Modern Dummy load

Wmacky · May 18, 2014

I just got through reading the older DIY dummy load thread, but didn't see where the design ever got updated. The DIY vesion, along with the current one availble at SL, seem limited to 1 amp draw. I would like an updated version that can handle the latest high power drivers / L diodes. That currently being 3.4 amps? I have a Fluke meter that can read up to 10 Amps max and was considering using that inste4ad og the drop resister. The reason being the added complacation of needing a different Ohm valve due to the additional current draw. Is that right? Changing the ohm valve then prohibs a quick easy translation from Mv to MA.

Thought on that? For the Diode I was thinking about using a 4 amp diode in a TO-220 package and mounting them on a long heat sink? Would these work?

C3D04065A - CREE C3D04065A - SIC SCHOTTKY DIODE, 4A, 650V, TO-220 | Newark element14 US

Is there better options? Why hasn't anyone updated the older design?

rhd · May 19, 2014

Wmacky said:
Is there better options? Why hasn't anyone updated the older design?

They have.... it helps it you use the search function

Many people have updated the "older design", including myself, Jufran88, Flaminpyro, and probably almost everybody else on the forum.

http://laserpointerforums.com/f67/heavy-load-really-high-current-10-amp-test-load-88040.html

Wmacky · May 19, 2014

Well I did seach, and read many threads but seemed to have missed that one. I'll check it out now...

rhd · May 19, 2014

Wmacky said:
Well I did seach, and read many threads but seemed to have missed that one.

and these....

http://laserpointerforums.com/f39/fs-selectable-test-load-up-3a-assembled-diy-kit-stock-63450.html

http://laserpointerforums.com/f67/x-load-custom-10a-testload-all-one-unit-83115.html

http://laserpointerforums.com/f39/super-3-amp-v2-1-test-load-78287.html

http://laserpointerforums.com/f67/new-test-load-78277.html

http://laserpointerforums.com/f51/dummy-load-high-current-2a-test-load-3a-52372.html

djQUAN · May 19, 2014

to the OP.

The diode you listed is a schottky type which has a lower forward voltage drop which isn't suitable (you can use more to get the same Vf but that gets expensive) plus that's a silicon carbide diode which is pretty pricey for what you intend to use it for.

Wmacky · May 19, 2014

Thanks for the links, and diode info. Looks like they are a bad choice!

Yeah, I'm still reading, but may take the easy path and go with Jufran88's board. I thought it was a 1 amp board, but 3 amps is much better. Still that leaves a hole for the drivers for the latest 445. I guess even with a heatsink slapped on top it won't handle 3.4 very well.

I wonder if I could utlize the board and upgrade componets to 4 amp duty. Not much room for additional heatsinks! RHD, I wish you ordered extra boards, or did you..............

rhd · May 19, 2014

Wmacky said:
I wonder if I could utlize the board and upgrade componets to 4 amp duty. Not much room for additional heatsinks! RHD, I wish you ordered extra boards, or did you..............

You're welcome to make some of my boards. I actually improved the design a bit, but never bothered ordering the improved version myself.

The improved version puts the resistor IC in line with the diodes physically, so that they're easier to heatsink (and there are now only 7 diodes instead of 8). It also staggers the diodes between rows, so that if you're only using 4 diodes, it uses 2 diodes in each row, instead of 4 diodes in one row and none in the other. This makes for better heat dissipation.

This is the diode used: Digikey

And even though the board itself suggests using a 1 ohm resistor, I would strongly suggest moving to a 0.1 ohm resistor instead. It doesn't really make the conversion hard (just move a decimal place in your head), and it saves you from dropping 4V over the resistor when you're testing 4A, etc. That's a lot of voltage drop.

Wmacky · May 19, 2014

rhd said:
You're welcome to make some of my boards. I actually improved the design a bit, but never bothered ordering the improved version myself.

The improved version puts the resistor IC in line with the diodes physically, so that they're easier to heatsink (and there are now only 7 diodes instead of 8). It also staggers the diodes between rows, so that if you're only using 4 diodes, it uses 2 diodes in each row, instead of 4 diodes in one row and none in the other. This makes for better heat dissipation.

This is the diode used: Digikey

And even though the board itself suggests using a 1 ohm resistor, I would strongly suggest moving to a 0.1 ohm resistor instead. It doesn't really make the conversion hard (just move a decimal place in your head), and it saves you from dropping 4V over the resistor when you're testing 4A, etc. That's a lot of voltage drop.

Thanks for all that!. Nevr had a board made. I wonder the time involved and minumium number. I'm very intriged! Thanks again.

rhd · May 19, 2014

Wmacky said:
Thanks for all that!. Nevr had a board made. I wonder the time involved and minumium number. I'm very intriged! Thanks again.

If you use Oshpark, the time involved is about 2 minutes once you have the board file. The cost on a board like that would be around $7, and they'd make you order 3 - so basically a $20 investment. Roughly.

CDBEAM777 · May 19, 2014

rhd said:
If you use Oshpark, the time involved is about 2 minutes once you have the board file. The cost on a board like that would be around $7, and they'd make you order 3 - so basically a $20 investment. Roughly.

MMMmmm..Wmacky..I am interested in one of these !!!!! !!!!!!!!! RHD...Thanx. for the design !!!

Lite'em Up CDBEAM=======>

Wmacky · May 19, 2014

rhd said:
If you use Oshpark, the time involved is about 2 minutes once you have the board file. The cost on a board like that would be around $7, and they'd make you order 3 - so basically a $20 investment. Roughly.

I just ordered the boards HAHA

Do you have BOM? I guess Other than the diodes, I just need the Resistor, and jumper pins?

rhd · May 19, 2014

Basically just need the diodes I linked, plus resistor, headers and jumpers (take a look at the schematic image for part numbers - but grab a different resistor - if you want 0.1 ohm - just find a high wattage 0.1 ohm TO-220 resistor - digikey has them)

You might want to think about something to use as a heatsink.

Wmacky · May 19, 2014

rhd said:
Basically just need the diodes I linked, plus resistor, headers and jumpers (take a look at the schematic image for part numbers - but grab a different resistor - if you want 0.1 ohm - just find a high wattage 0.1 ohm TO-220 resistor - digikey has them)

You might want to think about something to use as a heatsink.

Great thanks! A rep to you!

Wmacky · May 31, 2014

The boards arrived already, and look great. Though I have bought lots of custom made boards for various hobbies, I've never had any made myself. Much cheaper, and easier than expected, as long as you have a designer giving yo files to use! Have these prices dropped recently? Anyway, I still need to order componets next.

paul1598419 · May 31, 2014

Yeah, I have several, but the one I use the most is ten 10 amp rectifiers and a 1 ohm 1% resistor for quick measurements. I also have others, using 1 amp rectifiers and 3 amp rectifiers. If I am using a drive that uses a high output current and voltage I omit the resistor and connect one of my ammeters in series with the load. When in doubt, just measure the output voltage of the driver and add or omit rectifiers as needed.

The Lightning Stalker · Jun 2, 2014

I found some slightly cheaper diodes. They are SMT, so would require a different board layout, but would
make heatsinking a bit easier.

Digi-Key™

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