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MTD Briggs and Stratton Stator Rewind Charging System Upgrade

13K views 20 replies 5 participants last post by  38racing 
#1 · (Edited)
So I have this mid 90's MTD Tractor that has been converted from a riding mower to strict use as a winter snow blower as I got sick and tired of swapping blower and deck back and forth twice a year.
With a usual slowdown at work around this time of years, I started tackling this tractor with several fix ups and upgrades. I purchased a very good quality set of LED lights and mounted them after I yanked out the OEM bulbs and OEM reflector and tossed them for a field goal. I also added a 6 way set of strobing emergency lights, installed a 1,000 lbs strap winch for raising and lowering blower, tossed out OEM amp meter and installed an LED voltage/amp digital meter. Also custom mounted a full sized car battery for more CCA and rear weight.

After all this, I investigated into the charging system to see how she works. (B&S actually has lots of very nicely written and well documented information on their equipment in pdf files) I was disappointed to find out I won't yield optimum results with the current setup. The factory tractor is perfectly fine for running wimpy incandescent lights (which are ok for mowing lawn in the dark in summer), and is ok for charging the battery. Basically, I have the world famous dual circuit alternator.

This is basically two halves of two of their other alternators side by side. One side produces a/c power strictly for the lights. Other side produces a/c power as well, but is instantly tossed into a diode to change it to dc current for charging the battery. (This clearly doesn't provide me enough power by the fact my voltage drops to 12.0v when my lights are on). When all lights are off, I'll see a voltage as high as 17 at the higher rpm... The single diode is really not the smartest way we could be charging a battery.

Since Everything I added electrically requires DC power, I'm WAY down on amps, and have half the alternator doing nothing. :tango_face_sad: So looking over B&S' list of alternators, I was able to see I do have options. They have a somewhat expensive regulator that directly plugs into this alternator (with the removal of the exsiting diode) to then make it into a full dc regulated charging system. ( I still found this to be somewhat mickey mouse since we have two different gauge sizes of wire and turns going into the voltage regulator)
So a good chunk of us have a 696459 dual circuit alternator. I was now eyeballing the direct fit 696458 that can produce 10 amps on the flywheel with small magnets (flywheel most of us have). Or 16 amps if we have the flywheel with the larger magnets. Add in the 16 amp voltage regulator and we're good to go.

Now I'm also looking to upgrade my other MTD lawn tractor to LED lights and want to improve its charging system to use a real voltage regulator. Instead of purchasing two 696458 alternators, I decided to tackle rewinding one with some magnet wire I have laying around, and use the heavier gauge wire on one side to transform the other alternator from a 696459 to 696458. Then I just need to purchase some regulators.

So my research on my engine model had me convinced I had the flywheel with the larger magnets on my 19 hp. I managed to get a hold of an Onan 20a regulator for a good price. I decided to use this regulator incase my amps would be higher than 16 after I rewind this into a monster.

Long story short, I took it apart and found out I actually have small flywheel magnets on both tractors. No big deal, I still have plenty of amps available with my rewind. This made a lot more sense since my tractor does not have an electric PTO, or hydrostatic tranny. There was really no good reason why I would have had the larger magnets to begin with. Couple that with a dual circuit alternator, it really makes no sense.

So with all the B&S information on their alternators, flywheels, and tractor manuals in conjunction with all the other famous alternator/stator rewinding forums and pdf files I've read, I became convinced I can tackle this job.

So here we go; (To prevent confusion, I may call a stator an alternator and an alternator a stator. They're both the same thing, so don't get confused)

Our flywheel has 12 magnets inside it. They simple alternate N, S, N, S, N, S, N, S, N, S, N, S. (That being north aiming inward, then south inward, etc)

Now the dual circuit alternator has 12 poles that match up perfectly against all 12 of those magnets. EXCEPT that 4 of those 12 poles are basically dud poles that are for mounting the stator to the engine.

So we actually have 8 poles we only need to worry about rewinding.

Another thing I noticed: These alternators were NEVER dipped in any additional epoxy or resin for any added protection. They did use an epoxy in several locations to hold certain wires and parts in place, but other than that, you can completely unwind it quite easily.

For the record, the dual circuit stator has one end of the two magnet wires connected together and mounted to the iron frame of the stator core. Each wire then goes it's separate way (on one side) where it meets at the other end and the larger gauge wire is your a/c power for lights and the much smaller gauge wire is your DC charging with the diode.
Since this is split in half from 8, it's 4 poles per side of winding. The small gauge wire does 69 turns on each pole for a grand total of 276 turns. Two poles are wound CW, two other poles CCW.
The large gauge wire does the same thing, except that it has 29 turns per pole for a grand total of 116 turns. Once again, two are wound CW, two other poles are CCW.

