MGB VOLTAGE STABILIZER
- Wray Lemke

As of:  18 April  2006 


Knocking together the stabilizer.

        Rick Astleyís SOL website has an excellent stabilizer replacement page. In fact, his whole website is excellent and Iím in awe of his ability to explain things so well.  As you may know, this ainít my idea.  I didnít even know there was a ďstabilizerĒ until I went to his site.  My contribution is some construction hints and finding the Texas Instruments 10 vdc fixed regulator which makes this a breeze. Refer to his picture and description at:

http://www.mgcars.org.uk/electrical/replacement.html  

Some notes on soldering:

        Soldering ainít neurosurgery, so donít let it intimidate you. Itís not exactly like welding but close enough.  The idea is to heat the part and apply the solder pretty much at the same time.  When done right, the solder will flow onto the part or into the stranded wire.  Practice tinning (pre-soldering) some bare wire beforehand if you want to get comfortable.  You want the part to be heated as it comes into contact with the solder.

        Since I donít have three hands (canít speak for the rest of yaíll) hereís how we do it:  I take the roll of solder and unreel about 4Ē.  Then set the roll on itís side so it stands up with the unreeled solder sticking out.  This makes a convenient stand.  Take the iron in one hand and the wire in the other.  Position the wire right up at the solder, then bring the iron up to the wire.  Use the iron to guide the wire into the solder.  It will heat the wire just as itís getting to the solder and presto, the solder flows into the wire.  The instant it flows, remove the wire from the heat so the insulation doesnít start melting.

        The same method is used to tin the  regulator pins except this time you make the regulator stationary and bring the solder and iron to the pin.  Use some method of hold the regulator steady.  Even vise grips will work.  Gently clamp the regulatorís metal tab into the vise grips with the pins sticking up.  Donít clamp the plastic body!  Any method of making sure the regulator doesnít move around while your trying to solder it will work.  Tin the two pins just like you did the wire.  The solder should flow onto the pins.

The easy way first:

        As per Rickís page, you can simply solder two wires to Pin 1 (input) and Pin 3 (output) and put a screw through the hole on the mounting tab and mount it to the body where the old stabilizer was.  Use a couple of pieces of 20ga stranded hook up wire.  Donít use solid wire.  Never use solid wire where there may be any vibration, always use stranded.  Hook up wire is preferred, since itís more pliable.  I used a GMA (small) in-line fuse holder from Radio Shack (270-1238)for my input wire.  The wire is the right size and the holder is nice and small.  You can tie wrap a spare fuse to the wire.  A 1-amp GMA fuse should about right.

   Step 1:  Cut two pieces of wire 3-4 ď long.  You can make this any length you want but youíll just end up with a lot of excess under the dash.  Too short and there will be stress on the regulator leads.  Cut back about ľ to 3/8Ē of insulation off both ends of the wires.  Tin the ends.  By tinning, we mean to coat the part, or lead, with solder before you solder them together.  This makes life much easier when time comes to solder the wire to the regulator pin.

Cut the pins on the regulator down to about ĺĒ in length.  Cut the center pin up close to the body.  You wonít be using it unless youíre building the really cool stabilizer.

   Step 2:  Take the heat shrink out of the package and test the sizes by sliding them over the wires.  Pick a diameter that slides easily over the wire, with a little to spare.  Set aside the pieces youíve selected.

  Step 3:  Here is where youíll solder the wire to the regulator pin.  Youíve already immobilized the regulator to keep it from moving.  Hold the pre-tinned end of the wire alongside the pin and heat them both at the same time.  The solder already on them will flow together.  Do the other pin.  Youíre done with that.  Let things cool to the touch.

   Step 4:  Cut two pieces of the heat shrink about 1-Ĺ ď long.  Slide them down the wires and over the wire/pin solder joint.  Snug is okay, tight is not.  Go to the next size up if necessary.  Check for any sharp solder edges that might poke through the heat shrink. You can gently trim them with a razor knife if needed.  At this point you can shrink the tube onto the joint by rubbing the clean tip of the iron rapidly back and forth over the shrink.  Donít run it over the wire insulation, it will melt it immediately.  Or, if youíre brave, you could use a Bic lighter but you need to be careful.  Pass the flame back and forth over the shrink so it doesnít stay there very long.  The idea is to heat the shrink, not barbecue it.  I have an expensive gas solder iron with a vent that shrinks it nicely.  But you can get good results without one.  When the shrink shrinks, stop heating it.

