admax88
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Re: Acceptable input voltages for power?

Thu Mar 08, 2012 6:51 pm

How sensitive is the voltage regulator?

I'm planning on using mine in a mobile application.  I'm hoping to power it from lithium ion cells, however they generally only coming in 3.7V.

Would the device handle 7.4V without damage?  Or will I need a separate external voltage regulator.

Alternatively I'm considering using a boost converter to boost 3.7V cells to 5V, any concerns I should know about this?

Thanks for the help!

AlexPT
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Re: Acceptable input voltages for power?

Thu Mar 08, 2012 6:56 pm

Oh here: http://www.raspberrypi.org/archives/260

It got a fixed 5V input, and something whit 700mA at last.

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TheCrazyInventor
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Re: Acceptable input voltages for power?

Thu Mar 08, 2012 7:14 pm

You can TOTALLY forget powering the Pi from 7.4 volts. Don't even try. The input voltage must be between 4.75 and 5.25 volt IIRC. You can use a boostconvertor, but make sure it can output at least 1A for the Pi and perhaps anything else you decide to hook up (I know they keep telling us 700mA is fine, but it doesn't hurt to have a little extra).
"Anything that can possibly go wrong, does" -M

drgeoff
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Re: Acceptable input voltages for power?

Thu Mar 08, 2012 7:20 pm

I have a couple of these on order.

http://www.ebay.co.uk/itm/1607.....538wt_1179
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admax88
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Re: Acceptable input voltages for power?

Thu Mar 08, 2012 7:21 pm

Thanks for the info.

The FAQ (http://www.raspberrypi.org/faqs) says that you could power it off of 4 AA batteries.  Which would be a little over 6V when the AAs are fully charged.  So if it could power it off of 6V safely I wasn't sure how much higher it could handle safely.

Is there any issues with the fact that a boost converter is a stepping power supply?  How sensitive is the device to small rapid voltage fluctuations?

drgeoff
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Re: Acceptable input voltages for power?

Thu Mar 08, 2012 8:23 pm

admax88 said:


Thanks for the info.

The FAQ (http://www.raspberrypi.org/faqs) says that you could power it off of 4 AA batteries.  Which would be a little over 6V when the AAs are fully charged.  So if it could power it off of 6V safely I wasn't sure how much higher it could handle safely.

Is there any issues with the fact that a boost converter is a stepping power supply?  How sensitive is the device to small rapid voltage fluctuations?


If you want to use AA cells I'd strongly recommend rechargeable NiMH ones rather than alkaline use once and throw away.

1.  They are more economical

2.  They are more environmentally friendly

3.  They don't get much over 1.4 volts even when fully charged.

There should be capacitors on the output of power supplies to reduce voltage ripple to a small value.  There is also a capacitor on the input of the RP.
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AstonishingLee
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Re: Acceptable input voltages for power?

Thu Mar 08, 2012 8:31 pm

A simple solution would be to use a voltage regulator to reduce the voltage to the required level. The following would do the job

http://www.rapidonline.com/Ele.....1bd3d90a65

Simply connect the ground pin and a voltage above 5v to vin and it provides a steady 5v out on the third pin.

I can't see why this approach wouldn't be safe

Hope it helps.

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rurwin
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Re: Acceptable input voltages for power?

Thu Mar 08, 2012 8:33 pm

The specified voltage requirement for USB is 4.75V-5.25V. That is the standard range for 5V logic. Anything outside that range may cause damage to the RPi or connected USB devices.

The 7805 requires an input voltage above 7.5V, and requires a heatsink.

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Re: Acceptable input voltages for power?

Thu Mar 08, 2012 8:45 pm

AstonishingLee said:


A simple solution would be to use a voltage regulator to reduce the voltage to the required level. The following would do the job

http://www.rapidonline.com/Ele.....1bd3d90a65

Simply connect the ground pin and a voltage above 5v to vin and it provides a steady 5v out on the third pin.

I can't see why this approach wouldn't be safe

Hope it helps.



Straightforward yes, but remember the input voltage has to be higher than the regulated output voltage, I think you'd have to drive it with at least 6 AA batteries to keep on the safe side.

(I had a look - Maplins JG78K 6AA Battery Box Long @ 20p (eh?) )
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AstonishingLee
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Re: Acceptable input voltages for power?

Thu Mar 08, 2012 8:48 pm

Good point,  I stand corrected.

The 7805 is an option though with a 9v pp3 battery, even if it does mean putting some thought into heat dissipation.

It'll be interesting to see what sort of battery life we can get out of it.

drgeoff
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Re: Acceptable input voltages for power?

