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Re: Ballasting the secondary side of transformers

Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Chris,
Hey, a correction to my previous post. I was looking at the primary side of capacitive ballasting. The secondary side is of course different. Your 4kV output at 240Vac input with 15 amp limit yields 16000 ohms of reactance, so the limiting cap works out to 0.166uF. Certainly changes things. The C value is good but the voltage value would require strings. About 3 caps in series and 5 strings in parallel if using .1uF MOT caps rated at 2000V per cap. 15 total. Then, a 0.166uF value rated for the voltage should ballast to 15 amps ok on the hv side. Certainly possible using cheap multiple MOT caps. 

Take care,
Bart



Barton B. Anderson wrote:


Hi Chris,
Good point! Capacitive ballasting the hv side could be practical for some setups. Considering your 4kV output on the MOTs with say a setup of 240 Vac input with a 15 amp limit, your looking at about 80 ohms of reactance which puts the cap at about 166uF. What value did you use on your hv side and how did you connect it? (curious why the 7A draw open circuit).
A pig limiting to 40 amps would use 6 ohms of reactance, so about 440uF. Of course, it's a fixed ballast, but that's not always a bad thing (certainly can be done). Too bad, I once had about eighty 100uF 1.5KV caps lying around. Might have been able to series-parallel for test. Only have one now. Sadly, I disposed of them and I didn't have can crushers and coin shrinkers in my mind those days (dimensions were around 4"x5"x9"). When you move from Minnesota to California, the burden of heavy garage junk makes for rash decisions. 

Take care,
Bart

Tesla list wrote:


Original poster: "Breneman, Chris" <brenemanc@xxxxxxxxxxxxxx>

Are a resistive ballast and an inductive ballast the only options?
As I said in my last email, I'm trying out a capacitive ballast on the hv side, and it appears to be working. A capacitive ballast is much more feasible on the high voltage end because the capacitance doesn't have to be nearly as large. Also, I think there might be another plus for the hv ballasting, considering my setup in particular. Previously, I was using a MOT with the hv winding shorted as a lv ballast in series with two other MOTs with the primaries in parallel. Assuming that the MOTs have approximately the same inductance (particularly when the hv side is shorted), the ballast MOT will drop about 2/3 of the mains voltage, significantly decreasing the input voltage on the other transformers, and decreasing the output voltage. This is important in a system where a mere 4000 volts is the ideal output voltage. With a hv ballast, the impedance required to limit current to a sane amount should cause much less of a voltage drop. This appears to be the case with me. 
With a setup like this, there is however an additional disadvantage.
With the hv end open circuit, it draws about 7A from the mains, whereas with the lv ballast, it only drew around 3A. Also, considering a hv inductive ballast, could an ignition coil be used? The insulation should be sufficient for the hv, and it should have a high inductance, but I'm not sure what the current-carrying capacity is. 

Chris



-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Sat 4/7/2007 1:53 AM
To: tesla@xxxxxxxxxx
Subject: Re: Ballasting the secondary side of transformers

Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Bart,

Ballasting on either side should be equally effective at limiting the
current.  Of course, on the HV side, the inductance value needs to be
the turns_ratio (n) squared times larger because it has n times the
voltage to deal with and needs to limit the current to 1/n times the
current on the primary.  This assumes an ideal transformer between
the LV and HV ballast points.

LV ballasting:      + smaller inductance needed, lower voltage stresses.
                           - larger current means larger guage.
                           - core is needed to get the inductance and
saturation needs to be considered.

HV ballasting:      + smaller current.
                           - HV insulation needs to be considered.
                           - inductance needs to be n^2 larger.
                           - core is needed to get this larger
inductance and saturation needs to be considered.

These are all of the plusses and minuses that I could think of.  If
others, maybe someone else could chime in and comment on what is said.

Gerry R.


>Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>
>
>Can someone please tell me why we are still ballasting on the LV
>side of Pigs and PT's? This should be easy enough to do for a fixed
>current limit. The costs associated with a LV ballast almost demands
>we do this. The LV side is starting to appear very silly to me at
>the moment. Granted, there are HV concerns, but is it really a big
>deal? I get the feeling LV ballasting is simply convenient. However,
>it is also expensive (unless one builds a ferrite ballast).
>
>Just curious is anyone else has contemplated a high side ballast.
>
>Take care,
>Bart
>
>Tesla list wrote: