Need help to choose hard-wired 12v transformer

[Lemosteam]

This may be more of an electrical question than electronic, but here goes:

I purchased 6 sets of these to fill 2' x '2 drop in florescent housings in my train room.  I am just going to remove the U bulbs and ballast and hard wire them in.  The strips have an adhesive backing and I am just going to wind them inside the original fixture back and forth:
http://www.ebay.com/itm/151925685334?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

The strip does not come with a transformer.  I did not realize this until after the fact.

What I want is an 120v to12v hard wired transformer that will work with the specs as shown in the LED strip paperwork below:

4.8 Watts / meter,  12v DC, 60 LED / meter

This is a 5 meter long strip and I need the transformer to power three of them with one transformer , so I think this needs to be taken into account with the values above...

...so 4.8w * 5= 24w per strip, * 3 strips is 72w  Is this correct?

Would this work?
https://www.eclipseillumination.com/collections/low-voltage-transformers/products/hatch-rs12-80m-80-watt-dimmable-electronic-transformer

Seller recommended this, but will this run three sets? I know they are inexpensive but I really don't want to buy six of them if I need one per light.

http://www.ebay.com/itm/152147470889?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Any help is appreciated- at a standstill.  I really don't want to fry these things.

[SP-Wolf]

This may be more of an electrical question than electronic, but here goes:

I purchased 6 sets of these to fill 2' x '2 drop in florescent housings in my train room.  I am just going to remove the U bulbs and ballast and hard wire them in.  The strips have an adhesive backing and I am just going to wind them inside the original fixture back and forth:
http://www.ebay.com/itm/151925685334?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

The strip does not come with a transformer.  I did not realize this until after the fact.

What I want is an 120v to12v hard wired transformer that will work with the specs as shown in the LED strip paperwork below:

4.8 Watts / meter,  12v DC, 60 LED / meter

This is a 5 meter long strip and I need the transformer to power three of them with one transformer , so I think this needs to be taken into account with the values above...

...so 4.8w * 5= 24w per strip, * 3 strips is 72w  Is this correct?

Would this work?
https://www.eclipseillumination.com/collections/low-voltage-transformers/products/hatch-rs12-80m-80-watt-dimmable-electronic-transformer

Seller recommended this, but will this run three sets? I know they are inexpensive but I really don't want to buy six of them if I need one per light.

http://www.ebay.com/itm/152147470889?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Any help is appreciated- at a standstill.  I really don't want to fry these things.

John,

First - The Hatch power supply will not work - as it has a 12 VAC out put -- you need DC.

I would go with the recommended power supply. But, as they are rated at 36 watts - you would only be able to run 1 string per power supply.

Regards,
Wolf

[Lemosteam]

@SP-Wolf How about this one?

https://www.amazon.com/Henxlco-110V-260V-Transformer-Supply-Waterproof/dp/B01C2HS56Y/ref=sr_1_12?ie=UTF8&qid=1474387121&sr=8-12&keywords=12vdc+80w

With an 80w unit I would have to have two, correct?

[jdcolombo]

Peteski can provide a definitive answer, but I think that Watts = Volts X Amps

That means that if you need 72 watts at 12v DC, you need a transformer that will output 6 amps minimum (plus some safety factor - I'd probably add 10% at a minimum).  So you need 7 amps total for all three strings.

What I'd probably do is power each strip separately with a 2.5 amp or 3-amp, 12v DC supply.  2.5 amps at 12v = 30 watts, which is more than enough to power each 5-meter strip.

2.5 or 3 amp, 12v. DC supplies are pretty common.  Here's a 3-amp DC supply for $10 from Amazon:

https://www.amazon.com/RCLITE-Converter-Regulator-Transformer-Connector/dp/B01DIUG7J6/ref=pd_sim_23_1?ie=UTF8&psc=1&refRID=RKYVGV4RBXRRHFZT4PYD

If you are really set on powering three strips with just one power supply, here's an 8-amp supply from Amazon for $25 which would be more than enough for three strips:

https://www.amazon.com/HitLights-Supply-UL-Listed-Transformer-Voltage/dp/B00STTOS8Y/ref=sr_1_cc_2?s=aps&ie=UTF8&qid=1474391542&sr=1-2-catcorr&keywords=8+amp+dc

John C.

Addendum: the two supplies I linked above have barrel connectors on them, but it is trivial to cut off the barrel connector and hard-wire the supply.  You just need to make sure you know which wire is positive and which is negative.  Cut off the barrel connector, strip the wires, and then use a multimeter to tell you which wire is which.

[SP-Wolf]

@SP-Wolf How about this one?

https://www.amazon.com/Henxlco-110V-260V-Transformer-Supply-Waterproof/dp/B01C2HS56Y/ref=sr_1_12?ie=UTF8&qid=1474387121&sr=8-12&keywords=12vdc+80w

With an 80w unit I would have to have two, correct?

