1948 8n alternator making 20v

[blakefords]

Hello. I have a 1948 8n with a front mount distributor. I bought it with a 12v conversation and have been having issues with it burning up condensers. I replaced another condenser and wondered what my battery had for % and what the alternator was putting out. 12.2v battery and 19.8v while idling.

I have no idea the make of the alternator or its output. It is a 3 wire fire. One with battery post and 2 spades. I figured out if I ground one of the spades it makes the output 12.5v. There are no resistors or diodes on this machine I can find.

What do you guys recommend I start replacing due to such high voltage through the ignition. (Tractor runs but does bog and misfire under load pretty bad also the amp gauge is blown)

 

[wore out]

Hello. I have a 1948 8n with a front mount distributor. I bought it with a 12v conversation and have been having issues with it burning up condensers. I replaced another condenser and wondered what my battery had for % and what the alternator was putting out. 12.2v battery and 19.8v while idling.

I have no idea the make of the alternator or its output. It is a 3 wire fire. One with battery post and 2 spades. I figured out if I ground one of the spades it makes the output 12.5v. There are no resistors or diodes on this machine I can find.

What do you guys recommend I start replacing due to such high voltage through the ignition. (Tractor runs but does bog and misfire under load pretty bad also the amp gauge is blown)

Is the battery boiling, IF the alternator is really putting out that much voltage, likely it is.

On the other hand, many digital meters are confused by the electrical "noise" from the charging and ignition systems and give wildly inaccurate readings.

If possible, check the voltage with a simple analog voltmeter.

(HINT... DON'T ground the alternator's VR terminals.)

HOW do you know it is "burning up condensers"?

Typically, they are rated for hundreds of Volts.

Likely, either you've gotten a really bad batch of condensers, or you are doing something when replacing the condensers that temporarily corrects an "open" or a "short" in the distributor.

 

[old]

Hello. I have a 1948 8n with a front mount distributor. I bought it with a 12v conversation and have been having issues with it burning up condensers. I replaced another condenser and wondered what my battery had for % and what the alternator was putting out. 12.2v battery and 19.8v while idling.

I have no idea the make of the alternator or its output. It is a 3 wire fire. One with battery post and 2 spades. I figured out if I ground one of the spades it makes the output 12.5v. There are no resistors or diodes on this machine I can find.

What do you guys recommend I start replacing due to such high voltage through the ignition. (Tractor runs but does bog and misfire under load pretty bad also the amp gauge is blown)

12.2 volts at the battery when not running say you have a dead battery. Battery volts of a full charged battery should be 12.6 or more. Id charge the battery and check volts again and if you don;t get `12.6 take in and have it checked

 

[Jim.ME]

If you don't know what alternator you have, post pictures.

What are you using for a meter to test with? What are the points you are using for your voltage tests?

Are the battery terminals clean? Are the clamps clean and in good condition? Are the chassis and starter switch ends of the battery cables clean and good, and the points they attach to clean and bright? Is the ground cable grounded to the chassis or to sheet metal?

What do you have for an ammeter? If it is the type that the wire just loops past the back of, it isn't affecting anything other than it working. if it has terminals with wires attached it needs to be replaced if "blown".

 

[Farmalldude45]

Hello. I have a 1948 8n with a front mount distributor. I bought it with a 12v conversation and have been having issues with it burning up condensers. I replaced another condenser and wondered what my battery had for % and what the alternator was putting out. 12.2v battery and 19.8v while idling.

I have no idea the make of the alternator or its output. It is a 3 wire fire. One with battery post and 2 spades. I figured out if I ground one of the spades it makes the output 12.5v. There are no resistors or diodes on this machine I can find.

What do you guys recommend I start replacing due to such high voltage through the ignition. (Tractor runs but does bog and misfire under load pretty bad also the amp gauge is blown)

Where are you measuring 19.8v? At the battery or at the alternator battery post? With everything off, do you have battery voltage at the battery post on the alternator? Do you have wires connected to both of the spade terminals on the back of the alternator?

 

[blakefords]

Is the battery boiling, IF the alternator is really putting out that much voltage, likely it is.

