I need a sharp eyed Critique

[Glenn Ashmore]

I think I have finished the design for my watermaker control but I need
a second eye. I have looked at this thing until I can't be critical any
more. I can etch and bake SMT boards at home until I get it right but
this is a PTH and I am not going to drill all those holes so it has to
go to a board house.

I have put the schematic up on my web site with links to a BMP copy for
printing, my notes on how it is supposed to work and links to the
relivent datasheets. http://www.rutuonline.com/html/temp.html

I would sure appreciate some feedback before I send off the Gerbers.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[Boris Mohar]

I think I have finished the design for my watermaker control but I need
a second eye. I have looked at this thing until I can't be critical any
more. I can etch and bake SMT boards at home until I get it right but
this is a PTH and I am not going to drill all those holes so it has to
go to a board house.

I have put the schematic up on my web site with links to a BMP copy for
printing, my notes on how it is supposed to work and links to the
relivent datasheets. http://www.rutuonline.com/html/temp.html

I would sure appreciate some feedback before I send off the Gerbers.

Pin 4 of IC3 will never get much about 0.7 or so volts. How much current
will this dump through BE of Q1 do not know but IC2A will never change
state.

Similar overdrive is demanded from IC2D.

I did not dwell too much on the rest so I am sorry if I missed some clever
subtlety.




Regards,

Boris Mohar

Got Knock? - see:
Viatrack Printed Circuit Designs http://www3.sympatico.ca/borism/

void _-void-_ in the obvious place

 

[John Larkin]

I think I have finished the design for my watermaker control but I need
a second eye. I have looked at this thing until I can't be critical any
more. I can etch and bake SMT boards at home until I get it right but
this is a PTH and I am not going to drill all those holes so it has to
go to a board house.

I have put the schematic up on my web site with links to a BMP copy for
printing, my notes on how it is supposed to work and links to the
relivent datasheets. http://www.rutuonline.com/html/temp.html

I would sure appreciate some feedback before I send off the Gerbers.

Looks to me that the 741 is running pretty low on its common-mode
range, and that T1 (should actually be "Q1"... T means Transformer)
can never turn off no matter what the 741 does.

This whole thing is complex, so I'm not about to try to analyze its
functionality, except to say that it looks sort of like clasic
asynchronous spaghetti logic. Microprocessors are ideal for this sort
of thing, especially because you can alter their software any number
of times without making traces fall off boards.

Watch out for noise glitches from the 120v relay stuff getting into
the logic.

John

 

[Glenn Ashmore]

Looks to me that the 741 is running pretty low on its common-mode
range, and that T1 (should actually be "Q1"... T means Transformer)
can never turn off no matter what the 741 does.

That particular section was picked up whole from an existing circuit but
I better try and go back over it again.

This whole thing is complex, so I'm not about to try to analyze its
functionality, except to say that it looks sort of like clasic
asynchronous spaghetti logic. Microprocessors are ideal for this sort
of thing, especially because you can alter their software any number
of times without making traces fall off boards.

I wish. But this thing has to be repairable or at least made usable in
the Galapagos or South Georgia Island with bailing wire and gum. That
is why I stayed analog.

Watch out for noise glitches from the 120v relay stuff getting into
the logic.

I am trying to isolate the 120V in the board layout.

Thanks for looking.

John

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[Stefan Heinzmann]

I think I have finished the design for my watermaker control but I need
a second eye. I have looked at this thing until I can't be critical any
more. I can etch and bake SMT boards at home until I get it right but
this is a PTH and I am not going to drill all those holes so it has to
go to a board house.

I have put the schematic up on my web site with links to a BMP copy for
printing, my notes on how it is supposed to work and links to the
relivent datasheets. http://www.rutuonline.com/html/temp.html

I would sure appreciate some feedback before I send off the Gerbers.

You describe that the system operate on the 12V DC from a ship's
alternator/battery. Yet you use a 12V regulator (7812) to produce a
regulated 12V supply. That won't work. The 7812 needs 2V dropout at the
very least. Furthermore, although I don't know much about ships, isn't
the electrical supply on a ship very much like car supplies? I mean with
all the trouble from reversed batteries, load dumps, etc.: The supply
from hell? With that in mind I dare say that your circuit will not be
able to stand up.

 

[Glenn Ashmore]

You describe that the system operate on the 12V DC from a ship's
alternator/battery. Yet you use a 12V regulator (7812) to produce a
regulated 12V supply. That won't work. The 7812 needs 2V dropout at the
very least. Furthermore, although I don't know much about ships, isn't
the electrical supply on a ship very much like car supplies? I mean with
all the trouble from reversed batteries, load dumps, etc.: The supply
from hell? With that in mind I dare say that your circuit will not be
able to stand up.

The system will be operating while the diesel is running so the supply
voltage will be 13.5 to 13.9V. I tried to size things so I will get
acceptable results between 11.5 and 12V.

You are correct about dirty power. A boat system is much worse than an
automobile because of all the devices running off the batteries. Would
a switcher be more appropriate or should I go off board with a separate
heavily filtered supply?

