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paulz
Member
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# Posted: 10 May 2022 12:14pm
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I tested a few 12vdc wall adapters lately and they show about 17v open circuit. Why?
I have an old Stealth Cam at the house, takes 8 C batteries but also has an external 12v jack, which I have plugged into a wall wart. The batteries have been in there a long time and I noticed two were bulging. For some reason it seems the cam won't operate on just the wall adapter, needs the batteries installed. They were about dead, just put in new ones.
Anyway, just wondering why the wall warts test higher open circuit.
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travellerw
Member
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# Posted: 10 May 2022 06:06pm
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It depends on the design of the circuit. Years ago was the migration to "switched" designs. Essentially the power is turned on and off at a high frequency and smoothed using caps (very simplified explanation).
Depending on how that circuity is designed can affect the "no load" voltage. Cheaper/simpler designs are not stable until an actual load is applied.
Many "wall warts" are designed to be as cheap as possible and I suspect are using those simplified designs.
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gcrank1
Member
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# Posted: 10 May 2022 06:54pm
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The voltage 'pushes' the amps, which are very low in those devices. I suspect without the higher voltage stuff would take forever to charge.
??but I do Not know for sure and certain??
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paulz
Member
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# Posted: 12 May 2022 09:38am
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OK. They are generally used to power things, afaik, not things with batteries, like my camera example above. So no matter how small the current, eventually it will push 12v of batteries to 17v, and maybe explain why those C batts were bulging.
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gcrank1
Member
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# Posted: 12 May 2022 10:08am - Edited by: gcrank1
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Just gotta ask....
Are those batteries actually rechargeables?
Internally it sounds like maybe it needs the battery path to complete the run circuit, not really the battery power; though the bats may provide a sort of damper on voltage from the wart?
The unit specs should give the voltage range for operating the device.
I save up all those wall-warts from stuff I toss, each has input/output specs on it. Using one within your unit specs, jumpered to the bat tray terminals, should run it straight away without bats in.
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paulz
Member
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# Posted: 12 May 2022 10:16am - Edited by: paulz
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No. I'm not sure if they are even being charged by the external jack, or if they switch on if the external power goes out.
Only two of the 8 batteries had bulged, all were weak. If they are connected to the external jack, but never under load, they wouldn't actually be being recharged, assuming voltage was equal. They had been in there a year or two, I just replaced them with 8 more dollar store cheapies.
I'm not too concerned about this particular camera, it works, but more so using wall warts in general for things other than what they came with, and potentially blowing something out with over voltage.
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