Why NOT to test your diodes on batteries!

[Things]

I saw this in the other thread before it got closed.

You people are goofy as hell!!! First off I purposely killed alot of diodes in my own destructive TESTING!!! Using two generic AA batteries is not going to give you that kind of amperage!!! Lithiums yes alkalines no!!!

Which annoys me greatly when people don't back up what they think.

Why? Well the fact that "Using two generic AA batteries is not going to give you that kind of amperage!!!" is total garbage!

Just grab an AA battery, and shove it onto your DMM and measure the current.

Thats 8.8 AMPS! Not something you want to go shoving into your diode!

 

[photonaholic]

Well done...

 

[RJD]

I saw this in the other thread before it got closed.



Which annoys me greatly when people don't back up what they think.

Why? Well the fact that "Using two generic AA batteries is not going to give you that kind of amperage!!!" is total garbage!

Just grab an AA battery, and shove it onto your DMM and measure the current.

Thats 8.8 AMPS! Not something you want to go shoving into your diode!

You are not getting 8.8 amps from any AA battery! I am not correcting you to argue. I just want to explain to anybody reading this why it is incorrect information!

Ok first thing your trying to read amps on a battery that has less than 1A so you need to switch your DMM to 200m in the dc amp range, Now that your trying to measure the amperage in the correct range you will get a more accurate reading!
Batteries are rated in MILLIAMPS not amps. If it were true that your AA battery had a current of 8.8 amps that would eqaute to 8800 mA. There is no AA battery that I know of that has that kind of amperage!

There is an easy way to check this with or without a meter! If you do not have access to a DMM but know how many milliamps your battery is!
As a milliampere (milliamp or just mA) is 1/1000th of an ampere, we can convert mA to Amps by just dividing by 1000. Another way is to take the current in mA and move the decimal to the left three places to accomplish the division by 1000.
mA / 1000 = Amps

Here is my photo taking a milliamp reading note the position of the selector switch

So this brand new Duracell has 1/4 of 1/1000th of an amp or 25 mA!
This is all easy to prove using the basic rules and formulas that govern electricity. There is no sense :horse:and my only intent here was to correct the missinformed in regards to battery amperage!
Here is an example of how to obtain a incorrect reading on a DMM. Using that same Duracell in the pic I switched my DMM to ACV 200 and took a reading, the results 2.5 ACV! This is obviously incorrect that is why you must be sure your taking readings in the correct range!
No slight intended and hopefully no hard feelings
and thanks for reading!

 

[JLSE]

If you hook in a 1ohm resistor, cap and diode, you will not blow anything..

Straight to the batteries without minimal protection is bad, but not lethal to an LD if done properly (cap,res,diode)..

The problem that occours is with rapidly losing output as the voltage sags on the batteries. Current regulation is obviously the way to go, but you will not fry an open can red at 3v (2xAA), if anything, you wont see more than 225mW


* 16amps to the LD would be intersting though.

"So this brand new Duracell has 1/4 of 1/1000th of an amp or 25 mA!"

*25mA ? You sure thats not 250mA?

 

[photonaholic]

RJD is gone, so why have his "ghost" hanging around?

 

[lazerov]

You are not getting 8.8 amps from any AA battery! I am not correcting you to argue. I just want to explain to anybody reading this why it is incorrect information!

A short-circuited battery CAN supply that amount of current for a short time. And the battery in the first post is short-circuited. Furthermore, my cell phone jammer draws well over 3Amps and is powered from AAs. Once I accidentally short circuited these batteries and the wires started smoking! Your statement that a brand new alkaline can supply only 25mA is ridiculous.

Ok first thing your trying to read amps on a battery that has less than 1A so you need to switch your DMM to 200m in the dc amp range, Now that your trying to measure the voltage in the correct range you will get a more accurate reading!

If you switch the DMM to the 200mA range and measure the current of the battery the only thing that will happen is to burn out the fuse of the DMM. And when you are using the 200mA DC current range you are NOT measuring voltage but current (you stated that you are measuring voltage).

Batteries are rated in MILLIAMPS not amps. If it were true that your AA battery had a current of 8.8 amps that would eqaute to 8800 mA. There is no AA battery that I know of that has that kind of amperage!

