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Suggestions required for voltage/current regulator

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347sixtyseven

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Guys, i need a bit of advice on making a voltage/current regulator to run a few chargers for rechargeable torches at work.

The torches came from the US with 110v wall warts that power individual charging docks.

I want to run an Aussie 240v wallwart to power 5 of the charger units at the same time. The input requirements of the chargers are: 12v dc 500mA.

I got hold of an old ibm laptop power supply with a rated output of 16v and 3.36A.

Would it be possible to use this through a regulator of some sort to provide 5 outputs at 12v 500mA?

I am thinking of a voltage reg circuit using an LM317 but i am not sure how to go about the 5 x 500mA outputs.

I thought i could use the 317 circuit to provide the voltage drop and have it power 5 separate current regulators each set for 500mA.

I am assuming if i were to just put them all in parallel with no current control, whenever i took a torch out, the other chargers would get more than 500mA. Is this correct?


Any advice/recommendations greatly appreciated

Cheers

Gary
 
The torches came from the US with 110v wall warts that power individual charging docks.

240v wallwart to power 5 of the charger units at the same time.
requirements of the chargers are: 12v dc 500mA.
Each will take as much current as it needs if you supply 12vdc.

I got hold of an old ibm laptop power supply with a rated output of 16v and 3.36A.
Would it be possible to use this through a regulator of some sort to provide 5 outputs at 12v 500mA?
I am thinking of a voltage reg circuit using an LM317 but i am not sure how to go about the 5 x 500mA outputs.
I thought i could use the 317 circuit to provide the voltage drop and have it power 5 separate current regulators each set for 500mA.

I am assuming if i were to just put them all in parallel with no current control, whenever i took a torch out, the other chargers would get more than 500mA. Is this correct?
Not as long as they get only 12v.

Parallel 3 ea. 317s. Run the output of this composite to all five chargers.
If the current sharing in the 317s is not close enough (one regulator drops out too soon) tweak the output voltage of one or more regulators to be closer to, and preferably at, 12.0vdc.
 
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You might be able to adjust the voltage on the laptop power supply quite easily.

There will be a voltage feedback circuit that detects the output voltage, almost certainly with a voltage divider. Changing the voltage divider ratio will change the output voltage.
 
Parallel 3 ea. 317s. Run the output of this composite to all five chargers.
If the current sharing in the 317s is not close enough (one regulator drops out too soon) tweak the output voltage of one or more regulators to be closer to, and preferably at, 12.0vdc.


:confused::confused:

Using two 317s separately and hook up two respecively three chargers will do, too.

Boncuk
 
I forgot: add a 1Ω 2W resistor to the output of each 317 to make the voltage setting less critical as to proper current sharing.

Or, instead, a much simpler way is to drop the 16v to 12v by putting 4 or 5 3A diodes (1N5401, 12 cents at Hosfelt.com) in series. They don't need heat sinks.
 
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>347sixtyseven
> I am assuming if i were to just put them all in parallel with no current control, whenever i took a torch out, the other chargers would get more than 500mA. Is this correct?

I would say the other chargers would have more than 500mA available, but just because more than 500mA is there, they won't draw more than what they need. But I'm sure that 500mA rating is a minimum, and they may draw a little more or less depending on the quality of the 12VDC it gets.
Also, I looked up an LM317 and its data sheet says it has "Output Current Capability of 100mA". So that's far below what you need. Willbe, is that why you are suggesting putting three LM317s in parallel?
 
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>347sixtyseven
> I am assuming if i were to just put them all in parallel with no current control, whenever i took a torch out, the other chargers would get more than 500mA. Is this correct?

I would say the other chargers would have more than 500mA available, but just because more than 500mA is there, they won't draw more than what they need. But I'm sure that 500mA rating is a minimum, and they may draw a little more or less depending on the quality of the 12VDC it gets.
Also, I looked up an LM317 and its data sheet says it has "Output Current Capability of 100mA". So that's far below what you need. Willbe, is that why you are suggesting putting three LM317s in parallel?
Nah, my bad, I thought they were 1A regulators. I should look at a datasheet once in a while.

Let's talk about 16v and 3.4A. This voltage may go 10% or 20% more under no load, let's say ~20%, so it goes to ~19v. This is the Thevenin equivalent voltage of this power supply.

(19-16)V/3.4A = ~1 Ω. This is the Thevenin equivalent resistance.

Now you can calculate the current delivered to any load. If you know the load resistance looking into the charger (but it may be nonlinear, with breakpoints; plot the V-I curve) you can predict all currents and voltages with any setup.

You can even parallel transformers with unequal voltages by using current sharing resistors.

BTW, a DPST 10A relay was cheaper than a SPST 20A relay, so I paralleled the two 10A relay contacts so I could switch almost 20A. We were charging silver cells for aerospace stuff.
One contact set burned out rather quickly, so I took the hint and added 6" of #26 AWG wire in series with each contact set. No more problem.
 
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Nah, my bad, I thought they were 1A regulators. I should look at a datasheet once in a while.

Willbe,

You were not wrong. Our friend simply looked up the 100mA version. Below are members of the same family. They all work the same, are adjusted the same, etc.

ADJUSTABLE 1.2V TO ~30V LINEAR REGULATORS

LM317LZ = 100mA, T0-92
LM317T = 1.5A, TO-220
LM317K = 1.5A, TO-3
LM350T = 3A, TO-220
LM350K = 3A, TO-3
LM338T = 5A, TO-220
LM338K = 5A, TO-3
LM396K = 10A, TO-3 (15V max)
 
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Willbe,

You were not wrong. Our friend simply looked up the 100mA version. Below are members of the same family. They all work the same, are adjusted the same, etc.

ADJUSTABLE 1.2V TO ~30V LINEAR REGULATORS

LM317LZ = 100mA, T0-92
LM317T = 1.5A, TO-220
LM317K = 1.5A, TO-3
LM350T = 3A, TO-220
LM350K = 3A, TO-3
LM338T = 5A, TO-220
LM338K = 5A, TO-3
LM396K = 10A, TO-3 (15V max)
Thanks for the summary. . .
:)

10A in a L(inear) M(onolithic) IC regulator; I should buy some of these!
 
I guess this is a question i should have asked earlier.

If the charger units have input 12v 500mA written on them, is this an indication of the max they can handle or just the amount they will use?

So if i were to provide them with 12v dc @ 800mA for example would it damage them? Is providing more current than required more or less damaging than not supplying enough?

Sorry for the basic level questioning guys but unfortunately thats where i am at :)

Gary
 
Sorry to dig up an old post but i have just picked up this project again.

I made up a quick layout using 5 LM2937ET-12 regulators, they will regulate to 12v and roughly 500mA.

I have just connected 5 in parrallel to get my 5 seperate outputs. What i am after are suggestions for the input cap size, the notes for the regulator suggest 0.1 uF for one reg, not sure what i should use for 5 regs in parrallel.

Here is my rough layout, haven't put neg traces for output in yet.

**broken link removed**

Any assistance would be greatly appreciated.

Gary
 
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