For the way would my stator. I basically copied the way the 696458 is wound. It's actually easier than the description above for the dual circuit alternator. At no point do you connect any of the wire to the iron core of the stator. One wire is going to go in, you do all your turns and meet back at the beginning. One wire in, one wire out. This is about as simple as it gets. There's no additional wires. No confusion about delta or Y wiring. No 3 phase. This is just a single phase wind that isn't difficult.

Next thing I noticed was that my 16 gauge, (1.3mm) magnet wire was WAY larger than the wire used on the 10/16amp alternator. Since the engineers designed these to likely charge our systems optimally at around the 3000 rpm range, I decided to try and re-invent the wheel with changing the number of turns to try and miraculously pull more power out of small magnets.

I did run into some minor and large issues with using 16 gauge wire. The minor one is that could NOT fit 29 turns per coil. I believe I averaged about 26-28 per coil (keeping count was actually far more difficult than anticipated). But this lower level of turns didn't seem to negatively effect me in the end.
The large issue was that it made the stator so fat and juicy, that I was literally missing about 1 mm of clearance to the top of the flywheel when I mounted it back down with the giant nut! :tango_face_surprise

At this point, I was either to scrap the whole idea (because my stator was covered in red varnish and essentially put together to NOT be taken apart)
So I started with trying to etch out a groove all around the flywheel to allow the clearance of the magnet wire (this failed as the cast of the flywheel just eats bits). My next option was to lower the mounting bracket of the stator my trimming a hair off. There was plenty of room to do so, and this is what I did and it has worked so far. I would never recommend doing this. If you should attempt winding this yourself, use 18 gauge and nothing larger! Go for 29 per coil

In terms of winding the coils, this is probably the most important bit of information you want to keep track of: The rotation of CW or CCW is extremely important. This stator is particularly unique as you cannot just follow the typical "CW, CCW, CW, CCW" pattern. The reason for this is because of the 4 dud poles I mentioned earlier. When winding the poles, all CW wound poles MUST face either a North or South Magnet. Same situation for the CCW poles.
So basically, when you place the stator in the center of the flywheel, every SECOND magnet must be aligned with a CW pole, and every CCW pole must be aligned with the other magnets.

So when winding this stator, when you start with the first pole you can do the rotation CW, then you skip the second pole (because it is a mounting bracket) and then wind the third pole. This pole must be wound CW so that the magnets are aligned correctly to the right rotation. Once you then move to the wind the next pole beside it, you can switch rotation to CCW... Keep this same pattern going and you'll be fine. Remember: any two poles that are right beside eachother are wound in complete opposite directions. and any two poles on either side of the mounting bracket is wound in the SAME direction.

Pic 1 shows the stator completely stripped down naked. (notice how it's two halves put together). Pic 2 is with the plastic mounting pieces back on.
pic 3/5 is a side by side to a 10/16 amp stator with the size difference! pic 4, 6, 7 is the complete stator before red enamel was added ( used JB weld in specific spots similar to the OEM epox'd areas. Pic 8 is the final result before tossing it in.
 

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#2 · (Edited)
When you're done, you want to confirm you have ZERO continuity between your magnet wire and the stator core. You can also do a continuity check from wire to wire on the stator, the resistance will be very low, so you won't find any faults in the shielding, but if you have no continuity, you know you have a major problem.

I was able to salvage the OEM clip that had the male connectors inside. If you loose very closely, you can see a little tab sticking out that keeps it locked in, you press this down with a very small flat screwdriver and the molex comes right out. I used good quality crimps on my connections to the magnet wire. I didn't want to solder so close to the stator. I made sure to strip the enamel off the wire where I crimped it. Similar to how the stator was originally.

I installed the regulator on the metal panel where it gets hidden behind the cover of the tractor. It's in a nice spot where no heat is near it. I see many have this mounted on the engine directly, which makes no sense to me as you want to keep heat away from these.

I used an Innova timing light/tachometer to get an idea of my rpms in relation to voltage. Since we have a lost spark system, I was getting double the tach reading. With cutting those numbers in half. my lowest rpm setting was 1800 rpm, and highest was 3100 rpm.
I used a true rms high quality multimeter to measure amperage and voltage readings

At 3100 rpm, I was getting 24 vac directly at stator. At 1800 rpm I was getting 22 vac.
Briggs specifications calls for the 696458 to yield 20 vac with the small magnets, and 30 vac if you have the larger magnets. So these numbers looked pretty good.
After now installing everything, I used a 500a 75mv shunt that I use for measuring starter currents and whatnot. I used a load tester to bring my battery current down and force the regulator to dish out all she could. but she was very sporadic with the readings. It would jump from 1.5 to 4.0 to 2.5 to 3.2 mv... I could not get a solid number. So my true amperage production is a bit of a mystery. Perhaps I would have been better off trying the resistor before the regulator. Somehow I believe the battery and the shunting action of the regulator was interfering with this test.

