Kaidomain 50mW CR2 - inital review

[IgorT]

Wait.. You were charging the 3V battery at the 3V setting or at the 3.6V setting? I'm asking, because some people were complaining, that these batteries are impossible to charge above 3.3V on the 3V charger setting.


I did try charging one of them up to 3.9V, but i was afraid to go any higher. But if the green ones can behave almost like 3.6V batteries, i don't need the blue ones for the AMC driver to work!

I ordered the blue 3.6V ones from NewExcite (UltraFire shop on e-bay), but they are not answering my e-mails or anything, and i have an open dispute with them. I hope you ordered from another seller. (Your link doesn't work) I don't know if i'll ever get them, but it would seem the green ones from DX can do the job as well.


I did notice, that one of my cells has a higher internal resistance / lower capacity (or something) and drops in voltage much faster. It's the one i tried charging up to 3.9V, so i'm not sure if that's what damaged it or if it's a coincidence.

But if the 3V charger regularly charges them up to 4.05V... They're cheap, i guess i'll try. If they are Li-Fe-POs they can't explode anyway.


Did you perhaps measure the current for comparison with the blue ones?

 

[Benm]

My charger has no setting, it' intended for 3.6v CR123 size cells, but also charges CR2s with spacers obviously. I did keep an eye on the batteries while charging, didn't get hot or anything. Perhaps this way of charging will damage them, but at this price i'll risk it. They charge to 4.05 but drop off to 3.5 after just standing there for half an hour, the proper 3.6v versions remain over 4 volts for days.

I ordered the blue CR2s from the same seller... too bad you're having problems, but there is quite some positive feedback there, so i hope i'll just get mine.

I'll do a comparison with the blue ones when they get here. I have some other 3.6v CR2s (those blue ones from KD), but reviewing those won't do anyone any good since they are no longer available.

 

[IgorT]

Oh i see.. From what i read on CPF (AW's battery sales thread), the Li-Fe-POs are not supposed to be charged like that.

They are much safer, than Li-POs, so it's not really dangerous, but it's very likely, that i damaged the one, that goes empty much faster, by doing that test. Right now i have my charger set at 3.8V, and it would seem ok. 3.7 would probably be safer. Like you said, anything above 3.6V doesn't really hold for long.


I really hope we get those batteries tho.. There is a lot of positive feedback, but also quite a bit of negative, and the negative always says, he never responds to e-mails (actually, even the positive does). In fact, he doesn't even respond to PayPal, when there's a dispute.

Let me know, if you get the batteries, or any answers from the seller.

 

[Benm]

I'll keep you posted on the batteries - not sure how long its supposed to take to get here, but i'll post it once they do or if i have any problem.

Unfortunately, some bad news: My new KD50 is dead!

I was playing with it a bit, and at some point it just didnt turn on anymore. Replaced the batteries, bridged the switch and tried all the usual stuff, to no avail.

By the looks of it, the crystals are shot or somehow misaligned. I can see the pump diode is still working (i know how bright (or dim, ftm) it is supposed to be), and i'm convinced it hasnt died due to COD.

I opened up the laser for further inspection, which was surprisingly easy on the new version: no need to remove any glue, it comes apart to pieces neatly. The crystal set seems to be in place, but the glue holding it is a bit sticky to the touch, so it might not be as firmly in place as it should be.

Also, i can see the pump light going through the actual crystals looking from the side of the assembly, although i am unsure if its still properly aligned.

I guess i could try to RMA it, as i did no permanent damage or change to the unit by taking it apart. I'll contact KD about how to proceed and the cost involved (as the laser is only $25 i'm not sure its worthwhile, but i'm curious as to their response).



If you anyone has similar problems: DO NOT diagnose them by looking for the pump diode light unless your know exactly what you are doing, and know what it is supposed to look like! There is no real IR filtering in these lasers (apart from the crystal set coating, but the whole thing can come loose!), and looking straight into the barrel might very well damage your eyes even at some distance, and even if there is no green output at all.

 

[IgorT]

Since i just finished my LPM, i did some measuring of the two best KD50s.

The first one i bought measures at around 33mW, and this power is surprisingly constant even without regulation.
As the battery voltage drops, the power actualy stays the same, because this laser likes being hot and getting warmer compensates for the drop in current.

If i put in a fresh battery immediatelly after running it for a few minutes on another one, the power suddenly jumps to 46mW. This means, that with constant current, the power will start at 33mW and actually slowly climb to almost 50mW!


The second one i got (the best one) starts at 64mW (peak 67), and stays there for a while. After that, it starts dropping, untill it reaches 33mW, where it remains for a while. It should get better with current regulation. I hope it will stay above 40 then. Might need some additional heatsinking. Unlike the first one it prefers being cold.


