More voltage with LIPOLY battery

[hoffmann]

Hello everybody !!!
It is me again and I am comming back about the power supply I will need for my ADAFRUIT FONA 808.

I did the good student and I red all the details.
I understood well that I will have to use a LIPOLY battery.

But for the project I will need to use more voltage. (Solenoid) I will need like 10V.

What do you think about my strategy :

To use two battery LIPOLY 3,7V (same kind) ==> with two Powerboost 5v
One set would be for the logical part, and the other + the previous would give more voltage.

A little drawing is often better :

Sans titre.png (24.44 KiB) Viewed 446 times

Question : Do you see any problem with that ?


Thanks a lot again :)

Hoffmann

[hoffmann]

Up

Wha would be your general solution when you need higher voltage than 5 V for your enbedded project ?

[adafruit_support_bill]

As drawn it could not work since the PowerBoosts are sharing a common supply and therefore a common ground. Attempting to put the outputs in series will short 5v to ground.

The general rule for choosing a single power source for a project is to choose one that most closely matches the biggest load to avoid the inefficiencies inherent in voltage conversion. If you do need to regulate down, use a buck-style converter, since they are much more efficient than linear regulators.

[hoffmann]

So, to found 10 or 12 V, How do I do ? There are only 3.7 V LIPOLY battery...

[adafruit_support_bill]

LiPo packs come in a wide variety of voltages. This vendor has packs ranging from 3.7v to 89v: http://www.batteryspace.com/li-ionpacks37-89v.aspx
Most battery vendors will have a similar selection.

All pack voltages will be multiples of 3.7v - since that is the voltage of a single cell. For your application, the 11.1v packs would be the ones to use.

[hoffmann]

Thank you for your answer.

But I still have a « problem” :

I have my 11,1V battery connected to a buck converter 5V 1 A (Adafruit) but how do I connect it to the fona 808 which is asking for a 3,7 V input ?

And I am afraid that the 1A from the converter is not enough for the pike of the Fona ?

What do you think ?

Best regards

HOFFMANN

[adafruit_support_bill]

Connect a separate 3.7v cell to the FONA. The 5v input to the micro-USB will keep it topped-off.

Think of the 3.7v FONA cell as reserve power to handle the current peaks during a transmission, It is not your primary power source.

[hoffmann]

Thank you for your advice ! Really clever !
So I will put a 500mAh LIPOLY battery !


Thanks again !!! :)

[adafruit_support_bill]

That should work. 500mAh is typically sufficient as a power reserve.

[hoffmann]

Connect a separate 3.7v cell to the FONA. The 5v input to the micro-USB will keep it topped-off.
Think of the 3.7v FONA cell as reserve power to handle the current peaks during a transmission, It is not your primary power source.

I understood the philosophy, but one more question concerning the pinout of the FONA808 :

5V - this is the USB 5V from the microUSB connector when its in and powered. Good if you need to know when the microUSB is plugged in and/or want to recharge the battery from an external plug.

Is it the same 5V than the USB one ? Don you confirm it is an IN pin (if no USB connector) ? ==> Can I recharge the "secondary/separate 3.7V" battery by giving some 5V though this PIN ? (and not using the usb connector)

Question 2 : the "Bat" pin, is directly connected to the (+) from the batterie ? Same as the JST (+) pin ?
(Sorry but I didn't found the information.)
Thanks a lot

Hoffmann

[adafruit_support_bill]

Yes. You can see this in the schematic: https://learn.adafruit.com/adafruit-fon ... #schematic

[hoffmann]

You are super right !


Thanks !