Running LED drivers in parallel

Vormulac

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Hello all,

I have a question about driving LEDs.

I am in the process of replacing mains underlighters in and under my kitchen units with strip leds and I've encountered a problem. I want to have an equal length of led strip on each side of the kitchen, simply intercepting the lighting main ring where it comes out of the wall above the kitchen units and running it into a driver and then using the existing wiring that is behind the wall mounted cabinets to run the 12v dc to the new led strips. I did this on one side (Left) and it worked perfectly, but when I came to do the other side (Right) I discovered that the side I had already done wasn't in fact coming off the ring, but was in fact a spur from the wiring on the right, it's not coming from where the lighting ring comes out of the wall on top of the kitchen cabinets either, it's coming from where the underlighters are. This means I can't simply repeat the process because the spur would then be carrying 12v dc from the transformer on top of the unit.
The reason that this is an issue is that the led strip I'm using is 5 metres and rated at 72w for that length, as I was planning to use exactly half on each side I have two 50w drivers. So I can't use one transformer to drive the whole lot and I'd rather not buy a new 100w driver if I can avoid it (times are tough), so I was wondering if I can connect my two 50w drivers in parallel and they would function as a 100w driver?

This is what I had in mind.

www.dropbox.com/sc/iedvxlsvyjr1usx/AADt-pAgb_VLji3B0el5ccgfa

Can anyone help me?

Thanks!
 

Toaster79

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You have already split your strip in two halves and you already have two drivers? Where is the problem? Wire aech half to it's own driwer and you're good.
 

DIWdiver

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Well, I didn't completely understand your wiring description, but I gather that the remaining strip doesn't reach where you want to put the second transformer. It sounds like your original plan was to run half the string on each transformer, as Toaster79 suggests, but for some reason this won't work.

I would not be surprised if running them in parallel would work. Unfortunately, as they are connected to the mains, I would not recommend doing so unless the manufacturer indicates that they are made for that. You might well find in the manufacturer's literature somewhere, that it's okay.

To me, the bigger problem is that it appears you are using existing mains wiring for low voltage DC. I'm not an electrician, but it sure seems to me like any SELV wiring ought to be readily identifiable as such, and I imagine that your local electrical code dictates that it must be.

The first question I'd ask is whether it's okay to convert mains wiring to SELV. If not, you'll have to re-wire anyway, so your original question might be moot.
 

Ballz Deep

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Another thing to worry about is the type of wire that's already in place. If your using the currently installed wire going from your power supply to your LEDs you need to make sure its stranded wire, not solid wire. Im not sure I understood the diagram, but it sounded like you were trying to use the currently installed wire for the LEDs.
 

Ballz Deep

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The electricity flows mainly on the outer edge of the wire - not in the center. Having multiple strands of wire as opposed to one thick wire would give you more surface area, allowing more electron flow. This will decrease voltage drop. This applies to low voltage DC systems.
 
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Conte

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Hmm, that information is new to me, I'm going to have to look into that, but I don't think it's practically applicable in this case.

The mains wire he is working with more that rated for his application, assuming of course it's the typical 14g solid copper wire.
I noticed that his diagram lists the mains voltage as 230v. Which means he must be in Europe or something and I don't know what gauge wire they use.

The important thing is that he is using wire rated for the load. If it is, then this can be done safely. It may not be to code but as long as he knows what he's doing that won't matter unless he plans to sell the house.

Whether he can wire the drivers in parallel is another story. In theory yes, 2x 50w drivers will equal 100w of drive.
The question is if the driver circuit design will appreciate being linked up that way.

Unfortunately, that is driver specific. There is no general answer to that question.

You could integrate probably some diodes into the to wiring to prevent any voltage backwash from one driver to the other, but that complicated things.
The other thing you could consider is, typically mains wire has 3 conductors. Hot, neutral, and ground. Your LED system likely won't be using the ground wire.
IN which cause you could divide the the legs going to your LED's using the ground wire as a common negative, and the H and N wire to run + to each LED off their own driver.

This idea however, is slightly more advanced. I personally have the skill to do it correctly and safely, but not everyone does.

I would need to know more specifics about the components you're working with to know if this would even work.
Like photo's of the components, and or links to the components and data on how they are normally wired and their pinouts.
 

Conte

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You could also consider running them in series. It might be more friendly to the drivers.
 

DIWdiver

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The electricity flows mainly on the outer edge of the wire - not in the center. Having multiple strands of wire as opposed to one thick wire would give you more surface area, allowing more electron flow. This will decrease voltage drop. This applies to low voltage DC systems.

You are alluding to the 'skin effect', which is a very real thing. I once worked for a PhD professor who had me wind an inductor coil with special wire designed to minimize the problems of skin effect. What a HUGE pain!

However, the skin depth is inversely related to frequency, and is usually only significant at much higher frequencies than we are working with here. This site http://www.microwaves101.com/encyclopedia/calsdepth.cfm says the skin depth of copper at 1 KHz is 2mm. So unless you need wire thicker than 4mm (between 8 and 9 AWG) or frequency higher than 1000 Hz, you don't need to worry.

Also, to take full advantage of the surface area of each strand, the strands need to be insulated from each other.

The primary reason to use stranded wire is flexibility.
 

DIWdiver

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The important thing is that he is using wire rated for the load. If it is, then this can be done safely. It may not be to code but as long as he knows what he's doing that won't matter unless he plans to sell the house.

I strongly disagree. Unless he plans to demolish the house, it will eventually have a different owner. Electrical codes are there to protect me from you, as much as to protect you from you. Depending on the location it may not be illegal for a homeowner to violate code in his own house, but that doesn't mean it's safe or wise.
 

Conte

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Unless he plans to demolish the house, it will eventually have a different owner.

Well, that's kind of what I was implying. If he wanted to sell the house he would have to reverse it to pass inspection.

it may not be illegal for a homeowner to violate code in his own house, but that doesn't mean it's safe or wise.

The key term in my comment is "as long as he knows what he's doing". I've been a technician for 10 years, tho' not an electrician. I know without a shadow of a doubt that I personally could set something like this up and have it be as safe if not safer then code even if it wasn't exactly to code.

Code isn't even necessarily the safest way to do things. I've personally seen work done "to code" that was NOT safe for the application. For instance, an electrician who thinks he knows what he's doing wiring up mobile equipment, which at the time was my specialty, and my line of work I had to go redundantly beyond code.

But I digress. I understand where you're coming from. It's probably not something we should be encouraging.

You never know, tho', the Op could be a licensed electrician and know what he's doing, but simply does not know the drivers.
 
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