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Author Topic: External 5V power supply  (Read 655 times)
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Italy
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I need more current on 5V than an arduino can give, something around 2,5 A max and 1,5 A in normal use. My source is a 3cell Lipo(around 12V).
Aren't switching regulators a bad idea for shields and sensors?

Thank you
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No, I wouldn't automatically think so. 

http://chrisgammell.com/switching-regulators-and-switching-noise/

Depends on what you are doing.
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There's no need to power the Arduino from the same supply as your high-current
devices (in fact its good not to).

Here you can use the 11V supply to the barrel jack or Vin pin and use the Arduino's
built-in 5V regulator for itself and any sensors.

Provide a different regulator or converter for the 5V high-current stuff.  Keep high
current ground+supply wiring away from the Arduino or sensors.
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Hi olimex,

check this out:
 https://www.kickstarter.com/projects/pnmini/pnmini-positive-negative-power-supply-module-for-m?ref=home_location

Although it is rated at 2A, but from their test data, it supports up to 3A for positive output, and 2.5A for negative output. Looks like a good fit for your project.

https://www.dropbox.com/s/n4q602ssehkyu82/PNMini%20Datasheet.pdf



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Italy
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Hi olimex,

check this out:
 https://www.kickstarter.com/projects/pnmini/pnmini-positive-negative-power-supply-module-for-m?ref=home_location

Although it is rated at 2A, but from their test data, it supports up to 3A for positive output, and 2.5A for negative output. Looks like a good fit for your project.

https://www.dropbox.com/s/n4q602ssehkyu82/PNMini%20Datasheet.pdf


It' a little to late 1st of may, but very nice idea!

No, I wouldn't automatically think so. 

http://chrisgammell.com/switching-regulators-and-switching-noise/

Depends on what you are doing.


In the need of powering up a servo there is no problem, but a sensor yes!

Provide a different regulator or converter for the 5V high-current stuff.  Keep high
current ground+supply wiring away from the Arduino or sensors.

That's a good idea!
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Italy
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Actually my problem remains the GSM Shield, it drains a lot and I don't know if it can be affected by an switching regulator
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Actually my problem remains the GSM Shield, it drains a lot and I don't know if it can be affected by an switching regulator
Get a volt meter/amp meter combination, and put it between the power source and your Arduino to measure what the current draw is, and then you can use that in terms of sizing your voltage regulator.  You can find various versions of these meters.  For example, I did a simple search on ebay (you might want to look for an Italian or European vendor to cut down on the ship time): http://www.ebay.com/itm/Dual-LED-Digital-Volt-meter-Voltage-AMP-Power-Constant-Current-Voltmeter-Ammeter-/121284198811?pt=LH_DefaultDomain_0&var=&hash=item1c3d1a019b

This step-down voltage regulator will give you 3.5A to either 5v or 3.3v: http://www.pololu.com/product/2110.  It claims converting 12v to 5v with 2.5a is 90% efficient.  You would need to feed it at least 7v to get 5v out at 2.5a, so you could use a two cell lipo (7.4v) instead of 3 cell lipo (11.1v), but it may be better to stay with 3 cell.  You may need to worry about shunting the heat either from the voltage regulator and/or batteries at high amps.

If you need 7a, instead of 3.5a, there is a bigger converter: http://www.pololu.com/product/2111

Note, I haven't used pololu voltage regulators, except in tests, but I see a lot of people recommending them (it is on my to-do list).

If 2a is enough, you might look into the 18650 battery holders available, many of them have 1-2 usb ports plus an external port that can deliver 5/9/12 volts, and up to 2a.  For example, on this one, you could get 5v/2a via the external power cable: http://www.ebay.com/itm/1A-2A-Mobile-Power-supply-Six-18650-Battery-Charger-USB-5V-9V-12V-power-bank-/321266323477?pt=Battery_Chargers&hash=item4accf71015.  This just happened to be one that I found via search on ebay.  You would need to buy the 18650 batteries separately.
« Last Edit: March 21, 2014, 07:29:32 am by MichaelMeissner » Logged

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Actually my problem remains the GSM Shield, it drains a lot and I don't know if it can be affected by an switching regulator
Get a volt meter/amp meter combination, and put it between the power source and your Arduino to measure what the current draw is, and then you can use that in terms of sizing your voltage regulator.

Unfortunately that doesn't work for GSM shields.  GSM transmits in timeslots (usually
for 1/8th of the time), so the peak current requirement of a GSM shield can be lots
more than the average (which is all a multimeter will give you). 

You must read the datasheet for the shield and provide a supply that can give
at least as much current as the maximum it lists.  It can be several amps.
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Unfortunately that doesn't work for GSM shields.  GSM transmits in timeslots (usually
for 1/8th of the time), so the peak current requirement of a GSM shield can be lots
more than the average (which is all a multimeter will give you).  

You must read the datasheet for the shield and provide a supply that can give
at least as much current as the maximum it lists.  It can be several amps.
If it is several amps, you likely will need to get more serious about the batteries, than using plain multi-cell li-pos.

I have seen more expensive versions of the combined volt/amp meters that do have options to measure the max volts/amps over time.  Since I've never used a GSM shield, I didn't know the power varied so widely.  A data sheet will give you the min/max for a particular component, but it can be useful to just measure the system as a whole, to see how things interact in terms of the power budget.
« Last Edit: March 21, 2014, 09:24:57 am by MichaelMeissner » Logged

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If it is several amps, you likely will need to get more serious about the batteries, than using plain multi-cell li-pos.

Or put in a big capacitor to smooth out the peaks in current.

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Its a possibility, but you need around 10,000uF which is a tad too large really.
(for a max drop of 0.1V over a 577us timeslot at 2A).

2A is quite a large ripple-current rating too...
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Its a possibility, but you need around 10,000uF which is a tad too large really.
(for a max drop of 0.1V over a 577us timeslot at 2A).

I hadn't done the math, but 2A is quite a lot to sustain, yes... smiley


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Actually on the official GSM Shield there is already a large capacitor to help the linear regulator on Arduino in GPRS trasmitting.

Thank you to all of them who helped me here, now I'm going to think about the best configuration for my needs.
I'll write you back,

Luca
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