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Charger cable project

By Andrew Gibbs

Most of the 12V power supply cables fitted to my chargers approach 2 meters in length as supplied. This length is necessary so that when the charger is powered from a vehicle battery it can be placed safely on the ground, well away from the vehicle’s engine bay. However, I’ve often found such a generous length of cable rather inconvenient in a workshop environment, especially when a mains powered 12V supply is available close by.

Chargers often need connecting to a 12V workshop power supply. This is a less than ideal solution to the problem!

Another problem that comes up with a mains power supply is that some sort of method needs to be found to connect the charger’s power cable (which is invariably fitted with crocodile clips) to the 6mm output sockets of the PSU. One solution devised by one of my fellow club members was to use the clips to grip some male 6mm connectors, binding the crude assembly with tape. While this did work, it was clearly not an ideal solution!

Thinking the matter over, I decided to modify my own charger’s 12V power supply cable so that both problems were solved in one go. My solution involves cutting a short length from the middle of the supply cable, and then rejoining the breaks

The charger’s original cable has been shortened, and two alternative adapter leads have been made – one lead retains the original crocodile clips, allowing connection directly to a 12V battery, and the other much shorter lead allows connection to the 6mm sockets of a power supply output. No extra wire is needed.

with high quality connectors. By this means I created two alternative adapters to fit the shortened charger power supply cable:

1) A long adapter lead which allows the charger to be connected as designed, to a 12V battery using the original crocodile clips, maintaining almost all of the original full cable length, and;
2) A much shorter adapter lead which allows the charger to be safely connected to the PSU using a pair of 6mm gold connectors.

The photograph illustrates the idea, and shows the shortened main charger lead plus both adapter leads.

I’ve been really pleased with the convenience of this simple idea, which only took me about an hour to carry out. The work will of course invalidate the manufacturer’s guarantee but as my charger was more than a year old this didn’t matter to me. Should you choose to go this route as well, you do so entirely at your own risk. Of course, the work should only be done by someone suitably experienced in soldering and electrical matters.

Important safety precautions
As supplied, the charger’s power cable cannot be short circuited. However, once a break is introduced, this does become a possibility. For example, if the crocodile clips are connected to a 12V supply battery, and the other end of the cable is left free, the free ends could potentially touch each other, resulting in a short circuit.

The negative wire was shortened by about 1cm before assembly. This results in the male connector being positioned behind the female one. The resulting safety gap makes short circuits much less likely.

This could be disastrous, and just as serious as if the power wires of a large LiPo battery were allowed to touch each other, so a means has to be found to minimize this danger. So, before I describe how I carried out this project, I’ll first cover the important safety precautions necessary to deal with this issue. I’ve already developed ways to minimize the risk of short circuits with my batteries, so I used the same methods here:

Place connectors at different locations
By carefully trimming the supply wires, the connectors are located at slightly different physical positions. This greatly reduces the chance of a short circuit between the connectors of either of the two adapter leads. This physical spacing is illustrated in the photo below:

Make sure the exposed (powered) connector has negative polarity
The work is also planned so that the exposed (male) connector attached to the crocodile clip equipped adapter lead has a negative polarity. In this way, if this exposed connector end did accidentally contact the car’s bodywork or engine (which will be electrically negative), it would be a harmless negative-to-negative contact, rather than a dangerous positive to negative contact which could result in a disastrous short circuit.

Add a protective sleeve to the exposed connector
If desired, an additional protective sleeve can be added to the exposed connector. This precaution is detailed later.

Always connect an adapter lead to the charger before connecting to power
By simply making sure that an adapter is connected to the charger cable before connecting to power, the possibility of a ‘live’ exposed connector being present is eliminated, so no short circuit can occur. This precaution is discussed further towards the end of this article.

6mm gold connectors are ideal for this project. The more common 4mm size could also be used. A pair of 4mm male connectors (plugs) are also required to fit your power supply’s output sockets. The AA battery is shown for size comparison

Materials required:

• Three pairs of suitable male/female connectors. I had three pairs of 6mm gold connectors available and these proved to be ideal for my project.
• One pair of male 4mm gold connectors to match the PSU output sockets.
• Solder, plus some suitable heatshrink sleeving.

Connector notes
You don’t have to use 6mm gold connectors, but it’s important that whatever type you do choose, that they’re of excellent quality and a good, tight fit so they can’t easily be accidentally pulled apart in service. Using shielded connectors would be safer still than using the 6mm type I chose. Also, it might be wise to consider selecting a different type or size from whatever you use with the rest of your equipment to avoid any possibility of inadvertently connecting the modified leads in any way other than as intended.

