Battery Internal Resistance/ESR Thread

[WalledSonic]

The purpose of this thread is to evaluate and discuss the internal resistance of various batteries and (possibly?) test methods.

I’ll start this off by using the DC Load method to test some XS AGM, some K2 73Ah cells, and some K2/JYP 80Ah cells.  The DC load method was used because that’s all the equipment that I had available or was able to purchase quickly and on the cheap.  Here’s a link for more information on Load Test Methods.

http://batteryuniversity.com/learn/article/how_to_measure_internal_resistance

Calculation used was Rint = ((Vrest/Vload) -1) x Rload)

Where

Rint = internal resistance

Vrest = Voltage at rest

Vload = Voltage once load is applied

Rload = resistance of the load resistor

Now onto some pictures of the setup.  If there is something amiss please chime in so we can figure it out.

1ohm load resistors (although they test out at 0.9ohm)

I connected them in series on one end, and I can change the resistance by simply connecting my jumper wire differently. I have the opportunity to connect at 0.45ohm, 0.9ohm, and 1.8ohm.  Here's proof of half(ish) ohm, although I didnt use this low of a resistance for data collection:

So this connection would be 1.8ohm

This connection would be 0.9ohm

Here's the 73Ah K2 cells (not JY collaboration batteries)

The day before testing, I topped off all the batteries, including the JYP's in the back and the AGMs to the right. 

24 hours later, I actually took measurements.

Data for the lithiums:

Data for the D3400R AGM

Looking forward to some comments, suggestions, etc.  Thanks for looking!

[WalledSonic]

Lithium K2 and K2/JYP cells all tested out at 2.7 to 3.3 milliohms.

XS AGM tested out at 11.8 milliohms, about 4 times as much as lithium.  I need to put the data up of my stock wet cell lead acid battery, it was much higher.

ESR doesnt tell the whole story, as there is a stronger capacitive effect with the lithiums than with traditional lead acid. 

If you have batteries (specifically for or able to be used in car audio), please measure the ESR and post here for comparison.  I dont have any batteries older than 1 year old, so these are all rather new.  The K2 cells are 6 years old, but were never put into service.  Checking with Cameron at K2, he wouldnt tell me what the ESR should be, but he said he was happy to see them holding so well after 6 years.  After testing the brand new JYP's against them, it seems like the K2's were a great purchase at less than half the cost of a comparable JYP battery.

[rocking.that.eclipse]

I'd like to do some testing on this myself to see what kind of variation you have in different agm brands and the same with lithium

I bet there is little difference between brands for this test. 

I'd like to see what the difference would be if you were to use smaller connection straps. I have heard that the more cross sectional area the better that everything should "flow" and that you will see a big gain.

Also would like to see how caps fare on this test just to see if they are really less internal resistance than the lithium

 

[WalledSonic]

Thats a neat idea about the wires.  I assumed at only 100W at 0.9ohm, the 12AWG wire would be enough, but I will redo the test soon with larger wire for comparison.

[rocking.that.eclipse]

1 hour ago, WalledSonic said:

Thats a neat idea about the wires.  I assumed at only 100W at 0.9ohm, the 12AWG wire would be enough, but I will redo the test soon with larger wire for comparison.

I'm even talking the series straps too. If you decrease the cross section of those (say using 1/16" thick straps) that that will also change this test

I'm curious where the thresh-hold for this is (at some point you're not gaining anything by having a thicker strap)

Just things to think about