Dimmers and LED lamps
Dimmers! These can be really challenging.
A massive saving!
A rotary or dim press dimmer module were installed. These old halogen lamps get incredibly hot, and once on only after a few second they are far to hot to touch. The result is overtime, the holders, transformers can burn and cause major problems.
If one only wants to fix a few down lighters using the old halogen lamp, this can still be done as the old transformers are still available.
However, we recommend all these old halogen down lighters be replaced to LED lamps. The led lamps do not require a transformer.
Note: If you are purchasing the LED Dimmable lamps please check with this led lamp compatibility chart. We do not guarantee our dimmer unit and or labour if you so wish to purchase a lamp that is not listed. Click here to see if your lamps are or will be compatible.
 |  |  |  |
Please remember that you get non dimmable and dimmable lamps, in all shapes and size. Also different colour spectrum.
Typically the lower the Kelvin (K) the warmer the light, and the higher the K the cooler the light.
For example 3000K would signify a warm white, whilst a 4000K would be more cool white and 6000K a daylight effect.
Examples of dimmers that we install. Please note there are a lot of different cheap lights on the market, which do not dim correctly.
Why does a dimmer buzz/hum
Only a leading edge dimmer causes a buzz in transformers and in itself. When a transformer is operated on a normal non-dimmed AC cycle, it is quiet because it turns on “softly” when the AC starts off from zero volts.
On leading edge dimming the transformer experiences a sudden electrical and mechanical “shock” when it receives the sudden very high voltage and corresponding inrush current. A trailing edge dimmer and transformers being dimmed is quiet because the dimmer and transformer “thinks” it operates with a normal non-dimmed AC cycle – there is no sudden high voltage or inrush current that “shocks” the load
DC Dimmers
Use shielded cable for the bell-press wires as per the DC Dimmer data sheet if multiple DC dimmers are connected to one switch and are behaving inconsistently.
When a DC dimmer is wired directly to an electronic transformer, some transformers enter protection mode during the initial power up. Generally, the cable length is < 100mm. You can extend the cable length between the power supply and DC dimmer by 100mm should this occur
Dimmer Installation
LED’d not turning on at low intensity
If the LED lamps are turned off at a low intensity and turned on again, there could be a lengthy time delay before the lamps turn on, some turn on and some not. This occurs because the LED lamp is not designed to dim as low. Set the minimum intensity of the dimmer to suite the lamp’s turn on behaviour:
Dim down to lowest intensity
Turn the dimmer off, wait a couple of seconds and turn on again
Increase the light intensity and release the bell-press switch as soon as all the LED’s are on
Now set the dimmer’s minimum intensity as follows:
Press the bell-press switch 11 times (quick press, approximately 2 presses per second)
If the dimmer accepts the program setting, the lamps will go to full intensity.
The dimmer is now set to prevent the LED from dimming below this point. The setting is retained even after a prolonged power failure. In some cases, it might be required to increase the intensity slightly during step 3 to ensure reliable turn on of all LED’s.
More than one dimmer per wall box
There is no allowance in the IEC or SABS/SANS specifications for dimmers to be tested or qualified for more than one dimmer per wall box. It is however often desired to install more than one dimmer per switch box.
In these cases it must be kept in mind that a dimmer does heat up the air inside a closed space and two or more dimmers in the same closed space will hence influence each other’s maximum load and temperature ratings. Ideally the additional dimmers should be installed remotely (in the ceiling or roof), or the dimmers should be de-rated.
There is no de-rating factor available from the international specifications, but Shuttle recommends that the maximum dimmer VA rating be de-rated by 1.15 times the number of dimmers inside the same enclosure, as follows:
For example, if two 500W dimmers are being installed in the same wall box, each dimmer’s VA rating is de-rated to 217VA each. Similarly for three 500W dimmers, each dimmer is de-rated to 145VA.
The normal dimmer maximum load for non-unity loads must however still be obeyed. Hence in the example of the three dimmers, if one load has a unity power factor, that dimmer’s wattage rating is 145W and if the other two loads have a 50% power factor, each of the corresponding dimmers will have a maximum load rating of 73W
Dimmable MR16LED’s flick or flash when turned on at low light level
This is a function of the transformer/MR16 LED interaction. Since the transformer must first turn on using the LED lamp current feedback, the lamp and transformer reacts to the dimmer bus voltage once the lamp is stable.
A flash or flick can sometimes be observed if the lamp is turned on below approximately 50% intensity.
It was found that this is not a function of the dimmer brand or dimming method. If the transformer/MR16 LED lamps exhibits this characteristic, it will usually occur with any type of dimmer, whether leading edge, trailing edge, rotary or bell-press
Dimmable MR16 LED’s dim too quickly at low light level
As in the case where some of the MR16 LED turn off, it was found that a number of electronic transformer and MR16 LED lamp combinations exhibit a dimming curve very similar to that of conventional halogen lamps. Some however do not and might dim very quickly at low light output.
Activate the MR16 LED compatibility mode of the SDIM-T-LED.
