Can Ammeter Run Parallel?

[TheMonkey]

my car is '61 GM with an ammeter in the dash. the ammeter does not have values on the gauge, just charge or discharge.

i'm going to put in a 94 amp 12SI alternator, and i do not want to wire through the ammeter, as it could potentially be too much for the wiring. the original wire is prob 10 gauge.

but, could i wire a heavy gauge wire (maybe 8) from BATT term on alternator directly to battery terminal, and also run parallel to that, the 10 gauge wire through a 50 amp fuse, through the ammeter back to battery terminal?

that way, most the current would take the easiest path via 8 gauge wire, and the balance taking the long route through more resistive wire would maintain the functionality of the dash gauge (remember - gauge has no values)?

thanks, Scott.

[Karch]

Hey Scott,

I don't have real experience with this, but it seems to me that the ammeter will only read what is going through it, and if you have 2 branches, than the current will always choose the path of least resistance, just like water does in a river channel.

All the current out of the battery/alternator must go somewhere, and if you add all the current flows up, they will total what is going out the battery/alternator.

So, I think the answer to your question would be no, you can't wire it in parallel and expect to read the other wire.

I think in your case you are best off with a voltage meter. MAD electrical has information on these, and if it's not on their website, than I have it here in their little booklet that I purchased.

Just keep in mind the thing about least resistance. That is where the current will go.

[TheMonkey]

Hey Scott,

I don't have real experience with this, but it seems to me that the ammeter will only read what is going through it, and if you have 2 branches, than the current will always choose the path of least resistance, just like water does in a river channel.

All the current out of the battery/alternator must go somewhere, and if you add all the current flows up, they will total what is going out the battery/alternator.

So, I think the answer to your question would be no, you can't wire it in parallel and expect to read the other wire.

I think in your case you are best off with a voltage meter. MAD electrical has information on these, and if it's not on their website, than I have it here in their little booklet that I purchased.

Just keep in mind the thing about least resistance. That is where the current will go.

thx for the reply Karch. right... the meter would not read all the current. but remember, the gauge does not have values. so... if i'm charging 65 amps, and 40 is taking the high road, and 25 is taking the low road, the meter would register 25, but without numbers, it wouldn't matter. it would only read directionally. in fact, 25 amps would prob be nearly full blast on the gauge. what i would mainly want to know, is that 'some' current would still take the more resistive route. this scheme is mostly just to save myself from having a totally dead gauge in the dash.

i was thinking i could 'tune' how much goes through either circuit by size of direct wire, and or a resistor in either wire. for instance, if in the example above, 40 goes through fat wire, 25 goes through ammeter but the ammeter pins against full current, and i want it to read about 2/3 on the meter, then i could use a heavier gauge wire for the direct wire to positive battery so that more current would take that route, and less through the meter.

this is my thinking, i just don't know if there is a reason it would not work.

[shep]

Electricity like water is lazy and all of it will always take the path of least resistance. You could maybe have the gage reworked to read voltage and then wire it in parallel.

[TheMonkey]

shep-

so, are you saying that in my example above, if the fat direct can handle all the 65 amps, then 65 amps would take that route, and 0 amps would take the meter route?

thx, Scott.

[shep]

What I am saying is that no matter what size the cable all the current is going to try to pass through it, and none will go through your gage.

[TheMonkey]

I tested this. I think my idea will work. Check this out....

on my convertible (same year/model), i already converted to alternator. this is a car with very low current demand (all stock), so i only put on a 63 amp alternator. i wired it fully through the original ammeter because under full current load, the original wiring through the firewall can handle the load. so, my "BATT" terminal from alt is wired with 10 gauge wire through firewall, through ammeter, back into engine compartment, and onto the battery positive terminal post where starter wires to.

