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Wireless Dimming - Frequently Asked Questions

Q: How do I run a DC motor or actuator backward and forward?

I’ve had a small linear actuator on my trade-show table of tricks for years — some of you may have seen it at USITT Stage Expo, or the ABTT Show in London. It’s a little extendable “arm” that runs in and out using 2 channels of wireless D

MX control.How do you make a small DC motor or actuator change direction?
They change direction when you reverse the polarity of the power driving them: swap the red and black wires (the + and – leads) and they run the other way.

You need 2 channels of DC dimming, a small DPDT (double-pole, double-throw) relay, and — of course — the motor or actuator. One dimmer provides motor power, the other dimmer drives the coil of the relay. Connect the motor power through the contacts of the relay to provide one polarity when the relay is NO (normally open) and the opposite polarity when NC (normally closed).

Use a linear dimming curve for motor power. This lets you control motor speed. Use a non-dim curve for the relay, to ensure it is either open or closed. If you send dimmed power to a relay, it will chatter and not switch reliably.

Here’s a diagram of how to connect the relay to an RC4Magic DMX2dim dimmer. You’ll want to use a relay with a coil voltage that is the same as the motor, and run the whole thing at that voltage. A good choice would be 12V, but it can be anything from 6V to 24V when using our R3 dimmers; or 6V to 18V with our older dimmers.

There you have it: now you can make that drawbridge go up and down… or whatever else you want to do with a reversible DC motor.

reversible DC motor drive diagram

One dimmer provides motor power, the other dimmer drives the coil of the relay. Connect the motor power through the contacts of the relay to provide one polarity when the relay is NO (normally open) and the opposite polarity when NC (normally closed).

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Q: What wire gauge should I use with RC4 dimmers?

The wire gauge you use determines the maximum current you can safely pass through the circuit.  Too small a wire size will heat up and — in the worst possible scenario — melt, burn a performer, or worse.

The published maximum current rating for the DMX2dim is 15A total.  The latest versions are internally thermally protected.  When all is working as it should, the device will shut off before a fault becomes catastrophic.  This in no way excuses you from using appropriate external fuses for your specific application.

Using NEC (US National Electrical Code) guidelines as a reference point, 16AWG (American Wire Gauge) wire is the largest size you should ever need, and it fits in the screw terminals we provide.

Electrically speaking, the primary concern is resistance of the wire, measured in milliohms.  If you keep your wire lengths short, you can get away with much smaller wire than 16AWG.  NEC codes presume wire lengths of many feet.)

If you’re a pragmatist, do what I often do: run your application on a test bench with the wire gauge you’d like to use.  Run for the full length of time you will be using the device in performance.  Ensure the wire, connections, junctions, sockets, etc., do not get too warm to comfortably hold.  That’s what matters!  If there is little heat, there is little loss, and you’re good to go.  If any point has a resistance that is too high, it will become warm, or even hot.

Adjust your design and construction practices to avoid heat.  You’ll also get more light out of your lamps and more life out of your batteries.

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Q: Can I attach a battery charger while an RC4 dimmer is connected?

Yes!  We do it all the time. When we demonstrate RC4 products at tradeshows, we often have a battery charger connected at the same time.  We need to run all day for several days in a row, so it’s very important we keep our batteries charged as much as possible.

When a charger is attached, the voltage at the battery terminals will be higher than normal, but it won’t get high enough to cause any harm to your RC4 receiver-dimmers.  If all your dimmer levels are at zero while  doing this, that’s the end of the story.

On the other hand, you might want to operate the dimmers while you have the charger connected (just like we do in tradeshows).  In this case, keep in mind that when you bring a channel up to full you are delivering more than 12V to your load.  This will reduce the life expectancy of 12V lamps, while also making them appear brighter than usual.  If you are driving LEDs through a current-limiting resistor, higher voltage results in higher current, and you could be pushing your LEDs beyond their rating.  I would run the channels at less than 100%, just to be safe, when chargers are connected.


