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'[OT] 180mA to300mA circuit'
2000\04\20@065527 by Graham North

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Hi

One of my friends works on a tree harvester and asked me to make
him a circuit with a 24V output with constant adjustable current between
180mA and 300mA to control a solenoid.  He would like to control the circuit
with a pot.

I do have an idea how to do it, but thought I would ask the experts.

BTW the harvester uses a 24 V battery, so it is only a matter of controlling
the current.

Thanks

Graham

2000\04\20@103851 by Arthur

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pic with ladder output driving buffer amp or d/a amp to control a Fet or
Transistor emmiter follower ctt.

Art
{Original Message removed}

2000\04\20@120417 by Chris Eddy

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Arthur;
This surely will work, but at what cost?  Let's say worst case there is a
short circuit and 300mA.  The pass transistor must consume 24*.3 or 7.2W.  I
am sure there is a safer way.

One could use a PWM circuit.  Setup a Pchannel Mosfet to drive +24 to the
load.  Bring the load back through a sense resistor, say 1 ohm.
(0.3*0.3*10=reasonable).  Now add an opamp to drive the FET (possibly through
a buffer to drive gate capacitance).  Tie one input of the opamp to the
feedback resistor.  Drive the other input from the pot, divided down to match
the range of the feedback signal (0-3000mV).  This circuit would normally run
linear, and give the same results as the original idea.  ( if the opamp output
slams to a rail, the inputs are backwards)  Now add an R and C in the current
sense feedback path.  The opamp will break into oscillation.  The circuit will
now modulate around the target setpoint, and the FET will be driven on and
off.  The circuit will (assuming no parts fail) limit current even during a
short circuit of the load.

Chris Eddy

Arthur wrote:

> pic with ladder output driving buffer amp or d/a amp to control a Fet or
> Transistor emmiter follower ctt.
>
> Art
> {Original Message removed}

2000\04\20@143140 by Arthur

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The circiut i have in mind would moniter and close down if short ciriut or
over current
will do a circiut and post need to install some software first but will post
Saturday at latest.this will also include a spelling checker.
Besides the pic I see opamp a few resistors  a pot and two transistors
I am waiting for my new provider to give me details for my web site and when
he does it will make posting easyer.

{Original Message removed}

2000\04\21@072428 by Graham North

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If you could post the circuit then that would be great.

Thanks

Graham

       ----------
       From:  Arthur [SMTP:spam_OUTartbTakeThisOuTspamCABLEINET.CO.UK]
       Sent:  20 April 2000 19:28
       To:  .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
       Subject:  Re: [OT] 180mA to300mA circuit

       The circiut i have in mind would moniter and close down if short
ciriut or
       over current
       will do a circiut and post need to install some software first but
will post
       Saturday at latest.this will also include a spelling checker.
       Besides the pic I see opamp a few resistors  a pot and two
transistors
       I am waiting for my new provider to give me details for my web site
and when
       he does it will make posting easyer.

       {Original Message removed}

2000\04\21@081857 by Jinx

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The list helped me out a couple of weeks ago with a constant current
charger for a bank of large-ish caps that worked very well. It was simply
an LM317T.

24V to In, resistor between Adjust and Out, the output being taken from
the Adjust terminal. The 317T is rated for 37V in and 1.5A out with a
voltage drop stated as 3V, but I found it settled to 1.2V. If you're using
a nominal 24V battery (which could be > 27V when charged) would this
drop-out matter ? Should be OK for a solenoid. BTW, why use variable
current - is it a valve of some sort ?

If you try it, the current out is determined by 1.2/R, where R is in ohms.
So for 150mA it would be 8 ohms, for 300mA 4 ohms. A 1/4W 10 ohm
pot with 3R9 resistor in series would do.


{Quote hidden}

2000\04\21@085644 by Graham North

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This seems very simple, and so just the job!

Thanks I will give it a try.

Graham

       ----------
       From:  Jinx [SMTP:.....joecolquittKILLspamspam.....CLEAR.NET.NZ]
       Sent:  21 April 2000 13:08
       To:  EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU
       Subject:  Re: [OT] 180mA to300mA circuit

       The list helped me out a couple of weeks ago with a constant current
       charger for a bank of large-ish caps that worked very well. It was
simply
       an LM317T.

