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  #16  
Old 07-10-2015, 02:31 PM
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Originally Posted by vstech View Post
ok... best advice I can give for use of a charger with a car battery...

use a good quality charger... connect it to the battery before you plug it into the wall, and before you set the amp and voltage settings...

I've never been concerned with unhooking the charger from the car before charging...

but AVOID starting the car with the charger connected and charging. it's best to charge the battery, then unhook the charger, then start the car.
Quality charger is key. Cheap charger will not have the sensing and control logic of better chargers. Also the good charger will have more filtering, resulting in a smoother waveform. Cheap charger will have an ac component riding on the dc which is bad for your battery (and the car electronics).

The advice to disconnect the charger before cranking is solid. If you crank the car with the charger connected, you are effectively throwing a dead short across the charger output.
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  #17  
Old 07-10-2015, 03:05 PM
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Originally Posted by vstech View Post
..............
I've never been concerned with unhooking the charger from the car before charging...
......................
How will the battery get charged if you unhook the charger?
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  #18  
Old 07-10-2015, 03:17 PM
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Originally Posted by jay_bob View Post
Quality charger is key. Cheap charger will not have the sensing and control logic of better chargers. Also the good charger will have more filtering, resulting in a smoother waveform. Cheap charger will have an ac component riding on the dc which is bad for your battery (and the car electronics).

The advice to disconnect the charger before cranking is solid. If you crank the car with the charger connected, you are effectively throwing a dead short across the charger output.
Even the cheapest chargers have short circuit protection, so it's no big deal to crank the engine with the charger connected. I short the leads of my chargers all the time before use to see if it sparks, if it sparks I know it's on, and working.

The thing that you should never do is connect the charger wrong by reversing polarity of the leads. That could potentially fry the charger (if it does not have reverse polarity protection), or fry the alternator (depending on the voltage and current setting of the charger).

Edit: Why is an AC component on the DC waveform bad for the battery?
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  #19  
Old 07-10-2015, 04:28 PM
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Not so much bad for the battery as it is for the electrnics. But a battery is a dc cell, and ac current can overheat the battery.
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  #20  
Old 07-10-2015, 04:29 PM
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Originally Posted by funola View Post
How will the battery get charged if you unhook the charger?
Ha ha... oops
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My drivers:
1987 190D 2.5Turbo
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1987 190D 2.5-5SPEED!!!

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  #21  
Old 07-11-2015, 10:52 AM
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Originally Posted by vstech View Post
Not so much bad for the battery as it is for the electrnics. But a battery is a dc cell, and ac current can overheat the battery.
Where did you get this info from? Personal experience or pulled out of thin air? The old battery chargers with a transformer and selenium rectifiers have a little bit of AC ripple on top of the DC component but that does not overheat the battery. The new electronic chargers without a transformer have less AC ripple but does not charge the battery any better at the same charge rate.
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  #22  
Old 07-11-2015, 11:26 AM
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A battery will be CHARGED if you apply a higher outside voltage to the battery. This is like jumping a car with another battery. If you hook it up long enough then the battery voltage will go up, the jump battery voltage will go down. There will always be some AC ripples on the DC if the charger is plugged into AC unless you have a BIG FAT capacitor there to smooth it out. BIG FAT capacitor is expensive so draws your own conclusion. AC ripple does not hurt the battery so very few manufacturers put a BIG FAT cap in there.

As for AC component superimposed on DC. Actually the new and expensive charger with de-sulphate circuit uses the exact principle. High frequency AC superimposed on the DC to break up the sulphate, if any.
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