Hello, I am curious about the behavior of a 1N5401 (3A, 100PIV) rectifier diode I was selecting as a blocking diode between the output of a linear 12V to 15V, 1.5 Amp power supply and a deep-cycle battery. The part in question tested good on the diode test function of my Fluke 79 Series II DVM, and in a basic fwd/rev check in the ohmmeter mode.
However, when in-circuit, with anode connected to the PSU + output and the battery + to its cathode and PSU adjusted to 13.2 VDC at the cathode, all was well until I turned off the PSU to check for blocking. But the LED across the PSU output glowed slightly.
I replaced the diode with a 1N5407 (3A, 800PIV) that was handy and no such glow. I tossed the former unit.
I wonder if anyone here has seen such a thing. I have not in the past 40 or so years I've been in the field.
Thanks in advance for your insights, DAAB
However, when in-circuit, with anode connected to the PSU + output and the battery + to its cathode and PSU adjusted to 13.2 VDC at the cathode, all was well until I turned off the PSU to check for blocking. But the LED across the PSU output glowed slightly.
I replaced the diode with a 1N5407 (3A, 800PIV) that was handy and no such glow. I tossed the former unit.
I wonder if anyone here has seen such a thing. I have not in the past 40 or so years I've been in the field.
Thanks in advance for your insights, DAAB
A couple of things... diodes can be leaky as a fault mode. As a service tech I saw the issue many times.
However leakage for these diodes can be as high as 0.5ma at high temperature and high reverse voltage. Also, modern LED's can be extremely efficient and glow with literally a few ua of current. Finally if the diode was very dirty/contaminated then that could allow leakage too... unlikely though.
Its just not worth risking, bin it as you have done.
However leakage for these diodes can be as high as 0.5ma at high temperature and high reverse voltage. Also, modern LED's can be extremely efficient and glow with literally a few ua of current. Finally if the diode was very dirty/contaminated then that could allow leakage too... unlikely though.
Its just not worth risking, bin it as you have done.
I also have seen this from time to time. Usually caused by a leaky diode. The last one was on a battery charger that flattened batteries when in float mode. About as useful as a chocolate fire guard!
Thanks for your replies. This circuitry is the float charger for my RV deep-cycle battery. Since putting the 1N5407 in-circuit the float voltage has remained at 13.2 V +/- .01 V, without temperature compensation.
Funny thing, if not for the LED glow, I would have used the diode in some circuit with full ignorance. I think I'll use a similar setup to further test rectifier diodes from now on.
BTW, how would one implement suitable temperature compensation in this application? Mount the blocking diode adjacent to the battery, or even in contact with it?
Thanks again, DAAB.
Funny thing, if not for the LED glow, I would have used the diode in some circuit with full ignorance. I think I'll use a similar setup to further test rectifier diodes from now on.
BTW, how would one implement suitable temperature compensation in this application? Mount the blocking diode adjacent to the battery, or even in contact with it?
Thanks again, DAAB.
I could (slightly) light a diode having it one leg at hand and touching the other with the solder iron‼ Very sensitive.
For lower voltage drop, try 1N5819 Shottky diodes.
For lower voltage drop, try 1N5819 Shottky diodes.
The blocking diode doesn't need any temperature compensation. Cyclic and float charge regimes demand different charging voltages. This is as good as it gets explaining it all, the Little Red Book Of Batteries by Yuasa.
Good graphs and details here,
http://www.yuasaeurope.com/en-gb/industrial/products/np/
I had a 5 MM blue high intensity LED that was bright as the begeezus running at half its rated nominal current, amazing.
I was trying some Lambda FBL-00199 schottkys, 20A, 100PIV (tested 0.348 vfwd on the Fluke), but for some reason (another mystery), they did not have the rock-solid vfwd stability of the 1N5407, which in-circuit is measuring 0.721V vfwd with ~5.5mA current to the battery, which is floating at 13.2V as adjusted for.
In this app the lower voltage drop of the schottkys isn't needed, as the float PSU (International Power IHB-15-1.5) puts out more than enough voltage to overcome the blocker's V drop, with its max of 15.75 V output.
Thanks again for the replies.
Probably no mystery... the lead acid battery under charge (or at least when the charger leaves constant current mode and reverts to constant voltage as the battery approaches full charge) doesn't present a constant load. As the cell gasses, the current drawn is spiky and fluctuating and that difference will reflect in a difference seen in the forward volt drop across the diode.
This is true for forward voltage drop but the leakage current is much higher and more temperature dependent compared to a standard silicon rectifier like the 1N540x series.
- Well, that would explain the apparent flakiness I encountered when using the FLB00199's I had pulled from a couple of retired Lambda PSU's. Great for efficiency, but more to the story than meets the eye, so it is said.
here. So many details, so much to learn.
BTW the float voltage through the 1N5407 is now sitting at 13.19V, still rock-sold after 24+ hours.
I had done a lot of fussing around trying to get here with the schottky's. So what are they really good for, full-wave bridge, etc?
Again, thanks to all... DAAB-
There is no such thing as a perfect or universally applicable component.
High current schottky diodes are useful where the benefit of the much lower forward voltage (such as efficiency gains when used as a catch diode in switch mode power supply) is more significant than the cost such as lower reverse voltage breakdown and higher leakage current.
[QUOTE=VivaVee;3603645]There is no such thing as a perfect or universally applicable component.
High current schottky diodes are useful where the benefit of the much lower forward voltage (such as efficiency gains when used as a catch diode in switch mode power supply) is more significant than the cost such as lower reverse voltage breakdown and higher leakage current.[/QUOTE]
So you would not typically find them in a linear PSU? The FLB 00199's came from a couple of big Lambda SMPS's
I may not find a use for them, but they were mounted in really nice bracket assemblies, which will be handy when refitted with non-schottky rect. diodes to make some bridge or full wave (xfmr C.T.) builds.
DAAB-
High current schottky diodes are useful where the benefit of the much lower forward voltage (such as efficiency gains when used as a catch diode in switch mode power supply) is more significant than the cost such as lower reverse voltage breakdown and higher leakage current.[/QUOTE]
So you would not typically find them in a linear PSU? The FLB 00199's came from a couple of big Lambda SMPS's
I may not find a use for them, but they were mounted in really nice bracket assemblies, which will be handy when refitted with non-schottky rect. diodes to make some bridge or full wave (xfmr C.T.) builds.
DAAB-
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