Loads

[aLf]

Indy:

 

I am using a 500W transformer, 120/12V. I have two channels on the output, 250W each. One side has 115W, the second has 140W. The transformer will be plgged into an otlet that (only) handles the transformer. The outlet is supplied by an RelayLinve V2.5.

 

Am I OK? Any ideas on the scene/program?

 

Thanks,

 

aLf

[IndyMike]

Indy:

 

I am using a 500W transformer, 120/12V. I have two channels on the output, 250W each. One side has 115W, the second has 140W. The transformer will be plgged into an otlet that (only) handles the transformer. The outlet is supplied by an RelayLinve V2.5.

 

Am I OK? Any ideas on the scene/program?

 

Thanks,

 

aLf

 

Alf,

 

From your previous post, I think you meant that you have two channel outputs of "200" watts each (typo?). Also from your earlier post, you indicated that the transformer was 500W in/400W output.

 

As jerlands indicated, transformers are normally pretty efficient devices - my earlier example of and 80% efficiency is extremely conservative (i.e. military style derating). I'm very surprised to see that the manufacturer is quoting this low an efficiency. Can you provide a model number so we can review the transformer specs?

 

By the numbers you have a 80% efficient transformer with a 255W load on the output. input power consumption would be 255W/0.8 = 318W (well below the 480W rating on the SWL label).

 

If you're concerned about expansion (additional lamps), I'd suggest measuring the actual consumption by the transformer with your planned 255W load. My educated guess is that both the SWL and the transformer ratings are very conservative and that your system would be reliable with the full 400 watt load on the transformer.

 

If the worst were to happen (the load is in excess of the relay contact capability) this becomes a wear out issue with the relay contacts. It is not a safety issue. The relay contacts will simply wear out prematurely.

 

IM

[aLf]

Thanks Mike.

 

aLf

[jerlands]

Indy:

 

I am using a 500W transformer, 120/12V. I have two channels on the output, 250W each. One side has 115W, the second has 140W. The transformer will be plgged into an otlet that (only) handles the transformer. The outlet is supplied by an RelayLinve V2.5.

 

Am I OK? Any ideas on the scene/program?

 

Thanks,

 

aLf

 

The SWL is rated for 13a... My guess is the lower inductive rating has to due with line noise generated by the transformer. I wouldn't worry about it burning up but possibly not working reliably.

 

Jon

[Brian H]

More like the surge into the transformer when first powered on or the possible inductive spike when turned off.

I am not sure what Smartlabs added across the relay contacts to protect them. I know the ApplianceLincs have a RC Snubber network across the contacts; or at least the new ones do. The old one did not.

[ergodic]

I have my front and back landscape on separate 300W transformers connected to regular SL dimmers connected through GFIs -- which I typically run at about 50% at night. Other than a little buzzing from the transformers because of the line switching at mid-load it has worked fine for 2 years. (Obviously dimming isn't an option with LED landscape lights.)

 

If it were me personally, I wouldn't be comfortable running that close to the margins. Two separate, smaller transformers with an outletlinc, or sl relay/dimmers would be my choice. OTOH you're not really risking anything except premature failure of the controllers.

 

Regarding screw-in LEDs I'm using the Pharox with Insteon in a few places indoors and I can say it performs well. Like all LEDs the output is overrated some - I'd say about 40-50W equivalent. But it dims down to about 15%, no flicker, not much heat, no problems and good color. It does have a metal jacket around the lower base so the light spread is reduced below the bulb. Not cheap either of course.

 

If I could just find a decent dimmable MR16 50W halogen LED replacement for my ceiling downlights I'd be in hog heaven.

[IndyMike]

Hello ergodic and alf,

 

Alf has a bit different situation - he is using a relay unit to switch the transformer. The relay is rated for 15A (1800W) with a resistive load. SH has de-rated the relay to 480W for use with incandescent and inductive loads due to the surge current that these devices can draw.

 

The surge current drawn by incandescent lamps is predictable if you know the temperature of the filament.

 

My 50W floods show a resistance of 21 Ohms when cold. This bulb would draw a surge current of roughly 5.7 Amps when cold.

 

If 9 of the 50W floods were on a circuit (total load 450W) the cold resistance would be 2.3 Ohms (9 - 21 Ohm loads in parallel). This would draw a surge current of roughly 51 Amps (ignores inductance and other factors). So, SH has concluded that the relay contacts can handle in excess of a 51 Amp load (for a brief period until the filament warms) without degrading the life of the relay contacts.

 

Switching over to inductive loads - They do draw surge current and they store energy. This can result in overheating/arcing of the relay contacts at both turn-on and off. My earlier point was that the surge current of drawn by transformers is far less predictable. Max current draw occurs when the relay is switched during the powerline zero crossing and there is residual magnetism in the core. This is an exercise in probability. Relay arcing will occur (depending on the charge storage and contact speed) each time the relay is opened. I find it "conservative" that these inductive ratings are the same as the incandescent.

 

Moving to the transformer itself - As stated earlier, most transformers are very efficient (98% is common). Looking at Alf's transformer, I think they are including the "de-rating" in the specification. Most manufacturers quote 400W input/400 W output after de-rating 80% (the transformers can actually handle 500W). It appears that this manufacturer has included the Max 500 W input rating along with the de-rated 400W output.

 

Bottom line - I would expect that the transformer would draw an input power very close to the 12V load power (well below the 480W rating of the SWL). I also believe that the SWL inductive rating is conservative.

 

Once again, this should not be a safety issue. It could be a wear-out issue where the relay contacts degrade over time. For the reasons stated above, I do not believe this will be the case. If I am wrong, PM me and I'll ship out a relay SWL (I don't plan on going anywhere) .

 

IM

[aLf]

IndyMike:

 

Thank you so much for the thoughful (and very informative) answer(s). Do you work for UDI or SH? I wish I knew 10% of what you do with this stuff. Actually I wish you lived next door, I'd be bugging you for info all the time.

 

Again thanks. This landscape layout is in my vacation home and is used VERY sparingly. My guess is tha the switches and transformer will outlive me.

 

Regards,

 

aLf

[IndyMike]

Alf,

 

No I do not work for UDI or Smarthome. Just an aerospace engineer who's been around the block far to many times and is looking forward to a second career (I'm a ways past retirement age).

 

If I remember correctly, you're a pilot. If that's the case, I'd wager that you could teach me a lot as well. I'd love to add you to the neighborhood -

 

1 - 80 year old "craftsman" : designs and builds staircases for 7 figure homes in the area.

2 - Transmission shop owner/drag racer

3 - Physics professor at Notre Dame.

4 - Commercial construction engineer/contractor.

 

I really enjoy getting together with this diverse group (at my neighbors pole barn/pool table). I can't tell you how much I've learned over the years.

 

If you'd consider moving to Indiana, we can offer...well - Corn.

 

IM