Question about 0.01 resistor - SparkFun Battery Babysitter

Components & Accessories Power
1

Hello,

I have a technical question about the SparkFun Battery Babysitter board.

Here is the schematic: https://cdn.sparkfun.com/assets/learn_t … ematic.pdf

R11 going between SRP and SRN on the BQ27441, wouldn’t all the current in the “system” flow through that resistor? Meaning, that if I have a high current application, let’s say I want to draw 1 or 2A from my LiPo battery, that resistor wouldn’t be able to handle it. In fact, this resistor is probably only able to handle less then 100mA.

And the same thing if I want to charge my battery with 1.5A which is the max of the BQ24075 onboard.

So R11 should be a resistor with a high Wattage rating, correct?

I am most likely wrong, but I just want to double check this. :smiley:

2

Resistors are rated by the amount of power they can dissipate. Using Ohms Law, we can calculate that 2 Amps of current through a 0.01 Ohm resistor will only dissipate 40 mW. The charge rate on that device has “DIP-switch-selectable charge rates of 100mA, 500mA or 1.5A.” At 1.5 Amps, the dissipation is 22.5 mW. It’ll be fine.

3

R11 is used to measure current, so the full system current has to flow through it. As darrellg points out, the power dissipation is low due to the low value of the resistor.

4

Thank you both for replying!

n1ist:
R11 is used to measure current, so the full system current has to flow through it. As darrellg points out, the power dissipation is low due to the low value of the resistor.

So if I wanted the full 1.5A to be able to be drawn from the battery, I need a resistor that has enough wattage for that?

Just to clarify. thanks.

5

You don’t need anything, the board is already properly setup for you by SparkFun.

6

YellowDog:
You don’t need anything, the board is already properly setup for you by SparkFun.

Yes you are right. I just don’t know the exact spec of the resistor they used.