Internet of Holiday Lights RoadTest Plus (suppliment) Part 2

This is an update from this post http://www.element14.com/community/groups/arduino/blog/2015/04/03/iot-lights

Lights, Holiday and Electronics

Earlier in the year Christian and element14 sent me the kit for the IoT Xmas Lights.

http://www.element14.com/community/roadTests/1377

I was unable to enter in the challenge due to other commitments, so when I was offered the kit I promised to add something later.

Lights

My lights have finally arrived.

I looked around for LED outdoor fittings and was not happy with the options, so I went the Asian sourced bare RGB modules.

These are 30W RGB http://www.ebay.com/itm/261414473386

The image below was from the website.

          The size is 40 x 40mm across the white area

The first difference was the led string is orientated 90 deg to this image, and the tags on the left side cut to seperate the three strings.

It's possible this image represents a single colour version which the seller also provides.

Connecting it up

I hadn't placed too much thought when I ordered these, since I could wire them in parallel and drive them as three lights.

There are issues with load balance since current will flow through the lowest resistance module.

The usual solution is to place a limiting resistor in series, but with PWM and current control this sort of defeats the purpose.

After receiving them, I noted that it should be possible to cut the right side, which then seperates each LED string.

I could then wire all three modules in series.

There are issues with this as well, since the resistance of each module will differ, the voltage across (and therefore illuminosity) may differ.

LED's have a linear current v illuminosity curve up until it hiits the knee, where more current doesn't give very much more light.

At high current or fully on, you may never see any difference, but at lower current you might.

What to do ...

Spec Sheet

As with many of these asian sources, the specifications are a little lacking.

I returned to the site to see what there was and found this.

So my modules require 900mA and 20-35v across each.

In the first scenario where they are in parallel, I'd need to control 2.7A.

In the second scenario I'd need to use 60v - 95v at 900mA to run them.

It might have helped if I looked at the Infineon shield specs (and the module specs) before ordering modules.

The shield handles 6-48v max and 700mA average with a peak of 1A ...

It suddenly struck me ... this shield was only going to be able to run one or maybe two in series ...and probably not full current and not full brightness.!

Obviously this wasn't going to work.

Plan B

A Plan B is always there in case Plan A fails ...

My original intention was to fit three of these in Outdoor housings to illuminate a large concrete outdoor area we have.

The house is L shape next to this area, and the original intention was to mount one at the left side, one in the middle and another on the right side just above the bench seat.

Having large bright lights is fine, unless you are looking into them, so having three and facing downwards would provide illumination without being a nuisance.

The bulkhead lights on the walls have a cover half way down, so it washes the wall rather than being a bright object that you look directly at.

So can I change the number and/or location to still achieve the original intent.?

Will two lights work?

To provide the same area of illumination, they would need to be raised.

In order to raise them above the guttering, they need to be mounted on a J pole much like TV Aerials are.

We live in the country, and get clobbered by the North West wind.

The corner faces directly northwest, so sticking them on poles, is almost guaranteed to create noise from the wind around the pole, or the vibrations.

As our bedroom is beside one of these spots, that idea is out of the question.

Change locations

The view from this spot is uncluttered.

The lights are more decorative than necessity, so adding poles and mounting for this is not something I want to do.

A future plan is to add a structure to the area where my shadow is, and this would be suitable to add lighting to.

This doesn't exist, but was prewired for the day it does exist. (if I recall exactly where on the concrete to drill the hole ..)

Fit more Bulkheads

This idea has merit, but they currently have the mains wiring coming through the brickwork, so some redesigning to control them would be required.

Adding more bulkheads would have the same issues, but since it is not mains wiring the wire could legally be in the cavity ...

So Plan B is not going to work ...

Plan C

There should always be a Plan C in case Plan A and Plan B fails ...

I could order more shields.

This would allow flexibility in control, but could get rather complicated.

In effect I would need three controls or some form of switch in the APP to decide which lamp you are controlling.

I still wouldn't be able to have them at full brightness (900mA v 700mA)

Lower wattage modules.

The modules are available in 10W or 20W at similar low prices.

As the specs show, the same current and or voltage problems exist.

So my orignal plan to use these with the one Infineon Shield to illuminate the concrete area is not going to work.

However there is a lesson in this adventure.

READ THE SPEC SHEETS FIRST.

Mark