[TriEmbed] Need simple 1A controlled current power supply

[Dwight Morgan]

Great!

Sent from my iPad

> On Sep 26, 2016, at 4:15 PM, Rodney Radford <ncgadgetry at gmail.com> wrote:
> 
> I have ordered from Pololu for years and have been a promoter of them as well and not sure why I didn't think to check there.
> 
> I found what I needed and just ordered it:
> 
> https://www.pololu.com/product/2857
> 
> Thanx
> 
>> On Mon, Sep 26, 2016 at 3:55 PM, Dwight Morgan <dwight.w.morgan at gmail.com> wrote:
>> Shane sent out a resource site awhile back called pololu.com that might have what you need. I'm not sure but you could take a look.
>> 
>> 
>> Sent from my iPad
>> 
>> > On Sep 26, 2016, at 8:29 AM, Rodney Radford via TriEmbed <triembed at triembed.org> wrote:
>> >
>> > For the Southeastcon 2017 hardware robotics competition, one of the requirements is to be able to switch on and off a magnet field.
>> >
>> > The field is defined as number of turns, diameter, core, and the current - 1A - through it.  I need a simple (and cheap) way to implement this.  I will be building 8x of these for the competition and each school will be building one for their trial runs, so keeping it cheap and simple is better than elegant and higher cost.
>> >
>> > Initially I was planning on a very simple solution - a MOSFET switching current to the coil in series with a power resistor to drop the voltage.  At first this was a 5 ohm, 5W power resistor (since the coil is below 0.1 ohm), but then that changed to a 12 ohm, 12W power resistor as I switched over to using 12v to power everything since I needed that for the relays anyway (for another part of the design).
>> >
>> > This works, and is cheap and easy to build and if the coil is only on for a few seconds at a time, this is a great solution. However, a change in the contest stated that the coil is initially powered on (so robots can use it to navigate to the coil) and if the robot fails, it could be on for the full duration of the 5 minute competition.
>> >
>> > I tested this last night and it does work, but 12w through even a metal power resistor is HOT after about 30 seconds.  I would hate to use this for 5 minutes.  The cost is good - below $2 for the MOSFET and power resistor - but I am looking to see if there is a better solution.
>> >
>> > Some ideas considered:
>> > * use a lower voltage - would work, but I would need a lower voltage 1A supply
>> > * use a switched regulator - get the lower voltage *and* ability to control it
>> > * others?
>> >
>> > Any thoughts / suggestions?
>> >
>> > Btw, I will be bringing this in to the next meeting (next R&A/TAR and next Triembed) to show the progress on the hardware and software design. Most of it is done now and I hope to finish it in the next few days.
>> >
>> > On another issue - I watched a couple Eagle videos this weekend and was able to complete the schematic capture for the board and even routed a PCB. The routes were done with the auto-router and they were ugly, but functional. Not sure if I will just route it myself, or route some and let the autorouter finish, etc, but I need to investigate the design rules for the fab house first to verify I have spacings, hole sizes, trace widths, etc are correct before I dump too much more time into it.
>> >
>> > Thanx,
>> > Rodney
>> >
>> > _______________________________________________
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>> > TriEmbed web site: http://TriEmbed.org
> 
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