Help building a cell phone charger

[pierhogunn]

I need some ee help with a small project that I want to put together

My new Touch Pro cell phone eats it's 1340mAh battery like my 3 year old eats fudge, quickly, and with no remorse...

I would like to build a battery charger that can crank out 5V@1A for about 2 hours.

I have a plethora of 2600mAh NIMH batteries

Unfortunately, these batteries only produce 4.8V, so I doubt very much that 4 of them in series will provide the necessary voltage to charge the phone, I need 5V

does anyone have a schematic, and a parts list for a DC to DC converter that will turn 4.8V or 6.0V into 5V, and produce a 1A max current?

My plan is to take an altoids case, modify it to hold a 4 AA cell holder, a small circuit board, and a female USB jack and turn it into a phone charger... something that I could use to Charge my phone, or my wife's Ipod...

My experience level with building electronics is well, lets say level 0... I know which end of the soldering iron is the hot end, and I know that red is usually + and black is usually -

so any help you can provide.

Also, if this is even possible, I will post the pics and what not of the thing while it's being buit.

Something else that would be cool, is to take a 4D cell flashlight, and mod it into this sort of thing, since the rechargeable D-cells can be as much as 14000 mah...

[jziegler]

Dan,

A 5V, 1A DC/DC converter is not something that I would recommend as a DIY project. It would be relatively simple to get a schematic (and the big players in the DC/DC converter market have web tools or downloadable tools to help), but the layout of the circuit board for a DC/DC is critical for it to work properly, and that's not something that a DIYer can really do unless they are an advanced one. You really need to make a PCB for it, this is not something for a perf board or anything like that.

But, there is another option. There are power supply modules available that might do what you need. You basically feed that battery to the input and then have an output. There may be a couple other components that you would need. Since you would need just one of these, I'd suggest searching on digikey.com to see what you can find. In the index, select DC/DC converters from the power supplies section, and then choose 5.0V 1A from teh first output column, and the - for the next two. From there, I'd recommend through hole (easier to deal with if you don't do this stuff regularly) and select the input voltage ranges taht start with 4.5V. It looks like there are few choices, with this being the easiest to use:

http://search.digikey.com/scripts/Dk...me=445-2480-ND

Note that an output capacitor is specified.

If you have a 6v input, there are more (and probably cheaper) choices.

Jim

[Alex Franke]

Wow...

Are you sure the phone needs the full 5v to charge?

I think most regulators (like the 7805) will require 7V+ to get you a clean 5V -- I've used these with 9V batteries, but I don't know that these would have enough juice for you.

Have you considered using a dc/dc booster? Remember that the voltage will drop a bit over time, so build in some tolerance.

Battery charging can be tricky business, with lots of IC's dedicated to it specifically. Does the phone take care of all the details and just require a steady 5v? If not you could kill the phone battery...

Edit: This one looks promising: http://www.datasheetcatalog.org/data...756-MAX757.pdf

[pierhogunn]

Alex, that looks good, but the max output for these looks to be about 300Ma, which will just barley keep ahead of the discharge on my phone, which is usually 270ma... I need to kick the phone into "charge"

the phone is an HTC Touch Pro from sprint. It uses a mini-usb cable to charge/sync

[Alex Franke]

Alex, that looks good, but the max output for these looks to be about 300Ma, which will just barley keep ahead of the discharge on my phone, which is usually 270ma... I need to kick the phone into "charge"

the phone is an HTC Touch Pro from sprint. It uses a mini-usb cable to charge/sync

Ah -- Yeah, I missed that 1A part... Check out digikey like jziegler suggested. They have a pretty powerful search engine.

[LCHIEN]

sounds like the phone has the charging circuit, you just need the voltage with enough current.
Just look for an buy a 12V to USB charge adapter. This will plug into a car lighter socket and will regulate 5V to the 5V pin on the USB, which when plugged into your phone will charge the battery. The USB on this adapter of course is dead- no function. Some of them have a PC-en USB connector, you use the phones' USB cable to plug into this connector.
something like this
http://www.cellphoneshop.net/usbchcawicil.html
or this:
http://www.thetwistergroup.com/store...1499&source=fr

http://cgi.ebay.com/ebaymotors/SEIKO...mZ170284798663

you can also get AC/USB chargers, a wall wort plug in with a USB jack on it.

[SawDog]

Greetings,
OK...I'll admit, this device is a little lightweight for your needs (at a 400ma charge rate / 1000ma total battery capacity). But you may be able to modify it to suit your needs. And the support forum is pretty helpful.

I built one (I use it with my shuffle, Nextel, and Palm TX) and it works fine.

http://www.ladyada.net/make/mintyboost/index.html

Just a thought.

