400 mw spartan no driver

DrSid said:

Well .. the diode has voltage/current curve going up (higher voltage -> higher current) .. battery has it going down (higher current -> lower voltage). Where they intersect, there it will stabilize.

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(my bolding)

And just to complicate matters the diode "resistance*" will drop as it heats up and the battery voltage will drop as they discharge.

*Vf or forward voltage/voltage drop.

With alkaline batteries you could almost make this work, since they have a limit to the amount of current they can put out, they have a fairly high internal resistance.

Lithium batteries on the other hand, can put out dozens of amps in a short circuit. Laser diodes have very little resistance, and the hotter they get, they less resistance there is. Your diode should die very, very quickly without a driver, especially if you let it run for more than a few seconds. It gets into a "thermal runaway" situation, where the hotter it gets, the more current it draws, making it hotter, making it draw more current, which makes it hotter, etc. Worse still, lithium batteries suffer the same problem. The hotter they get, the more current they put out, which makes them hotter, until they catch fire and explode.

This is a very bad idea if you ask me.

But the voltage drop is as high as 4.3V at 1.5A (or somewhere around there) which is higher than a battery's voltage at full charge. The battery can't push enough current through it unless it exceeds this voltage. Also, the voltage sags a lot under load - Down to 3.7V or lower. If driving with only one lithium battery, the problem will be stability rather than over-current.

spartan diode with ricoh 3.7v battery

can someone tell me why the 400mW spartan (runs 2xcr123 batts) will not work with 2AAA but works with 3AAA batts? now ive got it running directly to an old digital battery battery 3.7v lithium rechargable i think its somewhere around 1200mA

2AAA give just 3V. Under load even less. That is safely bellow working range of this diode.
3AAA are 4.5V. I get about 200mW from that.
Your lithium has higher voltage, but it also holds under load much better. Still 1200mA seems way to high. Is it A130 ?

:horse:

udanis said:

That is such a HORRIBLE idea. Your going to burn up a perfectly good diode.

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not yet im now using the same diode in a smaller host with 2 cr2 batts, no driver and not even a single wire inside ,it still is more impressive than when i got it new. im still using the same heatsink just grinded it down.i mostly use it in quick bursts not to fry it.