using pulse charger as supplying power

Discussion in 'The Projects Forum' started by m.sabeeh, Jun 26, 2010.

  1. m.sabeeh

    Thread Starter New Member

    Jun 26, 2010
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    i have an electric bike having charger of 24v 1.26a. i needed 24volts DC for operating small fan. but when i used the charger of bike to supply power to the fan, it just started to turning it ON and OFF one or two time a second. i mean i am not able to use it for constant 24v DC. all i can search on internet is that it may be a kind of pulse charger. now i want to convert it into constant supply source. ;(
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Sounds like the fan is too much of a load for the charger. Motors take quite a bit more current to start than they use when they are running at speed; maybe 7 to 10 times as much.

    Chargers are not made for powering motors; they are made for charging batteries.

    However, if you connected the charger to a 24v battery (or pair of 12v batteries in series), then connected the fan to the batteries, you might have something that works.
     
  3. m.sabeeh

    Thread Starter New Member

    Jun 26, 2010
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    thanks for your reply. but now i have connected small 3v DC motor with it but it is still sending pulses to the motor like 3-4 times a second and motor isn't able to work continuously. im sure its a kinda pulsating charger. all i want to do is to cut some of its components and make it constant DC adapter.
     
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    I just now measured how long a small 12V motor would run on a charged 3300, 50V capacitor, charged to 12V,-- about 1/2 second, coasting for another 1/2 sec. Try connecting a diode from charger output to cap , cap to load. Other end of cap to other side of load. Watch your polarities.
     
  5. m.sabeeh

    Thread Starter New Member

    Jun 26, 2010
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    yp good advice but is there any way to make charger to give constant supply instead of connecting a capacitor at the output. i want to change something inside the charger couse surely it is giving 24v at the output but cause of some <snip> thing inside, it is giving pulsating output. thankx in advance
     
    Last edited by a moderator: Jun 30, 2010
  6. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    'don't care for your language. The basic power source is probably a DC generator or an alternator; if it's DC- use it , if AC, use a bridge rectifier to give DC.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    These forums are strictly "G" rated. Profanity is not allowed.

    The charger you have is using an on/off type of regulation. It's like a very slowly switching power supply. It is either fully ON or OFF. It was designed so that the average power out over time would be within it's limits. It could possibly be as simple as a transformer that has it's primary switched by a TRIAC controlled by a bimetal switch.

    If you removed the parts that perform that function, it is likely that you will burn it up, and/or burn up the thing that you are trying to power with it.

    You need to buy or build another supply that is specifically designed for your needs, rather than trying to "hack" an unknown circuit.

    Besides, with no photos, schematics, etc. it would be a very long shot to guess what's inside the charger.
     
  8. m.sabeeh

    Thread Starter New Member

    Jun 26, 2010
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    thanks sgt and bernard. k i'll probably like to build new one instead of buying. will you help me with this. i want 15Vdc with 1-2A "without using transformer". i know its possible using capacitive reactanc.
    by the way u sgtwook said that u dont know whats inside the current charger so for ur information it contains ONE MPT696 MOS power transistor, a CS3842A PWM control circuit, a LM324AN motorolla quad amplifier and capacitors, resistors and a small yellow kinda transformer i think ,etc
    well now i would like to build the new one with ur help :)
     
  9. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    You will find it difficult to get people to help you build a device connected directly to the AC power mains.

    This is a serious safety issue.
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    We could help you with a power supply, but the circuit MUST use a transformer or other inductive means to electrically isolate mains power from the output side. This is not a negotiable item.
    There are circuits posted on the web for such things.
    They are all extremely dangerous, as if any of the capacitors fail shorted (which they frequently do, and ALL capacitors will eventually fail!) then the output will be directly connected to mains power.

    This is why discussions of such circuits is not permitted on this website. There is one rule that overrides everything else, and that is covered in the announcement titled: "Forum Rules, Code of Conduct and Terms and Conditions of Usage" located here: http://forum.allaboutcircuits.com/announcement.php?f=5&a=3
    The third paragraph under 2. Appropriate Conduct begins:
    We want people to enjoy their experiments with electronics, but at the same time we stress that it must be done so in a safe and sane manner.

    Please do NOT attempt to build a "transformer-less" supply. Transformers are actually quite inexpensive; perhaps a few USD's - and MUCH less expensive than a funeral.

    I hope that you will discard the idea of building such an inherently unsafe device.

    OK, can you post some photos of the board, both front and back?

    It is very difficult to take good photos of circuit boards. The best lighting you can get (without spending money) is outside on a cloudy day. The light is very bright, but scattered. Trying to take photos in direct sunlight will result in very harsh and "contrasty" images. If there is full, bright sun, then drape an old white bed sheet over yourself and the board to diffuse the sunlight.

    Focus is another problem. If you have a camera with a "macro" function, please use it. It is much better to have a smaller, clearly-focused photo than a large poorly focused image. We need to see as many details as possible.
     
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