How do you test a Shottcky diode????

[(RIP) PLANK]

I am puzzled! I thought i knew all about diodes but these are beating me!

30 amp Shottcky blocking diodes:

I have used the diode check on my meter no 'beep' in either direction :nenau

I have put them in circuit with a 12v battery and I am reading 12v in both directions :nenau

what am i doing wrong? :doh

 

[Lazy-Ferret]

As far as I remember, a Schottky diode is the same as a normal diode, just a lower volt drop across it, about 0.25volt as opposed to about 0.7v across a normal diode, which generally means that they can switch faster when used in IC's.

As far as testing goes, it should conduct in one direction, and block in the reverse.

Sounds like yours has gone short circuit.

 

[(RIP) PLANK]

My thoughts exactly, I bought these from a supplier in the Czech Republic and when i told him they were faulty he sent more FOC. The new ones are the same :nenau

I am pretty convinced i am right, as i said i have tested them in circuit and out, and I am equally convinced in the posting them in a jiffy bag process could ruin them - could it? :nenau

any further thoughts before i get back to him? :nenau

 

[rustic]

Since they are 30 amp diodes, test as follows:-

From the positive of the battery connect to an old working head light bulb,
from the other side of the headlight bulb connect to one side of the diode, ie the side without the bar.

From the other side of the diode, connect to the negative of the battery.


The light will only light up when the diode is the correct way round.

Try it either way to make sure.
If it lights both ways, then the diode is kaputt.

Now with the diode conducting, and the bulb lit, connect the volt meter across the diode to test the voltage drop across it.

It should be less than 0.7 volts.

Let us know how you get on.:nenau


This test will work for any diode, BUT the bulb used must be of the correct wattage so that the current is within the maximum limit of the diode.

Even a light emitting diode with a current limit resistor will work.


NEVER connect the diode across a voltage source ie battery on its own, (this will destroy the diode) unless there is something to limit the current.


Best regards,
Rustic

 

[rustic]

Sounds like yours has gone short circuit.

No, open circuit, as there is a voltage across them.
If it was a short circuit, then there wouldn't be a voltage drop.

An electronic component that conducts both ways is called a piece of wire.
In fact 0 ohm resistors are manufactured, that in fact look like resistors, but are actually a link with a housing around it.
They are used by automatic assembly/insertion machines, and also space the short circuit link above the board, allowing other tracks to go underneath without the risk of shorting by a plain wire link.

Just thought I would add to the thread with some interesting facts...

Yawn yawn...:doh

 

[(RIP) PLANK]

Cheers rustic, so basically i need to test them under load :thumb2 I will give it a go :thumb2

 

[(RIP) PLANK]

Bingo! thanks Rustic, they do work! and with around 0.3/0.35 voltage drop so spot on. The low voltage drop was one of the reasons I wanted them

 

[rustic]

Bingo! thanks Rustic, they do work! and with around 0.3/0.35 voltage drop so spot on. The low voltage drop was one of the reasons I wanted them

Great.
:thumb2:thumb2

 

[(RIP) PLANK]

I have just sent an apology email to the seller :augie

 

[edgerton19]

Just a thought, 30A X 0.35V = 10.5 watts of heat at full load so you will need to use a good heasink to keep the diode junction temperature (Tjmax) below 125°C (or 150°C depending on the junction type).

 

[(RIP) PLANK]

It will never be at full load, but thanks for the thought. The idea behind using 30 amp diode in a 3 amp circuit was to lower impedance and increase current flow - though I could be miles out :augie

 

[solarman216]

It will never be at full load, but thanks for the thought. The idea behind using 30 amp diode in a 3 amp circuit was to lower impedance and increase current flow - though I could be miles out :augie

think you would be better off using a relay, no loss then, but could depend on what you are useing it for? Rick

 

[Lazy-Ferret]

It will never be at full load, but thanks for the thought. The idea behind using 30 amp diode in a 3 amp circuit was to lower impedance and increase current flow - though I could be miles out :augie

The main problem with a diode, is you loose that volt drop regardless of how much Current or Voltage you are passing through it, so no matter what with the Shottcky ones you have, you will be loosing 0.35volt, as to the more normal 0.7volt on a standard diode.

The main thing is keeping the operating temperature of the diode down, and at least with a Shottcky one, you have effectively halved the dissipated heat of a standard Diode, and then by using a 30amp one as well, in that nice big housing, you have given it a way of dissipating the heat easier. So right solution, even if the logic was just slightly off..:clap

 

[Kamsin]

After reading this topic with intrest i can say without any doubt that, I have no idea what the hell anyone is talking about.