Thu Mar 08, 2012 8:55 pm

As rurwin says, don't forget the heatsink.  It needs to get rid of 2 to 3 watts just powering the RP.

If you are running from 6 cells then almost half of the battery power is being converted to heat in a linear regulator.  If that is a concern the consider something like

http://www.ebay.co.uk/itm/3306.....3109wt_946
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drgeoff
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Re: Acceptable input voltages for power?

Thu Mar 08, 2012 8:57 pm

AstonishingLee said:


Good point,  I stand corrected.

The 7805 is an option though with a 9v pp3 battery, even if it does mean putting some thought into heat dissipation.

It"ll be interesting to see what sort of battery life we can get out of it.


A PP3 (aka 1604 or 6LR61) isn't really man enough to deliver 700mA.  A rechargeable version is only about 200mAH so theoretically would last 17 minutes.  In practice significantly less.

A non-rechargeable version will have such a high internal resistance that trying to take 700mA from it will result in much less than 9 volts.
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kertis
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Re: Acceptable input voltages for power?

Thu Mar 08, 2012 10:45 pm

I do not want to create another power related thread so I ask here. I have USB 3.0 external HDD, powered from one USB. Now it works with my laptop where are only USB 2.0 ports, but it works fine. The same with my tv (also works on one USB 2.0).

On hdd case, near the cable, there is an informaton, that this disk needs 900mA.

I'm going to buy 5V 2A charger to my R.PI, and a question is: is it going to work without Y cable only on one USB (this hdd do not have Y cable, one usb only)?

R.Pi draws  700mA + hdd 900mA = 1600mA so with 2A charger I still have 400mA for other stuff like mice or keyboard extra.

I found some posts and comments saying that from one 2.0 USB it is only allowed to draw max 500mA, but my laptop (and tv) can feed this external HDD from only one plug. Is any restriction on PI to give max 500mA from one USB?

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Re: Acceptable input voltages for power?

Thu Mar 08, 2012 10:54 pm

I'm surprised your HDD doesn't come with a Y cable, because the maximum specified power from USB is indeed 500mA. But I think many devices do not enforce that.

However, the RaspPi reportedly has self-resetting fuses limiting current to 100mA. So your HDD wont work unless you put a powered hub between the two.

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Re: Acceptable input voltages for power?

Thu Mar 08, 2012 10:58 pm

Or by voiding your warranty and removing 2 fuses, and possibly replacing a third... but I'd go with Rurwin's suggesting
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kertis
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Re: Acceptable input voltages for power?

Fri Mar 09, 2012 7:43 am

rurwin said:


I"m surprised your HDD doesn"t come with a Y cable, because the maximum specified power from USB is indeed 500mA. But I think many devices do not enforce that.


I have this drive: TOSHIBA STOR.E ALU 2S 

Specification says: On-bus power: max. 900 mA

This drive is sold with only one cable (with one plug). Perhaps they put inside low powered disk, and normally 500mA is enough to spin-up.


However, the RaspPi reportedly has self-resetting fuses limiting current to 100mA. So your HDD wont work unless you put a powered hub between the two.


Using powered hub is not a big problem, except one important thing. I could be difficult to spin down HDD when idle. I'm afraid that it could be even impossible.

kertis
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Re: Acceptable input voltages for power?

Fri Mar 09, 2012 7:43 am

rurwin said:


I"m surprised your HDD doesn"t come with a Y cable, because the maximum specified power from USB is indeed 500mA. But I think many devices do not enforce that.


I have this drive: TOSHIBA STOR.E ALU 2S 

Specification says: On-bus power: max. 900 mA

This drive is sold with only one cable (with one plug). Perhaps they put inside low powered disk, and normally 500mA is enough to spin-up.


However, the RaspPi reportedly has self-resetting fuses limiting current to 100mA. So your HDD wont work unless you put a powered hub between the two.


Using powered hub is not a big problem, except one important thing. I could be difficult to spin down HDD when idle. I'm afraid that it could be even impossible.

DaveDaGr8
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Re: Acceptable input voltages for power?

Fri Mar 09, 2012 6:42 pm

900 mA HDD may or may not work. I have an old drive with a y cable, and it works on one computer without it, but not on another so it's touch and go.

NO it will probably never spin down. BUT, my HDD plugged into my WD live never span down either so it'll be interesting to see if the HDD will ever spin down on the RP anyway.

Getting back on topic

I think we need a USB -> RP power cord.