   Step 5:  Mount the completed regulator to the body.  T'were me, Iíd put it right back to where it came from since the wires from the instruments are already there.  Before you proceed further, crimp a red male push-on terminal on the input (pin 1) and a female push-on terminal on the output (pin 3).  Use a sheet metal screw, stainless preferred, with a star washer to mount the regulator through the hole in the metal tab to the car body.  Just for fun put a piece of electric tape on the car body under the area where the pins stick out of the body of the regulator to keep them from touching the body and grounding out.  Donít put the tape under the body of the regulator, it, and the metal tab, must come into good physical and electrical contact with the body.

   Step 6:  Test.  Make sure that the two leads that come from the instruments are not touching any part of the car body.  Weíre going to verify that we have things right before we hook anything up and let smoke out that we canít put back.  Take your voltmeter (you do have a voltmeter, donít you? A test light wonít do), turn on the ignition, and check to see which lead coming from the car has 12 volts.  One will, and one wonít.  Turn the ignition off.  Connect that lead to the input wire (pin 1, male push-on) of the regulator.  Turn the ignition back on and read the voltage, to ground, of the output (pin 3, female push-on).  It should be right at 10 volts.  A little either way does not matter.  Ok?  Great, hook the output wire up to the wire going to the instruments and you daí man/woman.  Pat yourself on the back for a job well done.  Wrap each push on terminal with good electric tape for insulation, tie wrap the wires so they donít move, and youíre done.  It took longer for me to write this than it takes to do it.

Wandering thoughts:

1.  Use resin core solder, not acid core.

2.  Get a voltmeter if you donít have one.  Theyíre not expensive and can find problems that a test light canít.  If you work on your own car, you should have one.  The voltmeter can tell you if your alternator is working, the ohmmeter can tell you if a bulb is bad, the uses are endless.

3.  If youíre going to do soldering, get a 35 watt iron and a cleaning sponge.  Donít use a household sponge to wipe the tip, get an soldering iron sponge.  Radio Shack has them.

4.  When confronted with wires you want to solder that are corroded, donít panic.  Many times you can make the joint work if the strands in the wires arenít rotten.  This method is used when you canít cut the wires back far enough to get to good copper.  Spread the strands out and gently, gently, scrape them with a knife blade to remove the top layer of corrosion.  Stop when you see bright copper.  Roll the strands back into a bundle and gently, gently, scrape the bundle until you see bright copper.  Dip the scrapped wire ends into some non-acid flux, and tin them.  If they tin okay then you can solder them together.  Go to the hardware store and get a little tub of Laco non-acid flux.  It will last you forever.

5.  I recommend that you use someway of protecting the IC from accidental physical damage.  It will be in a place that will probably never get bumped but it still makes be nervous to have an IC hanging out like that.  You could protect it by mounting it in a heat sink, Radio Shack P/N 276-1363 - $.99.  The sides of the heat sink  stick up enough to provide protection to the IC legs.

Parts Needed:

Texas Instruments 10vdc Fixed Voltage Regulator. Available from Digikey, http://www.Digikey.com  I donít know if theyíll ship just one.  Probably not.  I order them a dozen at the time.  They cost me 75 cents ea. plus shipping and handling.  We have an account with them.  I can mail them to whoever wants them at my cost plus S&H.

Heatshrink Radio Shack P/N 278-1627 - $1.99

Push-on terminals - local hardware or I have them.  We use a covered version.

Or, for the really cool stabilizer:

Assorted LED's Radio Shack P/N 276-1622 - $2.49

Pack 1K Ohm Resistors Radio Shack P/N 271-1321 - $.69 These are ľ-watters, kinda large for this purpose, but will do.