TEST....

turned on lights with car off to drain the battery a bit. the ammeter drops about to 1/2 between no current and fully discharge. leave lights on for about 3 mins. then, i turn on car, and the ammeter reads about 3/4 between no current flow & full charge. but, if i connect a heavy gauge battery jumper between the "BATT" terminal and the battery positive terminal at starter post, then the ammeter drops to about 1/4 between no current & full charge. as soon as i disconnect the jumper, the ammeter jumps back up to 3/4 charging. if i turn off car, with the jumper connected, and lights on, the discharge is almost 1/4 discharge. as soon as i take jumper off, the discharge is back to 1/2. this works in both directions.

when car is off, or battery is charged, the ammeter settles back into the 'no current' point (but actually ignition is using very little that does not register).

the bubble top i am building will have heavy current demands from EFI & electric fan. i'm going to use a DC control at fan so startup isn't big, but i think this will work to have 2 paths of charging. i'll also have a volt meter as part of the add-on cluster just under the dash.

Scott.

[TheMonkey]

Shep- totally agree electricity takes path of least resistance. but, i think the reason this works, is because as soon as current begins to flow through the jumper cable, this *is* resistance, and all of the sudden, the marginal addition of current has an unused path through the ammeter that it can take. if my handheld digital ammeter was heavier duty, i would measure the amount of amps taking either path, but i suspect the path via the jumper was more amps than the 10 gauge wire through ammeter. this sort of showed up in the fact that ammeter dropped from 3/4 to 1/4 when jumper added.

[MonzaRacer]

Dont run an ammeter and the shunt type is very inaccurate and can fool you into thinking your system is functioning.
ALSO THE AMMETER GOES IN THE LINE THAT FEEDS THE WHOLE CAR(IE IF YOU PULL IT LOOSE ALL THE LECTRICAL SYSTEM DIES. IF YOU ONLY INSTALL IT IN THE ALTERNATOR ITS ONLY READING THE ALTERNATORS OUT PUT.
Use a round digital volt meter and tie it into the battery positive and negative or as near as possible.
Your voltage should be steady and I like to see it around 14.5/14.8/15.0 especially with all the new electronic addons.
As for a car not pulling a lot at idle figure the ignition and fule pumpalone will pull 10 to12 amps at least.
Figure 5 to 6 for stock EFI pumps, more for high pressuure/volumes may pull more, and a good HEI can pull around 4 to 8 amps.
COPS ignitions seem to be a lot easier but still if each pulls 2.5 amp per thats a lot and an alterantor will use 4 to 6 amps to make it power.
Again for safely sake use a digital volt meter and make sure your charging system voltage numbers stay steady under heavy load. I like to see running steady voltages to be in the steady 14.5 to 15.0 volts.
Trust me the computers dont monitor amps they monitor voltage and thats what you need to use too.
Now if you use older low output(re amps) alts use them one as it will be critical to maintaining a good charging system.
BUT if you run one your pulling in ALL of the battery voltage into and out of the passenger compartment and some racing orgs wont let them be in the car anyway as they can short out and cause a fire hazzard.
Amps guages are old school/old tech and no longer safe nor required.
Also if you just have to install it look for the junction that feeds the whole car as this is where it needs to be installed, not the alternator wire. Its supposed to show all of the current used by the car not just carge amps. But as for installing one on a nearly 100 amp alternator rememberthis its a solid battery voltage line into and out of the the passenger compartment and can short out of if you put something condiuctive in near it it can short too if it happens to connect by accident.
Lee Abel
AFTERMARKET PERFORMANCE

[TheMonkey]

Lee-

Thanks for the reply. Agree 100% that a 94 amp EFI car should not use an ammeter for the entire feed. That is the whole point of this.

My question is whether or not it is a bad idea to run 2 wires from the alternator - 1 direct, and 1 through the ammeter.

The ammeter would not read the full amperage, only what goes through it. But.... the ammeter has no values on the gauge. It would only show directionally, and relatively. For instance, the example above - if the car is requiring 65 amps, and only 25 goes through ammeter, it will still show that the car is charging, not discharging.

My only goal is to keep the original gauge functional and not dead.

I understand why ammeters do not work in today's cars. But, if there was a 50 amp fuse (or even 30 amp fuse) before it goes through the firewall, is it still dangerous?

Car would also have voltmeter in add-on cluster, so the voltage can be monitored for electronics.

Thanks,
Scott.

