I have a 3.7 V 10000 mAh Lipo battery, DC- DC 4A step up converter and a EFcom gsm shield
as in the picture bellow:
or the link of the picture:circuit
the battery is 1C and should provide up to 10A,
I used this step up to increase the voltage from 3.7 to 6 so that the GSM shield can operate, however I am facing a current problem that the current is not enough to make the GSM module work( which is the reason why I got it from the first place)
what am I missing out?
Hi,
Have you measured the voltage coming out of the DC-DC converter?
The spec says optimum performance with 5Vdc to 32Vdc INPUT, you are supplying 3.7Vdc.
What voltage do you have on the INPUT and the OUTPUT terminals when everything is connected?
Thanks.. Tom.. 
The device is rated abs max 4A on the input, not the output.
The GSM wants 3.7V supply directly, not 6V, they all do, they are mobile phone modules basically....
MarkT speaks the truth.
From the specs of your GSM
"the power supply range of SIM900 is from 3.2V to 4.8V"
TomGeorge:
Hi,
Have you measured the voltage coming out of the DC-DC converter?The spec says optimum performance with 5Vdc to 32Vdc INPUT, you are supplying 3.7Vdc.
What voltage do you have on the INPUT and the OUTPUT terminals when everything is connected?
Thanks.. Tom..
The input voltage is 3.7 and the output is also fine, i tried and it was adjustable 5V, 6V , 7V.
MarkT:
The device is rated abs max 4A on the input, not the output.The GSM wants 3.7V supply directly, not 6V, they all do, they are mobile phone modules basically....
There is an LDO in the shield that will step the voltage down that is why we need a higher voltage. The voltage at the gsm shield is always 4.2V ( because of the regulator) but the problem is with the current
The GSM shield is intended to be connected to a ~3.7 V power supply.
Why do you think it is a good idea to use a converter?
That GSM shield spec is very confusing. First it says it requires 3.1V-4.8V (I suspect that's the chip, not necessarily the full board)...and then it says to use the supplied 9V power supply with it. So 3.7V or 9V, which is it ?
Steve
Here is what the web page says about using their 9V wall power supply:
Make sure add using 9V Charger for power supply for your Arduino board and EFCom, The 9V Charger we will provide to you with EFCom Shild. Because of the power supply range of SIM900 is from 3.2V to 4.8V. The transmitting burst will cause voltage drop and the power supply must be able to provide sufficient current up to 2A.
If I interpret this correctly, they rely on the internal voltage drop of the overloaded wall wart to supply ~ 4V.
If so, this is one of the worst ideas ever.
I encourage the OP to look elsewhere for a GSM module.
jremington:
Here is what the web page says about using their 9V wall power supply:If I interpret this correctly, they rely on the internal voltage drop of the overloaded wall wart to supply ~ 4V.
If so, this is one of the worst ideas ever.I encourage the OP to look elsewhere for a GSM module.
the GSM shield has its input voltage (VIN) which gets stepped down to the voltage at the GSM sim9000 module (VBAT) to 4.2V, their voltage regulator steps the voltage from whatever value at VIN to this 4.2V at the GSM module input (VBAT).
now I fully charged the battery to be 4.2V, and stepped the voltage up to 9V and connected it directly to the GSM shield (VIN) (no arduino ), a little improvement took place, it managed to connect to the network.
when I connected the arduino, and tried to send a post request, it was not successful.
my question is, since the voltage at the GSM sim9000 meets the requirements (4.2V) and the boost converter should be able to provide enough current, is the problem with the GSM shield or the problem is because the boost converter's optimum voltage is between 5V- 33V and the battery is only able to provide 4.2V when fully charged??
Quite a bad design, with bad documentation on top.
And, of course, your improper use of the DC-DC converter adds to the problem.
If you insist on sticking with this module, buy a boost converter that is appropriate to the task. Pololu has a good selection.
Keep in mind that stepping up and then stepping down again wastes a ridiculous amount of power. Good luck with that approach.
jremington:
Quite a bad design, with bad documentation on top.And, of course, your improper use of the DC-DC converter adds to the problem.
If you insist on sticking with this module, buy a boost converter that is appropriate to the task. Pololu has a good selection.
Keep in mind that stepping up and then stepping down again wastes a ridiculous amount of power. Good luck with that approach.
actually power is critical for my application as I am planning to run it on batteries and a solar panel. what are other GSM shields that is power effective? I did a search and surprisingly the one I am using now is one of the best 3 out there !!
Hi,
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
Can you also post a picture of your project.
A picture/schematic is worth a thousand words.
Thanks.. Tom...
here is the picture of the actual circuit
rough schemtic showing the voltages at each point, VIn, VBAT
schemaic
