Powering LED Strings and SSRs

**mutleyrover** · 01-03-2015, 07:28 PM

I'm finding myself going round and round in circles thinking about powering my Christmas lights. So far I haven't yet had the time to get this hobby off the ground, maybe 2015 will be my year. However, I do have many questions!!

I'm looking at building a Renard Plus 32 or a Renard 64XC controller so will therefore need separate SSRs. Most of the light sets I have here (in the UK) are LED strings with fixed LEDs that can't be changed. They are low voltage and come with a plug pack (wall wart) that in general provides 24V DC.

Rather than have multiple wall warts I want to power more sets with fewer power supplies. My understanding is that I can use a Switched Mode Power Supply such as the Mean Well NES-350-24 to provide the 24V DC that I need to power a number of sets, as long as I stay well within the output current of 14.6 amps. Is my assumption here correct?

Also, I therefore assume that as most of my lights run on 24V DC, I would therefore use DC SSRs and provide power to them from the SMPS, with each SSR running 4 strings (channels). Am I thinking along the right lines, or is that just a load of rubbish??

I've added a couple of pictures showing the power supply I mean and also an example of the information given on the boxes of my LED light strings.

Thanks in advance for any help!!

**m00dawg** · 01-03-2015, 07:55 PM

I'm still new at this myself but yes I think you are on the right track.

One thing to keep in mind is voltage drops if you are running long cables. The drop will depend on the length and gauge of the wire and the amperage running through it. There are some calculators online you can use to get an idea. There is also some good info on the wiki though it is more focused on 5V and 12V. The principles are generally the same.

You may also want to make sure your LEDs are dimmable using DCSSR's. Most are but it can't hurt to check before you buy a lot of lights. And if you're buying a lot of lights, I would hunt around here to see if you might be able to get lights cheaper by jumping in our a pre-sale or group by. I dunno how many happen in the UK but you can end up saving quite a bit of money that way.

Hopefully some seasoned folks around here can give you better advice, but hopefully the above was at least somewhat helpful ;)

**mutleyrover** · 01-04-2015, 07:42 AM

Thanks for your supply. It's nice to know I'm thinking along the right lines!

I don't think I would be running cables that were that long so hopefully voltage drop shouldn't be too much of a problem. As for the LEDs I have, I'm not sure if they're dimmable or not. At this moment in time I have no controller built to be able to test them so I'll have to bide my time, but fingers crossed they are. I've got about 70 sets at the moment, all be it fairly short strings, so I hope they don't prove to be useless. I'm assuming DC SSRs are the right sort to use rather than AC SSRs when I'm using a DC Power supply.

Also, I noticed that some of the LEDs I have say they are 25V DC. Would it make much difference if these were plugged in to the same SMPS providing 24V DC, or should you use a separate SMPS adjusted to provide 25V DC. I'm no electrician so I'm learning as I go....

Better get shopping for things I guess!!

**P. Short** · 01-04-2015, 01:12 PM

Originally Posted by mutleyrover

Thanks for your supply. It's nice to know I'm thinking along the right lines!

I don't think I would be running cables that were that long so hopefully voltage drop shouldn't be too much of a problem. As for the LEDs I have, I'm not sure if they're dimmable or not. At this moment in time I have no controller built to be able to test them so I'll have to bide my time, but fingers crossed they are. I've got about 70 sets at the moment, all be it fairly short strings, so I hope they don't prove to be useless. I'm assuming DC SSRs are the right sort to use rather than AC SSRs when I'm using a DC Power supply.

Also, I noticed that some of the LEDs I have say they are 25V DC. Would it make much difference if these were plugged in to the same SMPS providing 24V DC, or should you use a separate SMPS adjusted to provide 25V DC. I'm no electrician so I'm learning as I go....

Better get shopping for things I guess!!

Two things to bear in mind:

The peak voltage for a 24VAC signal is around 33V (24V * 1.4), which is greater than the output of your 24VDC supply.

However, potentially offsetting the decreased voltage of the DC supply is the greater duty cycle. Depending on any filtering circuitry included in the 24VAC LED string, the turn-on voltage of the LEDs involved, and whether it is a half-wave or full-wave string, the duty cycle and hence the brightness of the LEDs may vary from when you use them with the AC transformer. They may be brighter or they may be dimmer, the only real way to tell is to try them and see what happens.

