DPRG
DPRG List  



[DPRG] Cheap high power H-bridge

Subject: [DPRG] Cheap high power H-bridge
From: David Peterson robologist at yahoo.com
Date: Tue Nov 27 16:27:56 CST 2001

Good to see your controller Chuck. Interesting choice of FET the IRF1010E.
The IRF1405 speced for the OSMC does have a few different charecteristics,
looks pretty decent. Rds-on for the 1010 is 12 mohms, where the 1405 is 5.3
mohms. Vds for the 1010 is 60v, for the 1405 it's 55v. Input capacitance is
3210 pF for the 1010, a bit better than the 5480 pF for the 1405, perhaps
improving PWM capabilities of an h-bridge. But because of that first Rds-on
value, the OSMC should carry more current with the same cooling as your
h-bridge. How are you driving your FETs on your board? Any luck with the
Black Ice water cooler yet?

David P

----- Original Message -----
>From: "Chuck McManis" <cmcmanis at mcmanis.com>
To: "D. Daniel McGlothin" <ddm_dprg at yahoo.com>
Cc: <dprglist at dprg.org>
Sent: Tuesday, November 27, 2001 12:22 PM
Subject: RE: [DPRG] Cheap high power H-bridge


> At 05:36 AM 11/27/01, D. Daniel McGlothin wrote:
>
> > > Interesting idea. Having been in the throes of designing a FET based
> > > h-bridge I thought I'd check it out.
> >
> >Are you aware of the OSMC http://groups.yahoo.com/group/osmc, an Open
Source
> >Motor Controller.
>
> Yup. And it is a damn fine project. The mailing list and the board layouts
> are excellent. Much better than the 'cheap' one mentioned at the beginning
> of this thread.
>
> >Quoting from their FAQ (in
> >     While the design has not been battle tested yet, it is expected to
have
> >an
> >     upper limit of less than 100A. To date, extensive testing/usage has
been
> >     in the 60 Amp range.
>
> This is an issue of course. Two things have to be true, one you have to do
> a thermal model of your FETs and then you have to validate your model. On
> my controller <http://www.mcmanis.com/chuck/robotics/projects/speed2.html>
> I spent a lot of time doing that and found out many misconceptions about
> MOSFETs (like the 'max Id' is in fact the current the FET can carry, it
> isn't) For TO-220AB lead frames the metal "legs" melt at 75 amps.
> Interestingly you can do better than this (get more current) if you fold
> the legs flat and solder as close to the "body" of the FET as possible.
>
> But the trick here is that to _test_ it, you really need a 100 - 150Amp
> power supply that can deliver 100 - 150Amps all the time. I use two HP KW
> supplies (0-60V, 0-60A) with one "slaved" to the other to provide a
maximum
> of 120Amps. I know of at least one person who salvaged a 5v 100Amp supply
> out of an old mini-computer and rewired it to deliver 12V @ 50amps.
Another
> solution of course is a pile-o-batteries. That limits your test time, but
> its a whole lot cheaper to set up.
>
> I've been tempted to bring my test setup to BattleBots and issue the
"speed
> controller challenge" which is to say, tell me what you think your speed
> controller is rated at, and we'll run it at 90% of that capacity and see
> how long it lasts. :-) But that would be kind of silly. If the speed
> controller works for your application you don't want to mess with it.
>
> >2.5) What is the maximum rated voltage?
> >
> >     You can go up to a maximum battery voltage of 50V. This is a
function of
> >the
> >     (typical) maximum voltage the FETs and FET driver chip used.
> >
> >     Note: Batteries have a significantly higher voltage "fresh off the
> >charger"
> >     so you won't be able to use 48V worth of batteries with the OSMC.
It is
> >     recommended that you limit your "rated" battery voltage to 36V or
so.
>
> There is also the margin for turn-around. So you've been sending your
motor
> "forward" and have built up a huge back-emf field, now you switch it to
> reverse. Your low side FETs will "see" the voltage of the input + the
> voltage over the motor for a brief period of time. That can be annoying if
> you're running near the FETs rated voltage.
>
> --Chuck



_________________________________________________________
Do You Yahoo!?
Get your free @yahoo.com address at http://mail.yahoo.com


More information about the DPRG mailing list