# COMMUNITY : FORUMS : TECH

## How can I multiply/double (or just increase) voltage in a DV 5v curcuit ???

ok i have the following parts to ue for this: (all leftovers from former project..)
:)

1x mosfet IRF510 power transistor 5,6A 100V

9x 2N3904 amplifier transistors 40V 0,2 A .0.625 W

~16x 1uF capacitors 50V

~99x recifier diodes 1A 50V

~35x 2k resistors  0.25 W

the idea is to charge a battery pack consisting of 4x 1,2-1,25V = 4,8-5V 3000mah AA nimh batteries using my 5v usb wall charger that has 1A output!

i tried connecting the battery pack directly to + and - and 'i think' its starting to charge but after 1-2 hours at full rate (5v 1a) it should be at least 50% charged (3 hours would be full charge -> 5W x 3 = 15W), but if i connect them they last for about 2 -3 minutes and then empty again!!

so after this im concerned that i might need at lest 6V-10V to achieve the desired effect !!

-> charge 15W NIMH batterpack with wall charger (nokia ac-60e.. 1-1,5A) i nless than 3 hours (as like a phone would need !!)

therefore i need a cuirciut (ONLY DC) to double my 5V OUTPUT to 10V (yiou shouldnt apply more than twice the curent of a batter pack)

or ideally 6-7 V but i dont know if thats possible without a swiching IC or more different resistors.. so just doubling would be nice at the moment!!

Downunder35m4 months ago

What you really need is a proper charging circuit - these batteries don't like being charged just with DC till full ;)

sblocc10 (author)  Downunder35m4 months ago

really??

and what must this circuit look like??

f.ex. i had seen one that chrges 2 pcs over a 5v mobile phone charger (or usb if you like).. and only has integrated a temp sensor that swiches the whole cicuit off if more that 30°C are reached..

4 months ago

Just ask yourself why people invented battery chargers and why you get specific ones for the various types of batteries out there ;)
You did not mention the use for the batteries either so maybe it would be easier to get a 7.2V RC battery pack and the corresponding charger for it?

sblocc10 (author)  Downunder35m4 months ago

i have a small arudiono project running (a weather station including a 96x64 oled display, as well as some extra stuff) with buzzer sound, led's etc etc..

plus i want to have it run and charge via a 4x AA nimh batteries, because that fits nicely in my setup-box.. has enough mAh at 5v .... i tested it with normal 1,5v batteries and it goes well for about few days..

i also got a brief instruction from allaboutciruits.com to charge 2xAA batteries with a PWM pin steering a IRF510 MOSFET all from a 5V source.. i got all together but the empty bateries have about 4,2 V and the arduino begins to startup at roughtly 4,5 V i guess and if i let it go for 4-5 hours at 1A 5V phone charger its almost done after minutes...

so i googled around for a voltage doubler and all i found were simple ac-dc converters with diodes and capacitors, as well as dc-ac converters which still need a switching 555 unit

then there are voltage dividers using only resistors.. a small child can figure out how to put that together !

so my question was how can i raise a DC voltage using 9 pcs amplifier transistors (or the 2nd power tarnsistor) that i currently have in my pocket, and the other parts listed above !!