Quick answer:
If you have two 2920L300/15 in parallel and a short circuit current of 16A the current will split equally between them, 8A each is still above their trip current and the trip will take about 20 seconds - assuming the battery can continue to supply 16A for 20 seconds.
If the chemistry, internal resistance and remaining charge of the battery is such that the maximum short circuit current it can deliver is less than 10A then two 2920L300/15 in parallel will see less than 5A each and the battery will probably run out of charge before they trip.
In the first case a pair of 16r300g would trip in about 8s. In the second case, once again, they may not trip.
Fully charged RC hobby LiPo packs are capable of delivering very high currents, a short circuit across one of these could easily deliver 40A. The polyfuse will trip in a fraction of a second - though a traditional fuse would still blow more quickly - , or may even be destroyed, the battery may still be damaged.
I have no idea of the short circuit current an IMR battery can deliver.
oops copied wrong row
| Part Number | I hold (A) | I trip (A) | V max (Vdc) | I max (A) | Pd typ. (W) | Max Trip Time Current (A) | Max Trip Time (Sec.) | R min (Ω) | R 1max (Ω) |
| | | | | | | | | |
| 16r300g | 3.0 | 5.1 | 16 | 100 | 2.3 | 15.0 | 1.0 | 0.0380 | 0.0975 |
| 2920L300/15 | 3.00 | 5.00 | 15 | 40 | 1.50 | 8.00 | 20.00 | 0.015 | 0.048 |
ecat's electronic component selection tip #1: Never trust summary tables or headline figures, track down the data sheets and, with a little help perhaps, try to make
sense of them
The data sheets for both of these
devices have a graph entitled 'Average Time Current Curves' so we're off to a good start.
The x & y scales on both of these graphs is logarithmic, watch out for that. Using the x-axis, Current, in the 16r300g graph as an example you see the 'leftmost block' goes from 1Amp to 10Amp then from 10Amp to 100Amp across the 'centre block' and finally 100Amp to 1000Amp. From left to right, putting a value at the bottom of each line that crosses the x-axis gives you 1, 2, 3... 9, 10, 20, 30... 90, 100, 200, 300... 900, 1000
From the table above the 16r300g has a trip time of
1.0 seconds at a trip current of
15.0A, we should be able to verify this against the graph in the data sheet (aka datasheet but my spell check likes the space between the two words).
From the table above the 2920L300/15 has a trip time of
20.0s at a trip current of
8.0A, we should be able to verify this against the graph in the datasheet too.
To compare the two we need look at a common trip current and see what the graphs can tell us. From the graphs the 16r300g trip time at 8A is about 8s. The 2920L300/15 trip time at 15A is about 6s.
So, 16r300g is faster but it's maybe 3 to 6 times faster, not 20 times faster as the table data may have you believe.
I do not like the trip time. I am not smart enough to know what that would come out too after doubling this chip up.
These resettable fuses are really just resistors with wacky temperature curves. When the current through them is less than the hold current their resistance is less than R Max. When the current rises above the hold current they start to heat up and their resistance begins to increases rapidly (the PTC you see in the data sheet stands for Positive Temperature Coefficient). If the current through them is sufficiently large, the temperature rise is rapid and the resistance becomes high enough to 'break' the circuit.
If you double up the chip, you're putting two resistors in parallel, so all things being equal each chip carries 1/2 of the passing current. This is where the graphs from the datasheet really help.
NB ambient/
device temperature also comes into play but this post is already long enough.
Disclaimer:
I am not an trained electronics or electrical engineer, my understanding my well be incomplete but I do try to err on the side of caution.
