How do you test a alternator?

[chas036]

I have 6 volt , one wire, positive ground alternator on my JD720D and I don't see any movement on my amp meter incating the battery is charging when the tractor is running. Is there some sort of check I can do to see if it is putting out power?

 

[John T]

A voltmeter on the battery can give you an indication of charging. A full charged battery will read around 12.6 volts but with the tractor running if the alternator is working it should rise from at least 13 volts up to even 14+ subject to RPM and state of battery and condition of alternator and its regulation. If battery voltage NEVER rises at fast RPM there's a charging problem, be it the alternator or wiring etc.

Next if you had a good working ammeter in series between alternators output and battery it should register how many amps, IF ANY the alternator is pumping into the battery.

John T

 

[mj]

(quoted from post at 21:03:59 07/08/16) A voltmeter on the battery can give you an indication of charging. A full charged battery will read around 12.6 volts but with the tractor running if the alternator is working it should rise from at least 13 volts up to even 14+ subject to RPM and state of battery and condition of alternator and its regulation. If battery voltage NEVER rises at fast RPM there's a charging problem, be it the alternator or wiring etc.

Next if you had a good working ammeter in series between alternators output and battery it should register how many amps, IF ANY the alternator is pumping into the battery.

John T -
I seem to recall a procedure for checking the output that required a large resistor and an ammeter. But, I don't much about it. I'm thinking that it was referred to as 'full fielding' the alternator?

John T

:?:

 

[DeltaRed]

Take it off and take it to your NAPA(or similar) store. they have a fancy 'load and amp test stand. I did so today.And got a new alt to replace the old nonworking one.BTW,my old '7' is now chargeing as it should.

 

[old]

John if a 6 volt battery has 12 plus volts it is super way over charged. NOTE he said he has a 6 volt alternator which is more then likely to be a generator

 

[chas036]

It is 6 volt alternator that I bought to replace the generator.

 

[old]

Either way be it an alternator or generator John is way off since a 6 volt battery can not put out 12 plus volts. What you need to do is take a voltage reading of the battery when it is not running then take one running. When not running a 6 volt battery should read 6.3 plus and when running if all is as it should be you should get around 7 volts give or take a little

 

[Steve@Advance]

With the engine off, check the terminal on the back of the alternator for voltage. It should read the same as reading across the battery. If not, there is a break in the connection from the alternator to the battery.

If the connection is good, start the engine, bring the RPM up to full throttle. Check the voltage across the battery. It should be higher than when checked not running, probably around 7 1/2 to 8 volts.

If you do decide to take it in for testing, BE SURE to tell the technician that it is a special 6 volt positive ground alternator! Depending on the test machine, it could damage the alternator if they don't make the proper adjustments!

 

[Rex Simpkins]

Rev her up and see if a screwdriver will stick to the back of it. If it draws the screwdriver to it it's charging

 

[John T]

"It is 6 volt alternator that I bought to replace the generator"

Indeed, they make 6 volt ALTERNATORS but true they are a bit expensive.

John T

 

[John T]

I agree Rich. Indeed to charge a 6 volt battery up to 12 is reallyyyyyyyyyyyyyyyyyyy overcharge lol look out for a possible explosion and warped plates and serious outgassing . Also, a 12 volt fully charged battery would register around 12.6 volts (since its 6 series cells of 2.1 volts each) and if hooked to a good charging system its voltage can rise to 13 to 14 or so while, of course, a 6 volt fully charged battery (oops that's what he said, my bad, thinkin 12) would only be half that, 6.3 full charged and while charging 6.5 to 7 volts.

Best wishes stay high n dry down there Rich, hope this helps

John T

 

[John T]

Mornin Rex, I have read of that but never tired it. If he has a simple DC Volt Meter its sooooooooooooo easy to as I posted above to measure battery voltage when she's not running (12.6 on 12 volt battery and 6.3 on 6 volt battery) and then test it running at fast RPM and if charging battery voltage will rise (13 to 14 or so on 12 volt battery and half that, 6.5 to 7 or so on 6 volt battery)

John T

 

[M-MAN]

If it's cranking it's charging. With such a low draw if you're seeing much gauge movement you have issues like a bad battery or poor grounds. Hook up some lights and the gauge will move.

