Kiln conversion 240v to 208v

[Magnet]

Has anyone converted their 240v kiln to 208v?  Specifically, I'm looking to do this on a Paragon Janus 27. If anyone has experience with this, I'd appreciate advice. I've already contacted Paragon; waiting.

From what I've gathered from the community here and locally, the conversion can simply require changing elements and/or reconfiguring the controller. I have a Sentry II on my Janus 27.

Thanks for any help.

[Magnet]

It appears that, for the Janus 27, it requires changing the elements to the 208 versions, and reconfiguring the transformer. 

[neilestrick]

Yes, it should just require an element change. It should not affect the peak temp, but double check with Paragon. All the listings I see for them show cone 10 for either voltage. You shouldn't need to touch the controller or transformer.

[Bill Kielb]

Looks like the terminal block is only two poles so if this is a three phase conversion then you will need to reapportion wire between the third phase in a balanced way. I assume three phase is available, generally it is the only way to get 208v. You may however be using only two of the three phases which will make this a little easier.

I attached the diagram that I think applies to your existing kiln and it is an interesting mix of  elements in series and parallel as well as glass only and ceramic only elements. This will need to be done with attention to how these new elements are distributed. At 11500 watts it should end up  about 55 amps on 208v.

an interesting kiln to be sure if this is the diagram for it. I have attached a copy and made several notes just to keep this straight in my head. Assuming the new elements will supply the same wattage ( which is typically the intent) they will likely draw more current so attention to proper guage wire size will be important as well. The note says all wires are  14 guage which will likely make them undersized for some element groups at the new voltage.

 

[neilestrick]

1 hour ago, Bill Kielb said:

 

an interesting kiln to be sure if this is the diagram for it. I have attached a copy and made several notes just to keep this straight in my head. Assuming the new elements will supply the same wattage ( which is typically the intent) they will likely draw more current so attention to proper guage wire size will be important as well. The note says all wires are  14 guage which will likely make them undersized for some element groups at the new voltage.

 

They usually try to keep the amperages the same, not the wattage, so that both single phase models can use the same breaker size. It simplifies things for the customer and for  the production crew. If the 208 volt model pulled the same wattage and 55 amps, it would have to use a 70 amp breaker instead of a 60, it would have to be hard wired, and it would have to have brach fusing in the control box. It would be a totally different beast than the 240 volt model. Instead, the 208 volt models simply have a little less power, but still enough to do the job. This is why the Skutt KM1227 and L&L E28T-3, etc, are only rated for cone 8. They pull the same 48 amps as the 240 volt models so they can remain a plug-and-play kiln with the same electrical hookup specs. They make different models that are higher powered and can get to cone 10 at 208V 1P. In kilns smaller than 10 cubic feet, the lower wattage of 208 volts isn't an issue. They're still rated to cone 10.

I work on a lot of 280 volt single phase kilns. It's silly, but for whatever reason, a lot of schools insist on just pulling single phase for the kilns even though they have 3 phase in the building. I even had a new school building do that last summer, and they ordered a 10 cubic foot kiln even after I explained that it would be under powered at single phase.

[Bill Kielb]

Hmm, the wattage is everything so decreasing it decreases the heating. Three phase amperage will always be lower than single phase for a given wattage in a comparison of 208v 3p / 240v 1p  but I get what you are saying . Most of my conversions have been opposite: that is to say three phase to single phase.

Wattage is king in maintaining your kiln rating and heating ability so when buying elements for the conversion generally I believe you would get equivalent wattage. Interesting that kiln manufactures are providing derated  kilns by trying to keep amperage the same.

if I look at keeping amperage constant a 208v 3 phase kiln at ten amps = 3600 watts or about 12285 BTU of heating

If I keep amperage constant 240v at ten amps = 2400 watts or about 8184 BTU of heating.

thats a heating reduction in excess of 30%, similar to what we would observe with elements worn in excess of 10%. This is considerably underrated.

I picked out a popular cone art as an example of what I am accustomed  to seeing. They offer the lesser single phase voltage but maintain constant wattage so they do not have to revisit the thermodynamics of their kiln. Makes sense to me. Constant amperage approach seems like it would lead to many very underpowered  kilns quickly. Kind of like buying a new kiln with fully worn out elements actually.

Good thing you have to make these recommendations and not me. Either way, his kiln appears a bit more difficult than just changing elements and will require some attention. He has several issues to address after he figures out if his kiln will be derated or not. 

 

 

 

[neilestrick]

51 minutes ago, Bill Kielb said:

if I look at keeping amperage constant a 208v 3 phase kiln at ten amps = 3600 watts or about 12285 BTU of heating

If I keep amperage constant 240v at ten amps = 2400 watts or about 8184 BTU of heating.

thats a heating reduction in excess of 30%, similar to what we would observe with elements worn in excess of 10%. This is considerably underrated.

I wasn't clear-they don't try to keep the amperage the same at both single and 3 phase. They keep the two single phase models the same, say 48 amps. For the equivalent 3 phase models, they would both be around 28 amps, although they usually up the wattage for the 3 phase models of the 10 cubic footers so they can get cone 10 power. But at 3 phase and higher wattage they'll still be under 50 amps, plug-and-play.

All of this mostly only applies to the kilns with plugs, those under 50 amps. For those over 50 amps, which must be hard wired and have branch fusing, they'll focus on the wattage because for those kilns the power is everything, and they're all built the same way regardless if they go 70 amps or 80 amps, and you'll see the 208 volt models have higher amperage than the same 240 volt model.

[neilestrick]

11 hours ago, Bill Kielb said:

So when you retrofit, you try and maintain the wattage for a given size kiln body correct? Assuming it’s not super insulated if it’s much bigger and insulated similarly there must be a point where it just struggles to perform,  I would guess that it is near impractical to go up by a cubic foot or two but maintane the amperage. At some point the thing really consumes more energy than available.

As I said, I am glad I do not have to sell any of these actually.

Here is something that may interest you, within a month or so I will do a full SSR conversion with lid switch etc... for safety. This will further allow the use of some cheap bonded nitride shelves in these kilns. I believe I will extend the element useability by approximately 25 firings and have to guess at the energy savings from the shelves which are probably half the weight. 

Any speculation on savings? You may have experienced this already.

Yes, each size kiln is made to have similar wattage at any voltage or phase, while having the same amperage at each phase, for kilns with power cords/under 50 amps. The 10 cubic foot models that have power cords do struggle on single phase power. The 240 volt models are cone 8, the 208 volt are cone 5. The 3 phase models are cone 10. This is why Skutt has the PK models, and L&L has the Jupiters and eQuads. They are cone 10 on single phase, but run on much higher amperage. They cost more, though, because of the additional parts needed to meet code with the higher amperage.

Back to the original question in this thread, the kiln listings I see for that model show it as being cone 10 at both 240 and 208 volts, which makes sense because it's only about 8 cubic feet. That should be confirmed by Paragon, though, because it is a unique kiln.

I'm going to start a new thread with your SSR comment, because I have some questions for you!

[Bill Kielb]

Agreed, I think he wants 11500 watts to get the design performance out of this kiln regardless of voltage. Still more complicated than just changing elements and or probably not workable just using 208 as single phase. My original  point was  cautionary and suggested this change requires careful  thought.