RE: [CAD_CAM_EDM_DRO] L297/L298 board concern

If unconnected, the current to the motor is maxed out, that's your
problem.
Figure Vref by calculating the voltage drop across your sense resistor
at the current you want. Ie. I have 0.5 ohm resistors, and I want 1.5
amperes, so:

I x R = V
1.5 x 0.5 = 0.750

So that's what I set Vref to. I measure from ground to pin 15 on the
L297, while turning the pot I connected to it.

Regards,
JJ

Be Kind, Be Careful, Be Yourself

> -----Original Message-----
> From: Rose, Gary [mailto:Gary.Rose@...]
> Sent: Friday, November 15, 2002 9:23 AM
> To: 'CAD_CAM_EDM_DRO@yahoogroups.com'
> Subject: RE: [CAD_CAM_EDM_DRO] L297/L298 board concern
>
>
> Yes, I was just looking at the board and there's a connection
> for Vref and I
> mistakenly left it unconnected. Just out of curiosity, what
> should Vref be
> for what current? If it's unconnected, what would the current be?
>
> Thanks again guys!
>
> Gary
>
>
> > -----Original Message-----
> > From: James Cullins [mailto:jcullins@...]
> > Sent: Friday, November 15, 2002 9:03 AM
> > To: CAD_CAM_EDM_DRO@yahoogroups.com
> > Subject: Re: [CAD_CAM_EDM_DRO] L297/L298 board concern
> >
> >
> > I believe it limits the current during run as well.
> > Jim
> > ----- Original Message -----
> > From: "Rose, Gary" <Gary.Rose@...>
> > To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> > Sent: Friday, November 15, 2002 7:46 AM
> > Subject: RE: [CAD_CAM_EDM_DRO] L297/L298 board concern
> >
> >
> > > Thanks for the good information on the Vref, I'm definitely
> > going to look
> > > into it.
> > >
> > > I'm not sure if that's my problem though. I was running
> > the motor on the
> > > bench using a clock generator and a power supply. The
> > motor was turning
> > > continuously, so I don't think the Vref circuit that lowers
> > the current
> > > after 100ms would even kick in there.
> > >
> > > I'm going to try lowering it anyway and see what I get,
> > anybody got any
> > > other suggestions?
> > >
> > > Thanks
> > >
> > > Gary
> > >
> > >
> > > > -----Original Message-----
> > > > From: JJ [mailto:jj5412@...]
> > > > Sent: Friday, November 15, 2002 7:41 AM
> > > > To: CAD_CAM_EDM_DRO@yahoogroups.com
> > > > Subject: RE: [CAD_CAM_EDM_DRO] L297/L298 board concern
> > > >
> > > >
> > > > I think the suggestion that the Vref is to high is
> > probably correct. I
> > > > checked my L298s yesterday after a 4 hour run, and they were
> > > > cool, close
> > > > to ambient. I have multiwatt-15 heatsinks clipped on
> with thermal
> > > > grease, and they're in an enclosure with a 100cfm fan
> > blowing directly
> > > > on them.
> > > >
> > > > Regards,
> > > > JJ
> > > >
> > > > Be Kind, Be Careful, Be Yourself
> > > >
> > > >
> > > >
> > > > > -----Original Message-----
> > > > > From: B Snowden [mailto:bsnowde@...]
> > > > > Sent: Friday, November 15, 2002 12:46 AM
> > > > > To: CAD_CAM_EDM_DRO@yahoogroups.com
> > > > > Subject: Re: [CAD_CAM_EDM_DRO] L297/L298 board concern
> > > > >
> > > > >
> > > > > Gary,
> > > > >
> > > > > I let the smoke out of one of my L298 also awhile back. Mine
> > > > > had a heat sink on it. What I have now done, cut angle
> > > > > aluminum to 6.75 in long. I have three L298's in a row. I
> > > > > connected the aluminum
> > > > > to the heat sinks of all three L298's. So what I end up with
> > > > > is a heat sink attached to the heat sink of the three L298's.
> > > > > When I get the board installed into a case, I plan to use
> > > > > a fan to draw
> > > > > air over the L298's. By adding the extra heat sink, I
> > > > > dropped the temp from about 230+ F to around 160 - 205 F. I
> > > > > do not know what the temp was when one of them smoked. The
> > > > > fan should cool it even
> > > > > more. I think you can get by without the extra heat sink,
> > > > > but it would need to be installed in a case where a fan would
> > > > > draw air over the L298's in a proper way. The extra heat
> > > > > sink allows me to run
> > > > > outside a case, and when I do install it, it should allow me
> > > > > more margin, provided I have proper air flow.
> > > > >
> > > > > Bruce
> > > > >
