New test load

The problem with that is your meter has be hooked up to it constantly. Usually I take my meter out and measure the total voltage drop while it is running, so you would need to use two meters.

You should have several meters anyway for precisely that reason. You often want to measure more than one parameter at a time. Efficiency, for example, isn't easy to do with just one meter.

I can only afford one fluke, and I don't trust my other meters much, especially when it is so easy to move a probe and measure it with the fluke. The best setup (IMO) is with my meter measuring total voltage and my scope measuring voltage over the resistor (channel 2 for probing around if i'm testing a new driver design), but for quick tests using one meter for both is fine.

Cyparagon said:

You're both missing the point entirely, I'm afraid. It's not about whether it will melt (that calculation is easy to make), it's about how accurate the reading is.

The resistance of a resistor increases at it heats up. If you send a lot of power to it, it heats up and the resistance slowly increases. With a constant current through it, the voltage drop across the resistor will increase as it heats up. The current appears to climb. This is a false reading.

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This depends entirely on the resistors though, and what they are made of. Some could even get a lower resistance with higher temperature, though that is very unusual.

It should, however, be in the datasheet how much the resistance will actually vary with temperature - at least within its safe operating range. Resistors are usually built such that their resistance doenst change much with temperature (compared to, say, using some length of copper wire).

One far more important aspect is, however, overseen here: The voltage drop of ordinary silicon diodes will go down significantly with temperature, possibly as much as from 0.7 to 0.5 volts at 1 amp. In normal, rectifier-like, applications this is only a good thing.

It will, however, lower the voltage your dummy load requires to have a certain voltage across it, and that can make it unreliable compared to a laser diode kept at room temperature by heatsinking. Obviously this only is a problem if the driver is not a perfect current source - but if it was, you might as well use a crowbar as the test load.

benmwv said:

I can only afford one fluke, and I don't trust my other meters much

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Even the crappiest of Chinese DMMs is going to be more accurate than a 5-cent resistor.

For this test, I am very assured in the test implant stability of the driver, running at different power levels.With the run load testing high currents (> 3A).Promote heat dissipation capability when running long test load is not too hot.I am very pleased with this achievement.

I'm still about 2 months away from actually selling anything, so there is plenty of time for testing to make sure it all works alright.
I got the screw terminals and jumpers in the mail today from digikey, and should be getting my copper bar soon. Once the copper arrives, i'll send one off to DTR for testing.

Here it is so far. Just missing the copper heat sink.

Copper came in today. Smaller than I thought it'd be. May very well need a bulkier heat sink. We'll see what happens with DTR's tests.
Hoping to get this one mailed off to him tomorrow, so he'll have it on Friday.

benmwv said:

I can only afford one fluke, and I don't trust my other meters much, especially when it is so easy to move a probe and measure it with the fluke.

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There are loads of decent enough 50$ multi-meters, the readings from them are more than accurate enough for this purpose. Fluke even has the 15B and 17B which are quite cheap (50-100$) and live up to the Fluke name in terms of quality. They certainly aren't as as good as the 400$ Flukes, but you get what you pay for.

Every good electronics lab should have at least two multi-meters for current and volts IMO.

with the heat sink on the back against the vias holes. I just ordered 1/2" copper bar that will cover from the white line to the edge of the board.

Where does the heatsink go on the component side
or the solder side ??

I also think the Heatsink radiating surface area seems
a bit low...:undecided:


Jerry

You can contact us at any time on our Website: J.BAUER Electronics

lasersbee said:

Where does the heatsink go on the component side
or the solder side ??

I also think the Heatsink radiating surface area seems
a bit low...:undecided:


Jerry

You can contact us at any time on our Website: J.BAUER Electronics

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the solder side will probably keep it cooler since it has a directly path to the component's footprint instead of doing through the package of the component.

I've ordered new copper which is twice as wide.
I've got 1/2" bar coming, as well as some small finned copper sinks to try out.

Make me wonder that DTR has tons of the M140 projector heatsink of the diode array.
If somehow the aluminum sink could match this testload then we shouldn't be worried about the overheating the diodes.

I think for this test load's purpose, they just want high thermal mass with good thermal conductivity, not so much for shedding heat into the air at any high rate.

Also, while mounting to the back of the board where the vias come through, maybe would like to employ some thermal tape or other method of redundant insulation besides soldermask if you wanted to.

Is the rest of the back layer of the board heatsinking for the resistors?

A very nice looking piece, there Have you been able to test if there is any resistance in the jumper connections at high currents? I wouldn't think there would be much, posts are big, and the piece of metal that connects them inside that jumper piece has fairly high cross section.

BShanahan14rulz said:

I think for this test load's purpose, they just want high thermal mass with good thermal conductivity, not so much for shedding heat into the air at any high rate.

Also, while mounting to the back of the board where the vias come through, maybe would like to employ some thermal tape or other method of redundant insulation besides soldermask if you wanted to.

Is the rest of the back layer of the board heatsinking for the resistors?

A very nice looking piece, there Have you been able to test if there is any resistance in the jumper connections at high currents? I wouldn't think there would be much, posts are big, and the piece of metal that connects them inside that jumper piece has fairly high cross section.

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The entire back side of the PCB is a copper layer, with vias holes that go to the resistors.
With just that bar, I was able to give it 3.3A for 20 seconds before i had to take my thumb off the top of the diodes (the driver was another story...i could smell that poor regulator)
I'd like to see 1 minute run times without the readings straying too far off.

DTR has all the proper equipment to accurately test it, so i'm mostly relying on him for the results.

I've got 1/2" bar coming which will cover from the white line to the edge (twice as wide as the current one)
I've also got small finned copper heat sinks coming. They are the Chinese ones made for RAM chips.
Not sure how i'll incorporate them until they arrive. I thought about lining them up and soldering them together into a strip to mount on the board.

I didn't get the test load mailed today, I got caught up with the lender over our new house, as well as working today so I can have tomorrow off. We're closing on our new house tomorrow, so i'm going to drop it off at the post office on our way to the title company.

Prices is really start to go up on these. I want a nice quality test load that a person only needs to buy once and it will last them for as long as they're into lasers, and be less than $30 retail. Though when I order in bulk it will drop the price by a few dollars each...

Blord said:

Make me wonder that DTR has tons of the M140 projector heatsink of the diode array.
If somehow the aluminum sink could match this testload then we shouldn't be worried about the overheating the diodes.

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He had mentioned this and is going to look into it. That would be a very limited source though....

Worst case scenario, I could have finned heat sinks cnc machined in china. Just not sure how long it would take me to move 500 of them lol