Category: Portable Power

What Battery?

4200

Sealed Lead Acid batteries have been the mainstay of portable power for a long time. While not inexpensive, they are not outrageously priced, and their voltage is a good match for Amateur Radio gear.

They do however have many disadvantages:

  • Lead is a dense element, good for Nuclear shielding, less so for humping about.
  • The voltage drops significantly during the discharge cycle.
  • Deep discharge can badly damage the battery, reducing its capacity.
  • In normal use you will get much less than the rated capacity out.

Amateurs have long looked for good alternatives, and currently the lithium iron phosphate (LiFePO4) battery fills the frame nicely, now that prices have become more reasonable.

These cells have a working voltage of 3 – 3.3 Volts, so 4 in series give 12-13.2 Volts, which is a great range for Amateur equipment. Best of all, the voltage  stays in useful range until it is nearly fully discharged.

This means that the useful energy you get out is much nearer to the Ah capacity of the battery than for Pb cells. Also your equipment doesn’t have to cope with a sagging input voltage.

The C rating shows maximum current draw, C x Capacity = Amps, so 30C x 4.2 = 126 Amps for the above battery.  This seems optimistic for such a small battery, but it gives me confidence that using it for a 100W rig peaking at 23 Amps will be fine.

4.2 Ah won’t run a 100W rig for very long, but I find having multiple 4.2 Ah batteries and swapping when needed is more flexible than just having a big one.

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Battery charger choice

Battery chargers for LiPo & LiFe batteries are a popular topic for discussion.

The one I chose is shown above. At 50W its not the highest power available but it charges batteries fast enough for me, and it was reasonably priced.

It is a very flexible charger, able to charge a wide range of batteries:

  • LiPo
  • LiIo
  • LiFe
  • NiMH
  • NiCd
  • Pb

It has a balanced charging connection for Li batteries of varying voltages & can charge all the battery technologies you are likely to come across.

A feature I particularly like is the ability to charge from mains or a 12v source. Just unplug the mains lead and plug in the DC cable, shown loose in the picture.

This means that if I have small portable batteries to charge and access to a car or other source of 12V such as a large bank of lead acid cells, I can use the charger for that.

I’ve changed the DC input and output connectors to PowerPoles to match the rest of my equipment.

I can’t comment on long term reliability, but will report any issues which arise.

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Connecting Batteries

Having moved to using LiFe batteries for lightweight portable power, I needed to make them compatible with the PowerPole connectors most of my equipment uses.

The 4200 batteries come with 5.5mm bullet connectors, so the easy way was to buy a bullet to banana plug cable from the same supplier as the battery and replace the banana plugs with PowerPoles. These cables have very flexible insulation, so are great when in use.

I noticed that an insulation gap appeared where the 5.5mm bullet connectors joined together, so to keep things safe and stop the connectors coming apart inadvertently, I covered the join with heat shrink tube and  I’ll keep an eye on it.

bulletcon

An alternative is to connect the PowerPoles directly to the battery.

plug1

You need to be very careful not to short the battery cables while doing this, and do take off any metal rings on your hands, as if you short via a ring you may lose the finger.

fingerringburn

I use 30A PowerPole inserts and you may find that the battery conductor is too big to fit. As I am not needing more than 30A, I just trim the cable strands off until they fit snugly, I also put a bit of thin heat shrink from the cable to the crimp part of the PowerPole.

You might be wondering where the fuses are, and they will be in the circuit which is connected to the battery. Putting them on each battery lead would have been clunky, and if reasonable care is taken, its unlikely that there will be a short across the PowerPoles on the battery.

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Power Distribution

When building Go Boxes, I used to find connecting together the power distribution cables for the equipment a hassle, until I found these Wago connectors in an electrical distributor. They are widely used in the UK for house lighting wires and come in 2,3 and 5 conductor capacity.

As they are quite small, I bought a box of 5 conductor units with the view that even if I only need 2 or 3 for some applications, they don’t use up much space, and if I need more connections than I thought, they are available.

power1

The connectors are rated at 32 Amps and capable of taking up to 4mm square cable, you just lift the lever and slide in a stripped cable, then push it down for a secure connection. Use one for +ve and another for -ve & job done. A decent length of the insulation slides into the connector so shorting to the metal panel below is not an issue.

The main picture shows a project I’m just getting started on with the first wires connected, and the pic below gives the part details.

Power2

I also use a lot of this Acrylic foam tape which is very sticky, holds well and doesn’t lose its grip with time.  While described as foam, the material is more a clear plastic somewhat stretchy gel, a couple of mm thick with adhesive either side. This helps if the surfaces are not completely smooth/parallel.

Its perfect for sticking these Wago connectors down, and for mounting other lightweight parts.

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