[MonzaRacer]

AS for the old guage its tied into the stock wiring and is probably a very simply ,very light shunt type(Ford did this on the Early fox mustangs too but if it shorts it wont charge so you have to add on an ignition wire to the factory regualtor plug, had to do that on my nephew 84 GT.
But if I had my druthers I would simply pull it apart and make it "look" like its working and ignore it. Simply make a small electromagnet and figure out how to tie it in to the ign, the only time it would look goofy is when you first turn car on but if it still works and thestock wiring is ther use it but if your trying to add it to a generator set up its only rated for about 40 amps at beat (probably about the same even with first Alts too.
If your adding one on I wouldnt.
But yes its still dangerous as the fuse is a limiter or resistor of sorts. Maybe a circuit breaker but it better be very high like 60 to 100 amps. But with a big alt its kind of moot till you know how its wired.If it takes all of the cars power production its not safe with an upgrade alt in my profesional opinion.
Lee Abel
AFTERMARKET PERFORMANCE
Good Luck

[TheMonkey]

thx Lee, i appreciate your thoughts.


... but if it shorts it wont charge so you have to add on an ignition wire to the factory regualtor plug...

but it would have a second jumper wire, so if it shorts or blows the fuse, then it would still charge through the jumper, right? ammeter would just be a secondary, lighter gauge circuit that 'invites' some current.

i read your posts a couple times, and after i tested for this, it's not clear to me why it wouldn't work or would be a bad idea.

i'm not trying to argue, just having a hard time understanding. sometimes i can be dense.

[TheMonkey]

to clarify the way i had it set up in my test....

charging wire from low amp alternator goes from alt through ammeter, back to pos battery terminal. everything works, and ammeter registers all the current flowing in the system. then.... just put a jumper cable between the alternator charge post directly to pos battery terminal. most the current goes through jumper, but some still goes through ammeter route.

i'm afraid i have not articulated myself very well. or perhaps you are very clear with what i have written?

[buns]

my car is '61 GM with an ammeter in the dash. the ammeter does not have values on the gauge, just charge or discharge.





Could you be more specific as to the make and model of your car? All my wiring diagrams for 1961 Chev show a warning light, no gauge.




https://static1.pt-content.com/images/pt/2007/07/gif3-1.gif

[TheMonkey]

sorry... Pontiac Bonneville.

i tried attaching a file to this, not sure how to do it... here's the image though....

https://static1.pt-content.com/images/noimg.gif

[TheMonkey]

guess it did attach :Alchy:

[TheMonkey]

buns-

when looking at the wiring diagram, remember that the car has been converted to an internally regulated alternator, so the generator & regulator go away, the red wire in the diagram from the regulator to ammeter has been taken off the regulator and wired to the BATT term of the alternator. the alternator sense wire (term #2) is direct from alt to the battery positive terminal, and the alternator excite wire (#1 terminal) is wired through an add-on dash light and to the ign 1 at the ignition switch.

for the test, i just jumped a battery jumper from BATT terminal to battery positive terminal in order to give 2 routes to charge (1 through ammeter). my existing car, this works fine without the jumper because it is small alternator and has low demands. i'm exploring a heavier duty wiring scheme for another build i'm working on with much higher demands.

[Damn True]

Lee is right. Ammeters are innacurate at best, if you must use one, it has to be wired in series. A voltmeter would be a better choice.

[TheMonkey]

i should take a picture of the meter and post it. it doesn't have any numbers, only dashes. accuracy becomes very relative without numbers on the gauge. without nums, only direction & functionality matter, which is what i care about.

so i thought it may work, i tested it works, i just don't want to have a fire.

[terryr]

There are types called Shunt Ammeters, that measure a percentage of the total. But the wire sizes have to be calculated properly.
When I upgraded an old Mustang with a new type 3G I added an extra wire to handle the load. After that the ammeter always read discharge, even when I tested the voltage at the battery. I suppose the current was trying to run backwards thru the meter. Eventually I put in a voltmeter.

