noob help

[dconnell]

hi guys noob ere with a lil prob,i want to use 2xlion batts in line each with a max output of4.2v/1200mah i want to reduce this 8.4 to around 4.5-4.7v they will be used to power a 2.5 ohm dual coil atomiser heater can i just do this with a straight resistor and and an on/off switch
cheers in advance

 

[dr pepper]

If you connected them in parallel you'd get 4.2, would that do the job?

Assuming the resistance of the heater doesnt change then something like a 2.2 ohm 20 watt resistor would do the job, be warned though resistance measurements are not allways meaningfull and you could overvoltage the heater if you select the wrong value.
Also using a resistor is highly inefficient, as much energy is wasted in the resistor as the heater element, there would be no advantage of having the 2 batteries, you could so this electronically with a switch mode regulator, however I assume being a noob you dont want to dive right into building power circuits.

 

[dconnell]

thanks for that,unfortunately at 4.2 it doesnt quite have the kick i need all im basically doing is replacing a variable voltage chip controller that fried, with a stable single voltage which is great at around 4.5-4.7 il give the resistors a try and see what the battery life is like,i used to get around 15hrs with the previous circiutry but that was all microchip,thanks for the quick reply
ps the heater can go to 6v but the sweet spot is at 4.7 to avoid burning issues

 

[alec_t]

Be aware too that unless the two batteries have the same capacity and start at the same charge state then one will discharge before the other and the discharged one may get reverse polarised, by current from the still-charged one, unless you have some way of monitoring their voltages and switching off before that happens.

 

[dconnell]

yep theyre chip protected and cut off at 2.75v