Recharging question (alternator)

[Richard]

My backhoe (JCB) has been hard to crank over. Charge battery, then it starts "right now".

Today, machine idling, I pulled cable off battery and put leads to it. It was getting maybe 9.?? volts instead of 14.?? volts.

I pulled battery lead off because I wanted to isolate the charge and take the battery out of the equation.

So, with 9'ish volts heading to battery, could my various contacts be a bit dirty/oxidized..... or do I just need to pull the alternator off and get it to a shop?

 

[Chewwy]

My backhoe (JCB) has been hard to crank over. Charge battery, then it starts "right now".

Today, machine idling, I pulled cable off battery and put leads to it. It was getting maybe 9.?? volts instead of 14.?? volts.

I pulled battery lead off because I wanted to isolate the charge and take the battery out of the equation.

So, with 9'ish volts heading to battery, could my various contacts be a bit dirty/oxidized..... or do I just need to pull the alternator off and get it to a shop?

Did you check the charging voltage prior to removing the cable connection? That reading would tell you much more about the alternators functioning.

 

[mrmikey]

Today, machine idling, I pulled cable off battery and put leads to it.

Good way to fry your alternator. Similar to holding your foot to the floor going up a hill and then popping it into neutral.
With a decent battery, i.e. one that's not deader than a nit and putting an excessive load on the alternator, at a fast idle you should read 14-14.8VDC. A fully charged battery with the surface charge bled off you should have 12.6-13 ± VDC.

 

[Harry in Ky]

My backhoe (JCB) has been hard to crank over. Charge battery, then it starts "right now".

Today, machine idling, I pulled cable off battery and put leads to it. It was getting maybe 9.?? volts instead of 14.?? volts.

I pulled battery lead off because I wanted to isolate the charge and take the battery out of the equation.

So, with 9'ish volts heading to battery, could my various contacts be a bit dirty/oxidized..... or do I just need to pull the alternator off and get it to a shop?

There could be other reasons why it's not charging, not just a defective alternator. Suppose you take it off, get it tested, and they tell you there's nothing wrong with it? Then what? Why not do a little trouble shooting before you get that far?

Personally, I know very little about JCB ,machinery or what brand/style charging systems they use so I have no specific details on doing that, but I'm sure others here can. If you can tell us what alternator it has, maybe some photos of the back side where the wires connect, I may have some ideas for you. Does it have a charge indicator light on the dash, and does it work?

 

[Williy]

Use a volt ohm meter and have some one start the tractor
and if the meter don't go to around 14 volts on start up your
voltage regulator if you have one could be bad or the diodes
rectifier is bad. you can replace the diodes/rectifier available
to purchase on line. But the first thing that you want to do is
make sure all connections are clean.
Also I believe that GM makes a one wire alternator for easy
replacement

willy

 

[ROUSTABOUT]

I worked for JCB as a field service mechanic in Little Rock. Alternator has a built in regulator. There are two types, a 9v activated field and a 12v activated field. Usually if a regulator is out, it doesn't regulate, so you will get 17v or so. Which, that could be your problem because it will boil out your battery dry. You didn't say anything about water level in battery. Modern alternators make AC voltage and convert to DC. So there are a few extra diodes that could be bad Never take one of these loose while running. You can do that on old 1972 farm trucks, but not this newer equipment. Just put an alternator on a Nissan used car. They had taken it to a mechanic. He didn't put the pulley on right, spun it off a few days later. So with me having a garage account at the cheapest parts house, alternator was $534.00 that was the second one. Shade tree guys did the first. Wonder it didn't ruin the engine overheating. 16 yo daughters car, their child, I have no child.

 

[Richard]

A bit of background.... I've had this machine for maybe 25'ish years. It has ALWAYS been a bad charging machine (had alternator off to shop several times)

Finally, my brother in law looked at it 5'ish years ago.... ascertained that the lead going from the alternator to battery had broken inside the harness. He bypassed it and from then on I got the 14+ volts.

Also, to be fully disclosed, it IS an older battery but, I don't recall how old. Wouldn't surprise me it's 5+ years old. They didn't take the date-dots off it so I have no clue when I bought it or when the warranty runs out (though I'm sure it's not under any warranty now)

I had put the leads on the battery the other day and if memory serves me, it was again, in the 9+ range but I'd feel more comfortable trying again to be sure.

It's also got the original ground wire going from battery to engine block (original for me meaning I've never replaced it over 25 years). I think the positive battery cable has been replaced once.

 

[Richard]

Machine is a 1550B and was made roughly 1985-87 I think.

 

[WranglerX]

Does your tractor have a "BATTERY" or "ALT" (alternator) lamp?... IS it functional.... If you turn key to on position (not starting motor) does the battery/alternator lamp light?.... Many alternator system need the voltage supplied through lamp to initialize charge sequence of alternator....
Disconnecting alternator from battery proves nothing as alternators need battery for a load and something to regulate to....

 

[5030]

My 'test instrument' is my hand. If an alternator is warm when rotating, it's fine (and charging). If it's not, it comes off and goes to the rebuild shop. Real simple for me and basically foolproof.