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RC4 Knowledge Base

How Much Power Does an RC4 Device Draw? How Big Does the Battery Need to Be?

RC4 Series 3 devices incorporate high-efficiency switching regulators. While other manufacturers often depend on traditional analog voltage regulators that dump excess voltage as heat, RC4 Series 3 regulators barely get warm and waste almost no battery power at any input voltage from below 6V all the way up to 35VDC.

Idle current — the power draw for just the device electronics when it’s waiting to do something — varies between 0.6W and 0.75W. We rate it in watts because of the wide input voltage range.  (And they actually work down to 5V, providing working range when starting with a 6V battery.)

To quickly calculate idle current draw, divide 0.75 by the working voltage. The result is in milliamps:

0.75 / 6V = 125mA

0.75 / 12V = 62.5mA

0.75 / 24V = 31.25mA

For batteries under 3Ah (i.e. 3000mAh), we recommend NiMH batteries. All battery types drop in efficiency as the load on them increases. You can tell this is happening when the battery gets warm — that heat is wasted power. The closer you get to the 1-hour capacity, the lower the efficiency becomes. Entertainment almost always demands the smallest possible battery, which means running at maximum rated draw. Under these circumstances, derate the published battery capacity specification by 25%.

So, if you have a 12V 2500mAh Sanyo Eneloop, the real battery capacity with a 2500mA load is 2500mA x 0.75 = 1875mA for an hour for a running time of just 45 minutes.  The smaller the load, the closer you get to the published capacity.  The published capacity is often based on a 20 hour running time.  That is, if you have a 125mA load on a 2500mAh battery it will run it work for 20 hours.

If that battery is powering only an RC4 Series 3 device with no additional load, or the load is very small, you don’t need to derate the battery capacity: 2500 / 62.5 = 40 hours of RC4 Series 3 device idle running time.

Now, for example, add 3A (3000mA) of LED lighting and you must derate that battery to 1875mAh. Then, 1875 / 3000 = 0.625 hours, which is just 37 minutes.  (For your own project, you’ll need to know the real amperage of your actual load, which could be just about anything.)

In most shows, the device load is not usually active 100% of the time. Color mixing, dimming, and off time all extend battery life. I would expect the described RC4 dimmer, battery, and 3A LED load to work reliably for an hour or more in a typical lighting design. This assumes every performance starts with a reputable brand of battery, fully charged, in good condition.  (Remember your show and lighting design might not be typical.)

One last thing to keep in mind: NiMH batteries are good for somewhere between 250 and 500 charge cycles. They quickly deteriorate when they hit end-of-life. It is not unusual to have a battery fail today that ran perfectly yesterday. After 300 full charge cycles, be ready with a replacement.

If you’re unsure about where to start, look at rechargeable NiMH battery packs build with AAA and AA size cells.  In my opinion, Sanyo Eneloop cells are the best performers and worth their additional cost.  Custom packs are easy to find online, and a wide range of standard packs are available online and in local shops.  The most common voltage for lamps and LED tape is 12V, but you’ll occasionally find things that run at 6V, 7.2V, 14V, 18V, and 24V.

James David Smith, President and Chief Product Developer
13604 Heathwood Court, Raleigh, NC, 27615, USA
Office 919-229-9953 | Skype rc4jds
Live Life Untethered.