Regulator/Rectifer-JMOR or anyone

I have a Kubota G4200 mower(use on farm) with a bad regulator/rectifier(I think). It has the small permanent magnet 2wire,alternator that is used on a lot of these mowers. My meter shows around 30-32 volts phase to phase on the alternator wires at wide open throttle. Each phase to ground shows 13.5-14 volts at wide open.

One of my questions is: Do these units really regulate voltage much, if at all? Or, do they just rectify the AC? I am only getting 2 volts output of the regulator now at WOT. It has not been keeping the battery up, obviously.

I have not priced one from Kubota yet. I read on the web where someone used a full wave bridge rectifier from Radio Shack to replace this reg/rectifier. Would it need any other electronic components?

Would a rectifier from a Kohler work? This mower only runs 1-2 hours per week, I let a neighbor use it to mow his yard, and kind of keep it as a spare.

Thanks for any help on this,

Garry

I lost the regulator/rectifier on a 20 hp briggs. It wasn't cheap, around $70 at lawn parts store. I wouldn't go with just a rectifier. I can't see why there would be a different regulator/rectifier used on a bota or any of them. I asked the lawn and garden parts store what makes the difference between mowers that just use one diode and those that use regulator/rectifier. He said the charging rate, size of coils under the flywheel. Proper charging is important for longer battery life. I would use just one diode and no regulator before I built a bridge without a regulator. If I thought a lot about the battery, I would get the OEM regulator/rectifier.

Go to ebay and see what one sells for. Bet they are cheaper than the $70 I paid.

I went to ebay. Need to revise post below. My regulator was a 3 wire. ebay shows a 6 wire device. The 3 wire regulators are very cheap. here is one for a grasshopper.
grasshopper regulator

Thanks George,
My reg uses two blue wires for AC input, red for output, black for ground, and a yellow wire that is unused/not connected to anything.

I guess I was wondering if it was only giving not over 14 volts on each phase to ground wide open throttle, whether or not the voltage really needed regulating. Aren't automobile systems regulated to around 13.5-14.5 volts all of the time?

Thanks for taking the time to look on ebay, I did the same, but missed the one you found. I will pay up if I have to, but am afraid to guess what kubota might want for one, if available.

Garry

At one time, alternators on small engines were unregulated. Basically the battery was the regulator.

I suspect your unit is a "shunting" regulator. Automotive regulators modulate the alternator field, but most small engines have permanent magnet regulators, so that's not possible. A shunting regulator simply shorts the stator to ground when its voltage exceeds the desired level. Obviously they get pretty hot when the electrical load is light.

Something is not making sense here. "Each phase to ground shows 13.5-14 volts at wide open". OK, that sounds pretty good. I assume this is AC. I'm guessing you have a peak-averaging voltmeter, so it thinks the non-sinusoidal voltage of the stator is about 14 Vrms. (If you looked at the stator output on an oscilloscope, it would be a clipped sine wave.)

Then you say "I am only getting 2 volts output of the regulator now at WOT". Huh? The alternator output is the battery input! So even if the battery is nearly dead you should see more than two volts.

Recheck your voltage AT THE BATTERY. Once you get a reading that makes sense, you can backtrack to the regulator/rectifier and alternator.

Assuming this is a single-phase alternator, it's quite possible you could substitute a stock full-wave bridge rectifier as suggested. Note that these devices have pretty small current ratings. You won't have a regulated output, but you might not have one now.

MarkB,
I was not too clear on where I checked what. I did check the unregulated output of the permanent magnet alternator at the wires coming out of the alternator, with them disconnected from rest of system. That is where I got 13.5-14 volts on each wire to ground. I used both a DMM and an older analog needle style meter for these readings.

Where I got the 2 volts was when I disconnected the red output wire of the regulator and checked it to ground with the alternator all connected back up. Engine running, of course. That is how I figured the regulator was bad. All wiring between alternator and regulator was checked and verified okay also.

With red regulator wire connected, I get battery voltage, of course. With engine running, a battery tester/voltmeter never moves from battery voltage, when connected across battery terminals.

If this alternator will only put out 14 volts maximum unregulated would say a 25amp 50 volt full wave bridge rectifier work? Would it handle the current? All it is doing is keeping the battery up, the lights are hardly ever used.

Thanks,
Garry

Garry, the 25A/50V bridge should be fine as long as you always have a battery installed. If you disconnect the battery, there's a distinct possibility you'll exceed the maximum reverse voltage for the bridge and blow it. I doubt the alternator can put out 25 amps, but it can certainly put out more than 50 volts peak if there's no load.

I suspect a center shorted to ground stator is your problem.
You should have around 30+ volts between the stator leads, but 0 volts from either stator lead to ground.

I worked on a JD 318 with Onan engine that had a stator shorted to ground at about mid point that acted exactly as you discribe. It still produced a normal 30+ V across the stator leads when isolated from ground, but 1/2 the stator was shorted to ground when connected to the rectifier / regulator.
With the engine stopped, use an ohmmeter to check continuity from stator leads to ground. Any connection from either stator lead means the stator is shot / shorted.

"At one time, alternators on small engines were unregulated."

NOT sure I agree with you about the time frame thing... low-end stuff is made that way, better engines like Kohler, etc. have had regulators for a LLLOOONNNGGG time! NOT sure about the "shunting" thing, either, once again, using Kohler for example, they used SCR's or triacs in the regulator and "grabbed: enough of the AC waveform from the stator to produce the desired charging current.

