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Author Topic: How constant is the voltage output on DVD batteries?  (Read 1627 times)

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Offline JD

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How constant is the voltage output on DVD batteries?
« on: February 13, 2013, 01:48:17 PM »
Just wondering if anyone has ever monitored the voltage output of the common 9v DVD batteries we all seem to use.
Is there a noteble drop in voltage as they discharge? If so, how much of a difference has anyone measured from full charge to a state of near discharge?

thanks

jd
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Offline hi and lo

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Re: How constant is the voltage output on DVD batteries?
« Reply #1 on: February 13, 2013, 02:41:12 PM »
From what I understand (having never personally examined the circuit inside one of these), the internal voltage of the batteries is ~7v and a switching voltage regulator is used to bring the final voltage up to 9v. This means the output voltage should remain relatively constant even as the internal cells deplete, but I've never taken any measurements to confirm.

kirk97132

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Re: How constant is the voltage output on DVD batteries?
« Reply #2 on: February 13, 2013, 04:15:24 PM »
yes battery pack voltage in DVD is 7.2 volts stepped up to 9.  Here are some tests on discharges:
http://lygte-info.dk/info/Batteries18650-2011%20UK.html

side note these are test on individual batteries.  My experience is most...not all...most DVD battery packs contain panasonic or sanyo cells from factory.
« Last Edit: February 13, 2013, 04:17:56 PM by kirkd »

Offline page

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Re: How constant is the voltage output on DVD batteries?
« Reply #3 on: February 13, 2013, 06:24:47 PM »
From what I understand (having never personally examined the circuit inside one of these), the internal voltage of the batteries is ~7v and a switching voltage regulator is used to bring the final voltage up to 9v. This means the output voltage should remain relatively constant even as the internal cells deplete, but I've never taken any measurements to confirm.

the tekkeons work on a similar principle with a regulator.

Those vary by unit but are within tolerances (using the voltage readout of the 722 and a bunch of test batteries). Some maintain the selected voltage better than others, and some sag (up to 0.4 or 0.3v under) and on rare occasion overshoot (but not more then 0.1v over). I found one out of the 4 I tested that was spot on exact, the rest were close enough.

While it would be nice to confirm, I can assume that the standard dvd batteries are similar in that it varies by unit.
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kirk97132

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Re: How constant is the voltage output on DVD batteries?
« Reply #4 on: February 13, 2013, 09:15:52 PM »
Like Page says "under load"  otherwise the voltage reading don't mean anything.

Offline JD

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Re: How constant is the voltage output on DVD batteries?
« Reply #5 on: February 14, 2013, 01:21:06 PM »
Thanks for the replies, pretty much what I had expected. I might bring a DC chart recorder home from work this weekend
and plot the output voltage as it discharges under load, just to be sure. I'll post the results here if I do.
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