[time-nuts] HP105B HP 105B 1 amp fuse blowing

[Scott McGrath]

As one who owns a 105 i had the battery properly rebuilt and basically have it on low rate charge and periodically discharge the battery

When rebuilding a 105 battery it’s important to replicate its characteristics 

Remember HP also intended I believe that the battery would also serve as a filter for the power supply.   As I dont recall any version of the 105 without a battery.



On Oct 10, 2019, at 4:50 PM, Taka Kamiya via time-nuts <time-nuts at lists.febo.com> wrote:

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 <roy.thistle at mail.utoronto.ca> 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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