Anyways, after many test runs with the blower. With all lights running, It stays well within the 14v region. Sometimes falls to 13.8v briefly, or even up to 14.7v. But otherwise fully capable of keeping her working good. Even when I power up and down the 1000lb winch, the load doesn't cause much of a voltage drop and it's as if the regulator is even keeping up with that! ...I also checked the temperage on the onan regulator with my hand, it was as cold to the touch. Not even any signs of even warming up. So far, so good!

Obviously I had to make some changes to the wiring. Fortunately this is fairly easy. I have a 6 point ignition switch. I used the location on the ignition switch that would normally have went through the OEM ammeter to go to the DC side of the regulator. This is the one particular tab that actually closes it off to ground when off, but opens it up to the B (positive 12v) terminal with the battery when running. I ran a heavier gauge wire to the battery solenoid for charging and put on a larger fuse. Both wires that come from the stator go directly to both the a/c a/c terminals on the Onan regulator.
 

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#3 · (Edited)
I should also mention the oem epoxy is pretty tough stuff, you need to be a bit meticulous in breaking it and cutting it without damaging the plastic pieces for the stator. Take your time and break it off carefully. You also want to keep the high temperature wire covering material where your stranded wire connects with the magnet wire. They can be reused once you break away the old bits of epoxy.

Measuring the OEM magnet wire (696459) with a precision caliper, shows it to .22" (23awg) with the coating for the thin wire. The larger diameter wire shows it to be .037" (19 awg) with the coating.
Copper alone without this coating will make the wire 24 gauge for the smaller wire and 20 gauge for the larger wire. Keep in mind the 696458 stator uses this 20 gauge wire for upwards of 16 amps with the flywheel with the larger magnets.
If I had to rewind this stator again, I would do so with 18 gauge wire (for maximum amps, and less resistance), or even 20 gauge wire as that obviously works for the 696458. I'd go with 29 turns per coil, or a bit less. The length of wire required is 44' in total. With 18 gauge wire, the turns will become fatter on the stator and may go over 44' slightly with 29 turns per coil. DO NOT use 16 gauge wire as I did! You will run into clearance problems trying to squeeze 29 turns per coil. You will run out of room between coils and make it too large that the flywheel will rub against the windings.

I also took some resistance readings on a perfectly working 696459 if any of you may be trying to bench test an issue with one.

(All resistance readings are done at room temperature with one end of the multimeter leads against the iron core of the stator with NO OTHER electrical power present!)

black wire (large gauge wire): .2 ohms
red wire (downstream of diode): 56.3 ohms
red wire (upstream of diode): 1.1 ohms

Checking the diode is another process that is can be checked with a multimeter with a diode checking option.

I also just discovered a similar thread on a JD tractor. http://www.mytractorforum.com/12-john-deere-forum/635729-jd-111-alternator-rebuild.html
It was for a 696457. Pretty much the same iron stator core, but this one is wound with a single wire to feed two diodes, or a single wire regulator. It basically produces 5 amps with small magnets, and 9 amps with large magnets.
 
#4 · (Edited)
Here's a modified picture to give a detailed visual of what you're trying to achieve when rewinding.:OHCAN

And as an added tip for those who may have trouble finding magnet wire, or can't get it. You, or your neighbor likely have an old TV laying around. Last one I tore apart had a massive pile of magnet wire wrapped all around the screen with black electrical tape. It's way more than enough wire to do this stator. Not 100% sure of the gauge of this wire. I think it was 18 or 20 on the 36" tv I tore apart. You just need to make sure not to cut it! You need to just take the time to unwrap the black electrical tape, and you'll find the magnet wire goes around and around the tv screen a whole bunch times. You just cut the starting and ending points of this wire and you'll have a big spool to work with.

Notice how if you picture the stator as 12 coils, you'll have CW, CCW alternating perfectly in regards to the poles of the magnets.
 

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#5 · (Edited)
Annoyed now that I think I tossed a dual stator because the small wire circuit had a break in it. I have a friend who has an Ariens with electric PTO and he's having problems keeping the battery charged. It has just the dual on it . It's a replacement engine that I put on it but the original was only a dual as well. Where in Ottawa is the copper wire a good price? I am not having any luck finding a 621 or 627 blower to throw on one of by 600 series MTDs.
 