Batteries are not rated in mA but in mAh (milliampere-hour) which has nothing to do with the maximum current of the battery. Maximum safe current is rated as "C". For example 10C means that the maximum current draw from a battery with capacity of 400mAh is 4A.

There is no sense :horse:and my only intent here was to correct the missinformed in regards to battery amperage!

If you're so concerned about misinformation, please don't create more of it.

Here is an example of how to obtain a incorrect reading on a DMM. Using that same Duracell in the pic I switched my DMM to ACV 200 and took a reading, the results 2.5 ACV! This is obviously incorrect that is why you must be sure your taking readings in the correct range!

Do you even know what ACV means? This is not only different range but different type of measurement. OP is correctly measuring in the 10A DC range.

 

[RJD]

You know, I was thinking the same thing nearly 9 amps from a AA cell??

That would be enough current to cause a light gauge wire to get so hot the insulation would melt and the wire would burn your fingers.

I have only seen that kind of performance from at least a NiCd or NiMh "C" cell or above.

Maybe we can re-work this thread to be more factual and informative before it gleans too many replies.

RJD is gone, so why have his "ghost" hanging around?

BOOOOOOO!!!:na: Sorry for my appearance I was hoping for a second chance here! I do not hold any grudges and have no desire to be disruptive to the forum I like it here and would like to stay if allowed! As far as my s/n I did not want to hide who I was or the fact that I was banned here under the s/n Ronnie James Diode (RJD). It is a shame to see so many usefull threads choked with the typical forum b/s so I am just going to ignore any ignorance and behave as civily as possible!

 

[aryntha]

This may be blasphemy, but I'm just going to mention it; I've actually had good luck testing diodes with a specific LED tester. (multiple slots for multiple milliamp ratings, made for the specific purpose of current-limited LED testing).

It's not a 'driver' per se, but it is a current limited device, it's cheap, convenient, and i've never blown one with one of these.

 

[Things]

No, I know perfectly why it was reading 8A. This was a fresh cell, and this was a DIRECT SHORT.

I have no doubt this thing was doing 8A, the battery started getting warm a few seconds after connecting it, thus why the picture was blurred. I had to do it quickly before I had a pipe bomb in my hands.

With some laser diodes, you may be saved by internal resistance, and in some cases not, so it's best just to not do it.

If your batteries only supply 250ma shorted, I think you may need to check how long they have been sitting on the shelf!

May I also point out that you had the DMM probe plugged into the wrong input. In your pic, it's plugged into the 10A plug.
Please learn how to at least use your DMM before you start coughing up more incorrect information.

The one underneath it says "V(Ohms)mA", thats the one you want. The 10A socket is essentially shorted to your - probe.

Aryntha: I have tested diodes using a LED tester as well fine, but that is in no way a direct connection to the battery, and typically the highest current rating is 50mA.

Lazerov is correct. Batteries are rated in mAh. If a battery is 2000mAh, this means it can supply, under normal conditions, 2A for 1 hour. If you connect it to a laser diode directly for a few seconds, it's very likely the diode is going to get a huge current surge!

 

[HIMNL9]

DMMs have different internal resistances, in different scales, you know ?

On 10A scale, some of them have 0.1 ohm, some others 0.05 ohm, and the better ones 0.01ohm, but at any effect, on a direct measure of this type, is a short circuit ..... and yes, fresh alkaline cells can give you so much amperes, also if just for few minutes (but considering that, for burn a LD, you just need a fraction of second, at that current, it's more than enough )

All the primary cells have two parameters, the nominal current-per-hour (Ma/h or A/h), that is the current that a cell can give you constantly for an entire hour, and a (never declared, usually), maximum short-current, that is the maximum current that the cell can give you in short-circuit conditions (and that, usually, kills the cell, with very few exceptions) ..... an AA cell, alkaline of good quality, can really easily give you 8 or 10 A for a minute or two, also if this ofcourse kill the cell ..... an exception that i've found, as example, is the Gates 2V Pb cells, where a 5A cell can give 500A for 30 seconds (yes, 500A), and still survive ..... so, never underestimate the quantity of energy that you can get from a cell, especially with delicate and expensives LDs

