Power supply question.

Guys,

I have an arduino project that will require 5V to operate few sensors that can only work with 5v not 3.3. The project needs to be powered by batteries, using solar cells to recharge it. The point is I can only find litium batteries of 3.7v here. so the questions would be:

  • Can I use 2 litium batteries in series to generate 7.4v ? I believe so, but more important, how can I recharge these batteries using the standard 5v cells ? Any idea ?

  • Would be feasible to implement a level shiftier from 3.3 to 5v ? What would be the implications of this ? And how could I do this ?

Many thanks in advance

few sensors that can only work with 5v not 3.3.

What kind of "sensors"? Are you sure they only work at 3.3V Do you have a link to the datasheet? There may be a way to use them without any additional circuitry.

  • Can I use 2 litium batteries in series to generate 7.4v ?

Yes.

I believe so, but more important, how can I recharge these batteries using the standard 5v cells ? Any idea ?

Lithium battery charging is tricky an you really need the right charger/circuit no matter what the source of the electricity. A low-power solar cell might work with a DC-DC voltage booster and some simple current limiting, but I'm not an expert on lithium batteries so I'm not sure.

DVDdoug: What kind of "sensors"? Are you sure they only work at 3.3V Do you have a link to the datasheet? There may be a way to use them without any additional circuitry. Yes.

Lithium battery charging is tricky an you really need the right charger/circuit no matter what the source of the electricity. A low-power solar cell might work with a DC-DC voltage booster and some simple current limiting, but I'm not an expert on lithium batteries so I'm not sure.

In fact these sensors are not 3v, they are 5v that's the main problem :-) Sensors are MQ135 (gas) DHT22 Temp/Humidity and standard rain sensor, they are all 5v. If you still need the datasheet let me know and I'd be happy to google and post it here, not a problem.

I already have the charger circuit for the lithium batteries is a $2 circuit you buy anywhere, including e-bay :-)

The whole point is: can I change voltage from 3.7v to 5v ? If yes how ?

And If I put the batteries in series to generate 7.4 instead, can I still charge them individually with 5v as input ?

Thanks

Would be feasible to implement a level shiftier from 3.3 to 5v ? What would be the implications of this ? And how could I do this ?

Yes it is, you can make a boost regulator to take the ~3v7 battery and up it up 5v. There are many chips that do this but I usually go to the TI Webench site

http://www.ti.com/lsds/ti/analog/webench/optimizer.page

And get it to do the work.

That said there are probably many off-the-shelf boards that do this as well.