The computer will pump out 1.5A/5A @ 5V in battery charging mode and an iphone charger puts out 1A @ 5V, so both of those options should run it. If your USB doesn't have battery charging mode, then you should be limited to 500mA ( but not always).

I have several of those Wall outlet -> USB chargers now and i'd suspect most other people do too. If not, they're damn cheap and can be picked up anywhere. As long as they put out 1A @ 5V you should be sweet. As an added bonus, they're fairly safe for kids to use too.

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Re: Acceptable input voltages for power?

Mon Feb 18, 2013 10:21 pm

i make an adapter of 6.2v 2.1A.
can i use it as power source for pi,or i have to take some modification?
plz tell me what will i do.


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mahjongg
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Re: Acceptable input voltages for power?

Mon Feb 18, 2013 11:09 pm

admax88 wrote:Thanks for the info.

The FAQ (http://www.raspberrypi.org/faqs) says that you could power it off of 4 AA batteries.  Which would be a little over 6V when the AAs are fully charged.  So if it could power it off of 6V safely I wasn't sure how much higher it could handle safely.
The FAQ is wrong!
The FAQ is talking about the very first prototype of the PI, which indeed had an onboard 5V regulator, so it could accept 6V input. The final PI's cannot, they need less than 5.25V.
In fact if you would ever apply 6V to the current PI's there is an over-voltage protection device that would trip and short the power, which would then blow the polyfuse.

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Re: Acceptable input voltages for power?

Mon Feb 18, 2013 11:15 pm

admax88 wrote:Thanks for the info.

The FAQ (http://www.raspberrypi.org/faqs) says that you could power it off of 4 AA batteries.  Which would be a little over 6V when the AAs are fully charged.  So if it could power it off of 6V safely I wasn't sure how much higher it could handle safely.
The FAQ used to be wrong!
The original FAQ was talking about the very first prototype of the PI, which indeed had an onboard 5V regulator, so it could accept 6V input. The final PI's cannot, they need less than 5.25V.
In fact if you would ever apply 6V to the current PI's there is an over-voltage protection device that would trip and short the power, which would then blow the polyfuse.

Now the FAQ says:
Yes. The device should run off 4 x AA rechargeable cells, but there may be stability issues as the batteries lose their charge. Using 4 x AA Alkaline cells will result in 6v and it is therefore recommended to use a voltage regulator.
Rechargeable cells are 1.2V, so four of them would create 4 x 1.2 = 4,8V which is just barely above the bare minimum of 4.75V, so the PI would work, for a very short time.
Normal batteries are 1.5V, and would create 6V, so you would need a regulator that is able to work with 6V input and 5V output, a "low drop regulator". Most of this need a minimum of 0.8V to work with leaving you again with a very small margin!

mrteach
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Re: Acceptable input voltages for power?

Mon May 26, 2014 3:35 am

Hmm I accidentally put 7.4-8v through the microusb of my pi... It didn't trip the polyfuse for some reason as I could see it start up on my monitor. It was blinking a bit but that could of been my monitor (trying to power it with the same battery).

I re-powered it using separate power sources and 5v on my pi. and it loaded the same screen which is normal... Will I see foreseeable damage to my pi? nothing smoked or anything. My pi doesn't have anything currently loaded on it. so it is the 'format' expand memory etc.. screen.

I did have a arduino smoke up on me once (voltage regulator melted)... it still worked... but replaced the voltage regulator in case.

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Re: Acceptable input voltages for power?

Mon May 26, 2014 4:44 am

mrteach wrote:Hmm I accidentally put 7.4-8v through the microusb of my pi... It didn't trip the polyfuse for some reason as I could see it start up on my monitor. It was blinking a bit but that could of been my monitor (trying to power it with the same battery).

I re-powered it using separate power sources and 5v on my pi. and it loaded the same screen which is normal... Will I see foreseeable damage to my pi? nothing smoked or anything. My pi doesn't have anything currently loaded on it. so it is the 'format' expand memory etc.. screen.

I did have a arduino smoke up on me once (voltage regulator melted)... it still worked... but replaced the voltage regulator in case.
The RPi has an over-voltage protection diode (D17) which works in conjunction with the polyfuse (F3). Your RPi is probably OK if it was not left on for too long. If too long, D17 might heat up and burn out. In that case the RPi would still work normally but your RPi would not be protected should you have another over-volt incident.
Unless specified otherwise my response is based on the latest and fully updated RPiOS Buster w/ Desktop OS.

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Re: Acceptable input voltages for power?

Mon May 26, 2014 11:09 am

if you want to power your mobile application from a lithium ion cell then the input voltage should be between 4.75 and 5.25 volt.

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