RS Isolating Transformer

[Mark Hennessy]

Yes, most definitely in phase.

If in doubt, use a lamp limiter

Mark

[Ian E G7OLT]

I use a 1.5V alkaline cell and an AVO meter to check secondary phase.

Connect meter on 1A range to one of the secondaries.

Connect battery to primary (making a note of the polarity) watch the meter. The needle will kick one way as the current starts to flow and the core saturates and the opposite way when you disconnect the battery and the field in the core collapses. Reverse the meter leads and test again. Mark the secondary lead that gives a +ve kick when the battery is first connected.

Connect the meter to the next secondary. Again connect battery to the primary ensuring the same polarity as before. Watch the AVO needle again. Reverse the meter leads and test again. Mark the secondary lead that gives a +ve kick when the battery is first connected.

You've now identified the relative phases of the secondaries. For parallel operation, connect the two marked leads together, for series operation connect the marked lead of one secondary to the unmarked lead of the other.

[pwdrive]

Never used that method, sounds like a good tip.

Lawrence

[Paula A]

All good stuff. I always treat each "side" of any isolating transformer as independent from each other and fuse according to maximum rating on the secondaries. It's bad practice to just rely on one line fuse to protect a transformer from a possible short/overload on the secondary side.

I'm a "rule of thumb" girl with mains.. it's +- 30% anyway and my big valve amp experience has taught me a lot of tricks to "get you home" when psu's go up the spout on the road.. most of them very scary

[Bushbaby]

This might be a stupid question but will I be ok to take earth from the mains side and run this into the earth connection of the secondary side (common earth) or will this be a problem (bang!).

Regards

Rob

[Skywave]

Generally speaking, it is usually wise to arrange all of your kit to be connected to one common earth - this being the incoming mains earth. If you just pause for a moment and consider why the incoming mains supply is furnished with an earth connection - then all becomes very clear.

Al.

[Bushbaby]

Hi Al,
I did think so but I wanted to check before doing anything.

Many thanks

Rob

[Bushbaby]

Hi All,
This evening I've had an opportunity to look at the output from this transformer using a 'scope. I have measured the outputs of the 55v - 0v- 55v on the lhs secondary output connectors (110v output - photos 1 and 2), the 60v - 0v - 60v on the lhs secondary output connectors (120v output - photos 3 and 4) and finally the 60v - 0v - 60v on the rhs secondary output connectors (120v output - photos 5 and 6). If I am correct(?) the outputs on the 120v lhs and 120v rhs appear to be in phase. Do I put a link from what was wired as the +ive lead on the 60v lhs to the -ive lead on the rhs in order to achieve a 240v output.

Thanks in advance

Regards

Rob

       
       
       

[Mark Hennessy]

Hi Rob,

Impossible to say as each trace is of one winding, and the triggering is from the incoming waveform. We need to see both secondaries on the screen at the same time to judge their relative phase...

Cheers,

Mark

[AlanBeckett]

This is where a dual beam scope comes in. Than you can put both outputs on the screen but trigger off one.
What do your other scopes do?
Alan