Hey John,

Looks like two would work.

Just one thing -- this is a true hard wired unit. You would also have get a plug for each of them.

I like the unit John C. has found - I think it would be a better solution. (Easier to hook up). As it is made for your type of strip light.
https://www.amazon.com/HitLights-Supply-UL-Listed-Transformer-Voltage/dp/B00STTOS8Y/ref=sr_1_cc_2?s=aps&ie=UTF8&qid=1474391542&sr=1-2-catcorr&keywords=8+amp+dc



Regards,
Wolf

Regards,
Wolf

[peteski]

The calculation is correct.


I would also not recommend to place a constant load of more than 75% of the supply's rated power (or specifically current) output, especially when using inexpensive supplies).  Also make sure to use heavy enough gauge wire between the supply and the lights.  That also depends on the length of the wire run.  We are probably taking 16, 14, or even 12 AWG wire.

[Lemosteam]

The calculation is correct.


I would also not recommend to place a constant load of more than 75% of the supply's rated output (especially when using inexpensive supplies).  Also make sure to use heavy enough gauge wire between the supply and the lights.  That also depends on the length of the wire run.  We are probably taking 16, 14, or even 12 AWG wire.

@peteski , what do you mean by output, wattage?  The light fixture are currently ( pun intended) 14 gage Romeo wire between them. With about an 8' run. I will mount the transformer in the first light after the light switch.  Is it OK to switch the transformer or would it be better ahead of the wall switch?

[peteski]

@peteski , what do you mean by output, wattage?  The light fixture are currently ( pun intended) 14 gage Romeo wire between them. With about an 8' run. I will mount the transformer in the first light after the light switch.  Is it OK to switch the transformer or would it be better ahead of the wall switch?

Should have been clearer (I corrected my post).  In this case it is the current rating (since the voltage is fixed at 12V).   Since power, current, and voltage are related, I could also say: its power rating.

If the total current consumed by all the LEDs lights is 6A (or 6A X 12V = 72 W) then I would recommend a power supply which is rated for roughly 20-25% more. So a 12V DC power supply rated for 90W or 7.5A should give a good margin of safety.

This is the first time I've heard about the Romeo cable. Is it terminated in Juliet connectors?    Auto-correct strikes again?  All this technology is going to kill us one of these days!  Hopefully self-driving cars are a bit "smarter" than our personal computing devices. 

14 AWG should be plenty robust for this application.  16 feet of 14 WG wire (since the current travels to and from the light fixtures) has a total resistance of 0.04 ohms.  At 6A the wiring will drop only about 0.24V.

I'm also curious why you haven't replaced the fluorescent tubes with replacement LED tubes?  I think they make them in the U-shape.  Also, will the LED strips provide enough illumination compared with the fluorescent tubes you were using?

[Lemosteam]

It's ok @peteski , you know all to well that electricity calculations drive me batty, but your explanation cleared that up. 

Each strip is roughly 16' long, so 300 LED jammed into a 2' X 2' fixture should generate a lot of light.  I have a 48" shop light with similar strips having less LED and it is quite bright.  I may have to lower the tape in the fixture, it is about 3" deep and I want to get the strips as close to the diffuser panel as I can get, but that's pretty easy with some lauan panel screwed to the ballast cover.

[jagged ben]

The calculation is correct.

...

What, no power factor?   

[peteski]

What, no power factor?   

In DC?! 
 

[peteski]

It's ok @peteski , you know all to well that electricity calculations drive me batty, but your explanation cleared that up. 

Each strip is roughly 16' long, so 300 LED jammed into a 2' X 2' fixture should generate a lot of light.  I have a 48" shop light with similar strips having less LED and it is quite bright.  I may have to lower the tape in the fixture, it is about 3" deep and I want to get the strips as close to the diffuser panel as I can get, but that's pretty easy with some lauan panel screwed to the ballast cover.

Got it!
Sounds like it will work just fine.

[Lemosteam]

@peteski , would this one work?  It's a leftover from my old house.  If it is 12v AC, Is it east to make a AC to DC conversion circuit with 100watt capability?

[peteski]

@peteski , would this one work?  It's a leftover from my old house.  If it is 12v AC, Is it east to make a AC to DC conversion circuit with 100watt capability?

What is it John?  I don't see any photos or specs.

It it is just a transformer and has enough amperage you would need to add a bridge rectifier. Then you would have unfiltered and unregulated power source.  You can add  a filter cap but that will also raise the voltage to probably around 14V (under load).   Maybe then add a voltage regulator, but that is getting more complicated. I think you would be better off getting a ready-made supply. They aren't very expensive.

[Lemosteam]

@peteski   Ugh. Sorry.

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