custom converter for cell phone?

Wayne, I'm having another of my periodic fits of rage against lithium ion proprietary batteries in cell phones. I'm interested in making a custom pack powered by an AA NiMH cell and a dc-dc converter (1.2 volts in, 3.6 volts out), preferably with a charging circuit included that could efficiently charge the cell inside the phone from a USB port. Got any thoughts about what it would take to build a suitable converter and would you have any interest in doing a run of them? A possible alternative would be to use two cells (maybe AAA's). An even simpler fallback would be to use three cells, but that gives up some charging convenience (I want to get one of those very small Eneloop 2-cell travel chargers).

What you're asking for already exists. But they don't work well at all, as a single AA cell just doesn't have enough capacity. The single AA chargers just don't have the current to charge more power hungry phones like Blackberries and Pocket PC's. (and probably not the iPhone either)



I'd be more interested in one that ran off of a single CR123, since AA ones are already commonly available.

It would be a far easier converter since most cellphones operate on 3.7V batteries.


I think this would be a perfect project since it's almost flashlight like, with an aluminum tube and tail cap.

-Ed

That thing in your picture is NOT what I want. It's a kludgy gizmo that connects to the phone with a wire, to transfer some juice from the AA cell to the phone's internal lithium cell. I want something that puts the AA cell completely inside of or attached to the phone with no wires flopping around and REPLACES the lithium cell, not supplements or charges it. I just never want to deal with lithium rechargeables EVER.

The capacity of an AA cell (2700 mah 1.2 volt nimh) is about the same as a typical cell phone lithium pack (3.6 volt 600-800 mah) and the volume is about the same too. The shape is a little different and the NiMH cell weighs a bit more. I don't care about a few grams of extra weight. Even if the AA's capacity is a bit lower, I don't care, since phones have a lot of standby time these days and with AA's it's easy to swap in a spare. I also don't care about high powered phones (I just want a simple voice phone with no camera or computer features) but for high powered phones it's ok to use two AA's if that's what it takes.

3xAAA might be simpler if the form factor of the phone allows it. I'm guessing there is already some voltage regulation between the li-ion cell and the phone electronics. The AAA's in serial fall in the voltage range of the li-ion so it might operate fine without further mod.

Charging might be an issue with them in serial and having a lower voltage than max on the li-ion. You could always just use a separate battery charger instead though and replace cells when you needed to charge though.

Yeah, I agree that 3AAA would be easier, I might do that if I hack something together for my own phone, but it would end up an ugly kludge that couldn't be charged in the phone. If I want to put something nice together it would basically require getting a custom made enclosure and charging circuitry, and getting some economy of scale by doing a run of at least modest quantity, at which point 1AA is far preferable to 3AAA.

Hmm, that's interesting.

Is there more capacity in the one Eneloop than the battery in the phone?

Something could be whipped up quickly.

What would be the physical dimensions or restrictions if something was made?

Board size (min X, Y) (max X,Y) Height or thickness?

Wayne

An Eneloop is 2000 mah so it's a bit less than a 700 mah 3.6-3.8v phone battery especially when converter loss is figured in. But it's not out of the ballpark. Also, I think self-discharge is not much of an issue with typical phone use, where you leave the phone in standby all the time so people can call you, and recharge it every few days.

I don't think board size constraints are terribly severe. Lets say 14mm wide, 50mm long, 14mm max component height, so it would fit in an AA cell slot. Might be nice to have a thinner version that could fit in an AAA slot though. It should be a reasonable add-on for some popular model of phone.

What kind of phone do you have? I guess you don't mind having a large frankenbrick of a phone.

Sounds pretty cool though. Are you at all opposed to having your phone powered by a single CR123? May not be common for other people, but for CPF'ers it's the next most common battery to a AA. Although some CPF'ers have more CR123's than AA's.

-Ed

Edwood said:

What kind of phone do you have? I guess you don't mind having a large frankenbrick of a phone.

Sounds pretty cool though. Are you at all opposed to having your phone powered by a single CR123? May not be common for other people, but for CPF'ers it's the next most common battery to a AA. Although some CPF'ers have more CR123's than AA's.

