1

I'm trying to power a heated lunch box I got from Amazon (this one) via this - 12 V 20000 mAh Li-ion battery pack, which appears to be 6x 18650s.

When I plug it in, the battery heats up significantly, though it's enough to heat up my food, I'm worried if it's a bad idea or not.

The battery specs are - battery discharge requirements:

  1. Input/output: two 20# line, 150 mm long

  2. Maximum instantaneous current: 10 A

  3. Maximum working current: 5 A

The lunch box has two PTC heater elements such as this one.

Can anyone help or explain if this is safe to continue or maybe introduce some current draw limits?

JYelton
  • 32,302
  • 33
  • 134
  • 249
YanO
  • 11
  • 2

1 Answers1

4

Judging from its size, that battery is more like 3 Ah, not 20 Ah as its label says. That works out to 60 Wh. A 110 W heater will discharge that battery in half-hour. A decent battery discharged over half hour (at a current of 2 C), does get hot, but not that hot. Either the heater is drawing much more than 6 A, or that is a low-resistance battery and is being operated way past its maximum power point.

I am puzzled by the heater you linked to because it is for 220 Vdc. And your battery is 12 V dc. Are you sure it's the one you're using? If so, that PTC heater is not going to behave as expected.

Davide Andrea
  • 16,164
  • 4
  • 33
  • 62
  • Just to clarify, I opened up the unit last week and saw that it has 2x PTC elements similar to the one I linked to on amazon(by the way these are not peltiers, since its hot all around the PTC element), the one on amazon is just for illustration purposes. I'm not sure which PTC they actually use in the box, by sight they look identical to the amazon one, they are not labelled. When I plug in my battery pack it works very well, it heats up the food nicely and lasts around 20-25mins, its just that the battery gets very hot, which is what concerns me. – YanO Aug 29 '23 at 22:26
  • IF (big if) the battery pack is 20Ah and it last around 20-25 minutes (let's say half an hour), you'd be pulling 40A from the pack... Either way, you're just pulling too much current from the pack. – RJR Aug 30 '23 at 11:43
  • is there a way to limit current draw? – YanO Aug 30 '23 at 12:00