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Posts posted by harrychoo

  1. Ahhhhh yes....... I should have checked the data sheet first. Yup, since the reference voltage is between the output pin and adjust pin (not adj pin to common... I guess I've been around TL431's too long), any resistance in series will screw up the load regulation (not line regulation). As for the capacitor C1..... I have had circuits with a LM338 oscillate under certain line/load conditions without out it ("conditionally stable").

    thanks for the reply.

    Actually, i still not fully understand the statement "any series resistance will screw up the load regulation"

    Can explain further?

  2. I explained why his circuit won't work with an old LM301. I also explained why a TL081 will work fine instead.

    Just change the LM301 with TL081 without any modification?

    Monitoring the voltage or current of a lead-acid battery charger is useless like watching grass grow. It gives little indication of how much the battery is charged. It would only show if the battery is shorted, but the smoke would also give good indication. It might show if the battery was disconnected.

    The reason i want to monitor is not want to know how far it is being charged but i want to terminate the charging once it full. Any idea?

    The mains is supposed to be a sine-wave. It will show short notches when high-current appliances turn on, and spikes when inductive loads turn off. Lamp dimmers cause interesting-looking small changes to the sine waveform.
    There isn't any reason to view the mains because there isn't much that you can do about it.

    Actually i need to view the main because i will implement inverter later part and i want to check its waveform. And the question i mean previously is, the neutral and live line both also output sine wave simultaneously? Or 180 degree out of phase or others?

    If the voltage and frequency of your mains changes enough to worry you, then it is broken and needs replacement.

    Same here too, i need to built an universal UPS system with AVR and different input AC voltage and 50Hz/60Hz. So i need to detect the input AC voltage in order to do the AVR and i need to detect whether it is 50Hz or 60Hz so i will output the same frequency on the inverter side.

  3. @audioguru

    I not sure where is Sasi  ???
    Is it mean that his circuit no longer work? Do you have any idea on how to monitor the charging process? Do we need to monitor the battery voltage OR charging current during the charging process? I might want to do this with microcontroller's ADC.

    Off-topic : Can I know how is the voltage waveform for our main AC? We have Neutral and Live line respectively but how the waveform gonna looks like in each of these lines with respect to time? Is it possible to view the 240VAC waveform by using digital or analog oscilloscope? Or do we need certain special equipments? What is the procedure?

    Can I know by using op-amp, can we built some circuit to determine the input AC and its' frequency with the usage of microcontroller?

    Thanks ya

  4. In your original circuit, the 0.22 ohm resistor ruins the LM317's voltage regulation since the resistor causes the output voltage of the circuit to drop with increasing output current. You would set the voltage-adjusting pot for the amount of trickle-charge current you want. I have re-sketched it for low cost.

    The output voltage depends on the output current. If its voltage is set to 14.4V across the battery at a low current for trickle-charging, then its charging voltage is limited to about 10.4V at 1.5A.

    About 15.1W at 1.5A for your circuit or for my 2nd circuit. It would be much less if the transformer is the odd voltage of 13V + 13V. In my 1st circuit, the two LM317's would share the dissipation but not equally.

    MP's drawing shows that the entire transformer's secondary AC voltage of 32VAC times 0.71 results in a peak voltage of 22.7VDC. My circuit shows it drop about 0.9V after the rectifiers.

    Can i know what is the main difference between your "Battery charger 2" with my circuit earlier other than those protection diode?

    The pot in your battery charger 2 is used to set current but not voltage? Can u explain why this can happen?

    Let say, i confirm that i want 14.4V at the battery there, then can I just replace the 500R pot and 1k res with a single res? If that so, what is my current?

    Last question is what is the purpose of the 0.22R?

    Thanks again
  5. Thanks audioguru and MP for the reply.

    Is it possible to make it using only 1 LM317? This is because almost all the battery charger circuit in the end market UPS system that I traced, they only using single LM317. And also I want to reduce cost if possible. If based on my earlier circuit, can I know what is the output current? How much power that the LM317 need to dissipate in my circuit and your circuit? Thanks a lot.

    Then from my circuit, is it consider as Full Wave Resistive Load? If yes, then it should contradict with audioguru circuit where the input voltage to his first LM317 is 21.8V. What is the input voltage to my LM317 then? If it is a Full Bridge Resistive Load, then the input voltage to LM317 should be around 14.4V (0.45 x 32V) but ain't it too low since the output voltage i also want 14.4V?


  6. Hi,

    I want to ask a question about transformer as i very confuse about the multitap transformer.