However, when my GF's Grandad passed away this year i ended up with load of stuff like this and again have no idea what its all for, but it does make my shed look good :naughty

There are capasitors,resistors, junction boxs, slidy bars thingy bobs, computer stuff and so on. Maybe i could build something that goes BANG! :lol

 

[(RIP) PLANK]

The main problem with a diode, is you loose that volt drop regardless of how much Current or Voltage you are passing through it, so no matter what with the Shottcky ones you have, you will be loosing 0.35volt, as to the more normal 0.7volt on a standard diode.

The main thing is keeping the operating temperature of the diode down, and at least with a Shottcky one, you have effectively halved the dissipated heat of a standard Diode, and then by using a 30amp one as well, in that nice big housing, you have given it a way of dissipating the heat easier. So right solution, even if the logic was just slightly off..:clap

I always think what an odd thing it is that when you wire something up with thick cables, say a second battery, you then put a fuse in line and all the power has to pass through a tiny wafer of metal! The fuse itself must add quite some resistance. This was also my thinking with the diode a 30 amp diode has a fair amount of metal in it with a good cross sectional area :thumb2

 

[Lazy-Ferret]

When I worked in the electronics lab at the University of Kent, we would be given excess stock from companies for free, and sometimes it was really just junk, other times, it was fantastic, especially all the military connectors from Amphinol.

Anyway, one time, this company sent us a load of resistors, the problem was, who ever had packed them for us, had just tipped all the values into a big bag and dropped them off, and to make things worse, they were Russian ones, that did not use our colour bands for identification, so we basically had a bin bag full of tiny red ceramic blobs, on two bits of wire. No one wanted to try and sort them out, but they seemed to good to throw away...

In the end, we would use them for soldering practice for the students, and they would have to built ladders, and cubes with them to practice getting a good clean solder joint..

One lunch time, it was raining, and us technicians were board, so we decided to see who could build the most impressive resister array from these resistors, which started out as complex cubes with cross bracing, and then ended up with us building models.I built a car, another guy built a church, and the other guy was doing a combined version of the Eiffel and black pool towers. when finished, they sat around for a few days, and we added and tweaked them, then one of the other guys decided to see what would happen if the tower got hit by lightning... so we took it down to where we had this 8 foot high vandergraph generator, that was fearsome... we put our little resistor tower under the vandergragh and set things in motion... Wow it was quiet spectacular, as the weakest resistance path burnt out, it would create a now one, which would then burn out and so on... those Russian resisters went in style as well, many exploding with great plumes of smoke....

Of course, being the responsible technicians we were, we cleaned up....

and then did it again with the church and car... :clap:clap

The good news was, we finally had a practical use for all those student practice bits, and the remaining resisters...

 

[Lazy-Ferret]

I always think what an odd thing it is that when you wire something up with thick cables, say a second battery, you then put a fuse in line and all the power has to pass through a tiny wafer of metal! The fuse itself must add quite some resistance. This was also my thinking with the diode a 30 amp diode has a fair amount of metal in it with a good cross sectional area :thumb2

I know what you mean.... but the fuse is designed to be able to dissipate the heat very effectively up to the specified current, and then when that is exceeded, it goes. That is why the larger ones tend to be flat, as that gives the maximum surface area to dissipate the heat.

But you are right, they do have a resistance, and the more current you draw, the warmer it gets, which in turn will actually increase it's resistance even more.

 

[(RIP) PLANK]

So you like my 30 amp shottcky for a 3 and a 1/2 amp circuit plan then :thumb2

 

[Lazy-Ferret]

So you like my 30 amp shottcky for a 3 and a 1/2 amp circuit plan then :thumb2

:thumb2:thumb2

After all that, what you making, anyway?:lol

 

[(RIP) PLANK]

After all that, the project has changed direction and I may not use the diodes at all. But it was to set up a small portable solar charging system for a caravan. The charge controller is (was) mounted at the panel end which meant the 4mm square cables were constantly live from the battery. My thoughts were that despite them being decent double insulated cable, they would - to a very small extent - drain battery power when out across the wet cold ground in the dark.

But, by removing the charge controller from the panels and mounting it on-board, very close to the battery (batteries) this is no longer the case. I know the loss would be minimal but in Britain in the winter every erg of energy helps :thumb2