8N - What is draining my battery?

jurtz · May 20, 2006

I bought an 8N from my brother last weekend and drove it home. I stopped it in my driveway, then re-started it an parked it. Went out today and the battery is dead. Found out that I left the key switch on all this time - is that what caused the battery to drain? I took the battery out to charge, and while it was out, I measured the resistance of the system at the battery terminals - around 50 ohms with the key switch off. That seems awfully low to me - it would mean a continuous 1/4 amp drain. Note - brother put in a new battery because he said the other one wouldn't charge - maybe something else is going on?

System particulars:

12V conversion
Side mount distributor
Resistor in series with coil
Regulator inside gennerator

jurtz · May 20, 2006

I bought an 8N from my brother last weekend and drove it home. I stopped it in my driveway, then re-started it an parked it. Went out today and the battery is dead. Found out that I left the key switch on all this time - is that what caused the battery to drain? I took the battery out to charge, and while it was out, I measured the resistance of the system at the battery terminals - around 50 ohms with the key switch off. That seems awfully low to me - it would mean a continuous 1/4 amp drain. Note - brother put in a new battery because he said the other one wouldn't charge - maybe something else is going on?

System particulars:

12V conversion
Side mount distributor
Resistor in series with coil
Regulator inside gennerator

Soundguy · May 21, 2006

( Found out that I left the key switch on all this time - is that what caused the battery to drain? )

Well, if the points were in a closed position.. then.. yeah.. you could/would have had about a 4amp drain on it. By the way.. generally when you do this.. the points are toast.. sometimes they weld together.. sometimes the heat melts the rubbing block, or the insulating grommets. Standard procedure after letting your ignition coill, ballast resistor, and points roast overnight is to replace them.

( and while it was out, I measured the resistance of the system at the battery terminals - around 50 ohms with the key switch off. That seems awfully low to me - it would mean a continuous 1/4 amp drain. )

Could be a couple things.. could be a bad diode inthe alternator trio, or other defect in the regulator. Could also be a miss-wired 3-wire type setup, and the previous owner wired power to the #1 (field excite) terminal, instead of to the #2 ( remote sense ) terminal. The remote sense terminal typically gets wired down to the charge stud, for tractor applications.. and it won't discharge the battery.. however.. if power is wired tot he field excite terminal on a 3 wire job, then it will deffinately discharge the battery by exciting the alternators field.. etc... As stated.. could be a defect in the alternatoras well.

( brother put in a new battery because he said the other one wouldn't charge - maybe something else is going on?
)

Ya think /forums/images/graemlins/confused.gif That seems kinda like tossing a rock into a pool and watching it sink, and then tossing another one in, and expecting it to -not- sink, without having done anything to cause that intervention...

It's really starting to sound like a bad alternator. I'd take it in to a store that offers free checks.. then if it is bad.. get a delco 10si or 12si to repalce it. Many junkyards have barrels of these for 25-50$ already checked...

Avoid the '1-wire' jobs.. get a '3-wire' one.. the 1 wire jobs take a very high rpm to self excite..

( Side mount distributor
Resistor in series with coil
)

Sounds like you are running a 6v coil, and using a dropping resistor to waste some power and dissipate it as heat... A much better and ideal setup would be to simply get a real 12v coil... Napa has a good one.. IC14SB... it's a real 12v coil.. don't use any ressitors with it. Using a real 12v coil meanus you can run a wider sparkplug gap to make use of the higher secondary voltage potential that coil should have.. also menas the system will be slightly more robust when corrosion sets in and starts degrading contacts... ( 6v systems suffer more from this due to the already low system voltage, and just barely adequate secondary votlage of the old style coils.. )

( Regulator inside gennerator )

Just to check here.. do you have a 12v alternator with an internal regulator.. or do you have a 12v generator.. they are 2 entirely different beasts... and have their own different troubleshooting info. My message was based on an alternator application..

Soundguy

Soundguy · May 21, 2006

( Found out that I left the key switch on all this time - is that what caused the battery to drain? )

Well, if the points were in a closed position.. then.. yeah.. you could/would have had about a 4amp drain on it. By the way.. generally when you do this.. the points are toast.. sometimes they weld together.. sometimes the heat melts the rubbing block, or the insulating grommets. Standard procedure after letting your ignition coill, ballast resistor, and points roast overnight is to replace them.

