cupcake
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Battery to power RPi and powered HUB

Tue Jul 31, 2012 4:09 pm

Forgive the ignorance in my questions, but I'm trying to put together a rover using the RPi. I want to it be fully wireless, meaning no power cable and no ethernet cable.

For stable wifi , I intend power a USB wifi adapter (and possible other USB addons, such as a webcam) using the CyberPower Hi-Speed USB Hub 4-Port. There are also some DC motors on the motors, but for simplicity I can just power those separately.

Now the question is, how do I best power the RPi and the powered HUB from the same power source?

Can I power the HUB directly and then power the RPi (and other USB devices) from the HUB? Meaning I just need to find a suitable rechargeable battery for the HUB.

Or would I need to power the RPi and the HUB separately? If so, can I rely on the power source providing 5V and adequate amps to both or will I need some sort of regulation in between?

Cheers.

ceros
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Re: Battery to power RPi and powered HUB

Wed Aug 01, 2012 4:26 pm

Umm I think that if you only plug a battery on the USB HUB you should be fine. The HUB will supply the 5v to the RPi so you wont have to bother dropping the battery voltage to 5v for the RPi. So basically, if you HUB is running on 12v, you can get yourself a 3s lipo.

The other way is feasible also.

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jbeale
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Re: Battery to power RPi and powered HUB

Wed Aug 01, 2012 5:42 pm

Yes, you can power the R-Pi using a USB to microUSB from hub to R-Pi. Then you just need to power the hub with +5V at enough current for the Pi plus any USB devices. One easy way is with a 12V battery (gel cell, motorcycle battery, etc.) plus a 12V -> 5V USB charger for use in a car. Those are readily available, for example
http://www.amazon.com/PowerGen-Dual-Hea ... B006SU0SX0

...that one is two amps; if 1A will do, they are even cheaper. If you have only the R-Pi and WiFi and nothing else, 1 A ought to be enough, but the cheap charger devices are known to be a bit loose with the accuracy of their claimed current rating.

Or, with a bit more soldering, you can get a step-down supply
http://www.ebay.com/itm/HRD-Series-DC-D ... 0738825099

or step-up power supply, if you are coming from a single Lithium cell:
http://www.ebay.com/itm/New-DC-DC-Conve ... 0549121759

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jackokring
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Re: Battery to power RPi and powered HUB

Wed Aug 01, 2012 6:47 pm

So if the HUB powers the Pi, and the Pi also sends data to the HUB via another USB cable, then an earth loop will form, if the HUB connects the power from the USB in B connector. Any reasonable design should not, as it would use isolation of the supply. Some badly designed USB HUBs may have problems. Check the resistance between the input USB metal shield and the output metal shield with no power connected to the HUB, with a multimeter.
Pi[NFA]=B256R0USB CL4SD8GB Raspbian Stock.
Pi[Work]=A+256 CL4SD8GB Raspbian Stock.
My favourite constant 1.65056745028

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jbeale
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Re: Battery to power RPi and powered HUB

Wed Aug 01, 2012 8:36 pm

There is no electrical problem using a R-Pi powered from the same hub that it uses for data connection (in fact that very configuration was suggested by one of the Pi's designers). The microUSB and regular USB cables both carry GND and +5V. Many hubs simply connect the +5V straight across from input to output, and all USB hubs use a common ground. In this case, it works OK. The power connections work in parallel, so you just have a lower impedance power path.

There could be a problem if you have significant high-frequency AC currents running on your ground lead, but the power-supply bypass caps on the R-Pi should prevent that from happening.

cupcake
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Re: Battery to power RPi and powered HUB

Fri Aug 03, 2012 12:00 am

Thanks for some great answers.

However, AFAIK powered HUBs still only provide a max of 500 mA per port. Isn't the RPi demanding 700 mA?

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mahjongg
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Re: Battery to power RPi and powered HUB

Fri Aug 03, 2012 12:20 am

Most hubs are electronically simple and do not limit current out of their ports, except for when a short circuit occurs.

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jackokring
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Re: Battery to power RPi and powered HUB

Fri Aug 03, 2012 12:37 am

jbeale wrote:There could be a problem if you have significant high-frequency AC currents running on your ground lead, but the power-supply bypass caps on the R-Pi should prevent that from happening.
I'm an electronic engineer, please explain as you seem to misunderstand the meaning of bypass capacitor as opposed to decoupling capacitor. Placing ground loops near strong magnetic fields can lead to self heating of the PCB tracks, ground bounce and many other microelectronic abuse effects.
Pi[NFA]=B256R0USB CL4SD8GB Raspbian Stock.
Pi[Work]=A+256 CL4SD8GB Raspbian Stock.
My favourite constant 1.65056745028

cupcake
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Re: Battery to power RPi and powered HUB

Mon Aug 06, 2012 5:22 pm

I was successfully able to power USB devices (wifi adapter, webcam) and the RPi using my CyberPower Hi-Speed USB Hub 4-Port - which makes everything a lot easier.

Thanks for the input, everyone.

Next step will be to replace the AC adapter with a battery.

calebzulawski
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Re: Battery to power RPi and powered HUB

Tue Aug 07, 2012 8:15 pm

What kind of battery are you planning on using?

I'm doing more or less the same thing with a Li-Po, I've worked everything out but I haven't built it yet.

cupcake
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Re: Battery to power RPi and powered HUB

Wed Aug 08, 2012 12:43 am

What kind of battery are you planning on using?

I'm doing more or less the same thing with a Li-Po, I've worked everything out but I haven't built it yet.
That is a good question. I'm in the process of deciding on one. I'm a little confused as to the various options that are available. I have a thread on that here,

In terms of NiMH vs LiPo, I understand that LiPo are better in most ways. However, it seems LiPos don't come in 5V but rather in multitudes of 3.7V. I figured I'd keep it simple and go for a 5V NiMH battery to avoid having to step up/down the voltage.

Grumpybeard
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Re: Battery to power RPi and powered HUB

Sat Mar 02, 2013 2:34 pm

Hi,

Did you get the powered hub working from a battery, im looking to do a rover build and need a battery power source to supply a hub.

Many thanks

Grumpybeard
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Joined: Sat Mar 02, 2013 2:04 pm

Re: Battery to power RPi and powered HUB

Fri Mar 08, 2013 9:47 pm

Anyone know of options for powering a 12v usb hub via lipo for example so it can power rpi and devices on rover? Thanks.

ridgelift
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Re: Battery to power RPi and powered HUB

Fri Mar 08, 2013 10:18 pm

Radio control hobby BEC's "battery elimination circuits" are step-down dc voltage converters by any other name. Most have a wide range of input voltages. The range of output voltages are limited to mostly 5VDC. It is a good idea to keep the battery voltage reasonably close to the output voltage to reduce overheating of the BEC. The ones I have tried run warmer (wasted power) if regulating voltages from the top of the advertised input voltage range.

http://www.hobbyking.com/hobbyking/stor ... -UBEC.html

http://dx.com/p/8s-5a-switch-mode-ultim ... ubec-45214

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