High amperage

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TCMind

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Lowell, Michigan
First off right up front, I am NOT an electrician (I am a fire suppression designer in detection & control, low voltage), but I do have a desire to understand what and why on my salon equipment. For my "after hours" job, my wife and I have a couple tanning salons. We had a tanning bed replaced and I have a couple of questions on the voltage and amperage of the new tanning bed.
The existing service to the new bed is as follows;
Single phase, 100 amp circuit breaker feeding (2) 3 AWG THHN along with a 6 AWG THHN ground. Approximately 60' to a 100 amp disconnect in the room with 100 amp fuses on each leg. From there, another 30' to the contactors in the bed.
Voltage is: 248VAC
The tanning bed (from the name tag);
Power Input: 19 Kw, Voltage: 220, Cycle: 60 Hz, Power Factor: 90%
Upon startup of the tanning bed;
The temperature of the fuses were: 71.5 degrees F
Inrush is 160 amps!
Voltage (after about 30 sec) was 241 VAC
After 1 minute the amperage settled in at 107 amps.
4 Minutes into the session, fuses were at 99 degrees and climbing.
Not feeling to "comfy", I shut it down. Now for the questions and understanding. Manufacturer says 100 amp needed for single phase, and #3 will work. He also states, that these beds are inductive systems, therefore as the voltage increases, so will the amperage draw.
1. Is a #3 the right conductor size? 2. If I have a buck-booster installed, I know it will help with the voltage, but will it help with the amperage?
Any comments on why we are getting such high amperage and helping me understand would be greatly appreciated.
Thanks, TC
 
TCMind said:
Voltage (after about 30 sec) was 241 VAC
After 1 minute the amperage settled in at 107 amps.
Click to expand...

There's a math problem (or as a friend would say, sompthin' ain't right)- that's over 25kva on a nameplate of 19kw. If the 19kw is correct, the PF is somewhere down around .74. Not good.

I'd have a discussion with the bed mfg, current should be more like 85-ish amp for that voltage, KW draw, and PF.

Also, is 99 deg Fahrenheit or Celsius? 99F (37C) would be perfectly OK.
 
I dont know squat about tanning bed bulbs, but is it possible you have higher wattage bulbs than what is recommended by the manufacturer?

100' or thereabout total distance shouldnt cause enough voltage drop to be of concern. If the beds are rated 19kW @ 220V, resistive* load, then at 248V they'd be 21.4kW. At 90% PF, now you're at 23.8kW.

Fluorescent bulbs are not purely resistive*, and will have an inrush on startup.

My guesses are the wrong bulbs for the bed, it is made to run on 208V vs 240+V, or, the bed is set to max, meaning the all bulbs are running 100% for the duration of the tan. or it is operating exactly as it is supposed to.

The 71.5* and 99*F ambient temperatures are not a concern imo.

#3 Cu at 75*C terminations for 100A is correct. There is not a problem there.

The nameplate amperage/wattage, is that just for the bulbs or for the unit, which could have cooling fans, electronics (aside from ballasts) to run the bulbs, etc? I dont imagine that the power factor of those kinds of lights is in the .9+ range; they very well may be .7-ish for dimming, so you wind up with a nice tan vs looking like crispy duck. Dimming ballasts generally arent as efficient as those designed to run full power.
 
Seems a 19KW unit would be more then sufficient for cooking a whole hog for a Luau :D

I kind of thinking you should verify you are using the correct lamps as a first step also.

Next step is maybe verifying any individual ballast isn't drawing excessive current, and maybe check out ventilation fan(s) to make sure they are within their proper ratings.
 
I did get back with the manufacturer, and this is the math he came up with;

[Unit input power] / [Voltage] / [Power Factor] = Amperage Draw. (Inductive system)

First with what is noted on the name tag:
19,000 / 220 / 90% = 96 Amps
Then with the voltage that we have:
248 - 220 = 28 V / 248 = .113 % increase
19,000 x .113 = 2147 + 19,000 = 21,147 W
21,147 / 220 = 96.123 / 90% = 106.8 Amps

As noted, after the inrush, it settled in at 107 Amps.

It looks like a buck/booster will be needed to get the voltage / amperage down.
 