( and while it was out, I measured the resistance of the system at the battery terminals - around 50 ohms with the key switch off. That seems awfully low to me - it would mean a continuous 1/4 amp drain. )

Could be a couple things.. could be a bad diode inthe alternator trio, or other defect in the regulator. Could also be a miss-wired 3-wire type setup, and the previous owner wired power to the #1 (field excite) terminal, instead of to the #2 ( remote sense ) terminal. The remote sense terminal typically gets wired down to the charge stud, for tractor applications.. and it won't discharge the battery.. however.. if power is wired tot he field excite terminal on a 3 wire job, then it will deffinately discharge the battery by exciting the alternators field.. etc... As stated.. could be a defect in the alternatoras well.

( brother put in a new battery because he said the other one wouldn't charge - maybe something else is going on?
)

Ya think /forums/images/graemlins/confused.gif That seems kinda like tossing a rock into a pool and watching it sink, and then tossing another one in, and expecting it to -not- sink, without having done anything to cause that intervention...

It's really starting to sound like a bad alternator. I'd take it in to a store that offers free checks.. then if it is bad.. get a delco 10si or 12si to repalce it. Many junkyards have barrels of these for 25-50$ already checked...

Avoid the '1-wire' jobs.. get a '3-wire' one.. the 1 wire jobs take a very high rpm to self excite..

( Side mount distributor
Resistor in series with coil
)

Sounds like you are running a 6v coil, and using a dropping resistor to waste some power and dissipate it as heat... A much better and ideal setup would be to simply get a real 12v coil... Napa has a good one.. IC14SB... it's a real 12v coil.. don't use any ressitors with it. Using a real 12v coil meanus you can run a wider sparkplug gap to make use of the higher secondary voltage potential that coil should have.. also menas the system will be slightly more robust when corrosion sets in and starts degrading contacts... ( 6v systems suffer more from this due to the already low system voltage, and just barely adequate secondary votlage of the old style coils.. )

( Regulator inside gennerator )

Just to check here.. do you have a 12v alternator with an internal regulator.. or do you have a 12v generator.. they are 2 entirely different beasts... and have their own different troubleshooting info. My message was based on an alternator application..

Soundguy

jurtz · May 21, 2006

Soundguy:

Thank you for your reply.

First, I took your advice and had the alternator tested and as you suspected, it was shot. Bought a remanufactured 12SI and installed it, and now I see about 15 volts on the battery while the engine is running at speed, and the battery shows about 13 volts when the engine is off. Based on what I have read elsewhere, this indicates everything is functioning as desired, correct?

One other important bit that I inexplicably forgot in my original post was that once running, the tractor will not stop running when the ignition is turned off. This was the case before the alternator change and after the new alternator. After a bit of research, I found a schematic for a 12V conversion on the Smiths Ford 8N website, and their schematic showed a diode placed in series with the "1" terminal on the alternator. This article further elaborated that if this diode was missing or shorted, the tractor would 1) not stop when the ignition was turned off and 2) would drain the battery when the engine was off (sounds familiar). So I got myself a diode and installed it as prescribed and now I can stop my engine with the ignition switch. /forums/images/graemlins/laugh.gif Would you concur on the use of the diode? There is no evidence my tractor ever had one, and I want to make sure the diode won't have any detrimental effect.

Also - your comment about leaving the ignition switch on - can I assume that since my tractor still starts easily and runs normally that the points were NOT in the closed position, and thus I dodged a bullet on the damaged parts?

jurtz · May 21, 2006

Soundguy:

Thank you for your reply.

First, I took your advice and had the alternator tested and as you suspected, it was shot. Bought a remanufactured 12SI and installed it, and now I see about 15 volts on the battery while the engine is running at speed, and the battery shows about 13 volts when the engine is off. Based on what I have read elsewhere, this indicates everything is functioning as desired, correct?

One other important bit that I inexplicably forgot in my original post was that once running, the tractor will not stop running when the ignition is turned off. This was the case before the alternator change and after the new alternator. After a bit of research, I found a schematic for a 12V conversion on the Smiths Ford 8N website, and their schematic showed a diode placed in series with the "1" terminal on the alternator. This article further elaborated that if this diode was missing or shorted, the tractor would 1) not stop when the ignition was turned off and 2) would drain the battery when the engine was off (sounds familiar). So I got myself a diode and installed it as prescribed and now I can stop my engine with the ignition switch. /forums/images/graemlins/laugh.gif Would you concur on the use of the diode? There is no evidence my tractor ever had one, and I want to make sure the diode won't have any detrimental effect.

