Reduced voltage starter

[fsck]

Does any vendor still sell resistive reduced voltage starters? I seek same to limit inrush surge on a large transformer.

This is 3 phase 208, FLA of ~50A application.

Thus far, I can't find a source: be it new, NOS or refurb.

Many vendors have tried to sell me SCR-based "soft-starters" but when pressed, admit such limits RMS, not instantaneous i. [I'm not sure how a SCR-based system could ever do so...]

 

[ozmosis]

I would have said a time delay relay and a resistor is common practice for this but wondering if your 208V/50A transfomer is what you mean by a large transformer.

 

[fsck]

Nope, It goes thus:

[120V NTE 40A source]->-[120/208:277/480v@15KVA]-->--[480:208/120@112.5KVA]

It's the latter I'm concerned about.

I have resistors [aka immersion heaters] staked out, and as for time delay, all we need is 3-5 cycles. That's less then the pickup time of an undelayed contactor...

 

[JohnWaa]

Autotransformer style won't do? AB still sells these.

 

[fsck]

I don't know how to predict the inrush of those; after all, they are transformers themselves. The resistors just solve the issue.

 

[JohnWaa]

Yeah, I didn't think so.

I think these guys might also deal in AC reduced voltage starters. Look on their projects page (they advertise that they refurbish old starters). It doesn't hurt to ask.

http://www.dccontactors.com/index.html

These guys might be able to build you something.

http://www.milwaukeeresistor.com/specialty.htm

Just curious, why don't you just build your own? They're pretty much dead simple. We used to stretch out larger fence springs and mount them to a phenolic board for our reduced voltage starters in the elevator business.

 

[fsck]

{dc contactors}

Interesting; I was just starting to see where the DC SSR technology now is; can we switch the 230VDC/~5A PV output with same or do I need relays.

Just curious, why don't you just build your own? They're pretty much dead simple.

That was my plan. And your reference to the resistor company is a big help. (Closer than the company I found in India; but not as cheap as the 2500W@120V heaters I found for $2.95 each.)

But the electrician is not at all sure how the AHJ will react to such, and recommended we find something looking more everyday ordinary. [I leave it to you code gurus to expound on what rules apply inside a closed 208V switchboard.]

 

[JohnWaa]

can we switch the 230VDC/~5A PV output with same or do I need relays.

It's DC, I don't see why not...

But the electrician is not at all sure how the AHJ will react to such, and recommended we find something looking more everyday ordinary. [I leave it to you code gurus to expound on what rules apply inside a closed 208V switchboard.]

Well, if you get it from a company like Milwaukee Resistor, then they will be able to point you in the right direction. But basically you will have to fuse it and enclose it inside a case or behind a plexiglass cover to keep it out of way of wandering fingers.

Milwaukee Resistor might also have a UL inspector available to look over the design, that's what one company I used to work for did. He would come out and inspect our panels before shipping them off to the jobsite.

 

[fsck]

It's DC, I don't see why not...

AC is easy to switch; use a SCR/Triac and it turns itself off for you half a cycle later.

With DC, it's a lot harder. I guess you now use high power IgFETS that didn't exist when I took the course. For years, there were GTO's but they are hardly "easy" to shut off.

 

[ScottyUK]

You might want to give Baldwin & Francis in the UK a call. They have the Reyrolle Belmos company somewhere in their family tree from NEI days and may still have some of the old designs. B&F don't do cheap very well, but they certainly do quality.


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If we learn from our mistakes I'm getting a great education!

 

[waross]

Instead of imersion heaters, which will only be approved when imersed in an approved hot water tank with approved overtemperature controls, why not use cheap and dirty strip heaters from chromalox?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[fsck]

why not use cheap and dirty strip heaters from chromalox?/

Oh, I likely will, if they makes ones sized for our use. But the immersion heaters are cheap enough to use/abuse while testing.

What would be best would be something like

http://www.milwaukeeresistor.com/brenclosures.html

I suspect.