Forums » General Electronics Discussion

Hi, I'm new to the forums. I'm a self-taught amateur hobbyist. I thought this would be an easy fix, but I've struck out so far.

I have a Pepper Pad 3 handheld computer that I'm trying to repurpose as a wall-mounted computer. My problem is that the power port broke off of the circuit board. I tried to solder it back on, but it broke off too close to the board and my soldering skills are not great. The device uses a 7.4v 3800mAh lithium polymer battery. What I'd like to do is find an AC adapter which will provide the proper DC voltage and amps so I can just connect it to the battery leads to power the device directly.

Searching online I have been unable to find an AC adapter that puts out 7.4v and 3800mA. Am I out of luck? Am I looking in the wrong places? Can I use a power supply with different voltage or amperage? The included adapter puts out 12v 3A. Can I hack something together (with basic soldering) that will put out the proper voltage and amps?

Please help.

Thanks, Ripberger

Hi Ripberger,

I think this is not a general purpose electronic forum but dedicated to simulation of (basic) electronics by a browser based JavaScript application (CL).

However, here are some thoughts regarding your question:

• a) DO NOT attempt to apply any voltage to the battery leads when the battery is still connected, it may explode.

• b) When you supply the P_Pad via the battery leads (see above !!! ) DO NOT supply the P_Pad additionally via the (broken?) power port, it would try to “charge” your new supply.

c) Don’t confuse the 3800mAh battery capacity with the current (power) consumption, you won’t need (full time) 3800mA, more likely 1.5A (but I dunno, just my guess).

d) The included adapter is rated 3A but this is to run the device and to power the battery charging (circuit) which could have been designed to supply up to 800mA into the battery (but I dunno, …).

e) You could use the included adapter but have to reduce the voltage from 12 to 7.4V which means linearly 4.6V x 1.5A = 7W (which is quite a power = heat ! ) but only if my estimation is correct.

This may be possible using a LM317 adjustable regulator but at it’s (1.5A) limit, check data sheet and application notes for suggestions.

CL has the LM317 to play with, but make sure to see:

https://www.circuitlab.com/forums/support/topic/ffgw6682/lm317-does-not-regulate/#comment_2631

f) The better choice would be a switching mode power supply (SMPS), you could probably install it instead of the battery, e.g. http://uk.farnell.com/tracopower/tsr-3-24150/dc-dc-5v-to-15v-3a/dp/2080627

Regards, Sancho

Great information! Thanks so much for your help. I have seen for sale a 7.4v 2A adapter, do you think that would work for my purposes? http://www.amazon.com/Adapter-CA-PS700-Canon-ACK-DC50-PowerShot/dp/B0084BBXX0

I’d try, that’s cheaper as one could do it anyway. And I'd order 2, because shipping to my place is more than 20 bucks.

Regards, Sancho

Cool, I'll try it. Thanks for your help!