BTW, you know the "bomb-battery" ? ..... years ago we do that as joke ..... taking a half-dead D duracell alkaline, shorting it with a piece of wire soldered on the poles, and placing it somewhere ..... also if half deads, they still had enough current for become boiling in some minutes, exploding at the end with a decent loud

 

[hydrogenman15]

I just tested a couple batteries on my DMM.
One was a alkaline aaa that had already been used quite a few times and read a voltage 1.4. It put out just over 2 amps. Another was a aaa alkaline that was 1.3v and it put out over three amps. I also tested two rechargeable aa's and they both put out over 10 amps.

The thing I'm wondering is, if aa's and aaa's can only put out 25mA's then how could a DPSS green pen laser be able to produce >100mW's green light? They cannot go above 50% efficiency if I remember correctly. Thats just my 2 cents.

--Hydro15

 

[JLSE]

"2A for 1 hour."

How do you get this number? 2A?

Ive tried direct batteries many times on different reds and even IR's, lol the diode will not see 2A. The red sees less than the IR with the lower voltage requirements. This was hooked straight to the LD, no resistor, nothing...

The availible current is dependant on the voltage of the load. If the voltage draw exceeds the 3v of two AA's the current becomes less and less.

Have you actually tested this?

 

[Things]

hydrogenman15, they don't put out 25mA, thats how

Wannaburn: Thats what mAh stands for, whether the manufacturer is telling the truth or talking crap is out of my hands.

 

[JLSE]

Im reffering to what happens when you hook up a LD to 2 AA batteries, not what the battery can do..

If the diode saw 2A, the entire kipkay flashlight hack would not have been so popular..
If your saying that the red LD sees 2 A, it wouldnt live past the first click of the switch.

Im not at any point saying its a good idea, which I reffered to in my first post. But doing so does not spell instant death for an LD.

I made a couple of pens back in the day, straight to 2xAAA's, and have even tried with 10440's and CR123A's.

Again, a really bad idea, but theres no sudden drop of current on the LD.

Even the 3.6v can only deliver 550-600mA on a fresh charge. Excluding anything larger than the CR123A, bigger battery, bigger current.

That said, the title 'Why NOT to test your diodes on batteries! ' is not valid as the LD never sees that kind of current.

 

[Things]

Yes, while the diodes may survive in a few cases, if you read through the RJD thread you will see why I started this thread. If someone bought a diode from you, connected it to AA batteries and killed it, then complained to you about you not shipping it properly etc, you can see why it's best if you DON'T do it.

It also depends largely on the battery. Some may have much lower internal resistance than others, which will mean instant death to your diode.

 

[HIMNL9]

mAh ..... Yes, that is usually the only data that the manufacturers say you (other than the voltage, ofcourse ) ..... mAh is the maximum current that, nominally, a fresh, new cell can give you for a whole hour, without burn or become damaged.

In the case of most of the "new" 2700mAh Ni-Mh cells, as example, it means that these cells, fully charged (when new and in good conditions), can give you a maximum of 2700mA (or 2,7A) for an entire hour, before become too much discharged, and still remain in good conditions (that means, you can recharge them and reuse them again, after you've left them cool down)

Ofcourse, this don't mean that the same cell can give you ONLY 2700mA maximum current ..... an AA size 2700mAh cell can, almost safely, give you 5000mA (5A) for half hour, becoming more hot and shortening the life cycle around half times ..... can give you almost 10A for approximatively 8 or 10 minutes (but it become boiling, and may become too much damaged for recharge it more than other 10 times, if you're lucky) ..... and can give you easily from 15 to 20A for a minute, but in this case the cell become burning, completely die at the end, and there's a good 50% of possibility that in a minute or few more it just blow in your hands, if the safety seal fails to melt and release the gas.

But the main problem, imho, is that the manufacturers never say these things, on their products ..... they just place a generic "do not short circuit" advice on the cells, without explain good the related risks (only on Li-Ion and Li-based cells there is some more advice, cause these cells can explode like incendiary bombs, in determinated conditions)