DC/DC converter stablelized?

[fryslan76]

Howdie people,

I am planning on dropping a few LiPo accu packs in my ROV to supply the power underwater for my Raspberry Pi, Arduino and USB or IP Camera. The Arduino can handle a power input from 20 till 7 volt so I should be oke with my 11.1V Lipo which will drop to about 7. The Raspberry and Camera however require 5V regulated USB style power. Anybody a good suggestion for a regulated power converter DC/DC I currently have my eyes on this one: http://dx.com/p/dc-12v-to-dc-5v-convert ... ack-147841 other suggestions or improvements are more than welcome.

Regards,

Sjoerd

[Joe]

Try an LM7805(Or just "7805"). It's a Three pin component that you can get at Radioshack for $2. It's not a DC-DC converter, it's a Regulator... basically it changes it's resistance real-time to maintain a steady voltage. You can input any voltage from 5V to 30V and you will get a 5V output, and can draw up to 1 Amp before it overheats. If it does get too hot it will shut itself down so it won't blow up and damage anything.

The three pins are to the power source, ground, and 5 volts out.

[jenswilly]

I agree: a 7805 regulator is a good (and cheap and simple to use) choice.

However, you might want to put a heatsink on it. If the input voltage is 11.1 V and output voltage is 5 V it will not be able to handle 1 amp but only about 400 mA (if the ambient temperature is 20 °C).

Fortunately, there are many cheap heatsinks you can bolt right on. Do a search for "TO-220 heatsink".

[fryslan76]

Thanks, i will look into this regulater. I will probaly need to source a bit more then 1A so there might be a problem there.

[fluxno]

7805 is not an ideal solution for battery applications, because:

7805 is a linear regulator, this means if you load have a 1Amp load, it will use 1Amp from the source. in example: 5V/1Amp out = 11.1V/1Amp in. in watt this translate to 11.1W in, 5W out = 6.1W wasted!
Use a switching regulator like the one you linked to. this regulator has 96% efficiency, meaning that a 5V/1A usage would result in a consumption of 5.2W from the battery. 0.2watt/4% loss.
and its completely cool.

There are finished switch regulators that are intended as 78xx replacements: http://www.tracopower.com/fileadmin/med ... s/tsr1.pdf http://www.recom-international.com/?id= ... R-78xx-1.0 http://www.recom-international.com/?id= ... 1.5%28L%29

[Joe]

If you need more than 1 amp you can just 'gang up' (wire in parallel) the 7805's.

Yes, the 7805 is not efficient... but I've never found that to be an issue on this power scale... the bigger issue is usually flooding... in which case the 7805 won't even know it's submersed in water, and will just keep running.

[fluxno]

If you need more than 1 amp you can just 'gang up' (wire in parallel) the 7805's.

Yes, the 7805 is not efficient... but I've never found that to be an issue on this power scale... the bigger issue is usually flooding... in which case the 7805 won't even know it's submersed in water, and will just keep running.

its not an issue for most people because of unawareness to the diffrence between a linear regulator and an efficient switching regulators.
linear regulators and LDO's are nice to use in-between a switching regulator and equipment sensitive to noise. though the diffrence between input and output is kept as low as possible to minimize the loss.

It wont matter that a 1$ 7805 works when the ras-pi,arduino and webcam dies.
a leak detector costs nothing when you have a ras-pi or arduino in the rov; http://arduino.cc/forum/index.php/topic,5961.0.html

[fryslan76]

I ordered the regulater I quoted in the opening post and a small Lipo accu to play around with, although I am leaning more and more to the use of a powerbank as power supplu for the arduino and webcam. Since these are getting cheaper by the week and have all the nasty control stuff allready inside.

[KR2_Diving]

Another thought may be to use the 5V out on the arduino. This is a regulated 5v out and may be enough to power your RasberryPi and camera.

From the Arduino Site:

5V.This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.

From what I can tell, this will output up to 500ma... but may be limited to 100ma depending on hardware configuration...

Just another idea for you to consider!

[fryslan76]

Another thought may be to use the 5V out on the arduino. This is a regulated 5v out and may be enough to power your RasberryPi and camera.

From the Arduino Site:

5V.This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.

From what I can tell, this will output up to 500ma... but may be limited to 100ma depending on hardware configuration...

Just another idea for you to consider!

A Pi uses about 1 up till 1.5 A, so that is a bit to much but thanks for the thougth.