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Old 05-11-2006, 11:17 PM
Mike & Lucia Mike & Lucia is offline
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Line voltage problem or math problem?

I'm working on a three transformer installation. Today we put power to two 300 Watt Cast Lighting units. My final readings have me baffled. Here's the particulars:

Licensed electrician (the client's existing relationship) installed a two separate dedicated lines, switched individually from inside the home with Intermatic EJ500 (Astronomic timers). Both are 118+ volts at the duplex.

Transformer #1 has 185 watts of lamp plus 240 feet of 12/2 divided over three runs. One on the 12v tap, two on the 13v tap. Actual readings come very close to Cast website voltage calculator. Lamps + wire is about 205 watts total. Calculator says I'll pull 15.4 amps on the common, actual reading is 15.3A.

Here's the puzzle.... on the primary loop I'm pulling 2.5 amps!!! How can that be? It should be reading about 1.5A on primary. And the box is buzzing. In my experience Cast breakers only buzz when they are about to trip.

Any ideas? Is my math wrong? Is there a problem in the circuit? Is the Intermatic timer hurting me? After I left I thought I should plug into a nearby unswitched outlet, but I was miles away. I'll go back next week. What else should I be looking for?

The second transformer has a similar situation... 195 watt of lamp, 14.9 Amps on low voltage side and 2.3 amps on line voltage side. Line voltage pull should be 1/10th the low voltage reading, give or take a point. No? Also buzzing, also 118+ volts, also switched with Intermatic unit.

I'm open to all ideas. Thanks,

Mike
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  #2  
Old 05-11-2006, 11:54 PM
freddyc freddyc is offline
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so your saying that you have about 120 ohms of unwanted or added resistance across each transformer??


If you actually have 205 watts of power required at the 118 volts you measured, then 1.73 amps is what you should see on the primary side at 100% efficiency. So your saying the transformer efficiency in each situation requires about 0.8 amps or about 55% efficiency from primary to 12 or 13 Volt taps?
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Old 05-12-2006, 03:23 PM
steveparrott steveparrott is offline
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Mike,

It sounds like the line voltage under the transformer load is too low. You mentioned that the voltage at the GFI's was 118 volts – my guess is that this is the voltage with no load. If, under load, the primary voltage is getting near 110v, then the transformer will not function optimally, it will buzz and the amp readings will elevate (v x a = w; with wattage fixed, a drop in voltage will raise amps). The discrepency between secondary and primary amperage will also increase because the transformer's efficiency drops when primary voltage drops too low.

If voltage drop on the primary is the problem, then the wiring to the GFI may be undersized (we usually recommend at least 10 ga.) or the Intermatic Timer may not be rated for the load and adding resistance to the line.

Addressing a similar issue, I posted a question on the NEC Code forum about testing equipment that can be used to test GFI's under load. You can read the thread here:

http://www.mikeholt.com/codeForum/viewtopic.php?t=26000
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  #4  
Old 05-13-2006, 07:26 PM
desert night light desert night light is offline
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Forget about Cast's MDL boxes and get a Justin/Vista transformer or a frog lights for that matter. You won't go back. Their constant power units will knock your socks off and will compensate for low incoming voltage. Torroidal transformers are not as good as the "old fashioned" coil and core. Don't believe bull crap said any differently.
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Old 05-14-2006, 01:02 AM
SamIV SamIV is offline
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I don't visit here as much but I noticed the Hot Shot Kid has changed his user name again to dessert night light and is at it again. Who do you thing you are fooling. Don't let this character get to you steveparrot.

Sam IV
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  #6  
Old 05-14-2006, 08:14 PM
desert night light desert night light is offline
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Stick to the facts and save the personal attacks. the facts is the facts.
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Old 05-15-2006, 11:31 AM
steveparrott steveparrott is offline
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To my knowledge, so called "constant power" units do not regulate incoming line voltage. I'd also like to hear if you have any evidence that EI-type transformers are better than toroidals.
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  #8  
Old 05-15-2006, 09:00 PM
desert night light desert night light is offline
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I've personally tested MDL's 600 w Torroidal (which is cast's with a cast label on it according to my distributor who was told by MDL) side by side and it is not nearly as powerful as Vista's constant output transformer. All of these claims about efficiency and less voltage drop compared to Vista's are unfair and are just not true. No , it does not regulate incoming voltage, neither does Cast's but it does hold up better under load and it is also more powerful right out of the box. I dare anyone to try for themselves and see the truth. It's bad when a manufacturer makes claims that their equipment is superior to competitors when it isn't true.
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Old 05-16-2006, 12:29 PM
steveparrott steveparrott is offline
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Desert,

I'm tempted to make no reply, but since you accuse us of bad behavior and are besmirching our reputation, I need to respond.

[QUOTE=desert night light] "I've personally tested MDL's 600 w Torroidal (which is cast's with a cast label on it according to my distributor who was told by MDL) side by side and it is not nearly as powerful as Vista's constant output transformer."

The "power" of a transformer is a direct function of wattage rating. A 600w transformer from any manufacturer is equally powerful.

Quote:
"All of these claims about efficiency and less voltage drop compared to Vista's are unfair and are just not true."
Check the online encyclopedia, Wikipedia, for an authoritative article on the subject. http://en.wikipedia.org/wiki/Transformer

From this article: "Toroidal transformers are more efficient (around 95%) than the cheaper laminated EI types. Other advantages, compared to EI types, include smaller size (about half), lower weight (about half), less mechanical hum (making them superior in audio amplifiers), lower exterior magnetic field (about one tenth), low off-load losses (making them more efficient in standby circuits). . ."

Quote:
"No , it does not regulate incoming voltage, neither does Cast's but it does hold up better under load and it is also more powerful right out of the box.
If you read the results of our comparitive study (conducted by an electrical engineer - posted as an article on the CAST website). You'll see that, under load, a torroidal transformer has approximately half the voltage drop at the tap compared to EI types. For example, the voltages of an unloaded vs. fully loaded 1200 watt toroidal transformer at the 15v tap are 15v and 14.25v (0.75v loss). On the EI model tested, the voltages were 15.8v and 14.4v (1.4v loss). These differences are directly due to the respective efficiencies of the transformers (95% vs 88%).
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  #10  
Old 05-17-2006, 02:31 AM
desert night light desert night light is offline
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And I'm saying I dispute your findings. Those are not the results I got when I tested two 600w transformers (MDL and Vista) on two seperate projects. In fact on one job,out of the box, I had 14V with 118V incoming without a load on the MDL and 15.4V at the vista. Loaded I had 12.8 and 14.4 respectively at the 15 v tap. Simple put, the transformers I tested did not have nearly the performance of the Vista's. I challenge anyone to take the same test. I have no affiliation with either company. I'm just a regular yard dog who puts in lights time to time. Obviously the info on your website is biased to show your product in a better light then your competition. In this case it's just plain false.
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