Portable USB battery power banks sold in stores are another power option. While designed to charge cellphones and tablets, we can use them to provide 5 Volt power for LED lighting. The main problem is the tendency to turn off automatically, but we got around that.

We tested eight models. What we learned can be helpful even if you don’t buy one listed here. Which is good, because the fast-changing consumer market obsoletes them every few months.

Test Results

They varied in power capacity, style and other differences not found in the documentation. An important difference was the undesirable tendency to turn off automatically. We found:

  • Three models (A,B,H) stayed on always (we liked that!)
  • Two (C,D) stayed on if a low current of 4mA and 8mA, respectively, was being consumed by lighting (usable in most any project)

That covers 5 of the 8 units and we liked them all. What about the other three?

  • Two (E,G) stayed on if a moderate current of either 36mA or 45mA was consumed (may need changes to get the current up in some projects, but not bad. We can work with that)
  • One (F) sporting three USB ports stayed on if 94mA was present on one port or if 125mA was present on either of the other two ports (better suited for larger projects). We expect power banks like this to be rare

In all cases, time was on our side. Lighting could fade too low for 10, 15 and in one case, E, even 60 seconds before the power bank shut down. If brightness returned soon enough, it would not shut down.

Of the units that turned off, they required either a pushbutton press to turn them on again or to disconnect the USB cable, then reconnect.

Today’s cellphones require faster charging than their predecessors. Only C, E, and F were rated at the 1 to 2 Amps needed. But the lesser units also worked for lighting projects consisting of a few PowerCookie Boards or less.

How long will power last for a bank that must be drawn down at a higher rate of say, 100mA to stay on? Such calculations are found below. In F’s case, which has a 10,000 mAh capacity, the answer is 67 hours of operation, almost 3 days.

Evaluating your own Power Bank

When firing up a new project, it is helpful to know how much current will keep the power bank turned on. An estimate can be made using the tables below. Narrow the range by adding or removing LED’s and trying again.

If a bank requires more current to stay on, more LED’s can be added that are constantly lit. If there are not enough LED Ports to do this, a Ditto can be added to the chain (upstream, where they won’t be dimmed, if necessary). All the better if the LED’s can be used in the scene. While adding cost to the project, it allows using a power bank you already have.

Here are the currents of various fully lit LED’s:

LED Type                  Current
Bare color…………28.0mA  2 Volt LED’s
Bare white,blue…..20.0mA  3 Volt LED’s
Wired, w/resistor…7.0mA

Here are the currents of boards:

Board                       Current
Morsel…………..4.0mA   typical
Light Valve……..3.0mA   typical
Ditto…………….5.0mA on/30mA off

Examples at fully on:

  1. Morsel plus 9 wired LED’s with resistors = 4mA + 9 x 7mA = 67mA
  2. Light Valve plus Ditto plus 6 blue bare LED’s = 3mA + 5mA + 6 x 20mA = 128mA

Not all power banks correctly estimate the average current where dimming is involved. They may need more current than expected.

Hours of Use Calculation

The electronic circuit that produces the 5 Volt output reduces the available milliamp hours (mAh).

To calculate: Take 2/3 of the internal battery capacity. 10,000mAh becomes 6,667mAh actually delivered through the USB connector to the Morsel or Light Valve. Then divide by milliamps consumed to get hours of use. Note that all rechargeable batteries lose capacity over time.

Hours of Use Table
Based on a small 2,600mAh power bank (Actual 1,733mAh)
with different LED's

Connected to Morsel            On Current    All On    50% On*
9 red, green or yellow LED's      257mA   6.7 Hours   13 Hours
9 White or blue LED's (Pictured)  185mA     9 Hours   18 Hours
9 Wired LED's with Resistors       68mA    25 Hours   47 Hours common configuration
Flashes & effects, mostly off      20mA    3.6 Days   5.8 Days

*More hours is often a better estimate. For example, flashing strobes may be on only a few percent of the time, greatly extending battery life.

Pictured, a Morsel with 2600mAh power bank. When embedded in a project, the blue LED’s will typically be replaced with wired LED’s of various colors that are snaked throughout the scene. The red USB cable may be hidden and brought out to an external access point so that a USB charger can reach it. There is no Off switch. The project will run until the bank is depleted.

Power banks that were thought to be “Always on” actually turned off when recharging. Only models C and E kept powering the Morsel while being recharged.

There are other specs not covered here. To avoid surprises, privately test the project for the full duration before a public showing.

Comparison with 3 x AA Battery Packs

AA Battery packs with nickel metal hydride rechargeable batteries and a connector suitable for G/5V pins are compared.  They may be found at hobby stores.

  • Three AA Nimh batteries each with 2,200mAH capacity in a battery pack roughly equals the power delivery of a 2400mAH power bank
  • They start out near 5 Volts, but average around 3.6 Volts, making the LED’s less bright compared to power banks, which keep 5 Volts consistently
  • Less brightness results in longer battery life
  • 3 Volt LED’s (blue, warm white and cool white) dim faster than 2 Volt LED’s (red, yellow and green) as batteries wear out
  • A typical project can run all day. Dimming is so slow as to be imperceptible to onlookers
  • Alkalines have perhaps 20% more watt-hour capacity than Nimh. If used in the same project, this comes in the form of slightly brighter LED’s. The average voltage is higher, holds steady longer, then drops off faster

We also tried out 3 x AAA battery packs sold as replacements for cordless phones prewired with a connector that mated to G/5V pins. As a rule, AA’s have about 2.5 times the capacity of AAA’s.

3xAAA pack, Ditto and streetlights

USB power sources are incompatible with battery packs. If they are plugged in at the same time, high surge currents will result from an uncontrolled recharge. This will likely burn out a USB supply and could harm the battery and PowerCookie Board as well.

AA / AAA Battery packs containing 4 batteries cannot be used. Their initial voltage is too high for PowerCookie Boards.

USB Cables

The lower priced power banks came with unreliable USB cables that quickly became intermittent. Maybe they just needed a gentle squeeze to slightly tighten the contacts. In our tests, we discarded them. Their replacements had no problems.

Note that the ComLink requires a different cable than those supplied with most USB power banks. It requires a cable containing power and data lines, rather than the stripped down power-only lines they usually include.

Safety and reliability

Power banks can take a certain amount of abuse, but they do have limits. While we did not burn any out, we cannot guarantee against their failing no matter how carefully our recommendations are followed.

Refer to the power bank’s safety information and recognize that any faulty circuit can heat up to high temperatures due to the energy supplied by such power sources. Follow safe construction practices and avoid locating electronics by flammable materials.

Conclusion

The main point is to know whether additional current is needed to keep a power bank from automatically turning off. This differs from AC adapters we tried, which stayed on.

We liked the power bank’s simple USB connection. The 5 Volt regulated power that was consistently bright. The small size and high capacity of different units. And we liked the convenience of setting up at a table when there is no outlet nearby.

It is useful to have more than one power bank, to make use of their differences, to have a swappable standby and to power multiple projects. Maybe even to charge a phone!

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