RE: [CAD_CAM_EDM_DRO] L297/L298 board concern

Vref sets the current for the chopper. The driver turns on, when the
voltage across the sense resistor reaches Vref, the current is turned
off. It stays off until the next oscillator cycle, when the whole
process starts over.

Sounds like your board has a circuit to lower Vref when there is no
activity for awhile, but Vref is definitely used when the motors are in
use.

My sense resistors are 0.5 ohms, so I set Vref to half the current I
want (0.750 volts on Vref = 1.5A on the motors.)

Regards,
JJ

Be Kind, Be Careful, Be Yourself

> -----Original Message-----
> From: Rose, Gary [mailto:Gary.Rose@...]
> Sent: Friday, November 15, 2002 8:47 AM
> To: 'CAD_CAM_EDM_DRO@yahoogroups.com'
> 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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> > this to be a
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> are there,
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> > http://groups.yahoo.com/group/jobshophomeshop I consider
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>
> OFF Topic POSTS: General Machining
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> to reach it if you have trouble.
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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.

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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