> > > > >
> > > > >
> > > > > stirlinguy wrote:
> > > > >
> > > > > > Guys,
> > > > > >
> > > > > > I have a L297/L298 board that seems to be getting
> > REAL hot. It's
> > > > > > basically just the circuit from the L297 datasheet. A
> > > > > friend of mine
> > > > > > had the board made up with another order. I built it
> > a few months
> > > > > > ago, got a motor spinning (I think I was only using about
> > > > 12v supply
> > > > > > then), then put in on the shelf. I was playing
> with it today.
> > > > > >
> > > > > > When I run it, the L298 gets really hot. In fact, I
> > didn't have a
> > > > > > heatsink on it and the smoke got let out. After
> > > > replacing the L298
> > > > > > (and adding a heatsink), it seems to work OK, but
> > still gets very
> > > > > > hot. I don't want to run it too much for fear more smoke
> > > > > may ruin my
> > > > > > day.
> > > > > >
> > > > > > I am using a 24V power supply, the motor is a size 23
> > > > that is rated
> > > > > > for 3A, but should work fine with 2. It is stone cold
> > > > when running
> > > > > > at low speed from the driver. The L298 on the other hand
> > > > could cook
> > > > > > dinner.
> > > > > >
> > > > > > Anybody else have this problem? I'm not sure if
> > there's something
> > > > > > else screwy with the board, but the amount of heat I'm
> > > > getting makes
> > > > > > me wonder.
> > > > > >
> > > > > > Thanks in advance
> > > > > >
> > > > > > Gary
> > > > > >
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> > > > http://groups.yahoo.com/group/jobshophomeshop I consider
> > > > this to be a sister site to the CCED group, as many of the
> > > > same members are there, for OT subjects, that are not allowed
> > > > on the CCED list.
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> > > > EXCEPTIONS........
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> > > > List Mom
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> > > If you wish to post on unlimited OT subjects goto:
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> > to reach it if
> > you have trouble.
> > > http://www.metalworking.com/news_servers.html
> > >
> > > http://groups.yahoo.com/group/jobshophomeshop I consider
> > this to be a
> > sister site to the CCED group, as many of the same members
> > are there, for OT
> > subjects, that are not allowed on the CCED list.
> > >
> > > NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY
> > POSTING THEM.
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> > > List Owner
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> >
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> >
> > OFF Topic POSTS: General Machining
> > If you wish to post on unlimited OT subjects goto:
> > aol://5863:126/rec.crafts.metalworking or go thru Google.com
> > to reach it if you have trouble.
> > http://www.metalworking.com/news_servers.html
> >
> > http://groups.yahoo.com/group/jobshophomeshop I consider
> > this to be a sister site to the CCED group, as many of the
> > same members are there, for OT subjects, that are not allowed
> > on the CCED list.
> >
> > NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY
> > POSTING THEM. DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO
> > EXCEPTIONS........
> > bill
> > List Mom
> > List Owner
> >
> >
> >
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> >
>
> Addresses:
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> Moderator: jmelson@... timg@...
> [Moderator]
> URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO
>
> OFF Topic POSTS: General Machining
> If you wish to post on unlimited OT subjects goto:
> aol://5863:126/rec.crafts.metalworking or go thru Google.com
> to reach it if you have trouble.
> http://www.metalworking.com/news_servers.html
>

http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
sister site to the CCED group, as many of the same members are there,
for OT subjects, that are not allowed on the CCED list.

NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.
DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
bill
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