These two are actually quite good, and will be great, when i'm done with them. It's interesting, that even tho they behave completelly different, they both average at 33mW.


The third laser (used/scratched) is currently not that good at all, and i haven't gotten around to measure it. Now that i've seen what 15mW of green looks like (the first one on the bad battery), it's possible that the used one is only 5mW or even less. I'm gonna try some aligning, but i think i should really return it. The weird thing is, that it was actually the most powerfull one for a very short time.

 

[Benm]

Hehe.. on those thermal issues: i really wonder if they do QC with the aircon on or off down there in hong kong - might explain some semi-doa's

 

[IgorT]

Sorry to hear that, Benm.

But it's odd to say the least. I've noticed the sticky epoxy in at least one of mine too, and it seems to be a common occurence in chinese lasers. It still holds tho.

But even if your crystals were badly misaligned or damaged, there should still be some green output. The only time i noticed just a dim red glow, and no green was when my bad battery was very empty. It measured at 2.4V outside of the laser, no idea what voltage it had inside. I also didn't measure the current.

 

[IgorT]

Hehe.. on those thermal issues: i really wonder if they do QC with the aircon on or off down there in hong kong - might explain some semi-doa's

That's very close to what i was thinking, when i got my first DX200 and noticed how much it was affected by small changes in room temperature.

Just different weather alone (colder or even warmer in China) could cause many bad surprises once these arrive to the buyer.

 

[Benm]

I thought of power supply problems too, but when i measure voltage and current that all looks normal. The glue is only suspect because it actually came loose in my other KD50, without mechanical abuse.

The temperatures must be a problem throughout the chain i think - different at the production site, QC in hongkong, and then again at the customer. I dont think much can be done about it though, the only way to really overcome it seems TEC as used in labstyle modules.

 

[IgorT]

The temperatures must be a problem throughout the chain i think - different at the production site, QC in hongkong, and then again at the customer. I dont think much can be done about it though, the only way to really overcome it seems TEC as used in labstyle modules.

Yeah, but while active cooling could push the output of one laser, it could actually completelly diminish the green in another.
If i put my first DX200 into a cooler, it was incredibly powerfull and stable, but if i put the second one into a cooler, it came out at around 5mW.
For max power, a driver would have to be made for the peltier, to keep the temperature stable, and different for each of these lasers.

Not so long ago, it was required to have the crystals in two pieces, so you could heat the first one and cool the second one at the same time. With new crystals, this is not so important anymore, but it looks like the NewWish crystals vary in quality a lot.


I kinda expected more out of the KD50s, seeing how bright they are. I'm actually surprised, that the brightness i was amazed at was sometimes only 20mW. I was thinking about reselling redrivered KD50s (with two batteries and a charger) locally, but i really expected them to be closer to 50mW.

When my friend gets his, i will measure that as well, and post the results. I hope it's the model you got.

 

[Benm]

For max power, a driver would have to be made for the peltier, to keep the temperature stable, and different for each of these lasers.

With TEC you can aim for any temperature lower than ambient, so as long as the crystal/diode match is optimal in a range of say 10 to 20 degrees, TEC can compensate to the optimum of a given set regardless of ambient temperature. One laser might always run at 12 degrees, another at 17, but that is a setting that has to be done only once for each laser.

Another way to go about it is to aim for temperatures a bit a above ambient, and just heat the assembly up to the desired temperature using a simple resistor. This sounds like something that could be achieved in a laser pointer, though probably way to complex for any company that can't even build a properly regulated current source.

But perhaps in some time the crystals will be even better and stability over a wider power range can be guaranteed.

I kinda expected more out of the KD50s, seeing how bright they are. I'm actually surprised, that the brightness i was amazed at was sometimes only 20mW. I was thinking about reselling redrivered KD50s (with two batteries and a charger) locally, but i really expected them to be closer to 50mW.

If you plan on doing any of that on a serious scale, i think the best way to go about things is to pick/bin the lasers.

I bet that the lasers that do not meet the temperature requirements could be used for something else. By the looks of it, it would be possible to retrofit the casing with a DVD diode and matching driver, making it into a powerful yet compact red. I might actually attempt that if returning it to KD is going to be a problem - the driver will be a big challenge though given the very small voltage drop allowed. Another issue is making it case-negative instead of case positive, but that should be doable given the size of the board and room for an additional little spring in the tailcap.

 

[IgorT]

The idea with a resistor as a heating element is interesting, but doesn't the pump already do way more heating, than a resistor could? In any case, the laser would have to be bigger simply for the sake of batteries required for the current.


I know a TEC could maintain any temperature you want. Even higher, than ambient, if you reverse the polarity. Unfortunatelly, even tho i work with electronics proffesionally, i don't know enough about them to design a circuit, that would regulate a TEC to keep a constant temperature. It might not even be that complicated, but i would have to ask one of my engineers to draw me a schematic.

