Perma-proto board ampacity

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drbrodie
 
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Perma-proto board ampacity

Post by drbrodie »

Can you tell me the ampacity of both the power and signal traces of the Perma-proto boards?

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adafruit2
 
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Re: Perma-proto board ampacity

Post by adafruit2 »

hi there's no such thing as intrinsic 'ampacity' of a PCB as it depends on voltage and length and ambient temp! :)
the signal traces are 16 mil wide, 32mil wide for the power lines. 1 oz copper - you can use a calculator to determine how much current traces of a certain length can carry given the voltages you are using

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damofromoz
 
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Re: Perma-proto board ampacity

Post by damofromoz »

Hi and a Merry Christmas to all,

I would like to run 12V through one of the Perma-proto boards (https://www.adafruit.com/products/1606). My idea is to power this circuit board with 12V, 3A power supply, and break out into somewhere between 2 and 6 separate circuits over long distances (10m or more) to power Raspberry Pis (@ 5V). These distances will be facilitated using UTP with Passive PoE connectors.

Each run of the PoE connections wired to the circuit board would have its voltage individually regulated using a Potentiometer (dial type), so that the Voltage can be set correctly for individual cable lengths (correcting for voltage drop) ensuring each Pi only receives 5V. Is there a better/easier way to do this?

I used this calculator (http://www.eeweb.com/toolbox/external-p ... ax-current) using the following inputs:

Trace Width: 16mil (I think this means milli-inches? - is this right? I'm Aussie so we are all metric here).
Trace Thickness: 0.034798mm (based on 1oz copper being a thickness of 0.000034798m - http://electronics.stackexchange.com/qu ... -trace-len)
Temp Rise: 10C
Ambient Temp (35C - I live in tropical climate)
Length: 20cm (I know its a mixture of 16 and 32mil trace, but this is being conservative and about the length of the PCB)

The calculator outputs the following:
Max current: 1.2amps
Trace Temp: 45C
Resistence: 0.000657ohms
Voltage Drop: 0.000788Volts
Power Dissipation: 0.000949Watts

But the calculator doesn't ask about input Voltage. My question is whether this perma-proto board can cope with 12V, and this many Raspberry Pis (between 2 and 6 Pis) with this type of arrangement and these calculations? Have I worked this out correctly (or have I misunderstood some units?). If this won't work, what would be an alternative approach?

Thanks in advance.

Regards,
Damien.

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damofromoz
 
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Re: Perma-proto board ampacity

Post by damofromoz »

Hi Again,

I wonder whether using something like this VERTER Buck-Boost (https://www.adafruit.com/products/2190) might be a simpler and more reliable approach to my previous post. It does the conversion of voltage at the Pi, rather than at the source, so it can ensure nice 5V no matter what voltage it receives (as a result of voltage drop from varying lengths of cable).

I did have a question though. If I use something like a VERTER, or even the UBEC Buck (https://www.adafruit.com/product/1385), and connect it directly to the 5V and GND pins on the GPIO header of a Raspberry Pi, is there no fuse protection? For instance, if powering a RPI via its micro-USB connector, there are some protections in place such as a fuse and a capacitor. If I am going to connect the VERTER or UBEC directly to the 5V & GND pins on the GPIO header, should I also add a fuse and capacitor? Or is this not necessary with these converters?

Thanks again. :)

Damien.

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adafruit_support_bill
 
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Re: Perma-proto board ampacity

Post by adafruit_support_bill »

If the wires are long, you are better off keeping the voltage high and using a buck converter (e.g. UBEC) at the point of use. Wiring direct to the GPIO bus does bypass the on-board fuse. We do have USB connectors in the store, so you can wire one of those up to the UBEC output and feed power via the USB port.

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damofromoz
 
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Re: Perma-proto board ampacity

Post by damofromoz »

Hi Bill,

Thanks for the prompt reply.

Rather than wiring up a usb connector, I'd like to put something like the UBEC or VERTER 5V inside a RPI case, and have it all self-contained, rather than external.

What if I used my own fuse, connecting between the positive of the Buck (whichever one I use), and the 5V pin on the GPIO header? I had a look on adafruit store, but couldn't find a 2A fuse (for Model B+), so how about something like (http://www.ebay.com.au/itm/MF-RHT200-FU ... 5b0248e95c)?

Would that provide sufficient protection?

I wouldn't normally worry about the fuse, except I plan to locate the raspberry pis in my ceiling and I want to avoid any fire hazards.

Thanks again for your assistance.

Regards,
Damien.

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adafruit_support_bill
 
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Re: Perma-proto board ampacity

Post by adafruit_support_bill »

For fuse recommendations on the Pi, I'd check with the raspberry Pi forums. I suspect you would want something with a similar rating to what is on-board.
http://www.raspberrypi.org/forums/

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