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Power issues

Wed Aug 08, 2012 12:28 pm

I'm currently using a newer model BlackBerry charger with an output of 5V 750ma. I have a USB keyboard, wireless USB mouse, and network cable attached to my Pi, but upon powering on the keyboard still lags, meaning that there's a delay when I type, and letters get repeated. I know this is caused by the power adapter not being high enough to handle the output, but is there any reason why a 750ma charger wouldn't work? I was looking at this one and was wondering if it would work better? ... 40v-129498

Any advice appreciated. Thanks.

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Joined: Tue Jan 17, 2012 2:38 pm

Re: Power issues

Wed Aug 08, 2012 12:38 pm

There may be no problem with your power supply. You can test the voltage by using the instructions at ... r_problems

Remember that a cheap power cable can cause power problems.

It is possible that the keyboard is drawing too much current and is overloading the 140mA polyfuse on the USB port.

See also ... ey_presses

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Re: Power issues

Wed Aug 08, 2012 12:43 pm

tail -f /var/log/syslog
How To ask Questions :-
WARNING - some parts of this post may be erroneous YMMV


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Re: Power issues

Wed Aug 08, 2012 1:21 pm


I wonder how much power does the wireless mouse dongle use? Could it be drawing enough to impact your keybaord functioning?

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Joined: Wed Aug 08, 2012 1:43 am

Re: Power issues

Thu Aug 09, 2012 12:20 pm

In looking at the power rating on my keyboard I noticed that it's drawing 1.4A which is more than what my charger can provide. I will be replacing it with a keyboard that uses less power.

Is a 750mA charger good enough to use with a Pi, or should I invest in a 1000mA one?

Thanks for your help!

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Joined: Sun Jul 29, 2012 9:06 pm

Re: Power issues

Thu Aug 09, 2012 12:55 pm

1.4 Amps? Does it has a buildin heater or something? The usb specification does not allow a device to consume more than 500mA. Low power usb devices should stay below 100mA. Keyboards and mice are normally low power devices. It's hard to say if a 1 Amp supply will work better than a 700mA supply. It all depends upon the output voltage, the ripple on that voltage, and the stabilisation of it under different load conditions. I currenty use the RS components 1.2 amps one. They have been on backorder for a while, but I got a mail today that they shipped my second one. So I assume they have them back in stock.
I have 5.02 volt between TP1 and TP2. This is with not much additional usb loads. (Pi to self powered usb hub and devices connected to that.)

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