Just noticed the new Maxflex at http://www.taskled.com/maxflex.html
Just noticed the new Maxflex at http://www.taskled.com/maxflex.html
"If an optional 3mm or 5mm status LED is connected, the user can configure the status LED to warn when the voltage reaches Medium (status LED lights constant) or Low (status LED flashes). Now with on-board 100 ohm series resistor.
Onboard pullup resistor on switch input to provide reliable performance of external momentary action switch when used with longer wires."
O man,…. I was really looking forward for some improvement on output voltage so you could drive 7 SSC P4 @ more than 500mA…
24V x 700mA = 16.8W output. At 90% efficiency that's 1.7W that you need to get rid of from maxflex to prevent it cooking.
Also going to higher voltage requires changing components that I'm not willing to do at this stage.
Besides, the moment I support 7 LEDs folk will want 8 so they can use 2 MC-E's... it never ends...
Want high voltage and power - use CCHIPO - there is a reason that it is large
Any idea when these will be ready to ship?
(bookmarks order page)
Still planning on making a modded Maxflex myself to enable driving 2 MC-Es. Just because I can, and will then have something relatively unique! I'm assuming the relevant components are the same as on previous MaxFlex boards (ie a 35V Schottky) - I already have the 50V caps to swap in!
p.s. hope your family problems worked out OK.
Just FYI, chris, my MC-E (in series) is only showing a Vf of just under 12.5V at 500mA (using analog meter on power supply). So you're talking about maybe 27-27.5V for two at 700mA. But check it out before frying anything...
Last edited by dnlwthrn; 10-29-2008 at 01:12 PM.
Even as it stands, to run 24V @700mA requires thermal potting compound (not just arctic alumina epoxy) to try and get heat off the top of the package also. I'm talking about being able to run the driver for extended periods of time at that power level.
On maxFlex3 I have added more thermal vias (12 now versus 9) and also expanded the thermal path a bit on the top of the PCB (switcher IC side). Of course all those things are just helping a few percent more than before - so just an optimization versus a major improvement.
Anyhow, I don't have any plans at this time to change the design. Maybe when I have some spare hours to play with I'll see how the driver works at 28V with some changed components - it needs to be stable and safe over the long haul otherwise folk will be destroying drivers and I'll be the one having to deal with returns and unhappy emails...
The switcher IC has a Thermal coefficient of 37C/W and max junction temperature of 125C.
So at 24V x 700mA we have about 2W of heat being dissipated in the switcher. That's close to 80C rise in package temperature. Assume ambient of 30C in the housing (it would be more than that...) and we have ~110C junction temperature... You can see we're pushing the limits already...
Do you have a recommended potting compound/process? I saw the warning about potting in the tech notes for the Fatman, and don't know that much about potting compounds...
The potting is required at the higher power levels - say above 1.5W - though it all depends on ambient temperature. If you have maxFlex inside the LED housing and it is 'cooking' then you will have trouble.
Turning on the thermal protection in the menu system would be a good idea and backup plan to protect the driver.
Current plan is to run either a triple XR-E or a single MC-E (series wired) off a 7.4V LI-Ion pack. The other will probably run off a Fatman (which I currently have).
Anyway, I've seen others suggesting pushing the thermal capabilities even more within the existing voltage limits - running 1200mA at ~20V to 3 MC-Es wired 2s2p!
@ full 1200ma from a 14.8 v 4.8 mah li ion
the forward voltage of the setup was just under 19 volts .
it has done 2 rides so far and with the newness at the moment full power got used for most of the ride just to pee off the other riders .
( they were short rides ) but when the wow factor is over then low is plenty with full for when needed
My Maxflex lives in some copper pipe inside my stem with the thermal protection set at 50 the lowest and no problems with it dimming so far so I can only assume it is quite happy
I've had no problems driving 2 strings of 6 dies with maxflex2. I've used my big light (http://www.candlepowerforums.com/vb/...d.php?t=188209) constantly since February with no issues, and I run it at full power alot! My theory on maxflex cooling is a bit different than the norm and I'd be interested to hear George's opinion. I have the driver AA'd directly to the housing as close to the emitters as possible and I'm depending on the enabled thermal protection to keep the LEDs and driver at a safe temp. The protection is set to 60deg and it doesn't trip unless I'm stopped with the light running full blast. This method of using the thermal capability of the maxflex to regulate LED temperature has been the cause for some discussion on this and MTBR forums, and most seem to think that it is a bad idea. It's worked for me so far and I'd build another light with this setup in a heartbeat. Thoughts, comments, ideas?
Last edited by StevelKnievel; 10-30-2008 at 09:11 AM. Reason: spelling
Using the built in temperature monitoring of bFlex, nFlex or maxFlex (and now d2Flex) to limit the LED temperature is certainly NOT a bad idea. The primary intention to provide temperature limiting of the driver was specifically to keep the entire "system" within reasonable limits.
nFlex and bFlex are very different thermally than maxFlex due to the typical usage of the drivers. With maxFlex being a boost, many folk are tempted to drive 5 or 6 LEDs and at full 1200mA output and thus the total power through the driver is much higher than the typical 3 LED configuration (at 1000mA) of nFlex and bFlex. The efficiency of maxFlex can also be several percent less than nFlex/bFlex due to it being a boost converter and thus having much higher input current (and thus losses).
So, overall maxFlex will typically be running hotter and cooling/temperature control is more critical. The temperature sensing is performed within the uController (calibrated prior to shipping) and there can be a thermal lag between the switcher IC getting toasty and the uController sensing it. In some rare circumstances (higher power situations) this can cause the switcher to overheat before the uController can back down the current since it takes time for the heat to spread across the PCB and warm up the uController. In these rare situations using thermal epoxy on the switcher top side (inductor side) and letting a bit more ooze from the thermal pad/heatsink attach to the uController (the chip next to the golden thermal pad) will help with the heat coupling.
Ok, so I just got notice from my assembly house that they shipped a decent sized batch of maxflex3 drivers this morning, which means I'll have them in hand tomorrow.
So, finally the drought will be over!
Order placed.... (gets excited)
Now I just need to get my order from Cutter to show up... Could be lots of lights being built this winter!
I have no experience with thermal-potting resin. However I'm planning to give it a try. Here's a pic (that I posted earlier on MTBR), which shows how I'm proposing to do the first light. Later I'd do a Znomit-style light in a similar manner (if it works of course).
Basically the plan is to wire up the whole circuit and test it on the bench first. Then once I'm happy it's all working just I'd pour the potting-goop into the sawn-off Berocca can, and leave it to set. Then test it one more time, before sliding the assembly into the housing, and AA'ing them into place. Or maybe I should use Artic-silver grease, so it can be easily disassembled for troubleshooting? Anyway, here's the pic....
Since my previous post, I've started reading-up on thermal-potting resin, and the more I read the less I liked the sound of it. Then I re-read George's post #13, and now I grok what he's saying about Arctic Alumina being sufficient if you provide an adequate heatsink. Consequently, I've gone right off the potting-resin idea that was shown in the pic. Instead, I'll just just do this:
- AA bond a small Alu pad, covering the maxFlex's heatsink spot
- Apply a generous squidge of AA, covering both switcher IC & the Alu pad
- Stick the lot directly onto a heatsink mounted on the back-cap
Sounds simpler than the potting idea