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Power bifferboard from 12VDC battery

Bifferboard presents it self as a very efficient device, requiring only 1W of power (5VDC @ 200mA) when used with 1 USB pen drive and Ethernet interface dis-connected, 1.5W (5VDC @ 300mA) with Ethernet interface connected, making it ideal for a battery-powered device. For that it is necessary to convert the 12VDC of the battery to the 5VDC required by Bifferboard, meaning that it will need an electronic circuit for this conversion.

There are several electronic circuits/pre-assembled chips available to convert 12VDC to 5VDC but some are more efficient then others, also less linear and not so stable (introducing some noise into the 5VDC converted power supply). For better efficiency is is advised to use 5VDC Switched Regulators (also known by 'Step-Down Voltage Regulator'), meaning that this may reflect on some noise on the converted value, requiring extra components to filter that noise! To select an efficient Switched Regulator you should first evaluate your 'load' (what devices are you going to connect to the Bifferboard and measure the current that will drain form the power supply) so that you could check the datasheet of the regulator if the efficiency of that chip will comply with your needs. One Regulator may be very efficient when operating with a higher load but not so good when you remove part of that load (e.g.: Bifferboard with or without  webcam connected).

Note: The following chips/circuits/solutions serve only has a guide line and are highly dependable on the selected load and you may not achieve the same results!
If you have achieved a better performance with other chips/solutions feel free to update this page. Please take extra care to specify your test conditions and make a list of the devices connected to bifferboard.

1) LM-2575-5 Pre-assembled 5VDC Switched Voltage Regulator

For the first test it was used a pre-assembled Switched Regulator based on the following chip:
http://www.national.com/mpf/LM/LM2575.html

http://shop.ebay.com/i.html?_nkw=LM-2575-5&_sacat=0&_odkw=LM-2575-5&_osacat=0&_trksid=p3286.c0.m270.l1313
(this chips are a bit expensive, there are other solutions to be tested, will serve as base for the following experiences)

It can accept input voltage up to 40VDC and supply an output current of 1A
Also requires and external polarized capacitor to be connected to the input (+ of cap to Pin1) and GND (- of cap to Pin2). Used one 220uF/25V.
Also requires and external polarized capacitor to be connected to the output (+ of cap to Pin3) and GND (- of cap to Pin2). Used one 220uF/25V.

Pin1 (picture 1 -> left pin): Input (connect to 12VDC battery)
Pin2 (picture 1 -> middle pin): Ground (connect it to GND of battery and Bifferboard)
Pin3 (picture 1 -> right pin): 5VDC Output (connect it to Bifferboard VCC)

Note: Bifferboard VCC is the middle pin on the connector.


Example on how to connect the polarized capacitors (middle point is GND, pin2):

1.1) Hardware used for the tests

- Bifferboard
- Homemade Serial connector with Max3232 chip
- 4GB USB Pen Drive for the root_fs (DANE-ELEC)
- 4 Port USB2.0 Hub (TRUST)
- 12VDC 7Ah battery (YUASA NP7-12)
- Logitech Quickcam Pro 9000 webcam

1.2) Testing Bifferboard + PEN_USB_ROOTFS + Serial Cable Connected + Ethernet Dis-connected

Note: before making measurements bifferboard needs to boot to the end and get to the Idle Status (+- 25 secconds).

From battery: 12.9VDC @ 117mA -> 1.509W
From bifferboard: 5.6VDC @ 230mA -> 1.288W

1.2.1) Efficiency:

Efficiency = (1.288/1.509)*100 = 85.35%

1.2.2) Battery Max time capacity - Teoric Value:

Battery Max time capacity (Teoric Calculus) = 7000 (mAh) / 117 (mA) = 59.83 hours

1.3) Testing Bifferboard + USB_HUB + PEN_USB_ROOTFS + Serial Cable Connected + Ethernet Dis-connected


