Why is my step up converter not increasing voltage and why output is a little lower than input?

My step up converter is not working ,it wont increase the voltage . I used a multi meter and the output ends up being lower than the input like for example when I connected the battery to it, the battery was at 8.40v and I checked the output and it was 8.10v . I was trying to make a DIY speaker for the first time,  I am new to this. 
step up converter  is called a MT3608 LM2577. I got it off of aliexpress.    


The battery i used is off a battery pack .it is 8200 mah and 9v

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y8492b3 months ago

Second thoughts, since some modules may be designed with the pot shorting clockwise, put the pot midway, and keep the input voltage below 6 volt, until the sense of the pot has been established.

Moral of the story on this one, as always, is to get and check the datasheets for all the devices in your designs.

y8492b3 months ago

The problem with most of the MT3608 and SX1308 modules is not the device, but the same flaw in the circuit design. If you look at the datasheet for these, which actually the same, you will find that the absolute maximum voltage allowed on the FB pin (feedback) is 6v.

Unfortunately, this can be easily exceeded because of the simple use of a 10k pot in the resistor divider from VOut to the FB pin. In operation FB is expected to be about 0.6V, but as the 10K pot can be reduced to zero, it can put VOut on the FB pin.

As the pot is turned (usually anticlockwise) the voltage on FB will increase, until it exceeds 0.6 volt and the device turns off. At that point the module will simply pass through the voltage from VIn to VOut via the inductor and diode.

Which means when the pot is connecting FB to VOut and VIn exceeds 6v plus a diode drop, the device will be destroyed.

Other than modifying the circuit, the best approach is to always turn the pot fully clockwise (most designs), then apply voltages and very slowly start turning anticlockwise for the required output.

Alex345 (author) 6 months ago

i got the step converter that is 6a and can supply 100 watts is there any resisters i should use so I wont surge damage my components and so the volume will not lower.

iceng6 months ago

When the booster power is greater then the amp power a resistor is not that useful and I believe the heat-sink will help the boost survive first power on..

iceng6 months ago

Here are some fuse facts worth consideration;

A fuse is a lot slower to blow (melt sag open a circuit) then a semiconductor (tiny solid state PN junction can smolder to death)..

But then the booster has that nice metal heat sink => device to cool the Solid State PN Junction for a moment more time before junction reaching 130'C..

So it is a race between fuse and junction..

Also a 6A fuse probably will work a few seconds at 6 amps..

Yes, there are different speed fuses.. Please avoid all automotive fuses..

I show you the very fastest Fluke meter fuses I can get, but not on a Sunday so I repaired it.. See how fine the fuse wire material is compared to the readily available buss fuses..

The last is a 5A 32V fast mini buss fuse that may be able to save your booster from accidents.. I would get ten..

FaceFluk1.JPGBatt2.JPGFuse5.JPGfast 5A32V.jpeg
Alex345 (author) 6 months ago

when told about the fuse do you think that an 6amp fuse could work temporarily so it wont kill the booster

Alex345 (author) 6 months ago

and would that 6a converter still give that volume problem

Alex345 (author) 6 months ago

the new one i bought is similar to the old but wont work because its only 2a and would be killed by the amp so ill have to wait to but that other new one then. but is there a way I can still use the new 2a one i bought or maybe with out the converter without the volume going down or with out damaging anything if not ill just wait

Alex345 (author) 6 months ago

so should i try getting bigger step converter. Because the amp can go to 28 v and the new boost i orderd can go to 28v to

iceng Alex3456 months ago

Nice find it has a maximum of output 6A..

Assume your amp is using 100W then the boost voltage out = P/A= 100/6 = 16.6 vdc...

iceng Alex3456 months ago

If the amp can use a 100 watts then any booster must also be able to supply 100 watts...

Watts are output volts x amps and the battery more...

Example P=VxA and A=P/V

@ 28 volts Amps = 100/28= 3.6 Amps

@ 14 volts Amps = 100/14= 7.2 Amps

If 3.6A kills your Booster then 7.2A will also kill it at any loud note...

