My meter is not the best. Specially grabbing button tops.
However I refuse to spend 70 bucks in the “good” one.
Since I’m not building packs.
I measure 4 or 5 times and average.
Readings fluctuate from .002 ohms to .140 ohms. In different batteries.
What is the maximum resistance permissible without losing power.
Thank you for your kind replies.
Cheers.
Unno, I just tested some otherwise decent cells that came with a usb fan, and those were bouncing around in the upper 100s (160-190, usually). Capacity was still spot-on.
They’d be absolutely fine in a low-stress light, up to a coupla amps, but not beyond. Try to fire up a pocket-rocket, and forget it.
It’s like asking, “How many hp do I need in my car’s engine?”. If it’s just a small road-rat you’re using to tootle about town, not much. If you intend to pull a trailer with a coupla horses in it, you’ll need a lot more.
Thank you for your reply.
Amps I know, since I vape. Mostly with VTC4s and VTC5As.
Let’s say I want to power an EDC 18. Maximun IR without losing power?.
Cheers.
20 to 30 mOhms is typical for a higher drain 18650. The EDC 18 uses a FET driver so there will be a continuous decrease in brightness with increasing IR.
Also there’s a good chance your IR meter is not accurate, even if you average a number of readings. See some of HKJ’s charger reviews. With most chargers the IR function returns nonsense.
Any IR increase reduces the power in a direct drive light, I made this estimation graph the other day : Calculator Suite - GeoGebra
It’s approximative but it gives an idea, with my PL42G2 it works decently well, within 1~2A of actual measurements.
Put the led parameters (a and Rf), led amount (Nleds), bat voltage (Vin), Rcircuit, which is total resistance : IR cell + resistance of the flashlight circuit, maybe between 15 and 25mOhms for the EDC18 if it has good springs (no idea).
With the same meter, same temperature, same method—then you could probably detect a weak cell that is falling out of family with the rest, if you kept records over time.
Manufacturer and vendor IR measurements are done at 1kHz to measure impedance using a standard method. An oscilloscope could also be used to measure the initial inrush surge current and voltage as another method. A low frequency or DC static measurement reflects more of the chemical reaction rate and varies greatly with temperature, but as stated above could be useful to detect a weaker cell.
Every charge/discharge cycle puts wear on a cell and reduces it’s life. Cells only contain energy not power; power is determined by and dissipated in the load device.
You don't really need to squander money in a meter to measure the internal resistance of batteries. A couple tools plus a good technique is all you need.
First of all you must understand that a battery, as a practical voltage source, has a very low resistance value. So low, that contact resistances are comparatively significative and need to be screened out. Therefore, it is a lot better to measure the voltage variation over a battery's terminals when the current flow to the battery changes. This can be done with a precision power supply, a few neodymium magnets for interconnection, a good multimeter in mV scale and some helping hands to keep the probes over the battery terminals, or some other way to accomplish this. Interconnected everything this way, voltage delta in the battery terminals can be observed while the current flow is varied some known extent.
Other good way is to use a proper battery tester. They do internal resistance measurement, but this is not what I am referring to, and my EBD-M05 could do that better (measures consistently, but low). With a properly calibrated battery tester it is possible to discharge test at two different current rates, and obtain a good internal resistance measurement by dividing the voltage difference between two curves plotted at different rates by the current delta (for example 1A and 5A in an EBD-M05). Read voltage values at around 10% - 15% progress in the discharge curves, to minimize resistance reduction by temperature.
Phew!
I’ve drawn some conclusion out of this thread.
a) I’m an ignorant as far as batteries are concerned.
b) There are a lot of guys with a lot of talent here.
c) My readings give me an idea of which ones read higher.
d) I learned about a capacity tester (Barkuti).
e) I’m very grateful to all of you for your time and effort.
Cheers.