Stock 1940 Amp gauge & an Alternator

[andyd]

My 1940 Dodge is a hotrod........lol.......has been since 1973 when I installed the 318 Poly V8 & auto........it has all the stock instruments hooked up and has had a Lucas Alternator rated at 50 amps as the battery charging animal for the past 45 years..........this alternator has seen better days & I have some issues as to whether it is up to the job even after being rebuilt by the local sparkie..........so I have obtained a new alternator a Delco type that is rated at 100Amps............has anyone here installed a late model alternator with a similar charging ability but still using the original Ammeter that only indicates up to 35amps?........an inquiring mind,(mine) would like to hear from other members.........thanks....Andy Douglas

[maok]

Hi Andy, both my dodge and airstream have the one wire alternator, rated at 100amps, work fine with the original 30amp ammeter.

 

You will find that the alternators don't output anywhere near their highest output under 2000rpm, more like a 1/3 of the max rating

[Sniper]

Load determines the current draw.  If your 40A unit was sufficient unto the day then adding a 100A unit isn't going to do anything more for you.  Unless you plan to upgrade or add more load, or you get a short.  Now the new unit might have better low speed charging ability, so that is something to consider.  You can always put a fuse or fusible link on the alternator output to protect the system.

[andyd]

The issue with the old alternator was that a diode or some such animal had gone to valhala and the sparkie that I go to had to obtain a 2nd hand alternator to obtain a replacement part, he advised that new parts for that alternator were no longer available so that is why I went with the new unit..........I still have the "reco'd" alternator on the car and it appears to be working o/k but I don't trust it any more but was worried that the new alternator and its charging ability will "overload" the ammeter............and of course the two alternators both have wiring terminals that are completely different in name............lol.............fun,fun,fun............andyd

[DJK]

The alternator is only going to charge what the system requires, like Sniper said, unless you add something that requires more current draw, it will be able to keep up with the demand.

[Adam H P15 D30]

Just don't do anything that will require the alternator to put out full capacity. This includes:

-Jumpstarting another car with your engine running

-Running with a low battery

-Any electrical short

-Shorted cell in your battery

At best your amp gauge will pop like a fuse, at worst it'll burn your car to the ground.

Maybe run a 40-50a circuit breaker in the primary line from the alternator?

-OR-

Upgrade the primary wire from the alternator to 4ga to handle 100 amps should the need arise.  That could make you amp gauge inop though...

 

I get rid of amp gauges...

[andyd]

Adam..........as the car still runs the original gauges including the amp gauge and there is no volt gauge that will fit the amp hole I am stuck with it......as mentioned the Lucas alternator has been there for 45 years with the stock gauges..........so far I haven't had any issues with it and occaisonally do "rev" the engine so far without a problem...........but the Lucas alternator as mentioned is only a 45-50 amp one...........the only high draw item in the car is a 16" fan mounted on the radiator, when used the amp gauge shows a 15-20 amp load........the car has never been used to jumpstart another, it has a battery isolator switch that is always turned off when the car is parked and the battery is always kept charges , etc...........its an interesting conumdrum..........lol............andyd

[Adam H P15 D30]

Just some food for thought.  Here is how I tackled the amp gauge conundrum when I switched to a 70a alternator and I kept my stock gauges.

I bought an aftermarket mini volt gauge.  Here you can see it sitting next to my amp gauge.

 

I removed the amp gauge and attached the volt gauge in its place.

 

I glued the stock needle to the volt meter's needle and added a little color (optional).

 

In the end, when the needle is straight down, that's 12v, anywhere to the left is charging.  If it were not for the colors, nobody would know.

 

[andyd]

Adam............you have got me thinking.........lol.......thanks.......andyd

[Kahunah]

I have the 100 amp GM alternator in my '41. When I rewired the car I put fusible links on both ends of the charging/load circuit. I also bridged the terminals of the ammeter with a fusible link. The gauge still works though, I could be wrong,  in theory only showing half the actual current flow. I have peace of mind knowing the circuit is absolutely protected.