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803t and fake leadlight






I've never used a lavadrive but I assume you could wire 4 1N4001 recitifer diodes in series and use that as a dummy load.

To open the leadlight pull out the laser module by pulling on the top cap with something (I stuck the top cap in a vice and a pulled on the barrel to get it out).
 
if your allowed to tell me what is the test load made out of.
 
look at the assembly pdf on the bottom of the link, it tells you everything and how to put it together. ;D
 
jamilm9 said:
can i just use 4 diodes
Click to expand...

Sure you can - but most likely you will find that the 4 diodes cost more than the test load that Rkcstr offers for sale ;) They are nice quality - and not too difficult to assemble, either ! At his current pricing, with free postage - you really cannot beat it !
 
SenKat_Stonetek said:
[quote author=jamilm9 link=1215121962/0#7 date=1215198031]can i just use 4 diodes
Click to expand...

Sure you can - but most likely you will find that the 4 diodes cost more than the test load that Rkcstr offers for sale ;) They are nice quality - and not too difficult to assemble, either ! At his current pricing, with free postage - you really cannot beat it ![/quote]
Huh? 4 recitifer diodes in series should cost less than 20¢
 
jamilm9 said:
can i just use 4 diodes
Click to expand...

You can just use a number of diodes as a dummy load.

But when using this dummy on the LavaDrive, you have to make 100% sure the total Vf (forward voltage) of the dummy load is OVER 2.5V.. 3V would be safer.

If a load has a Vf of under 2.5V, the LavaDrive will go into "overdrive", and pump a load of current through it. You would not be able to adjust it, and it would not be the same as in the end.

If you make sure the Vf of the load is OVER 3V, then the current through the dummy will be the same as the current through any LD. Silicone diodes have a Vf of 0.6-0.7V.. So i would use at least five.. Four could end up being right on the edge, depending on the exact type of the diode you get..

Schottky diodes have a much lower Vf, so you would need even more of them.


Rkcstr's dummy has two Vf settings. Onehas a similar Vf as a red LD, the other a similar Vf as a blu ray.. But selecting the right one only matters with a linear driver, which needs a certain voltage ABOVE what the LD needs. With a boost driver, it doesn't really matter, but still select the higher Vf load, for the above mentioned reason.
 
Haha, no, don't use 20.. LavaDrive can't boost the voltage that high..

Vf is the forward voltage of a diode.. Silicon diodes have a Vf around 0.7V.. Red LDs have a Vf of around 2.7-3V.. Blu Ray LDs have a Vf of 5-5.7V.. The Vf changes with the current in all of them.


The Vf of a diode determines the voltage the driver will have to put out for a certain current to flow through it.
If the Vf of the load was under 2.5V, the LavaDrive couldn't handle it, and would dump a lot of current through the load.

You need to make sure the total voltage drop of the load is over 3V to be sure the LavaDrive is operating correctly.

I just checked rkcstr's dummy load.. In the red setting the Vf is 2.3 - 2.7V, depending on the current, so it's possible, that it would not be enough.. In the blu setting it's 4.2 - 4.9V, depending on the current, so it would work without a problem.


Since you have loads of diodes, just use six of them in series, and you'll be fine.. This way, their total Vf will be above 3V for sure..

You can also add a 1 Ohm resistor in series with the diodes, so you can then measure the current by measuring the voltage drop across it in mV..

With a 1 Ohm 1% resistor, the voltage across it in mV is the same as the current THROUGH it in mA (U = R x I)...
So if you set your DMM in 2000mV range and just measure across it, the number on the display is correct for both the voltage drop in mV as well as the current through the entire dummy load in mA.
 
Oh, ok.. If that resistor is in series with the load, it is also meant for current measuring in the same way.. But you have to multiply the result in mV by 10 to get the current in mA..

But if you put another 1 Ohm into the dummy load, you can just measure there.. Nothing would change. It wouldn't influence the current. I sometimes put a 1 Ohm resistor in series with an LD (on the driver output), so that i can measure the current there, without detaching the diode and risking killing it with the output cap charging too high.. Also, the LavaDrive should NEVER be powered up without a load.


Anyway, you can measure the current through ANY resistor this way.. It's just Ohm's law - U = I x R..

So if R = 1 Ohm, this means U = I.. If R = 0.1 Ohm, U = 0.1 x I, or 10x U = I...

If the resistor was 5 Ohms, you could again do the same, but you would have to calculate.. With 1 Ohm, I = U.. With 0.1 Ohm, I = 10x U.... With 5 Ohms, I = U/5...


The reason Lava used a 0.1 Ohm is so that less power would be lost on it. This way, if you measure a voltage drop of 12mV on it, the current is 120mA...
 
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