[Amps] Plate transformer current unknown

[Will Matney]

Angel,

One last thing, since that core is that big, measure the thickness of an outside leg. A 4 inch core shows a 2 inch leg, and a 3 inch core shows a 1-1/2 inch leg. We might be able to tell from it then.

Best,

Will

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On 5/3/05 at 1:38 PM Will Matney wrote:

>Angel,
>
>If the transformer stack is 11" wide X 9" high then about the closest
>thing to a standard EI lam is a 4(3)MH which has a 4 inch center leg and
>is 10" high X 11-1/8" wide. Now if the stack is 10" deep, that makes 4 X
>10 = 40 square inches. That sounds a little big to me though as generally
>a rectangular stack is used mostly which would have been 4 X 8 inches or
>36 square inches of core area. Anyhow, lets work this backwards;
>
>a = 0.16 X sqrt P
>
>P = a / 0.16 ^2
>
>40 sq in / 0.16 = 250 then 250 ^2 = 62,500 watts. (12 kilogauss at 60 Hz)
>36 sq in / 0.16 = 225 then 225 ^2 = 50,625 watts. (12 kilogauss at 60 Hz)
>
>One should note, I'm not sure as I didn't go back and check, I may have
>wrote 0.61 for the formula where it should be 0.16. Sorry about that if I
>did.
>
>The turns per volt will roughly be 5 / a or 5 / 40" = 1/8 TPV, and 5 / 36"
>= 3/16 TPV.
>
>Something dont sound right about those measurements for the core, double
>check those and only measure the core itself (lamination stack W X H X D)
>as the depth is what I thought about. The next stock lam is a 3" but RCA
>could have had a custom made like a 3-1/2" leg. For 3-1/2" at 10" deep
>would be 35 sq in., and for a 3" leg, 30 sq inches. 3-1/2" would be 47,850
>watts and at 3" would be 35,156 watts. An approximate weight using a 10"
>stack with the 4(3)MH lam would be 258.75 pounds. By your dimensions
>given, maybe 200 pounds. If it's that big, it may well be this size in kVA
>or in watts.
>
>3000 x 1.414 = 4242 VDC. 50,000 watts / 4242 VDC = 11.75 amperes (with no
>losses).
>
>Assuming a 5% PS loss, 11.75 X 1.05 = 12.34 amperes.
>
>Keep in mind thought that the lead size will be in conduit rating for
>amperes. Here, 18 gauge is 13 to 18 amps for chassis wiring.
>
>Remember that these figures are ballpark ones and not exact.
>
>Best,
>
>Will
>
>*********** REPLY SEPARATOR  ***********
>
>On 5/3/05 at 12:05 PM Angelo Karabetsos wrote:
>
>>I am unable to calculate anything to do with windings or core due to the 
>>fact it is in a metal case encapsulated in black epoxy. I discovered this 
>>after removing the lid. I'll say one thing, it's darn heavy and hard to
>>move 
>>around without anywhere to grab. The secondary wire gauge looks to be
>>about 
>>18ga and the dimensions are 11"x9"x10" and has a RCA nameplate. Not too
>>much 
>>more information I can determine. Now I know what to look for at flea 
>>markets.
>>One other question. What should the B+ voltage be after rectification.
>>Lets 
>>say 3000v secondary through a fullwave bridge rectifier and a bank of ten 
>>470uf 450v caps? I read somewhere to multiply by 0.9 and that should be a 
>>good rule of thumb. What I am trying to determine is how to calculate the 
>>proper transformer for the job and keep voltage drop under load to 
>>respectable figure. Not an easy task to figure out with surplus parts.
>>
>>Angelo
>>
>>>From: "Will Matney" <craxd1 at ezwv.com>
>>>Reply-To: craxd1 at ezwv.com
>>>To: amps at contesting.com
>>>Subject: Re: [Amps] Plate transformer current unknown
>>>Date: Fri, 29 Apr 2005 11:28:25 -0400
>>>
>>>Angelo,
>>>
>>>Really you cant tell that way (using the resistance) unless you know
>>the 
>>mean lenght of turn, how many turns per layer, and how many layers they
>>are 
>>in the winding. This then would give you how long the wire is and you
>>could 
>>then use the resistance and the length to determine the wire size. If
>it's 
>>possible to use a micrometer or a wire gauge to see what the secondary
>>wire 
>>size is, then one can find out what its rating is. In amateur service,
>>ICAS 
>>used anywhere from 700 to 900 circular mils per ampere. CCS uses anyhwere 
>>from say 1000 to 1200 cir. mil. per amp. If you can find the wire size,
>go 
>>look at a wire chart for how many circular mils it has and divide by the 
>>above numbers to determine its current carrying ability. IE, 10,000
>>circular 
>>mils running at 1000 cir mil per amp = 10 amperes.
>>>
>>>Best,
>>>
>>>Will
>>>
>>>
>>>*********** REPLY SEPARATOR  ***********
>>>
>>>On 4/29/05 at 3:01 PM Angelo Karabetsos wrote:
>>>
>>> >I would like to find out the current rating of a transformer. 
>>Primary
>>> >voltage taps 0v-110v-115v-208v-230v and secondary taps  
>>3450v-0v-3450v and
>>> >secondary resistance of 53.5ohms from 0v to 3450v tap and
>107ohms 
>>from
>>> >3450v
>>> >to 3450v tap. All measurements done with a simple DMM. The 
>>commercial
>>> >amplifier it came out of has a plate current meter with a max 
>>reading of
>>> >600ma. How could I find out the CCS or ICAS rating?
>>> >Cheers Angelo
>>> >
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