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Q: When I assign a DMX channel to a dimmer, the dimmer comes on and stays on. Why can’t I dim it?

This is the most common technical support call we get. (In fact, for weeks at a time it’s the ONLY call we get!)

There is another channel up in your system.  You may not be aware of it or know what it is, but it’s there and it’s a lower DMX channel number than the one you want to assign to the dimmer.  When you press the Set button on the dimmer, it finds the lowest DMX channel that is not off.  Your dimmer found one, but it’s not the one you have in mind.

Common causes of this, in order of likelihood:

  1. House lights. We have seen many installations where house lights are assigned to a low channel, like DMX channel 1.  And you have your house lights up while you’re assigning channels to your RC4Magic dimmers.
  2. Work lights.  Same idea… your work lights are on, and they’re using a low DMX channel.
  3. A complex fixture profile sets some channels to something other than zero. In this case, when you clear your console and all channels are “off”, channels controlling moving-light motion axes, for example, might be at 50% to park the light at home position.  You need all channels to be actual zero.  Not home for your moving fixtures.  Not the middle of a scroller gel.

How to find the problem:

The best way is to use a DMX data tester, like a Goddard Design DMXter, or a Fleenor Gizmo.  Connect it right at your RC4Magic DMXio transmitter.  Look at the channel levels.  Find the first one that is not zero.

How to work around the problem:

Use an alternate source of DMX data to configure your RC4Magic dimmers.  It may be an arduous task to figure out how to get your expensive and complex lighting console to actually clear all DMX channels.  Instead, grab a Pocket Console or DMXter and use that.

It doesn’t matter what your data source is when you assign channels to dimmers.  Channel 452 on your DMXter is the same as channel 452 in a universe of your console.  The dimmer remembers your settings forever until you change them, so you can move your transmitter back to your lighting console and it won’t matter at all if other channels are up.  It’s only a problem at the moment you need to press the Set button.

Is this hassle really worth it?!?!

Well… yeah.  : )

Other DMX products provide dipswitches, or rotary controls, or a display and up/down buttons.  Any of these options take up more space than the size of our entire DMX2dim 2-channel dimmer.  You love the size of our little units.  But now you have to figure out how to get one DMX channel on at a time.  Only when you’re setting things up.  Then you’re done.

Now that we’re in the age of Remote Device Management (RDM), settings could be done that way, with no switches on the dimmer at all.  But you’ll need an RDM controller.  Do you have one yet?  Most of our customers do not.  In a few years you will.  We’ll be ready for you when you do.  Have a look at our RC4Magic CS1 Control Surface — it’s a small DMX console with built-in wireless and RDM controller features coming soon.)

As of March 2011, we offer RC4MagicPC — an easy-to-use USB dongle and Windows app that lets you access features and functions in your RC4Magic devices on your PC screen.  Power up a dimmer, read its settings, change them, send them back.  This also lets you see which DMX channel was up when you pressed the Set button.  That’s kinda handy, don’t you think?  Call us for more information.

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Q: How can I trigger a Look Solutions Tiny Fogger?

Look closely at this image.

Although it shows the original yellow-label RC4Magic, newer units connect exactly the same way.

This configuration powers the DMX2dim dimmer from the Tiny Fogger battery. The 1/8-inch miniplug remote control port on the Tiny Fogger provides ground on the sleeve (braid), and power on the tip (red). The trigger input (white) causes the fogger to run when it is shorted to ground. The DMX2dim dimmer switches on the negative side: when the dimmer is turned on, the negative output terminal connects to ground. Thus, it can be directly connected to the trigger input of the fogger. Again, that’s the *negative* side of the dimmer output, marked DimA- (or DimB-) in black.

We bought a 1/8-inch stereo miniplug-to-miniplug cable at a local electronics store and cut it in half, yielding *two* Tiny Fogger hookup cables. Every miniplug cable I’ve ever seen had red on the tip contact, but you might find a cable that puts white on the tip, or uses different colors. Thus, I recommend testing with a meter to find the two power lines (ground and +12V), then short the remaining line to ground to confirm that it triggers the fogger.

