17mm & 20/26/27mm single-sided DD/FET driver release: A17DD-SO8 / A20DD-SO8 / etc

Wow, learn something new every day! (I could have already known that, and forgotten it, and learned it, and forgotten it again)

Now I need to do some research, so I’ll be armed with more stuff to forget. Vicious circle, is it not?

:stuck_out_tongue:

One way figure out whether it’s the PTC is to remote-mount the battery. I know that this flashlight does not make it easy, but it’s probably possible with a sliding clamp to hold the cell, a nice jumper cable clamp for the GND/Bat- connection, and some copper rod or whatever for the BAT+ connection.

Or you could just solder some big hookup wire directly to the light engine.

I’m assuming that if it is the PTC then the problem is the heat from the emitters, not the cell self-heating or anything.

The PTC is a thermal switch to help prevent overheating of the cell causing pressure build-up. From what I’ve been able to find online, if the PTC is triggered the cell will most likely be useless. This cell is working fine, recharging fine, working some more. So it really is doubtful that it’s the PTC causing issue here. (Positive Thermal Coefficient) This is the primary information I found. And just now, looking to double check what I was writing, I found this information that contradicts the previous articles (4 different sources)

“Problem
Most commercial, cylindrical lithium-ion cell design are
equipped with a positive thermal coefficient (PTC)
current limiting switch to provide hazard protection
against short circuits external to the cell. This device,
shown in Figure 1, is thin annulus consisting of a
specially irradiated polyethylene laminated with a metal
on both sides [1]. When exposed to an overcurrent
situation, this normally conductive polymer heats up and
changes phases to become several orders of magnitude
more resistive. Once the short is removed, the PTC cools
down and returns to its electrically conductive state. This
device has been a very effective method of providing
reliable short circuit protection in low voltage battery
assemblies. ”

This would explain why, after several seconds, the firmware caused a flash indicating power had been applied, even though I had not taken the light apart or opened it. The switch in the cell reset and power was again available.

So, is 15A+ the top end for the Efest 35A Purple cell? Leave it to me to have found that, huh? :stuck_out_tongue:

Now I will test the Sony VT C5. :bigsmile:

IMO the issue is that you are subjecting the cell to a very high temperature (although a 15A drain at the same time probably doesn’t help ;)). HKJ successfully tested the Efest ‘35A’ cells at 30A, with strong results at 20A.

The Sony C5, fresh off the charger, didn’t quite allow 14A (13.61-13.91) and showed 3784 lumens at the highest, dropping down to 3450 by the time it was too hot for me to hold my thumb opposing the switch. (54 seconds, as per the video I took while doing this.) I should also point out that I was taking a tail amperage reading with a 14” long 12Ga wire through the clamp meter while the light was in the light box. So the lumens output was lower than if the light had been assembled.

This light with it’s chunk of copper under the quad only dropped 340 lumens in 54 seconds at extreme power levels, I’d say that’s not bad at all!

Point here being that your A17DD-S08 driver is a very capable little single sided slimline device!

Hahahahaha, tell your hand thanks for taking one for the team! https://www.youtube.com/watch?v=qPr-xsQvhgw

The meter is set at X10 (so 10970), the number shown is then multiplied by .345 to get Lumens. This is the multiplier for my lightbox.

Stock clicky DBCstm? ALOT of amps to be running thru a stock switch man

Still awesome as hell bro…all them amps! WOOO!

3000 lumen sleeper…guy is all, look at my light, and you MELT his with a click of the switch :smiley:

It’s an e-switch with a ramping firmware and a sleep mode. Uses very little (some 40uA) current when not in use. A long press bypasses memory for the lowest position and hold, have to release to start ramping up from there. A double press goes straight to the max level. Single press from any position when on turns it off. Release the ramping and start again within a second and it reverses, otherwise it continues in the same direction if pressed again after one second. 64 steps, top to bottom in 2 seconds, or vice verse.

I find this very handy with the big draw lights, the most options to get the optimal light for the situation or conserve the cell or both.

Under the copper plate that holds the spring in the tailcap is a very strong magnet that holds the light even with this big chunk of Cu in the head. So I can also stop a pacemaker with it. :stuck_out_tongue:

And it does over 4000 with an Efest 35A, 4147 to be exact. :stuck_out_tongue:

Holy hot stuff Batman, that thing is a portable reflow oven. Glad you found a use for the copper. Let me know if you see anything else in my builds(rare as they are) that you might use.

Trying to follow the logic on how the top of that cell heated up so fast, I think I might be on to something.

I’ve got a spring on the driver, with a 22 Ga wire inside to carry current, right? So this ends up making a point of contact at the cell that is on the very small side. Okay for 6A, but with 15A… maybe not so much! With that much current flowing through a small space what does it do physically to the wire and spring? Heats em up! Immediately!

So I’m going to put a 5/16” diameter brass post on the driver this morning. Far more current carrying capacity and a major contact surface improvement, giving full contact to the top of the cell. That should solve the PTC shut down issue. I’ve already put a solid copper plate at the negative end, with a beefy spring and also wire bypassed…I’ll put a copper top on that spring for a larger flat surface as well. :wink:

The Sony C5 is a flat top, it ran 54 seconds on the light box without shutting down. The button top Efest shut down within 10 seconds. Smaller top plate, smaller contact surface. (granted, the spring with wire soldered in still gives a small surface contact either way) Could simply be that the Sony has higher quality components.

