Searching \ for '[PIC]: Mosfet speed control of 12V DC motor' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/power/batterys.htm?key=12v
Search entire site for: 'Mosfet speed control of 12V DC motor'.

Exact match. Not showing close matches.
PICList Thread
'[PIC]: Mosfet speed control of 12V DC motor'
2001\10\08@093301 by Gary Neal

flavicon
face
Guys,

       I've been trying forever to get a speed control circuit to work for
driving a 12V DC motor from a battery using MOSFETS.  So far all I've
managed to do is blow stuff up.  Here's what I'm trying.
       Using single 12V battery to try to drive DC motor with ~30A max current
using 3 IRLZ44N mosfets in parallel and controlling them with a
PIC16F870.  Have mosfets on huge heat sink (even though they haven't run
long enough yet to get hot).
       Using an LM7805 to get +5V for the PIC.  Have caps on both input and
output of 7805.  Source of mosfets is tied directly to ground.  Drain goes
through motor then to +12v.  PIC outputs PWM signal to gate of
mosfets.  Have 220 ohm resistor in series with this PWM signal and have a
22kohm pulldown resistor to ground on this line.
       Everything works fine with motor disconnected.  Get good switching of
mosfets.  But, when the motor is connected things get all screwed up.  When
I try to adjust the duty cycle, it basically shuts down the PIC.  Have to
disconnect power and reconnect before it will start again.
       I put oscope on the +5v bus.  It swings quite a bit when the mosfets
switch on/off.  I'm guessing the PIC is going into brownout or something
like that.
       Does anyone have a simple solution to this problem?  Or, a fairly simple
drive circuit that will accomplish what I want.  I've searched the net and
can't find a good example.

TIA,

Gary Neal

--
http://www.piclist.com hint: To leave the PICList
spam_OUTpiclist-unsubscribe-requestTakeThisOuTspammitvma.mit.edu


2001\10\08@101130 by Chris Carr

flavicon
face
This crops up about every month on this list. Look in
the Archives for Driving Mosfets.

Basically you are only applying a 5 volt drive to the MOSFET Gate and this
is not sufficient to turn them fully on (Look at graphs in the Datasheets).
Put a transistor buffer between the
PIC output and the MOSFETS so the Gates are driven by 12 volts.

Chris Carr

{Original Message removed}

2001\10\08@103619 by Spehro Pefhany

picon face
At 09:21 AM 10/8/01 -0400, you wrote:
>Guys,
>
>        I've been trying forever to get a speed control circuit to work for
>driving a 12V DC motor from a battery using MOSFETS.  So far all I've
>managed to do is blow stuff up.  Here's what I'm trying.
>        Using single 12V battery to try to drive DC motor with ~30A max
current
{Quote hidden}

Where's the current from the motor inductance going?  Have you a Schottky
diode across the motor or are you using an active circuit? Or.... ?

Best regards,
Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam@spam@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
     /.-.\
    (( * ))
     \\ //     Please help if you can:
      \\\      dailynews.yahoo.com/fc/US/Emergency_Information/
     //\\\
    /// \\\
    \/   \/

--
http://www.piclist.com hint: To leave the PICList
piclist-unsubscribe-requestspamKILLspammitvma.mit.edu


2001\10\08@104657 by Quentin

flavicon
face
The IRLZ44N's are logic gate inputs, Full on @ 5V.
My bet is Gary's problem might be the way he connects up the three
Mosfets in parallel.
Sorry, Gary, got no answer for you. Tried it ones, blew up the Mosfets
and then decided in a split second the project (hobby) was not important
enough to search an answer for and left it at that.
:)
Quentin

Chris Carr wrote:
{Quote hidden}

--
http://www.piclist.com hint: To leave the PICList
.....piclist-unsubscribe-requestKILLspamspam.....mitvma.mit.edu


2001\10\08@105325 by Allen Mahurin

picon face
Sounds like your motors are bogging down your battery
(your power supply's not "beefy" enough).  There may
be other factors as well, but my first suggestion
would be to try using a different supply for the PIC
(isolate the supplies between the PIC and the motors).
At the very least, this would tell you if it is a
brown-out problem or not.

