How are you measuring them.
If you get too many in series you won’t get enough voltage out of a DMM to turn them on. If you estimate you would expect something like 0.6 to 0.7V across each you don’t have to go too many to exceed the available test voltage. My Multicomp DMM measures 3.24V on “Diode Test” function so you can see at 0.7V 5 diodes would be too many to turn on. I think a bit over 3V is pretty typical for this sort ov thing.
Yes, they are extremely difficult to read sometimes. Sometimes easier to discard and purchase new ones so you have some sort of chance of knowing what they are. Put them in a small plastic sealable bag and carefully mark the bag. This helps.
A little watchmaker’s magnifying eyepiece is handy here.
Cheers Bob
Hi Kimmo
Normally a DMM has a diode test function. This is required as the voltage at the meter leads is usually not sufficient to turn on a diode or transistor junction in resistance mode. My DMM has about 3.25V here. The idea is that when reversed biased the meter reads nothing (different meters have different ways of doing this) and forward biased it reads the voltage drop across the diode which is normally between 0.1 to about 0.7V depending on the diode type. An open circuit diode will read nothing both ways where a shorted one will read zero (noughts) or a very low voltage both ways.
Your method of connecting the diode in series with the power lead is valid. Just measure the voltage drop which as above width be some hundreds of mV depending on type. Just make sure there is enough resistance in the circuit to keep the current within diode spec. This is getting back to the reading the type problem as you really need to know this to know what the max current is. But if you can keep this down to just a few mA you should be able to cover most bases safely.
Cheers Bob
Hi Kimmo
Yes. Open circuit with just the diode connected to a power supply going nowhere (I am assuming that is what you mean. There are are a lot of ambiguous statements requiring guesswork around here).
If you don’t have a circuit you will get no current flow so no voltage drop.
The other way you could read your query is that you have a faulty open circuit diode. Then you will get no voltage drop in any situation.
Easier to use the DMM diode test function really.
Cheers Bob
Hi Kimmo
Very much a case of you gets what you pays for with this type of thing.
Fluke probably are the benchmark here. as a point of interest quite a lot of the gear used for calibrating other instruments are Fluke (Fluke Calibrator). You are really paying for accuracy, stability and repeatability.
You don’t have to go to Fluke. I have 4 DMMs acquired over the years. The 2 most recent being a Uni-T Model UT71B which developed faulty resistance mode function and a Multicomp Pro Model MP730624. Both pretty good instruments and are not frightened to publish real, accurate and complete spec figures. I think the Multicomp Pro was under (just) $100 from Element 14.
Also when measuring a voltage both these instruments are within a few mV of each other (2V and 20V ranges) so that s a bit better than most “entry level” devices. Specs are freely published so evaluate for yourself.
Actually DMMs as good as they seem are not the be all to end all. In the real world they still require a calibration check every 12 months, even the Fluke.
I have often wondered just what this calibration check really means. I think it means you can be pretty confident the last few measurements you made and the next few you are going to make will be pretty accurate. As long the instrument under check passes OK. As for the rest of the same ???Who knows.
But you have got to draw a line in the sand somewhere. For active instruments (DMM, Sig Gen etc) the period is 12 months and for Passive (no active bits) the cal period used to be 5 years.
I might mention here that for tooling like crimp tools, wire wrap tools and similar the check is EVERY DAY before use.
Cheers Bob
If you are now referring to the 2 converters of your original post the last time I looked you were going to put them in parallel.
But I could be misreading a new intention and you want to put 2 converters in series.
I don’t know, I have never had the reason to try it. My first question would be Why would you want this? You would be looking at 2 lots of conversion efficiency and could get so lossy as to be useless.
Cheers Bob
It’s a general question for future reference; those little boost converters are quite cheap compared to most comparable items I’ve seen, and every now and then I might want more than 12V…
I guess I’d be better off with a slightly more spendy adjustable converter.
