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Charge a 6V battery with a 12V battery tender?

Jeff S

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OK - electronic folks...

I've got a 6v battery in my 1974 F7 that needs charging (so the lights will be visible in daylight, so it'll pass inspection). I have a 12v battery tender, or I can buy this cheapo charger from China.

Any way to make my existing 12V charger work - like putting the battery in series with a big resistor? Or, should I just buy the china charger and wait for the slow boat to arrive?

Cheers, Jeff
 
Register it as an antique and skip the inspection! You'll have to find a 6v charger.
 
Well, yes and no.

In electronics there are laws for dividing voltage across a load. If you have 12 volts and want 6 volts it is "possible" to calculate the additional load that would have to be in series with the 6 volt battery to carry the balance of the other 6 volts.

The easiest way would be to put two 6 volt batteries in series and charge them both as if they were a 12 volt battery. The cost of another 6 volt battery will likely be more than the cost of the charger you have listed.

If you are not versed in building a voltage divider by calculating it out with Ohm's Law, then it is probably best to buy the charger that will do it for you. Even if you are versed, the dynamics of dealing with changing currents during a charge cycle are simply more complicated than necessary and having a device designed to do it well is the better choice.

I have three battery maintenance charters and two of them have a switch on the front to select 6 volt or 12 volt operation. One is 12 volt only.

If you will be charging motorcycle batteries for years to come it might be worth ponying up for a 6v/12v switchable charger that will serve you for a while.

Here's a [ame="http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=6%2F12+battery+charger"]few on Amazon[/ame] to choose from.

Look for the ones called Maintainer/Maintenance/Smart chargers, as these will reduce the current as the battery becomes fully charged and will maintain the voltage without damaging the battery while on long term charge.
 
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Dude, check your closet for a wall wart that is the correct voltage and amperage. CT90 guys have been using them for chargers for year. Any Goodwill is likely to have a basket full of them for $1.95.

Maybe 7.5v and 400 to 600 mA. Most will be labelled and bring your reading glasses.
 
Register it as an antique and skip the inspection! You'll have to find a 6v charger.

Could do, but doesn't that mean I can only (legally) ride it at shows and events? I plan to ride this thing around town, commute on it, etc...

MotoTex said:
the dynamics of dealing with changing currents during a charge cycle are simply more complicated than necessary

Yeah - that's what I was figuring. Off to amazon for a 6v charger...
 
If you go the route SL350 suggests, remove the battery from the OEM 6V power supply that came with some random appliance, as soon as the battery is fully charged.

The type of supply designed to provide a constant voltage and current to some device can eventually damage a battery from over charging, and in some cases may lead to fire or explosion of a battery.

A wall wart that is designed for charging a NiCad or a NiMH battery shouldn't be used for other types of batteries either. Each has its own characteristics and requires a unique charging style to prolong battery life and avoid other more dire consequences as a result.
 
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