[How-to] Build a battery power adapter cable for your Piratebox (MR3020)

Hey all.,
I have created a how-to document for making a Battery power adapter cable for the Piratebox on the MR3020. I am currently using a version of this power cable on my own Piratebox, and wanted to share a newer version that I made yesterday. It will allow users to keep all the original hardware intact.

The power adapter cable will:

[*] Allow you to run the MR3020 on Batteries
[*] Output 5V which is required to run the MR3020

The document can be found HERE

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Edited 1 time(s). Last edit at 04/29/2012 03:15AM by pabell.

How long does the MR3020 run on a 9V battery block ?

Hi

If you want to increase the battery life of the MR3020, its not the voltage you have to increase, but the storage capacity of the battery pack (Wh = Ah * Voltage). Actually high voltage can damagage the circuits!
I think the MR3020 consumes 5 watts when running. You have a 5V battery pack and you also know its Ah rating (given, at least for rechargable batteries).

So roughly you can work with
Wh = watts * running time in hours (this is for your router, 5 Watts)
Wh = Ah * voltage (This is for the battery pack, where the voltage should be fixed 5V)

to get an estimate how long you can run it.

Ubuntuhak, playing and tinkering with Ubuntu!

Matthias,
The 9v connector is just for using with Battery holders, They all come with that attachment to make it easy to connect to other things. In any case, my box is running on 12 Volts (8 AA) batteries. This is then passed through a +5v 7805 regulator. I put them in 25 days ago.

Keep in mind:
I don't keep my piratebox on all the time.

I used the same battery pack for a wireless repeater. Based on those results I would say the should last about 10 days.

A more thorough test of the battery pack on this unit will need to be done for actually numbers

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Edited 2 time(s). Last edit at 04/29/2012 10:19AM by pabell.

Nargren,

Thanks for the math behind it.
I am using a fixed +5 Regulator,(which is mentioned in the documentation 7805)

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pabell Wrote:
-------------------------------------------------------
> Nargren,
>
> Thanks for the math behind it.
> I am using a fixed +5 Regulator,(which is
> mentioned in the documentation 7805)

Hey,

yes I know, I've read it, nice work!
I just wanted to clarify this voltage-battery life situation.

Ubuntuhak, playing and tinkering with Ubuntu!

Not a math guy, but would you say it will last roughly 5hrs? in always on mode >
><

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Well, its more physics

And it really depends on the Ah rating of your battery pack...
Also without too much detail, you maybe don't want to fully depleet your batteries, just to keep them last longer. If you use just standard rechargeable AA batteries, who cares

If you want to build a battery pack that lasts for days, just throw 20 of your battery packs next to each other and connect them in parrallel, have fun

Ubuntuhak, playing and tinkering with Ubuntu!



Edited 1 time(s). Last edit at 06/28/2012 09:14PM by Nargren.

I was at a surplus store and they had a 10 AA battery pack for $1.50. I picked it up because they didn't have the 8. Would I be better off putting all 10 batteries in it? Or is that too much for the regulator? Would having 10 batteries make a difference in battery life?

Distribution,
For this tutorial, I purchased regulators from Radioshack. the max input voltage is 32 Volts 10 AA batteries would be 15 Volts well within the threshold of the regulator. Keep in mind though that not all +5 regulators are the same. I have some which have a max input voltage of 10 Volts so I run those using a 9v battery.

When I get home I will update this with the 2 different 5v regulators I have used.

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pabell Wrote:
-------------------------------------------------------
> Distribution,
> For this tutorial, I purchased regulators from
> Radioshack. the max input voltage is 32 Volts 10
> AA batteries would be 15 Volts well within the
> threshold of the regulator. Keep in mind though
> that not all +5 regulators are the same. I have
> some which have a max input voltage of 10 Volts so
> I run those using a 9v battery.
>
> When I get home I will update this with the 2
> different 5v regulators I have used.

I think I have the same one as you, max input is 35V. I guess I should've just went by that, but will it do anything for battery life? I assume it will, but I don't know. I'd like to see if there's a difference using regular batteries and ProCells. I use ProCells in my camera flashes, and they last a really long time. May be something to consider. You can find them on Amazon, usually not so much in stores.

7805A - Max input 35V - This is what I used for this tutuorial.
7805C - Max input 10V - I ordered 20 of these from Newark.com these would be great for running a Pirateboxes with single 9V batteries.

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What is the minimum amount of current does the TL-WR703N require? I looked around, but can't find the answer. It seems my battery pack only ouputs 600mAh, and while the router boots up... it acts weirdly and doesn't supply DHCP addresses to wifi clients.

Mofosyne,

This is from the open-wrt website: http://wiki.openwrt.org/toh/tp-link/tl-wr703n#power.consumption

Power consumption

This router is standardly powered via USB at 5V. The voltage regulator inside is unknown, but its input voltage should be at least between 3.7V - 5.5V, but not over 5.5V. The device will get damaged at too high voltages. Maximum current draw at 5V is 185mA (OpenWrt boot), average current draw with WiFi at 18dBm is 100mA, without WiFi 80mA. Hence the average router power consumption is 0.5W, which is incredibly low.

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Well the level of the 4battery pack is around 4.89v, when hooked to the piratebox. Which is clearly within 3.7V - 5.5V . It is accessable, but not by wifi (because of lack of DHCP again).

So my guess is that it works best if it is regulated to be at 5.0V and 5.5V at least, any lower and some function like DHCP won't work.

Mofosyne,
If you use the power cable that I have in the instructions with a usb cable, you will get the right voltage for your particular device.

