Powering Arduino, Rpi and DC motors from battery

Hi guys,
I bought a 12V battery 6800mAh and I want power from this battery Arduino and Raspberry Pi and possibly DC motors. I built a schematic as I show at my upload image. I know that arduino has its own regulator and 12V for it is not problem, but for Raspberry Pi I need range from 4.75 to 5.25V. When I use this regulator at ouput I show about 4.9V. But to the Rpi I have connected USB WiFi dongle, USB camera and Ethernet cable and when I use 5V 1A adapter from my HTC mobile all is OK. But when I use 4.9V it was reseting, but when I measure voltage at output of battery there was 4.7V and output of regulator 4.9V I mean it is impossible, for this reason I go to charge this battery and next I will post a reaction. But I need to know, that is possible powering Arduino and Raspberry Pi via this way. And then when all will be ok, what I need when I go to power DC motors?..Now I power it from 6.7V another battery, it only powers DC motors, but I want rebuild it only at one battery, what I need? 6V regulator or what?..but I think, that I need there something more or not?..Thanks for reply…

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Raspberry Pis draw a pretty significant amount of current, especially if you start adding things like WiFi.

A 1A supply into a regulator only rated for around 1A, assuming a properly sized heat sink, seems pretty low.

So, I tested a regulator 7805 with full charged battery. Battery output shown 12.28V and stabilizator`s output with no connected Raspberry Pi 4.99V. When I connected Rpi with all devices (WiFi,camera and ethernet). It showed at multimeter about 4.98-4.97, I had regulator without heat sink it it got soo hot and after 10 sec voltage went down to 4.92 and then I switched-off my battery with switch on it. I have idea that for this high temperature 7805 cant hold a regular voltage or what?...I will mount a fan but it will help?...oder I bought DC-DC converter and all will be ok...Can I build DC-DC converter on my own? (I think it is hard?)...because it is my project to school and I want build things on my own (those that are possible).

Thanks

s3ky: it got soo hot and after 10 sec voltage went down to 4.92 and then I switched-off my battery with switch on it.

That means the regulator went into thermal shutdown, because too much current was being drawn.

With a proper heatsink a 7805 in a TO-220 package can handle 1A (possibly more depending on the design). Without a heatsink it may only handle 250-500mA depending on the input voltage.

s3ky: Can I build DC-DC converter on my own? (I think it is hard?)...because it is my project to school and I want build things on my own (those that are possible).

It really depends. A 7805 is a DC-to-DC converter, but it is a linear regulator. Switching supplies are far more efficient, but are more difficult to design. Not impossible, just difficult. There are people who spend their entire careers understanding power supply design.

[quote author=James C4S link=topic=192642.msg1424755#msg1424755 date=1381499225] With a proper heatsink a 7805 in a TO-220 package can handle 1A (possibly more depending on the design). Without a heatsink it may only handle 250-500mA depending on the input voltage. [/quote]

It also depends on how many volts you ask it to throw away.

12V down to 5V is a 7V drop - which is a lot.

Thanks for all responses, but I have another question. Its my project to a school and I want buy things as little as possible and for this reason I want to build DC-DC converter on my own. I checked that 7805 is not right way and I find a schematic as this http://www.eleccircuit.com/12v-to-5v-3a-dc-converter-step-down-regulator I know that I didnt create this schematic but still beter than buy DC-DC converter as that: http://www.ebay.co.uk/itm/Car-Power-Supply-DC-DC-Regulator-Converter-12V-to-5V-3A-15W-/141018153851?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item20d556437b ...But I want to know how differencies are between that 2 things? ..Thanks

The DC-DC converter is a much more efficient solution. The schematic you linked to is just a way of increasing the output of a 7805 to more than its 1A rating, which you don't need to do since your 7805 works OK until it heats up. Either put a heatsink on the 7805 to stop it going into thermal shutdown and accept that you will be wasting a lot of power in it, or buy the DC-DC converter. Don't try to make your own switched-mode DC-DC converter, it's definitely not something for novices to attempt.

DC42: What about this one?...http://www.ti.com/lit/ds/snvs107c/snvs107c.pdf

In principle you can use that, however correct selection of the inductor and capacitor, and correct circuit layout on a good printed circuit board, are critical. See pages 11-20 of the datasheet. You risk damaging your Arduino and Pi if you get any of these wrong. It's much easier and safer to buy a ready-made board.

Yes you are right I MUST use specific components and be really careful, but when I build it and test on cheap product and everything will be ok I dont care or?

For only US$ 12, you can save yourself a lot of effort with this: http://www.pololu.com/catalog/product/2177 On the other hand, building your own switching regulator would definitely be a learning experience!