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Old 15th November 2004, 11:28 AM   #1
sdoom is offline sdoom  Germany
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Default Question on charge controllers

I donīt wanna start a new discussion wheather a CAP is useful or not. I use two of them in my car and I found it to be helpful.

But my Caps dont have any fancy electronics or LEDīs . From the values I got from the manf. I think they have real low resistance. My Question is about the autom. charging-curcuits. I found this on the net, can anyone tell me if this is really used by the companies or is it just a DIY-curcuit ?

If so , the FET will add itīs on resistance making the "capacitor-effect" worse. (I know that the FET is used in "wrong" direction, but I heard that it is ok when the FET is fully openend)






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Old 17th November 2004, 04:42 AM   #2
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Default really used?

sdoom,

I've never opened any of the huge car caps, so I can't comment on whether they are actually used. I've only used standard 25v/100,000uF caps paralleled, and I know they don't have any such gizmo.

It seems counter productive. As you say the fet has a series resistance which is probably greater than cap, so it will always 'get in the way'. The slow start is cool, but any fet the manufacturer can afford to put in with the cap is going to add a few tens to hundreds of milliohms of resistance (RDSon), you only have 12ish volts to push current, if the fet adds even 20milliohms (0.02) of resistance it will drop too much voltage for the cap to be useful for currents in the high 10's to 100 amp range, and as you know big amps draw more than this...

So I'm guessing it is not used by the high end car audio people, perhaps one of them can offer some real info...

Stuart
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Old 17th November 2004, 09:51 AM   #3
sdoom is offline sdoom  Germany
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Hi Stuart

Thx for your posting. And this is exactly what I would like to know
I really have no doubt that the cheaper models use curcuits like shown on the picture, maybe thatīs the reason why the cheaper ones fail . Probably better ones use more and very good MOSFETīs , as the resistance of paralleled MOSFETS should drop...... but who knows
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