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Why modify a USB extension cable and not the microusb cable itself?

CuriousC Wrote:
-------------------------------------------------------
> Why modify a USB extension cable and not the
> microusb cable itself?


CuriousC,
I did it this way so that if you needed to return the unit to the store you can. Moding the microusb cable voids the warrantee.

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pabell Wrote:
-------------------------------------------------------
> CuriousC Wrote:
> --------------------------------------------------
> -----
> > Why modify a USB extension cable and not the
> > microusb cable itself?
>
>
> CuriousC,
> I did it this way so that if you needed to return
> the unit to the store you can. Moding the microusb
> cable voids the warrantee.


So you can modify the microusb cable if you don't have a warranty or don't care about it?

CuriousC Wrote:
-------------------------------------------------------

> So you can modify the microusb cable if you don't
> have a warranty or don't care about it?


Yes you can, the End result will be the same. Obviously wiring would also be slightly different.

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For my late MR.3020 (i think it died yesterday) i was using a MiPow SP4000-BK PowerTube 4000mAH. It worked very well and kept the router alive for a long time. I have a lot of these Powerpacks.

starbug,

what your experience with the MR3020 and your fully charged 4000 mAh pack? How long did it last usually?

Posibilities of Better Hardware

Ok, you piratebox people may be good coders but electronics isn't your thing, I see. It is mine. So, here's how it actually works.

Your device requires 5v at x amps. This is true of the MR3020 and of my own pi. So long as the supply is giving it exactly 5v and can sustain the required number of amps, it'll be happy.

The energy capacity of the battery is the current capacity in amp-seconds times the nominal voltage. However, just to mess with all of us, batteries are generally labeled in amp-hours. The conversion factor is, of course, 60*60. Important thing: Energy = (constant) * voltage * mAH.

Now, pabell mentioned the 7805. The same chip as in the instructions. This is one of the classic components everyone uses - it's a cheap, very capable, very reliable linear voltage regulator. The 'linear' has a technical meaning, but there are two important implications:
- The thing is dead simple to wire up. No messing around with inductors or stability. Just power in and power out.
- It's also horrendously inefficient.

A linear regulator works by essentially 'throwing away' the excess volts. So, for example, you may run your piratebox off of a 9v, 1500mAH battery (likely a load of 9V cells in parallel). The 7805 gets 9V in, and throws away 4V of that, passing the remaining 5V on to your piratebox. So your 9v, 1500mAH battery is in effect turned into a 5v, 1500mAH battery. You've thrown away 4/9ths of your battery capacity through inefficient regulation!

Pabell's suggestion of hooking together 10 AAs into a 15V battery is actually a very wrong approach - the 7805 would take this 15V and throw away 10V, instantly wasteing 2/3 of your battery capacity! A much better approach would be to make them into two banks of 7.5V, then connect these in parallel*. Batteries in parallel add capacity (eg, two 3v 300mAH in parallel are the equivilent of one 3v 600mAH).

The excess energy has to go somewhere, of course. Conservation demands it. It ends up as heat: The regulator can get quite toasty.

If you want to use the battery efficiently - a must if you're going to make this compact or run it on solar - the 7805 isn't going to do it. You'll need something called a switching regulator - they are much more complicated to use, but you can buy them as pre-assembled modules with all the supporting components. Swap your 7805 for one of those and you're looking at around a 30% improvement in runtime before the battery goes flat.

In short, pabell's cable design works (almost), but it's very inefficient. Greater efficiency is at the expense of greater complexity.

Also, he left out the heatsink and smoother caps. You might get away without a heatsink on a light load, but without smoother caps there will likely be stability issues - that likely explains the reports of DHCP issues, though I'm surprised it didn't just crash the box completly. Stick a decent cap each side of the regulator - I'd go for about 220uf, but with linears adding too much never hurts so you can use whatever you have lying around.

Here's a (rather pricy, I assure you they can be had cheaper!) example switching regulator: [www.ebay.co.uk]


All this is assuming you're running it off of perfectly ordinary household batteries or rechargeables. If you want to really make the box last you need to start dealing with lithium-ions and a boost converter, which is a much more complicated subject.

* Make sure you balance them, or you're going to shorten the life of your cells as well as waste energy.



Edited 1 time(s). Last edit at 05/12/2013 09:01PM by SuriRaven.

SuriRaven.

Thanks for you for your input. I am sure you will agree that there is more than one way to do things. My approach works very well for me. And others. I am far from an Electronics genius, nor was that claim ever made. I would be more than happy to collaborate with you on a more efficient design if you'd like.



Regards,
Pabell.

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Making really efficient designs is rather complicated, but your less-efficient design does work. You just need to make two small changes, really:
- Add smoothing caps.
- Put the 7805 on a heatsink. Based on my experience, you can't get away without one.

That's three components and a heatsink, about as simple a supply as you can get. I'll have to write up some sort of a guide, as these things can get very complicated indeed when you start dealing with recharging too. For most people, the best approach is often to just buy one of those little battery-powered phone charger boxes - they contain all the required circuitry ready-assembled and tested, and it's a lot easier to upgrade the battery in one of those than it is to build from scratch.

looking forward to your documentation.

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Edited 1 time(s). Last edit at 05/13/2013 06:45PM by pabell.

What's the current consumption on an MR3020? The 7805 is rated up to 1A, with suitable cooling. Enough for a pi, and presumably for an MR3020, but not if you're going to run a 2.5" hard drive as well.

One draft: [birds-are-nice.me]

Long way to go, but it's a start.

SuriRaven,
Great info, I will incorporate the capacitors into my design and document Ver 2.

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