3-phase 400 V Sauna Heater on 1-phase 240 V?

Discussion in 'The Projects Forum' started by owenfw, Jun 30, 2010.

  1. owenfw

    Thread Starter New Member

    Jun 30, 2010
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    Ok, so I'm an electronics novice. I don't intend to do the project described myself...I'm just trying to figure out if it's possible before I find someone to do it for me. I'm also in contact with the manufacturer, but they aren't great at responding to emails.

    The sauna heaters sold in the US are lame. There are tons of great models available in Finland, which I can easily import, but of course they aren't designed to run on US power.

    The heater I would like to buy is a 7.5kw heater with 3 2.5kw resistive elements from ikikiuas.fi. The wiring diagram is here:

    [​IMG]

    1: power
    2: timer
    3: thermostat/overtemp
    4: elements
    5: output restriction

    So, simple question: this is designed to run on 400V 3-phase power, which is available in most residences in Finland. Can I do this using 240V 1-phase power and a higher amperage breaker than the unit expects (3x16A)? What would be involved?

    Thanks to anyone willing to help me out. I really appreciate it.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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  3. Dx3

    Member

    Jun 19, 2010
    87
    7
    The problem is that the 400 volt heaters will use a lot less current at 240 volts...not more. You will not need to put in larger breakers. You will get about 900 watts from each heater. This seems like a good reason to buy heaters designed for the right voltage.
     
  4. owenfw

    Thread Starter New Member

    Jun 30, 2010
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    Thanks. The problem is those heaters (most of which are coming from Finland, modified for our market) remind one of the 1980's in terms of design. They are the bottom of the line or obsolete models. Finnleo sells one more contemporary model (the Saunatonttu), but even that gets ridiculed in Finland as looking like a waste bin! The problem is that the market in the US is so small compared to Finland that it doesn't really pay for the manufacturers to update their lines here.
     
  5. owenfw

    Thread Starter New Member

    Jun 30, 2010
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    Lame. I was afraid of something like this. So basically not only would the wiring need to be altered, but the heating elements themselves would need to be swapped out.
     
  6. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    I haven't calculated it out, but the diagram is a Y config. Why not 240 single phase. Your wattage will be lower, but might still be reasonable.
     
    Last edited: Jun 30, 2010
  7. owenfw

    Thread Starter New Member

    Jun 30, 2010
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    I'm a bit wary of a solution that yields lower power, since the heat-up time on this particular unit is already longer than most since it's heating 140 kilo of rock rather than the usual 40 or so. Usual time is about 40 minutes and this type is over 60.

    I'm going to keep pestering the manufacturer to see if they'll modify one for me, but I'm also going to start thinking about other less optimal solutions.
     
    Last edited: Jun 30, 2010
  8. owenfw

    Thread Starter New Member

    Jun 30, 2010
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    Thanks to everyone who replied so quickly. Great community here.
     
  9. awright

    Well-Known Member

    Jul 5, 2006
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    Assuming constant element resistance and neglecting the rather epensive option of using a transformer to boost voltage to 400 and rewiring all elements in parallel, you will get only (240/400)^2 or 36% of the rated input power on 240 volts. This translates to 1/0.36 = warmup times about 2.8 times longer than normal for the power rating. Remember that if you operate on a voltage radically different from 400 volts you will have to change the timer (or the timer motor) and the contactor.

    Assuming you want to spend from several hundred to thousands of dollars on a 240v/400v boost transformer of at least the power rating of your sauna, you would draw 5Kw/240v = 21A or 6Kw/240v = 25A or 7.5Kw/240v = 31.25A or 10Kw/240v = 42A from your line. Not out of reason except for the cost of the transformer. Here's where it gets a little trickier. I'm not familiar with inductrial electrical wiring, but I don't think 400 volts is a common voltage in the U.S. so you're going to have to search for a transformer with the desired secondary voltage. Two alternatives are (1) get tricky with auxiliary boosting or bucking transformers to trim the easily obtained 480v to 400v or(2) get a higher powered sauna than you want and operate it below rated capacity.