On the other hand, many digital meters are confused by the electrical "noise" from the charging and ignition systems and give wildly inaccurate readings.

If possible, check the voltage with a simple analog voltmeter.

(HINT... DON'T ground the alternator's VR terminals.)

HOW do you know it is "burning up condensers"?

Typically, they are rated for hundreds of Volts.

Likely, either you've gotten a really bad batch of condensers, or you are doing something when replacing the condensers that temporarily corrects an "open" or a "short" in the distributor.

I charge up the condenser with my meter on ohms and watch it build. Untill it shows OL then switch to volts and watch the condenser discharge. Found it on YouTube. Tested one out of the distributor and tested a new one. The burnt ones don't take a charge and disapate fast.

 

[blakefords]

Where are you measuring 19.8v? At the battery or at the alternator battery post? With everything off, do you have battery voltage at the battery post on the alternator? Do you have wires connected to both of the spade terminals on the back of the alternator?

19.8v is positive output side of alternator and negative battery post.

 

[blakefords]

If you don't know what alternator you have, post pictures.

What are you using for a meter to test with? What are the points you are using for your voltage tests?

Are the battery terminals clean? Are the clamps clean and in good condition? Are the chassis and starter switch ends of the battery cables clean and good, and the points they attach to clean and bright? Is the ground cable grounded to the chassis or to sheet metal?

What do you have for an ammeter? If it is the type that the wire just loops past the back of, it isn't affecting anything other than it working. if it has terminals with wires attached it needs to be replaced if "blown".

I don't know alot about these tractors and bought it as is. New battery and it tested good. Terminals are clean and it cranks healty. Im using a fluke meter. The chassis ground (on frame under gas door) is clean and has low resistance when checked from battery neg to chassis ground bolt. As I can tell my grounds are makeing contact but definitely could have less paint around them.

 

[Jim.ME]

I don't know alot about these tractors and bought it as is. New battery and it tested good. Terminals are clean and it cranks healty. Im using a fluke meter. The chassis ground (on frame under gas door) is clean and has low resistance when checked from battery neg to chassis ground bolt. As I can tell my grounds are makeing contact but definitely could have less paint around them.

That appears to be a Delco type 3-wire alternator,

You have grounded the terminal that is supposed to have a switch powered wire for excitation. That wire may need a diode, resistor or an inddicator light in it to prevent run on if the ignition terminal of the switch is used for power. The second spade is supposed to have a sensing wire from it to the alternator battery post. For starters wire it correctly and see what happens.

 

[blakefords]

If you don't know what alternator you have, post pictures.

What are you using for a meter to test with? What are the points you are using for your voltage tests?

Are the battery terminals clean? Are the clamps clean and in good condition? Are the chassis and starter switch ends of the battery cables clean and good, and the points they attach to clean and bright? Is the ground cable grounded to the chassis or to sheet metal?

What do you have for an ammeter? If it is the type that the wire just loops past the back of, it isn't affecting anything other than it working. if it has terminals with wires attached it needs to be replaced if "blown".

Amp meter has a few components routed through it. Starter solenoid, ignition and alternator output.

 

[blakefords]

If you don't know what alternator you have, post pictures.

What are you using for a meter to test with? What are the points you are using for your voltage tests?

Are the battery terminals clean? Are the clamps clean and in good condition? Are the chassis and starter switch ends of the battery cables clean and good, and the points they attach to clean and bright? Is the ground cable grounded to the chassis or to sheet metal?

What do you have for an ammeter? If it is the type that the wire just loops past the back of, it isn't affecting anything other than it working. if it has terminals with wires attached it needs to be replaced if "blown".

Amp meter has a few components routed through it. Starter solenoid ignition and alternator output.

 

[blakefords]

That appears to be a Delco type 3-wire alternator,

You have grounded the terminal that is supposed to have a switch powered wire for excitation. That wire may need a diode, resistor or an inddicator light in it to prevent run on if the ignition terminal of the switch is used for power. The second spade is supposed to have a sensing wire from it to the alternator battery post. For starters wire it correctly and see what happens.

