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how to bypass the safety on a battery charger? Answered

ive been working on a cd welder for battery tab.. very simple car audio capacitor with a battery charger. today i rebuilt the whole thing with new leads wiring and new battery charger that will shut off when it hits a full charge. now it wont charge at all because it apparently wont charge anything thats not a car battery with proper voltage already existing. since the capacitor dumps the charge and leaves nothing, the charger just thinks there is nothing there. can anyone give me a crash course in float chargers and how they work so i can single out what i need and bypass everything else



3 years ago

A simpler solution would be to use a different charger for the different battery or capacitor.

How was NASA ?

I am still down here, down at hamption messing around with my brand new shiny RIGOL SD1054Z oscilloscope. I have been capturing data like capacitor charge/discharge curves, I have learned how UART and FTDI serial communication works, and got to trigger on in it and view data in real time!

My project is to create a arduino program that spits out random data from lots of different sensors and log the data and when it was received into a file to make it possible to test radio systems, such as the Xbee radios. I have learned a lot about those, and how to use them, about how the buffer inside them works and it's purpose, etc etc etc.

Cool man...

Just this evening, I have figured out how to use an inverter (common emitter NPN w/ pullup) and a 555 to trigger off of a UART Tx from an arduino, so that I "trigger" off of the initial start bit, and the rest are ignored until the next start bit is encountered. I did this with a monostable 'one shot' circuit and tuned it with a pot and my tongue at the right angle. Works a treat at 9600 baud!

The next step is to put together another 555 which will serve as a clock for the 8 bits of data, and those 8 bits of data need to go into a 74LS164 shift register, and once the data has been 'shifted' into the shift register, I will need to activate all my LEDs at once, preferably with one transistor. I think the "ground rail" of the LEDs will actually be a collector of a 2N4401, and the transistor can be turned on to enable the LEDs. The shift regester acta like a buffer, holding the data until I print it to the LEDs using that transistor.

My goal (for this small personal project to learn how to use 74 series stuff) is to make something that will display the 8 bytes of data in real-time (well technically only after the byte has been transmitted)

I am just past the half-way point.

The smart charger is looking for a base voltage. You can use any small charger, like an unused wall wart, that would charge the cap to that base voltage then switch over to the smart(dumb) charger to finish charging. I have do this to get my drill batteries charged sometimes when they are at end of life.

A car charger is designed to charge 12V Lead Acid batteries. If you don't use a 12V lead acid battery, then you'll need to redesign the charger for a lower voltage battery, or connect the lower voltage battery(s) in series to form a virtual 12V battery. Sorry, that's just the way it is. If your intention is to charge a capacitor, use the battery and a post regulator to do that job. It is not the job of a 12V lead acid battery charger, nor is it likely to provide the low output impedance path suitable for the high momentary currents often encountered when charging a discharged capacitor.


3 years ago

Two bits, four bits / Six bits, a peso / All for Zero chargers / Stand up and say so!

I don't understand why a battery charger is used for a capacitor, especially a smart charger.
Smart chargers are too smart for the job, as mentioned a constant voltage supply with suitable current limiting is the best and fastest option here.
You also get the charging circuit as a spare part for exisisting capacitors...
That way you have proper charging, current limiting and a voltage display.

I don't understand why you want to use a battery charger to charge a capacitor.

Why not just use a constant voltage source in series with a resistor?

Choose the resistor R, so that V/R is a little less than the max current the source can comfortably supply, and the time constant for the charging capacitor is R*C.


3 years ago

I hate "smart" battery chargers. I have run into this problem with car batteries with no charge and/or other problems. The charger thinks there is either a bad, shorted, or missing battery and will not charge. I have a dumb charger that puts out voltage when it's plugged in no matter what. I sometimes need to use it to get some charge on a battery before the smart charger (which has higher amperage ability) will actually start working. I never tried to get around the problem as it appears to be an integral part of the chargers circuits. I would try to get a cheap, dumb charger if they even exist anymore. and use that.

Sometimes smart just isn't smart.