[Amps] Transformer heating (problem?)

[Carl]

A Variac would be a big help here.

Then place a 100W bulb across the secondary with an AC ampmeter.

Also use a meter in a 240V leg.

Then crank up the voltage until the bulb has about normal brilliance. 
Record meter readings, do the math to calculate efficiency.

If youre close to a transformer company have them reassemble if they 
concur its an assembly issue.

Carl
KM1H
----- Original Message ----- 
From: "David Craig" <davidhcraig at verizon.net>
To: "Jim W7RY" <w7ry at arrl.net>; <amps at contesting.com>
Sent: Thursday, February 12, 2009 12:47 AM
Subject: Re: [Amps] Transformer heating (problem?)


>    Hi Jim,
>
>    Purchased it from WA1JOF about 2 years ago when I started this 
> project-
> I can't recall if he ever used it, though I doubt it given the severe
> current loop problem it had when I powered it up the first time.
>    Is a "Heritage", marked 240V on the primary & "common", "2800", 
> "2875",
> "2925" & "3000" on the secondaries.  I have not checked primary 
> current draw
> on it, but with some work placing a meter between the transformer 
> primary &
> the relay/filament/etc I could do so.  Guess that is the logical next 
> step,
> though it obviously is drawing more than the few mils from the 
> equalizers &
> the dropping R given the heat.  It does this every time I power it up, 
> or at
> least I presume so given that I have only had it online for a couple 
> weeks
> and isn't on much given that 6m isn't exactly open regularly this time 
> of
> yr.
>
>    73 Dave
>
> ----- Original Message ----- 
> From: "Jim W7RY" <w7ry at arrl.net>
> To: "David Craig" <davidhcraig at verizon.net>; <amps at contesting.com>
> Sent: Thursday, February 12, 2009 12:18 AM
> Subject: Re: [Amps] Transformer heating (problem?)
>
>
>> What is this transformer's history? Where did it come from? What was 
>> it
>> used for? Some sort of intermittent duty type of device like an 
>> industrial
>> welder or similar? Is it really 240 volt primary? How much current is 
>> it
>> drawing on the primary when it does this?
>>
>>
>>
>> 73
>> Jim W7RY
>>
>>
>>
>>
>> ----- Original Message ----- 
>> From: "David Craig" <davidhcraig at verizon.net>
>> To: <amps at contesting.com>
>> Sent: Wednesday, February 11, 2009 8:37 PM
>> Subject: [Amps] Transformer heating (problem?)
>>
>>
>>>    Corollary to a previous issue with a B+ transformer I passed thru 
>>> the
>>> group a while back, which before I repaired it had a current loop 
>>> due to
>>> bad/no insulation on the core bolts.  Transformer has a 240V 
>>> primary,
>>> 2800-3000V secondary rated at 2 amp CCS.  Is installed & in use on a 
>>> HB
>>> GS35b 6m amp.  When "module" testing the amp the transformer taps 
>>> met
>>> specs, measured with a Simpson 260.  Calculations based on 
>>> measurements
>>> then indicated a 12.5 to 1 ratio.
>>>    Fast-forward to completed amp...After some occassional use (~30
>>> minutes of total operating time) am having the following "issues." 
>>> The
>>> 3000VAC secondary tap is now only putting out 2700VAC with line 
>>> voltage
>>> measured at 243VAC  (240V mains line is 10 guage wire, a 10 ft run 
>>> from
>>> the breaker box & then 6 feet of 12 guage line to the amp... 
>>> original
>>> measurement taken with same lines).   The even more disconcerting 
>>> problem
>>> is that after a couple hours of sitting at "idle" (amp on, power to 
>>> B+
>>> but no RF) the transformer iron is getting hot- enough that you 
>>> wouldn't
>>> want to keep your hand on it for long, and particularly so near the 
>>> left
>>> & right sides of the core. (Yes, I checked the plate meter & no 
>>> current
>>> thru tube, bias relay fine).
>>>     Lamination bolts remain cold so no more current loop around the
>>> mounting brackets....   I am baffled as to why this thing is getting 
>>> hot
>>> just idling.  There is no "bleeder" per se on the PS, just 6 x 220k 
>>> ohm
>>> Rs across each of twelve 450V caps in series.  The only other 
>>> constant
>>> current draw is a 5 MEG dropping R to the B+ meter.  I am baffled as 
>>> to
>>> why the transformer laminations would get hot with almost no current
>>> draw, and am concerned that once I really work this thing out during 
>>> a
>>> contest or Es opening the heat is going to short the secondaries.
>>>    Any ideas as to what could be going on?  Is this normal, or as I 
>>> am
>>> beginning to think, an 86 lb misdesigned piece of junk??? Any input
>>> appreciated.
>>>
>>>    73 Dave N3DB
>>> _______________________________________________
>>> Amps mailing list
>>> Amps at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>>
>>
>>
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>
>
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