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18650 Battery Question - Battery Powered Heaters Answered

Hi, I have a question before I begin a project.  I have carbon heater fabric that I want to make heated grips for my snowblower with.  I want to connect the ~0.5 meter x 15mm carbon tape to 2x18650 cells.

Are there any precautions I need to take to make sure I dont "short" the batteries and cause damage/explosion etc?  I know technically I am shorting the batteries and making heat.. but how do I know if it is damaging the batteries or putting myself at risk for explosion?  


Do the math. Measure the resistance of your carbon tape and calculate how much current will flow (take into account the inner resistance of the batteries). Then check the batteries' data sheet.

Im not sure I understand how to calculate out what you said above.

Are you saying it is only dangerous if more amps are being pulled than the batteries can put out? I can put my multimeter in amp mode and its pulling 1.8amps from 2x18650 batteries in a series and about 1 foot of carbon tape - but I only tested it for a few seconds because the carbon fabric heated up super quick.

If my batteries arent heating up, can I call it safe?

First, you can't pull more amps out of the battery, than the battery will give (okay, technically you can by applying an external, reversed voltage, that's not exactly pulling any more).

Okay, so you took the direct way and tried it. If your carbon fabric heats up very quick but your batteries stayed cool, you should be safe. A cool (i.e. not hot) battery is a safe battery. 1.8A is not that much for a battery, at least not for short times.

But if your heater element heated up in seconds, you may want to increase the resistance (thinner / longer carbon tape) or decrease the voltage (put the batteries in parallel instead of in series) as your snow blower will have to be working for minutes/hours. Or you can try to add a driver stage with some kind of PWM modulation (switch on for a short time, the switch off for some time and vary on/off times according to the needed heating energy)..