I am building a battery pack using lithium-ion batteries salvaged from laptop batteries.
I have to boost the nominal 3.7 to 5 volts. The battery voltage will vary from 4.2 to 3.0 volts
I purchased a boost converter from banggood but the output voltage varies if the input
voltage changes even a little bit. I thought converters regulate the output over a range of
input voltages. Is this not the case ?

 

I thought converters regulate the output over a range of
input voltages. Is this not the case ?

Depends upon the design of the converter.
What are its specs?

 

It's bangood so the spec are pretty thin.

Description:
DC Boost Converter 2A Power Supply Module 2V-24V To 5V-28V Adjustable Regulator Board

Item Name: DC Boost Converter
Max Output Current: 2A (Recommended for use in 1A)
Input Voltage: 2-24V
Max Output Voltage: 28V (Recommended for use in 26V)
Efficiency: > 93%
Dimension: 30x17mmx14mm

Features:
Smallest volume Adjustable DC boost converter in the market,can be easily installed in small devices.
Use MicroUSB input,with the USB charger or mobile power through the phone data cable can easily get 9V, 12V, 15V, 18V, 24V common voltage.
Very convenient to use.
Ultra wide input and output voltage, high conversion efficiency.

Note:
The output voltage should be greater than the input voltage.
Peak output current should not exceed 2A.

Package Included:
1x DC Boost Converter

 

There may be a minimum load required for the output to stay
in regulation. If it has been left out of datasheet put a load on
it, say 50 mA or so, to see if it starts regulating.


Regards, Dana.

 

Hello Dana,

I had a 20 Ohm load on the output but it seems there is no regulation going on.


Thanks for your reply.

 

Have you tried adjusting the output voltage?

 

Yes I have, there is a multi-turn pot on the board to adjust output voltage. It is more like a fine
adjustment though.

 

Yes I have, there is a multi-turn pot on the board to adjust output voltage. It is more like a fine adjustment though.

If the output is adjustable from 5V-28V, I wouldn't call that "fine".

 

The potentiometer is a "fine" adjustment. For a set input voltage the output can be adjusted maybe + 1 volt above the input voltage. You can get the output from 5 - 28v but the input would have to be close to the output. That's what I meant by fine.

 

The potentiometer is a "fine" adjustment. For a set input voltage the output can be adjusted maybe + 1 volt above the input voltage. You can get the output from 5 - 28v but the input would have to be close to the output. That's what I meant by fine.

So you mean you can't adjust it for a 28V output with a 5V input?

If it can only be adjusted for 1 volt around the input voltage then I would not call that an "adjustable regulator".

 

Yes, that's correct. I can't get near 28v with a 5 volt input.

I have a 20 volt power supply that can deliver 1.5 amps that I am using to drive the board.
I have a 20 load on the output.
I can only apply 4.5 volts to the input before the input is drawing 1.5 amps.
The output voltage is 6.3 volts, so the output current is 6.3 volts /20 ohms.

I got these on banggood but they are also sold on Amazon. Mixed reviews, some people with the same experience I am having.

 

Really sounds like a defective unit.

 

I got these on banggood but they are also sold on Amazon.

Being sold on Amazon means nothing.
Amazon will sell anything that's legal. They do no check the quality of what is being sold.

 

Really sounds like a defective unit.

NOTHING in that specification mentioned any sort of regulation. AND, since regulation is a plus, any description of a regulated device would include it. So what you have is a fixed-ratio DC to DC converter. What you need is a regulated converter, which would probably cost a bit more.
Now you can see that if the specification does not say "regulated output", it does not have a regulated output. While you can certainly add a regulator it will reduce the overall efficiency of the system quite a bit, and for a battery powered system that usually matters.

 

The description says you can get 15V with a USB charger for input. It is defective.

Bob

 

The description says you can get 15V with a USB charger for input. It is defective.

Bob

Not only defective, but also non-regulated.
Not everything posted on the internet is correct. And not everything sold on amazon is as good as they say it is.