I bet even if you get it down to drawing 96 amps, the fuses will still be much warmer then 99 degrees, that isn't anywhere near "hot" yet.

If rated for 220 volts you probably do get more life out of some components if you get the voltage lowered though.
 
TCMind said:
I did get back with the manufacturer, and this is the math he came up with;

[Unit input power] / [Voltage] / [Power Factor] = Amperage Draw. (Inductive system)

First with what is noted on the name tag:
19,000 / 220 / 90% = 96 Amps
Then with the voltage that we have:
248 - 220 = 28 V / 248 = .113 % increase
19,000 x .113 = 2147 + 19,000 = 21,147 W
21,147 / 220 = 96.123 / 90% = 106.8 Amps

As noted, after the inrush, it settled in at 107 Amps.

It looks like a buck/booster will be needed to get the voltage / amperage down.
Click to expand...

I am fascinated by this since so many tanning bed manufacture's want 240V for their beds and claim that they can't run on 208V. This is the first time I have heard of one of them saying they need less voltage.
 
ActionDave said:
I am fascinated by this since so many tanning bed manufacture's want 240V for their beds and claim that they can't run on 208V. This is the first time I have heard of one of them saying they need less voltage.
Click to expand...

I have worked with a few Wolff tanning beds. They are marked 220 volts and when I conversed with the manufacturer's rep he stated that 240 volt wasn't OK. (I don't remember if I ever had one at 208 volts, so I can't say in that direction.) In a nut shell they required a buck boost transformer we installed. A 100A tanning bed though?
 
ActionDave said:
I am fascinated by this since so many tanning bed manufacture's want 240V for their beds and claim that they can't run on 208V. This is the first time I have heard of one of them saying they need less voltage.
Click to expand...
I don't see where anything has failed yet, OP shut it down when fuse temp of slightly overloaded fuse reached 99 degrees, which if you let the thing run continuously at rating those fuses would be expected to be too hot to touch. I can see lamp ballasts lasting longer though if supply voltage were closer to 220 volts presuming they are actually rated for 220 volts.

Next question is do these ballasts draw more if voltage is high or not? Since emphasis was put on it being an inductive load, we have to assume they are magnetic ballasts. I don't know enough about what regulates lamp current within such a ballast, but if whatever does keeps lamp at a fairly constant wattage then current has to go down if voltage goes up. Blower motor will definitely draw less current at the higher voltage level, but is only a small percentage of the total load.
 
:) I think the tanning bed folks have a consortium with the transformer folks. There seem to be more buck & boost transformers for tanning beds than any other critter.
 
augie47 said:
:) I think the tanning bed folks have a consortium with the transformer folks. There seem to be more buck & boost transformers for tanning beds than any other critter.
Click to expand...
They aren't the only ones. Seems to me they should include whatever devices they need to run on standard nominal voltages as required by NEMA, etc.

I have heard all kinds if ignorant comments from field techs about voltages. Have yet to have the factory design engineer support some of the crazy things you hear from field techs.

Either label the equipment correctly or build it correctly.

It must be a lack of training or something. I had a service department tell me a dehumidifier failed because it was in a damp area. My response was a bit tart.
 
Thanks, guys
Yes, everything is magnetic ballast. My smaller beds (24 lamp at 100 W each) absolutely love 240 V, and at that voltage they tan like crazy. The "medium" beds (52 & 64 lamps at 160 W each) run pretty good, except every once in while I need to replace the jumper wires feeding the capacitors. They start to get a little crispy. The biggest beds are high pressure (between 600 to 1000 W lamps) and that was what I was dealing with here 39 lamps @ "about" 500W each. The rating of the ballast trumps over the wattage of the lamps, so even though you may have an "over-wattage" lamp in there, the ballast wins. As for running a bed at 208 V, I have never heard of one setup that way in the 32 years I have been doing this. This will also be the first buck/booster that I am having installed at my salons, and as ActionDave says, it is not normal to require LESS voltage.
 
TCMind said:
The biggest beds are high pressure (between 600 to 1000 W lamps) and that was what I was dealing with here 39 lamps @ "about" 500W each.
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My good golly gosh!
Nearly 20kW most of it dissipated as heat!
You could make a lot of cups of tea with that............:D
 
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