A Battery IR Question....

[dreamer_1uk]

Hi all.

I have a question for a battery expert.

I know on batteries that the higher the Internal Resistance, the better the punch, well the IR number on the packs, should it be high like IR 25 for a higer resistance or a low number for higher resistance?

Its one of those things whats been bugging me and ive heard 2 different answers.

Any help would be greatly apreciated!

Thanks,

Dale

:D

[Nutter]

uhh.. hehe :D

The lower the internal resistance, the better the punch. The lower the IR number on a matched cell, the lower the internal resistance is (duh).

Think of it this way.. what does IR stand for? Internal Resistance - resistance is something that is slowing the flow of electrons (electricity) out of the battery, and punch is determined by how fast the power from the battery can get to the motor. So logically, the more resistance to the power getting out of the battery means the less punch there is.

*edit: oh yea, one major, major, MAJOR point - you can't compare the IR numbers between cells matched by different companies, as they ALL have their own way of determining those numbers. Same goes for voltage and runtime. For instance, an IR of 21 on a SMC cell might be the same as an IR of 4.2 on an Integy cell (never trust Integy cell numbers also - they tamper with them).


-Nutter

[dreamer_1uk]

Hi,

Thanks again Nutter.

:D

[TyceCCSU@aol.com]

Nutter and dreamer_1uk,
The resistance #'s that are in the range of 2-5 range use a calculation called "Actual Resistance" but is labeled the same as "Relative Resistance"..both are labeled "IR". By the way, Relative resistance is usually in the range of 15-35.

The difference between the two are quite different, but measured the same when matching, the numbers will vary from matcher to matcher due to climate controlls and # of cycles.

Actual Resistance is the resistance of the cells chemistry when discharged. Battery's have a natural tendency to discharge and this is why the Actual Resistance is much lower with respect to it's range.

Relative Resistance is measurement of resistance when charging, simply stated.

Which method is better, definetly Actual Resistance, it'll show you how the cell will react while in your car/truck. In addition, IR is noticible by the top drivers or oval pan cars, it acts as a sort of "bucking" or "shorting" effect. Lower IR allows much smoother acceleration, and much more predictible acceleration. Most of us aren't good enfough to notice the effects.

[highroller]

Knowing what the number mean is the best way of picking a good set of cells: run time, voltage, internal resistance and cutoff default. The most important is the cutoff default which most matcher's using a 5000 and the cutoff voltage should be .90. Any one using a different value can influenece the numbers by making them look better than they actual are. For stock racing voltage and IR are the most important 1.14-15 (18-23) @30amp, 1.17-19 for 20 amp. You'll see higher voltage numbers in the 1.15 with some rare 1.16 with the NiMh while 1.14 are considered top for Nicads. At the 20amp rate the numbers tend to be around 1.17 for Nicads and 1.19 for NiMh. Another clue to how well the pack will perform is how tightly matched the numbers are, some use 360, 363 with 1.13 , 1.12 while other use all 360 runtime with 1.13 voltage cells.