Trickle chargers and positive ground systems A cautionary Tale

[phil.auldridge]

I love my Ariel Square 4, and ride it frequently. However, I have learned that the peanut-sized battery in these bikes, even when new, just won't hold a static charge indefinitely. So I've resorted to a common care tactic: hooking up a trickle charger/battery maintainer.

It is not hard to find a 6 volt unit on Amazon, and even more and more inexpensive Chinese units that offer dual voltage, both 6 and 12 volts. However, with few exceptions, most all chargers do require that the connecting cables be hooked up in the proper polarity.. i.e., black wire to the negative battery terminal, red wire to positive.

Unfortunately, this situation poses two distinct problems:

1) the NEGATIVE charger terminal (usually ground, but the power source on our positive ground bikes) is NOT a protected terminal on the supplied connector.. it is the positive side of the connector which has a rubber coating, but the negative side is just a bare contact.
2) The inline fuse supplied on most chargers in on the Positive wire. But with our British "reversed polarity" systems, you get a fuse on the GROUND side of the circuit, making it absolutely useless for protecting the circuit.

I've installed such a charger on my Ariel, and recently got firsthand experience of the inherent dangers of such a connection.

I had gone out to ride my bike. The charger was hooked up, so I disconnected it, but then got distracted and forgot to replace that little rubber protective cover that comes on most chargers.

I gave the old gal a good kick, and, as always, she fired right up on first try and settled into a nice smooth idle.. well, for about 10 seconds. Then, all of a sudden, the engine just quit without warning. As I am scratching my head, I see something glowing underneath the seat!! OMG.. that bare charger connection (you know the NEGATIVE wire, the one connected to the POWER side of our Brit Bikes), had touched the frame and created a direct short. If course, turning off the key does NOTHING, since the cable is connected directly to the battery, and that side is NOT protected by the inline fuse!

Miraculous, as I was hopping around trying to decide how to circumvent a complete meltdown, I guess the bike shifted, and the wire was no longer touching the frame. But not before ALL the insulation completely melted off that wire, and the wire itself almost burned in two! Whew!

I carefully disconnected the charred mess, praising the biker Gods that the damage was confined just to that one charger wire.

Lessons learned:
1) When installing a charger pigtail on a positive ground system, move the inline fuse to the BLACK (Negative) wire (or just install a second fuse on that wire if you prefer.
2) NEVER leave that disconnected charger pigtail connection without carefully replacing the rubber cap to protect the bare terminals.

Even better"? Replace the connectors on each end with fully protected connectors on both wires, such as these RC Lipo Cables from Amazon:

https://www.amazon.com/Pairs-Female-Con ... 99&sr=8-40

[SED]

Good catch! All my bikes are negative ground so haven't had to deal with this. Lucas up to 1951-52 is negative ground.

I did have a weird problem with the negative battery wire coming loose during a ride because of dumb spade connectors on the 6v AGM battery. Negative wire vibrated off battery and there was no feedback to the regulator so generator goes into full capacity charge and blew out all the light bulbs and melted the new solid-state voltage regulator. $$$

There is a fuse on the positive battery terminal and another stock fuse in the headlight but neither blew. What would protect from this? Fuse to ground?

[phil.auldridge]

only thing I could think of would be to run the coil power wire (positive in your case) through a relay, whose negative "trigger" post comes from the negative wire to battery (or to chassis ground). That way, if connection between battery negative and ground is disconnected, the relay contacts would open, depriving the ignition coil of power, and the engine would die.

[SED]

Only problem is itsa magneto ignition.