A3977 based boards and MAX ratings was Re: Arcsin 3 axis

Hello,

IMO poor board and/or power supply/system design has made these
A3977 "facts" true for SOME folks.

Do you really think that the Allegro engineers simply pulled the
number 35 out of the sky?

I don't.

A VERY common 24volt transformer, when full wave rectified and
capacitor filtered, will be about 34volts DC. Hmmmmm...

34volt common power supply. 35 volt part. Coincidence???

Steve Stallings PMD-150 drive based on the A3977 works with 34 volts
reliably. (He even gets it to work at 3amps per phase!)

Fred Smith has said the same about his A3977 based drives.

Tom Scarince's THS drives seem to work reliably for me with a 34v
linear supply...

Hope this helps,

Ballendo

P.S. The HobbyCNC board uses an SLA7062M driver chip rated at 3 amps
and 44VDC. I've run them 3axis at 34volts with 3amp motors for eight
hours straight. No problems, other than IMO excessive chopper noise.

The ArcSIn, and Jim Fong's Embeddedtronics driver board, use National
Semiconductor's LMD18245, which is rated 3 amps and 48 volts. Most
know that National pretty conservatively rates their devices...

The LMD18245 is a JEWEL of a driver chip, IMO. Just very expensive in
comparison to others that are available.

P.P.S. Good point about the breakout costs and build time needing to
be accounted for...


In CCED, "turbulatordude" <dave_mucha@y...> wrote:

> > The only thing I see about the unit is that the cost is

relatively

> high
> > compared to the Xylotex (2.5A @ 35V 3 Axis = $145.00) and three
> Gecko's
>
>
> The A3977 chip is maxed out at 35 volts and is unstable at that
> voltage. Back EMF will blow the chip if run from a 35V supply.
>
> As I undrstand they are very stable with a 24 volt supply.
>
> As I see the contenders
>
> Xylotex 24V @ 2.5 amp
> HobbyCNC 44volts @ 3 amp
> ArcSin 48V @ 3A
> Gecko is 80V @ 7amp
>
> the Gecko is really made of components that are rated for
> 10amp/100volt. As a device, it is rated by the manufacturer for 80
> volts and 7 amps. (20% less volts, 30% less amps) and at that

7A/80V

> use, it is a brick.
>
> If you de-rate the A3977 chip from the 2.5A/35V in the same manner

to

> 1.75A and 28 volts, it too should be rock solid.
>
> I don't know the HobbyCNC or ArcSin components well enough to know
> they are rated for the max of the parts or de-rated for the
> application.
>
> Also, the HobbyCNC and ARCSIN as well as the Xylotex have parallel
> ports on board whereas the Geckos do not. That means the $114 each
> for the geckos is not a full system but add between $25 and $150

for

> a parallel port breakout board to get a comparative Gecko price.
>
> ($114 x 3 + $25 = $367 for a 3 axis Gecko)
>
> The ArcSin is right between the Xylotex and Gecko.
>
> the ArcSin is Fully Assembled whereas the HobbyCNC is a kit. Add

for

> your time to get a better comparison of those two.
>
> Dave