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harrychoo

Transformer and LM317 Question

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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.

xformer8au.th.jpg


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?

lm3171ln.th.jpg

Thanks

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Hi Harry,
Please convert schematics to a GIF or PNG file type on your hard drive the attach them directly to your post or reply. JPG file type is used for photos and appears fuzzy with schematics. Your file storage ImageShack server is usually to busy to work.

An LM317 can be a current regulator or a voltage regulator but not both at the same time.
I have made both for you. ;D

post-1706-14279142610373_thumb.png

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Harry,
It sounds like your question is mostly about how to calculate current and voltage ratings when using different rectification methods.
I have attached some diagrams with formulas. Hope it is helpful.

BTW- I also prefer to use jpg. Your picture looks fine when I click on it and it turns into a larger clearer image.

MP

post-555-14279142613846_thumb.jpg

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Thanks audioguru and MP for the reply.

@audioguru
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.


@MP
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?


Thanks

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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.

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.

If based on my earlier circuit, can I know what is the output current?

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.

How much power that the LM317 need to dissipate in my circuit and your circuit?

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.

post-1706-14279142615582_thumb.png

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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

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

D3, D4 and C1 aren't necessary.

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

The circuit regulates the voltage poorly with the 0.22 ohm resistor, and doesn't regulate the current.
The circuit is just an amplified power resistor and changing the pot's setting changes the resistance.
The pot setting also limits the max voltage when there is low current.

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?

Make it, set it and measure the pot and resistor's total resistance. Replace them with a resistor of the same value. Then the current depends on the battery's voltage. High current when the battery's voltage is low and low current when the battery's voltage is high. Just like a power resistor fed from 14.4V.

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

It senses the current then the LM317 effectively duplicates and multiplies its value.

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Is that ok and what happens if i omit the 0.22R?

Can u help me in this too?
http://www.electronics-lab.com/forum/index.php?topic=5518.0

Actually, i plan to make a similar charger with monitoring either by using comparator or microcontroller ADC and will cut off off the charging process once the battery is fully charged.

Any idea on this?

Thanks  ;D

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The .22 ohm resistor does not ruin the LM317's voltage regulation. D5 is another story as far as regulation... it's forward voltage will change with current and temperature. The point that is regulated is the "node" from which the feedback is taken. In this case the "output" side of the .22 ohm. The .22 ohm also helps a little with power dissipation. As the current increases, some of the power that would have been dissipated in the regulator, is now dissipated in the resistor. Also, don't be to fast to get rid of the capacitor C1 on the "adj pin". These regulators can and will oscillate sometimes without it!!! If you leave it, the worst that can happen is the transient response will be a little slower.

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Hi Harry,
Where's Sasi?
His old LM301 doesn't work with its input voltages anywhere near its positive supply.
The circuit was probably designed for an old LM307 which is no longer made it and a TL082 work fine with their inputs at the positive supply.

Hi Indulis,
The datasheet for the LM317 describes how it amplifies the value of a resistor of only 0.05 ohms to ruin its excellent voltage regulation. The 0.22 ohm rersistor in this circuit is 4.4 times worse.

The LM317's I have used without a capacitor at the adj. pin work fine without any oscillation when their circuit has the recommended input and output capacitors. 

post-1706-14279142616305_thumb.png

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@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

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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").

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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.


Thanks

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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?

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Just change the LM301 with TL081 without any modification?

If you compare the old LM301 with the newer TL081 you will see that the LM301 needs the 100pF capacitor but the TL081 won't work properly with it. Remove it.

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?

You have selected a circuit that reduces the charging current when the battery's voltage and current reaches amounts set with pots. You don't trust the circuit? You don't trust your settings?

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?

Neutral is nearly the same as ground. For safety, you will use optical or a transformer for isolated coupling.

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.

Pretty complicated, good luck.

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Hi Indulis,
The heatsink tab is connected to the output terminal of an LM317. To avoid having output current in the wire connected to the voltage-setting resistor, my LM317 project uses the tab as the output terminal and the output pin for the voltage-setting resistor. Then the voltage regulation with changing load current is so good that I measure hardly any change in voltage at the output. ;D

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