Using MOSFETs as low voltage drop diodes 99MOSFETswitch

A MOSFET can provide a very low loss switch when diodes ( even Schottky diodes ) will not do.

 

Above we see two circuits that operate as follows:  If  A is more positive than B then MOSFET Q1 will turn on and M1 ( motor1 ) will run.   If  B is more positive than A then MOSFET Q2 will turn on and M2 ( motor2 ) will run.   The designer should select MOSFETs with a low turn-on resistance and a low gate turn on voltage.  Note that these MOSFETs are being connected in the reverse fashion from what is normally expected.  This reversal is to avoid having the instrinsic MOSFET body diode cause problems.  The MOSFETs must be the N channel variety.

For low voltage turn-on  ......  less than 1 volt .....

check out    http://www.aldinc.com/ald_epadfaq.htm

Here are some possibilities to be found at DigiKey

99guspuppet

Voltage regulator for small engine

Magnet on rotating shaft moves past a coil.  The two ends of the coil are available from the small engine.  The unloaded voltage peak of the pulse is about 37 volts.

I want to make the pulses into DC using a full wave bridge ( 25 Amp , 50 V ).  I guess I could get by with a single diode if I chose to connect the coil up properly.  The LM317 is an adjustable regulator.  If I adjust the output of the LM317 to about 14V , the SCR should trigger on each pulse and feed the current into the battery until the battery reaches 14V minus the SCR trigger voltage ( Which will be about 13.3 V )

I am wondering if I could remove the fullwave.  This would require the SCR to tolerate a reverse voltage of  14V.

Repairing 1990 Miata Clutch Hydraulics Master / Slave DIY

Date of manufacture is 08 / 1989

  The top photo shows the passenger side front wheel.  

      The second photo shows the slave cylinder which is accessed by looking past the passenger side front wheel.  You cannot see the flexible hose.  You can see a hard line slave loop.  Just to the right of the hard line connection is the air bleed nipple which is covered by a light gray rubber cap.  ( I lost said cap while flailing around near the slave. )

       The 3rd photo shows the master clutch cylinder located at the driver rear side of the engine compartment.  The smaller aster clutch cylinder is behind the master brake cylinder.  You can see the hard line leave the master and go over the top of the engine at the back of the engine.

The 4th photo shows the connection between the hard line ( that runs from the master ) and the flexible hose that goes to the slave cylinder.

[  A good article about slave cylinders ==> http://www.miata.net/garage/slavecyl.html   ]

I started looking at the clutch hydraulic system because the clutch pedal started by getting soft and then after a few days ... went to the floor with no activation of the clutch.  The clutch was always engaged.  I drove about 20 miles ....  I put the shifter in first gear ;  then I started the engine ... shifted gears without the clutch ...... turned off engine when I had to stop for a light.  I only had to stop 3 times because traffic was very sparse and I was able to time the lights.

One great thing about this is that the slave cylinder is not buried inside the transmission.  Other cars bury the slave cylinder in hateful , hard to reach places.   Starting at the master, I disconnected the hard line and had an associate pump the clutch.  I had my thumb over the fluid outlet from the master.  I could feel pressure and could not hold the fluid from coming out.  I reconnected the hard line and went to where the hard line connects to a flexible hose.  I disconnected the hard line at this connection and put my thumb over the opening.  Pumping the clutch caused nothing to happen at first.  I think this meant there was air in the hard line.  Then there was pressure.  I reconnected the hard line.  I went down to the front wheel and removed the front wheel.  I loosened the air bleed at the slave which I could reach just behind the front disc brake.  I pumped the clutch a few times and re-tightened the air bleed.

2011m10d20
Now I have discovered there is a steady leak  ( a drip every 5 seconds ) from the slave.  At first I thought it was leaking from the piston assembly.  I removed the slave from the Miata.  The slave is held on by two bolts.  One is kind of hard to reach and requires a open end wrench and some contortions.  Perhaps is would be easier on a lift.  Maybe a flex coax drive would help. ....... Anyway , I got the slave out and took it apart.  I was surprised to find corrosion and a blob of gunk/dirt/  inside the piston barrel.  Perhaps the DOT3 fluid was absorbing water and that lead to corrosion.  I cleaned everything up and reassembled the slave and reinstalled the slave.  I was surprised to see the same steady drip ... it was coming from the air bleed nipple.  I tightened the nipple as much I thought safe...... The nipple still leaked.  ( I am leaving out  a lot of false moves and cursing from this story )  I created a rubber seal from some rubber I had laying around.  It was a cylinder about 5 mm in diameter and about 5 mm high.  This seemed to seal the leak.  It also made it more difficult to bleed the air from the clutch line.  Now the clutch is stiff and seems to work.  We shall see how long the clutch works.

2011m10d25    Clutch still leaks  ( takes about 24 hours )

You may contact me to ask questions at y e s    at    n o p e 9  dot com


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