Good luck,

ATM


--- Gary Neal <EraseMEgln103spam_OUTspamTakeThisOuTMAIL.PSU.EDU> wrote:
{Quote hidden}

__________________________________________________
Do You Yahoo!?
NEW from Yahoo! GeoCities - quick and easy web site hosting, just $8.95/month.
http://geocities.yahoo.com/ps/info1

--
http://www.piclist.com hint: To leave the PICList
@spam@piclist-unsubscribe-requestKILLspamspammitvma.mit.edu


2001\10\08@113339 by Bob Blick

face
flavicon
face
Hi Gary,

I notice you didn't say you were using freewheel diodes(in parallel with
motor).

They should be fast rectifiers rated for at least as much current as your
MOSFETs. The heat dissipation will be as high or higher than your MOSFETs,
so you must heatsink them. With the low voltages you are using, you can
probably use schottky rectifiers and that will cut the heat in half, but
it will still be substantial.

You must have them. That's why parts are dying now.

Cheers,

Bob

--
http://www.piclist.com hint: To leave the PICList
KILLspampiclist-unsubscribe-requestKILLspamspammitvma.mit.edu


2001\10\08@120558 by Olin Lathrop

face picon face
>         Everything works fine with motor disconnected.  Get good switching
of
> mosfets.  But, when the motor is connected things get all screwed up.
When
> I try to adjust the duty cycle, it basically shuts down the PIC.  Have to
> disconnect power and reconnect before it will start again.
>         I put oscope on the +5v bus.  It swings quite a bit when the
mosfets
> switch on/off.  I'm guessing the PIC is going into brownout or something
> like that.
>         Does anyone have a simple solution to this problem?  Or, a fairly
simple
> drive circuit that will accomplish what I want.  I've searched the net and
> can't find a good example.

High speed switching of 30A requires lots of careful attention.  Think very
carfully about the full path the 30A will take and make sure the PIC is well
isolated from it.  A single common ground plane is not enough.  You want the
ground isolated except at one common point.  You may also want to put a
diode in series with the 5V regulator input, with the cap on the regulator
side of the diode.  This will prevent short term droops in the 12V supply
from collapsing the 5V supply.  Also try to eliminate spikes as close to the
motor as possible.  You do have the right kind of flyback diodes accross the
motor, right?  I haven't looked up the FET you are using, but it can go to
full on with 5V gate drive?  For this kind of power, I'd rather use a FET
that might need 10V but has lower on resistance.  Of course that requires
a FET driver circuit, but you've got 12V available so that's not a big deal.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, RemoveMEolinTakeThisOuTspamembedinc.com, http://www.embedinc.com

--
http://www.piclist.com hint: To leave the PICList
spamBeGonepiclist-unsubscribe-requestspamBeGonespammitvma.mit.edu


2001\10\08@121016 by Jonathan Miller

flavicon
face
----- Original Message -----
From: Gary Neal <TakeThisOuTgln103EraseMEspamspam_OUTMAIL.PSU.EDU>
To: <RemoveMEPICLISTspamTakeThisOuTMITVMA.MIT.EDU>
Sent: 08 October 2001 14:21
Subject: [PIC]: Mosfet speed control of 12V DC motor


> Guys,
>
>         I've been trying forever to get a speed control circuit to work
for
> driving a 12V DC motor from a battery using MOSFETS.  So far all I've
> managed to do is blow stuff up.  Here's what I'm trying.
>         Using single 12V battery to try to drive DC motor with ~30A max
current
> using 3 IRLZ44N mosfets in parallel and controlling them with a
> PIC16F870.  Have mosfets on huge heat sink (even though they haven't run
> long enough yet to get hot).
>         Using an LM7805 to get +5V for the PIC.  Have caps on both input
and
> output of 7805.  Source of mosfets is tied directly to ground.  Drain goes
> through motor then to +12v.  PIC outputs PWM signal to gate of
> mosfets.  Have 220 ohm resistor in series with this PWM signal and have a
> 22kohm pulldown resistor to ground on this line.
>         Everything works fine with motor disconnected.  Get good switching
of
> mosfets.  But, when the motor is connected things get all screwed up.
When
> I try to adjust the duty cycle, it basically shuts down the PIC.  Have to
> disconnect power and reconnect before it will start again.
>         I put oscope on the +5v bus.  It swings quite a bit when the
mosfets
> switch on/off.  I'm guessing the PIC is going into brownout or something
> like that.
>         Does anyone have a simple solution to this problem?  Or, a fairly
simple
> drive circuit that will accomplish what I want.  I've searched the net and
> can't find a good example.
>
> TIA,
>
> Gary Neal
>
########################

Try :

1:Check motor actually works ( straight across batt)
2: Put Schottky across motor, cathode to Positive. This should clamp voltage
to rail.

