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rurwin
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Re: Potential power source

Wed Mar 21, 2012 10:09 am

alexeames said:

I keep mine in an ammo box in the garage, when not in use.
Some years ago I was involved with an amateur theatrical event, and they asked me to provide some special effects. I sourced some stage maroons (firework bangers with an electrical fuse) in small, medium and large and I made a control board to trigger them.

At a rehersal I tried the gear out for the first time. Everyone went outside, and I wired up the control board to a small maroon, which I placed in an ammo box. Because I though there might be some flying debris, I closed the lid to the extent it was resting on the box. I was not stupid enough to close it firmly or clamp it down.

When I fired the maroon, the sound was terrific, the ammo box opened out like a fruit bowl, and the (previously hinged) lid flew so high that we had time to wonder where it had gone before it landed.

The idea of using special effects was quietly shelved.

Now, where did you keep those batteries again?

Tharic-Nar
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Re: Potential power source

Wed Mar 21, 2012 10:57 am

I was looking around for something similar too. Wanted to avoid Lithium batteries since when one goes bust, need a completely new unit, so I like to stick to good old AA sources. Something like this should be able to handle things.

There is the small issue of 4x 1.2v batteries only supplying 4.8v for a device that needs 5v; I don't know how picky the RPi will be over supplied voltage and if the battery pack will step it up to 5v. Most of the NiMH batteries I have are the 2000mAh, low discharge type. I'm just wondering if this will work.

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alexeames
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Re: Potential power source

Wed Mar 21, 2012 12:21 pm

rurwin said:


Now, where did you keep those batteries again?


Lol. The difference here is that I don't expect or want them to go bang. But if they do, would it be better that they were in a metal box or there was nothing to contain or retard the fire? I think it's better in a box, than not in a box, but I have had this discussion with others before who disagree. One guy told me to drill a hole in it because he'd seen a case where someone opened an ammo box which had contained an explosion and it took his face off when he opened it.

Tharic-Nar, you can get a device to regulate the voltage up to 5v - a few quid on ebay.
Alex Eames RasPi.TV, RasP.iO

ajwillys
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Re: Potential power source

Wed Mar 21, 2012 12:43 pm

Thanks everyone for the information.  I guess these are definitely out of the question, for my skills at least.  I'll probably go the boring simple route of getting a USB battery pack.  Thanks!

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Re: Potential power source

Wed Mar 21, 2012 3:15 pm

Ah, it would appear to be an inefficient battle using these external 5v charger packs. After digging, most of this has been discussed in another thread. Basically, if we were to use a 5v external battery pack, half the power would be lost in heat due to the RPi's power conversion. In order to get better efficiencies, we would need to replace the default power regulator (this was a cost decision). We could still use a USB battery pack, but we'd only get a couple of hours out of it.

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alexeames
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Re: Potential power source

Wed Mar 21, 2012 4:42 pm

That will still be true however you power your Pi though. If you want best efficiency running from batteries changing the reg is your way to go. If you're powering from mains it's questionable whether it's really worth it (unless you like tinkering, which a lot of us do )
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kathryn
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Re: Potential power source

Thu Mar 22, 2012 12:43 am

The extra current capacity is not a drawback; in fact, it is a bonus.  The device will only draw what it needs.

Looks interesting to me - of course, it costs more than the Pi itself, but then again...  I wonder how much it weighs (I couldn"t tell that from the site)

Does this mean that my iPad charger (2.1A) will work?

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alexeames
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Re: Potential power source

Thu Mar 22, 2012 8:35 am

Kathryn said:


Does this mean that my iPad charger (2.1A) will work?


If  it fits micro USB (for the Pi end), yes it will.
(Or you have a cable or adaptor for it to make it fit micro USB)
Alex Eames RasPi.TV, RasP.iO

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Re: Potential power source

Sat Mar 24, 2012 12:01 am

Bingo!

http://www.7dayshop.com/catalo....._id=108549

Supplies uninterrupted power to your
iPhone/iPod.
Charge the internal battery through the iPod USB cable or AC
adapter (Charging time around 2 Hours)
- Battery Capacity: 3.7V /
1900mAh
- Input: 5V 500mAh
- Output: 5V 500mAh
- Size: 67 x 62 x 15mm

Ostendo ignarus addo scientia.

pygmy_giant
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Re: Potential power source

Sat Mar 24, 2012 12:08 am

err... maybe not bingo actually, unless 2 in parallel...?

Think maybe:

http://www.ebay.co.uk/itm/New-.....1e6c86ef3d

instead with step-down switching regulator....?

1x Battery for Casio NP-100 camcorder - 7.4V and 2400mAh or similar - £9

Ostendo ignarus addo scientia.

pygmy_giant
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Re: Potential power source

Sat Mar 24, 2012 12:23 am

or even: http://www.ebay.co.uk/itm/5000.....19cee0afdb - Universal 5000mAh Portable External Power Source Pack Battery Charger for iPhone, iPad, iPod, HTC, Samsung, Motorola, etc... - £12.99 ?
Ostendo ignarus addo scientia.

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Re: Potential power source

Sat Mar 24, 2012 9:37 am

pygmy_giant said:


err… maybe not bingo actually, unless 2 in parallel…?


