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motorcycle battery tender/charger... help

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ktg08

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It's been 20 years since I graduated with my associates degree in electronics... have not studied circuits since. Am trying to build a battery charger/tender for my motorcycles. I have a workbox full of 0.25 watt resistors, some diodes, some transistors... I have a transformer that's rated at 12Vdc 1000mA. Its no load voltage is around 15V.

I want to make it simple. The ideal setup would be something that I can leave plugged in continuously and only applies a voltage to the batteries when they drop below, say, 12V.

I have an idea in my head... if I can somehow use the 0.6V minimum drop across the base/emitter to turn on/off a transistor and allow the circuit to charge.

Any help appreciated
 
Transformers produce AC, not DC so it's got to be a proper little power supply, not just a transformer.

Just connect two diodes in seires to limit the open circuit voltage to 13.8V and add a 2.2:eek:hm: 3W power resistor to limit the current, in case you connect a flat battery to it.

There's no need to cut off the power, a lead acid battery can float charge at 13.8V all the time without being damaged.
 
ok so everything in series. gotcha. by a flat battery do you mean 0 volts? and does a 0 voltage battery act like a closed circuit? in that case wouldn't a flat battery (in this circuit) draw about 6 amps or is there a standard internal resistance to a lead acid battery?

yes, what I have traditionally called a transformer does rectify the voltage to dc
 
As far as a lead acid battery is concerned, 10V to 11V is flat.

A battery that's discharged beyond this voltage range might be dead.
 
ktg08 said:
ok so everything in series. gotcha. by a flat battery do you mean 0 volts? and does a 0 voltage battery act like a closed circuit? in that case wouldn't a flat battery (in this circuit) draw about 6 amps or is there a standard internal resistance to a lead acid battery?
A dead battery with voltage close to zero will likely have a high resistance so the charging current would be low.
 
It's been 20 years since I graduated with my associates degree in electronics... have not studied circuits since. Am trying to build a battery charger/tender for my motorcycles. I have a workbox full of 0.25 watt resistors, some diodes, some transistors... I have a transformer that's rated at 12Vdc 1000mA. Its no load voltage is around 15V.

I want to make it simple. The ideal setup would be something that I can leave plugged in continuously and only applies a voltage to the batteries when they drop below, say, 12V.

I have an idea in my head... if I can somehow use the 0.6V minimum drop across the base/emitter to turn on/off a transistor and allow the circuit to charge.

Any help appreciated
Have you build this battery tender?
I am looking at building the same thing, do you have any circuit diagrams available?
 
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