37 P4 ammeter

[Lew]

I run a 30 amp 1 wire alternator leftover from my Model A days in my '36 Ply without any changes to the stock system including the ammeter and all stock fuses. The 30 amp version seems more than adequate for the radio and lights, etc. The only change was to modify the existing generator mounting bracket bolt setup slightly.The alternator is a GM type with internal rectifier available at most Ford Parts suppliers.
LR

[chetbrz]

I have put a one wire 6volt alternator (60a?) on my P4. The car has the factory 20a fused ammeter, and the fuse now occasionally blows after starting, disabling the lights, etc. The current fuse is a 32v, 20a fuse. I suspect that the alternator is "topping off" the battery after starting at a rate greater than 20 amps. The ammeter is initially pegged at 20 amps for several seconds after starting before dropping down to a "0" amp draw on the meter after about 30 seconds. When the sealed beam headlights are turned on the needle barely moves before returning to "0".

If my above theory is not correct, what else might be happening? The car has a new wiring harness and battery with over 30 days of daily use without problems other than 10a discharge with generator/regulater and sealed beams on. Four days without any problems using a friends 6v alternator (30a?) borrowed from his Model A. Headlights are bright and additionally grounded to the body, not just to the headlight bucket.

Any help is appreciated. Thanks in advance.

Phred,

I use a single wire 6 vdc positive ground high output alternator in both my cars, the 48 & the 29.  If you are running the output of the alternator through a 20 amp fuse you will trip the fuse.  The alternator is capable of putting out 60 amps but with a normal battery 20 to 30 after starting for a short time to revive the battery is normal.

In my 29 I do not run the output of the alternator through the original amp gauge because it was never designed for that type of current.  On my 48 P15 I do run the output through the gauge and it works fine.  If my battery is poor it will run 30+ amps to the battery.   Once the battery is restored it will drop to provide a trickle charge.  (1 to 3 amps)

Try a 30 amp slow blow.

Good luck,  Chet?

[elmo]

I think by the way you describe your problem that your gen could? be the problem ,but for starters is the 10 amp disharge showing at idle speed or normal running if at idle thats normal or close to normal with every tihng switched on , but whats not normal is for it to keep blowing fuses , i still believe you have a short somewhere  , new harness or not , perhaps something was not hooked up right i doubt if your ammeter is the fault unless its not connected the right way ,even then all it should to is show a discharge and not blow fuses , they are not voltage consious and will take 12 volts with no problems , unless its a faulty unit , if it was mine i would be looking for an old time auto elecrician to look at it , and also check the gen out.

[TodFitch]

my simple reply is you have a short some where

My simple reply is that you have an "electrical system" that was all set up to work together and then you replaced a component with one capable of putting out three times the current as the rest of the system was designed for. Which is a recipe for problems unless you are careful.

If that alternator is actually putting out 60 amps on start to top up the battery, then not only is your ammeter being over stressed, but so is all of your primary charging circuit. Those wires, now old and with some corrosion on their connections, are not designed for that type of current and could be a fire hazard.

[elmo]

my simple reply is you have a short some where

[Phred]

I have put a one wire 6volt alternator (60a?) on my P4. The car has the factory 20a fused ammeter, and the fuse now occasionally blows after starting, disabling the lights, etc. The current fuse is a 32v, 20a fuse. I suspect that the alternator is "topping off" the battery after starting at a rate greater than 20 amps. The ammeter is initially pegged at 20 amps for several seconds after starting before dropping down to a "0" amp draw on the meter after about 30 seconds. When the sealed beam headlights are turned on the needle barely moves before returning to "0".

I don't want to put an aftermarket ammeter or voltmeter on the car. ASSUMING my above theory is true... If I put a larger fuse in the ammeter (say 30a to start with) will this brief "overage" damage the ammeter so it won't show normal fluctuations in current draw? Or is there a different 20a fuse to use? If so, what type?

I have noticed on e-Bay some of the dash clusters offered have a 20a ammeter, and some have a 30a meter. Why the difference? Truck/car, Radio/no radio?

If my above theory is not correct, what else might be happening? The car has a new wiring harness and battery with over 30 days of daily use without problems other than 10a discharge with generator/regulater and sealed beams on. Four days without any problems using a friends 6v alternator (30a?) borrowed from his Model A. Headlights are bright and additionally grounded to the body, not just to the headlight bucket.

Any help is appreciated. Thanks in advance.