Draw up to 1A from VIN?

The "Eleven" is our Uno-equivalent Arduino-compatible board, but with a number of improvements including prototyping area, a mini-USB connector, LEDs mounted near the edge, and the D13 LED isolated using a FET. [Product page]
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rvalue
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Draw up to 1A from VIN?

Post by rvalue » Sat Nov 12, 2011 4:39 am

If I'm supplying power via the jack at 12v (SMPS plug 'wart' rated to 1800ma), can I safely draw up to 1000ma from VIN, or do I need to split the load power earlier?

If I do need to do that, would you recommend soldering onto the jack posts?

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jonoxer
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Re: Draw up to 1A from VIN?

Post by jonoxer » Mon Nov 14, 2011 12:57 pm

I expect that 1A would be OK through the track, vias, and VIN header, but it'll be pushing the limit of the header. Soldering to the pads under the DC jack would certainly be a good way of avoiding the issue.

I'm curious to know what you're doing that'll pull so much current! Care to share?
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rvalue
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Re: Draw up to 1A from VIN?

Post by rvalue » Fri Nov 18, 2011 5:52 am

Sure, the plan for the first project is to thermally control a 120mm cooling fan for my computer desk - it's got a shelf that neatly fits my Mac mini, external hard drives, and space for an XBOX 360 - but I'm not comfortable running the XBOX in there with just convection circulation. That thing is HOT... and an excuse to dig out the remnants of my electronics knowledge.

I've gotten a hold of an Eleven now; and the solder pads under the jack do seem to be a good way to go. (A good picture of the underside of the boards on the product page or getting started guide would be a nice addition ;) )

<ramble>
The fans I have easy access to are 12v PC cooling fans; I've got a variety of sizes (and powers) to test with, from 180mA 40mm up to the 1A 120mm I have in mind for the final build. I think I'll start with one of the smaller ones anyway then, to avoid having to potentially modify the power inlet a second time when I find a good power adapter.

The fans are a 3-pin variety, with some form of tachometer signal on the third line that I'm hoping to be able to also tap into. From teenage experiments in controlling them when PC noise started to annoy me, they respond a lot better to PWM than DC voltage control, the larger ones wouldn't self-start much below 9v or keep running reliably around 6.

For starters (and not least to limit the amount of bad solder work I expose the project to) I'll probably just try to control speed at a barely- or in-audible level. I've seen a couple of motor control sketches around that seem reasonable for that.

As a second stage, I'd like to tap into that tacho signal to dynamically raise the minimum 'drive' (terminology? load cycle?) of the fan somewhat if it stalls out (gets dusty, etc.) Being able to get the absolute speed from it would be nice, but I wouldn't say necessary at this point.

Lastly, is the 'obvious' temperature-based control, by either analog reading of a thermistor or one of those fancy sensor ICs. I'm leaning toward the IC at this point, mainly because they seem cooler.
</ramble>

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jonoxer
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Re: Draw up to 1A from VIN?

Post by jonoxer » Fri Nov 18, 2011 6:14 am

Your post got me wondering how the speed sensor or computer fans works, and a bit of Googling found this good explanation:

http://electronics.stackexchange.com/qu ... eed-sensor

Looks like the best approach would be to connect the sensor wire to a spare interrupt pin (perhaps D3) on the Arduino, and do some counting / timing in software to determine RPM. It'd actually be almost the same as the Water Flow Gauge project from Practical Arduino:

http://www.practicalarduino.com/project ... flow-gauge
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rvalue
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Re: Draw up to 1A from VIN?

Post by rvalue » Fri Nov 18, 2011 6:40 am

Wow, great tips Jon!

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Re: Draw up to 1A from VIN?

Post by rvalue » Sat Nov 19, 2011 4:37 am

Power tested a bunch of the fans last night, I think for this project I'll go with the Zalman 120mm Quiet Fan. Airflow was excellent and it was nearly inaudible even at full power. It says 0.35A on the housing, but I measured it at just shy of 400mA - that's still a lot less than the 1A of the top powered one - I may even end up running a pair of them in the final build.

Either way, that's a lot more leeway in the power supply and routing than I originally hoped for :mrgreen:

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DJ-Dwayne
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Re: Draw up to 1A from VIN?

Post by DJ-Dwayne » Thu Oct 30, 2014 10:56 am

The previous comments concur that drawing 500ma - 800ma from Vin should be ok????????

Just built a 5v volt meter and got to thinking.......
Just and an external regulator (one with a bit more grunt then the on-board one) and use it to make a battery charger using thermo and delta-V cut off.

Me got a bit of studying to do........ :D
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