connex electronic soft start questions

[BigE]

I hear that the designer of the connex electronic soft start posts here.... or maybe someone can help that has experience...

I'm trying to implement a soft start circuit for a 2.4KVA Toroid. This is going to provide isolated/balanced power -- nothing more.

I've seen a bunch of designs, and the relay with either resistors or NTC thermistors look the simplest to implement.

Being lazy, I spotted a product, which claims to limit inrush to 8A, and operates at a max of 24A at 120 volt -- these specs appear to do the trick for the 2.4 KVA toroid.

Connexelectronic

Would this device work for me? or, should I roll my own, and risk blowing stuff up? I'm fair with a soldering iron, but I've forgotten most of my University electric stuff. Consider me a newbie....

The spec sheet for the transformer I am using is here:

http://shop.plitron.com/specs/901600.pdf

Any help pointing me in the right direction would be most appreciated.

[Atilla]

It looks decent to me - solid relays, series of thermistors, standby trafo, even comes with a decent manual. You should be fine with that one, but you'll still need to rate your fuses accordingly.

[BigE]

How would I rate the fuse? Since I will be plugging it into a 15A line, do I use a 15A fuse?

Can I just change the outlet and breaker to 20A? It's a dedicated line....

Is there a schematic for it anywhere?

I don't think I can buy a 30A relay for that money.....

I know, too many questions.

[Atilla]

It all depends on your current draw. 2400VA/110V -> maximum current draw under load.

But that's a lot of current. And also higher than the max current of the thermistors in that Connexelectronic board. What are you making, that requires 2.4kVA transformer?

[peranders]

With an external resistor you may use my design but the condition is that the continious current never exceed the rating of the relays which is 8 or 10 amps. It's also worth noticing that you will problably break the circuit with no output.

[AndrewT]

Originally Posted by BigE

I'm trying to implement a soft start circuit for a 2.4KVA Toroid. ................... I spotted a product, which claims to limit inrush to 8A, and operates at a max of 24A at 120 volt -- these specs appear to do the trick for the 2.4 KVA toroid.

what is the normal maximum current of this transformer?
Do you have a supply that can meet that demand?

Does the transformer have dual primaries to allow operation @ ~230Vac?

[BigE]

I am using it to supply balanced/isolated power to my system, a la equitech,.

specs are here:

http://shop.plitron.com/specs/901600.pdf

Yes, it has dual 115 primaries for 230 Volt operation, among others..... Secondaries are 60-0-60. The original thought, was for the unit to have 5 independent balanced outputs, each capable of delivering 4.15 amps.

[AndrewT]

Hi,
then wire it for 230Vac connection.
The maximum primary current is ~ 2400/230 ~10A.
With 230Vac you need ~23r to limit the start up current to ~10A.
20r would do and allow close rated fusing @ 10A.

A cold CL60 is ~15r. A pair of these in series feeding the series connected primaries would also do the softstart function and still allow close rated fusing @ 10A

If you choose to connect it as a 115Vac transformer you need a 21A supply.
Does your internal wiring and socket outlets support a 21A supply?

[savvas]

I've ordered 2 pcs and they arrived in about a week (no custom's taxes etc). Come Monday I'll have them installed. I'm using 2 x 700VA trafos
You could also try this cheaper one (30A) although I don't if it has the remote function of the connex

[savvas]

After some hours of testing I can say that this circuit works as it supposed to do. Strange enough when is not active (powered with switch in off position) and no load is applied it outputs 230V. Well I ain't gonna worry about that 'cause when my big toroids (700VA) are connected it works perfectly.

I surely can say that because I had a problem with toroids shutting down my house fuse. So far so good...
Currently I'm using it with a simple toggle switch but any low voltage low current switch will do (I'll put a Bulgin switch later on). There is also a remote control feature.
I don't know how many watts it drows (when powered it outputs ~1.1V when not active/off) but I'm gonna put a rocket switch before it anyway.