B7100 Charging System Troubleshooting

[John C]

Got Back from attending a relatives funeral at 2:00am this morning after a 650 mile drive. Got up at 7:00am went to the garage and tried to fire up the old tractor to find a dead battery! (first time she failed to start in the 3 years I've owned her) Used the booster to get her running and do what needed to be done figured that the charging system would get the battery back up until I could find out what exactly was wrong. when I was done I tested the battery and it tested bad which didn't surprise me since it was in the tractor when I bought it! Went down to Walley World who didn't have a 22NF Battery so stupid me checked the little electronic battery finder wizzard thingy and guess what battery that thing spec'd for a B7100? A cheezy little $23.00 lawn tractor battery!! NOT!! So after a bit of comparing I ended up with a 51R-4 with 435CCA. It was the same length as the 22NF I took out. Terminals were the same, it was a bit narowwer and just a bit shorter. took it home and installed it along with a new ground cable and it fired right up only problem is that I put my battery test meter on to check out the charging status only to find no difference in voltage with engine running than when engine stopped! Steady @12.8 volts so I opened the throttle to about 3/4 and noticed the volt meter read 12.9 volts so I let her run a while at 3/4 throttle and watched the voltmeter it slowly climbed 12.9 wait a full minute 13.0, wait another minute13.1, another couple minutes 13.2, and so on until finally quit climbing at 13.5 volts. As soon as the throttle is returned to idle voltage drops back to 12.8 volts. According to my charging system meter (designed for automotive use) to be considered healthy a charging system should produce between 13.5 and 15 volts. I don't know if that same standard applies to Kubota tractors? and if it does are there any components I should check other than just rebuilding the alternator right off the bat? I am an industrial electrician by trade but vehicle charging systems have always been difficult for me especially when they are apparently working sometimes! any help would be greatly appreciated!!

 

[John C]

OK new development! I was at my local kubota dealer to order decals and asked them for some technical advise troubleshooting the charging system. They told me to unplug the alternator start the tractor and measure AC volts from the alternator, so this I did. The results are at idle 13.0 volts AC, at about 1/4 throttle I get 20.8 volts AC, at about half throttle I get 28.4 volts, and at full throttle 32.4 volts. may I assume from these results that the regulator is the culprit or is there some further testing I need to do?

 

[John C]

Another new development that I hope will save everyone alot of trouble trying to troubleshoot a problem that may not exist! It seems that the voltage regulator may actually do too good a job of regulating the voltage! After replacing the battery I wanted to check out the charging system just to make sure I didn't have another problem. Testing the voltage while the engine was running lead me to believe I did have a charging problem since I did not see any increase in voltage. I then checked the open circuit AC output of the (dynamo) to find it working just fine putting out 32 volts at full throttle. So now my focus narrowed to the regulator but I got busy and never got around to testing or replacing it! Weeks went by and I was sure that the battery would be dead each time I'd go to start the tractor however It never was so yesterday I threw the volt meter across the battery and guess what! now I have 12.5 volts engine off and 13.8 volts engine running at idle and 14.2 volts at 3/4 throttle. So my conclusion is that the new battery was hot enough to shut down the voltage regulator untill I ran the battery voltage down and allow the regulator to open up and allow the battery to charge! I wonder how many good regulators have been replaced simply because they did their job too well!

 

[eserv]

Ya! Sometimes we keep on fixing things till they're broke don't we?
Ed

 

[Ob1kubota]

Mr John you are absolutely correct with this observation " Steady @12.8 volts so I opened the throttle to about 3/4 and noticed the volt meter read 12.9 volts so I let her run a while at 3/4 throttle and watched the voltmeter it slowly climbed 12.9 wait a full minute 13.0, wait another minute13.1, another couple minutes 13.2, and so on until finally quit climbing at 13.5 volts. As soon as the throttle is returned to idle voltage drops back to 12.8 volts. " Every thing is fine.. batteries just become big heat sinks once the electrolytes give up in fact the Lead Acid battery is made up of plates, lead, and lead oxide (various other elements are used to change density, hardness, porosity, etc.) with a 35% sulfuric acid and 65% water solution. This solution is called electrolyte, which causes a chemical reaction that produce electrons. When you test a battery with a hydrometer, you are measuring the amount of sulfuric acid in the electrolyte. If your reading is low, that means the chemistry that makes electrons is lacking. So where did the sulfur go? It's resting on the battery plates and when you recharge the battery, (reverse plate polarity) the sulfur returns to the electrolyte, and the cycle life begins producing free electrons on the molecular level again supplying current flow to needy loads. It's a beautiful thing .