Tools required

• Soldering iron and bit-cleaning equipment (e.g. damp sponge)
• A means of holding the connectors while they are soldered. One way to make a ‘helping hand’ is to glue a wooden clothes peg to a small block of wood.
• Sidecutters to cut and trim the power supply lead.
• Wire strippers to strip insulation off (a knife can also be used with care).

Soldering safety
Soldering is potentially dangerous and should always be carried out with safety in mind. Soldering produces fumes which are best not breathed in, so take care to ensure adequate ventilation. Also, use some form of eye protection such as safety glasses and take care to wear clothes which cover you fully in case of solder spattering – solder burns on the legs for example are no fun! Also, its well worth having a bowl of clean, cold water ready nearby to use in case of accidental burns.

OK, let’s get started. Here’s how I carried out my project:

1. First, I drew a diagram of what I intended to do so I would have a plan to follow

Click for a larger image Here’s the diagram I used to plan my own work. You can print a copy of this diagram by right clicking and selecting ‘print’.

2. Before doing any work, I made sure the + and – leads would still be able to be identified after cutting them. In my case, a black line ran along one lead, clearly identifying it as the negative (-ve).

3. I then measured up the existing charger lead, and decided where I was going to cut it. My lead measured about 170cm (66in) before cutting.

4. Gathering my courage (!) I then cut the charger’s power supply lead. I chose the half-way mark, leaving me about 85cm (33in) still attached to the charger. I then took other the 85cm portion with the crocodile clips and laid it aside.

5. I also cut a further 15cm (6in) from the end of the lead still attached to the charger, so that the portion still attached to the charger measured about 70cm (27in). This was also put aside.

6. Next, I trimmed exactly 1cm from one wire of each of the three ends that would receive connectors (refer again to the diagram if this helps):

a) I cut 1cm from the +ve wire from the cable still attached to the charger
b) I cut 1cm off the -ve wire of the crocodile clip equipped lead.
c) I cut 1cm off one of the -ve ends of the short free length, leaving the wires of the other end equal in length.

The completed 12V Battery Adapter Lead. This should always be connected to the charger before it is powered up, eliminating the possibility of exposed live connectors touching each other.

7. Now the soldering can begin. I took the free end of the crocodile clip equipped lead and soldered a pair of 6mm connectors to it, taking care to make sure that the that the negative (black) end is the one fitted to the male connector. Let’s call this completed adapter the 12V Battery Adapter Lead.

8. A second matching pair of 6mm connectors was then soldered to the free end of the lead still attached to the charger so that it could be reconnected to a 12V battery using the newly made 12V Battery Adapter Lead. Great care was taken to ensure that the correct polarity was maintained – in other words that the original connections had been re-established by the connectors.

The almost completed PSU adapter lead. The far end has a pair of male 4mm connectors, and the near end a pair of 6mm connectors. The last remaining job is to fit a length of red heat shrink tubing to the female connector.

9. Having checked again that the polarity was correct, colour-coded heat shrink tubing was fitted to all four 6mm connectors, using red for positive and black for negative.

10. The third pair of 6mm connectors is then fitted to the unequally trimmed end of the short piece of lead. Before doing this, I made sure that when the connectors were in place that it would match the charger’s connections. I also made very sure that their polarity matched those of the 6mm connectors which I’d just fitted to the charger. Once completed, let’s call this short part the PSU adapter lead (see photo)

11. Finally, a pair of male 6mm gold connectors was fitted to the other end of the

The almost completed adapter leads. Two pieces of red heat shrink tube remain to be fitted.

short adapter lead to match the PSU. In this case, no difference in lead length was required. Lastly, red and black heat shrink tubing was added, again making certain that the polarity was correct.

13. One more job is to consider if you wish to fit an additional length of heat shrink over those connectors that could be involved in a short circuit. The photo illustrates this excellent idea:

14. A last, but most important job is to once more check everything very carefully before connecting power to the charger.

Here, an additional length of oversized sleeve has been fitted to a completed connector. The sleeve is shrunk at one end only, so the additional sleeve overhangs the exposed connector, shrouding it and reducing the chance of a short circuit to almost nil. Its presence makes joining the connectors slightly more cumbersome, but this price is well worth paying for the increased safety.

In use
There are only two issues to take care of when using the modified cables – a short circuit can be avoided simply by making sure that one adapter lead or the other is always connected to my charger. This way, there is no exposed end to be involved in a short circuit. The other issue is remembering to take the 12V Battery Adapter Lead when I go flying, and that’s easily taken care of simply by keeping it in my flight box.

Conclusion
In use, the adapter leads have proven to be very convenient. No longer do I have the problem of connecting the charger to my PSU, nor do I have an over-long charger cable when using a workshop PSU. Job done!