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[Glenn Ashmore]

Pin 4 of IC3 will never get much about 0.7 or so volts. How much current
will this dump through BE of Q1 do not know but IC2A will never change
state.

Similar overdrive is demanded from IC2D.

I did not dwell too much on the rest so I am sorry if I missed some clever
subtlety.

I see what you meam. Maybe I should pull them up and drian them through
pin 5 of the 2907. That would reverse the logic but swapping the
function of the two chips would solve that.

As you can see I know just enough to be dangerous.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[Stefan Heinzmann]

The system will be operating while the diesel is running so the supply
voltage will be 13.5 to 13.9V. I tried to size things so I will get
acceptable results between 11.5 and 12V.

That still rules out the 7812 as a voltage regulator. It would regulate
only above 14V input, so it is virtually useless. It would not be much
more than an overvoltage protection device. Low dropout regulators would
offer a possibility to have regulation with inputs only slightly above
12V, but no linear regulator will give you 12V output from 11.5V input.

I think it would be wise to design the circuit such that it works down
to 9V input voltage. You may have a shorted battery element, or you may
have short drops in input voltage due to other consumers being switched
on (i.e. motors), or you may have corroded or loose contacts.

Additionally, you want the regulator to survive reverse input voltage
conditions and input overvoltage up to 60V. This is what is typically
required from automotive circuits. Special regulator chips are available
for this type of application. They will be more expensive than a 7812,
however.

You are correct about dirty power. A boat system is much worse than an
automobile because of all the devices running off the batteries. Would
a switcher be more appropriate or should I go off board with a separate
heavily filtered supply?

If you really need regulated 12V for your circuit you'll need a
switcher. You may try to design your circuit for lower operating
voltages, however. This would allow linear regulators to be used, which
are much easier to design. The latter is the thing I'd try first.

 

[Leeper]

This part will handle a decent over voltage,
http://focus.ti.com/docs/prod/folders/print/tps40050.html ,
and I've seen a Linear Tech part or a Maxim part that could take 60V, don't
remember the part number.

 

[N. Thornton]

The system will be operating while the diesel is running so the supply
voltage will be 13.5 to 13.9V. I tried to size things so I will get
acceptable results between 11.5 and 12V.

You are correct about dirty power. A boat system is much worse than an
automobile because of all the devices running off the batteries. Would
a switcher be more appropriate or should I go off board with a separate
heavily filtered supply?

I havent looked at the circuit as I have to dash, but 12v lead acids
will cover the range apx 10v to 15v, and wire Vdrops will reduce the
lower end further. Having kit that only functions between 11.5v and
12v isnt going to be a lot of use.


Regards, NT

 

[Glenn Ashmore]

I have decided to go off board and use a Power One DC/DC converter that
works from 9 to 18VDC. A side benifit is that it has a remote on/off so
I can shut the whole system down from the cockpit.

Many thanks for all the suggestions. I have modified the circuit on the
breadboard and now it seems to be working stable. Next step is to add
some long control lines and blast the whole thing with some RF and
alternator noise.

I havent looked at the circuit as I have to dash, but 12v lead acids
will cover the range apx 10v to 15v, and wire Vdrops will reduce the
lower end further. Having kit that only functions between 11.5v and
12v isnt going to be a lot of use.


Regards, NT

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[GPG]

Some ideas


V+
| V+
.-. _|_
|_/_| start relay
| | |
'-' |
| o--------+
High speed -|<------o | |
| | |
low speed -|<------o \ o \ o
| relay \ \ start
oil -|<------o \. \.
| o o
pressure -|<------o |\| | |
|-----|-\ | |
stop -|<------o | >--------o--------+
+-|+/
| |/|
V+ |
| |
.-. |
| | |
| | |
'-' |
| |
o-----+
.-.
| |
| |
'-'
|
|
===
GND

LM311 will do. Note start switch will not operate if fault present.

V+

|
High speed: .-.
| |
| |
'-'
|
|
V led
-
|
pin5 o---------+---------o op



pin4 o---------+
|
GND

Low speed:

V+ V+
.-. .-.
| | | |
| | | |
'-' '-'
| |
| |
| V led
| -
| |
| o----------o out
| |
| ___ |/
pin5 o---|--|___|--|
| |>
.-. |
| | |
| | ===
'|' GND
pin4 o-----------|
=|=
GND

Pressure. Delete output transistor and resistors. Swap + and - inputs of
op amp. BTW R8 right side should have been GND

High/Low board. Delete capacitors connected to pin 4. Add ripple filter
caps to pin 3, use above outputs.
Delete IC2 and all transistors

Boost pump relay. Pin 1 should be ground, shift D3, R15 accordingly,
Add protection diode.

Backwash. Remove wire P1 to 2, wire P1 to 12V (lowers drive from 555).
If flush switch is momentary close, C7 is not needed, decrease R18 to
help prevent false trigger. Connect power up reset to ensure state at
power on.
V+
|
.-.
| |
| |
'-'
|
.--------- reset
|