An NTC or PTC resistor could perhaps be used with a 317 type circuit, but it probably wouldn't be able to handle the current, so the measurement would have to be amplified somehow. After that, the circuit would have to keep the resistance of the sensor constant, an additional pot could adjust the temp, and that would be it. (If i'm way off, or said something stupid, please correct me) EDIT: I better ask my engineer.


I would love to do something like that for myself, but for the KD50, i could just measure them and sort them accordingly, now that i have a meter. What does pick/bin mean? EDIT: Or did you mean this?

For the reds, i found some cheaper, and better looking hosts of a similiar size, that should preform great with some special batteries i just ordered. (I'm ordering batteries from AW on CPF from now on. He has some very usefull sizes i didn't even know existed.) I don't want to sell these for insane amounts of money, so i don't want to scrap a KD50 just for the body. Also the drives for the diodes cost almost twice here, what they cost in the US.


I don't want to do it on any "serious" scale, as i already have enough work (too much sometimes), but more like a hobby. I would still do it very proffesionally, and even provide exact measurements with each of the more powerfull ones. The weaker ones could be sold as "toys", at the same price they were bought, to prevent losing money.

But since there are no lasers whatsoever to be bought in my country, it could actually become interesting. When i was looking for a cheap laser pointer to demolish just for the collimator lens, i could only find one type of 1mW red, that was actually more expensive, than a KD50. So.. Who knows...

 

[IgorT]

I think i was way off in my above description. My engineer suggested something else entirelly.

But i found an interesting constant temperature circuit, like the one you mentioned, that uses a 5W 40 Ohm resistor as the heating element:
http://www.solorb.com/elect/constemp/

Could this be somehow adapted to regulate the current through a Peltier, by switching the thermistor with a PTC and using diodes capable of a higher current? The circuit description says a lower resistor value would damage the transistor and the diodes. But the transistor datasheet says it is capable of 8A.


EDIT: I did some digging on Peltier temperature controll, and came up with this:
http://www.bit-tech.net/modding/2001/12/03/pwm_fan_controller/1

It's a PWM constant temperature fan controller, that is capable of high currents. Peltier manufacturers recommend PWM for temperature controll of TECs. It's a very simple circuit, but the IC might be hard to get. I'll try to order some samples. I've been thinking of something like this for a long time now.

 

[Benm]

Temperature control would probably involve using an opamp to compare a temperature sensor to a reference, and switching a peltier or heater using the output. Since heating or cooling are relatively slow processes, the design would have to include some hysteresis for good results.

This circuit http://www.solorb.com/elect/constemp/ looks pretty decent although i can't see any hysteresis, just some basics to prevent oscillator (capacitor/resistor in the feedback circuit). The 1n4001 diode is rated 1 amp and that limits the current even with a cooled transistor. It would be better to have a PWM controlled circuit though, saves power and heat in the transistor.

These things arent terribly hard to design, but i'm sure it will take a lot of tinkering to get it working propery.

The idea with a resistor as a heating element is interesting, but doesn't the pump already do way more heating, than a resistor could? In any case, the laser would have to be bigger simply for the sake of batteries required for the current.

The pump draws around 300 mA at 2 volts, so that's 600 mW. It's not very hard to get similar heating power from a simple resistor run on batteries. It will mean that the unit would require more power at lower temperatures - the resistor only needs to kick in when the diode alone doesnt raise the temperature enough.

Basically you could design it so that it requires no extra heating at, say, 30 degrees ambient, and gradually more extra heating with lower ambient temperatures. If you aim for 40 degree diode temperature, you'd use equal amounts of power for heating and diode at 20 degrees. Quite a waste, but perhaps worth the stability.

 

[IgorT]

I understand. That would be very usefull, if you wanted a super stable laser. But it's overkill in such a cheap unit. I'll just go with increasing heatsinking in one, and decreasing it in the other, so it reaches full power sooner. It's possible i made it slightly worse, when i made the lower ring contact the module in that one..


BTW, i found some buck ICs, that are specifically meant for regulating the temperature with a Peltier. Since they do everything by themselves, and only require a few external components, they might be the best solution for this, and the efficiency would be a lot higher, than with any other kind of regulation. It might be better to start a new thread for that tho..

EDIT: I ordered samples of MAX1968 and 1969. One of them can power a TEC with constant temperature at up to 6A, the other at +-3A, so it can both cool and heat, to keep a constant temperature if it's lower or higher, than ambient. I'll start a new thread, when i get them.

 

[Benm]

Sounds very interesting, good for a new thread indeed!

Btw, no reply to my support request from KD so far...