Battry discharge

[LarryC]

I have a new battery, the regulator is only 1 yr old and checks out with the shop manual testing, the alternator puts out 12 volts (the shop manual says it should be 14) after charging the battery it starts fine running for 2.5 hrs and retuirning to barn, shut off and on restart the startere clicks like a dead battery, battery reads 12 volts anyone have any ideas, thanks.

 

[Anonymous Poster]

A fully charged battery will show over 12.6 volts, this is with the engine off and no load. The charging system is not putting out properly if you're only reading 12 volts with engine running. Check fan belt tension, battery wire to alternator possibly even fuses, not sure on the orange things. Anyway, if all that fails, pull the alt and have it checked at an auto parts store or alt repair shop. If I've missed something, you'll know soon enough... /forums/images/graemlins/grin.gif

 

[Bird]

glennd has it right. A fully charged battery should have 12.6 volts; not just 12 volts, and the alternator needs to put out 14 (actually I think it should be 14.2 to 14.4) volts to charge the battery.

 

[normde2001]

Can't add much to what Glenn said, other than the 12v you are reading is probably coming from the battery and not the alt. unless you are checking directly from the (unhooked) alternator. You can unhook the alt. from the reg. and run briefly. A good alt. should put out 20-30vac.

 

[Anonymous Poster]

Alternator put out 20-30 VAC ?? Alternators put out DC, they have diodes in them to recify the AC to DC. Also all alternators I have seen will put out nothing with the regulator disconnected. They require a field current to activate/regulate their output.

 

[normde2001]

I guess it depends on what he really has. Sometimes the diodes are in the regulator. (At least in some Yanmars).

 

[Anonymous Poster]

Oh ok, Thanks for the info Norm, Not a Yanmar man myself, not sure the origional poster is either. MOST alternators put out DC and if they have an external regulator, will not put out when it is disconnected. However most Briggs and Kohler type engines have an alternator under the flywheel and will act as you describe, putting out a higher voltage AC with the regulator disconnected.

 

[BB_TX]

Larry - Did you clean and tighten your cable connections? Not just the battery end, but also the engine and starter end? Those symptoms can also indicate a bad/loose/dirty connection. Use a wire brush and make sure all surfaces are clean. Sometimes there is a white crusty looking buildup inside the clamp that is hard to see just by a quick look. The special battery brushes work great for that.

 

[Chief]

Larry, is this an Honorable Discharge or Dishonorable? /forums/images/graemlins/wink.gif Seriously, I agree with Bird on the alternator output. Have you checked to see if you have a slow discharge drawing amperage away from the battery while it is setting. Try touching one of the battery cables to the battery terminal with everything turned off. If you see a small spark; something is drawing juice. Make sure all of you connections are CLEAN and tight at both ends of each battery cable. Check each battery cell with a hydrometer to eliminate the possbility of a bad or shorted cell. A shorted cell can do what you are describing. Good luck.

 

[LarryC]

I charged the battery, it read 12.9 volts last night unhooked. Took the alternator to a repairman yesterday it apparently has a bad rectifer, should be ready sometime today, the repair is 1/2 the price of a new alternator so i went with that with some misgivings I usually like to put on New when something's amiss on the tractor. I'll let you know how it works out, thanks for the help, hope I don't need more at least on this particular repair.

 

[patrickg]

LarryC, Don't know how much a new one would cost but 1/2 for replacing a diode is kind of high! A diode (press or stud mount) should only be a few bucks, at most, and labor to install considerably more.

Should this sort of thing happen again... diodes are one of the common failure poiints in an alternator (after brushes). A cheap meter will detect a bad diode and they are easy to replace, Bird has done it, several times.

Patrick

 

[Bird]

</font><font color="blue" class="small">( Bird has done it, several times )</font>

Nope, always let someone else do it. /forums/images/graemlins/laugh.gif I was working in my dad's auto parts store when alternators started replacing generators in cars. Dad threw a little annual barbecue and invited all the mechanics in town, and had factory reps there to explain new things to the mechanics, and I'll never forget that.

The rep mentioned to the mechanics that "I know a lot of you just short across the two terminals of a generator with a screwdriver to see if you get a spark" to see if the generator is working. He said, "You can do that with an alternator, too, and if you get a spark you'll know it was working before you did that". He then explained about replacing diodes, but told the mechanics, "You don't want to do that; just replace the alternator with a rebuilt one and send the old one in to be rebuilt." Quicker and more profit. /forums/images/graemlins/shocked.gif