The fact that 25V supply is dropping to 23.4V shows it is drawing far more
current than it is rated. I am assuming this is a regulated power supply.
Does the power brick actually shuts down at 500mA or does it let the the
voltage drop and try to supply what it can? Maybe one or more Nicad has an
internal short? That will cause and over-voltage situation per battery and
thus over-current. I've recently seen a brick power supply go into oscillation
and produce 3x rated voltage when too much current was drawn. (and blew the
circuit)
Also, different batteries has different charging rates. As far as 105B
document goes, it says 24V 0.5Amp supply but that is for default configuration.
Designed charge rate is 390mA (page 3-4) and is current controlled by A5Q3.
I would actually measure how much current is drawn there. Since the fuse is
already blown, just put an am-meter across the fuse and see....
---------------------------------------
(Mr.) Taka Kamiya
KB4EMF / ex JF2DKG
On Thursday, October 10, 2019, 4:00:41 PM EDT, Roy Thistle
<[email protected]> wrote:
Hi All:
A 105B (quartz oscillator) is blowing the 1A fuse, after it is on about 1 hour.
The fuse appears to have just melted (not a black mark as the result of a
flash, in the case of a high current short.)… just looks like the fuse wire
(inside the glass capsule) melted into some little blobs, for about 1/4 the
fuse length, near the middle. It wasn't a fast-blo or slow-blo fuse... just the
normal kind.
I think the unit is drawing just a little too much current, as the result of
the batteries needing charging (I had the fast charge option on when the fuse
blew.) And so, the fuse heated up, and finally melted. Not sure why the
batteries were not charging normally... but 20.1 volts is what I measured
across the pack, initially, and 23.4 V after about 45 min of charging.
I am charging the batters, from a power cube, at 510 ma, and dropping (cube
gives 25V, 500mA max)… the batteries are 20 C size NiCads, wired in series...
that of course is a retrofit.
I don't want to put another fuse in, and blow that too, without some reasonable
explanation of why the first one failed!
Please, any comments, or hints/suggestions... much appreciated.
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