    In the circuit i put below, can i know what is the voltage for V1 and V2? Is it 16V or 32V? And is it V1 still an AC?
    The diode is 1N5399.


    Then below is the transformer that connected to LM317 to regulate the output voltage to charge my 12V 7Ah SLA battery.

    D1,D2,D3,D5 = 1N5399
    D4 = 1N4148
    C1 = 0.1uF
    R1 = 0.22R 5W
    R2 = 240R
    R3 = 2.54k

    The charging voltage is to be set at around 14.4V from R2 and R3. So my question is how we set the charging current? Is it thru R1? If yes, then what is the formula to change R1 so that i can get different charging current? From the LM317 datasheet, i only can get the load impedance that related to R1 which is

    Z1 = R1 x (1 + R3/R2)

    Any realtion between this and the charging current?



  7. I have been study this type of charger quite a while.

    Now i wish to charge 12V 7Ah SLA battery.

    To charge the battery, u need a constant voltage and current source. First, u need to charge the SLA battery for 2.4V/cell. Charging current should be around 0.1C. The charging current will drop throughout the charging process.. When it reach like 10mA-40mA, u need to stop the charging process or change it to float charge which is 2.35V/cell, else it will be overcharged.

    I had built the charger using LM317 and some pot. However, now i wish to do it in switching type charger.

    I try to use some switching regulator like HA17384/385 or UC3844 current mode PWM to do the switching and with some opto-coupler and TL431 to do the feedback. All this i wish to do it with flyback topology.

    But now i still in study stage. I had study quite some of the application notes but still I not too understand how to produce constant current source in switching type. I manage to do cosntant voltage but not constant current.

    Any idea?

  8. Wow, after having not reading my own thread for 2 weeks, it end up with so many discussions. Bravo.

    For Arun > Is it possible for me to get the manual or reference book for UPS? I want focus in the battery charger and sine wave inverter study. My rough spec will be 12V 7Ah SLA battery charger(might be more than 1 piece) and for inverter is about 500W or more than that. If possible, i hope the reference book can cover every spec and explanation so i can see the difference from that.
    And yeah, i'm from Malaysia. So anyway for me to get this?

    For all>
    Battery charger

    For the battery charger, I would like to know more about the charging voltage, current and charging time. Is it efficient for us to use LM317 to charge the battery? As far as i know, to efficiently charge a SLA battery, we migh consider the charging voltage and temperature as well.

    For the charging voltage, as i know, to charge a low energy SLA, we need to use cyclic charge 1st (2.35V-2.4V/cell) until the charging current drop to a minimum value (3% of the rated current), then we have to change the charging state to float charge (2.25V - 2.3V/cell)

  9. Is it the LM317 used to set the charging voltage? When i chg the output of LM317, the charging voltage (at anode or cathode of diode consider as charging voltage?) also chg.

    If as u mention, if IC2 made to be constant current source and because of this, the output voltage equals the battery voltage, then how will it charge? I thought it only will charge if the output voltage higher than battery voltage?

    The charging voltage i have to adjust before or after the battery is inserted?

    Is it when the charging current drop to a low constant current source, it indicates fully charged?

    Thanks audioguru

  10. Hi all,

    I'm lack of knowledge on how to read the spec, types of different transformer. I also not sure about the schematic representation for a certain transformer.

    For example, given me an unknown transformer, i not sure how to see the specs (how many volt to how many volt and its VA) and the types and application of the transformer. I also not sure about the transformer schematic configuration. Let say the transformer is with 6 pins, i'm not sure which pins are in primary and secondary and how the schematic (or symbol) look likes.

    And is it possible for me to find datasheet for transformer?


  11. I have built this battery charger according to this site


    I manage to charge the battery but it very slow.

    Can i know what charging voltage should i use. What i mean is what is the output voltage from LM317 should i make? It seems like even i increase the output voltage from LM317, the output voltage at the diode (anode) also same...looks like it depends on the battery.

    And how do i know whether it is fully charge or not? Is i t possible to modified the circuit so i can know the battery is fully charge without probing the current or voltage?


  12. Hi all.

    I'm plan to design a switching charger for a Sealed Lead Acid Battery with ratings 12V and 7Ah.

    I plan to use current mode controller either UC3844A from Unitrode or HA17384 from Hitachi.

    Can i know where can i find the schematic for this? And i also not sure how to control the charging voltage and current by using switching mode..

    Or any other idea to design switching charger out of that 2 switching regulators?

    Need more info on this.


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