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Discussion Starter #1
I've used a bad boy charger all last year with my 120
volt system.

Now I'm working a 72 volt bank.

So coming into the AC outlet:

1- on the black wire a transformer that has been
rewired with taps.

2- then both the black and white would go into this
huge variac transformer.

3- then that output would go into a bridge.

4- perhaps put a 5uF cap in series.

---------------------------
Do I have the tapped transformer in the right spot?

I would dial the variac to the correct voltage,
without the batteries connected, and mark those spots.


thanks

Michael Golub

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Discussion Starter #2
mike golub wrote:
> I've used a bad boy charger with my 120 volt system. Now I'm working
> on a 72 volt bank...
>
> black wire to a transformer with taps...
> black and white to huge variac transformer...
> variac output to bridge [rectifier]...
> perhaps a 5uF cap in series...
> ---------------------------
> Do I have the tapped transformer in the right spot?

A variac itself is a tapped transformer, so you don't really need both a
variac and a separate tapped transformer. Your charger could just be the
variac, with a bridge rectifier on its output, and whatever meters,
fuses, fan, timer, etc. you want to be comfortable using it.

There are several ways a capacitor might be used. You can put a big AC
rated capacitor directly across the AC input; it acts as a power factor
corrector, to reduce the AC input current for a given DC output current.
Or, you can put a DC rated capacitor across the output; it acts as a
filter to reduce the ripple current in the batteries. Or, you can put a
very big AC rated capacitor in series with the AC input, to act as a
lossless dropping "resistor".

You might be suggesting that the tapped transformer is not being used as
a transformer, but rather as a tapped series inductor. It has much the
same purpose as the series capacitor -- it acts as a lossless dropping
"resistor" to limit the peak charging current or voltage.

--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in -- Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net

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Discussion Starter #3
Yes that tapped transformer would act as "bonn"
inductor. I'll make it out of an old microwave
transformer. I cut out all the old wires, and then add
new ones. Last time I use 12 gauge, but I guess I can
use smaller wire, because the "E" and "I" plates
absorb the current?

But was I correct that this inductor should go before
the variac, on the black 120vac wire?


You might be suggesting that the tapped transformer is
not
being used as
a transformer, but rather as a tapped series inductor.
It
has much the
same purpose as the series capacitor -- it acts as a
lossless dropping
"resistor" to limit the peak charging current or
voltage.
--- Lee Hart <[email protected]> wrote:

> mike golub wrote:
> > I've used a bad boy charger with my 120 volt
> system. Now I'm working
> > on a 72 volt bank...
> >
> > black wire to a transformer with taps...
> > black and white to huge variac transformer...
> > variac output to bridge [rectifier]...
> > perhaps a 5uF cap in series...
> > ---------------------------
> > Do I have the tapped transformer in the right
> spot?
>
> A variac itself is a tapped transformer, so you
> don't really need both a
> variac and a separate tapped transformer. Your
> charger could just be the
> variac, with a bridge rectifier on its output, and
> whatever meters,
> fuses, fan, timer, etc. you want to be comfortable
> using it.
>
> There are several ways a capacitor might be used.
> You can put a big AC
> rated capacitor directly across the AC input; it
> acts as a power factor
> corrector, to reduce the AC input current for a
> given DC output current.
> Or, you can put a DC rated capacitor across the
> output; it acts as a
> filter to reduce the ripple current in the
> batteries. Or, you can put a
> very big AC rated capacitor in series with the AC
> input, to act as a
> lossless dropping "resistor".
>
> You might be suggesting that the tapped transformer
> is not being used as
> a transformer, but rather as a tapped series
> inductor. It has much the
> same purpose as the series capacitor -- it acts as a
> lossless dropping
> "resistor" to limit the peak charging current or
> voltage.
>
> --
> Ring the bells that still can ring
> Forget the perfect offering
> There is a crack in everything
> That's how the light gets in -- Leonard Cohen
> --
> Lee A. Hart, 814 8th Ave N, Sartell MN 56377,
> leeahart_at_earthlink.net
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>

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Discussion Starter #4
I've been using a bridge & variac for years as a charger. Is there any
problem with ripple? Do I really need to put a capacitor in to smooth it
out? Lawrence Rhodes....

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Discussion Starter #5
mike golub wrote:
> Yes that tapped transformer would act as "bonn"
> inductor. I'll make it out of an old microwave
> transformer. I cut out all the old wires, and then add
> new ones. Last time I use 12 gauge, but I guess I can
> use smaller wire, because the "E" and "I" plates
> absorb the current?

The wire still needs to be sized big enough to carry the required
current without getting too hot. #12 is good for around 20 amps open
air, but less if it is all bundled tightly together.

> But was I correct that this inductor should go before
> the variac, on the black 120vac wire?

If it's before the variac, the inductor sees higher voltage and lower
current; therefore it needs more turns of smaller wire.

If it's after the variac, it sees more current and less voltage (because
for your 72v pack, the variac is stepping the voltage down and the
current up).

Since you don't really know what inductance you'll get except by trial
and error, just make an educated guess and try it! :)
--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in -- Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net

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