Are the diodes/resistors tractor specific or based off alternator output?

 

[Jim.ME]

It sounds like you have an ammeter with two terminals to hook wires to, not the OEM type one wire just loops behind.

A diode with a minimum rating of 1.5 amps @m 50-volts is required, larger is ok. 1N5402 and 1N5404 are a couple 3-amp ones commonly used. They are polarity sensitive and have to be installed with the - side towards the alternator.

Do you have a wiring diagram to work with? If not search for Wiring Diagrams by JMOR and find one for the conversion you have. He made many and they are frequently referenced here

 

[blakefords]

It sounds like you have an ammeter with two terminals to hook wires to, not the OEM type one wire just loops behind.

A diode with a minimum rating of 1.5 amps @m 50-volts is required, larger is ok. 1N5402 and 1N5404 are a couple 3-amp ones commonly used. They are polarity sensitive and have to be installed with the - side towards the alternator.

Do you have a wiring diagram to work with? If not search for Wiring Diagrams by JMOR and find one for the conversion you have. He made many and they are frequently referenced here

I'll do some diagram reading

 

[Jim.ME]

I'll do some diagram reading

good idea

 

[Mad Farmer]

They sell pre-made plugs for the 3-wire Delcos that have the diode already inline on the exciter wire.

You need the diode or a light/lamp inline or the alternator can back feed the coil when you turn the key off. Then the tractor keeps on running.

I miss having a Radio Shack nearby........

 

[blakefords]

They sell pre-made plugs for the 3-wire Delcos that have the diode already inline on the exciter wire.

You need the diode or a light/lamp inline or the alternator can back feed the coil when you turn the key off. Then the tractor keeps on running.

I miss having a Radio Shack nearby........

Radio shack was handy. Ok I will look for a pre-made set. Thanks

 

[Jim.ME]

If you don't want to chase a diode and parts to make your own harness, you can get a harness that plugs directly into the alternator with a diode already in the excite wire that you run to the ignition switch and a ring terminal so the sensing wire ready to hook to the battery post of the alternator. Below is one example found on eBay (I have no connection to this seller, only showing as an example).

Alternator plug with diode

I would not recommend the type that say they make a 3-wire alternator a one wire alternator. Those hook the excite wire with diode to the sensing wire at the alternator connector and can cause a steady drain on the battery. (Sorry YT/PartsASAP.)

 

[Mad Farmer]

If you don't want to chase a diode and parts to make your own harness, you can get a harness that plugs directly into the alternator with a diode already in the excite wire that you run to the ignition switch and a ring terminal so the sensing wire ready to hook to the battery post of the alternator. Below is one example found on eBay (I have no connection to this seller, only showing as an example).

Alternator plug with diode

I would not recommend the type that say they make a 3-wire alternator a one wire alternator. Those hook the excite wire with diode to the sensing wire at the alternator connector and can cause a steady drain on the battery. (Sorry YT/PartsASAP.)

Similar on Ebay plug and play adapter with diode, has less wiring/connections/connectors provided.

 

[wore out]

Hello. I have a 1948 8n with a front mount distributor. I bought it with a 12v conversation and have been having issues with it burning up condensers. I replaced another condenser and wondered what my battery had for % and what the alternator was putting out. 12.2v battery and 19.8v while idling.

I have no idea the make of the alternator or its output. It is a 3 wire fire. One with battery post and 2 spades. I figured out if I ground one of the spades it makes the output 12.5v. There are no resistors or diodes on this machine I can find.

What do you guys recommend I start replacing due to such high voltage through the ignition. (Tractor runs but does bog and misfire under load pretty bad also the amp gauge is blown)

The #2 terminal is "Voltage Sense" and MUST be connected to the alternator's large output stud or the alternator will produce excessive voltage!

As to the diode, I use 1N5408 diodes, which are rated at 1000 Volts and 3 Amps.

WAY overkill for this application, but don't fail occasionally as the lesser-rated diodes sometimes do.

NO reason not to, the are under 10 cents apiece on Amazon.