For you guys who want to build the really cool stabilizer:

        The technique is pretty much the same as regards the wiring for the regulator.  Where the challenge comes in is making it all fit into an old stabilizer case.  Thereís enough room and it makes a better installation.  I cut off the long edges that hold down the plastic top to the stabilizer with a Dremel tool and a cutoff wheel.  Then bend the two short edges back and lift out the old guts.  Remove everything from the plastic top and throw it into the bin with the ZS carbs.  The regulator fits just right along the side of the case.  Drill a hole through the case and mount the regulator inside after youíve wired it.  I wanted to use the original attachments for the push on terminals but they showed too much resistance so I brought my wires out through the plastic top.  I also attached a small red LED through a hole in the top.  This LED is connected to the output and ground legs of the regulator via a 1k resistor and really thin flexible wire and lights up when the regulator is working.  The soldering work is a little more delicate but not that hard to do.  Drill a small hole the size of the LED in the plastic top and push it into this hole.  Solder a 1K 1/8 watt resistor onto the long leg of the LED and one thin wire onto the other end of the resistor.  This wire goes to the output of the regulator.  Slide a piece of heat shrink over the resistor and LED leg and shrink it.  Solder the other thin wire to the shorter leg of the LED, heat shrink it, and solder to the center (ground) pin of the regulator.  Mash the legs of the LED down so they lay against the plastic top.  Keep in mind that you have to get the wires that are attached to the regulator and LED into the case so leave just enough slack that they will fold into a loop as you press the top back into place on the case.  Bend the short edges of the case back over to hold the plastic top down and crimp your push-on's to the wires.  The big advantage to this, even without the LED, is that the IC is physically protected from harm and the case can be re-installed where it was removed from. The regulator gets itís ground from the case being attached to the car body.  I cut a new piece of plastic to fit the top of the case using the old one as a template.  The old one looked like crap and the holes werenít where I wanted them.  Any piece of stiff plastic will do.  I happened to have some pieces that were dividers from a parts bin.

Note: The 1/8 watt 1K ohm resistor is no longer available from Radio Shack.  Theyíre tiny, but thatís all you need.  You can use the ľ watt resistor but theyíre bigger.  Check with a local electronic parts supply house for the 1/8 watters.  Theyíll have them.

        You can find all kinds of neat things to use the LEDs for.  Any 12 vdc project.  Just put a 1K resistor in line with the positive 12vdc to limit the current and youíve got a cool indicator light.  Eddie Petty and I are thinking of mounting some high intensity LEDs in his brass knock offs.

For you guys and girls with positive ground cars:

        Iíve found a device that will do the same thing for positive ground cars as the LM317 on Rick Astleyís website . It will give the same results as the 10 vdc TI regulator but will have to be strapped down with the resistor divider network like the LM317 in order to give you 10 vdc out.  Putting it into an old case would be a lot more challenging than the 10 vdc TI regulator due to the increased parts needed, but Iím working on an alternative, maybe using Chuckís idea of an Altoid box.  As soon as I decide on the easiest way to build one, Iíll post it.  Rickís mounting idea using the heat sink is probably the way to go.

        The LM317 and itís negative output cousin the LM2991 are variable output voltage regulators. You have to tell them what voltage you want by using the equation:

Vout = Vref (1 + R2/R1) + Iadj(R2)  for the positive regulator.

Vout = Vref (1 + R2/R1) - Iadj(R2) for the negative regulator.

Vref = 1.21 or -1.21 depending.

        This gives you the two values of resistor to use to get 10 vdc out.  It will put out 10 vdc as long as the voltage is higher (or lower in the negative version) than 10 vdc + 1.21 volts.  The input can take voltages up to about 25 volts or more and still put out 10 vdc.

        The TI regulator is a fixed regulator and doesnít care a fig about dividers and equations.  Feed it anything above 11.2 vdc, up to about 30 vdc, and it puts out 10 vdc.  Anything below 11.2 volts and it just shuts off.  Cool, huh?

        Please let me know if you have ideas that are better than these or if Iíve made a mistake.  Iíll use someone elseís hard earned experience in a skinny minute.  We can all figure this stuff out, but if someone else already has, then give him credit and use the knowledge.  Just because a strong man can left a heavy weight doesnít mean heís anxious to do it all the time.  

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