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Battery Powered Variable Power Supply

Braeden Hamson

Feb 18, 2016
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Hello there,

I've posted about this before but I'm looking for more info. So I'm wanting to make a portable variable power supply that has a regulated voltage and current. Like those nifty bench power supplies. This one would use a laptop battery, It's made of 6 UR18650A. I found this nice guide on making one, I honestly picked it because it explains everything well.

http://www.electronics-lab.com/proj...-power-supply-with-current-control-0-002-3-a/

I'm looking for efficiency above all. Do you guys think this is a good candidate for this project. Also I'd obviously remove the transformer and FULL-BRIDGE RECTIFIYA. Maybe it would be more efficient to have an arduino control the circuit? There will already be one in this project to run the power measurements.
 
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Audioguru

Sep 24, 2016
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13 years ago I helped fix the project you linked because it had many overloaded parts, was not reliable and did not produce its rated 30VDC at 3A. The improved project has some very long threads about it at electronics-lab.

Recently there are a few very cheap Chinese copies that also do not work. The copies are being replaced by a mess of parts that have a voltage and current display but we think their new simple circuit does not have voltage or current regulation because it has no ICs.

Six 18650 lithium-ion cells are 18V when a part of the circuit must sense low battery and disconnect them and are 25.2V when fully charged. When the battery has discharged to 18V then the maximum output from the project will be only about 13V. The circuit also has a negative supply that is provided by the transformer and rectifier. Will you use two more battery cells to produce the negative supply?
 

Braeden Hamson

Feb 18, 2016
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13 years ago I helped fix the project you linked because it had many overloaded parts, was not reliable and did not produce its rated 30VDC at 3A. The improved project has some very long threads about it at electronics-lab.

Recently there are a few very cheap Chinese copies that also do not work. The copies are being replaced by a mess of parts that have a voltage and current display but we think their new simple circuit does not have voltage or current regulation because it has no ICs.

Six 18650 lithium-ion cells are 18V when a part of the circuit must sense low battery and disconnect them and are 25.2V when fully charged. When the battery has discharged to 18V then the maximum output from the project will be only about 13V. The circuit also has a negative supply that is provided by the transformer and rectifier. Will you use two more battery cells to produce the negative supply?


Thanks for the heads up, I will steer clear of that circuit. Any recommendations? The laptop pack already has a battery maintainer circuit attached. It has 9 pins that connected it to the laptop, so that will be interesting to figure out. I was hoping to make use of that, otherwise I'd build that separate to this. Also, I don't fully understand what a negative supply is. Is that a way to get a greater voltage difference? I really don't need anything fancy for this project. The simpler the smaller, the better.

All I want is volt and current regulation, and ~2 amps and maybe 20 volts. If I can get more that'd be good too.
 

kellys_eye

Jun 25, 2010
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There are a lot of buck/boost modules with built-in volts and amps metering along with CV and CI capability available from your favourite Chinese retailer. 'any' volts in, any volts out basically. Search eBay using buck boost as search word.
 

Audioguru

Sep 24, 2016
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A current regulator usually reduces the output voltage of the power supply until the current is at the current setting. If the output is shorted then the current regulator must force the output voltage to zero but it has a diode in series with its output so the output of the current regulator must go to a negative voltage for the output of the series diode to be at zero volts. Then the current regulator needs a positive supply and a negative supply that are produced with the transformer and diodes in the mains electricity powered project.

The improved project we are talking about has excellent voltage and current regulation. Boost and buck regulators use an oscillator so they have output ripple and not very good regulation.
 

Audioguru

Sep 24, 2016
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The requirements have conflicts:
1) A portable variable power supply that has a regulated voltage and current. Like those nifty bench power supplies.
2) I'm looking for efficiency above all.

A linear power supply has excellent voltage and current regulation but has poor efficiency.
An efficient switching buck-boost converter does not have excellent regulation but it might be good enough.

A switching pre-converter followed by a linear regulator will be fairly efficient and have excellent regulation but is not "The simpler the smaller, the better.".
 

Braeden Hamson

Feb 18, 2016
234
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Feb 18, 2016
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The requirements have conflicts:
1) A portable variable power supply that has a regulated voltage and current. Like those nifty bench power supplies.
2) I'm looking for efficiency above all.

A linear power supply has excellent voltage and current regulation but has poor efficiency.
An efficient switching buck-boost converter does not have excellent regulation but it might be good enough.

A switching pre-converter followed by a linear regulator will be fairly efficient and have excellent regulation but is not "The simpler the smaller, the better.".

What's the tolerance on the buck-boost regulator? I suppose this thing doesn't need to be a perfect piece of equipment, if I were to do serious work on something I'd use a lab power supply. To be honest this project is more for me to learn about these types of components. The use cases I can think of for this are charging random batteries (as its a regulated current supply) and replacing batteries for testing purposes. I will also have a 5 v output so the device can act like a USB battery bank. This would be its main use, as well as a backup battery for my laptop maybe. This would be done by setting the supply to say 18 volts and 2 amps and plugging it in with custom connector. All this being said, I have never encountered any situations where I need exact voltages and currents. But I am just beginning.
 
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