From battery: 12.8VDC @ 174mA -> 2.227W
From bifferboard: 5.1VDC @ 350mA -> 1.785W

1.3.1) Efficiency:

Efficiency = (1.785/2.227)*100 = 80.15%

1.3.2) Battery Max time capacity - Teoric Value:

Battery Max time capacity (Teoric Calculus) = 7000 (mAh) / 174 (mA) = 40.23 hours

1.3.3) Battery Max time capacity - Real Value:

Note: for the real test it was necessary to launch a script into bifferboard that would log the actual time every 30 seconds.
Battery was also charged to the max. It is not advisible to dis-charge acid batteries to complete Zero! They will not last long!

Log Start Time: 28-04-2009 01:00
Log End Time:  29-04-2009 12:00

Battery Max time capacity = 35 hours

Difference from Teoric value to Real Time is expected due to 80.15% of efficiency.

1.4) Testing Bifferboard (boot from flash) + Serial Cable Connected + Ethernet Dis-connected

Note: For this experimental test it was used the flash image from the group->files->binaries: initramfs.ALSA.USBAudio.DHCP.bzImage
This uses DHCP to set Ethernet settings, so it is required to temporary connect it to network (detach cable after boot sequence completed).
Using this compact flash image will permit bifferboard to run without the need of external USB pen drive.

From battery: 12.8VDC @ 80mA -> 1.024W
From bifferboard: 5.6VDC @ 152mA -> 0.851W

1.4.1) Efficiency:

Efficiency = (0.851/1.024)*100 = 83.13%

1.4.2) Battery Max time capacity - Teoric Value:

Battery Max time capacity (Teoric Calculus) = 7000 (mAh) / 80 (mA) = 87.5 hours
Number Days =  87.5h / 24h = 3.65 Days

1.5) Testing Bifferboard + USB_HUB + PEN_USB_ROOTFS + Logitech Quickcam Pro 9000 +Serial Cable Connected + Ethernet Dis-connected

i) camera connected but not in use by software

From battery: 12.7VDC @ 210mA -> 2.667W
From bifferboard: 5.1VDC @ 410mA -> 2.091W

ii) camera connected and in use by mjpg-streamer

From battery: 12.7VDC @ 260mA -> 3.302W
From bifferboard: 5.1VDC @ 520mA -> 2.652W

1.5.1) Efficiency:

Efficiency (i)  = (2.091/2.667)*100 = 78.40%
Efficiency (ii) = (2.652/3.302)*100 = 80.32%

1.5.2) Battery Max time capacity - Teoric Value:

Battery Max time capacity (Teoric Calculus) (i)  = 7000 (mAh) / 210 (mA) = 33.33 hours
Battery Max time capacity (Teoric Calculus) (ii) = 7000 (mAh) / 260 (mA) = 26.92 hours

1.6) Testing Bifferboard + USB_HUB + PEN_USB_ROOTFS + Logitech Quickcam Pro 9000 +Serial Cable Connected + Ethernet Connected

i) camera connected but not in use by software

From battery: 12.7VDC @ 270mA -> 3.429W
From bifferboard: 5.1VDC @ 560mA -> 2.856W

ii) camera connected and in use by mjpg-streamer

From battery: 12.7VDC @ 340mA -> 4.318W
From bifferboard: 5.1VDC @ 640mA -> 3.264W

1.6.1) Efficiency:

Efficiency (i)  = (2.856/3.429)*100 = 83.29%
Efficiency (ii) = (3.264/4.318)*100 = 75.59%

1.6.2) Battery Max time capacity - Teoric Value:

Battery Max time capacity (Teoric Calculus) (i)  = 7000 (mAh) / 270 (mA) = 25.93 hours
Battery Max time capacity (Teoric Calculus) (ii) = 7000 (mAh) / 340 (mA) = 20.59 hours

// NN
ċ
r6040-ip101a-power-save.patch
(1k)
Biff Eros,
May 7, 2009, 10:55 AM
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