Why not? It says output 5v. It's probably got a step-up regulator in it. Or were you thinking 1900 mAh not enough?
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poing
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Re: Potential power source

Sat Mar 24, 2012 9:57 am

I wonder about how hard the 700mA figure is. The model A is rated @ 500mA while the only difference is an extra USB port and an Ethernet port. But when you work from batteries you're not likely to have a Ethernet cable attached, so maybe 500mA would be just fine?

rmm200
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Re: Potential power source

Sat Mar 24, 2012 3:10 pm

I probably missed an obvious reference - but I think folks will be amazed at how little power the Pi actually requires. The 500ma and 700ma figures are the max that should be drawn over the power lines, which includes downstream use. With a powered hub and an independent display, I would expect the Pi to use less power than any cell phone. Most cell phone power is used by the internal display and transmitter; neither of which Pi has.

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Re: Potential power source

Sat Mar 24, 2012 3:27 pm

mAh is not a measurement of current strength, it is a measurement of current sustainability.

if the battery is rated for 500mAh when fully charged, it will power a device that draws 500mA for 1 hours, or a device that draws 1000mA for 30 minutes.

for beginners: when you are dealing with batteries, don't get "mA" and mAh" confused.

drgeoff
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Re: Potential power source

Sat Mar 24, 2012 4:22 pm

rmm200 said:


I would expect the Pi to use less power than any cell phone. Most cell phone power is used by the internal display and transmitter; neither of which Pi has.


All the statements in that last sentence may be true but that does not mean the expectation expressed in the first sentence necessarily follows.  The phone's display and transmitter are switched off most of the time.  The phone's CPU is also idling most of the time.

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Re: Potential power source

Sat Mar 24, 2012 4:35 pm

Well the current draw of the Pi is certainly easy enough to measure, but the Wiki does not have it. Could someone with a dev board hang a meter on the power line of a booted-up Pi with an active hub for peripherals and a display? I for one would like to see the numbers.

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rurwin
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Re: Potential power source

Sat Mar 24, 2012 4:37 pm

It isn't that easy. The current draw depends on lots of variables including how hard both of the processors are working and the pattern of that work.

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Re: Potential power source

Sat Mar 24, 2012 4:57 pm

rurwin said:


It isn't that easy. The current draw depends on lots of variables including how hard both of the processors are working and the pattern of that work.


the "variables" are fairly controllable, some PSU benchmark for idle, 50% CPU and 99% CPU load on a selected OS (Debian or whatever) both with and without a graphical UI installed and no peripherals connected would ease most of my curiosity at least.

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Re: Potential power source

Sat Mar 24, 2012 7:46 pm

rurwin said:


It isn't that easy. The current draw depends on lots of variables including how hard both of the processors are working and the pattern of that work.



I was pretty specific - booted up. Nothing else would be running except steady state. Not even logged in. Fancier numbers under load could come later.

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Re: Potential power source

Sat Mar 24, 2012 10:25 pm

Most ATX PSUs have a 5V standby, negating the need for any fans to be running.  The 300W unit I sometimes use as a bench PSU, has a 5V 2A standby output, more than enough for a PI.

For a different battery option, LiFePO4 maybe worth a look. They are more robust than LiPo batteries, less likely to catch fire and don't mind a bit of abuse.  They weigh slightly more than a LiPo and can't deliver as much current, but for a 700mA PI, that shouldn't be a huge concern.

Hyperion have a range of LiFe packs for RC receivers and transmitters: http://media.hyperion.hk/dn/fg3radio/.

Finally, I noticed earlier B&Q have some 1A USB plugs at the moment for £3.98, which seems pretty reasonable to me and would hopefully be a good quality unit.

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Re: Potential power source

Sun Mar 25, 2012 8:51 am

PIrate said:


For a different battery option, LiFePO4 maybe worth a look. They are more robust than LiPo batteries, less likely to catch fire and don't mind a bit of abuse.  They weigh slightly more than a LiPo and can't deliver as much current, but for a 700mA PI, that shouldn't be a huge concern.
Hyperion have a range of LiFe packs for RC receivers and transmitters: http://media.hyperion.hk/dn/fg3radio/.


Robot Birds are the UK Hyperion dealer (but you can also buy direct and import them yourself)…

http://robotbirds.com/catalog/.....ts_id=4734

I've only ever tried LiFEPO4 as a 7 cell power pack for a 60" plane. They were the original A123s and did the job well. These new Hyperion packs look interesting – the main plus is the much greater resilience to abuse. For someone not already accustomed to using lipos, these would be a good bet. (Still need a special charger though)
Alex Eames RasPi.TV, RasP.iO

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Re: Potential power source

Thu Mar 29, 2012 10:07 pm

Wii Fit battery packs are the way forward for me - £1 with USB charging lead from Home Bargains - input 5V DC 600ma - output 5V DC 100ma - exploration with screwdriver reveals tiny regulator board and what looks like a lipo battery - gonna cram 6 in a plastic box - need to figure out best way to wire it though - don't want to start a fire!
Ostendo ignarus addo scientia.

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Re: Potential power source

Fri Mar 30, 2012 11:22 pm

darn need 1 more to make 700ma and have cleaned out the shop - will look again tomorrow...
Ostendo ignarus addo scientia.

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Re: Potential power source

Sat Mar 31, 2012 9:10 pm

pygmy_giant said:


Wii Fit battery packs are the way forward for me - £1 with USB charging lead from


I bought a cheapy cable it was made with six strands of 0.08mm Dia cable. Power capacity of about 200mA!

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