SD Stereo Electrical Power Oddity

[leesweet]

Here's something I can't figure out.  It applies to a Max, but should be the same for all SD series with 240 power.

Background.  240 appliances get power from two single phase 120 lines run 'against' each other, thus 240 VAC.  If you want to run a 120 VAC piece of equipment in that unit (such as you do in a clothes dryer, for lights, timers, etc.), you usually run one of the power legs aganst the neutral power line to get 120.  (I know this because I've read a lot of house wiring books!    ).

But, the manuals for the SD spas explicitly state that they do *not* use the neutral line to the spa (it stops at the GFCI), just the two 120 legs and the ground.  How the heck do they run the stereo (and, come to think of it, the other electronics), which must (I assume) be 120?

They could have 240-based equipment, but that's expensive custom stuff, and a long shot.

They could balance it off the ground wire, but that's not code and illegal, as far as I can tell.

So, how do they do this?  A transformer, to step the 240 to 120, perhaps?!

[J._McD]

Don't assume anything, everything runs off of the 240 feed including the step down, they have it figured out.

[johnvb]

They could use a tranny to step from 240vac to any other ac voltage. If it is a true marine stereo (as used in boat installs) it would be 12volts dc, then a simple ac to dc converter could be used.

[Brewman]

It it a transformer.  The pumps and heater run off the 240, the rest runs off the transformer.  
I had the same question you did when we got our Optima, and when I saw the wiring diagram, I saw the transformer.
Brewman

[leesweet]

Heh. Thanks for both the comments!  Us EE's are too analytical, but inquiring minds want to know *how* things work!

Good point on the marine stereos running off 12VDC! I was one that brought that up, and should have twigged to that point, since I was a boater for many, many years (too many years of "standing under a cold shower tearing up $100 bills...!").  Since many spas are 240 VAC, a lot of electronics would (duh!) have to either be 240 or have a stepdown to feed what they need.

The corollary question is why no spas (most?) seem to have the neutral wire.  I "assume" that it's because of the cost of running 3 wires (plus ground) vs 2 (plus ground) over what may be a long run (if the GFCI is in the breaker box)?

The things you learn here.  The collective mind is awesome!

[J._McD]

"The corollary question is why no spas (most?) seem to have the neutral wire.  I "assume" that it's because of the cost of running 3 wires (plus ground) vs 2 (plus ground) over what may be a long run (if the GFCI is in the breaker box)? "


Because you need continuous heat application in a spa you need 240 volts.  Spas using 4 wire hook ups have something operating on 120 volts, like motors, blowers, ozonators etc., and they are less expensive , thus the need to have a neutural wire or they are convertible 120/240 systems and everything is based on 120 volts except the heater only.

240 volt motors cost more and are larger and more efficient and are not used by ALL manufacturers.  The heater pulls 22 amps, each motor pulls 11 amps on hi, the blower 8 amps, plus circ pump, ozonator and other electrical components.  Add another motor to the mix and you can easily see you have exceeded the amp capacity of a 50 amp breaker.

For this reason the SD operates on 50 or 60 amps and will make a difference in the AWG #8 or #6 wire that is used.  Cost difference of 50 or 60 should be approximately $20 to $30 in materials and I would simply recommend going 60 amp hook up then you have got it all covered.

The heater, pumps, blower and ozone all operate on 240 volts, everything else utilizes low voltage for controls, lights, stereo etc.  This is more efficient and longer life expectancy lower kw consumption.

[Brewman]

You need to run #6 awg copper for 50 or 60 amp breakers.  You can go down to 8 awg for 40 amp breakers.  The only cost difference between a 50 and a 60 amp spa installation should be the cost of the breaker itself.  In my case, the Square D 60 amp breaker was $15 or so cheaper than the same Square D 50 amp breaker.  This was for the pro line of breaker.  I dont' think that Square D homeline series has a 60 amp breaker.  It didn't 2 years ago when I wired our spa.
Brewman