dave_p
Posts: 28
Joined: Sun Mar 04, 2012 2:11 pm

Best place to connect power?

Tue Oct 09, 2012 12:28 pm

I want to use my (version 2) Pi with a USB disk drive and a USB TV card, powering everything from a single 5v 3A supply. Where is the best place to apply the power? The normal micro-USB has a poly fuse which will blow at the estimated 1.5A drawn by this rig. I could connect to TP1 and TP2, but some of the PCB traces on the board are awfully thin and I don't know whether those points have a low-resistance connection to the 5v bus. Alternatively, since most of the power is being drawn by the USB peripherals, I could connect to the power contacts for the USB connectors.

I don't want to get involved with USB hubs or any more cabling, just solder the PSU wires somewhere on the board. Any thoughts?

drgeoff
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Re: Best place to connect power?

Tue Oct 09, 2012 1:48 pm

I can think of two possibilities:

1. Keep the heavy current to the USB peripherals off the RPi board altogether. Open the power connections in the USB cables and feed power in there (and in parallel to the RPi's power socket or PCB at the socket.)

2. Feed power to the power pins of the USB sockets and to the PCB just after the polyfuse.

Dilligaf
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Re: Best place to connect power?

Tue Oct 09, 2012 2:21 pm

Easiest would be gpio pins 2(power) and 6(ground) you can use an old cd audio or pc fan connector

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abishur
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Re: Best place to connect power?

Tue Oct 09, 2012 2:38 pm

I would keep TP1 and TP2 unused and available for testing, but dave_p made a good suggestion about using the 5V rail pins in the GPIO strip. You might want to put *some* kind of protection there though. Like a voltage clamp.

It might also be worth while to split the power cable into two connections. One going through the micro usb plug and another going to the 5v rail after feeding it through another 1.5 amp poly fuse. This would allow for a total of 3A to be pulled from the power supply but would still provide a modicum of protection in a surge situation.
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drgeoff
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Re: Best place to connect power?

Tue Oct 09, 2012 3:10 pm

Dilligaf wrote:Easiest would be gpio pins 2(power) and 6(ground) you can use an old cd audio or pc fan connector
But are the PCB tracks between those GPIO pins and the USB sockets thick enough? That is why I didn't add that method to the two that I suggested.

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abishur
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Re: Best place to connect power?

Tue Oct 09, 2012 4:35 pm

drgeoff wrote:
Dilligaf wrote:Easiest would be gpio pins 2(power) and 6(ground) you can use an old cd audio or pc fan connector
But are the PCB tracks between those GPIO pins and the USB sockets thick enough? That is why I didn't add that method to the two that I suggested.
Everything I've heard would indicate that the 5v rail PCB tracks are a uniform thickness throughout the board (well maybe different at TP1/2 but that's only for the initial contact, once you get beyond that initial spot it returns to the same thickness). And that thickness should be sufficient to support the additional current draw we're talking about :-)
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dave_p
Posts: 28
Joined: Sun Mar 04, 2012 2:11 pm

Re: Best place to connect power?

Tue Oct 09, 2012 4:56 pm

Many thanks for the comments. I've connected my power feed to the 5v and 0v pins of the USB sockets (with a beefy 'idiot diode' upstream to guard against connecting the wrong way round) and everything is working well.

dnetman99
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Joined: Thu Nov 29, 2012 7:38 pm

Re: Best place to connect power?

Sun Jan 13, 2013 11:53 am

Is there anyway you can provide specs for what you built in the way of powersupply? I am new to the power side and want to make sure I do not fry everything I have in the box.

dave_p
Posts: 28
Joined: Sun Mar 04, 2012 2:11 pm

Re: Best place to connect power?

Sun Jan 13, 2013 4:11 pm

I didn't build a power supply, I bought one. Maplin order code L45BL - not the cheapest but Maplin's have a shop just down the road.

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