I'm using a ZB2L3 battery capacity tester (all I have on hand at the moment) to test some 12v LiFePO4 batteries (4s8p A123 cells). First I used the included ceramic 5 watt 7.5 ohm resistor; it pulled ~1.5 A, got very hot (temp gun says 350 to 400+ F (177 to 204 C)), had a very unpleasant smell and after only two tests it broke apart. I did set up a fan to help cool it about a quarter of the way through the first test, but I guess it didn't matter. I then remembered there's a science to this resistance thing (d'oh!), realized this resistor was likely meant for 3.7v li-ion testing (rated for 5 watts, but was doing 20 watts.../).
So I calculated and looks like I could use a aluminum 25 watt 8 ohm resistor I had on hand. I started a new test with a new battery with the aluminum resistor. It's pulling 1.7 A, so it's doing ~23 watts, which is within 25 watts, but it also gets very hot; temp gun says 310+ F/154+ C without cooling, 228 F/109 C with cooling.
Is that amount of heat normal for a resistor and I just need to find better ways to keep it cool or am I still not using a more suitable resistor for capacity testing these 12v LiFePO4 batteries?
So I calculated and looks like I could use a aluminum 25 watt 8 ohm resistor I had on hand. I started a new test with a new battery with the aluminum resistor. It's pulling 1.7 A, so it's doing ~23 watts, which is within 25 watts, but it also gets very hot; temp gun says 310+ F/154+ C without cooling, 228 F/109 C with cooling.
Is that amount of heat normal for a resistor and I just need to find better ways to keep it cool or am I still not using a more suitable resistor for capacity testing these 12v LiFePO4 batteries?