Speakerguy
Active Member
OK, I need to supply 1.5W of power through a resistive heating element for 30 seconds, then have it auto shutoff. I need a battery, a fuse, and whatever amount of nichrome wire it takes for the right resistance. I've never used PPTC fuses before, so I'm not sure if this is feasible. Also, this must be VERY compact (1.25" x 1.25").
I've got a 3.7V lithium polymer on hand. Here are the specs:
Kokam High Discharge LiPo Battery
Part Number: KOK145T
Kokam 145 mAh High Discharge (5C) Lithium Polymer Single Cell with a Bare PCB Attached.
Size: 27.5mmH x 20.5mmW x 4.5mmT
Weight: 3.5 grams
Ratings: 5C Max. Cont. Discharge
Outputs: 3.7V Nominal, 145 mAh
At 3.7V I need 9.1ohms @ 400mA to get 1.5W power dissipation.
So basic question, is there a PPTC/Polyswitch solution for this? I don't know how sharp the knee in the curve is for them when they cutoff. Also, this will be in close proximity to the heater, which could (and hopefully will) reach 90 degree C.
Actually, it would be real nice to put this right next to the heating element, so it would kick back on as soon as it fell below some threshold value (70 or 80 degree C say) and then have it heat back up to 90 degree.
I just don't know if a polyswitch is a feasible part to use for this. It would make this a lot simpler and cheaper than using a PIC12 and a FET and a thermistor and a switching regulator for the PIC and all that, which would kill it as far as the space I have to cram this in.
Thanks for any help!
I've got a 3.7V lithium polymer on hand. Here are the specs:
Kokam High Discharge LiPo Battery
Part Number: KOK145T
Kokam 145 mAh High Discharge (5C) Lithium Polymer Single Cell with a Bare PCB Attached.
Size: 27.5mmH x 20.5mmW x 4.5mmT
Weight: 3.5 grams
Ratings: 5C Max. Cont. Discharge
Outputs: 3.7V Nominal, 145 mAh
At 3.7V I need 9.1ohms @ 400mA to get 1.5W power dissipation.
So basic question, is there a PPTC/Polyswitch solution for this? I don't know how sharp the knee in the curve is for them when they cutoff. Also, this will be in close proximity to the heater, which could (and hopefully will) reach 90 degree C.
Actually, it would be real nice to put this right next to the heating element, so it would kick back on as soon as it fell below some threshold value (70 or 80 degree C say) and then have it heat back up to 90 degree.
I just don't know if a polyswitch is a feasible part to use for this. It would make this a lot simpler and cheaper than using a PIC12 and a FET and a thermistor and a switching regulator for the PIC and all that, which would kill it as far as the space I have to cram this in.
Thanks for any help!