Current carrying capability

Hello - I am putting together a circuit that will power an arduino and a sim800 sms module or an a6 sms module. I am mounting it on blank pcb board. I am using a mosfet circuit to send power to the sms bouard. Both sms module's specs say they will draw 2 amps during sending. I have read that 2 amps is not even measureable on an amp meter because it happens so fast. How do I know if my pcb board will handle this amperage and how do I know if the wire will handle the amperage? I am confused about wire gauge for chassis use and power transmission. They are hugely different. I would like to use 24 gauge wires.

Please give me your thoughts.

Thank you,

Anthony

If your circuit is working fine. It means that your board can handle 2 amps current. For the transmission cable, you should measure the voltage from where wire connected to the board with a scope. So If you observe voltage drops during these 2 amps bursts and this voltage drop cause troubles like resetting the module etc. use shorter and wider wire.

Well for the wire this is easy there are tables. Just "google copper wire ampere rating". There can be values for cables and for wires inside of a box/product. Usually the value for the cable is low, because there are multiple wires and more insulation making heat transfer harder. So a single wire with single or no isolation can carry more current.

For the pcb there are similar tables and plots available but since this is depending on more factors, they differ more. Since you can over specify a bit just go on the save side. On the other hand if the current flows only for a short amount of time the heat can dissipate and you do not need over specify the width of your traces.

Make sure you have some nice capacitors on your board to buffer the short bursts of current.

Thank you for the responses. This helps me a lot.

the only problem may occur for the board is again the voltage drop. If you measure the voltage provided to the GSM module. you can see that your board can handle or not. Just use proper decoupling capacitors, use wider traces (0.5 should be okay for 2amps). There will be no problem

0.5mm is too thin, 0.5 inches is excessive! 0.125" or 4mm will carry 2A for an arbitrary distance on a PCB pretty much, you can skimp a little for shorter runs.

If your module draws 2A very briefly then you need a capacitor across the supply as close to the module as physically possible. The capacitor will supply the 2A spike in current. As to value, maybe try something like 470μF, exact value unimportant. I know for sure there are people on here who know how to calculate a correct value for this, maybe one of them will come along and tell you not only a different value but also why.

Thank you. I will plan on a capacitor. I am wondering does a capacitor eat up any battery life? I would think any charge left in it when the circuit is off would drain out slowly. Btw- my project will shutdown and then start again when a rtc trigger and circuit.

PerryBebbington:
If your module draws 2A very briefly then you need a capacitor across the supply as close to the module as physically possible. The capacitor will supply the 2A spike in current. As to value, maybe try something like 470μF, exact value unimportant. I know for sure there are people on here who know how to calculate a correct value for this, maybe one of them will come along and tell you not only a different value but also why.

GSM current spikes are quite long, capacitors not very viable I'm afraid, 33,000µF or something crazy is needed. The supply must be able to supply > 2A. All the hardware assumes a 3.7V LiPo cell is available for power (for which 2A is not the slightest issue)

Got it. Thanks. I am using a 3000mAh lipo. I was planning on boosting the voltage to 5v through a boost circuit capable of 3A. The gsm modules I have, an a6 thinker and sim800 have a 5v input.

Thank you,

Anthony

GSM current spikes are quite long, capacitors not very viable I'm afraid, 33,000µF or something crazy is needed.

Thank you. ++Karma;

aiannar974:
Got it. Thanks. I am using a 3000mAh lipo. I was planning on boosting the voltage to 5v through a boost circuit capable of 3A. The gsm modules I have, an a6 thinker and sim800 have a 5v input.

They also most likley have two diodes in series to drop the 5V down to something the GSM module itself can handle...

If you're powering by LiPo battery, check on this. Saves the boost converter. An 8 MHz Pro Mini will also work just fine on whatever voltage comes out of that LiPo battery.