**mutleyrover** · 01-04-2015, 03:59 PM

Originally Posted by P. Short

Two things to bear in mind:

The peak voltage for a 24VAC signal is around 33V (24V * 1.4), which is greater than the output of your 24VDC supply.

However, potentially offsetting the decreased voltage of the DC supply is the greater duty cycle. Depending on any filtering circuitry included in the 24VAC LED string, the turn-on voltage of the LEDs involved, and whether it is a half-wave or full-wave string, the duty cycle and hence the brightness of the LEDs may vary from when you use them with the AC transformer. They may be brighter or they may be dimmer, the only real way to tell is to try them and see what happens.

Now I'm confused!! The LED strings I've got have a variety of transformers (wall warts) that all seem to have different labels. My thinking was that LEDs are DC so all of these transformers take our 240V AC supply and change it in to a low voltage DC supply, which then powers the LEDs. That's why I was under the impression that a SMPS would work well to power a number of sets from one supply.

The pictures show just a couple of the wall warts that come with my LED strings... so many different figures, some 24V, some 30V although they don't say whether the output is AC or DC (apart from one!).

**m00dawg** · 01-04-2015, 12:53 PM

Yes, if they are DC lights, you need DCSSRs, though take note that you would hook the lights directly up to the SSR which you will then hook into the power supply. Note that some controllers include SSRs and some do not, so you'll want to figure out which setup works best for you. Depending on how you have things setup. Just be sure that, if you go the integrated route, you get a controller that has integrated DC, not AC, SSRs.

As far as 25V vs 24V, that's actually a good question. It depends on how things are wired up as to what effect that will have, but it will likely just make things slightly dimmer on your 25V strands. If you have a voltmeter/multimeter, you can check what voltage is coming off your 24V and 25V PSUs to see how big of a difference it is. Be aware that some PSUs require a load applied to them to give you accurate readings (so basically you have to measure the voltage with the light strands connected). You could also just try connecting your 25V strands to 24V if they are similar to each other and see what happens, though I would do the multimeter tests first.

**mutleyrover** · 01-04-2015, 03:50 PM

Originally Posted by m00dawg

Yes, if they are DC lights, you need DCSSRs, though take note that you would hook the lights directly up to the SSR which you will then hook into the power supply. Note that some controllers include SSRs and some do not, so you'll want to figure out which setup works best for you. Depending on how you have things setup. Just be sure that, if you go the integrated route, you get a controller that has integrated DC, not AC, SSRs.

My plan is to build a Renard board with off board SSRs. my thinking is either the Renard Plus 32 or the Renard 64XC although I can't decide which is best!!!

**m00dawg** · 01-04-2015, 04:49 PM

At least in the states, I tend to see ~ indicating AC and the === being DC. A quick test with a multimeter will tell you though, so I would do that regardless of what the labels say to know for sure.

The LEDs themselves work of DC though you can have both AC and DC LED strands though their wiring often differs between the two types. To my knowledge, you can't mix and match AC and DC SSRs, so you need to know what you're actually dealing with before you can figure out which type you need.

On the controller side, though, since you want to use external SSRs, that won't really change things much. Either of your choices should work, and don't forget about the group by going on for the Renard SS boards. I'm not sure if that includes the UK, but it's worth checking out since it can save quite a bit of money.

**mutleyrover** · 01-04-2015, 05:04 PM

Figuring out what I'm dealing with in the first place seems to be the hard part!! I really need to crack on and build a controller so I can start some tests! I have ordered a Mean Well SMPS (pictured in my original post, so I guess I can connect a set directly to that for a trial run....

**m00dawg** · 01-04-2015, 08:22 PM

If it were me, I would invest in a voltmeter. In the states they can be had for as little as $10 and that would avoid risking your LED strands. A controller won't get you much if you don't know what sort of SSR to purchase, after all.

If you're going to build a controller, you should have a voltmeter anyway to be able to test to make sure the correct voltage is going to the correct pins, etc.