How to choose automatic voltage levels from a battery

[Nikhil N]

Hi..
I have a 40 volt (2.5Ah) , Lithium Ion battery. I need to use this battery for 20V application as well as 40V application. How to make an automatic voltage level chooser module for respective application?

 

[sophiecentaur]

To convert the 40V to 20V efficiently, you can't just use a Resistor in series (sorry if this is blindingly obvious to you). You will need a Switch Mode voltage converter which will lose very little energy in the conversion.
I found this link (one of many) that is possibly along the lines that you need. (Dropping the extra few volts could be done with two or three power diodes without too much power waste, if you can't find a unit with possible 40V input. Have a rummage on Google.

 

[berkeman]

Hi..
I have a 40 volt (2.5Ah) , Lithium Ion battery. I need to use this battery for 20V application as well as 40V application. How to make an automatic voltage level chooser module for respective application?

What is your current requirement for the 20V application?

 

[sophiecentaur]

automatic voltage level chooser module

I just read this again. What could you possibly mean by that requirement? Even a Human needs to read the rating on the side of equipment in order to know what supply voltage it should be provided with. This would truly be Machine Intelligence

 

[russ_watters]

I just read this again. What could you possibly mean by that requirement? Even a Human needs to read the rating on the side of equipment in order to know what supply voltage it should be provided with. This would truly be Machine Intelligence

I was thinking the same thing. I built a little power supply box for my telescope that can take an ac (to dc psu) or direct dc input and provides 12VDV out for the telescope and 5VDC out for a USB hub: a simple double-throw toggle switch selects the active input and a voltage converter like the one linked takes 12V down to 5V for the hub. The trick was that "12V" isn't 12V, so i had an additional one for that.

 

[sophiecentaur]

But you had an 'intelligent demand' circuit. This guy wants an 'intelligent source' circuit.
Perhaps the easiest way would be to have two different plugs and sockets, one for each voltage so the 20V system couldn't access the 40V supply and vice versa. That's so simple that I have only just thought of it.

 

[russ_watters]

But you had an 'intelligent demand' circuit. This guy wants an 'intelligent source' circuit.

Yes. And still manual.

Perhaps the easiest way would be to have two different plugs and sockets, one for each voltage so the 20V system couldn't access the 40V supply and vice versa. That's so simple that I have only just thought of it.

I have that too; and with different style plugs so I can't mix them up.

 

[Nikhil N]

What is your current requirement for the 20V application?

Current required is 1.5A

 

[berkeman]

Current required is 1.5A

So at 30W output, you should be using a Buck DC-DC voltage regulator. You can probably find one off-the-shelf that will do what you want.

 

[gmovercl]

Hi..
I have a 40 volt (2.5Ah) , Lithium Ion battery. I need to use this battery for 20V application as well as 40V application. How to make an automatic voltage level chooser module for respective application?

Like berkeman said, you can use one step down converter to supply both your applications. Adjust the duty cycle to adapt to either of your applications. However, you need to dig into some more design aspects if this is being designed for some application outside academic course/project work.

 

[Windadct]

If you want to build this device there are a lot of options, and you should specify a lot more then the current and the voltages. ( Quality of the DC: regulation and ripple, temperature, efficiency, complexity) However if you are just looking to buy one, search for DC/DC converter. 40 and 20V are odd voltages. 48 and 24 are more common.