you run the AC is the fan... say 10amps as a guess. I am still not sure where you would be using the AC at night though... isn't it cold in the desert at night?

So here is the picture I have in my head: AC cranked, stereo at full blast, headlights and aux lights on... total = 73 amps. Say you have the stereo at 1/4 volume, total = 54amps. Not really likely if you ask me. But if that is how you drive your FSJ.. more power to ya.

I sure wish JYG was on here to settle this debate... He knows EVERYTHING!

Quote:
Originally Posted by DieselSj
Quote:
Originally Posted by BRUTUS
I agree with you but what I was getting at is that under normal operating conditions, the engine runs off the alternator by itself. The battery is only used for the radio, CB, lights, fans, etc (once it is started and running)
Not exactly. The alternator powers everything while the engine is running.

I am sorry, I have to laugh at this one... The sarcastic devil on my shoulder is telling me to say "NO, you are wrong sir... The alternator powers everything while under normal operating conditions once it is started and running!"

EDIT: I read that wrong... if you aren't running any MAJOR electrical devices it will run off the alternator, TRUE. I watch my ammeter every time I turn my fans on full bore and it tells me how much is being drained from the battery and replaced by the alternator. If the engine ran off the alternator NO MATTER what electrical accessories were running, why would stereo guys put capacitors near their amps? An ammeter would be just as useless (IMHO) as a voltmeter if everything ran off the alternator.
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Current Jeep Status:Under The Knife
Current Homepage Status: RUNNING

Last edited by BRUTUS : 12-27-2006 at 03:01 PM.
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  #18  
Old 12-27-2006, 03:14 PM
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BRUTUS BRUTUS is offline
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Quote:
Originally Posted by aerocorey
The only non-stock items this truck will ever see is an MSD 6A and a Howell TBI. I might change the alternator, but it will be to a stock newer style with an integrated regulator, and I may not do that. My goal with this truck is to keep it close to stock, restore it, and possibly show it. Should I still bypass the ammeter? Is this something I should be concerned about bursting into flames in the garage one night? I'm not oppsed to any modification, and I'm thinking about going to a Painless harness, but I don't want to modify just for the sake of needless modification on this particular rig.

No the ammeter doesn't just burst into flames... I suspect that if enough current passes through it and it has some sort of internal defect it will short... and since it isn't on a fuse, it will continue to short until the connection is broken or the battery goes dead = fire. If you are going to show it in anything but a loudest stereo competition, you should be fine. I mean your truck has survived like it came from the factory for the last 18 years... if you aren't adding heavy electrical mods to it... no problem.

I would say that instead of doing the painless wiring harness, get the harness made by Zach with ZMjeeps.com on this board. I have heard of problems with the painless harness not fitting perfectly but I have never seen any complaints about Zach's harness!
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Current Jeep Status:Under The Knife
Current Homepage Status: RUNNING
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  #19  
Old 12-27-2006, 03:21 PM
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aerocorey aerocorey is offline
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Thanks for the tip on harness. I plan to keep the original 1 speaker AM radio. It's classy!
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Current
87 GW "Big Bear"
76 J20 project "Ox"
90 GW parts rig "Velma"
77 J10 parts rig "NoMo" (as in "no more Jeeps, Corey!")
94 YJ "Coop"

Past
88 GW "Hercules" (had to sell in '08, curious who has it now)
83 Wag parts rig "Shaggy" (used to build Herc, then scrapped)
73 J4000 (had to sell due to PCS in '07)
75 Cherokee "Jerry Lee" (sold in '13 because I'm an idiot)
74 Cherokee "Dino" (used to build Jerry Lee, then scrapped)
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  #20  
Old 12-27-2006, 03:22 PM
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Great Pharoah Great Pharoah is offline
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Quote:
Originally Posted by BRUTUS
Ok... so maybe it is safer to bypass the ammeter but count me in the "living dangerously" category. I am keeping my ammeter!

Facts: I have a 110amp alternator and a functioning ammeter, I also have a 17amp electric fan (puller) and a 14amp electric fan (pusher) and my dash is very much in tact so far as a 33 year old dash should be. Has been for the last two or so years that I have had 31amps worth of fan installed.

I do however disagree with the "reasons" stated above...
Lights on at night... 55W (low beam) and 65W (high beam) = 5amps
High output stereo... 300W (rough guess for typical FSJ'er) = 25amps
Aux lighting... 400W = 33amps

AC uses gasoline to compress refrigerant through the belt run off the crank pully. AC only uses electric power to engage the clutch to turn it on or off. Once it is holding the clutch engaged... it doesn't use any current (think of the flow analogy above - pressure [voltage] holds the clutch engaged) The only thing electric when you run the AC is the fan... say 10amps as a guess. I am still not sure where you would be using the AC at night though... death valley maybe?

So here is the picture I have in my head: AC cranked, stereo at full blast, headlights and aux lights on... total = 73 amps. Say you have the stereo at 1/4 volume, total = 54amps. Not really likely if you ask me. But if that is how you drive your FSJ.. more power to ya.

I sure wish JYG was on here to settle this debate... He knows EVERYTHING!



I am sorry, I have to laugh at this one... The sarcastic devil on my shoulder is telling me to say "NO, you are wrong sir... The alternator powers everything while under normal operating conditions once it is started and running!"

When you installed your 110 amp alternator, did you run your alternator output thru the stock wiring, or did you connect it directly to the battery through a fusible link? If so then the alternator is not charging through the ammeter, so you are safer. But then the ammeter readings are not accurate since not all the current is not flowing through the ammeter but only what the the electrical system is drawing from the fuse box through the ammeter itself. Also if the fans are connected by relay with the current source coming from the battery positive post, with the higher output alternator outputing directly to the battery then the ammeter never sees those 31 amps. Once again it is safer, but the ammeter gauge reading are meaningless since a lot of current and the charging circuit are in pararel with the ammeter instead of in series with the ammeter. I'll stand by my statement that high current through the ammeter is dangerous. The stock ammeter is good for about 60 amps, running 73 through it WILL burn it up just as running 15 amps through a 10 amp fuse will blow the fuse. If you have the charging circuit seperate from the ammeter, then the ammeter is just decoration anyway, so why not be even safer and bypass the thing completely?
GP
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American Jobs should be for Americans.
Some Cheros run at 75, and some do 69,
But if I can get mine to start and run at all, I think I'm doing fine.

Big Mike
"Whoopi" 80 Cherokee Golden Hawk. 360/727/208
Horseshoe Bay, Texas
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