12V Generator Problems

 

  I'm trying to build a 12V generator using plans from the following page:
http://www.homepower.com/files/mark8.pdf
  However it seems that the schematic for the electronic field regulator is
flawed. I cannot get it to function at all, and I suspect that some errors
have been made in the schematic. First of all, the output of the LM723
should be pin 10, not pin 9 as the schematic states. Second, isn't the LM555
supposed to be a timer chip and not a regulator?? Perhaps it was supposed to
be an op-amp or something.
  Has anyone else tried to build this thing, and can perhaps give me some
advice?
  Any help would be much appreciated.

 

The LM555 is used a s a PWM controller.  It uses the LM723 pin 9 (whis is a
Zener connected to pin 10) to drive the internal LM555
opamp. Vz appears to be the anode of a 6.2v zener connected to Vout.

Check your wiring. What in the voltage at pin 9? Do you see pulses at pin 3 of
the 555?

Cheers

 



I do not have datasheets at hand for the two parts in question.
But note that the pinning of the device will vary according to
its packaging.  Today it is not unusual to find the same device
available in several package styles and each package has a different
pinout.  It's rather annoying that the schimatic doesn't denote
package style nor does it have reference desigantors for the parts.

That said...

The 555 is indead a timer.  It is used here as an astable multivibrator.
It's uotput is (as beat I can tell) a constant frequency.  But the
duty cycle (ratio of high and low times) is variable.  The 555 by
it's self determines the constant current charge charge rate.  The
LM723 monitors system voltage and when it gets too high it reduces
the charge current by pulling the control input to the 555.  By
pulling the control input it reduses the pulse width duty cycle
and if need be, completly turn it off.

To bench test this circuit, connect a battery to the input terminals
and a automobile tail light bulb to the output.  If you have a meter,
that would be good too.  disconnect the wire from the output of the
LM273 that goes to the LM555.  This allows the 555 to run without
interfearence from the LM273.  Once you get the 555 part of the
circuit working, reconnect the LM273 and work on debugging that
part of the circuit.

 

  That makes a bit more sense. I didn't realize the 555 output was pulsed,
maybe that's why I got so confused. I have a scope I will use to do some
more precise troubleshooting.
  One more question; the PNP transistor I'm using (the big one on a
heatsink) seems a bit strange. When testing with an ohmetter (actually the
diode check function of a DMM) it appears that there is a damper diode from
collector to emitter. I checked half a dozen identical transistors and got
the same results. The transistor shown in the plans doesn't suggest it has
any built-in diodes. Might my transistor be the wrong type for this? (it
crosses to an NTE 104)
  Thanks again.

 

The NTE104 should be fine, There is no CE diode in that part. And it would not
affect the circuit.
Make sure your are using a 2N2222A for Q1, or a transistor with an Ic rating of

(beta is ~100).

You'll need a Mica Insulator for the 295.

Pin 4 of the NE555 is the reset, so the 1k pot on the LM723 must be for the High
voltage limit. He could have used a opamp or
comparator.
The 50k pot on the NE555 is the Charging current.

It looks like under low voltage the NE555 output is a square wave with a duty
cycle dependant on the 50k pot..
Once the voltage gets to the High limit the NE555 is forced into reset.

The Author either didnt know how the circuit worked or the publisher left out
the details on how the circuit works.

Cheers