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I have a general question. I have a GSM module (adh8066 link to data sheet below) that I purchased from sparkfun. In the data sheet, it states that in tx mode, the module can draw up to 2 amps @ 12v.HOWEVER, the datasheet states that the module only needs 3.4V～4.5V (4.0V is recommended).

The BOB for this has a recommended voltage of 6-12v with 2 amps. I am curious about this because an iphone 4 battery is rated at 3.7 volts. Is there a major difference in these cell modules, or is a 3.7 volt battery able to provide a peak amperage for short periods of time or is the iPhones cell module a completely different technology? It's a little confusing since the data sheet stated 3.4-4.5 but the module can draw 2a from a 12v source.

The reason I am curious is because I wanted to power the adh8066 with a battery and receive 3-5 texts per day and have the battery last for 3 months (perhaps unreasonable). Is there a reasonable sized rechargeable battery that would power this GSM module?

EDIT- I have been reading a bit more. Would a 3.7 volt battery rated for 2500mah work to power the gsm at 1-2 second bursts of 2 amp?

ADH8066 BOB link

ADH8066 datasheet

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The breakout board clearly has a voltage regulator on it which explains the different voltage requirements.

The module itself wants ~4V. This is designed for use with cellphone batteries which output 2.9V-4.2V depending on their state of charge. It should work fine with any reasonably sized Li battery (tiny ones under 500mAh may not work).

However, you'll need to measure its power consumption in the "on and able to recieve SMS" state. I suspect this will be in the 100mA range based on my experience with similar modules. You'll need to work out exactly which level of "standby" this is for that module.

Achieving 3 months will either require that it's off most of the time (e.g. power up every 3 hours to check for SMS) or a large pack of many Ah.

Edit: look at the BOB schematic. First page has a spx29302 linear regulator from the power jack to regulated 3.8V. This is a convenience to let you power it off anything. The higher the input voltage the more will be wasted in the regulator.

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  • \$\begingroup\$ Thanks, you answered this perfectly. Do you think the breakout board is using 12v just because its a common power supply? Why not use a 4.2 volt ? Or, would the 4.2v supply have issues supplying the peak current? \$\endgroup\$
    – Brad
    Commented Feb 19, 2015 at 14:56
  • \$\begingroup\$ See edit - Mains-4.2V supplies are not a common item. Mains-12V are everywhere, as are "12V" batteries (although many of those are 14V) \$\endgroup\$
    – pjc50
    Commented Feb 19, 2015 at 15:32

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