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Thread: Transformer exceeding rated outut.

  1. #1
    DIY Junior Member RealRobD's Avatar
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    Default Transformer exceeding rated outut.

    I have this wall charger for a little hand vacuum. The output rating is 15v but it's actually putting out 19v. You think this is what most likely shortened the rechargeable batteries life?

  2. #2
    Nuclear Engineer nukeman's Avatar
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    It sounds normal (unless you are having other issues). These transformers don't usually have a very stable voltage (especially when there is no load). When you are testing, it may show 19v, but when it is actually charging, it is probably closer to 15-16v.

    Internally (in the vacuum), there is probably some voltage regulation that will take whatever is coming in (whether 15v or 19v) and take it down to whatever is required to charge the batteries (say 12v or 9v). Some devices will also have circuitry to avoid overvoltage, reverse voltage, etc.. However, with the constant demand for things to sell for less and less money, some of this additional circuitry may be removed from the device (since it might add 10 cents per unit (or whatever)).

    In short, everything sounds normal. I wouldn't worry about it.

  3. #3
    DIY Junior Member RealRobD's Avatar
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    Okay I see now. With a load it's at 14.9v
    The batteries won't charge beyond ~13v and under load they only put out ~1.9 so I guess they're kaput.
    Oreck considers this a "disposable" unit. And batteries are unavailable.
    I always have to fix stuff instead of throwing it out, but this time I'm out of luck :P

  4. #4
    Nuclear Engineer nukeman's Avatar
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    My guess is that they probably get the pack from another supplier. I'm sure with a little digging, you could find something with the right voltage, capacity, layout, and connector. It may or may not be worth the trouble, though.

    The other issue is that maybe the charger isn't working correctly and the batteries are okay. You may replace the pack and still be out of luck. Is it a Ni-Cad pack? How old is it? The life of the batteries can depend on several factors. Some batteries can form a "memory". On these, if you ran the batteries down to 50% everytime and then charged them up, after awhile, the battery will perform like it only has 50% capacity. Temperature, over-charging, how long it sits unused, etc. all play a factor into battery life. Also, with it being a "disposable" unit, I'm sure the quality of the original pack may not have been all that great either.

    You may have one or more dead cells in the pack. In this case, the pack may appear to be charged, but putter out when a load is put on it.

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
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    It is not unusual at all for the (cheap) battery charger's regulator to allow that high of a voltage when you are just measuring it with a high impedance multimeter (the meter 'look's like an open circuit, i.e., unloaded, to the charger). The voltage when actually trying to charge the batteries is the real test. FWIW, to get batteries fully charged, it is normal to have to apply a higher voltage than they can develop on their own. For example, your alternator on the car (depending on the battery type) might normally be putting out 14.5vdc or so for your 12vdc battery to charge it. There definitely is an upper safe limit, but yours seems to be within the safe and normal range.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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