 

[John T]

Yo M Man, very good point, if he has a 720 pony start diesel when the pony isn't running and drawing coil current and there's no lights on THERES VERY LITTLE BATTERY CURENT DRAW and an alternator will bring that small battery voltage up so fast after start up I wouldn't except much ammeter movement after that. A volt meter on his battery would still be a good indicator.

John T

 

[Ray from Pa]

I never herd of a 720 John Deere with a 6 volt system.

 

[El Toro]

You should see about 7 volts across the battery terminals with the engine running. Hal

 

[teddy52food]

That test will show that the regulator has the rotor energized, but if the stator or diodes are bad it won't charge. Voltmeter is still best.

 

[wilson ind]

Put a 12 volt on John Deere with pony start and someone will be buying some very expensive pony ignition parts.Never seen a 720 or 730 Pony start with 12 volt.

 

[buickanddeere]

Depends . Spark ignition are 12V . Diesels are either 6V or 24V .
I don't know why anyone would install a butt ugly alternator on a two cylinder instead of repairing the generator .

 

[John T]

Ray, the JD 720 Diesel used a gas pony engine cranking motor and had a 6 volt battery, starter, ignition and generator, I owned a bunch of them and farmed almost 200 acres with one and a 730 Diesel electric start.

John T

 

[John T]

Me either Wilson, alllllllll the 720 pony starts I used and bought and sold for yearrrrrrrrrrrrs were 6 volt systems. The Distributor was a Wico also of course 6 volts.

See you at Elnora I hope

John T

 

[old]

The magnet test does work but again all it does is tell you the thing has been excited

 

[El Toro]

You should have 7 to 7.25 volts on a volt meter with the engine at a fast idle on a 6 volt battery. Hal

 

[wilson ind]

yes Elnora reserved camp site lot 43. See you, maybe Gold Leaf Deere and others.

 

[mj]

(quoted from post at 04:49:09 07/09/16) Rev her up and see if a screwdriver will stick to the back of it. If it draws the screwdriver to it it's charging

Darn it! I KNEW THAT........BUT FORGOT! Thanks for reminding me!

 

[Rich'sToys]

If you don't have a meter is there a way to check them with a test light? Just curious.

 

[Eagle Beagle]

Old trick, first thing is to let engine cool off. Then turn on headlights and start engine. After about 15 seconds, touch the laminated metal center section of the alternator and if its charging, it will be warmer to the touch than aluminum end sections.

Or turn on headlights, then see if they get brighter after it starts.

Beagle

 

[oldtanker]

(quoted from post at 08:29:14 07/09/16)
Depends . Spark ignition are 12V . Diesels are either 6V or 24V .
I don't know why anyone would install a butt ugly alternator on a two cylinder instead of repairing the generator .

I can't see why a person would keep a generator when alternators are so much more reliable that a generator charging system. Especially today with the junk VR's available. All my 6 volt stuff has been converted to 12 volt with alternators! I haven't had to replace or polarize a VR in years! They are all converted to electronic ignition too! Which is good because the last time I bough Standard brand points they were defective!

Rick

 

[jimmi]

(quoted from post at 00:28:02 07/09/16) It is 6 volt alternator that I bought to replace the generator.

When you replaced the generator, did you remove the old voltage regulator? If you did, did you hook the alternator up to the "load" side, not the "battery" side of the ampmeter?

You need to rev the RPMs up to get a one wire alternator to start charging. The one wire alternator regulator is typically set at 7.8V.

 

[Owen Aaland]

(quoted from post at 22:06:13 07/09/16)

(quoted from post at 00:28:02 07/09/16) It is 6 volt alternator that I bought to replace the generator.

When you replaced the generator, did you remove the old voltage regulator? If you did, did you hook the alternator up to the "load" side, not the "battery" side of the ampmeter?

You need to rev the RPMs up to get a one wire alternator to start charging. The one wire alternator regulator is typically set at 7.8V.

I am going to assume that we are talking about the Delco 10SI alternators. Other than popularity, there really is not much reason for the 6v unit to be much more expensive than the 12v version since the only difference if the regulator. The 6v regulators will be one wire, self exciting units. To convert the alternator to positive ground requires a rectifier bridge with the diodes installed opposite the normal rectifier bridge. A small piece of wire, a few insulators, and a couple different screws are also needed. If you need to excite the alternator, with the engine running, connect a jumper wire from the #1 terminal to the case. If you need to test the regulator you need to short the regulator test tab to the now negative output post. You need to insure that the test probe does not contact the now positive ground case.