640 rewire

[4fwd1rev]

Converting a 640 from a 1 wire alternator to a 3 wire, replacing all wiring switches, and gauges (all corroded, shot, etc). With the great info I've seen on the forum, I think I can do it.

I'd like to have on the panel a voltmeter and an alternator charge warning light (no ammeter). Can that be done?

Here's thanking you in advance.

 

[old]

Yes that can be done. As for the gauge sorry I can not help but as for the light that is a simple thing just get the correct light bulb that Chev had for there system

 

[Kurt-NEPA]

As old said, the charge light is just a bulb in the sensing wire. You have two options hooking up a 3 wire Delco alternator. Using a diode or a small lamp. Just use the lamp option and poke the lamp though the dash.

Hooking up a volt meter instead of an ammeter is easy. Two posts on the back of a volt meter. Wire one to ground and the other to switched side on the terminal. (the post with the wire to the coil). If the meter swing the wrong way - reverse the wires.

Maybe this diagram helps. Then again maybe it will confuse you. But it shows how to hook up ammeter and a voltmeter.

 

[souNdguy]

aqs kurt an old said.

IMHO.. a voltmeter and a warning lamp are kinda useless. an ammeter tells you so much more about the charge system..

 

[Hal/Eastern WA]

However most ammeters are not made to take the amount of charge most alternators can put out. And it is possible to FRY an ammeter if the internal regulated alternator senses that the battery is pretty far down.

Some years ago my son and I put a Delco alternator in an old IHC Scout that had a bad old style Motorola alternator. The rebuilt Delco was less than half the price of the special order Motorola, which also might have needed a new external regulator. We hooked up the Delco, made the appropriate wiring changes to get rid of the external regulator, and started it up. The ammeter immediately pegged on the plus side and after a minute or two, started to smoke a little. We shut down the engine and put the battery charger on to get the battery fully charged. After a couple of hours, we started it again, and the ammeter read a slight charge for a minute or two and then was at the middle. My son drove the Scout that way for a couple of years and the ammeter continued to work fine as did the Delco alternator. But we could see and could smell that we had damaged the ammeter a bit. Probably it would have burned up if we had continued to allow the much higher powered alternator to charge heavily.

In looking at the wiring diagram for that Scout, it appeared that it ran ALL of the power through the ammeter. The ammeter could handle the 30 or so amps the old Motorola could put out just fine, but probably the 60 amps the Delco could put out would have melted it and even possibly might have caused an underdash fire. Live and learn!

I don"t know if there are ammeters that can handle 60+ amps, but I won"t be trying to run that much power through a factory ammeter again. At least if the vehicle runs the whole output of the alternator through the ammeter.

IMHO, a voltmeter is an easy addition that will tell you the condition of the battery, and is a better choice than adding an ammeter. Good luck!

 

[JMOR]

(quoted from post at 23:17:55 09/12/12) Converting a 640 from a 1 wire alternator to a 3 wire, replacing all wiring switches, and gauges (all corroded, shot, etc). With the great info I've seen on the forum, I think I can do it.

I'd like to have on the panel a voltmeter and an alternator charge warning light (no ammeter). Can that be done?

Here's thanking you in advance.

ust use Kevin or John's diagram (never remember who's is who's) and replace diode shown with warning lamp & connect existing ammeter wires together (shown as single wire in diagram).

 

[souNdguy]

If you think that a voltmeter is going to tell you the condition of the charge system.. you know very little practical electrical theory.

a volt meter will tell you system voltage.. that's it.. nothing more!

an ammeter tells you very many things. for instance.. if you see high charge current, but do not have any loads switched on.. then you know you have a drain / short or bad cell in the battery.

as long as that drain is below the charge system max.. you'd NEVER know on a volt meter.. as the alt vreg will keep voltage up even at high charge current!!

todays ameters are shunt-voltmeters... the shunt inside should be fine for a 63a alternator, even if the scale won't show it.

alternators are for topping off batteries that started a vehicle.. you should not 'charge' a dead battery with an alternator.. that's what a battery charger is for.

shows what you know about electricity...

glad i went to a different college for my engineering degree than you did

 

[BruceR TN]

And, if the battery is too dead (i.e. had to jump start the tractor), it won't excite the alternator which, in turn, won't put out any charge. Correct?

 

[souNdguy]

depends on the design. many will still likely bootstrap with sufficient rpm. it's still terribly abusive to charge a stone dead battery with your poor alternator.. battery chargers are made for that.

 

[Hal/Eastern WA]

I have never claimed to be an engineer, just a guy that has had some experience tinkering with various vehicles for a very long time. And I did write that I was presenting my opinion.

Our misadventure with the Scout really got our attention. The ammeter got real hot, smoked some and we were surprised that it still worked after that. We never thought about the fact that the battery charge was pretty low when we first started the Scout with the much more powerful alternator. I agree that using a battery charger is the proper way of charging a low battery and that is what we did, after the hot ammeter incident. I also wrote that the Scout worked fine when the battery was near full charge and the alternator was only adding a small charge. But it concerned me that the ammeter appeared to be the weak link in the charging system, and if somehow the battery got discharged a bunch again, and if my son got the Scout started, there was a very real chance that the ammeter could get hot again.

Maybe modern ammeters are built differently that older ammeters, and can take a much larger amount of amperage than the older ones can. I don"t know.

But I believe that it was and is a reasonable concern to present the possibility of the problem that we ran into. Had we not been paying close attention, the ammeter in the Scout dash very likely would have been destroyed, and that very possibly might have caused an underdash fire that might have ruined the old Scout. I think it can be dangerous to run all the potential power output of a much more powerful alternator through an ammeter that was designed to handle the potential power of a lesser alternator.

I would hate for someone else to run into the same problem my son and I did, just because I was too lazy to write a couple of paragraphs about it. Their outcome might not have been as good as what we experienced.

You are right, a voltmeter shows the system volts and nothing more. But those voltage readings change at different times. A voltmeter can tell me if my battery is most likely charged enough to start the engine of a vehicle that has not been started in a while. And then it will tell me if the charging system is operating OK, as the voltage will be somewhat higher after the engine starts. And since very little power is run through the voltmeter, it is highly unlikely that it would ever be a fire hazard, which under the circumstances I described, an ammeter might be.

Like I wrote, our experience really got our attention fast, and it is lucky that we didn"t burn the Scout and the garage down. It was a close call!

Good enough defense? Everyone is entitled to their opinion...remember people skills, please!

 

[souNdguy]

really.. what I see.. statistically, is a single bad occurence that a rule has been developed off of.

not always the best situation to make defining rules.

I don't doubt any of your situation. I just think of it as probably a low probability type situation.. not a high probability situation.

people skills?

got plenty.. didn't see the need to sugar coat anything or leave X's an o's at the bottom of a message.

I'm guessing most people are adults here and should be able to have a strong conversation.

have fun.

soundguy