Bypassing the onboard Arduino Voltage Regulator

[Cerin]

I'm trying to design a standalone Arduino Mega + Lipo device, but I'm finding this difficult as nearly all Lipo batteries (and Lipo riders) only handle 3.7V input and provide 5V regulated output, while the Arduino's onboard regulator requires 7V input to give the AVR it's regulated 5V.

If I wanted to use a Lipo rider that provided a 5V regulated ouput (e.g. this), how difficult would it be to bypass the 5V regulator on the Arduino Mega?

I'd like to simply wire two lipo riders in series for an ideal 7V supply, but all the advice I've heard recommends against that due to concerns with charging difficulty.

[Krodal]

You could apply +5v to the Vin. The voltage regulator will lower the voltage, but the Mega will still run at 4.5V.
Connecting the +5V to the 5V pin of the Arduino board is many times discussed. The voltage regulator could be blown in some cases, but others say that it should be possible.

[retrolefty]

I'd like to simply wire two lipo riders in series for an ideal 7V supply, but all the advice I've heard recommends against that due to concerns with charging difficulty.

And that is good advice as battery packs of Li-Pos used in various series/parrallel arrangment need to be comprized of carefully matched cells. So don't make you own but don't be afraid to purchase Li-Po packs of whatever voltage/current capacity you require. I use a two series cell 1500 ma pack from a old toy R/C helicopter that works great. It's about the same length as an arduino board and about 80% as wide and I attach it to the arduino board with rubber bands. I did jumper across the arduino on board series polarity protection diode to gain back the voltage drop it creates so I could run the pack closed to it's end of charge voltage of 6vdc. And of course with all Li-Po cells and packs you must use a charger rated to work with that cell or pack.

Here is a selection of 2 cell Li-Po packs from just one vender: Note there are five pages of 2 cell packs.

http://www.hobbyking.com/hobbyking/store/uh_listCategoriesAndProducts.asp?idCategory=86&LiPoConfig=2&sortlist=&CatSortOrder=desc

Lefty

[kf2qd]

I have read many of the horror stories about how dangerous LiPos are, but unless you are using the batteries near their max discharge rate they are very reliable and safe. I have several electric RC aircraft and have abused the LiPo packs and have had no problems with capacity or life. And they have not been balanced chraged, yet they have stayed very well balanced.

[retrolefty]

I have read many of the horror stories about how dangerous LiPos are, but unless you are using the batteries near their max discharge rate they are very reliable and safe. I have several electric RC aircraft and have abused the LiPo packs and have had no problems with capacity or life. And they have not been balanced chraged, yet they have stayed very well balanced.

I too have had no dramatic problems (no fire!) with many Li-Po packs I've used in past R/C aircraft models. However I once simply forgot that I had left a small current load (maybe 50-100 ma) attached to a Li-PO pack overnight and the next day when I discovered it the terminal voltage was zip and the charger refused to recharge it. So overdischarge of a Li=Po pack can 'brick' the pack unless there is some form of undervoltage detection and disconnection to protect the pack.

Lefty