New Holland TN70A alternator issues

   / New Holland TN70A alternator issues #1  

LCH76

New member
Joined
Feb 14, 2022
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5
Tractor
New Holland TN70A
Tractor stopped charging battery. Put in new battery - same issue. I had a mechanic tell me the alternator was bad, soooooo, I purchased a new alternator and installed it. Now the tractor starts and runs, but the battery dash light now stays lit even with the tractor off and the key off!

I am at a loss. Can anyone help? Any ideas?

Thanks in advance.
 
   / New Holland TN70A alternator issues #2  
My thought is your voltage regulator is bad. Try unplugging it and see if the light goes away.
 
   / New Holland TN70A alternator issues
  • Thread Starter
#3  
Thank you for your reply, I will try that.

I did take the battery out and put it on a charger. That charger indicated that the battery was had only a 50% charge. It did finally get up to 100%. I am going to put it back and see how that was affecting things.

Prior to charging, the battery was reading 12.4 volts according to my multimeter.
 
   / New Holland TN70A alternator issues #4  
Tractor stopped charging battery. Put in new battery - same issue. I had a mechanic tell me the alternator was bad, soooooo, I purchased a new alternator and installed it. Now the tractor starts and runs, but the battery dash light now stays lit even with the tractor off and the key off!

I am at a loss. Can anyone help? Any ideas?

Thanks in advance.
I'm guessing your alternator has a plug in connection. Make sure that your ground connection is good, both at the battery and chasis ground and at the alternator to engine connection and the voltage regulator. Other wise I'd suspect the voltage regulator may be damaged.
 
   / New Holland TN70A alternator issues #5  
Thank you for your reply, I will try that.

I did take the battery out and put it on a charger. That charger indicated that the battery was had only a 50% charge. It did finally get up to 100%. I am going to put it back and see how that was affecting things.

Prior to charging, the battery was reading 12.4 volts according to my multimeter.
Also I should clarify to unplug the voltage regulator when the tractor is not running.
 
   / New Holland TN70A alternator issues
  • Thread Starter
#6  
Thank you for the suggestions. I also appreciate your reminder about unplugging the voltage regulator when the tractor is not running. When the charging system is involved I usually don't make connections unless I take the ground off the battery.

I did check the plugin connection on the alternator. It is tight.

I may just not know enough about this. I've been doing my own maintenance/some repairs for years. I shy away from alternators and fuel injectors stuff. Thought I had the skills to do this, but this light staying on surprised me.

It is possible the battery is just bad? I can only get it charged to about 12.45 volts or so. Should it be higher. I am thinking of taking it and having it tested tomorrow.

Thanks again for the replies! I hope to learn more from this site.
 
   / New Holland TN70A alternator issues #7  
One thing to keep in mind is that the battery light is turned off by two wires being "+". Power on one side comes from the key and the other wire goes to the alternator. Without the engine running, key on, the light is on because the alternator is "-" as the alternator isn't charging. When the engine starts and the alternator puts out more voltage than the battery has in it, the light goes out. So either the new alternator is not charging or the wires are hooked up wrong. This tractor is a newer model so most likely the voltage regulator is built into the alternator or worse, the dash.

Also you have a multi-meter. Test the volts at the battery terminals without the engine running. When the engine is running the battery volts should be higher. Right after starting it can be as high as 15 - 16 volts but should settle to around 14.5 to 14.7. The alternator should always put out more volts than the battery has in it. Otherwise it won't charge.

A fully charged battery should read around 13.2 volts. (2.2 volts/cell x 6 cells). That number is also somewhat temperature dependent.
 
   / New Holland TN70A alternator issues
  • Thread Starter
#8  
Thanks again for all the replies. I am learning a lot.

Pmsmechanic, you gave me another piece of valuable info and I think I am making progress.

As of now, I had the battery tested and NAPA says it is good. I charged it again and it is reading 12.8 volts across the battery terminals. When I start the engine I get a reading 14.6 volts across the battery terminals. Would this not indicate that the alternator is charging the battery now?

At this time the "battery" indicator light only comes on if I turn the key OFF.

If I start the tractor the battery light goes off and everything looks normal.

I've cleaned all the connections I can get to. I double checked the wiring hookups to the new alternator. At this point does anyone think it would hurt to run this tractor and just disconnect the battery when not in use?

Thanks again for all of your input and patience.
 
   / New Holland TN70A alternator issues #9  
Thanks again for all the replies. I am learning a lot.

Pmsmechanic, you gave me another piece of valuable info and I think I am making progress.

As of now, I had the battery tested and NAPA says it is good. I charged it again and it is reading 12.8 volts across the battery terminals. When I start the engine I get a reading 14.6 volts across the battery terminals. Would this not indicate that the alternator is charging the battery now?

At this time the "battery" indicator light only comes on if I turn the key OFF.

If I start the tractor the battery light goes off and everything looks normal.

I've cleaned all the connections I can get to. I double checked the wiring hookups to the new alternator. At this point does anyone think it would hurt to run this tractor and just disconnect the battery when not in use?

Thanks again for all of your input and patience.
I would say yes it is charging. The light being on when the key is off is probably why the battery is discharging over time. If you unplug the voltage regulator the light may turn off. It could be back feeding the light and drawing current.

My thought is one of two things. Voltage regulator is sticking or key switch is not breaking connection.
 
   / New Holland TN70A alternator issues #10  
As of now, I had the battery tested and NAPA says it is good. I charged it again and it is reading 12.8 volts across the battery terminals. When I start the engine I get a reading 14.6 volts across the battery terminals. Would this not indicate that the alternator is charging the battery now?
Yes
At this time the "battery" indicator light only comes on if I turn the key OFF.
Which is as it should be because the alternator is "+" because the tractor is running and the alternator is charging, and with the key off, the key is "-". Two "+" turn the light off. The key on is "+"and the alternator charging is "+" so the bulb goes out.
At this point does anyone think it would hurt to run this tractor and just disconnect the battery when not in use?
You should be ok running the tractor. You should be able to park it with the battery connected but here is a way to check. With the battery disconnected put you multi meter between the battery post and the disconnected battery cable end. Positive or negative doesn't matter. You want the multi meter in series with the battery. With everything on the tractor switched off there should be next to no ohms measurable. .05 of an ohm or less I believe. Any more will drain the battery over time.

K5lwk also has good info.
 
 
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