Power Consumption

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prologic
 
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Power Consumption

Post by prologic »

Hi All,

I'm trying to do some power consumption calculations. My project consists of:

* Arduino Uno R3
* Adafruit CC3000 WIFI Shield with UFL Connector
* Adafruit Motor Shield V2
* NEMA-17 200 step 12V Stepper Motor
* Lock-style 12V Solenoid

I know some of the power requirements:

* Stepper = 350ma/phase (I'm double stepping so 700ma)
* Lock-style Solenoid == 650ma

Both of these devices only run twice per day (morning and night) and at most a minute.

* CC3000 ship == 92mA typical (plus tx power?)
* Arduino Uno == 45mA (no load)

Any help would be appreciate!

Right now I'm powering this system with a 2.2Ah 12V battery with a 5W Solar panel -- but I believe I have grossly under estimated and calculated the power requirements ;/

Thanks heaps!

cheers
James

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prologic
 
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Re: Power Consumption

Post by prologic »

To help with this question I've created a Google Docs spreadsheet:

https://docs.google.com/spreadsheet/ccc ... sp=sharing

I think I just need an extra pair of eyes and some clarifiction(s) on some of the shields power consumption.

cheers
James

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adafruit_support_bill
 
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Re: Power Consumption

Post by adafruit_support_bill »

* Stepper = 350ma/phase (I'm double stepping so 700ma)
* Lock-style Solenoid == 650ma

Both of these devices only run twice per day (morning and night) and at most a minute.
Are you removing power from the motor when it is not running? Stepper motors consume maximum power when not turning.

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prologic
 
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Re: Power Consumption

Post by prologic »

Yes I am :)

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adafruit_support_bill
 
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Re: Power Consumption

Post by adafruit_support_bill »

Just to clarify, let's get the terminology straight:
Column B is labeled "Power(A)". Assuming that is Amps, it should be "Current (A)". Power (V * A) is Watts as you have in column D

The lower section of Column D is labeled "Total Power(W)" That should be "Watt-Hours" (W * H)

Amp-Hours (A * H) is another useful number to have. I think that is what you have on the bottom line, labeled as "mA@12vDC"

So you are looking at a little over 2Ah or 24Wh per day. With a 5W panel at 80% charge efficiency, you can get that in 6 hours of good sun. You will want a battery of 2Ah or larger for storage. It is better to err on the generous side to help you through the occasional overcast day. If you live in an area where days are short and/or overcast days are the norm, you may want to up-size your panel too.

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prologic
 
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Re: Power Consumption

Post by prologic »

Thanks for the clarification on terminology.
I have to admit I haven't been that careful or precise with that!

I will review and correct as appropriate.

What about the Motor Shield and CC300 shield?
Do we assume 92mA typical for the CC3000 (from the CC3000 Datasheet)?
The only power draw information I can find on the Motor shield
are the drivers.

cheers
James

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clarkj
 
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Re: Power Consumption

Post by clarkj »

Hi James!

I've done a lot of these sort of things, and have spotted a few things that you should be aware of.

First, if you're using the Arduino's on-board regulator, it's a linear regulator, so it only translates the voltage, and for every mA of current it outputs requires (a bit over) a mA of current input. You can use an off-board switching regulator to get around this, though (a) there will be a slight loss "back into" the onboard regulator, and (b) the switching regulator can produce some RFI (Radio Frequency Interference), though for most folks that's not a major issue.

Second, you've sized your battery to hold about one day's power. There are several problems with this: First, since you're (apparently) charging the battery from a solar panel, you need to consider the location and how many days of cloudy weather you can see in a row. Also, you need to consider how good the charging will be in winter -- the further you are from the equator, the fewer hours of sunshine you get during the winter, so you need to make allowances for that in sizing your solar panel (and remember it needs to be able to "catch up" for a run of cloudy days). If you end up with a solar panel that has the capability of putting more than 10% of the power into the battery per hour (for example, with your 2.2 Ah battery, if the solar panel can produce more than 0.22 A) you really need to have a charge regulator to avoid destroying the battery from overcharging. (I'm inclined to include a charge regulator for anything over 5%.) And finally, even "deep cycle" batteries can have a shortened life expectancy if they're very heavily discharged. (There are exotic batteries that can live with a lot of total discharges, but you're not likely to be using them.)

I know the above sounds like a big hassle, but I want to encourage you to go ahead, and want you to succeed! Applying some simple "rules of thumb" I've learned from dabbling in solar, I can see three options:

1) Change to a switching regulator for powering the Arduino and logic boards, go to at least an 11Ah battery, double or triple the size of the solar panels (you can also put 5W panels in parallel), and find a charge regulator.

2) Change to a switching regulator for powering the Arduino and logic boards, go to a 20Ah (or more) battery, double or better yet triple the solar panels, and skip the charge regulator.

3) Don't change to a switching regulator, use a 40Ah (or more) battery, up the solar panel arrangement to at least 50W, and add the charge regulator.

My preference would be option 2.

Good luck!

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