Best bang for buck step down transformer? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 17 Old 03-16-2017, 03:47 PM - Thread Starter
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Best bang for buck step down transformer?

In my HT equipment room, I have:
1 x 120v 20amp quad outlet
1 x 240v 30amp surface mount junction box (run to the breaker box on the other side of the house, but not connected)

Up front, needing power, I have:
2 x JL f113 (2000w time limited peak)
2 x SDA 4600 (class D, 4 channels @ 600w)
1 x SDA 8300 (class D, 8 channels @ 300w)

Back of the room, needing power, I have:
2 x JL f113
Projector (1200w max)
SSP & EQ (don't know, but I assume not much)

I am assuming the intent for the 240v was to use a step down transformer and plug everything into it. What is the best bang for the buck for 240v/30a -> 120v/20a (or 15a) out?

I have 3 other alternatives:
1) Tear into my DD+GG shell to run a sub panel from the outside service panel (which shares a wall with the equipment room) and run more power off of it, or
2) Put my rack in the mechanical room next to the breaker box and run new lines, or
3) "convert" the 240v run into a 120v run and power everything in front off 2 x 120v 20amp circuits.

 

 

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post #2 of 17 Old 03-16-2017, 04:31 PM
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What size is your main house panel? 200 amp? This 240v~30 amp disconnect...you might be able to run a pony panel off of this 30 amp disconnect to power your equipment. Your gear might be pulling 34 amps at full bore.
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post #3 of 17 Old 03-16-2017, 04:57 PM
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What i meant was , I dont think you need a step down xfmr. This disconnect may have fed a hot tub at one point. The disconnect probably has two hot phases sitting inside waiting to feed a future panel. Post a pic of the insides of this disconnect if you can.
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post #4 of 17 Old 03-16-2017, 07:00 PM - Thread Starter
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The outside box that connects to power grid is 400amp. The 2 inside panels are 100amp each, I believe.

I will spare you the back story, but I know the 240v / 30a line was intended for a step down transformer. I just don't know which one or how exactly it was intended to be used. So I'm considering the step down transformer as a possible option. But if it doesn't make sense now (or never did) then I'll go a different way.

I am going to have a remodel contractor handle electric & HVAC. But I need to tell him what I want to do. They were leaning towards making the 240v line into a 120v, but deffer to the AV guy to spec power requirements. He's covering his bases by looking at peak output of every device and sizing circuits that can handle it, which comes out to 9 dedicated 120v / 20a circuits. That's 180 amps and I will definitely need a new sub panel. But I also think it's ridiculous overkill. So then we're back to if I don't want to follow their recommendations, then what exactly do I want to do?

 

 

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post #5 of 17 Old 03-16-2017, 07:19 PM - Thread Starter
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^ which is why I was asking about the transformer. If I could find one that was cheap enough, I think roughly 60amps of 120v would be plenty of power. But the audiophile brands are expensive. I was hoping GE or some huge oem supplier of transformers would have a utilitarian commercial version at a fraction of the price

 

 

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post #6 of 17 Old 03-16-2017, 07:32 PM
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60 amps is overkill for a home theater. Thats enough power for a summer cottage in Canada ( wink wink) I think you need a second opinion from another electrical contactor. 240 volts in the US is meant for two 120 volt lines/ phases in a single panel. Sounds like you have two.... 100 amp panels in your home already from a 400 amp " main" feed.
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post #7 of 17 Old 03-17-2017, 10:14 AM
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How many wires are in that 30 amp 240 volt circuit and what color are they? If you have 3 wires, plus ground (usually black, red, white and bare), you are in luck. You can use it as two 30 amp 120 volt circuits (one on each phase) with no need for a stepdown transformer, for a total of 60 amps. If it s just two wires, plus ground (usually black, white and bare), it can easily be wired as a single 120 volt 30 amp circuit. In either case, you do not need a stepdown transformer.
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post #8 of 17 Old 03-18-2017, 03:56 PM - Thread Starter
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Quote:
Originally Posted by DaveClement View Post
How many wires are in that 30 amp 240 volt circuit and what color are they? If you have 3 wires, plus ground (usually black, red, white and bare), you are in luck. You can use it as two 30 amp 120 volt circuits (one on each phase) with no need for a stepdown transformer, for a total of 60 amps. If it s just two wires, plus ground (usually black, white and bare), it can easily be wired as a single 120 volt 30 amp circuit. In either case, you do not need a stepdown transformer.
It is the 3 wires, as you said: black, red, white, and bare copper.

