filament tx problem

[dave dove]

just bought cheap 12v tx
to supply heavily regulated filament power
only problem is:
it's got two 12v secondaries....
if i'd known i would have bought 6+6
can i use just one secondary
without causing problems?

dave

[John Caswell]

Hi Dave,
Yes is the answer, but why not just parallel up the two secondaries, making sure that you get "start" to "start" and "finish" to "finish" connected together. If you get them wrong them the transformer will hum and get hot fairly quickly, so put a DMM on them before you switch on.

Regards

John aka Dr John

[dave dove]

hi john

thanks for that
each secondary is rated 2A
will that double the current rating?
what am i looking for on DMM?

dave

[Clive]

If you've wired them out of phase you'll be looking at a short circuit, if not then about 12V. 50/50 chance unless you can spot some clue about the windings.

[dave dove]

walked the dog
thought a bit
if i attach a load
to each secondary
and then measure
i'll get either -ve or +ve reading
presume i just match them up....

dave

[John Caswell]

Hi Dave,
No all you will get is a 12Vac reading so if the windings are not marked start and finish it is pot luck, therefore mark one of the wires from each pair then connect the marked pair together, and the unmarked pair together. Place your DMM acoss the pairs set to 20Vac connect mains, switch on. Should give you about 12-14Vac. If it is lower than 12Vac, swap one pair of ends over and recheck. When happy that you are getting 12Vac mark both pairs correctly.
As the windings are 12V @ 2A in series you will get 24V @ 2A, in parallel you will get 12V @ 4A

John aka Dr john

[dave dove]

thanks john

dave