I think I’m going to buy the charging adapter; seems like the best with minimal DIY (just cut one end right?)
Just cut up an old extension cord and jam them in the holes.
My DMM reads 0.03 Ohm in 200 Ohm range. Still I got much lower Amps out of one driver, it drops in the flashlights, damn bad connections add resistance.
Will make 2.5mm^2 silicone gold banana plug leads. Wire can be bought at electronics store or online, or at hobbyking probably, not sure about the quality there though.
I just picked up a set of "Tenma" DMM leads on sake at MCM Electronics online. I'll report back on them when I get a chance to compare. I was looking for decent replacement leads, not just for tailcap current measurements. I believe "Tenma" is their "house brand". I used to deal with MCM back in the mid 90's.
-Garry
So I've had my new Tenma multimeter leads from MCM Electronics for about 3 weeks now. I got them for $8.49 on sale with $5.00 shipping (I think it was a promo of flat rate $5 shipping on all orders or something) along with another set of test clip leads. They come with various thread on probes (as seen in the photo below). The leads are 18ga and rated 2000v, and the banana plugs are stamped "1000v CAT III 16A". They are 3.5' long and the wire feels nice and flexible. The probe ends and banana plug ends are made of a soft comfortable flexible rubber. When I used my short homemade 12ga test leads to check the resistance of each lead I get a reading of 0.0 / 0.1ohms (display toggles between 0.0 & 0.01) when my meter is set to the "200 Ohm" setting.
I compared some tailcap readings between two different lights using both sets of leads (my short 12ga homemade ones and these Tenma's) using the same protected Tenergy 2600mAh 18650 @ 4.21v as follows:
1) An XP-G C8 modded with a 1.4A Nanjg 3 mode driver:
Tenma leads:
Hi - 1.68A
Med - 0.52A
Low - 0.08A
12ga leads:
Hi - 1.68A
Med - 0.52A
Low - 0.08A
2) A P60 host with the famous Ultrafire 3 mode XM-L drop-in (direct drive on high):
Tenma leads:
Hi - 4.34A
Med - 1.28A
Low - 0.23A
12ga leads:
Hi - 4.80A
Med - 1.44A
Low - 0.26A
The comparison test seems reasonable to me. I used to get much lower readings with my old meter leads. I'd say they are acceptable and I recommend them as a cheap set.
Product Photo:
-Garry
Those are a nice looking set of leads Gary. Id imagine they should be good for at least 3.5A in taking reliable measurements. Thanks for posting your results.
Number 12 AWG solid copper should read approximately 1.6 ohms per 1000’ at 20C but because of contact impedance you need to use Kelvin clips or some other four terminal method to measure this.
If you put a lead in series with a car battery and a headlight you may get a relatively constant 3A through the test lead. Then you can measure the voltage across the lead taking care that your voltmeter prods do not touch the connections that pass the current. This four terminal method cancels out the effect of contact resistance at each end.
For #12 at 3.0A with DMM test leads 2’ apart you should read 3.0 x 2 x 1.6/1000 = 9.6 mVdc. With lights in parallel you can pass more current but the test lead resistance will increase due to I squared R heating.
In any case your test lead plus ammeter shunt resistance should be at least 5x less than the circuit impedance - for a 4v, 3A light this impedance is 4/3 ohm.