Quote:
Originally Posted by eq1
So, using my example, if it were 8000 mV, 7500 mV, and 3500 mA, the result would be N mOhms? The result is 0.143, the same as before...
|
8,000 mV = 8V
7,500 mV = 7.5V
3,500 mA = 3.5A
change in Voltage = 0.5V @3.5A
V=IR
0.5/3.5= 0.143 Ohms
not mOhms ... the reason is that the metric prefix is just a scale it is not the unit itself ... milli is a prefix to Volt ... 1 V / 1000 = 1mV ... the division by 1000 is not the voltage term it is a multiplier.
In the original form:
V=IR
To keep the same ratio of V=IR but in milli scale ... you multiple both sides by 1000.
0.5V * 1000 = 500mV
3.5A * 1000 = 3,500mA
In the form of the V=IR equation ratio
(0.5V * 1000) = (3.5A * __ Ohms * 1000)
When you divide both sides by 3,500 mA you take away the 3.5 and the 1,000 leaving only ___ Ohms ... it is no longer mOhms.
Same effect happens any time you do algebra when one side is the product of two terms multiplied... weather the equation is F=MA or V=IR or E=MC^2 ... etc.
To avoid confusion some people always convert to base units before using ratio equations ... which ever method is easiest for you.
Quote:
Originally Posted by eq1
Do you know the pair-ordering of the subpack pairs as monitored by the 10 voltage taps?
|
Not off the top of my head ... but it is easy enough to determine ... use a multi-meter to check for continuity between the connector that plugs into the BCM and the junction board on the side that makes contact with the stick... or if the sticks are still in place ... check for continuity from the bolt to the plug pins.
( added: As I recall there is a resistor inline, so it won't be a dead short )
Quote:
Originally Posted by eq1
I was using the 'stabilize' strategy at first, but it wasn't very consistent, or easy or clear to decide when the current had stabilized... So I switched to 1 minute. It may matter whether you're using a high or low discharge rate. At first I was using 10 amps and sometimes it took a while for the level to stabilize, and/or the readout jumped around a lot nearing the top end... It wasn't that bad at only 3.5 amps...
|
If the battery discharging device you have does not stabilize current flow quickly your alternative method is reasonable ... just keep in mind that consistency becomes even more important ... your 1 minute results are a bit further from true ohms and are more on the side of relative ohms ... meaning don't expect your tests to give the same Ohm numbers someone else testing the same battery with a different method would get ... your method can be fine as long as the numbers you get for stick A are compared to stick B using the same method... because you aren't really looking for true Ohms ... you are using the tests to compare it to other sticks ... it is a relative comparison type of testing ... as such relative ohms and not true ohms is fine.