battery not holding a charge

bigjake

New User
The battery on my Snapper lawn tractor is not holding a charge. I'm not sure if the battery has just gone bad or if the charging system is not working properly. Measuring DC voltage across the battery with tractor running, it will start a little above the idle battery's voltage then slowly rise 1/100 of a volt every couple seconds until it reaches 16V then it holds steady there. Is 16V normal or is that too high and I have a bad rectifier?

The strange this is that I measure 29 V AC at the battery with the tractor NOT running and about 36V AC with the tractor running. Normally I think this would mean a bad rectifier but with the 29V when not running, I'm not sure if I just have a flaky voltmeter or not. It's just a cheapo from Harbor Freight. Is it even possible to measure AC on an idle battery? I do get proper AC voltage readings if I plug into a wall outlet. I don't want to just buy a new battery then have the charging system ruin the battery and if it is the charging system I may just buy a new tractor as I think this one is about 18 years old.
 
Your meter is likely to be way out of calibration so your reading is false. Pull the battery and have it load tested that will tell if it is the problem or not.
As for the charging system on lawn mowers it is a simple alternator and one single diode so it either works or it does not but to really see if it is you need an analog meter because of the interference of the engine spark
 
Are you saying that the rectifier is part of the alternator?

What DC voltage should I expect to see on the running tractor?
 
If you put a good multimeter onto the DC Volts scale, then you
should see 12 volts across the positive and negative posts of the
battery when the engine is not running.



Start the engine and run it up to 3/4 throttle. The voltage
should now read around 13.6 volts DC.

If it doesn't, then you have a charging problem.

But that is not to say that your battery is problem free. It should
be load tested. If it has removable cell caps, then it should also
be tested with a hydrometer.
 
(quoted from post at 11:38:00 07/01/14) If you put a good multimeter onto the DC Volts scale, then you
should see 12 volts across the positive and negative posts of the
battery when the engine is not running.



Start the engine and run it up to 3/4 throttle. The voltage
should now read around 13.6 volts DC.

If it doesn't, then you have a charging problem.

But that is not to say that your battery is problem free. It should
be load tested. If it has removable cell caps, then it should also
be tested with a hydrometer.

so if the 16 volts I am seeing is accurate, is there a seperate rectifer that needs replaced?
 
I am familiar with Snapper tractors. I have no idea what make
and model number of engine is in that tractor.

All I can do is suggest that you look on the engine for the ID tag.
Write down the model and spec numbers. Go that engine
manufacturers website and try to find the engine manual. The
spec number is important because most manufacturers offer
several charging systems and the spec number is what identifies
them.


In my opinion, 16 volts DC at the battery terminals is way too
high and indicates a bad rectifier/regulator. But before
condemning that item.. get the battery fully tested.
 
NOT a rectifier but a small diode so small it almost looks like part of the wire it is in
 
A true full charged battery should read at a min. of 12.5 volts if not more nothing less. If he gets only 12 volts is is not a full charged battery
 
The issue was not whether the battery was fully charged. It was about whether he could see a voltage difference between a non-running engine and a running engine so that he would know if the charging system was working.

I fail to see the merit in nit-picking over a 1/2 volt on that test.
 
Never over 14.5 volts. Well, I have seen some working systems go over 14.5 briefly with a weak battery, but they usually come back down fairly quick.

Are all your testing numbers taken with the old battery in the circuit? I have seen bad batterys that consumed so much power that an accurate diagnosis of the charging circuit was impossble.
 
(quoted from post at 19:26:20 07/01/14) Never over 14.5 volts. Well, I have seen some working systems go over 14.5 briefly with a weak battery, but they usually come back down fairly quick.

Are all your testing numbers taken with the old battery in the circuit? I have seen bad batterys that consumed so much power that an accurate diagnosis of the charging circuit was impossble.

Yes, I am measuring the voltage across the battery with the engine running. How do I measure the voltage output of the alternator without the battery in the circuit? do I just disconnect the battery and still measure at the Pos and Neg battery wires?
 
Big Jake.

If your engine is equipped with a true alternator
charging system, then it will have a stator coil behind the
flywheel with two wires exiting it. On most engines those two
wires produce up to 36 volts AC.... not DC..

You need to find those two wires, disconnect them from
wherever the are connected to. Start the engine and with your
multimeter set to the AC VOLTS scale, put the probes across
those two wires with the engine running at 3/4 throttle.

Alternator stator coils on Kohler and Onan engines are attached
to a rectifier regulator. The outer case of that rectifier/ regulator
is grounded to the frame of the tractor. There is one wire that
exits the rectifier regulator and if you put your multimeter on DC
VOLTS and place the probes onto the case of the rectifier/
regulator and that third wire, you should read about 13.6 volts.

A full wave rectifier consists of 4 diodes wired in a bridge
pattern. A half wave rectifier uses 2 diodes. I am unaware of a
single diode being capable of producing DC but I am always
willing to learn.

It would be helpful if you finally disclosed the make, model and
spec number of this engine you are working on.
 
Tom-MANY of the briggs eng sold/in use today have dual alt stators(2 seperate windings) & use 1 winding for lights(AC) & 2nd winding is used for battery charging with an inline diode on stator output & diode is rated for 1.5A-4A depending on pn of stator,these are unregulated 1/2 wave charging system's,tecumseh also used this system on many of their eng,especially in the HM series,I have 2 HM100 eng with a single wire output from alt & a 7A inline diode for charging battery(1/2 wave,unregulated).The single diode system has a high AC ripple content to it but the battery can usually handle this/doesn't care.
 
You have either a rectifier/regulator or a diode for converting the AC volts to DC volts. Get a wiring diagram for your engine. Here's a diagram
for Kohler. Hal
a161875.jpg

a161876.jpg
 
(quoted from post at 21:13:30 07/01/14)
It would be helpful if you finally disclosed the make, model and
spec number of this engine you are working on.

Snapper LT140H38ABV Series A Hydro
engine: B&S 14HP model:287707 type:0228 0 code:9409264A

btw, engine itself runs great but due to age and other minor issues , I'm considering a "new" used tractor. I started another thread asking input on an 8 year old Toro.
Thanks guys.
 

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