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ZNR transient suppressors / Makita DC18RA charger

Discussion in 'Electronic Repair' started by N_Cook, Sep 9, 2013.

  1. N_Cook

    N_Cook Guest

    In what circumstances do they fail open versus low ohmic
    Specifically panasonic ZNR V10 241U
    A Yankee in Limeyland with a Makita fast battery charger
    misreads 110V~240W as 110V~240V and connects to 240V mains and a fatal
    sizzle. The transient suppressor , in there to suppress transients not
    sustained overvoltage, seems to have protected the electronics by going
    ohmic and blowing the 8amp internal fuse and part shattering itself in
    the process. But >8 amps seems to be a tall ask for such a small device,
    was he just lucky?
     
  2. Leif Neland

    Leif Neland Guest

    N_Cook tastede følgende:
    8 amps seem to be an overrated fuse, around 2.5A would correspond with
    265W.

    The transient supressor should not draw 8A for longer than a few
    milliseconds.
    It should only eat transients.

    But if he's lucky, the suppressor will have succeded when it heroically
    sacrificed itself for protection of the electronics.

    To survive that overvoltage, it should probably be much larger and
    pricier.(sp?).
    The beancounters didn't think the price of a large protector multiplied
    with the probability of 240V compared with the price of a small
    protector was worth it.

    Leif
     
  3. Jeroen

    Jeroen Guest

    VDRs over a constant voltage source always fail catastrophically.
    This is because they have a negative temperature coefficient, so
    if they heat up then they draw even more current, etcetera.
    This happens immediately due to gross over-voltage, but it can
    also happen gradually due to repeated suppression of short high
    voltage pulses. That is because the grains fuse together and thus
    the voltage threshold gradually drops until the NTC effect kicks
    in. Then you get thermal run-away and over-current. And this is why
    there must always be a fuse in series with the VDR to save the day.
    So it seems to have worked exactly as intended. I would expect that
    if you replace the VDR and the fuse - by the correct types - then
    everything will work again. Some people would of course first test
    without the VDR, to see what is the chance of a successful repair.

    Good luck
     
  4. N_Cook

    N_Cook Guest

    T5A fuse will be going back in there. Owner will be using with his 1500W
    autotransformer. I'm assuming that variable demand is usual for these
    sorts of charger, monitoring current draw at 240V, before stepdown Tx,
    1.3amp for 7 seconds, .3amps for 2 seconds, (2.6A/.6A at 110V) while the
    battery is well beolow 80% charge. I'll monitor the timings as the
    charging progresses but so far seems ok
     
  5. N_Cook

    N_Cook Guest

    original , assuming www info as to identity was coreect, ZNR ... 241U
    remained on the component = ZNRV10D241U , then 150 sustained max V and
    2mS energy of 30J, replaced with larger 140V max, 40J and T5A fuse.
    More headroom should he do the same but no guarantee that the transient
    suppressor would not go open.
    Monitoring 240V mains during charging (double for 110V into the charger)
    approx .1amp (L), .3amp(M), 1.3 amp(H)
    first few minutes in region 5-6 sec M, 2-3 sec H
    5 minutes in few seconds L, 5-7s M, 1-2s H
    8 minutes in 2s L, 17 s M, never H from then on to 12 minutes and L ,
    saying 100% charge.
    When I first measured the batt voltage, as received, I thought it was
    1.5V for this Lion 18V, 1.5Ah, perhaps I made an error with the DVM
    probes/reading. Or can li-ions be driven that low and recover (well no
    bad batt yellow LED at any time on the charger)
    After intial minute or so of try out with battery, was 18.1V and after
    charge 20.1V , all with no load
     
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