pleione
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Re: Power Supply / Charging Circuit

Sun Sep 18, 2011 4:22 pm

I'm in the process of putting together the design of a suitable power supply for the RasPi.

For the RasPi we'd need 5Vdc and for other elements of my designs I'd need 12V and 9V.

I can get the various voltages pretty easily with LDO voltage regulators like the LM78xxx, but what's best way to charge the batteries in circuit?

I plan to use NiMh 1.2V cells, but don't want to have to remove them to charge and have to disconnect the circuit.

I'm guessing something like this once finalised would be almost universal across the board for many projects, how about coming up with a circuit and list of components that are readily available and easily adaptable.

obarthelemy
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Re: Power Supply / Charging Circuit

Sun Sep 18, 2011 4:28 pm

Good news for you: the raspi needs 6-20V.

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abishur
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Re: Power Supply / Charging Circuit

Sun Sep 18, 2011 4:40 pm

For the battery charging aspect, I'm planning on doing a similar thing using the Maxim DS2715. Give it a look and see if it would or wouldn't work for you as well.
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Lob0426
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Re: Power Supply / Charging Circuit

Sun Sep 18, 2011 4:59 pm

Has anyone found a charging circuit similar to that maxim for LiPo?
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pleione
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Re: Power Supply / Charging Circuit

Sun Sep 18, 2011 5:06 pm

I'll take a look, thanks abishur, I had been looking into the http://www.maxim-ic.com/datash...../1666/t/al Maxim Max712/13

Still trying to get my head around the 1W quoted for power, over on the wiki it mentions that for the video test the RasPi was pulling around 350mA at 7.5V, that's a bit more than 1 watt, more like 2.5W - I can't find the page now (typical)

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Lob0426
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Re: Power Supply / Charging Circuit

Sun Sep 18, 2011 5:50 pm

The 350ma I believe included the mouse and keyboard also. USB keyboards are like 25ma and USB mice are around 100ma for optical. I don't know what the power consumption of roller mice is, but lower than optical. This also was a development board that has extra stuff on the board that will not be on production boards. The board alone without the keyboard and mouse would be lower. if you set it to a task and then unplugged everything it would probably be 1watt. I think that 2.25watts that he tested it at with everything attached is phenomenal! I am figuring it at about 7.5watts with a USB HDD for continuous operation and adding in a surge due to the HDD up to 10 watts. It will probably be less! Never hurts to figure high and be wrong.
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Blars
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Re: Power Supply / Charging Circuit

Mon Sep 19, 2011 8:39 am

Also, the one watt figure is for an A board, the B board has a bit more to power. The alpha board may have a liniar regulator rather than a switcher as well. The two USB ports could add 5 Watts more.

RITRedbeard
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Re: Power Supply / Charging Circuit

Tue Sep 20, 2011 6:53 am

Charging as in plugged in and charging like a laptop? I was thinking the same thing since my goal is to turn a Raspberry Pi into a much more efficient netbook for my needs.

Any idea on circuit diagram and parts?

scologic
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Re: Power Supply / Charging Circuit

Tue Sep 20, 2011 9:57 pm

Linear technologies have a nimh recharging and charge in use circuit, and I've got a test board for it(if i can still find i).
If your interested PM me.

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