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Variac vs. Light Dimmer

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Old 05-02-2010, 10:15 AM
  #1
KW_Counter
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Default Variac vs. Light Dimmer

I hooked a 15 volt 400 mAh walwart into a variac.
I plugged the walwart into a watt meter and plugged
a 2,000 mAh 4 cell NiMh battery into the watt meter.
A used the variac to set the charge current to 200 mAh
based on the watt meter.
This process worked well for a forming charge.
My question: can I substitute a light dimmer for the variac?
I'm not sure what the output of the dimmer is and if the
transformer in the walwart will still work properly.
Thanks,
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Old 05-02-2010, 12:52 PM
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JPMacG
 
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Default RE: Variac vs. Light Dimmer

The Variac is a better choice in my opinion. The Variac will preserve the sinusoidal waveform of the voltage input to the wall wart. The dimmer chops up the input waveform into pulsed pieces of the sine wave. The wall wart may possibly overheat if operated on the chopped up waveform. However, I understand that wall warts with UL listings are designed and tested not to be a fire hazard. I'm not saying it won't work, I'm just saying the Variac is a more appealing solution.
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Old 05-03-2010, 08:40 AM
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Default RE: Variac vs. Light Dimmer

I agree, a variac is a better method.
However, how many people have one?
A quick Google search found a 3A for $45 and a 5A for $109.
I am asking to see if a dimmer is an affordable alternative.
Thanks,
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Old 05-04-2010, 02:40 PM
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richrd
 
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Default RE: Variac vs. Light Dimmer


Quote:
ORIGINAL: KW_Counter

I agree, a variac is a better method.
However, how many people have one?
A quick Google search found a 3A for $45 and a 5A for $109.
I am asking to see if a dimmer is an affordable alternative.
Thanks,
KW_Counter
Yes
Like has been said poor AC waveform but the transformer does not care nor the battery
another but! your wattmater will not give a Accurate data with pulsed current an distorted voltage so the more you decrease the voltage the more error in meters unless you use a scope.

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Old 05-05-2010, 04:15 AM
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mehrshad
 
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Default RE: Variac vs. Light Dimmer

you can't use a dimmer if you have a rectifier and a large capacitor, because the peak voltage is the same.
if you use a rectifier without any capacitor,you can use a dimmer,no problem.
but why you don't buy a digital charger?!

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Old 05-05-2010, 08:36 AM
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Default RE: Variac vs. Light Dimmer

Mershad,
I have a Triton II charger which I use regularly and enjoy.
However, it is a peak detector and not good for doing a "form charge".
Some of the other peaking chargers I have seen have the same issue.
This is a method I came up with out of stuff I already have.

Thanks everyone for your input.
I knew the dimmer would not have a pure sine wave out.
I wasn't sure what the effect would be from it.

Thanks,
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