Hi Dick,
I believe you are misinterpreting the KVA rating in the table. The KVA refers
to the power dissipated in the load (i.e., your amplfier) and not the KVA
rating of the buck-boost transformer. The actual power rating of the
transformer is just the current through the secondary times the number of
bucking volts supplied.
For example, let's say your actual line voltage is 250V and the amplifier draws
14 Amps, which correspnds to a power rating for the amplifier of 3.5KVA. (That,
by the way, is the peak power. The average power is probably about half that.)
Now suppose you want to reduce the line voltage to, say, 238V, and we'll assume
the amp still draws 14 Amps at this lower line voltage. You are bucking the
voltage by 250V-238V = 12V. The bucking transformer will then have to carry 14
Amps of current, so its power rating will be 12Vx14A=168W. An ordinary filament
transformer with a 240V primary and a 12V secondary rated at 14A would be
perfect for this application. I wouldn't buy the Hammond buck-boost
transformer, because you'll be spending a lot of money unnecessarily. The
Hammond transformers are designed for industrial, continuous duty application
at full rated load. You'd be paying for a lot of capability which you don't
need. Personally, I'd think a 12V filament transformer rated at
10A or more would be adquate for your amplifier.
There is one more consideration, which may complicate things slightly. If your
amplifier is designed for the US market, it may require a neutral line which in
the US is at 0V, with the L1 and L2 lines each being 120VAC (out of phase with
each other). Most likely, that's not the case with a Quadra, but you should
check to be sure. If you do require a neutral line, then you'd need two
filament transformers, each having half the required voltage rating ( e.g. 6V
instead of 12V). It's a minor complication.
In principle, you could also use a Variac,which is an autotranformer, to get
the reduced line voltage, although I don't recommend it. Unlike an ordinary
transformer, which has a primary and secondary winding, an autotransformer has
only one winding. A slider on the winding (or a fixed tap) picks off the
desired voltage. You do not want to use a Variac for your situation, because
the full line voltage appears across the variac, which means you'd need a
variac rated at 3.5 KA. That would probably weigh about a hundred pounds and
would be very expensive. A variac would be gross overkill merely for reducing
the line voltage for your amplifier.
I get the impression, Dick, you are making this a harder problem than it really
is. All you need is a filament transformer whose secondary voltage will drop
your line voltage by a few volts, to get it into the recommended range for your
amplifier. You can probably find a dozen or more suitable transformers on eBay
or QTH.com for well under $50.
73,
Jim W8ZR
From: Richard Solomon [mailto:dickw1ksz@gmail.com]
Sent: Wednesday, June 25, 2014 9:37 PM
To: Jim Garland
Subject: Re: [Amps] Buck-Boost Transformer Selection
I found this web site while looking up how to connect the transformer.
http://www.hammondpowersolutions.com/files/HPS_Catalog_BuckBoost_Section2.pdf
According to it, using it with the Quadra (14 Amp @ 240 vac), I need a 3.5 KVA
Transformer.
That's quite a bit larger than what you say I need.
Still confused ...
73, Dick, W1KSZ
On Wed, Jun 25, 2014 at 10:17 AM, Jim Garland <4cx250b@miamioh.edu> wrote:
Hi Dick,
You don't need a 1.5KV rating. Let's say you want to drop the line voltage
by 12V and suppose the maximum current drawn from the AC line by the
amplifier is 15 Amps. You'd thus need only a 12Vrms/15A transformer (180W).
Because of the limited duty cycle of the Quadra, probably a 10-12A
tranformer would work fine.
73,
Jim W8ZR.
> -----Original Message-----
> From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Richard
Solomon
> Sent: Wednesday, June 25, 2014 11:06 AM
> To: amps@contesting.com
> Subject: [Amps] Buck-Boost Transformer Selection
>
> I have a lead on a late production Quadra so I guess I better
> invest in a B-B Xfmr to get my sometimes 250 volt line down
> to something acceptable to my new little friend.
>
> Question is on the rating for the Xfmr ... I expect I should get
> something rated for the load, say 1.5 KVA (considering the
> rating is for CCS use not ICAS).
>
> Now I find lots of them over on the evil empire, but looking at
> the specs on the label is confusing:
>
> One I found says:
>
> Max Volts 264 Max Amps 62.5 1.5KVA
>
> The current rating does not make sense. How can I sort this out ??
>
> Thanks, Dick, W1KSZ
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|