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I have a camera battery charger which is driven from a 12V (measured 12.2) switched mode wall wart rated at 1A. All three items (charger circuit, wall wart and battery) are stock, but all three heat up pretty quickly, which got me worried. The items work - the battery gets charged - but all items, especially the wall wart, are very hot in the end. I measured the current through the wall wart cable to be 1.5A. Now how should I go about limiting it?

I thought about adding a 4 ohm resistor in series with the wall wart supply, as I calculated would be adequate. I also thought about adding a few diodes in series to drop the voltage, but I was worried, it might interfere with the internal circuitry of charger (there's a couple of ICs and inductors and what not in there, too complicated for a beginner like me to reverse engineer).

Or would I need an active current limiting circuit?

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Many chargers use a fancy charging method called pulsed or burp charging:

enter image description here

(from http://www.mpoweruk.com/chargers.htm)

A high current is used to charge for a certain pulse length, and after, the battery receives a short discharge pulse. Effectively, this increases the charge speed, however, this method depends on certain calculations for the optimal voltage and current to charge with.

If you change the input current and voltage of the charger, you can't expect this to work properly anymore, which may harm the battery and/or increase the charge time.

Therefore, it would be the best not to use these devices together, but to get a power supply rated for 1.5A.

However, if you bought these items together, there's (almost) nothing to worry about. Many devices get hot during normal use (especially wall warts). And if it booms, you have your warranty.

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  • \$\begingroup\$ Thanks, the thing with warranty is that the camera was bought some 10 years ago and only recently I gave it second thought as of why it gets so hot only recently, seeing as I am getting into electronics and the label on the wall wart should not really be bubbling. Maybe I should go the higher rated PSU way indeed:) Will wait for other peoples input and possibly accept this answer. \$\endgroup\$
    – Limiter
    Dec 18 '14 at 19:29
  • \$\begingroup\$ @Limiter depending on the kind of battery and the storage method, I could imagine that the high current draw is caused by the battery being degraded, and then it may be not safe at all to continue with this one. Is there perhaps a way you could try a new battery? \$\endgroup\$
    – user17592
    Dec 18 '14 at 19:32
  • \$\begingroup\$ perhaps indeed, now need to start looking for a source for Olympus DSLR batteries, since the company died out :/ I love that camera though, even after 8-10 years of usage so replacing it will not be among the options. \$\endgroup\$
    – Limiter
    Dec 18 '14 at 20:07
  • \$\begingroup\$ Although I have not noticed any losses in battery time, although I use it maybe a few times a month nowadays, and charge maybe biannually. \$\endgroup\$
    – Limiter
    Dec 18 '14 at 20:12
  • \$\begingroup\$ @Limiter if you don't experience any losses, maybe try charging the battery the first few times in a well-sealed box (preferably with a 1.5A power supply of course), so that you don't destroy anything if it booms. If it seems to work, I think you can assume there's no problem. \$\endgroup\$
    – user17592
    Dec 18 '14 at 20:35
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Protecting an inadequate power supply from overload is possible using A PTC current limiter or NiChrome heater wire resistance in the range you suggested.

But a far better solution is use an old PC PSU with 20A @12V capability. These tend to cost about $15 http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=3843504&csid=_61&rrpl=item_page.content1&rrstr=ClickCP&rrindex=0

A 5% pre-load is often necessary on the 5V for stability.

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  • \$\begingroup\$ Thanks, I luckily have one oldschool PSU laying around, which I kept, because it's one of these old types, which require no load. This will reduce portability tho :( \$\endgroup\$
    – Limiter
    Dec 18 '14 at 20:09
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Modern battery chargers (especially for the relatively new LiPO batteries) are not a dumb power supplies, but they have a specific time-current pattern, that is maximizing the charging efficiency, protecting the battery and helping it's lifetime. So limiting the current would be a really bad idea.

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