Rule the Waves: Charge Ahead with Li-Ion Batteries

How much power is enough to rule the airwaves the way you want? You hope that you have a truly powerful battery bank, or you’ll be out of business. Say you’re on the DMX-40 Morse Code Decoder Transceiver and you’ve got a full schedule. You can’t afford for your rig to quit. You’re drawing QRP power, but then there’s this tiny case full of little batteries and a day–or night–of Morse coding ahead. Encoding and decoding, to boot. Do you have the juice?

What’s the truth about batteries?

For starters, let’s explain a few things about PreppComm’s robust lithium-ion battery bank. We ship you this  portable power source with the Pro Station GO Bag and with the Combo DMX Plus GO Bag. You’re in charge of a 28 amp-hour battery bank (at 3.7V). That’s about 20 amp-hours at 5V, and about 8 amp-hours at 12V, when you consider the voltage conversion and loss. Eight amp-hours is a lot for a battery bank the size and weight of the PreppComm super capacity power bank, and ours actually performs according to the spec.

Believe me, many other batteries don’t.  For example, some of my flashlights say they come with 4200 mAh batteries, but they actually measure about 450 mAh!  Seriously! This is typical if you don’t buy the more expensive mainline batteries from the big names like Sony and Samsung.

How much and how accurate?

But back to the topic of long-lasting energy. Thanks to a question from a customer in our PreppComm Community (That’s preppcomm.mn.co.), we have a power update for you! Complementing the battery bank instructions, these tips help you maintain your PreppComm outfit. What’s not to like about getting the most out of this surprisingly high power battery bank?

Looking at the case, you see two USB connectors:  one rated at 1 amp, the other at 2.1 amp.  When you plug in the voltage conversion cable (5V to 12V), make sure you plug into the 2.1 amp connector.  While the 1 amp connector works fine for the DMX-40 in receive mode, it will fail in transmit mode.

Why?  First of all, the transmitter only draws about 550 mA when the key is down, so why is 1 amp not enough?  Well, to clarify the riddle, you are making a simple voltage/amperage conversion.  12V at 0.55 amps is 6.6 watts.  How much current do you need at 5V to get 6.6 watts?  P=EI, so I=P/E or 6.6/5 = 1.32 amps!  And then, if you throw in  85% efficiency for the conversion circuitry in the cable assembly, you get 1.55 amps.  So, as you can see, 1.00 amps at 5V will not do.  The battery bank circuitry will cut out and the DMX-40 will reset.

Secondly, consider the issue around accuracy of the percent readout.  It’s supposed to tell you the charge state of the battery bank, but it’s not accurate when your battery bank arrives.  It has not been calibrated.  That is for you to do.

Calibrating your battery bank charge indicator

To calibrate your percent readout, first discharge the bank until it shuts down, and then charge it fully.  Don’t stop when it says it’s charged to 100%. (You need to presss the button to see the display).  The battery is really fully charged when the “IN” indicator stops blinking, not when the percent reading is 100%.  Now, and only now, is the readout fairly accurate.

To put it another way, remember the early days of cell phones? Phone manufacturers used to tell you to complete this cycle, as well. Similarly, if you charge the bank to where it appears fully charged, but don’t confirm it with the “IN” light, it will be somewhat accurate at the start. So while your tough little battery bank may seem full, it’s not yet reading true. As it discharges, though, the accuracy drifts.

So how long will my DMX-40 run?

Following the procedure outlined above, you’ve given the battery bank system a complete reset. As a result you’ll derive much better accuracy of the reading and less headache about how long your batteries will last.

PreppComm’s robust battery bank is rated at 28,000 mAh, at 3.7 volts.  If you do the conversion to 12 volts, you get about 8600 mAh.  The DMX-40 draws about 160 mA average with the LCD backlight on, and about 120 mA average with the LCD backlight off, assuming the following:  25% transmitting/75% receiving, and around 50% keydown during transmit time, 100% LCD backlight on.  That comes out to about 50-60 hours of operation.

Obviously, the LCD backlight is not lit all the time; it shuts off after three minutes if there is no activity.  So, all things considered, except maybe on Field Day, this might equate to 10-12 days of operation at around four hours each day.

Furthermore, you would deploy the solar panel included in the GO Bag to restore power from that bright orb up there. Indeed, you will continue using your DMX-40 for as long as sunlight or bright daylight pours down on you. To sum it all up, roughly an hour of sun, or four to six hours of bright daylight restores all the power you consume. That means…forever, just about.