I bought a used SW amp gauge with no instructions. How do I hook this into a one wire alternator? Thanks
you want to connect it in series with the wire that connects the rest of the electrical system, to the battery. And be really careful with the wire size and routing, the wire needs to be big enough to handle the current, and make sure it won't get shorted to ground under any conditions.
What Jim said just remember you don't want to know how much the alternator is putting out you want to know how much is reaching the battery after the loads are taken out.
You might be better served by using a voltmeter rather than an ammeter. Any significant charging problem will show up in reduced voltage output and the wiring for it is much simpler and need not be heavy gauge. The fact that you bought the used ammeter doesn't require you to use it. All true 'car guys' have shelves of unused parts we thought we needed at the time we acquired them. Ray
If you replace the 1 wire alternator with a 3 wire alternator, you can use an idiot light, which is even more useful. It lights up where there's a problem. That's what I have in my hot rods.
Amp meters are a fire hazard. Old generators put out 30 amps but a new 1 wire alternator output may be 100 amps. A voltmeter is much safer and won't burn your rod to the ground. Amp meters disappeared in new cars in the mid 80's due to fire hazard. You could still install for looks but I recommend you NOT connect the wires. It pulls all the juice inside the car right under the dash. If it ground accidently your ride is gone.
The ammeter itself is the main fire hazard. It has to be rated for the maximum charging system output, and I've never seen any aftermarket one rated for more than 60 amps. Typical modern alternator output is now around 100 amps if not more. Even if wired with the right-sized wire, the gauge can catch fire... That's not actually true. By the early 60s, direct-read ammeters had pretty much disappeared in OEM applications (due to the fire hazard aspect), being replaced with shunt-type or inductive ammeters. Inductive ammeters had no 'direct' connection to the charging system and rarely failed, but still required the high-current 'main feed' wire to pass through them. By the late 60s, these had disappeared, being replaced with shunt types. While these were 'directly connected', these read only a small portion of the current and were intrinsically safe from a fire hazard standpoint, but required special 'calibrated' circuit wiring connections to read semi-accurately (accuracy wasn't their strongpoint). Their problem was they were sensitive to current spikes and gauge failure wasn't uncommon, and once the gauge failed, you had no way to monitor the charging system even though it still worked.
i worked on a 55 T bird a long time ago, the owner installed an ammeter, a nice SW with matching oil pressure gauge. The ammeter was wired in using zip lamp cord. Mopars had direct reading ammeters for a long time, and they are still giving people fits.
Yep, that old SW ammeter will NOT be rated to take the out put of most 1 wire alternators, especially since most spike really hard when they get the rpm up enough to excite and start charging in the first place.
These guys are right Wayne, if wired correctly every bit of electricity being used in your car except the starter is going through the ammeter and even if it has a shunt it is still dangerous, all of that electricity is going through your dash. Do you want the main feed going to the panel in your house going through the living room first, I think not. Use a voltmeter and you won't need as many fire extinguishers.
i have to agree with all the above on the use of ammeters , but if you still want to use it this is how they are wired: output of charging system goes to + side of the gauge , then from the - side of gauge to the + side of the battery. all power for the system comes from a wire on the + side of gauge...there are no other wires attached to the ammeter gauge this way it shows power going in and out of the battery..and not what the charging system is putting out.
I have 4 cars, three have volt meters and one has an idiot light. I removed the amp meters years ago when I updated the charging systems. As others have stated, volt meters are safer and indicate the charging voltage not the load.
Shunt type ammeters don't have the 'main current' supply at the dash, which is why they were adopted. The gauge operates on about 1 amp, much safer. But these aren't practical for DIYer installation because of the calibration issues. I'll point out one more thing; if running a generator, an ammeter is a better choice for monitoring charging system performance. A generator can put out adequate voltage but fall short on current, something a voltmeter won't show.
If you have a 100 amp alternator I dought you will ever see the amp meter go to 60amps. Charging a battery a 60amp very seldom happens. I have a tractor with a 150 alternator if you run the battery down trying to start it in the winter it will only charge about 30 amps when it starts. you are seeing what the battery is getting not what the alternator is putting out.
In that case, I think they are one and the same. The alternator puts out what is 'useable'...sort of like an ignition coil only produces enough voltage to overcome the resistance in the wires/plug....not it's full potential...unless required. Ray
The typical wire on a 100 amp alternator could not handle 100 amps for any amount of time. The largest wire I have ever seen is a #8 AWG which is rated at continuous 40 amps. Granted for the most part it is in open air which raises its limit. I personally would not have a problem using #8 wire to an ammeter and return but I've been an electrician for 45 years and know how to insulate it.
Post #10 is not actually true. Factory Amp gauges in late 60's cars were made "semi accurate" due to excessive warranty claims. The new car owner with 12mo, or 12oo mi warranty would complain of charging problems. This all happened when they were idling at a traffic light with the heater on high, wipers on, headlights and rear defroster on. This resulted in the car maker making a working amp guage show dead center if the alternator belt fell off the car and was laying on the highway.
a shorted amp gauge hooked to a 100 amp alt is not the problem it's the 800 amp battery on the other end.
That's funny, the amp gauge in my '70 Montego with the gauge pack showed both charging and discharging. So does my '75 Ford truck and my '85 motorhome...
Thanks guys, I'm going with a voltmeter. I'm a retired electrician. I understand short circuits and fire hazards.
Like I said I know how to do it but I didn't either. To be honest I didn't want any added gauges so I plug a volt meter into the cigar lighter when I want to see what's happening. Good luck.
Here's a tip on what not to do, DO NOT run hot wire thru hole with clutch Rod, wears thru, melts wire harness, my first rewire experience, what a mess ! Back in 1966 or so. LOL
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