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Old 9th May 2009, 12:21 AM   #41
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Steerpike, thank you very much for the explanation!

The test resistors were placed after the bridge rectifier.......

mains AC -> capacitor -> rectifier -> resistor

I measured the DC current after the rectifier, not the AC current before it.

My meter is a Fluke 111 and the motor run cap measures 7.45uF with it. AC line voltage is ~119.
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Old 9th May 2009, 03:08 AM   #42
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Quote:
Originally posted by Steerpike


Certainly the capacitor wastes no energy. But safety isolation would require a transformer, and if you are putting in a transformer I think you can do better than a simple resistance charger (which is what the capacitor effectively is, as seen by the battery)

Nickel-cadmium and Nickel-metal-hydride like constant current.
Lead-acid batteries like to be charged with constant voltage; constant current charging them over a long time period shortens their life.

Constant voltage can be achieved very efficiently by means of a switched mode power supply - several ICs exist to do this with minimal support components.

An old AT computer power supply should work - with a small modification to set the voltage.
An AT power supply will not put out enough power for a fast charge. That and modifying it for enough voltage is not something most EV builders would do for the first build, let alone try to build a switcher from scratch. (A typical EV pack ranges from 72v for a compact to over 250v for a large truck, at a few dozen to few hundred Ah.)

Most EV systems are isolated from the chassis to avoid a wire grounding out causing a short circuit. Many cheaper EV chargers are nonisolated switchers as isolation is not required. Just a circuit to verify isolation of the pack from the chassis.

Note that pulse chargers for lead acid batteries are basically current sources that are electronically switched on and off. The idea is to start with a constant current charge until a threshold voltage is reached, at which point the current is modulated as a form of slow PWM. It actually works better than traditional CC/CV charging if implemented correctly.
http://www.duoregen.com/images/PDFs/Ak_Uni_Charging.pdf
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Old 9th May 2009, 05:40 PM   #43
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Ok, I had no idea, and still have no idea what an 'EV' is.
I was thinking 12V 6 cell car battery in connection with an old computer power supply (upping the 5v to 13.8v)
 
Old 9th May 2009, 08:22 PM   #44
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Quote:
Originally posted by Steerpike
Ok, I had no idea, and still have no idea what an 'EV' is.
I was thinking 12V 6 cell car battery in connection with an old computer power supply (upping the 5v to 13.8v)
EV = Electric Vehicle. As in electric cars and trucks.
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Old 9th May 2009, 09:14 PM   #45
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Oh, like a toyota prius? Or is that different & classed as a hybrid? They hardly exist here in Africa!
(We still have leaded gasoline)
 
Old 9th May 2009, 10:00 PM   #46
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This is an interesting thread.I once completely flattened my car battery by leaving the lights on.My charger kept going off on overload,so I hooked up 12V from computer power supply for half an hour.Then the charger could handle it.
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Old 9th May 2009, 11:43 PM   #47
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Sorry to go back on topic...

I tried it with a dead (I mean DEAD ) sealed 12V, 7AH battery. Left it going overnight and presto! It charges now! Load tested it with an 8 ohm dummy and it seems as good as new.

Thanks EWorkshop1708
 
Old 10th May 2009, 03:23 AM   #48
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Quote:
Originally posted by Steerpike
Oh, like a toyota prius? Or is that different & classed as a hybrid? They hardly exist here in Africa!
(We still have leaded gasoline)
Most hybrids, including the Prius, are a form of EV. (Note that some hybrids, such as the hydraulic hybrid and the "Amy Aldrich" gas/water hybrid, are not EVs.)

What I had in mind are homemade EVs, such as this one:
http://jerryrig.com/convert/
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Old 18th May 2009, 08:20 PM   #49
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Quote:
Originally posted by MJL21193
Sorry to go back on topic...

I tried it with a dead (I mean DEAD ) sealed 12V, 7AH battery. Left it going overnight and presto! It charges now! Load tested it with an 8 ohm dummy and it seems as good as new.

Thanks EWorkshop1708
Sweet!!! Your very Welcome!

Did you use a capacitor, or a light bulb?

It's nice to get some use out of dead batteries.

I see how you folks are trying different methods of the high voltage charging. I'm in the process of designing a new one too, that should be safer from error, and runs cooler.

I'm also considering a plan for making a high-current version, with a powerful transformer. I found you can also desulfate an old 12V car battery if you use 3 car batteries in series (36V, hundreds of amps) to charge it with for about 1 minute, until you hear loud bubbling, then it also takes a charge from the charger again.
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Old 8th June 2009, 05:35 PM   #50
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Update on the 120V desulfator charger.....

I built a new one out of different parts, and put it on some batteries.

This new one uses a 4.7uf capacitor on the AC side of the bridge rectifier. I also added a large 4.7ohm wirewound resistor for reverse-battery protection, and a 0.22ohm metal-film resistor on the AC side to act as a fuse under any faults.

I love the new capacitor desulfator. NO wasted heat!!!! No excessive power usage either!

I notice, the capacitor charger has a higher peak current than a lightbulb charger. When you put the clips to the batteries, I get a pop, like a small arc! I guess that's the capacitor charging, and that may help on stubborn batteries. I wonder if the peak pulses from the Capacitor on 60Hz, may desulfate a battery better than a series lightbulb that soaks up most of the energy.

I tried this new desulfator/charger on my lead batteries, but I even fully charged a small Ni-Cd with it. This seems like a rather safe charger, being there's no heat, and it charges with such a low current.

Now this one can be left on for hours and days, without energy waste.
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File Type: jpg desulfatorcap.jpg (17.8 KB, 991 views)
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