[Amps] Plate transformer current unknown

[Will Matney]

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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