> At this stage I'd rather try and get an off the shelf system so that I know
> someone has already put in the hard work tracing down all the foibles of the
> system and we don't have to find out what they are when the magic blue smoke
> escapes yet again. High current DC motor driver design is not a simple thing
> as many people can attest to and, for a critical system at least, is best
> left to the experts.
> Also what you spend on buying parts piecemeal pretty quickly adds up to near
> enough the cost of one of the driver modules anyway.
> http://www.pololu.com/catalog/product/1456 or
> http://www.pololu.com/catalog/product/1457
> Pros: They are very nice drivers, have built in current sensors (30A limit)
> and are easy to get.
> Cons: No overcurrent or thermal protection, overcurrent can't be done with
> the current sensor as it maxes out long before the controller does (for
> peaks anyway)
> http://www.dimensionengineering.com/SyRen25.htm
> Pros: configurable++, Overcurrent and thermal protection.
> Cons: Kinda overkill, bit more expensive, 1 week lead time.

> On 4 September 2011 23:04, Triffid Hunter <triffid.hun...@gmail.com> wrote:

>> On Sun, Sep 4, 2011 at 10:34 PM, Lemming . <inert...@gmail.com> wrote:
>> > The problem we keep running into with this thing is the
>> > rather horrendous amount of current this motor seems to draw when, and
>> > that the batteries are more than happy to provide it!

>> Any ideas exactly how much that is? DC resistance of the motor and
>> ohm's law should give a good ballpark figure.

>> My proposal should be good up to a few hundred amps, if you use decent
>> mosfets, ie ones with low Rds(on), Vds(max) of at least 30v and a
>> package you can bolt a lot of to a heatsink without much work.

>> I would suggest IRL3803, because I have a bunch of them and they can
>> carry 15A with /no/ heatsink and a mere 5v gate drive. With a
>> substantial heatsink (eg 2c/w), one should be able to carry over 60A.

>> 8 of those in parallel on a big heatsink, plus a good diode or 10 to
>> catch the flyback pulse, and a reversing switch that can handle the DC
>> current (but not necessarily the switch-off arc) should solve your
>> door woes. They'll need a decent gate driver, 74hc244 perhaps with one
>> output per gate. IRL3803's downside is its high gate charge (140nC)
>> which means at 10mA gate drive, it takes about 14uS to switch.

>> Futurlec carry IRL3803 at $0.90/ea but you may not want to wait for
>> their postage, see what else is available. Perhaps you already have
>> some suitable mosfets in the space waiting to be discovered?

>> I don't know if jaycar and friends carry anything with a usably low
>> Rds(on) - maximum for this is about 10mR. Last time I checked, their
>> mosfet selection was less than stellar, but that was several years ago
>> now.

>> --
>> You received this message because you are subscribed to the Google Groups
>> "hackerspace_brisbane" group.
>> To post to this group, send email to
>> hackerspace_brisbane@googlegroups.com.
>> To unsubscribe from this group, send email to
>> hackerspace_brisbane+unsubscribe@googlegroups.com.
>> For more options, visit this group at
>> http://groups.google.com/group/hackerspace_brisbane?hl=en.

> --
> You received this message because you are subscribed to the Google Groups
> "hackerspace_brisbane" group.
> To post to this group, send email to hackerspace_brisbane@googlegroups.com.
> To unsubscribe from this group, send email to
> hackerspace_brisbane+unsubscribe@googlegroups.com.
> For more options, visit this group at
> http://groups.google.com/group/hackerspace_brisbane?hl=en.