  Regards
          Jonathan





> --
> http://www.piclist.com hint: To leave the PICList
> piclist-unsubscribe-requestEraseMEspam.....mitvma.mit.edu
>
>
>

--
http://www.piclist.com hint: To leave the PICList
EraseMEpiclist-unsubscribe-requestspammitvma.mit.edu


2001\10\08@121354 by Roman Black

flavicon
face
Can you show your circuit Gary? Or mainly the PIC
psu section and the motor drive components.
-Roman

Gary Neal wrote:
{Quote hidden}

--
http://www.piclist.com hint: To leave the PICList
RemoveMEpiclist-unsubscribe-requestspam_OUTspamKILLspammitvma.mit.edu


2001\10\08@125630 by Lawrence Lile

flavicon
face
Gary,

I'd second some of the ideas already mentioned -

flyback diodes are number 1 potential problem,

tie your grounds together at a single point with a ferrite bead, separate
ground for power components, separate for digital compontnts, all running
back to a single point at your heavy power supply, and make sure no ground
loops  can inflict induced power into your digital circuitry.  You could
even justify separate supplies, keep that nasty noisy 12V completely away
from your PIC.

Consider using a mosfet driver.  A 22K pulldown resistor isn't going to turn
off your mosfets very fast at all. A 220 ohm series resistor isn't going to
turn them on very fast either (although better than 22K!)  You can cook up a
mosfet driver out of discrete transistors, or get one already built in a
chip from International Rectifier, ST, and many others.  You need to turn
these mosfets on and off very fast to minimize power dissipation, and every
time I've tried to get away without a mosfet driver I've met problems.

--Lawrence

> {Original Message removed}

2001\10\08@144234 by Spehro Pefhany

picon face
At 11:55 AM 10/8/01 -0500, you wrote:

> You need to turn
>these mosfets on and off very fast to minimize power dissipation, and every
>time I've tried to get away without a mosfet driver I've met problems.

OTOH, be careful if your driver is *too* good, the source inductance can start
to cause major transients at the 40A level. It doesn't take many nanohenries
or inches of conductor to get major (many volts) transients happening.
Consider
slowing it down deliberately to reduce RFI and such problems. Unless your PWM
is very fast it may not make much difference. A series gate resistor of
~20R per
MOSFET is not uncommon. A PIC output has an output impedance of perhaps 100R
around the threshold, so the switching will be a bit softer. Easiest MOSFET
driver is two transistors in complimentary emitter follower configuration. You
can put a resistor from input to output to get a bit more drive at DC.

Try to visualize the current flow and look at each piece of wire or conductor
over about 1/4" as an inductor, particularly if the 40A is flowing through
it.

You need a fairly decent scope to see these things happening too.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
RemoveMEspeffTakeThisOuTspamspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
     /.-.\
    (( * ))
     \\ //     Please help if you can:
      \\\      dailynews.yahoo.com/fc/US/Emergency_Information/
     //\\\
    /// \\\
    \/   \/

--
http://www.piclist.com hint: To leave the PICList
EraseMEpiclist-unsubscribe-requestspamspamspamBeGonemitvma.mit.edu


2001\10\09@031424 by Vasile Surducan

flavicon
face
Gary, if nothing works about other piclisters where saying then:

- use a large capacitor value near mosfet stage from V+ to gnd.
- of course diodes are required closely to motor coil and not far away
 from it
- use a carefully printed board at 30A
- use small resistors in mosfet sources to equalise the current flow
- +5V must be supplied with a separate circuit ( 7805) directly from
battery

Vasile


On Mon, 8 Oct 2001, Gary Neal wrote:

{Quote hidden}

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


More... (looser matching)
- Last day of these posts
- In 2001 , 2002 only
- Today
- New search...