DIY - 12V Mini UPS 

It's not working for me. Before connecting to boost converter, bms output voltage is 11.68 v but as soon as I connect it to boost converter, voltage drops to 0.67 V. And so can't step up the output for 12v. But when I connect boost converter directly to battery output, it works, which is not advisable !!! Please help with this

@@viralindia8951 if your bms output is 11.6v then you can easily use it as 12v. There's no need to use a boost converter. Also, there is a limit to the input voltage for the boost converter. You should check the specification.

Tested and approved as correct!

my thoughts EXACTLY

What should the diode rating be?

@@AtlantaTerry anything would do a 1n4007 has a rating of about 700v.

While your at it could add an inline fuse that would blow before the ones on the battery did as those are harder to get to.

Sorry where would the diode be connected?

Yes. I need a small UPS for my Raspberry Pi system.

Sure he has a sense of humour , I like it too.

The precision sensor, "between hot/cold."

What step up transformer did you use?

Can you please help by giving a list of the components you use? I am looking into building one but don't know where to get the components online.

@@jithinramesh3022 The two main places that people source parts for electronics projects are AliExpress and Banggood. They're both Chinese websites which allow you to essentially get the parts for the cheapest price and they usually have global free shipping. I would personally recommend Banggood because I usually get my items within a week and a half when ordering from there vs AliExpress which can take weeks but usually not over a month. I live in New Zealand which means components ordered from these sites get here a bit faster then other parts of the world. As for your question regarding the components that Aji used I might recommend trying a premade board that essentially does everything the BMS in the video does in a single package. Something like this: www.banggood.com/18650-Lithium-Battery-Boost-Module-12V-Charging-UPS-Uninterrupted-Protection-Integrated-Board-With-C-p-1280431.html?rmmds=search&cur_warehouse=CN

@@ChillarPunter with 3S battery and 12V router no step up or step down converters are needed. Router will still work, even when supplied with 9V (3S battery at 1% charge)

For 3s, the Charging voltage should be greater than 12.6. How did you get this voltage with 12V adapter without using step up convertor?

No, my router works 11v-18v. Although rated at 12v. It doesn't work anything less than 11v. So step up is mandatory. Schottky diodes are also required.

Too much protection than any oth product which is made officially 🤣😅😆

ok

That or one of those crimping type strain reliefs that just snaps into the hole a lot of appliances use. If space is the issue as in that small case one of those snap in might take less room.

hi. yes the BMS monitors the voltage of each cell, that's why it has a lead between the cells. it's the yellow wire in my schematic.

thanks for clarifying this. I know what they are for, just didn't know how to call them in English.

hi. 1- yes you can use a battery holder, but I prefer to solder the cells. I test all the cells before I use them, so very rarely I had problems and need to replace cells. I prefer soldering the cells, because with battery holders there may be an imperfect contact in time between the cell and the holder, also the plastic enclosure needs to be bigger. 2- a diode will block the current from one direction, but it also has a small voltage drop. so the charging voltage will drop below 8V, which is not enough to charge the cells. the charger LED is using only a few mA, it doesn't make any difference in the 6 hours working time of the UPS. it remains like this for now. 3- the voltmeter display is using 17-20 mA, depending on how many LEDs are lit. so yes you can save a little energy by disconnecting it. you can add a capacitor and a microswitch to the voltmeter. when you press the microswitch for 1-2 sec, the capacitor is charged and the voltmeter will remain on for a few sec, enough to read the value. 4- the BMS has over discharge protection at around 2.9V per cell. you can check the UPS voltmeter, when the voltage decreases to under 6V, the cells are almost discharged and it will shortly turn off. I did this test in the video. 5- this step up converter doesn't have short circuit protection, so you can add another fuse on the positive output terminal. or you can use another (bigger) type of step up converter, with short circuit protection included.

with exactly same build you need one more step down DC to DC board to lower 12V from power supply to 8.5-8.4V to charge the whole mini UPS, all the rest stays the same.

@@baniakrulez Thanks. Will do.

I wanted to have a very stable 12V output. other people will probably make it for some other devices that may need a stable voltage. this is possible only with a dc converter. it will last longer with a step up converter, because it's using the entire battery capacity. and I wanted it to be small, with 3 cells it needs a bigger plastic enclosure.

yes a diode will block the current in the reverse direction, but it also has a forward voltage drop of around 0.9V so the charging voltage will drop under 8V, which is not enough to charge the cells. the charger LED is using only a few mA, it doesn't make any difference in the 6 hours working time of the UPS.

"LED": Light Emitting DIODE. So why would you need a second diode?

@@AtlantaTerry simp

No, he's Romanian.

@@George-sp1sr Aaahhh i see...

Este doar un volt/ampermetru pus intr-o carcasa. :)

that's nice

hi. if you used a buck converter, then it means you have a bigger battery pack. but the current limit of the buck converter is for the converter output, not the converter input (the battery pack). the input current and output current of the converter differs, depending on the load, converter efficiency and battery pack. there is nothing wrong with it, just don't set a lower output current than your router needs.

I have the battery pack charging FROM the buck converter output, that way when the battery is flat, it charges at constant current (1.65A for my cells... they're 3500mAh so ~0.5C charge) up until the preset voltage is reached for full charge, then it switches to constant voltage mode and then the current drops quickly down. I still use a boost converter on the battery pack to the UPS output to keep the voltage constant as the battery voltage drops. I then use a much higher voltage power supply (24V, ~1A, 25W) because its slightly cheaper and also I get better efficiency stepping down from higher voltages with the buck (>90%). The buck isn't strictly necessary and your design is elegant.