Word of caution: DO NOT ALLOW THE POWER SUPPLY LEADS TO SHORT TOGETHER. The Tiny Fogger battery is quite powerful and a dangerous situation could result.

1/8-inch Tiny Fogger miniplug —-> DMX2dim dimmer screw terminals:
sleeve —-> negative power input (ground)
ring —-> negative (Dim-) output of dimmer (channel A or B, you choose)
tip —-> positive power input (+12V from Tiny Fogger battery)

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Q: What is the best rechargeable battery to use with a 4W LED?


What is the best battery solution for a portable dimming situation? We are using a 4 watt LED lamp and need it to run for 10 minutes and have 4 hours of standby time.

Thanks for your Help



Hey Andrew,

We must calculate the battery requirement for the load (4W for 10 minutes), then add the standby current for the receiver and dimmer. An RC4Magic DMX2dim draws approximately 200mA.

First, we need to choose a working voltage. If you are using LED devices with built-in current limiting, they are probably designed to operate at 12V. In that case, 4W / 12V = 333mA. Thus, the running load is 333mA + 200mA for the receiver electronics = 533mA.

A very common small 12V sealed lead-acid (SLA) battery is rated at 1.2Amp-hours. This A/h rating is based on a 20 hour discharge rate. On other words, it can deliver 60mA per hour, for 20 hours. But battery chemistry gets less efficient when the load is higher. In fact, if you put a 1.2A load on that battery, it will work for only 30 minutes (or perhaps slightly less) before discharging to the lower limit recommended by battery manufacturers. The efficiency curve is non-linear.

1.2A / 533mA = 2.25. If the battery efficiency curve were linear, a 1.2A/h battery would drive the dimmer with 4W load for over 2 hours. Worst case, you will get better than 1 hour. That’s a whole lot more than the required 10 minutes.

1.2A / 200mA = 6. If the battery efficiency curve were linear, a 1.2A/h battery would drive the RC4Magic DMX2dim receiver, with the load turned off, for 6 hours. In fact, it will be less — approximately 4 – 5 hours. That meets the specified requirements.

Thus, I recommend using a 1.2A/h SLA battery. It’s small, readily available, and quite inexpensive.

However, these current requirements are low enough that NiMH batteries could also be considered. This is particularly viable if you are using an LED component, without built-in current limiting. Then you can choose a low operating voltage, and use a simple resistor for current limiting. In that case, I recommend using a pack of 4 AA cells. Each cell produces 1.25V, for a total of 5V. Although this is less than the 6V specified as the minimum voltage for the DMX2dim, it does work. Just remember that you don’t have much room for the battery voltage to drop further, before the dimmer electronics will cease to function.

At lower voltage, 4W demands higher current. 4W / 5V = 800mA. The standby current for the dimmer-receiver is unchanged at 200mA. So you need to deliver 1A for 10 minutes, 200mA for 4 hours.

Capacities of AA cells vary, but a common mid-range value is 2000mA/h, which is 2A/h. This means you will get longer running times than noted above for a 1.2A/h battery. Just be sure to calculate the current-limiting resistor value properly. You’ll find a useful calculator for this at http://ledcalc.com/.

I hope this helps!


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Q: Why are my lamps weak and blinking off and on?


When channel levels are brought up, the load (lamp, motor, etc.) operates for a brief moment then goes off. A second or so later, it comes back on. The problem appears cyclical or intermittent.


When a lead-acid battery is measured with no load it reads approximately 12V. This is true even for a substantially discharged battery. RC4 electronics require very little current to operate, and a discharged battery still provides enough power for the receiver to come on and indicate traffic.

Here’s the problem cycle:

  1. When RF control data indicates an output level, the output driver delivers battery power to the load. If the battery is under-rated or under-charged, voltage will drop substantially under load.
  2. When the battery voltage drops much below 5V the RC4 receiver will shut down. This disconnects the load from the battery.
  3. With the load disconnected, battery voltage drifts back up. (It eventually drifts back up to 12V, unless the battery is seriously damaged). When battery voltage climbs above 6V, the RC4 receiver comes back on and starts monitoring control data again.