#6 · (Edited)
I'm not entirely sure. The last time I purchased any, was online long ago. I have heard you can try phoning up a starter/motor/alternator repair business and asking them for a price on x gauge by x length. They may yank some off their spools for a decent price. If that doesn't work, there's active electronics and gervais electronics. But then you're paying retail.
Don't feel too bad for throwing it out, it's not expensive to replace used. This is more for someone who enjoys tinkering and trying something new. If we kept everything we "thought" we may need, we'd all be hoarders. :fing32:
 
#7 ·
...... If we kept everything we "thought" we may need, we'd all be hoarders. :fing32:
Shush, don't let my wife hear that. She didn't hear friend at supper last week saying his b-in-law had a mower for me.
I have found wire online. Some seems to be artist or craft copper and some noted as soft. Is soft better for making the windings? I was looking at the briggs alternator stuff. The tri-circuit produces AC on one wire so I assume like the dual, one end of wire is attached to the stator frame. And there is a one wire in/one wire out regulator for that. I have a used one of those regulators.
 
#9 ·
Keep in mind you'd be looking for a particular type of wire commonly called magnet wire, or enamel wire. It's far more rare to find and is very specific to winding motors, transformers, alternators, etc... You will not find this at most major retails stores as the demand is just not a money maker for them. All the other electrical wire is not the same.
The magnet wire actually looks like it's bare copper, but it has a very thin but pliable and strong jacket that allows it to be wrapped all around itself in the many circles without just direct shorting the electricity across itself. Since we know copper is a good conductor, making sure our windings are not shorting against each other is important...

Back to when I was winding the stator: At the start and end of this wire, I have to carefully but aggressively scrape the coating off to get down to the copper for my crimp connectors to make proper continuity.

You can get very specific with the type of magnet wire for this job. On many DIY stator rewinds, they involve stators that are based within the engine crankcase of an ATV, dirtbike, or streetbike. It can get quite hot in these areas, and engine oils, or old acidic oil can break down a stator much faster with one that wasn't built with the proper materials.

Fortunately with the mowers, we're sitting elevated on top of the engine away from any excessive heat and oils (provided the top seal is in decent shape).
 
#11 ·
I like your tenacity! <-- Not sure that fits, perseverance may be better. What the heck, subscribed to follow this.
 
#13 ·
I just re-read my initial thread and thought I'd try and fix some of my many errors. I was actually blown away by how many grammatical and spelling errors there is. I'll quote some of the major ones.

For the way would my stator.
"For the way I wound my stator.

I decided to try and re-invent the wheel
I decided NOT to try and re-invent the wheel
:fing20:


On another note,
I just found an old 12v cigarette lighter heater in my garage. It clearly says it's 10amps. Since my amperage testing on the shunt didn't pan out the way I wanted, I'm going to temporarily attach this to the tractor to get an idea of how many amps I'm getting.

Another tip I wanted to mention, When finally getting the flywheel to crack loose, you need to be extremely careful in how you remove and put it back on. Picture the magnets like they're fragile pieces of glass. I chipped my magnets in a couple of places when the flywheel went slightly sideways putting it on/taking it off. It needs to come off very straight and go on very straight with lots of care. Make sure everything is very clean so that no debris can be spun around and damage the magnets or stator. :tango_face_wink:
 
#15 ·
I just re-read my initial thread and thought I'd try and fix some of my many errors. I was actually blown away by how many grammatical and spelling errors there is. I'll quote some of the major ones.



"For the way I wound my stator.



I decided NOT to try and re-invent the wheel
:fing20:


On another note,
I just found an old 12v cigarette lighter heater in my garage. It clearly says it's 10amps. Since my amperage testing on the shunt didn't pan out the way I wanted, I'm going to temporarily attach this to the tractor to get an idea of how many amps I'm getting.

Another tip I wanted to mention, When finally getting the flywheel to crack loose, you need to be extremely careful in how you remove and put it back on. Picture the magnets like they're fragile pieces of glass. I chipped my magnets in a couple of places when the flywheel went slightly sideways putting it on/taking it off. It needs to come off very straight and go on very straight with lots of care. Make sure everything is very clean so that no debris can be spun around and damage the magnets or stator. :tango_face_wink:
for about 90 minutes after a guy makes a post here on MTF.. there is an 'EDIT' feature that u can use to make corrections to what u just posted.. I've used that a lot in the past & still had some mistrakes later..
 
#20 ·
I have the same stator like yours. My copper wire has burned out, and I have to rewind it. The thickness of the wire is 0.95mm with insulation. I have a transformer with a 0.80mm thick wire, can I use that wire? What happens to the voltage then? One coil has 24 windings.
 
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