9v battery based charger for the TyTn

[alokhk]

hi guys.
im trying to build a charger for the tytn that would charge from a 9v battery rather than using the wall charger so that i can use the tytn when im trekking (which i do a lot).

ive used a 7805 linear regulator to pull down the output voltage of the 9v battery to 5v @ 1 amp as specified on the wall charger. ive also hacked the mini usb cable to short pins 4 and 5 so that the tytn draws power from the battery pack.

the problem i face is this:
the tytn does seem to draw power from the battery pack and charges from 90% to 100% in a matter of minutes. but once the battery meter goes below 90%, no matter how long i connect the tytn to the charger it refuses to charge. but the indicator light stays orange (or amber) and the battery status says its charging, but still the tytn continues to lose power over time. any ideas why this is happening? or what i am doing wrong? any help would be greatly appreciated... thanks in advance!

[Zigtek]

My guess is that you are trying to use a PP3 type small rectangular 9v battery. If so you will find that the battery can't supply enough current to charge the unit. If you look in the Magician forum here (http://forum.xda-developers.com/showthread.php?t=247154) this seems a much better alternative, as a decent set of NiMh AA batteries can supply 2700mAh, which should be more than enough to charge your TyTn.

[alokhk]

thanks man! will try it out tomoro.. did that before i hacked the cable.. havent tried since... will do it and post what happens.! cheers

[alokhk]

nope! it still doesnt work :(

i tried connecting 4 1.2v NiMH batteries directly to the hacked usb cable and the orange led comes on and the battery status says charging... but still it loses charge.

i also tired using 4 AA alkaline batteries with a diode to pull down the o/p voltage and the results are same as the above...

the AA battery pack output was 5.2v @ ~1.2A which is pretty much the same as the wall charger

[schriss]

I got this: http://www.boxwave.com/products/batteryadapter/index.htm
http://www.boxwave.com/images_bw/products/thumbnails/batteryadapterpro_led_lg.jpg
but it barely charges TyTN, very slowly. Is TyTN that power hungry? I don't know. Been using 4x2700mAh.

[alokhk]

well there must be something im doing wrong! i cant figure out what though... it cant be the input voltages or the current.. and the cable i use is the one with pins 4 and 5 shorted.. why the hell doesnt it work??? :confused: :confused: :confused:

can anyone help me? point me in the right direction????

[schriss]

My TyTN did charge some but faster in the beginning and soon almost stopped charging, maybe the voltage drops as batteries drain and TyTN doesn't like that or maybe 4x2700mAh is still way too small for TyTN.

[alokhk]

alright that might have been the reason, so this is my workaround.

i connected 2 9V batteries in parallel with the set 4 1.2V NiMHs.. after passing this through a diode i get an output voltage of around 5.3V @ 1.3A.

the connection in parallel helps maintain the voltage of the battery pack at a level more than that of the tytn and prolong the time for a voltage drain.. so in theory the tytn should atleast jump from say 60% to 70% and the diode should prevent the tytn from charging the battery pack.

inspite of all this, the result remains unchanged!:( tytn led glows orange, battery status is charging and the phone loses charge!

what the hell is happening here?!?!?! :confused: :confused:

[Radimus]

check this out:
http://www.aximsite.com/boards/mobility-site-news/211196-gomadic-pack-light.html#post1522281

[Nicky]

When I go away and don't have ready access to power (camping etc.) I use one of these Clicky (http://www.addonsworld.co.uk/product.php/34984/3822/).

I have found they work fine. Only thing I would say is that the 3 to 5 charge cycles is optimistic, I find I get about 2 charges out of a set of 4 batteries.

[Crash Override]

as far as I remember the 7805 is a 1A max voltage regulator, I would suggest trying the 78S05 - same pinout, 2A version, it seems to be the delivered current which affects charge rates on the phones.

[yo3gjc]

or you can put in paralel on a heatsink few 7805's. Don't count on 1A for 7805, is gonna die quick, be more conservative :-))