Dimming does not work: checking DALI, 1-10 V and the wiring

On and off works, dimming does not: what that already tells you

An LED luminaire that runs at full output but does not respond to the dimmer hardly ever has a faulty driver. A 1-10 V driver with no control line connected sees an open circuit and goes to 100 percent. A DALI driver without bus voltage falls back to its 'system failure level', which is almost always set to maximum at the factory. So the luminaire appears to work perfectly, until someone turns the dimmer.

Start with one question, therefore: which dimming principle does the driver use, and which one does the dimmer send? You will meet three systems: analogue 1-10 V (or 0-10 V), digital DALI or DALI-2, and leading-edge or trailing-edge phase control on the 230 V line itself. They are not interchangeable. The datasheet is decisive, because the word 'dimmable' on its own says nothing.

1-10 V: polarity and an open control line

With 1-10 V every driver feeds a small current onto the control line, usually less than 2 mA, and the dimmer pulls the voltage between plus and minus down to a value between 1 and 10 V. The control line therefore has a polarity. If plus and minus are swapped, the luminaire sticks at full output or at minimum. Check this at every luminaire: a single wrongly connected driver pulls the whole line down with it.

Measure the DC voltage between plus and minus with a multimeter. At the full setting you should read around 10 V, at the lowest setting around 1 V. If you read 0 V at every setting, the line is short-circuited or the dimmer is faulty. If you always read around 10 V, the line is interrupted: a terminal not made off, a core cut short, or a control cable that was never pulled in. The last one is common in halls that previously had non-dimmable luminaires.

Mind the difference between 1-10 V and 0-10 V as well. With 1-10 V the driver supplies the current and the dimmer sinks it; with 0-10 V the control unit sources the voltage itself. A simple potentiometer dimmer for 1-10 V will therefore not work on a driver that only expects 0-10 V.

DALI: bus power supply, addressing and 230 V on the wrong terminal

DALI is a digital two-wire bus with a nominal bus voltage of 16 V DC. The drivers are polarity-independent, so swapped DA cores are not a problem here. What does go wrong regularly: the bus power supply is missing. A DALI line needs its own bus power supply; the total bus current on one line must not exceed 250 mA. If the supply is missing, you measure 0 V between DA+ and DA- and all luminaires burn at their failure level.

Does the whole line respond to a broadcast command (all on, all off) but not per group or per luminaire? Then the drivers have not been addressed. New drivers have no short address from the factory, and neither does a replacement driver. Have the controller address the line again and assign the groups. One line holds at most 64 short addresses and 16 groups; if you are at that maximum, a new luminaire gets no address of its own and only responds to broadcast commands.

The third classic is 230 V on the DA terminals. The DALI bus may run in the same cable as the mains, for example a five-core installation cable, because the bus is not a SELV circuit. Precisely because of that, a mix-up in the junction box is easily made, and 230 V on the DALI input destroys the driver. Also keep to the maximum line length: 300 metres at 1.5 mm², with at most 2 V voltage drop.

The wrong dimmer on LED wiring accessories

In homes, hotels and offices, dimming happens on the 230 V line itself. A classic rotary dimmer for incandescent lamps works with leading-edge phase control (triac) and often has a minimum load of 40 to 60 W. LED drivers want trailing-edge control instead and together often draw only 20 to 30 W. The result: the dimmer does not start, hums, or the luminaire flickers at the lowest setting and suddenly jumps on as you turn it up.

Then replace the dimmer, not the luminaires. The LED rotary dimmer from the Liregus Modern series handles both leading-edge and trailing-edge control from 3 to 100 W, which makes it suitable for small LED loads. Check the datasheet for an adjustable minimum against flicker at the lowest setting. The rotary dimmer from the Liregus Alfa series, rated 40 to 400 W, is meant for larger loads; with LED, check that the total load stays above 40 W. And never dim a non-dimmable driver on a phase dimmer: it will eventually cost you the driver.

Step by step: six steps to the cause

• Step 1, establish the dimming principle. Look up both the luminaire and the dimmer datasheet: 1-10 V, 0-10 V, DALI, DALI-2 or phase control. If they differ, the search is over.

• Step 2, trace the control line. Is the dimming cable actually connected at every luminaire?

• Step 3, measure. 1-10 V: DC voltage between plus and minus, 1 to 10 V depending on the setting. DALI: roughly 16 V at rest between DA+ and DA-, never 230 V.

• Step 4, isolate one luminaire. Connect a single luminaire directly to the dimmer with a short control cable. If that works, the fault is in the wiring or the number of drivers.

• Step 5, address DALI. Have the controller run a fresh addressing cycle and check the group assignment, also after replacing a driver.

• Step 6, check the phase dimmer. Minimum load, leading or trailing edge, and the adjustment screw for the minimum.

How to prevent it on a new project

Choose one dimming principle per room and record it on the installation drawing. For halls that is usually DALI-2 or 1-10 V. In the ATRIA series you will find the 120 W flat high bay with a 0-10 V dimmable Meanwell driver and UGR<21, the UFO high bays with 1-10 V dimming from 71 euros excl. VAT, and the linear low bay with DALI. Pull the control cable in straight away and label plus and minus at every junction box.

For wiring accessories the rule is: choose the dimmer to suit the driver, not the other way round. Lichtplein supplies businesses only, with up to 5 years of warranty on luminaires. If in doubt, send your luminaire list with your quotation request.

Frequently asked questions