You need a power supply that limits output current to whatever it was designed to deliver...

Alex345 (author) 6 months ago

would that work for when i can buy another part

Alex345 (author) 6 months ago


Alex345 (author) 6 months ago

whoops the amp can only go up 24 v and the step up can go supply 28 v but that still would still kill the step up is there a way i can use the step up with out killing it because i wont be able to buy something that could give more amps for a while

iceng6 months ago

Good !

You realize the amp can try to pull 100 watts from a booster that can only deliver

14 volts at 2 amps thats only 28 watts.. No wonder anything above a whisper will blow the booster...

Alex345 (author) 6 months ago

btw the amp is 2x50w each speaker is 50 watts

Alex345 (author) 6 months ago

ok thank you ill i am going to do that

iceng6 months ago

Why don't you use two batteries in series = under 18 VDC ? Give you double the time too..

But lets do the math for current... Output current over 2A max kills the unit and the efficiency is only 75% at full output... So lets work with 1.5 amps average where maybe Eff=90% >> 1.1 loss.. Put a 1.5 a fuse on the output later a 2A fuse.

Before energizing with the amplifier adjust the pot to deliver 14v You may have put some small load in order to make the booster work use an incandescent

Average Input current = 1.5Aout x (14v/8.8v) x 1.1 loss = 2.7 Amps input..

Any way, a quarter ohm resistor in series with the input will cut back 1amp input..

You make a o.25 ohm resistor by putting four one ohm 1/2 watt resistors in parallel..

Be sure to click the pic to see the whole image !

Dummy Load.PNG
Alex345 (author) 6 months ago


Alex345 (author) 6 months ago

how can i stop the surge current damage

iceng Alex3456 months ago

A resistor in series that is removed with a switch after 20 sec.

And I can't, until I know the circuit you are feeding the 14 volts to...

Fiure the R.

Alex345 (author) 6 months ago

The new one I ordered is from different seller

Alex345 (author) 6 months ago


iceng6 months ago

BTW I'm ordering two just to see the output..

iceng6 months ago

What is voltage are you trying to boost up to ?

Alex345 (author) 7 months ago

it bought a new one and i have another problem my diy speaker when turned on is at first loud but then the volume lowers even without the boost module

iceng Alex3457 months ago

Sounds like you are surge current damaging your modules.

When you first generate the higher output voltage.. There is initially a 3 to 7 times current draw that could over load the unit... BTW did you first adjust the output pot without a load for the exact voltage you want ?

Then you could be draining the little battery.. Remember the battery must supply more current in proportion to the voltage increase and 93% efficiency means 7% is used to run the booster... Battery Current A = Speaker Current x (Vout/Vin) x 1.07

Alex345 (author)  iceng6 months ago

i checked without load nothing happens

Alex345 (author) 7 months ago

how do i check with out load

iceng Alex3457 months ago

Simply remove the out wires and put a volt meter on the output and try the pot again..

Alex345 (author)  iceng7 months ago

It wont do anything

Alex345 (author)  iceng7 months ago

I wont do anything

iceng7 months ago

What happens when you turn the pot one way or another ?

Alex345 (author)  iceng7 months ago


Alex345 (author)  Alex3457 months ago

niether decrease or increase

Alex345 (author) 7 months ago

But it wont do anything when i turn the screw. nothing seems burnt

Alex345 (author) 7 months ago

When i bought it. it said boost

Yonatan247 months ago

Did you check that it's a step down (buck) vs. step up (boost)?

Did you check with load or without load?

Are there any burnt components - could you have ruined it?

Is your multimeter working properly?

Buy another one!

iceng Yonatan247 months ago

Wow...... Good advice Yonatan,

Can I assume that you can read schematic drawings now ?

Yonatan24 iceng7 months ago

Nope. Nothing has changed since then.

#1 - because I was lazy to read Chinglish.

#2 - tip that I know from checking regular power supplies

#3 - from experience (hint: wrong polarity and... BOOM! :)

#4 - also from experience (messing up an expensive multimeter so it shows that an 18650 battery is 20V :)