solving others' bad designs

[SceneryDriver]

Just a bit of a vent. Yesterday made me want to spit nails:

I inherited the care and feeding of a large rotating neon sign that's being moved to a new location. Power to the 90VDC motor and neon transformers are fed through a 5-conductor slip ring. Originally installed neon transformers had 120V primaries. No big deal, except the original sign builder was trying to pull almost 23A through slip rings rated for 15A.

Brought this up to the client, and they agreed to swapping the transformers to units with 277V primaries. They also wanted dimming, so we agreed to design a new control panel to accommodate. There were also other voltage supply issues as well (below).

Opened the sign to swap the neon transformers, and ended up doing a complete rewire; line voltage was wired with stripped out SO cord and taped splices, and the HV wiring was held in place with masking tape (UL listed masking tape, I presume).

New location has 208V 3-phase available, but no neutral was pulled. Getting the neutral added at this point is practically impossible. Getting a 277V circuit is even harder. Since we are building a new control panel anyway, we elected to have a custom transformer made to power everything: 277V for the neon transformers, 120V for the DC drive, and 24V for the dimmer module's phase reference.

I ran this by the neon transformer manufacturer, and told them I was planning on ordering my custom transformer as an autotransformer for the 208V --> 277V boost, since it was lighter and smaller that way. Was told this would work fine.

Went to power up the sign yesterday afternoon, and the sign would flash but not stay lit. Called the neon transformer manufacturer, and was told that the neon trafos were tripping on ground fault / overvoltage since neither supply leg was referenced to ground. Apparently, the transformers expect to be connected to a 480/277Y system, and they need one leg as neutral referenced to ground... failed to mention that little detail before I had the custom transformer made.

I now have a beautiful custom transformer that's a beautiful doorstop. I have to call my trafo builder on Monday to see if he can work a minor miracle and fit an isolation transformer in the footprint of an autotransformer, since the panel is already built and installed. On a completely unrelated note, anyone want a nice custom transformer?

I definitely broke out the good bourbon last night.


SceneryDriver

 

[hbiss]

Apparently, the transformers expect to be connected to a 480/277Y system, and they need one leg as neutral referenced to ground...

I would want them to explain how that works. I assume these days that transformers are no longer used. Neon power supplies or drivers are solid state, but why would they be designed to expect to see a neutral referenced to ground? Is it to sense if there is a HV fault to one side of the line feeding it?

-Hal

 

[SceneryDriver]

I would want them to explain how that works. I assume these days that transformers are no longer used. Neon power supplies or drivers are solid state, but why would they be designed to expect to see a neutral referenced to ground? Is it to sense if there is a HV fault to one side of the line feeding it?

-Hal

These aren't solid-state HV supplies. They're big (supposedly) dumb iron-and-copper transformers. They apparently have a protection circuit that will shut down the trafo under two conditions: HV ground fault, and input overvoltage. It apparently senses input voltages with relation to ground, and if it thinks the "neutral" voltage is too high, shuts off the trafo. Why it measures with relation to ground, and not simply voltage between the input conductors, is beyond me.

I emailed my transformer guy this afternoon, and he said can build me a replacement isolation trafo so I can derive ground-referenced 277V from my available 208V, and he can ship by next Wed. It'll even fit in the space I have. He is indeed a minor miracle worker.

Traditional HV neon is a weird beast. I'm used to electrons that are well behaved, and stay in their wires. Electrons that are actively trying to escape the wire and bite me are another thing entirely. There are LED replacement solutions for real neon that look almost as good, but there's really somthing unique about the glow of real neon. No doubt it'll look extremely good when we're all said and done; it's just been a PITA getting everything to work.



SceneryDriver

 

[petersonra]

It doesn't sound to me like it was a bad design at all as it worked for all these years.

I do a fair amount of retrofits of control systems for old machines. There's a lot of weird stuff people do that don't make much sense. I don't get too excited about it I just fix it and make it right. I can't spend a lot of time worrying about why someone did something weird 30 years ago.

 

[Hv&Lv]

It doesn't sound to me like it was a bad design at all as it worked for all these years.

I do a fair amount of retrofits of control systems for old machines. There's a lot of weird stuff people do that don't make much sense. I don't get too excited about it I just fix it and make it right. I can't spend a lot of time worrying about why someone did something weird 30 years ago.

