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Super Capacitator Charging

JoeBrown

May 14, 2022
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Should this work to avoid blowing up a power supply and killing a 5V Super capacitator.
If I use a 5V Regulator rated for 0.5 Amp. My power supply12V supply and have 24ohm Power Resistor (6W) in line on the input of the 5V Regulator then can I hook up the Capacitator to the output of the 5V Regulator without destroying the regulator? Would the resistor limit the current down the 0.5 amp limit of the regulator?
 

danadak

Feb 19, 2021
182
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Feb 19, 2021
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Most regulators have current and thermal limiting. If the reg goes into thermal limiting
it will oscillate at real low freq because of the thermal time delay inherent in a thermal
mass heating and cooling. Basically reg shuts off, cools down, then turns on again. In
your case it may be the current limit will probably control the feedback loop. So the reg
will charge at the current limit rate.

Many have a stability problem with C loads requiring a minimum ESR in the output C.
So check the datasheet for limitations.

"Normally" one would use a Ilimit R in series with output, so the regulator is always
in control, eg. not in dropout.


Regards, Dana.
 

CircutScoper

Mar 29, 2022
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Mar 29, 2022
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Should this work to avoid blowing up a power supply and killing a 5V Super capacitator...?

No. A 12V supply, even though limited to 12V/24ohm=0.5A, will try (however slowly) to charge your 5V supercap to 12V, which will (eventually) overvoltage and probably destroy the cap.
 

Bluejets

Oct 5, 2014
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No. A 12V supply, even though limited to 12V/24ohm=0.5A, will try (however slowly) to charge your 5V supercap to 12V, which will (eventually) overvoltage and probably destroy the cap.
OP has a 5v regulated output on the 12v supply......
 

JoeBrown

May 14, 2022
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May 14, 2022
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Was looking at this for my 3V 35F Capacitators . and using this 3V Regulator
https://www.digikey.com/en/products/detail/rohm-semiconductor/BA30DD0WT/4004784
My thought was if the Resistor was on the input side it would keep the Regulator from hitting its max current limit all the time while it initially started its charge. Once the Capacitor reached a charge where it's resistance was about 1.5ohm the regulator could safely charge the capacitator the reset of the way and the full voltage drop would be across the capacitator and not shared with another resistor in series on the output. But I was not sure how a resistor on the input would affect the regulator. Or do I need to look at this as power consumed regulator side 3Vx2A=6W and on the 12 volt power supply have a 24ohm resistor = (12V² / 6W), So I would be starving the regulator the needed current. I know just the basics and am trying to understand all the little terms with a regulator. Sorry for the rather newbie questions but this just made sense to me.... at the time. I know resistor and regulators are pretty inefficient way of doing things since all the excess energy is burnt off as heat. Maybe start putting a grilled cheese on top of heat sink for the regulator and put the heat to good use?
 

danadak

Feb 19, 2021
182
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Feb 19, 2021
Messages
182
Be aware of transient behavior of reg on startup, load connect (violating super cap
limits) -

upload_2022-5-15_6-22-48.png

Your datasheet has no graph, I took this one from a generic reg.

Also its operating conditions regarding output C ESR....


Regards, Dana.
 
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