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[DPRG] thermal glue

Subject: [DPRG] thermal glue
From: Daryl Gallatin dgall723 at mail.dal.devry.edu
Date: Mon Dec 23 14:35:01 CST 2002

Ok I will try that

The 50hz PWM may be a problem too, like it has been suggested.

I thought the motor was turning, when in fact it wasn't
It was on, but not turning and the voltage ion both nputs on the motor were approxiametly .25 volts. Like it was locked.

I have tested it without PWM and just had a 1 to the enable pins, that turned the motors(very fast) but it still got hot.

SO I need to use a freq between 500hz and 5k?

I had read that using it in the hearing range can cause the motor to hum

My H0bridge, and opto isolators are wire wrapped. Is therea way to use this ground plate?

I do not have specs on the motors. I picked them up at tanners to use as test motors.


>>> "rljordan" <rljordan at airmail.net> 12/22/02 09:33 AM >>>

Try to run the motor from the HBridge directly, with no CPU control.
If you can't get the HBridge to run the motor that way, the CPU and
PWM will not run it either.

Second, IF you are running locked antiphase with the CPU, 50% duty
would have the motor locked so it would not turn. This is the highest
load your would typically put on the HBridge.

Third, If the motor is being PWMed at the correct frequency, the
heat and power will be lowest. I was driving a cheap 12 VDC motor
at a PWM frequency that was very ineffecient for that motor. When
I changed the freq, the motor turned OK. I had to get a better motor
to use the smaller HBridge, or a much more powerful HBridge, due to the
losses in the cheap motor

Hope this helps.

Bob Jordan

-----Original Message-----
>From: dprglist-admin at dprg.org [mailto:dprglist-admin at dprg.org]On Behalf
Of David Peterson
Sent: Saturday, December 21, 2002 3:02 PM
To: Daryl Gallatin; DPRGlist at dprg.org
Subject: Re: [DPRG] thermal glue

Hey Daryl,
  One thing to consider, is that at a 50 Hz rate you are pulsing your
motors at, may be a constant stall condition, upping the amount of current
trying to go through the motor and h-bridge. This wouldn't seem to be above
the electrical time constant of the motor, and maybe not even over its
mechanical time constant, so your motor may always be trying to go-coast,
go-coast from near low speed current draw, or forward-reverse,
forward-reverse at low speed if trying to drive in locked-antiphase mode..
If you are trying PWM to control speed, might try a significantly higher
frequency to smooth things out a bit. Have any specs about that 6 volt motor
you are trying to drive?

----- Original Message -----
>From: "Daryl Gallatin" <dgall723 at mail.dal.devry.edu>
To: <DPRGlist at dprg.org>
Sent: Friday, December 20, 2002 6:58 PM
Subject: Re: [DPRG] thermal glue

> ok , cool. :)
> This so called "snap-on" heat sink I also got doesn't work as advertised.
> >>> MIKE DODSON <MDODSON at MA.ATTBBS.COM> 12/20/02 16:02 PM >>>
> I use  OMEGABOND 101. I will give you some.  You can look up the  specs
> Mike Dodson
> Daryl Gallatin wrote:
> >Will this thermal glue work for a glue on Heat sink for the TI SN754410
H-Bridge driver. Darn thing   overheats in about 30 secs with only small 6V
DC motors
> >and I'm pulsing the motors at 50hz
> >
> >
> >http://www.1coolpc.com/adhesive.htm
> >
> >
> >Mouser, Jameco  and digikey don't seem to sell the glue, though they do
sell the glue on heatsink.
> >Neither does radioshack
> >
> >I also have a snap on heatsink, but its not as easy to get on. Looks like
the snap may end up touching all the pins
> >
> >
> >Thanks
> >
> >DAryl
> >_______________________________________________
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> >
> >
> >
> >
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