how best to wire mr11 and mr16 led replacements?

[danieruz]

Hi!

Planning to replace some halogen mr11 and mr16 lighting in two separate rooms with led mr11 and mr16. Just understanding electricity basics and wanting to get things right, I've read up quite a bit on allaboutciruits.com, so I'll throw out my plan and hope for some help from those willing

Let's take the bathroom first: we currently have 4 mr16 20W halogen bulbs. I've looked at the wiring and they're all wired in parallel to a power supply providing 12V AC, rated 35-105W (the transformer is converting from 230VAC). I've purchased 4 6W led mr16 replacements. I plan on replacing the transformer with a led driver that is rated for the watt range I'll be using (20-40W so I have headroom for higher wattage bulbs if I want them later) So:

1. Should the driver be AC/DC? If the bulbs support both, I'm seeing most of the led drivers supplying DC, so that's probably best?
2. serial or parallel? I'm seeing many people on the internet simply replacing the halogens with led replacements and leaving the wiring (which is usually parallel for halogen setups, I'm assuming), which is a bit confusing to me: How are these mr11 and mr16 leds working in parallel off the driver, don't we end up with the current through each led too low? Something to do with their internal driver? My understanding is that LEDs generally are in series, that way, we maintain current throughout, and just step up voltage, right?
3. I've seen some people say that these bulbs actually want ca 3.7V (being a noob, that's a bit confusing to me since the bulb says it's a '12V', but hey...), so one should plan the driver accordingly, so in the above case, I'd want 4x3.7V = at least 15V? I see most led drivers say they can provide up to x volts, then mention the current they can provide, so how do I know how much current these mr11 and mr16 leds need? They also don't seem to care about polarity, even if used with DC?

summarize: led driver that supplies at least 15V DC, ??mA, then string them in series?

In the kitchen: we have 10 mr11 20W halogen bulbs, that I'm replacing with mr11 3w led. the seller says DC is best, and assuming a roof of 4V forward voltage on each of these, if I string them in series, then I need a driver that can supply up to 40V, and ??mA?

Hopefully I'm being fairly clear; I suppose a part of the problem is that equipped with my new found knowledge of how to use ohm's laws;-) these bulbs are a bit of a black box for me since they just say how many watts they use, but don't tell me forward voltage or current, argh!

When I get the bulbs, is there a good way to run some simple tests on the bulbs with a multimeter and power supply to find their 'sweet' spot, both in terms of voltage and current? Should I even care, or just get a driver that comes close with some headroom and call it good?

Thanks in advance for any tips/advice!

 

[wws944]

All you should have to do is plug your new LED bulbs into the existing sockets with the existing transformers.

 

[danieruz]

Thanks for your reply.

All you should have to do is plug your new LED bulbs into the existing sockets with the existing transformers.

Yes, perhaps I'm over-extending in detail on this; I've looked around at what people are saying about these bulbs, and it seems they have pretty much everything they need internally to regulate voltage, current, etc.

But I can't just plug them into the existing setup since the total wattage of the LED bulbs falls below the specified wattage range of 35-105W on the current AC transformers, so I still need to replace the transformers at least. I suppose when the LED bulbs come in the mail I can connect them to a 12V power supply and use a multimeter to see how much current they draw, then I can buy appropriate led drivers, and string them in series. Hopefully this will be sufficient!

 

[wws944]

I'd still bet the existing transformers will be fine.

One thing you may have a problem with though, is if you use dimmer switches. Some dimmers need a minimum load or there may be some 'flicker' in the bulbs. A work around for this is to keep one halogen lamp in the chain.

 

[danieruz]

It's at least worth a try before replacing the transformers!