    But what kind of heating elements are used in saunas? Is it basically a water heater element submerged in a pot of water generating free steam that heats rocks above? If the element is fully submerged you might be able to substitute common domestic water heater element(s) which are very cheap. You would have to check mounting conditions and maybe have an adapter made from whatever metric mounting configuration is in the sauna to a U.S. standart thread or hole pattern. Check with element manufacturers to be sure they can operate with only a few inches of water pressure - their power density at the surface of the element may require 60 psi or so water pressure to avoid overheating due to boiling at the surface. You can get a 6Kw water heater element for less than $50 at your local supplier or from Grainger.com., but you probably want three lower powered elements wired in parallel. See the 2E300 2.5 Kw screw-in low power-density element for $16 at grainger.com.

    If the heating method is not a submerged element, you are on your own.

    Since you state that you are not skilled in wiring, please have an electrician set it up for you.

    awright
     
  10. Norfindel

    Active Member

    Mar 6, 2008
    235
    9
    According to the diagram, the heaters are connected between a phase and neutral, right? Doesn't that means that they run at 240v already?

    Here we have 3-phase 380v and 220v between any phase and neutral (industry only, houses have just 220v single-phase).

    Wouldn't be possible to modify it to power all the heaters with one phase? It would require much bigger wires for the increase in current, but an expert could probably do it. The bad news, is that it has a 3-phase motor, also, and who knows what else.

    You should ask an expert for this specific area. It could be possible to do, but i bet this doesn't gets done too often, to say the least.
     
  11. 5&under=sorcery

    New Member

    Jul 4, 2010
    28
    0
    If the 3 phase line to line voltage is 400, (and it better be because if the line to neutral voltage is 400, the line to line voltage would be 693 volts. In a house? I don't think so) then the actual phase to neutral operating voltage on this wye connected system would be 231 volts, close enough to our common residential single phase line to line voltage of 240 volts. So, the heaters are actually being driven at 231 volts, at least as best as I can tell given I don't read Swedish. At 2500 watts this calcs to 11 amp per heater at their 230 volts single phase. Our 240 volts single phase calcs them to 10.4 amp.
    This work around assumes their branch circuit wire to the elements is good for AT LEAST 20 amp. We can protect our 10.4 amp loads at 15 amp and #14 THHN wire but this is less than ideal because not all American systems run a full 240 volts, and it will potentially be continuous duty. (over 3 hours at a time requiring a 20% increase in calced amps) So 10.4X1.2 is 12.5.
    12.5 amp minimum (assumes full 240 voltage ) is pushing the edge of a 15 amp circuit breaker especially if there are other loads in the panel (creating voltage drop and higher current draw) and the panel is on the hot side of the house creating high ambient breaker temperature. It's penny wise and pound foolish to not wire them with #12 and protect them at 20 amp. The cost difference in materials is not even worth mentioning. So, if you disconnected the common line from 2 of the 3 units, leave it on one unit, (assuming it and the other factory wires will legally carry 20 amp) and ran an extra #12 copper type THHN wire to the off-end of the other two units, you could then run your 3 units on three, 2-pole 20 amp circuit breakers without fear that the breakers would trip due to thermal overheating in normal use. NOW, you can't run their motor anyway because it's a 3 phase motor. Don't even go there. Over here you would need to run a separate single phase motor and circuit because we had to convert the internal wiring to 3 single phase circuits for our elements. If having water moving over the elements any time they are on is necessary, some kind of device and interlock between the elements and water movement that looks at whether the water is actually moving, not merely whether the motor is running, is necessary. The impeller could come off the shaft and the motor would be running but no water would be moving. Such a device may well already be built into the unit.
     
    Last edited: Jul 5, 2010
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