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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.    

https://www.aliexpress.com/item/DC-DC-Adjustable-Boost-Module-2A-Boost-Plate-2A-Step-Up-Module-with-MICRO-USB-2V/32668154181.html?spm=2114.13010608.0.0.a2VAYu



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

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Alex345 (author) 1 month 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.

iceng1 month 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..

iceng1 month 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) 1 month ago

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

Alex345 (author) 1 month ago

and would that 6a converter still give that volume problem

Alex345 (author) 1 month 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) 1 month 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 Alex3451 month 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 Alex3451 month 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) 1 month ago

would that work for when i can buy another part

Alex345 (author) 1 month ago

https://www.aliexpress.com/item/100W-DC-DC-DC-3-35V-to-3-5-35V-LTC1871-Booster-step-up-Step-up/1967921037.html?spm=2114.01010208.3.2.Wtmu8t&ws_ab_test=searchweb0_0,searchweb201602_2_10152_10065_10151_10068_10130_10136_10137_10060_10138_10155_10062_10156_10154_10056_10055_10054_10059_10099_10103_10102_10096_10148_10147_10052_10053_10142_10107_10050_10051_10084_10083_10080_10082_10081_10178_10110_10111_10112_10113_10114_10181_10182_10033_10078_10079_10077_10073_10070_10123_10124-10051_10112_10033_10077,searchweb201603_1,ppcSwitch_5&btsid=05706ec8-0728-496c-8d1b-9c46fd2d2a4c&algo_expid=671bd1d8-c0e5-4bbf-9477-8224dd05ee03-0&algo_pvid=671bd1d8-c0e5-4bbf-9477-8224dd05ee03

Alex345 (author) 1 month 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

iceng1 month 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) 1 month ago

btw the amp is 2x50w each speaker is 50 watts

Alex345 (author) 1 month ago

ok thank you ill i am going to do that

iceng1 month 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) 1 month ago

circuit

IMG_20170426_170809230.jpgIMG_20170426_170816441.jpgIMG_20170426_170823746.jpgIMG_20170426_170831182.jpgIMG_20170426_170836427.jpgIMG_20170426_170844272.jpgIMG_20170426_170903878.jpgIMG_20170426_170908262.jpgIMG_20170426_170915872.jpgIMG_20170426_171543855.jpgIMG_20170426_171552920.jpgIMG_20170426_171613678.jpg
Alex345 (author) 1 month ago

how can i stop the surge current damage

iceng Alex3451 month 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) 1 month ago

The new one I ordered is from different seller

Alex345 (author) 1 month ago

14v

iceng1 month ago

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

iceng1 month ago

What is voltage are you trying to boost up to ?

Alex345 (author) 1 month 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 Alex3451 month 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)  iceng1 month ago

i checked without load nothing happens

Alex345 (author) 1 month ago

how do i check with out load

iceng Alex3451 month ago

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

Alex345 (author)  iceng1 month ago

It wont do anything

Alex345 (author)  iceng1 month ago

I wont do anything

iceng1 month ago

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

Alex345 (author)  iceng1 month ago

nothing

Alex345 (author)  Alex3451 month ago

niether decrease or increase

Alex345 (author) 1 month ago

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

Alex345 (author) 1 month ago

When i bought it. it said boost

Yonatan242 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 Yonatan241 month ago

Wow...... Good advice Yonatan,

Can I assume that you can read schematic drawings now ?

Yonatan24 iceng1 month 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 :)