Reducing power on a heating element 1

[aboynamedclint]

I am the chief engineer on a 150+ foot yacht which has a Jacuzzi installed on the top deck for the owner to use at his liesure. The Electricity provided to the bus by the Gensets is 208Vac, 3 phase, and the Main breaker in control panel is 3 phase as well. There is a 12 kW (rated for 230/400 Vac) heating element in the water stream to warm the water, which keeps tripping the thermal overload protection every time it comes on. It is also distorting the schedule 80 PVC pipework causing it to sag and bend down stream. The element itself is wired delta with each phase connected to 3 of 6 legs, and each leg bridged to another. The ground is connected to the case. How do I re-wire the element in a wye configuration to reduce the voltage/ power though the element? As I understand it, the element will use less power and take longer to heat the water, but will not trip the thermal protection. I've read this thread (thread238-135327) and these guys seem to understand this a lot more than me, I hope you can help!

 

[Skogsgurra]

Your picture shows three heating elements connected in delta, just as you said. To connect in wye, remove the straps and leave the wires where they are.

Then re-arrange the straps so that they go from the three now free connections towards the center and connect them together there. The geometry should make that possible since you will be working with likesided trangles.

Make sure that the center connection is well insulated from the tube visible in the center of the picture.

Make an insulation check before applying any voltage to the heater.

Good luck!

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[aboynamedclint]

Hi Gunnar,

Thanks for the reply but the center connection isn't a connection at all. It is a hollow tube for the thermostatic protection probe. I only have a ground terminal visible near the top. Are you suggesting that I take the three now free connections and join them together separately?

 

[aboynamedclint]

Hi Gunnar,

By reading your message again, and studying the picture futher, if I joined L1-red, L2-white, and L3-blue on the left side, and bridged red-white-blue on the right side, is that effectively what you suggested?

 

[itsmoked]

aboynamedclint; Like this.



Keith Cress
kcress -

http://www.flaminsystems.com

 

[aboynamedclint]

Problem solved!! thanks guys! for the record, I bridged the three legs on the left side using two of the copper bridge bars, and put the live legs to the other sides. Turned out much neater (and safer) than joining three wires in tge centre. Thx again!

 

[Skogsgurra]

Smoked: Thanks for running the store while I was out. It is Sunday, after all, and even I need a few hours off now and then.

aboynamedclint: I think you got it, even if your descriptions sounds somewhat alarming. Yes, I meant the three bars (I called them straps) to be connected to each other in the center. They will meet neatly right above the tube for temperature transducer and the junction shall be isolated from that tube. Any other way of connecting the three elements in a star connection is OK. The one Smoked sketched is also right, but I have no idea why you moved one of the incoming wires from one terminal to the other (identical) terminal? To avoid contact with the tube?

aboynamedclint: Please show us a picture of what your connection looks like now. We are resposible people and do not want anything to go wrong. Also, we do not want angry phone calls during nights.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[itsmoked]

On my sketch I had to move one wire because otherwise one element was not going to be hooked directly to a phase with the straps removed. (The red element had wires going to both physical ends of it.)

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Skogsgurra]

Yes! I see that now. The guy that installed it first time didn't bother to do a "nice" installation. Good catch.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[itsmoked]

Well that fits.. with a system that as wired from the factory allows the PVC piping to start melting.


BTW aboynamedclint, if there is some reason the flow has been reduced then you will have this same issue. I would be checking for flow obstructions, or limitations, caused by a failing pump impeller or clogged filter, etc, as typically factories aren't shipping systems that spontaneously melt.

Further if the water is hot enough to let the plastic melt it may be entering the hot tub hot enough to injure someone this to could happen if the flow drops for some reason.



Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Have you done a continuity check on the elements? It does make a difference when changing connections. If the start and end of each element are across from each other then you have connected it correctly.
If the end of each winding is beside the start you will have to use itsmoked's diagram.

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

 

[waross]

Please read my last sentence as
"If the end of each winding is beside the start you may want to use itsmoked's diagram." It will give a symmetrical connection.
You may have one element only in use instead of three elements at reduced power. Either way, the output will be about 1/3 of the original.

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

 

[itsmoked]

Hi Bill. You lost me.
If you look closely at the picture you will see that both ends of each element are color coded with a colored ring. They don't come back next to themselves but across from each other.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

My bad. Based on the colors,I think that your diagram will work, but white and white are the only pair directly across from each other. I make it 4 combinations of three adjacent terminals bridged will work and 2 combinations will not work. Bridging with the existing straps appeals to me when it is possible. I would be happier checking continuity.
Did I see it right or should I give up and go to bed? LOL.

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

 

[itsmoked]

GO to bed...

Keith Cress
kcress -

http://www.flaminsystems.com

 

[aboynamedclint]

Here is a close-up of how I ended up wiring it, much neater and safer than three joined wires in the centre.

 

[itsmoked]

Ah that works.
Thanks for the picture.

Carry on.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[aboynamedclint]

And here is a wider angle of the whole install, showing the thermal protection device in place as well.

As for the issue of flow, I will be upsizing the pipework when I get to a shipyard and replacing the distorted PVC.

And as far as the heat, It's funny because my predecessor who wired this up in the first place last year, actually used a bimini jumper on the thermal protector. This was because the element would keep "tripping" the unit off. I'm positive that this is the reason that the pipe work is now pooched, thanks to the heater running constantly with no safety in place. I can only imagine what a swimmer would think when they stepped in the tub. Maybe thought the chef was going to add some veggies and chicken stock.

All is well now, Voltage is still at 208Vac, and amperage has been reduced from 25A on each leg, to just over 8A. I'm much happier with this outcome.

 

[LionelHutz]

It's possible it was not meant to be powered from 208VAC in the original configuration. Is there a data plate on the heater giving the voltage of each element?

I was also thinking the same as waross as far as double checking the heating elements. You just never know.

 

[aboynamedclint]

Yup, as I stated at the start, it is rated for 230/400Vac.