[Elecraft] OT: More PS ?s...

[John Clifford]

I solved my adjustable voltage problem... there wasn't a problem (only with
the operator!).

However... I've been doing a little more thinking about this to see if I am
trying to do this right.

I have been looking at the schematic
(http://www.alinco.com/pdf.files/Service/dm330ser.pdf, p.21) and don't see
any reverse voltage protection.  At power off and after I let the voltage
dissipate to 0, I did a resistance check and got about 90 ohms... which
indicates to me that a battery across this guy when the power's off is going
to either blow my inline fuse or blow something in the power supply.  So, I
know I don't want to hook up a battery without some sort of protection...
right?

I picked up several Motorola MR2535L diodes at the local Active Electronics.
Motorola IDs this part as being a member of their rectifier family, but upon
looking at the data sheet it seems that this is a zener diode, rated
nominally at 20v/35A.  Minimum breakdown voltage is 24v, so I should be safe
from reverse current with a 12v battery... right?  The only other question I
have is whether or not what I'm trying to do is a good application for this
part.  I can't tell from the data sheet
(http://www.eicsemi.com/eicsemi/pdf/MR2535L.pdf) whether or not this diode
is intended for this application.  Although it is rated at 20v/35A, will it
be good for steady-state usage of 20 amps or more, or is it designed to
handle these voltages  and currents for only very brief periods of time as
it shunts reverse voltage?

What about hooking three or four of these up in parallel, in series with the
positive wire?  Would doing this give me considerable leeway as far as
voltage/current handling goes?  Would it also decrease my voltage drop (I
should be able to treat diodes like resistors when it comes to voltage drop,
i.e., .6v / 4 would give me .15v drop 'cuz of 1/4th the resistance, right?)?

Is anyone else doing something like this (running a battery in parallel with
a switching power supply)?  How are you doing it without destroying your PS
when the power is turned off?  Are you using a relay instead and triggering
it off of the AC line?  I was hoping for something more elegant (more solid
state!) than that....

 - jgc

John Clifford KD7KGX

Heathkit HW-9 WARC/HFT-9/HM-9
Elecraft K2 #1678 /KSB2/KIO2/KBT2/KAT2/KNB2/KAF2/KPA100
Ten-Tec Omni VI/Opt1

email: kd7kgx@arrl.net