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Questions regarding stock Ammeters


Andydodge

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Whilst my car, a 1940 Dodge is 12 volt and hotrodded with a 318 Poly its had the original instruments all along, since the V8 installation......the car has had a Lucas 3 wire alternator since the mid 1970's which was rebuilt by the local sparkie last year.......the problem I'm having is that when started the ammeter needle will sometimes go to the right of the centre mark showing I suppose, a charge of  5-8 amps.....however more often than not the needle will flick to the left n starting, showing what appears to be a discharge of, maybe 5-8 amps..............however it will sometimes flick back to the right and show that its charging............last week I took the car out for a drive, it started fine, however after a 15-20 minute drive I parked the car, and came back, 15-20minutes later and it barely started, after some very slow winding over it started......I drove straight home and put the battery on the charger which it showed it needed a charge...........the guy who rebuilt the alternator said that it was charging fine  after he did the work, however I am wondering if anyone has had an issue with a stock Mopar ammeter deciding to pick & choose when it will let the electrical gizzmos thru to the battery?..........I've noticed a few NOS 1940 Dodge Ammeters listed on ebay and have thought about getting one but have not jumped to this yet........the car has a battery isolator switch which is used every time the car is stopped and/or parked so any comments or thoughts..........anyone?..........thanks........andyd      

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Andy, there is a good chance there is a rusty short somewhere. I had a similar event in my '28 Chrysler a couple of years ago, when I turned on the head lights it would show a discharge of about 5-10 amps, turn the lights off the ammeter would go back to zero.

 

As you know, its a process of elimination.

 

ps; rusty shorts tend not to burn a fuse.

Edited by maok
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These ammeters are held in middle by small springs. They can can rarely get tired.

I suspect one of 3 diodes is leaking. This is a common problem. They will show 12 volts but current will be lower

But having an external regulator, could also be connection issues. Only way to find out is with an oscilloscope, viewing the three waves simultaneously.

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Ammeters usually don't conduct, not conduct, then conduct again.  Not going to say it can't happen, I've seen some weird electrical things over the years.

 

But I wouldn't bet on that.  A simple heavy gauge jumper bolted to the two studs on the ammeter would bypass it for testing purposes.  Head, if you can route it safely it might be easier to jumper between the output stud on the alternator and the battery positive (assuming negative ground system).

 

Not real familiar with the Lucas setup, but I'd be looking at the regulator and wiring as that is more likely to be flaky than the ammeter. 

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Thanks guys, it has an internal regulator AFAIK....well theres no separate regulator , and accessing it to hook up a jumper wire is not good and .........lol......finally the batteries in the trunk so its all fun & games...lol.......will throw tha battery back in today and see what the gauge reads when I start it, will recheck the connections and charging but may need another visit to the sparkie.............will see...............andyd 

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Much as I dislike fooling around under the dash, you can still jumper out the ammeter and see if that removes the problem, disconnect the battery first.  Might get one of those plug into the cigar lighter voltmeters so you can monitor the system voltage, not as fast acting as the ammeter but it'll show if it's charging or not.  Basically if it never goes above 13v and starts falling as the engine is running it's not charging.

 

I had to go educate myself on the Lucas setup, seems on of the wires is a turn on wire that is switched by the ignition switch.  That might be where your issue lies.

Edited by Sniper
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School in session .... Lucas=prince of darkness .. class closed.

 

I dunno just seem surprising to me that after switching to a V8 with 12 volt that Lucas would be involved.

 

I once had a 1969 Triumph motorcycle and never had a good battery with Lucas.

One day at work the Boss walked in and said "headlight is turned on your motorcycle"

I was really confused because the battery never took a charge for over 2 years.

Not saying was a bad battery, just a bad charging system .... today I cant even explain the zenor diodes & rectififers I replaced to make it work properly ... just never did work.

 

Los hears Lucas ... throws arms in air and screams like a little girl & runs away.

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I'm gonna stick my head out and say, Lucas systems are not worse than any other systems. Looking and 1940s-70s, their untraditional way of using electrics, AC instead of DC and people's lack of understanding electrical flow has had many frustrated. Yes Lucas system is complicated, but not hopeless. Positive earth adds to the confusion.

 

I'm fascinated that they where one of the pioneers of alternators, three wave AC chargers and semiconductors usage in vehicles. All modern car generators use this setup today.

Their Zener diodes was a smart weight reduction (crude) method. (Crude like people using resistors as 12-6v reducer ?)

Lucas's series wound generators differed from US and German shunt generators. These also has different regulators. 

 

I'm gonna stop now, I think I'm already in a line of fire LOL

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 The reason the car has a Lucas alternator is that when I was building the car the closest Auto Electrical shop to my work was the one I pestered continually regarding wiring questions etc and when I decided to swap from the original generator in 1975 after the V8 swap in 1973 this shop was who I went to, remember this was before the internet, and all the various sources for bits & pieces..........this alternator was bought new from them and as these guys knew the car and what the wiring setup was it was where I sourced various electrical things............and no I don't drink warm beer, in fact I also prefer my red wine with a couple of ice cubes in it, buggar this room temperature thing.....lol...........anyway I had a "feel" for any loose wires under the dash, checked the various connections in the engine bay and gave it a couple of pumps............started right up no problem and the gauge needle went positive and settled down to just past the postive edge of the centre mark on the gauge at a fast idel.............let it run for a few minutes and turned it off.........started it up a few more times and it seemed o/k..............left it for a 20 minutes and went thru the proeedure again and it, the needle seemed to sit just on the negative side of the centre marker...........................................so am gunna take it down to the local sparkies again this week and see what they say..............lol...........will update the thread .........oh....and heres a pic of the engine bay & alternator........andyd  

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Thumbs up for the ice cubes in the wine, same here.

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