20-0-20 amp meter
- Thread starter oldspert
- Start date
P.S.
Well-known member
Assuming your 20-0-20 ammeter doesn't have a problem or internal resistance, it will be fine.
Charlie Stephens
Well-known member
Since original amp meters are hard to find and repros are junk (at least they used to be) I would run a "shunt" to carry some (maybe half) of the current around the amp meter. Attached is a picture behind the dash on my '32. In a Model A I would probably just run two wires from the output of the alternator and connect one to each of the terminals on the amp meter. Be sure that each wire is heavy enough to carry all of the current to keep from having a fire if the amp meter fails. Just remember that the amp meter will show half of the current.
Charlie Stephens
Attachments
Bought my 6 volt +ground alternator from Ken Davis here in the DFW area and he said no need to change to 30 amp ammeter.
http://www.kendavismodela.com/Alternators.html
http://www.kendavismodela.com/Alternators.html
Bill G
Well-known member
Even though the alternator is capable of 37 amps, it won't be running at that rate rarely, if ever.
How much of a load do you currently have? With the car motor turned off, turn on everything electric. Lights, horn, turn signals, wipers.... What is the maximum reading when using everything. If it doesn't go over 20 amps with no charging going on, it also won't with a higher capacity alternator while charging.
On the charging side of things, I have a Nu-Rex high output alternator and a 20amp meter. Right after starting, the charging grate will momentarily swing up a little past 10 amps and then settle back down to near zero while running. If your battery was really shot, you might get over 20 amps on full charging, but still, probably not.
For other things, such as shorts, etc, hopefully you are running with a fuse, and if your fuse is 30 amps, it should not let your current go over 30 amps anyway. 30 amps should not kill a 20 amp ammeter. They are more rugged than that.
My opinion is that you should probably never see any current issues. An alternator with a capacity of 37 amps is its capacity, and does not imply that it will always be putting out its maximum current.
How much of a load do you currently have? With the car motor turned off, turn on everything electric. Lights, horn, turn signals, wipers.... What is the maximum reading when using everything. If it doesn't go over 20 amps with no charging going on, it also won't with a higher capacity alternator while charging.
On the charging side of things, I have a Nu-Rex high output alternator and a 20amp meter. Right after starting, the charging grate will momentarily swing up a little past 10 amps and then settle back down to near zero while running. If your battery was really shot, you might get over 20 amps on full charging, but still, probably not.
For other things, such as shorts, etc, hopefully you are running with a fuse, and if your fuse is 30 amps, it should not let your current go over 30 amps anyway. 30 amps should not kill a 20 amp ammeter. They are more rugged than that.
My opinion is that you should probably never see any current issues. An alternator with a capacity of 37 amps is its capacity, and does not imply that it will always be putting out its maximum current.
rotorwrench
Well-known member
On one of the helicopter types I used to work on, it experienced a dead short to ground of an 8 gauge wire between the alternator and the buss due to insulation deterioration. This system was a 70-amp system with a De arsonval type 70-amp reading ammeter and a 70-amp alternator set up for 24-volt operations. The short caused that 8-gauge wire to burn and it even melted the insulator bushings at the alternator output terminal. The amp meter was damaged as well. It still had a swing to it but the needle would never go back to "0".
A 37-amp alternator, such as a model A, would also burn the wire but it doesn't have a de arsonval meter and it's generally only 6-volts. It may burn the inside though and change the properties of the permanent magnet inside as well. Maintain the wiring in good condition with tight terminal connections and you can use what ever amp meter you want. It only shows what the current draw is at any given time less the charging rate. With headlights on and engine running plus the brake light on still won't peg a 20/20 meter. Now if you install a stereo and air conditioning with a heater then all bets are off.
A 37-amp alternator, such as a model A, would also burn the wire but it doesn't have a de arsonval meter and it's generally only 6-volts. It may burn the inside though and change the properties of the permanent magnet inside as well. Maintain the wiring in good condition with tight terminal connections and you can use what ever amp meter you want. It only shows what the current draw is at any given time less the charging rate. With headlights on and engine running plus the brake light on still won't peg a 20/20 meter. Now if you install a stereo and air conditioning with a heater then all bets are off.
A regulated alternator won't push more than a couple amps into the battery under normal running conditions. It's the discharge from the battery in the other direction due to overload that could hurt the ammeter.
37 amps is the maximum to expect from the alternator; it produces only what is required by the load, as Bill G implied.
37 amps is the maximum to expect from the alternator; it produces only what is required by the load, as Bill G implied.
JOES31
Senior Member
I run the Powermaster 6V alternator, and just like Dick M. said, it's not a problem. I just don't know why the Powermaster instructions state that you shouldn't run the alternator through the amp gauge. Nobody I know does that, in our club and everything is fine.
rotorwrench
Well-known member
Without being specific, they are telling folks not to trust them. The reproduction meters I see don't hold a candle to an OEM original. There aren't many ammeters made to fit the Ford dash so there are not a lot of choices out there. A person can use a shunt or a shunt wire to protect the ammeter but some calculations have to be done to get the wire length correct for the shunt bypass amount so the meter will have some known indication to go by.
