TN 75D Alternator Question

[motorjock]

Ok, I need to run a question by you professionals. My tractor is in the shop for some maintenance and sensor malfunction. They tell me the alternator is charging off and on. They remove it and take it to an alternator shop to get it checked out. Find out today that the alt. shop hooked it up said nothing was wrong with it. NH mechanic puts it back on and says when the rpm's are below about 1600 it's not charging all the time and when it goes above that it charges fine. So I talk to the mechanic today and he gives me a couple options. 1. leave it alone and if the battery light comes on just make sure you have rpm's high enough to kick it off (which all of my mowing of course is above that 1600) and he says it may last 10 months or 10 yrs. says this is what he would do if it was his. 2. Replace it with a rebuilt alternator which they said is almost $500. Cheapest I've found on line is $395. I was told that if something had been wrong with it the alt. shop they could rebuild it for about $75. Mechanic thinks that the alt. shop hooked it up to their electric motor and it probably simulates something over 1600 which shows it's working correctly. I think I'm going to have the service mgr. call the alt. shop and see if they will just open it up anyway and replace whatever they replace when they rebuild them and then put it back in the tractor. That way at least the insides are replaced and if it works.. great and if not, I'll just keep it high enough for the light to stay off. Sorry for the length...Any other ideas?? I find plenty of replacement alt.s online the say for the TN75D, but they are 45 or 65 amps. Mine is 85 and can't find anything but NH rebuilds.

Thanks in advance for your comments and suggestion..

 

[mojoinco]

Take a look at the alternator and at online 'images' (do a search for the alternator, then select the 'images' option on the top left edge). I bet you find out who made that alternator. Then you can search on that brand and find out what else uses that general model. Cars, trucks, motorcycles usually buy from someone else. An NH version may be insignificantly different. I found that with Volvo and other European cars, Subaru & Japanese, Triumph & Kawasaki & Suzuki. I wouldn't be at all surprised that it is Japanese. The alternator shop could tell you.

 

[howierd3866]

all my tractors as long as its over 700 rpm its charging....as for a new alternator just have the alternator rebuild it for $75.00 thats all we do.... in over 30 years never bought new one...good luck

 

[mojoinco]

This reminded me of a conversation I had a year or so ago with my local (former NH, now JD) dealer. My TN55 shows the 'not charging' warning light on the dash when started until I rev it up a bit. It goes off, then I let it idle down.

He said he remembered there was a software update that is supposed to fix the false warning. Not sure if this is true or applies. Worth checking it out.

 

[motorjock]

Thanks mojo..just saw your post...I'll run it by the service guy...

 

[RickB]

motorjock, I agree completely with your NH mechanic, I've seen this exact thing as well. Some guys live with it indefinitely, some swap out the alternator. Replacing diodes within your alternator probably will cure it. I agree the alternator shop probably didn't do a slow speed test.