       24V to In, resistor between Adjust and Out, the output being taken
from
       the Adjust terminal. The 317T is rated for 37V in and 1.5A out with
a
       voltage drop stated as 3V, but I found it settled to 1.2V. If you're
using
       a nominal 24V battery (which could be > 27V when charged) would this
       drop-out matter ? Should be OK for a solenoid. BTW, why use variable
       current - is it a valve of some sort ?

       If you try it, the current out is determined by 1.2/R, where R is in
ohms.
       So for 150mA it would be 8 ohms, for 300mA 4 ohms. A 1/4W 10 ohm
       pot with 3R9 resistor in series would do.


       > From: Graham North <graham.northspamspam_OUTLANDINST.COM>

       > Hi
       >
       > One of my friends works on a tree harvester and asked me to make
       > him a circuit with a 24V output with constant adjustable current
       > between 180mA and 300mA to control a solenoid.  He would like to
       > control the circuit with a pot.
       >
       > I do have an idea how to do it, but thought I would ask the
experts.
       >
       > BTW the harvester uses a 24 V battery, so it is only a matter of
       > controlling the current.
       >
       > Thanks
       >
       > Graham

2000\04\21@112624 by tcrist

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OK,  Here's my two cents...

24V----|----|----------|
      |    | LM317    |    ------------    ------------
     ---   | TO-3     |---| 4ohm 1/2 W |--| 10 ohm POT |---- Iout
  1uf---   |----------|    ------------    ------------   |
      |         |                                         |
     ---         -----------------------------------------
      -
Iout ~= 1.25/(4+R(POT))
Iout ~= 300mA when R(POT) = 0
Note the 4 ohm is use to limit max current when the POT approaches the zero
resistance stop.  7.2 Watts when max current is applied to an output short.
The TO-3 LM317 will have no problem handling this power @ 3 C/W theta JC
(Unless, of course, you are shredding trees at an ambient of greater than
130C).

<facious comment please disregard> Remember to use a PIC16C72A running a PWM
@  10% D.C. to illuminate an LED to show that this circuit is ON.  This is,
after all, the PICLIST.

Tim Crist

{Original Message removed}

2000\04\25@235102 by Gennette, Bruce

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If you don't mind wasting a little power you can do it the 'brute force'
way.
You will need a 10 Amp switch, a 10 W, 47 Ohm resistor and a 10W, 100 Ohm
wire wound pot.  Set the whole lot up in series with the battery and
solenoid.

By the way, a 24 volt system is actually at 27.6 volts while the engine is
running.

       Switch        47R          100R Pot
         ____
Bat+ ----/   -------/\/\/\/\-----/\/\/\/\/\/\/\
                                     /\        Solenoid
                                      |       _  _  _  _
                                      \------/ \/ \/ \/ \--\
                                                           |
Bat- -------------------------------------------------------/

As usual use a fixed width font (like courier) to view the ASCII diagram
undistorted.

With the pot pick up arm at the right (full resistance in circuit) there
should be about 180mA through the solenoid  -- 27.6V / 150R = 184mA
With the pot pick up arm at the left (min resistance in circuit) there
should be about 550mA through the solenoid  -- 27.6V / 50R = 552mA

Bye.

       {Original Message removed}

2000\04\26@034016 by Graham North

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Sorry to be a pain.

I have found a LM317, in a T0220 package but cannot find a pin out for it.

The only pin out I can find is for a T018 package.

If you know the pin out could you let me know it please.

Thanks

Graham

2000\04\26@043658 by Arthur

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Graham
heatsink down pins toward you pin1 is left name of pin :=ADJ[1]
pin 2 := Vout [commom to heatsink]
pin 3 :=Vin

hope this helps
Art

----- Original Message -----
From: Graham North <@spam@graham.northKILLspamspamLANDINST.COM>
To: <KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU>
Sent: Wednesday, April 26, 2000 8:37 AM
Subject: Re: [OT] 180mA to300mA circuit


{Quote hidden}

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