First,as RMM said,you must measure current and voltage on highest(no PWM) mode.
Parasitic resistance for first driver is 6.22mOhm (miliOhm) which sounds about right,slightly higher than mosfet Rds;
but something is wrong for 2nd one, 21.34mOhm is too high for that mosfet? Value should be similar to first driver.
For fair comparison,it's important to measure parasitic resistance at same battery voltage,because mosfet's Rds usually starts to grow rapidly at voltages <4V(of course,that depends on mosfet)
My not so able bodied and not so willing partner in crime made it a big issue this morning. Geesh, just wanted a little help! lol
miliOhm huh, I was guessing on the Ohm connection studying Wikipedia on Ohm’s law. lol
I did both repeatedly, the Clamp meter is Auto sensing and gave me Voltage on the first one, then mV on the next and wouldn’t switch over. So I did them each repeatedly, arguing with the cranky wife, we both yelled at the kid, and ultimately I tested them again by myself holding the amperage leads on the cell with my tongue. Now it’s me that’s cranky! Vroooom! I started! Woohoo!
I’ll charge up the cell I used and try again. With peace and quiet the prevalent factor.
Nice job Dale! Sorry, very busy at work now - no time for BLF during working hours and long days. Was just about to try a Mattaus v1.0 driver in the X6 - not sure if it's worth it now, but using 20 AWG of same exact length each, it will still tell me how they do in the exact setup, same light, same LED, etc.
Not a thread - just finished some tests with the BLF17DD v1.0 using the de-domed XP-G2 S2 and got about 0.15A to 0.18A higher, depending on the cell (SAM 25R or LG HE2). Best #'s for each driver:
A17DD-S08: LG HE2 @4.23v: 3.78A @tail
BLF17DD: LG HE2 @4.22v: 3.96A @tail
Same host, same LED (didn't even remove the LED - it's screwed down), same 20 AWG wire lengths for LED wires, same 22 AWG wired driver spring setup (different spring but don't think that should matter), same batteries.
Conclusion:
Well, with just one sample of each, there can be variables I'm sure: quality of reflows, tight driver mount, battery charge differences, FET variations, etc.. Seems slight edge to the old BLF17DD which is kind of what I suspected, but since I only tried one A17DD-S08 up to this point, I can't say anything definite from this - too little data, not enough samples tested, don't 100% trust my methods, measurements, etc. It's not lab level for sure... I would trust djozz more than myself - absolutely .
Several other options are discussed in this thread. Did you look for those? Rufusbduck suggested one I really liked and I think there were a couple of others which sounded OK too.
Exactly. We would need very precise measurements and tightly controlled test conditions if we were actually out to prove that one is better than the other. But to prove that the info from the datasheet applies in the way we thought it would? No problem, you and Tom E have already done that, in spades!
All that said, anyone wants to play around with testing different FETs, here are 3 which all appear to have some superior characteristics:
PSMN0R9-30YLD - rufusbduck pointed this one out, it has very similar characteristics to PSMN3R0-30YLD but is better. Slightly lower Rds(on) and slightly lower Vgs. Also significantly higher “total power dissipation”. We expect the lower Vgs to ensure that the FET remains more “fully open” on single cell setups.
SiR800DP - comfychair pointed this one out to me in reference to this driver by PM weeks ago. I forgot about it until I went looking for FETs which I thought might work properly with the QX7136-based A17LDQX driver and it turned up again in that context. Much lower Rds(on) than our selections so far and even lower Vgs than RBD’s selection. Again, the low Vgs should help keep the FET fully turned on.
SiS414DN - Another one which turned up during my search for good FETs for the QX7136. Low maximum current handling, 20A “package limited”. I’m not really sure exactly what a package limit involves, since we know that PowerPAK® SO-8 can handle at least 50A (the SiR800DP is spec’ed for that) and the graph in the datasheet goes way beyond 20A. Even lower Rds(on) than SiR800DP, but only slightly. Similar Vgs characteristics to SiR800DP. Lower Qg than SiR800DP, but I doubt that that will help us any. Costs less than the other two FETs in this list.
Typically we look at Rds on as tied to gate voltage but after slogging through some of these data sheets I see that it also varies with drain current and temp just not as dramatically. Which makes sense since resistance in most things goes up with temp. To test more would you start with the third possibility in the hope of seeing gains at lower cost in spite of the current limit or with CC’s suggestion to find the possible upper limit?
It’s already been pointed out elsewhere (by comfychair probably, and maybe others) that we achieve diminishing returns once Rds(on) gets low enough. IMO it’s already “low enough”. The difference between 10 milliohms and a hypothetical 0 milliohms is probably under 0.2A for an XP-G2, assuming we are at/near/under 5A. That’s just not very exciting to me. (Consider that we are already <7 milliohms! How low do we expect to get?)
I wouldn’t have listed all 3 if I didn’t think that they were all just as worthwhile to test. That said, the maximum gain anyone can expect to see for an XP-G2 is probably around 0.1A, maybe 0.15A - and it doesn’t matter what FET package we are talking about, we’re that close to true DD here. The higher the current, the higher the gains, but there’s still very little to be had!
Sorry wight, I just know that a relatively few out there are looking for every last mA. I totally agree it’s not much and to most of us not worth the added expense but until my own head hits the wall something keeps me leaning forward. Although the low on state voltage of the one I suggested was what caught my eye at first, it’s the lower “elbow” in the curve that made me want to bring it to attention. We may not gain anything at all but at this relatively early point developing these drivers I’d still like to confirm what the different options offer.