-Ed

Click to expand...

CR123A's might be interesting in a pinch, but they're primaries and using them every day would be wasteful. As stated I'm looking to completely replace the lithium cell with an AA NiMH and run on the AA all the time, not just in a pinch.

I don't have any particular model of phone in mind. I'd like a simple one with a flip cover on the keyboard to avoid the so-called butt calls. And if I'm doing a quantity run of the AA system then it should be a popular phone model so there would be other users who might want similar setups. But basically I'm willing to buy whatever phone is best suited to this scheme. I don't care much about the phone size within reason. What we call a frankenbrick today would have been considered tiny just few years ago. As an example, I'd be really happy with a Nokia 5100 size phone but they don't make them that big any more. Another idea is something like a Nextel, which is quite rugged.

Try ericsson r250, it used 4x NiHM AA 1500mA sealed battery pack.
You may cut out the internal cover and replace the battery.
It builds like a tank, really like a "water bottle" size compared to now.
Good luck!

paulr said:

CR123A's might be interesting in a pinch, but they're primaries and using them every day would be wasteful. As stated I'm looking to completely replace the lithium cell with an AA NiMH and run on the AA all the time, not just in a pinch.

I don't have any particular model of phone in mind. I'd like a simple one with a flip cover on the keyboard to avoid the so-called butt calls. And if I'm doing a quantity run of the AA system then it should be a popular phone model so there would be other users who might want similar setups. But basically I'm willing to buy whatever phone is best suited to this scheme. I don't care much about the phone size within reason. What we call a frankenbrick today would have been considered tiny just few years ago. As an example, I'd be really happy with a Nokia 5100 size phone but they don't make them that big any more. Another idea is something like a Nextel, which is quite rugged.

Click to expand...

Why would you have to resort to CR123's in a pinch? There are plenty of high quality Rechargeable CR123's available. You get the performance benefits of Lithium in a convenient package, without the added weight and lower performance of AA's.

But it seems you have your heart set on using AA's. Although as mentioned AAA's would be better size-wise. And three of them in series could provide the voltage needed, with as little step up in the voltage as possible to reduce the heat generated by a regulator.

What you are asking for is definitely a one-off solution. I'd recommend sending Wayne a spare or dead battery that he could take apart and use the existing housing as an interface for your new AA/AAA powered battery.

I still like the idea of a CR123 based back up battery, I'll start a separate thread on that one.

-Ed

CR123A refers to a non-rechargeable 3v cell I believe. There are some rechargeable 3.6v 123A-sized cells that are sometimes called R123A (I don't know if that designation is technically correct though). Anyway I don't see any reason to want to run a phone on one. If I'm going to use a cylindrical li ion cell I'd use an 18650. The point of wanting AA/AAA is their economy and easy availability and to not have to use special chargers, plus most of my other devices already use them. I want to use the exact same batteries and chargers in all my devices (phone, GPS, multiple digital cameras, music player, flashlights, 2-way radios, electric shaver, etc). One advantage of 1AA vs 3AAA is that it should be possible to include a USB charging circuit in the 1AA pack and still have it fit the phone. That would give the additional option of charging the battery inside the phone in the customary way, instead of removing the battery and using an external charger. 3AAA is a reasonable plan though, I agree.

Re Ericson R250: it looks like it's discontinued, and that it uses a li ion pack: http://www.m-99.co.uk/ericsson-r250.html

It was 2000 year model.
Mine was bought locally, it uesd 4x Ni-MH, not Li-ion, but not easy to open the back of battery.

http://cgi.ebay.co.uk/Ericsson-R250...7366538QQcmdZViewItem?IMSfp=TL0807091016a5151

It works for GSM 900/1800 only, mostly not work in US.

I think 1AA really is the right way to go, despite the extra electronics. Look at the popularity of 1AA flashlights on this site (Fenix etc) compared with 3AAA lights.

Anyway I'm still interested in this. There was a slashdot post a few days ago about 3D printing services. That might be a good way to make the enclosure/battery cover in low quantity.