…And the cycle starts all over again.

In some cases, exactly the same symptoms are caused by undersized wire or poor connections between the battery and the RC4 receiver. These cause resistance, resulting in a voltage drop at the receiver when the load increases (Ohm’s Law).

This cycle through steps 1, 2, 3 and back to 1, results in the symptom described. The actual cycle time varies with battery size, battery charge, the size of the load, power levels selected, and wire sizes used. Eventually the battery is damaged and fails to drift back up enough to continue the cycle.

To prove this is happening, put a volt-meter across the power input terminals at the RC4 receiver. The voltage will drop when the load comes on. When the voltage drops enough, the load will go off. When the voltage drifts back up enough, the load will switch back on.

If these voltage fluctuations are apparent at the receiver but not at the battery terminals, then wire and connections are at fault you must conduct adequate current from the battery to the receiver to avoid these unwanted voltage drops.


  1. Be sure the battery is rated large enough for the intended load for the operating time you require.  Prove this by directly connecting the battery to the load and testing without the wireless system in the circuit at all.
  2. Ensure the battery is fully charged using a smart charger that accurately detects the condition of the battery.
  3. Be sure wire gauges are large enough, especially between the battery and the receiver/dimmer.
  4. Be sure connections are tight and strong. Hot wires or connections are probably causing problems.

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Q: Why are my fades not smooth? Why do the lamps blink in and out?


Fades are not smooth, channels intermittently black-out for a second or more.

Cause 1 (most likely):

The RC4 system depends on RF signals getting from the transmitter to the receivers. An antenna is under the top cover of each RC4 wireless device  one at the transmitter, and one in each receiver.  (This, by the way, is why we use tough ABS plastic enclosures: they are transparent to radio waves; metal cases are not.)

RC4Magic operates in the 2.4GHz band using spread-spectrum digital radio. Although output power is quite low, high frequency signals bounce easily and receivers are very sensitive. This means that receivers can find good data most of the time.

The system will not work, however, if the tops of the plastic enclosures are blocked with batteries or metal coverings. Signals must be able to get in and out of the top of each box, both at the transmitter and at each receiver.


Make sure the top area of each plastic enclosure — usually marked on the label as the RF Hot Spot — is not blocked by batteries or metal obstructions. These block radio signals.

Small clusters of wiring, gridwork, bars across the top of the enclosures, etc. generally DO NOT cause problems. Make sure there is a path for SOME signal to get through and the system should work fine.

Where quasi-line-of-sight is attainable:

  1. Position the transmitter overhead, above the stage or other area where receivers are positioned. The top of the transceiver should be facing down, towards the receivers.
  2. Position receivers facing up, towards the transmitter tranceiver.

Where line-of-site cannot be acheived, or there are numerous obstructions between transmitter and receiver:

  1. Position the transmitter transceiver so the top of the box is facing the ceiling above the stage, or the back wall if it is largely clear. Signals will bounce back and flood the stage. Avoid metal obstructions or large harnesses of wiring in the signal path.
  2. Position receivers so the top of each box is facing the same way as the transmitter. Reflected signals will bounce directly into the receiver antennas.

RC4 technology is VERY tolerant of signal degradation and electrical noise. Most users have no problems… in fact, at the time of this writing only a handful of radio interference problems have ever been reported with an RC4 system. If you think you’re suffering radio interference problems, FIRST be absolutely certain your batteries are good and you are within the 200 – 300 foot operating range.

Cause 2 (less likely):

In early 2011 it came to our attention that a firmware bug was inadvertently released.  If you are experiencing choppy dimming and/or very long connect times when a receiver is first powered on, please contact RC4 for free update.  This update is free.  If your unit is out of warranty, all you pay is shipping.  If it is in warranty, we pay the shipping both ways.  We apologize for this inconvenience.

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