Also - your comment about leaving the ignition switch on - can I assume that since my tractor still starts easily and runs normally that the points were NOT in the closed position, and thus I dodged a bullet on the damaged parts?

Farmwithjunk · May 21, 2006

The "old guy" who works in the shop at the local auto electric shop I use put me on to a good set-up on the one wire GM alternators. He gave me a "12.7 volt, low cut in" model they sell to a lot of street rodders who do a lot of cruisin'. It "auto-excites" at 975 RPM Had to use my original pulley on their reman alternator.) Mine is on a diesel with very little power demand once started, so that helps. Battery stays at 12.2 to 12.7, and the tractor starts instantly, even cold starts well at 7 degrees, so there's little demand on the starter curcuit too. By having the relatively low voltage output of 12.7, it won't overcharge even if run "wide open", but maintains a good battery charge. Simple and effective.

Your milage may vary

Farmwithjunk · May 21, 2006

The "old guy" who works in the shop at the local auto electric shop I use put me on to a good set-up on the one wire GM alternators. He gave me a "12.7 volt, low cut in" model they sell to a lot of street rodders who do a lot of cruisin'. It "auto-excites" at 975 RPM Had to use my original pulley on their reman alternator.) Mine is on a diesel with very little power demand once started, so that helps. Battery stays at 12.2 to 12.7, and the tractor starts instantly, even cold starts well at 7 degrees, so there's little demand on the starter curcuit too. By having the relatively low voltage output of 12.7, it won't overcharge even if run "wide open", but maintains a good battery charge. Simple and effective.

Your milage may vary

Soundguy · May 22, 2006

( Would you concur on the use of the diode? There is no evidence my tractor ever had one, and I want to make sure the diode won't have any detrimental effect )

The diode is the prefered method of field isolation.. you could have also used a trailer marker lamp that used a 194 bulb in line with #1, and when you turned the ignition on, the light would have glowed, and then stopped glowing when the alternator kicked in.. could also have uses a low value power resistor, or even a seperate switch in line.. like a momentary switch.. like a doorbell button... start the tractor.. hit the switch for a second, and then the alt excites.. etc.

The diode is pretty much the best way for many reasons. 1, it works great to prevent back current, thus no battery draining when the key switch is off.. and no 'running on' when the key is turned off. Also.. diodes, when they fail, mostly fail open, rather than shorting. . thus if the diode dies.. you just won't charge.. vs draining the battery. Lastly, the diode protects the alts vr. In certain situations, if your ignition switch goes open, thent he alts vr is providing power tot he coil to run the tractor.. this back flow is bad and hard ont he vr.. and will/may eventually kill it.. perhaps this is what happened to your last one.

( can I assume that since my tractor still starts easily and runs normally that the points were NOT in the closed position, and thus I dodged a bullet on the damaged parts )

Yep.. ya got lucky!

Soundguy

Soundguy · May 22, 2006

( Would you concur on the use of the diode? There is no evidence my tractor ever had one, and I want to make sure the diode won't have any detrimental effect )

The diode is the prefered method of field isolation.. you could have also used a trailer marker lamp that used a 194 bulb in line with #1, and when you turned the ignition on, the light would have glowed, and then stopped glowing when the alternator kicked in.. could also have uses a low value power resistor, or even a seperate switch in line.. like a momentary switch.. like a doorbell button... start the tractor.. hit the switch for a second, and then the alt excites.. etc.

The diode is pretty much the best way for many reasons. 1, it works great to prevent back current, thus no battery draining when the key switch is off.. and no 'running on' when the key is turned off. Also.. diodes, when they fail, mostly fail open, rather than shorting. . thus if the diode dies.. you just won't charge.. vs draining the battery. Lastly, the diode protects the alts vr. In certain situations, if your ignition switch goes open, thent he alts vr is providing power tot he coil to run the tractor.. this back flow is bad and hard ont he vr.. and will/may eventually kill it.. perhaps this is what happened to your last one.

( can I assume that since my tractor still starts easily and runs normally that the points were NOT in the closed position, and thus I dodged a bullet on the damaged parts )

Yep.. ya got lucky!

Soundguy