Dimmable MR16’s do not turn on
Most electronic transformers employ self oscillating methods which rely on the load current for oscillation, hence the characteristic minimum load requirements.
Since LED lamps consumes much less power (current) than it’s halogen counterparts, it could be that the lamp current is too little to initiate the transformer oscillation and hence turn on. This is especially a possibility if the supply voltage is relatively low and with a low total load on the dimmer.
Follow manufacturers recommendations for transformer compatibility and minimum number of MR16 LED lamps per transformer. If this is according to specifications, activate the MR16 LED compatibility mode of the SDIM-T-LED.
When dimming down, the LED’s turn off
Although the dimmer did not turn off while dimming down, the LED’s, especially some MR16’s with electronic transformers, do turn off. This is once again a function of the control circuit electronics as above and/or the interaction and characteristics of the MR16/transformer combination. It was found that if the dimmer’s lowest light output level is adjusted to prevent certain electronic transformer and MR16 LED lamp combinations from turning off a low light output, other combinations of transformers and LED’s do not dim low enough, which would limit the effective dimming range.
In order to address the two extremities, the dimmer’s minimum light output level was designed to allow an acceptable dynamic dimming range for most popular transformer/MR16 combinations. The disadvantage is that some combinations might turn off at low dimmer output.
Dim up and down around the point where the LED’s turn off. Then increase the light output slightly and set this level (MINDIMT) as the dimmer minimum level (11 clicks).
Dimmable flicker at low light output
There are many different types of control circuits employed in dimmable LED’s. Some of the circuits or control IC’s might not be able stabilise the LED at very low light output, especially in areas of low supply voltage. This however usually only occur at fairly low light output
Dim to the lowest light level and then increase the light level to where the light output is stable. Set this level (MINDIMT) as the dimmer minimum level (11 clicks).
Two way switching does not work
Most two way switching problems are caused by some interference on the two white control wires. Some basic checks can be done. Remove all the two way switching connections and check the dimming operation. Next connect a remote bell-press switch with completely separate wires (hence not in the conduit or existing harness – run loose wires on the floor for a distance to the other switch).
Check operation, if the dimmer operates correctly, inspect the wire harness for possible short or incorrect wiring
Make sure that there are no mains live, neutral or earth connected to the two white wires or any bell-press switch connected to the white wires.
The lights dim down too much
Dim to a comfortable low light level and set (MINDIMT) this level as the dimmer minimum level (11 clicks).
Can a dimmable MR16 LED be used with a wire wound transformer?
Preferably not. Shuttle does not qualify any dimmer model to be used with wire wound transformers due to the possibility of dimmer and/or LED damage. In fact, a number of prominent dimmable LED manufacturers/suppliers issued release notes which state that the LED’s are not to be dimmed when powered from wire wound transformers.
Unless the wattage load on the wire wound transformer is close to the VA rating of the transformer, the back EMF can be very large. If the real load is close to the VA rating, most of the back EMF is only caused by the transformer leakage inductance which is normally only about 1-4% of the total inductance (depending on the size and winding method).
The problem with LED is that one would place a “replacement” lamp on the transformer – that is light output replacement, not wattage replacement. For instance, a 200VA wire-wound normally had 4x50W halogen lamps. Now the 4 halogens are for instance replaced with 4x10W LED’s and the 200VA transformer only has a load of 40W which implies that the total circuit now becomes hugely inductive (same with a 1x10W LED on a 50VA) and the power factor deteriorates significantly.
When not being dimmed, the much larger energy stored (causing back EMF) is simply returned to the mains without a problem, unless there is a brown-out. During a brown-out, the voltage is momentarily interrupted and it can cause a much higher back EMF to be generated.
Fortunately this would generally not cause a problem since it’s for a very short time. If the under-loaded wire wound transformer is however dimmed, the problem becomes significant. Essentially the voltage to the transformer is interrupted during each cycle and the EMF generated will over stress the dimmer and failure will occur unless a dimmer specifically designed for an inductive or so called “motor” load is used.
Choosing between low voltage or 230vac dimmable LED lamps
In the case of dimmable LED’s the advantages of the direct 230VAC products makes this the preferred choice. Most often the MR16 LED lamp is not supplied with a transformer. This then not only brings compatibility of the LED and transformer into question, but also compatibility of the transformer and dimmer and in most cases the compatibility of the dimmer/LED/transformer combination.
There are three very complex and physically different electronic technologies that must be optimally matched. If not matched, the lamps could flicker, dimming range be limited, lamps might not turn on at all, etc. etc. On the other hand, a 230VAC dimmable LED lamp is a complete unit which does not require additional and very much unknown electronic modules to operate.
This not only makes it much easier to ensure dimmer compatibility (avoid possible MR16 flashing when turning on or off), but remove a possible weak link from the lighting system.
A good example of a maintenance issue is if the client has low voltage LED’s installed and a failure occurs. The maintenance crew must have not only spare LED lamps, but also spare electronic transformers, since they do not know which failed, LED or transformer. If the transformer failed, they should ideally ensure that the same brand and model of transformer is replaced, else the LED lamp might not react the same as the others.