I was thinking of getting this step down transformer from TripLight. It is ~$1,000 from almost anywhere.

https://www.tripplite.com/6kva-6kw-s...~SU6000XFMR2U/

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post #9 of 17 Old 03-18-2017, 04:40 PM
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Quote:
Originally Posted by rabident View Post
It is the 3 wires, as you said: black, red, white, and bare copper.

I was thinking of getting this step down transformer from TripLight. It is ~$1,000 from almost anywhere.

https://www.tripplite.com/6kva-6kw-s...~SU6000XFMR2U/

Rabident... I dont think you are fully grasping what we are saying. Your black and red cables are your 120v phases each ( phase to phase=208 v) with a white neutral and a bare ground. DON'T buy a step down xfmr. You dont need it. Get an electrician buddy to replace the disconnect with a multi circuit pony panel for your theater. A pony panel is all you need with circuit breakers.
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post #10 of 17 Old 03-20-2017, 12:44 PM
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There are specific instances where a stepdown transformer is preferred. These are usually very high end and expensive installations where there is a need to isolate the power from outside interference. If the need is simply to have 120 volt circuits, you can save the $1000 cost of the isolation transformer. This diagram shows how it works.


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post #11 of 17 Old 03-20-2017, 12:50 PM
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Quote:
Originally Posted by 69glamboy View Post
Rabident... I dont think you are fully grasping what we are saying. Your black and red cables are your 120v phases each ( phase to phase=208 v) with a white neutral and a bare ground. DON'T buy a step down xfmr. You dont need it. Get an electrician buddy to replace the disconnect with a multi circuit pony panel for your theater. A pony panel is all you need with circuit breakers.

This is correct except for "phase to phase=208 v". That is true in commercial installations where there are three phases. But in standard single phase power, as installed in most homes is the U.S., phase to phase would be 240 volts.

Last edited by DaveClement; 03-20-2017 at 12:54 PM. Reason: Corrected to say that single phase power is installed in most homes in the U.S.
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post #12 of 17 Old 03-20-2017, 03:47 PM
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Lol. My bad. I keep forgetting I'm posting from Canada (208v phase to phase up here) I have a hard enough time not to slip up and spell theater~ theatre... ; )
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post #13 of 17 Old 03-20-2017, 05:19 PM
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Quote:
Originally Posted by 69glamboy View Post
Lol. My bad. I keep forgetting I'm posting from Canada (208v phase to phase up here) I have a hard enough time not to slip up and spell theater~ theatre... ; )
Not to mention that all of the speed limits are in kilometers per hour and the gas is priced by the liter. Every time that I visit, I have to get change my way of thinking. Plus, your money is colorful and made of plastic. Ha ha.


I live less than 100 miles from the border and I will be visiting the Vancouver area again in less than two weeks. In all seriousness, I do think that the metric system is fundamentally a better system all around, I'm just not used to it.
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post #14 of 17 Old 03-20-2017, 05:24 PM - Thread Starter
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Quote:
Originally Posted by 69glamboy View Post
Rabident... I dont think you are fully grasping what we are saying. Your black and red cables are your 120v phases each ( phase to phase=208 v) with a white neutral and a bare ground. DON'T buy a step down xfmr. You dont need it. Get an electrician buddy to replace the disconnect with a multi circuit pony panel for your theater. A pony panel is all you need with circuit breakers.
I don't have an electrician buddy, unfortunately. The GC I had out last week said they are no longer allowed to make 2 x 120v lines out of that type of wiring. They said they could make it into one 120v line if I wanted. They mentioned the possibility of a sub panel, but I assumed they were talking about from the main exterior service.

But either way, it will mean tearing into the drywall to install the panel, install new outlets, and run the wiring to them. The xfmr seemed like an easy way to use what was already wired. It gives me a bunch of outlets to plug into & I assume surge protection as well. For non-buddy pricing, what do you think it would cost to install a new sub panel, breakers, wiring, outlets, and fix any drywall damaged in the process? Do you think it would be significantly cheaper vs $1,000 for the xfmr?