Do you have reliable knowledge about "shunting regulators" being the norm? If so, I will concede defeat!

Bob,

I was speaking generically of small engines, including outboards, motorcycles, etc. For example, regulated alternators didn't appear on outboard motors until the mid-eighties, when increased electrical power demands necessitated higher-output alternators.

Shunting regulators are quite common on motorcycles, and I assume that's the design used on most small engines. It's really the only way you can implement a regulator using SCRs. Silicon-controlled rectifiers are curious devices: you can turn them on but not off. (A triac is just two SCRs back-to-back in parallel.) The behavior of SCRs isn't a problem when switching ac, since the signal turns itself off every half cycle. Now in the case of lighting dimmers, SCRs are used exactly as you describe: the SCR is triggered partway through the half cycle, so only a portion of the waveform is passed to the load. But lighting dimmers are open-loop devices with no feedback loop. Voltage regulators are closed-loop devices; they need a means of turning the power OFF as well as on. Since an SCR can't turn off, the solution is to short out the stator output using the SCR as a shunt.

The link below has the schematic for a rudimentary shunting regulator, and a good discussion of the theory of operation.
Shunting regulator

(quoted from post at 19:03:42 08/06/13) Thanks George,
My reg uses two blue wires for AC input, red for output, black for ground, and a yellow wire that is unused/not connected to anything.

I guess I was wondering if it was only giving not over 14 volts on each phase to ground wide open throttle, whether or not the voltage really needed regulating. Aren't automobile systems regulated to around 13.5-14.5 volts all of the time?

Thanks for taking the time to look on ebay, I did the same, but missed the one you found. I will pay up if I have to, but am afraid to guess what kubota might want for one, if available.

Garry

Click to expand...

My experience with two wire Reg/Recs is that they need non-grounded single phase AC input. In your case this would be the two blue wires. As Jon posted your stator appears to be shorted to ground, if this is the case, replacing the Reg/Rec will not fix your problem.

You measured 13.5-14.5 on each phase to ground. I suspect this is a open circuit (no load) measurement and as such the voltage will be much lower with a load. I do not believe this will charge a battery - beside adding a diode will drop it another 0.7 volts.

You can test your Reg/Rec using a battery charger with the diode removed (simply shunt across it). This gives you single phase AC input for the two blue wires.

Gary Seems like there are a lot of electrical experts on here. Here is what will solve the problem. Your regulator part number is 15531-64603 Kubota list cost $ 104.40
New dyno Kubota part number (latest) 15531-64017
List price $ 203.01 Most time a cleaning will fix any problems in the dyno unless a bearing down. Probably shorted regulator fairly common on those units. Most of my customers charge the battery mow the lawn and forget it till next time they mow.

The rectifier converts the AC voltage to DC and regulates your charging voltage to the battery.
Your neighbor should pay for 1/2 the cost for a new rectifier/regulator for using your tractor.

If the battery is only used for starting you could just use your battery charger to recharge your battery before being used. I do that on my Troy Bilt tiller that has battery start. One charge will last all summer. The battery isn't used on the ignition. I keep the pos battery cable connected to the starter. When making a start I just touch the ground cable on the negative post of the battery. Hal

Where I live all my neighbors either have their own mower or they pay to have it mowed about $40.00 per week. I wouldn't loan my tractor. Hal

Well that was one of those great ideas that didn't work out. Got a bridge rectifier($5.00) and heat sink($2.00) at Radio Shack and wired it up to my alternator. With engine at full throttle, output from the rectifier was 24 volts. Connected to battery and the voltage steadily climbed from 13 volts to 17 volts before I pulled the plug. Trying to make a 12 volt battery into a 24 I guess. I know there was potential dangerous situation there too. Also the rectifier got pretty hot in the minute or so that it ran. Another lesson in my limited knowledge of things other than a simple DC circuit!

I would like to have it charging, so I guess I will get an real reg/rec. Maybe the one George Marsh linked. It does not do too bad with the Battery Tender connected between mowings. Just one more thing to remember.

As for loaning it out, it is a spare extra mower, and I would rather having it run for an hour a week than sitting like it has done before. There are other unmentioned circumstances concerning this also.

Thanks for all of the posts everyone.

Also, I have checked to output of several 2 wire alternators over the years(Kohler,Kawasaki,etc.) and they all show a voltage when one wire is checked against ground. My wife's sisters John Deere/Kawasaki did that a few weeks ago, and had no output from regulator. New reg. from Deere($75) fixed it. But I still see what you are saying about a shorted stator.

Thanks again,
Garry

(quoted from post at 13:23:10 08/07/13) Gary Seems like there are a lot of electrical experts on here. Here is what will solve the problem. Your regulator part number is 15531-64603 Kubota list cost $ 104.40
New dyno Kubota part number (latest) 15531-64017
List price $ 203.01 Most time a cleaning will fix any problems in the dyno unless a bearing down. Probably shorted regulator fairly common on those units. Most of my customers charge the battery mow the lawn and forget it till next time they mow.

Click to expand...

This electrical "expert" predicts that between $100 and $200 will be spent on a regulator / rectifier that is not needed, while the money would be better spent on a new stator which by the OP's description, is shorted to ground, and can not function that way. BTDT

Jon H.

I put a ohm meter on the stator windings. Through the winding's two wires showed little, if any, resistance. Checked each wire to ground and showed OL(open line?). To me, that shows no short to ground in the windings. Is there another way to check it?

Rectifier would not pass current through one of the AC wires to the DC output wire.

Garry

Sounds like a good stator and blown rectifier to me.