Hal

[pierhogunn]

sounds like the phone has the charging circuit, you just need the voltage with enough current.
Just look for an buy a 12V to USB charge adapter. This will plug into a car lighter socket and will regulate 5V to the 5V pin on the USB, which when plugged into your phone will charge the battery. The USB on this adapter of course is dead- no function. Some of them have a PC-en USB connector, you use the phones' USB cable to plug into this connector.
something like this
http://www.cellphoneshop.net/usbchcawicil.html
or this:
http://www.thetwistergroup.com/store...1499&source=fr

http://cgi.ebay.com/ebaymotors/SEIKO...mZ170284798663

you can also get AC/USB chargers, a wall wort plug in with a USB jack on it.

Thanks for the links, I a, looking for something that I can use when i am on the field at the scottish games, where I will be using the handheld all day, with no access to AC power...

or on an airplaine, etc

[gerti]

Upconverting voltage is tricky business, especially at higher currents and decent efficiency. Downconverting (eg from 6V to 5V) is MUCH easier. Alex is right, a 7805 typically requires more than 7V.

But there are "Low Drop" voltage regulators. For example LP3872ET-5.0 can provide 5V up to 1.5A with an input Voltage of 5.38V or higher. Datasheet: http://cache.national.com/ds/LP/LP3872.pdf

So if 5 batteries are OK, that plus a couple of capacitors would do the trick.

[gerti]

Of course you could save yourself some work by entering the words

HTC Touch booster battery

in Google...

[cwithboat]

[quote=Alex Franke;385642]Wow...

Are you sure the phone needs the full 5v to charge?

/quote]

I think Alex is right. Try the 4.8 Volts directly into the phone. It is hard to design a circuit that is more precise than 4%. Usually the engineer will try to allow for at least 10% slop in the input so the phone should work within the range of 4.5 to 5.5 Volts. Remember that the line voltage charger supplied with the phone is very cheaply made, so the chances of it supplying an exact 5V is very low.

[Bigbit]

Have you considered something like this:

http://www.apc.com/resource/include/...e_sku=UPB10%20

I had a similar issue with a T-Mobile Shadow where the 980 mah battery just didn't cut it. This APC unit recharges via a computer USB to APC MiniUSB connection and has its own USB connector so that you use it as the charger to recharge your device. They have several adapters / tips to deal with special connectors like iPods and cell phones (sold separately). My Shadow handles standard MiniUSB, so I did not need one, and I already had a USB to iPod adapter.

I am very happy with mine - use it frequently on international airplane trips to keep my cell phone and iPod fully charged.

[LCHIEN]

[quote=cwithboat;385796]

Wow...

Are you sure the phone needs the full 5v to charge?

/quote]

I think Alex is right. Try the 4.8 Volts directly into the phone. It is hard to design a circuit that is more precise than 4%. Usually the engineer will try to allow for at least 10% slop in the input so the phone should work within the range of 4.5 to 5.5 Volts. Remember that the line voltage charger supplied with the phone is very cheaply made, so the chances of it supplying an exact 5V is very low.

FWIW the official USB 2.0 specification document says that the hub (or in this case charger must present 4.75 to 5.25 V (that's the acceptable range) with a maximum drop of 125 mV in the cable. And the 125 mV drop is with a 100 mA load; a 1A load (if that's what it really is) will create a much larger (1.25V loss) which further complicates things. (www.usb.org)

If you use NiMH batteries, the nominal voltage is 1.2V per cell, but there is a slight decline as the cell discharges. In order to get full capacity from a miMH cell, an end voltage point is specifed in testing for MaH and that is usually 0.9V per cell. So to get full use of the energy in the battery the normal practice is to designe the circuit to work down to a battery voltage of 0.9 to 1V per cell. If it only works from 1.2 to 1.3 volts then you will only get part of the advertised run time per charge. Incidentally its not uncommon to find the cell voltage as high as 1.4V per cell when just charged, so that must be accounted for too. (e.g. you may damage a load which is expecting no more than 5.25V with a 4-cell stackup of 5.6V). Modern high density ICs are very picky with operating and maximum voltage specifications and are easy to damage.

Electrical engineering is easy when all the components are ideal... 1.2 volt batteries put out 1.2 volts all the time and 5V sources are 5.00 volts and wires are lossless, but in real life, 1.2 volt batteries are 0.9 to 1.4 volts and 5V sources are 4.75 to 5.25V and circuits must be designed for that range minus whatever losses due to cable lengths you have. These are all static and doesn't even start taking into account temperature effects and dynamic loads.

[pierhogunn]

I wonder if I should wait to see what the prismatic batteries will do when they are "officially" announced at this years CES.

I wonder what the current/voltage/rechargability of these things is going to be