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Discussion Starter #1
This tractor been sitting for 4 years, started it last week. Battery not charging and lights not working. I read a few posts concerning this issue so this is what I checked.
I have two wires coming from under the flywheel neither one has a diode (no voltage reg either). I have 28 AC volts at the two wires, at 3/4 throttle. It has a B&S engine 15.5Hp model 28N707.
Only getting 12.5 DC volts at the battery while running. It has a amp gauge in the dash that shows negative amps while running. I am thinking it is the ignition switch. Can someone confirm or send me in the right direction.
Thanks
 

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I would first confirm that the ammeter is wired in the proper direction. It is easy to get the terminals crossed while doing work in the cramped area under the dash. If you have a powered PTO clutch, it should show a draw from the battery when engaged if the charging system is not operating. If it shows a charge... then you know the wires have been crossed, or your PTO is generating charging current. Not likely.
There is a PDF document showing all the B&S charging systems which may be helpful. I do not have it at hand as I don't own one.
I do think 12.5v is not necessarily bad, but I am pretty sure you should see above 13V with the engine running as noted. The simplest systems had a diode buried under heat shrink inside / near the square plastic connector from the engine electrics/ignition to the chassis wiring. It was not regulated as far as I know, just pulsed DC to charge the battery. If you have the schematic from your owners manual, follow the wires leading to the battery from the engine(stator under the flywheel). There should be a regulator or diode in there somewhere. A quick thought is to check the voltage on the chassis side of the connector, after the diode(if you find it). That should be charging voltage. I think the smallish 28ci size would be likely to have one of the simpler systems.

tom
 

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Discussion Starter #3
2460140

I did find a piece of shrink tubing but it just slide along the wire, nothing underneath.
It has a mechanically mower blade engagement ( lever arm).
Still can't find the diode.
Do you think it could be in the ignition switch?
 

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Did you just jump the old battery to get it going?...or new battery?...does it have lights?...you could turn them on to check the amps draw
 

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Do you see any movement with the amp meter when switching off and on?..even though not coming on?...there has to be either a bad switch or a short where a wire has been rubbed bare of insulation and in contact with the chassis
 

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Discussion Starter #8
No movement in the amp meter when turning on/off lights.
I am getting 28 AC volts at the ignition switch. When I turn on lights the 28 AC volts goes to the head lights.
I think it is the ignition switch.
Do you know how to determine the part number of the switch? switch.jpg switch back.jpg
 

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Discussion Starter #12
Thanks guys but I no longer think it is the switch. I found a wiring diagram that show the location of the diode although I can not physically find it. I will remove the shroud and flywheel tomorrow and look there.
 

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If your 28n707 is like mine it has the dual charging. The stator is wound with two different sizes (each side) of wire with two leads. They both produce AC. You could measure each (before diode) by setting vom to AC and red wire to lead and black to ground (but I don't think measuring across the leads and set to AC applies to the dual, but does to other rectified/regulated systems. One lead remains AC to feed the lights. The other lead has the diode just before the connector that converts it to DC for the battery. I just looked at one and I can't determine which lead is connected to which size of winding wire. Do you currently have a connector like the amazon one withe wire leading back to the stator? If so the diode is right above the connector. Try testing each pin of the connector to ground at both ac and dc on the meter and see what you get. If you have proper connectors already you can trace which pin goes to light and which goes to charge battery. Then testing would be simpler as you know which to test for ac and which for dc. But as I said you test each to ground, not to each other.
 

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Discussion Starter #16
The connector shown on amazon looks like the one I have on the 2 wires coming from the stator. I check voltage today from the two wires coming from the stator. Both wires tested together 29 AC volts, tested individually 9 AC volts each.
 

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Discussion Starter #17
Another note is the bulbs in the headlights are 12Volts DC. So I think the Amazon connector with two diodes should take care of my problem. Part is not expected to be delivered until 15June. I will post how things work out.
 

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Those light bulbs don't really care if they see DC or AC. Most mower lights use the AC unless the keyswitch is designed to have lights on with engine off. Then they get powered by DC from the battery. That's done too when the engines get AC from the 2 stator wires to a rectifier/regulator which only passes on the regulated DC. Lights have to use that DC.
Did you measure those voltages at full rpm?
 

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Discussion Starter #19
Yes full throttle.
THe bulbs are standard car turn signal bulbs #1156, I didn't know they can handle AC too.
 
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