BLF SRK FET Board discussion thread

Is there anything similar you have to do with the other RMM SRK driver? I can’t get mine to work either. Or is it just solder and play (so to speak)?

It’s labeled to have an inductor there. If you don’t use the inductor it needs to be bridged. There are a few threads going up with separate discussions of each board and where they exist I add links to them. Much development and discussion goes on in the Oshpark projects thread where it gets lost in the noise. I have mentioned before the need to have separate discussion threads for each board(or at least each family of boards) and that is being done slowly but these are all new enough that that hasn’t been done for all of them. I’m sure Rich will do what he can to add info on his site as well so thanks for pointing this out.

Now that Werner has found your answer if you would like to retitle this thread it could become the needed discussion thread for the SRK FET board.

Ok…so to be clear, I need to jumper the Batt+ pad to the L1 pad?

[quote=Rufusbduck] Now that Werner has found your answer if you would like to retitle this thread it could become the needed discussion thread for the SRK FET board. [/quote] I'd be happy to. What would be the best title for it?

Oh! Thanks for all the help guys!! I will let you know tonight if it works finally.

Yes the two pads that look like T’s laid on their sides facing each other., that will get you going.

Yes, BAT and LED+ must be connected with something, either a jumper or an inductor. Big schottky diode at D2 is not needed if not using an inductor.

with inductor:

without inductor: (ignore wires going off to bottom left, those are for bench testing only, removed before installation)

If Richard is selling these as 'assembled' and complete ready-to-run, they should also really have that jumper installed as well. (For some reason he's against using the inductor/diode parts, I don't understand his reasoning for not using them and he doesn't understand my reasoning for them, I can only tell you I use them because they give a much nicer low end and allow lower sub-1-lumen lows even with reasonable minimum PWM values.)

The big electrolytic cap is no longer needed, that was to patch the issue of whiny noise when using older versions of firmware, no longer needed when using the silent fast-PWM firmwares.

Does that reduce maximum output? He's mentioned a mod that would allow much lower lows.

Reduction in max output depends on which inductor you pick, both the DC current rating and the inductance rating. Comparing ~15A-rated 0.58uH inductor to a ~15A-rated 1.2Uh inductor, the 0.56 will have less damping effect on the lowest modes but also the least impact on the straight DC 100% mode. The 1.2uH will give a lower low but with slightly less output on 100% mode. But it's in the range of a few milliohms. With a ~4mOhm Rds(on) FET you can afford to sacrifice a little at the top end and not see a big hit in total output.

I don’t know if you know just how relieved to have this finally working! I was about to completely give up on my modding skills and be so discouraged that I stop again for a while. I can’t WAIT to see some impressive results for once!

On a side note, I tried modding my TR-S700 with a couple of the FETs Richard sells (it's a FET driver to start with) hoping they would allow more current to the emitters but I only gained just under 200 lumens. Still only 3745 OTF with 7 LEDs and 3*26650. Not at all what I was hoping to see. :(

http://www.digikey.com/product-detail/en/ETQ-P6F0R6BFA/PCD1393CT-ND/308387 or http://www.digikey.com/product-detail/en/ETQ-P6F1R2HFA/PCD1307CT-ND/281422, I found both on ebay for much cheaper. Anything with similar specs will do the same job, and we tried to lay out the inductor pads on the board to be compatible with just about anything in that size range regardless of manufacturer. Lots of stuff out there that will work.

This is the diode needed at D2 if using the inductor - http://www.digikey.com/product-detail/en/MBRS540T3G/MBRS540T3GOSCT-ND/918011 - or, again, something of similar specs. It just needs to be able to shunt the leftovers stored in the inductor when the FET is turned off via PWM in the less-than-100% modes.

Multi-cell buck or boost drivers don't rely on the ultra-low resistance FETs anything like a single cell direct drive driver does. Multi-cell stuff has enough voltage overhead that a high resistance FET is easily compensated for.

Same voltage as an SRK as they are parallel cells.

Thanks. That's what I needed to know to build one of my SRK's. I had been wondering why the C+ pad was so big. Now it makes sense. It needs to be able to handle different things. I'll place an order on Digikey tonight.

How are the LEDs wired? Got any pics of the driver innards?

The emitters are wired in parallel. Here is a pic of the emitters on the sink:

Here is the driver. At the time of the pic I'd already upgraded the LED wiring and bridged the sense resistor pads but IIRC they were always empty but don't hold me to that. Since the pic I've replaced the two FETS with two 70N02 FETS. Marginal gains with either mod.

Thanks Johnny, the link is in.

Yup, just saw that in the picture…no inductor, jumper the pads

Ebay seller 'rfextra' has lots of goodies, if you don't need a large enough quantity to get the price breaks from Digikey or Mouser. The big diodes are fairly cheap at retail in small numbers, the inductors are not.

IRF 60V/3A Schottky Rectifier 30BQ060TR,SMC,Qty.50 - $6.99
http://www.ebay.com/itm/150201700078

Coilcraft 1.2uH 12.3A Power Inductor MLC1260-122MLC, RoHS, Qty.10pcs - $6.99
http://www.ebay.com/itm/181286346884

Coilcraft 0.8uH 12.4A Power Inductor MLC1250-801MLC, Qty. 10pcs - $6.99
http://www.ebay.com/itm/160974587402

Coilcraft 0.68uH 12A Power Inductor DO3316P-681HC, Qty. 10pcs - $5.99
http://www.ebay.com/itm/160664715456

Panasonic 1.2uH 14.2A Power Inductor ETQP6F1R2HFA. Qty. 5pcs - $4.99
http://www.ebay.com/itm/400433611169

Panasonic 0.58uH 19A Power Inductor ETQP6F0R6BFA, RoHS. Qty. 5pcs - $4.99
http://www.ebay.com/itm/400257620168

OK. I'm about to flip my shit! Soldered the pads and still nothing. Examined all the soldering points on the chips and they appear to be OK. Checked switch continuity yet again and it beeps when I press the button. What the hell is going on here??? Apply power directly to the LED pads and it lights up. Has anyone ever got a defective board from RMM? I'm at my wits end with this issue.

I've also applied power directly to the cell side contacts to rule out the battery tube to head contact issues. Nothing.

Have you checked for ground at MCU pin #2 while the button is pressed, and no ground when it's not pressed?

Did you build this with a parts kit or was it pre-assembled?