Edit: I just read Dave's responses. So there is some benefit in theory to the step down transformer that might apply to HT? I knew it existed, but I've never been sure if it really mattered. Like maybe it was a throwback to analog recording studios and not really needed in HT since everything has moved to switching power supplies and class D amps (which all mine are).

 

 


Last edited by rabident; 03-20-2017 at 05:29 PM.
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post #15 of 17 Old 03-20-2017, 05:54 PM
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I'm not absorbing what your GC said about not being able to work with "that type of wiring". Sounds like a kooky statement...Unless its some code issue for your area. Get a second or third opinion from an electrical contractor about installing a sub panel with circuits. Estimates are usually free and then you can compare what each will be doing for the price. ***See whom is more honest. ( you will need a thorough plan to describle what you want them to do and what plugs / will go where) Now for this step down xfmr... This thing will be good for your immediate stereo gear if it is in proximty to where this unit is installed .I'm hoping you aren't planning to run extension cords from the back of it to other areas of the room. This step down xfmr unit will also be useless for switches for your room lighting. Let us know which path you go down.
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post #16 of 17 Old 03-20-2017, 06:19 PM
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Quote:
Originally Posted by rabident View Post
I don't have an electrician buddy, unfortunately. The GC I had out last week said they are no longer allowed to make 2 x 120v lines out of that type of wiring. They said they could make it into one 120v line if I wanted. They mentioned the possibility of a sub panel, but I assumed they were talking about from the main exterior service.

But either way, it will mean tearing into the drywall to install the panel, install new outlets, and run the wiring to them. The xfmr seemed like an easy way to use what was already wired. It gives me a bunch of outlets to plug into & I assume surge protection as well. For non-buddy pricing, what do you think it would cost to install a new sub panel, breakers, wiring, outlets, and fix any drywall damaged in the process? Do you think it would be significantly cheaper vs $1,000 for the xfmr?

Edit: I just read Dave's responses. So there is some benefit in theory to the step down transformer that might apply to HT? I knew it existed, but I've never been sure if it really mattered. Like maybe it was a throwback to analog recording studios and not really needed in HT since everything has moved to switching power supplies and class D amps (which all mine are).

The electrician's response doesn't make a lot of sense to me. I have never heard of not being able to make two 120 volt outlets out of "that type" of wiring. It is very common. In fact, it is frequently used to put two different circuits onto one outlet. You break the tab off between the hot connections on the outlet, attach one to the red phase and the other to the black phase. They share a common white return (without the tab being broken off). You can't use a standard 15 or 20 amp outlet with a 30 amp breaker, but you can use the existing 10 gauge wire. Just use a 20 amp circuit breaker. The thicker wire will give you more stable power with less voltage drop. You don't need to tear out any walls or buy anything special. You literally just need a circuit breaker and an outlet. Let's see, a circuit breaker is probably between $25 to $50, depending on the brand and model. Cheap outlets are around $1. The good ones are around $5 or so. I'd say that is a lot cheaper than a $1000 step down transformer. http://www.easy-do-it-yourself-home-...g_diagram.html





Or you can have the black wire feeding one or more duplex outlets, and the red wire feeding one or more duplex outlets like the picture I posted earlier.



This really isn't rocket science. It should be really simple for any electrician to understand and implement.

Last edited by DaveClement; 03-20-2017 at 06:26 PM. Reason: Added comparitive pricing.
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post #17 of 17 Old 03-20-2017, 06:54 PM - Thread Starter
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Most of us are SME's for something. When I try to explain stuff to someone that has no clue, what I say often doesn't get relayed properly. I assume that is the case here (with me being the guy that has no clue about electrician stuff). Also, I didn't talk to the electrician, just the GC. It sounded like it was a recent code change. He said they used to be able to do it, but they aren't allowed to anymore.

I was going to use the transformer at the bottom of the rack to power everything in the rack. There are couple subs up front that I thought I could extend power to. These were originally spec'd for the room: http://www.richardgrayspowercompany..../powerlink.pdf What I got was unterminated romex in a junction box at each end. By junction box, I mean an empty power receptacle box with a blank faceplate on the front. I was thinking they could terminate the equipment room side with an inlet, and the front wall with an outlet. Then I could power the subs with the xfrmr through the wall.

 

 

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