[MonzaRacer]

Thats what hes trying to make but the type of system he has wont do it the meter is too heavy internally. If you want to find a volt meter ,gut it and fasten it behind the factroy guage face, ad a pin slighty under the center point and make sure it "looks" like it has a amps guage and is "charging" I talked to a company that does retoreation and they do this every day but its time consuming. Thier big problem is making the fac ammeter "look" like its charging and show a certain charge as its a volt meter.
Good Luck

[68nate]

I don't see why it would be a problem. current= voltage multiplied by resistance. Should roughly divide current by two as indicated in your test. One thing to keep in mind is that a 20 guage wire and 8 guage wire would have about the same RESISTANCE, but it wouldn't take much CURRENT to let the smoke out of the 20 guage wire.

[MonzaRacer]

Wrong the 20 guage wire will have more resisitance. All of the power will go through the 8 guage.
AS amperage goes up the wires will heat, more so for the smaller one BUT if the lagerone can keep up with the power flow nothing will be going through the little one, or not enough to mean anything.
The unit in the car wont respond as its very "heavy " inside if factory unit handled all of the current.

[TheMonkey]

... nothing will be going through the little one, or not enough to mean anything....

when i tested this, a meaningful amount went through the smaller gauge wire through the ammeter. remember, when i split it, just more than half went through the bigger wire. i tested it, it worked the way i want it to.

[baskin]

TheMonkey; your theory is correct, to be more exact, you’ll find a wire resistance chart here http://www.stealth316.com/2-wire-resistance.htm What you’ll need to do to calculate the split is to first find the resistance of each path, then convert that resistance to conductance (1/R) and then find the percentage of conductance for each path. As an example, let’s say you have 10 feet of 10 gauge bypassing the ammeter, giving a resistance of .0102 ohms, and 15 feet of 12 gauge running through the ammeter path, giving a resistance of .0243 ohms. The conductance of the bypass path = 1/.102 = 98.4 S, the conductance of the ammeter path = 41.15 S, and the percentage of current through the ammeter = 100* 41.15/(41.15+98.4) = 29.49%. The resistance given is at 77F and will rise about 6% for every 20 degrees F but, given both paths are at relatively the same temperature, it won't change the final numbers much.

For safety reasons, you'll want to use a fusible link on both paths, the correct gauge for that should be 4 gauge numbers higher than the wire being used, eg; 10 gauge wire would require a 14 gauge fusible link. Finally, remember that the function of the link is to get hot enough to melt the copper on overload, which will also melt solder, so although you can solder the connections to the link, they need to be primarily attached mechanically (crimp connector)

[TheMonkey]

baskin: you rock :bananna2:. that's the information i was looking for. resistance is something i can measure, and that formula seems straight forward.

i was thinking about using a 40 amp circuit breaker before going through the firewall to the ammeter, but i'll check that against the math for the wiring.

cheers,
Scott.

[68nate]

Wrong the 20 guage wire will have more resisitance. All of the power will go through the 8 guage.
AS amperage goes up the wires will heat, more so for the smaller one BUT if the lagerone can keep up with the power flow nothing will be going through the little one, or not enough to mean anything.
The unit in the car wont respond as its very "heavy " inside if factory unit handled all of the current.

Yes, I said "roughly" the same RESISTANCE. Take your Fluke to each and what do you get? About 0.1 on the 8 guage and maybe 0.3 on the 20 guage. Just saying resistance has nothing to do with how much current a wire can handle. In a DC PARALLEL CIRCUIT, the available voltage and the resistance of each circuit controls how much current flows through each circuit.

[baskin]

baskin: you rock :bananna2:. that's the information i was looking for. resistance is something i can measure, and that formula seems straight forward.

i was thinking about using a 40 amp circuit breaker before going through the firewall to the ammeter, but i'll check that against the math for the wiring.

cheers,
Scott.

The lowest resistance you can accurately measure with an ohmmeter is about an ohm, below that, the lack of resolution and contact resistance makes for a pretty inaccurate reading. What you can do is essentially build your own ohmmeter, just go down to radio shack and pick up a couple of 20 ohm, 20W resistors. Connect them in parallel to ground, connect the other ends of them through the wire you want to measure to the positive side of the battery. With a battery voltage of 12.6V applied, each resistor will draw 12.6V/20 ohms = .63A, for a total of 1.26A. Measure the voltage across the wire and divide it by the current in order to get the resistance. This is exactly how an ohmmeter works, but with a far lower current which limits the accuracy in measuring low resistance loads.