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• ## Re: [Electronics_101] Re: HV measurement?

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• ... -=-=-=- Here they are: http://www.tinyuploads.com/images/94bOVy.jpg There s *two* of them. I m not sure I have anything with current capability at 12 vac
Message 1 of 18 , Mar 1
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> Excellent idea. However, expect 12AC in to give 270 Vac out.
>
> Good thinking.
>
> Larry

-=-=-=-

Here they are:

http://www.tinyuploads.com/images/94bOVy.jpg

There's *two* of them.

I'm not sure I have anything with current capability at 12 vac to drive these...

Dave
• ... The inductance may be quite large, so it may not take much current to drive the primary. Just try any low voltage transformer you may have at hand. Radio
Message 2 of 18 , Mar 1
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>
> I'm not sure I have anything with current capability at 12 vac to drive
> these...
>

The inductance may be quite large, so it may not take much current to drive
the primary. Just try any low voltage transformer you may have at hand.
Radio Shack has some.

[Non-text portions of this message have been removed]
• Ahh, no problem. Since 12 V is 1/10 of nominal voltage, I suspect a 2 A 12 V transformer will be adequate. Radio Shack may have such a transformer. Even if
Message 3 of 18 , Mar 2
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Ahh, no problem. Since 12 V is 1/10 of nominal voltage, I suspect a 2 A 12
V transformer will be adequate. Radio Shack may have such a transformer.

Even if it is loaded down, you measure the voltage going in and out of the
transformer. So it drops to 2 V, just move a little faster before the 12V
transformer heats up. Ratio is the same independent of the input voltage.

Larry

From: Electronics_101@yahoogroups.com
[mailto:Electronics_101@yahoogroups.com] On Behalf Of Dave C
Sent: Saturday, March 02, 2013 12:59 AM
To: Electronics_101@yahoogroups.com
Subject: Re: [Electronics_101] Re: HV measurement?

> Excellent idea. However, expect 12AC in to give 270 Vac out.
>
> Good thinking.
>
> Larry

-=-=-=-

Here they are:

http://www.tinyuploads.com/images/94bOVy.jpg

There's *two* of them.

I'm not sure I have anything with current capability at 12 vac to drive
these...

Dave

[Non-text portions of this message have been removed]
• What is the function of the cap banks being switched into the HV circuit? http://www.tinyuploads.com/images/zM9dUJ.jpg Thanks, Dave [Non-text portions of this
Message 4 of 18 , Mar 2
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What is the function of the cap banks being switched into the HV circuit?

http://www.tinyuploads.com/images/zM9dUJ.jpg

Thanks,
Dave

[Non-text portions of this message have been removed]
• ... They control the amount of current going through the UV lamp. i=C dv/dt. More capacitance - more current - more power into the lamp. One could replace
Message 5 of 18 , Mar 2
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On Sat, Mar 2, 2013 at 2:01 PM, Dave C <davec2468@...> wrote:

> What is the function of the cap banks being switched into the HV circuit?
>

They control the amount of current going through the UV lamp. i=C dv/dt.
More capacitance -> more current -> more power into the lamp.

One could replace the capacitors with resistors, but the resistors would
waste a lot of power as heat. The capacitors don't waste power.

[Non-text portions of this message have been removed]
• Transformers have a specification that is known as magnetizing current ...it takes X amount of current to make all the eddycurrents in the core happy @ a
Message 6 of 18 , Mar 2
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Transformers have a specification that is known as "magnetizing
current"...it takes X amount of current
to make all the eddycurrents in the core happy @ a given
voltage/frequency...

That might be more than a typical Radio sHack xfmr can supply; measuring
the output V of the RS xfmr would
be a minimalist way of checking that it was, in fact, overcoming the
magnetizing current requirement.

Randy

On 3/2/2013 1:21 AM, Jan Kok wrote:
>
> >
> > I'm not sure I have anything with current capability at 12 vac to drive
> > these...
> >
>
> The inductance may be quite large, so it may not take much current to
> drive
> the primary. Just try any low voltage transformer you may have at hand.
> Radio Shack has some.
>
> [Non-text portions of this message have been removed]
>
>

--
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[Non-text portions of this message have been removed]
• Dave, Why do you want to measure the transformer output voltage? Is the lamp not turning on, and you re wondering if the transformer is OK? If you are in the
Message 7 of 18 , Mar 2
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Dave,

Why do you want to measure the transformer output voltage? Is the lamp not
turning on, and you're wondering if the transformer
is OK?

If you are in the US, you have ready access to 120VAC. You could put 120VAC
into the primary and expect 675VAC out. Maybe a bit more if the output is
unloaded. Some meters will measure 750VAC directly without needing a high
voltage probe.

If you want to measure the floating transformer output under normal
operating conditions, you could use TWO high voltage probes, or the
equivalent homemade voltage dividers. Make sure to GROUND the bottom ends
of the voltage dividers, connect the inputs of the voltage dividers one to
each output of the HV transformer, and measure the voltage between the
outputs of the two voltage dividers.

Note that you don't need super high megohm resistors for the voltage
dividers, because the current you will draw is insignificant compared to
the currents normally flowing in the circuit. For example, you could use a
10 Meg 1% 1W resistor and a 10K 1% resistor to get a 1000:1 2% divider.
Just check the maximum working voltage spec for the input resistor is
substantially greater than the voltages you expect to see -- and stand back
when taking measurements anyway!

If the lamp is not working properly, describe the symptoms and we'll try to
diagnose it.

On Fri, Mar 1, 2013 at 8:36 AM, Larry Beaty <lbeaty@...> wrote:

> Excellent idea. However, expect 12AC in to give 270 Vac out.
>

Really? I would expect about 67.5VAC out. (Remember, normal input is
480VAC.)

[Non-text portions of this message have been removed]
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