LD driver configuring questions

[jors]

I have no problems on mosfet with 12v driving single 9mm 445 Nichia or single 1W 520nm at full power.
However mosfets are attached to main big heatsink baseplate with fans below.
Those Mosfets are capable of this and much more, but big!! heatsink is required.
Are you testing CW full 5v modulation? Try with Dac, overall power is less due pulsed modulation.

[catalanjo]

Yep, like I said "NEED is perhaps a bit of an exaggeration .....you could put a ruddy great heat-sink on the FET"

Here you have an example of " a much bigger heat sink will spread the heat (approx 5 to 7W @ 1amp), and thereby reduce the temperature along with the paranoia!" ..... straight from the first hand experience of a guy who has produced one of the best builds this year!

Cheers
PS. Just had a quick "butcher's" at the pics of the heat sinks you are using ....they are really TINY .... even if you cut down to approx 2W (minimum for 1 amp) dissipation in the driver, you will probably have to go bigger, (despite the best possible PSU.) ...Try an L bracket and a plate.

[jors]

hahaha many thanks, but no no, just learning from the masters like you

..... straight from the first hand experience of a guy who has produced on of the best builds this year!

Cheers

[catalanjo]

I ain't a master .....just plain OLD...with a lot of water under the bridge!
Cheers

[Maltes]

Bad news, looks like my driver or diode died...

I replaced the mosfet heatsink with a big one.


I did notice that the heat on the mosfet itself was greatly reduced, maybe in the <40C range and the other components like the capacitor weren't getting hot anymore, although still a bit warm. It was interesting how even this heatsink was getting so warm because I was only running the diode at 1W.

The experiment only took 5 minutes until the laser output was cut. I checked the housing and it was a bit warm, the cables were cool, the driver was warm, the driver heatsink was warm. But nothing close to what the case was with the small mosfet heatsink in my previous experiment.
I tried turning it off and on again, it won't lase anymore.

Maybe there was already some damage done to the driver? Or maybe the diode died for some reason?

I'm not sure at this point.

EDIT: I checked the power pins for driver to diode while diode was disconnected with a multimeter. It was 12.5V. Is that normal?

[dkumpula]

Those heat sinks look adequate to me. When a diode dies, it generally stops emitting a coherent beam and instead has a dim LED glow to it. Is that what occurred or did the diode just go completely dark?

[Maltes]

Thanks for teaching me about that. No there is not even the faintest glow from the diode.

[catalanjo]

@ @ "I checked the power pins for driver to diode while diode was disconnected with a multimeter. It was 12.5V. Is that normal? "

If driver output is open circuit, it would be normal that its voltage rises to almost PSU voltage, as it is trying to push current through an extremely high resistance, (air), and will push with all potential available to it.

With a decent size heat sink the driver would be OK even if its output is in short circuit ....@1 amp it is still only 12W.

@ David ....I assume you are referring to last pic ...but look at the earlier ones ......"normally" you would have fan air flow in a projector,...but only when it's fully built.
12W into those little heat sinks (earlier post) would achieve an extremely high temperature unless cooled by a forced air.
Using finger on driver instead of temp sensor to protect diodes requires FET to run in the 30C warm to 45C hot range. In normal ambient temp=24C and with a small 10W soldering iron attached to that little (earlir post) heat sink for a while would you really expect to be able to grab it by hand at the hot end ?


@" I checked the housing and it was a bit warm" ....how long after laser had cut out did you do this ? ..
...@ "a bit warm" = ??C?.....@ "I was only running the diode at 1W." .... how were you measuring this?...... and lastly ....... When it was lasing was the laser power approx as expected ?


I know it sounds harsh ...but you don't need the diode to check that the driver is working OK, you just need an amp meter capable of reading full PSU current..... put it across the driver output, fiddle with the pots and make sure they do what it says on the tin.... it would have been prudent to have done this before connecting the LD.

Cheers

PS.
If your diode has really died I think it might help to look at this this crap pic, which although a bit misty, shows safest way to wire LD, for first timers, using DTR modules (so as not to touch diode at all). They arrive shorted and this method maintains the LD shorted throughout entire build process until safely connected to pre-tested driver .
The little red silicon bits are just end stops for the bigger red and black sleeves which are loose (as is the yellow joining two diodes in series).
supplyleads-siliconsleeves.jpg
This arrangement (which starts by opening a 5mm gap in silicon insulation using just fingernails) permits shorting and volt measuring, dis/re-connecting and re-insulating & final lasorb connection (within 20mm of diode) as often as required.

[dkumpula]

@ David ....I assume you are referring to last pic ...but look at the earlier ones ......"normally" you would have fan air flow in a projector,...but only when it's fully built.
12W into those little heat sinks (earlier post) would achieve an extremely high temperature unless cooled by a forced air.

Yup, Cat, I was referring to the last pic. I fully agree that the tiny ones in the earlier posting wouldn't be adequate for anything more than a 5mw diode (if that). The larger ones looked suitable for short-term testing purposes (i.e. 5 minutes at a time) of a 1W diode even without a fan, but I'd watch the temp just to be sure. Permanent installation on the optics plate as you and Jors suggested earlier with active cooling is the proper end-game, of course.

-David

[Maltes]

" I checked the housing and it was a bit warm" ....how long after laser had cut out did you do this ? ..

Before it cut. I couldn't measure the temp, but I think it was around 35C. But that is the surface temp of course. Got cool very quickly after the diode stopped lasing.

"I was only running the diode at 1W." .... how were you measuring this?

Laserbee


I also want ahead and checked the signal and power cables for any shorts. And checked the voltage on the driver and PSU again, same 12.5V.

I finally got a fresh Simpledrive 5A and swapped it. Same.
So not the driver... Could be PSU (unlikely), cables and connectors (or solder connections) or the diode.

But diode is not lasing or giving weak glow. I'll remove the heatshrink on the diode pins and check if theres anything wrong like bad solder job...