AnTek toroid transformers

[Scratchy]

Do a google search for: Toroid Inrush
You will find out why you are chewing up fast blow fuses like halloween candy.
As WithTarragon says, just start it up with a 100W light bulb in series.

BTW, a 20A breaker on a 14AWG household branch circuit is asking for touble.
Your home insurance can be rejected in the event of a fire, even if this was not the actual cause of the fire.

[uzernaam]

well i figured i'd play it safe and proceed one step at a time during my amp build. i started with identifying the transformer coils, then powering them up one at a time, then in parallel and checking output voltages. all with a fuse on my power so that in case something goes wrong, the fuse pops first before anything else could do some real damage.

i guess my question was what fuse rating is normal during startup of a 500 va transformer even with the secondaries not connected to anything.

i'll try the lightbulb idea. my guess is the phase of the input coils may have been wired wrong, or it just sucks up a lot of amps for a split second on turn-on. (probably the latter)

i'll try a slightly larger fuse once i work this out. maybe slo-blow.

[Scratchy]

OK, I've done the Google search for you:

When a transformer is first energized a transient current up to 10 to 50 times larger than the rated transformer current can flow for several cycles. This happens when the primary winding is connected around the zero-crossing of the primary voltage. For large transformers, inrush current can last for several seconds. Toroid transformers can have up to 80 times larger inrush, because the remnant magnetism is nearly as high as the saturation magnetism at the "knee" of the hysteresis loop. This is caused because the transformer will always have some residual flux density and when the transformer is re-energized the incoming flux will add to the already existing flux which will cause the transformer to move into saturation. Then only the resistance of the primary side windings and the power line are limiting the current.

Based on this, your 500VA Toroid can draw up to 320A when first switched on.
Hence the use of soft start circuits for these types of transformers.

[gorgon53]

I just surfed the net to get a picture about todays toroid transformer specs.
There seems to be only a few manufacturers that have:
- decent datasheets
- decent designed transformers.
AnTek seems to be one of the few still left uncorrupted by bad busnes ideas.

Far to many (also earlier decent manufacturers) have toroids that are made like this:
- less copper, more iron, higher op. temp, lousier in almost all respects.
- cheap high loss iron and lower temp grade wire.
For instance a 25year old toroid of a certain manufacturer was rated like this:
160VA, 50Hz, max temp rise full load 46degC, copper loss 12.8W, iron loss 1.1W, wire
max temp 180degC, 1.6kg, Rdc primary, Rdc secundary, measuring conditions a.s.o.

The same manufacturer offers now:
160VA, nom. voltages without reference to regulation, 50-60Hz, copperlosses 24W, wire max. temp 130degC, 1.8kg, produced in India....

- to cover up how much worse those transformers really are they offer not much data
other than the above.

Am glad at least AnTek seems not (yet) go this path. I hope at least those who understand transformers will appreciate that and bring also othere decent manufacturers to our knowledge.

[Scratchy]

Generally you get what you pay for.
If you are shopping on cost alone, then you will likely end up with a crappy xfmr.
I have just one word:
Plitron

[gorgon53]

Plitron is propable ok and they are certainly not cheap.
Looking at the sparse "specification" of the general purpose toroid I would not like to put my money on them. There is really NOT enough info on the datasheet to make any conclusions about theyr performance in an intentended application. I do not like to buy a "cat in the bag" and to decide about a purchase just by looking at the pricetag.