Amen to that...
I do the same to older metering and substation controls. I usually just shrug and say they worked with what they had...
I read a records book that’s filled out on a relay every time a sub control operates or someone inspected this air blast breaker.
We removed the breaker for a new project at this station. It was Installed in 1954. Interesting to read how they came to the substation only to find the substation tripped out, yet no one had called in an outage.

 

[Todd0x1]

Do you have room to add a little 277v 1:1 isolation transformer for the neon, you could bond one leg of its output?

 

[drcampbell]

... (UL listed masking tape, I presume) ...

I'm not aware of listed masking tape, but I am aware of nuclear-grade duct tape.

PC 624 Premium Nuclear Grade Cloth Duct Tape - Shurtape

PC 624 nuclear grade duct tape for the construction, operation and maintenance of nuclear power facilities. Durable, conformable and meets ASME NQA-1.

www.shurtape.com

Doesn't it give you a nice warm feeling inside, knowing that nuclear powerplants are held together with graded duct tape?

... Interesting to read how they came to the substation only to find the substation tripped out, yet no one had called in an outage.

Maybe the same event took out the telephones?

 

[zbang]

Bad design? Maybe not. Bad workmenship? Oh, you betcha.

If it weren't for the shipping cost, I'd consider dropping the now-doorstop on the sign transformer company's rep.

 

[ptonsparky]

It doesn't sound to me like it was a bad design at all as it worked for all these years.

I do a fair amount of retrofits of control systems for old machines. There's a lot of weird stuff people do that don't make much sense. I don't get too excited about it I just fix it and make it right. I can't spend a lot of time worrying about why someone did something weird 30 years ago.

I’m starting to see some of that on my own stuff.
Recent additions to a program. Three groups of motors that should, I think, have been identical in logic, but aren’t. Why I did them differently? IDR. Notes aren’t adequate. Now I’m adding two more sets. I should choose two different logics to make it interesting for the next guy.

 

[Hv&Lv]

Maybe the same event took out the telephones?

Nah. Rural areas did t care as much because they weren’t used to it.
We have an old bill 9n display at the office that says in effect, “my power went out last Tuesday in the storm. When you get a chance, could you turn it back on?”

 

[ptonsparky]

Nah. Rural areas did t care as much because they weren’t used to it.
We have an old bill 9n display at the office that says in effect, “my power went out last Tuesday in the storm. When you get a chance, could you turn it back on?”

My Dad would tell us, they will come around in a day or two, you'll live.

 

[SceneryDriver]

Do you have room to add a little 277v 1:1 isolation transformer for the neon, you could bond one leg of its output?

I don't have room for an additional isolation transformer, but I do have room for a new custom transformer; it will have an isolated 277V winding instead of an autotransformer winding, so I can ground one leg and make the neon trafos happy. My transformer guys is building it and shipping on Wednesday, and it'll fit in the space I have.



SceneryDriver

 

[SceneryDriver]

Bad design? Maybe not. Bad workmenship? Oh, you betcha.

If it weren't for the shipping cost, I'd consider dropping the now-doorstop on the sign transformer company's rep.

The sign was originally intended for use only at a 3-day event. I guess you can get away with passing almost 24A through a 15A slip ring and associated wiring for a few days. Now that it's being permanently installed, that won't work long term.

Thing is, our shop doesn't cut corners like that, 3-day event or not. It doesn't leave our shop if it's not safe. That probably makes us more expensive than other shops, but we also don't have callbacks for something melting while in use. It would've cost the other shop next to nothing to do it right the first time when they built it. It cost a lot more for us to re-hash everything at the last minute.

Don't think sending the transformer to the neon trafo manufacturer hasn't crossed my mind. It's almost 60lbs though. I don't want to pay the UPS charges



SceneryDriver

 

[Todd0x1]

I don't have room for an additional isolation transformer, but I do have room for a new custom transformer; it will have an isolated 277V winding instead of an autotransformer winding, so I can ground one leg and make the neon trafos happy. My transformer guys is building it and shipping on Wednesday, and it'll fit in the space I have.



SceneryDriver

Nice! That's pretty fast.

 

[SceneryDriver]

Nice! That's pretty fast.

He's great!

Universal Transformer Co.

https://utranco.com/

(972) 784-7700

If you need a custom/weird transformer, they're the place to call.



SceneryDriver