Does that sound right?

Thanks Scott, that copper sheet has been really coming in handy! :slight_smile: The really thick stuff not as much as the thinner, scissor cut capable sheet. But I’ve used the thicker stuff as well, albeit with some more work getting the piece desired. :wink:

Edit: I might even see higher current with the blockages addressed! :bigsmile:

It’s hard to say for certain, and I already mentioned some of this, but here goes:

  • HKJ managed to get full 30A discharges out of the ones he tested.
  • The PTC responds directly to temperature, not current.
  • I think it’s a temp issue, not a current issue.
  • The PTC on the Efest may simply be using different materials which change more aggressively with high temperatures.
  • I think a battery spacer which blocks the flow of heat from the pill to the battery is what you need. Maybe stainless or maybe delrin/whatever with a 12AWG solid copper wire hammered into the middle.
  • If problems persist then maybe your Efest batteries are mildly damaged? Although I thought a PTC was supposed to be tough, repeatable, and difficult to damage by it’s nature.

Ever hold a wire on cell while pulling high current through it? Current IS heat! You can’t have high current through a wire in a transition without some heat, the springs get hot that’s why bypassing their current handling makes it work.

HKJ didn’t test 30A on the cell installed. Big difference. I’m sure his connection wasn’t a pinpoint of solder by spring contact either.

Yes, high temperature causes the polymer to cease being electrically conductive. The design is to protect against a short circuit, high current-high heat-shutdown. After cooling the physical properties of the polymer switch are supposed to go back to normal and continue being electrically conductive again, according to experts that put together a paper from Cambridge, NASA and YALE.

At any rate, putting the solid brass contact in place of the spring was one too many times working on it. It’s DIW.

I realize that a high-resistance path (such as a small contact point) generates heat. I’m a little frustrated that you find the need to mention all that again. OTOH I suppose it’s only fair since I was repeating myself as well.

It’s your light: if you’re happy with it on the Sony cell then there’s certainly no need to ‘fix’ the light’s behavior with the Efest cell.

Working again, soldering on the brass post caused the diode to lose contact on one leg opposite the battery contact.

I mentioned it again for 2 reasons, one to be sure I was understanding it correctly and 2 this is an open conversation that others with as little understanding as myself can get it.

And besides, isn’t the actual pcb of the driver a FR G10 laminate? Doesn’t this separate the battery contact from the pill? Isn’t most of the heat brought through at the contact point itself, regardless of being surrounded by FR G10 or Delrin or whatever?

I don’t know these things, just going on reasoning and what little common sense I have left to me…

All fair enough. I agree, it seems that most of the heat must be finding it’s way back through the positive contact… or the battery tube?

I’m not really certain what the best way to block the heat transfer is. A stainless steel spacer might be an OK option, assuming that the heat is coming through the positive terminal.

I had it too tight with a beefy tail spring and the glass lens broke. Cutting a UCLp down to fit, then I’ll see what the Efest cell does on it with the brass contact.

Had to come in, cordless drill battery died and my backup wasn’t charged, go figure.

Efest 35A runs 15.10A at start, fresh off the charger. It’s down to 14.10A at 36 seconds and the head of the light was uncomfortable to hold onto. Stuck the cell back in the charger, showing 4.06V.

Little power hungry beastie is what it is! The FET on this A17DD-S08 performs just fine, both it and the MCU now have a thermal pad on top of em.

I find it amazing that a single cell can run that kind of power. Crazy stuff. And I love it!

Thanks Wight for a job well done with this driver! This will be a staple for me now, the single sided layout is just so much easier to build and install.

Edit: might should mention that in all the rebuilding and messing with this light, 2 of the 4 XP-L’s have become de-domed…one was mysteriously so and the other had a loosened dome that I pulled off with my fingernail. Lucky that they oppose each other on the board so it looks ok.

Edit II: Cell recharged, 4416 lumens at start, 3743 at 30 seconds. Efest 35A works fine now.

Thanks for the complements and for keeping us up to date. I’m glad that the Efest is playing nicely now. So do we think it turned out to be contact resistance after all? (eg the heat from high current across high contact resistance was tripping the PTC?)

I addressed multiple issues by putting thermal pads on both the MCU and MOSFET, and also gave that larger contact point for the cell. The combination works, not sure if any one would have done it stand-alone.

This host is really a bad choice for this, as it has poor head-to-heat sink contact and no cooling fins at all. I’m thinking of using a mix of JBWeld and copper sanding dust to fill in around the copper heat sink in the head, there’s enough space for a 22ga Silicone coated wire to fit all the way around from about 1/4” up from the base of the heat sink…so a little more than 3/4” of the heat sink has no host contact. I really should have used a larger diameter copper bar to start with and totally filled the head, but I used what I had.

This design puts all the thermal path contact right down there at the driver, no contact anywhere else.