How to test charging system?

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322
Location
TN
Craftsman Model # 247.288841 (MTD made) w/ 19.5 B&S Gold Model # 31P677-3373-G6 For about a month now when I go to start my tractor it acts as if the battery is nearly dead. Just get a click on the initial attempt. A few more bumps and it usually spins just enough to start. I am thinking the battery is going (or gone bad) but would like to verify it is not the charging system but cannot figure out how to test such. I put my meter in Vdc accros the battery terminals with it running and got 15.7 Vdc and it started rising and went to 17 Vdc. First thought is the system is overcharging but just not sure that is a valid test for a mower. My manual indicates the alternator is a part # 696459. The Briggs site list this a dual circuit regulated or rectified circuit. What I cannot tell is if my mower has a regulator. The manual does not list one but on Briggs website in an alternator ID guide they show a regulator part # 790292 but I am thinking that is something not used on all mowers. I have a extech DMM so can do some testing if I know where and what to check for. Thanks
 

JHZR2

Staff member
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46,141
Location
New Jersey
17V at the battery terminals with the battery attached? Sounds like the charging circuit is bad, or else impedance is so high that current can't flow and the voltage is practically open. I'd try to connect another battery, even if a car battery, via some heavy leads (jumper cables) without the suspect battery in the circuit. Make sure the car battery is fully charged, in good condition, and then leave it running a while to stabilize. Even if it's 17v, the current shouldn't be high enough to offgas too much. And with far lower impedance, charge voltage should drop.
 
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36,471
Location
ME
Does the battery have any moisture around the vents? It could have been overcharging for a while and boiled it dry to a point where it now demands attention. Does it actually have an alternator? I would imagine the battery charging to be part of the magneto. If it has a motorycle style regulator, it just shunts extra current away to heat. If you can find "it", see if its 1) warm or 2) if cold, a charred blown up mess.
 
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2,689
Location
South Carolina
Take your meter and check another mower that is similar. 17 volts is too high, but with a bad batt, that could explain. Def check electrolyte level and see if covering the plates, if possible to do so. If I can get one of those batteries to last more than one season, I feel lucky. I think I would be looking for a replacement battery. Sounds like plates are badly sulfated.
 

tnt31

Thread starter
Messages
322
Location
TN
Originally Posted By: eljefino
Does the battery have any moisture around the vents? It could have been overcharging for a while and boiled it dry to a point where it now demands attention. Does it actually have an alternator? I would imagine the battery charging to be part of the magneto. If it has a motorycle style regulator, it just shunts extra current away to heat. If you can find "it", see if its 1) warm or 2) if cold, a charred blown up mess.
It is not an alternator as I think of one but the manual refers to it as such. Here is what it looks like: http://www.ebay.com/itm/696459-OEM-Brigg...=item4182a8c15d
 
Messages
5,722
Location
Charlotte, NC
Sounds like a bad cell, not shorted but high resistance, Most consumer rated B & S motors are unregulated. Actually, the battery is the regulator. The current output of those engine alternators are limited so as not to overcharge the battery. On my rider the open circuit voltage is ~17vdc. The voltage on a fully charged battery is right at 14.5vdc. (running). I've never needed to add water to the battery. BTW: The charging circuit uses a single diode. Wayne
 
Messages
1,680
Location
CT
http://smallengineinformation.com/?page_id=435 http://eu-en.myfaqcenter.com/Resources/B...ical_system.jpg you need to start from the beginning. a magnet passes by copper windings and induces electrical current on that winding, that's it. the magnets are in your flywheel, the copper winding is called the stator (think stationary). the electrical current generated is always AC because of the rotation, the faster the rotation the higher the frequency of the AC and the more power generated. on simple applications the stator can be sized and with the engine expected to never run past 3600 rpm the AC output from the stator wouldn't go over 20 watt... all you need is 1 amp at 13 volts or more. power = volt x amp. headlights run fine on AC, if you slow the engine down you observe headlights get dim and flicker, but at 3000 rpm there's no flicker because AC frequency is too high to notice. You can also charge the battery with AC current as well. To have DC current then you need a rectifier which can be nothing more than a single diode if the tractor is simple and all you need is that 13 watts to only charge the battery. as the tractor gets fancy with electrical accessories and you use a large stator capable of producing 10 to 30 amps (few hundred watts) then you need a regulator/rectifier unit to limit voltage. your problem of 17 volts charging at the battery leads me to believe you have a bad regulator which you said you have one #790292. also be aware for the regulator to work properly it needs good connection to battery ground as a reference so it knows where 14 volts is. a bad battery can cause the regulator to malfunction, so like was said hook up a good car battery in parallel or as a substitute. the fact you have 17 volts means your stator is not fried, it is working. the problem is either a bad wire or connection to ground, bad battery, or failed voltage regulator. you should take your tractor battery out, put it on a good charger over night to properly charge it then let it sit for 2 days and see if it holds a charge. the other thing you said battery seems weak when starting, a bad regulator/rectifier can cause battery drain when engine not running. use your meter to measure DC current with engine off, disconnect one battery lead and connect meter in series to measure current. if you see more than 5 milliamp you most likely have a bad rectifier/regulator box. your alternator 696459 shows up as dual circuit. http://www.ehow.com/about_6567282_dual_circuit-alternator-briggs-engine_.html your rectifier in this case is a diode inline on the red wire, or the wire going to DC voltage regulator. the black wire from the stator is not ground, it is the AC hot wire going to your headlights. ground is the metal of the engine block and the frame of the stator all connected to negative side of the battery.
 
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