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Small UPS with lithium batteries

Navig8tor

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Hi all.

First of all, let me say that I am not an engineer, only an electronics hobbyist "wanna be", so please bear with me...

I want to build a mini ups to ensure uninterrupted power for my router and fiber ONT during grid power outages.
The battery pack will be assembled from 18650 lithium batteries;
It must have passtrough function, so when AC power is on and the battery is fully charged the power goes straight to the connected devices and when AC power fails the battery pack will provide power for the devices without interruption;
It should have 2 DC output connections with 2 amps and selectable voltage (9 and 12 volts) and one USB port (5 volts, 2 amps).
Again, I am no engineer, so I need a simple schematics and the list of components needed to buy and assemble everything together.

Any help or advice will be apreciated.
Thanks in advance.
 

KlausST

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Hi,

Post a drawing.
Especially how the AC is involved.

Klaus
 

Carry for cents bazar

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It will be best to buy the modules, instead of creating a new PCB.

The idea to use 18650 batteries is not very good. They don't last long.

First get a 2A charger, second get an empty battery bank box container. Connect the charger to the battery bank and then the battery bank with a USB cable to the LM2577 module. The module will turn the voltage from 5V to 12V or anything else you want. Its adjustable. Some battery banks have a 12V quick charge or USB C. Normally they can be charged with 1.5A max. It takes about 12 hours to charge a bank with 8 batteries. They give 2A output max. The module should be set when you receive it, but if something is wrong, turn the potentiometer back and forth 10 times and measure the voltage. This is a multiturn potentiometer. Make sure not to exceed the 9V or 12V or your router. A little doesn't matters, but not more or less than a volt.

AC -> charger -> battery bank -> 2 USB output ports with 1 module LM2577 per each port -> from the LM2577 to the router or something else.

Components:
1. Charger from you.
2. Battery bank (does not contain the batteries). It has only 2 USB output ports. The efficiency of the LM2577 is 80 to 92%, so you will get 8W-9W, hopefully its enough for you. 8W/12V = 0.67A, it looks enough for a router. Sometimes the module causes a problem, because its a switching power supply. Switching power supplies have a higher efficiency than linear ones.
3. LM2577
 
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Navig8tor

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Here's my drawing...image001.jpg
What I need to know is what to fit inside the mini UPS case and in what order (apart from the batteries - 3 x li-ion 18650 connected in series).
I think I will need a step down voltage converter before the BMS and a step up voltage converter after the batteries.
I also believe there is a need for a relay to direct the current past outside the batteries charging circuit and directly to the output when batteries are fully charged and AC is on and through the batteries when AC is off.
 

Carry for cents bazar

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Here's my drawing...View attachment 163255
What I need to know is what to fit inside the mini UPS case and in what order (apart from the batteries - 3 x li-ion 18650 connected in series).
I think I will need a step down voltage converter before the BMS and a step up voltage converter after the batteries.
I also believe there is a need for a relay to direct the current past outside the batteries charging circuit and directly to the output when batteries are fully charged and AC is on and through the batteries when AC is off.
You are over complicating things. Please check what I wrote.
 

d123

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Hi,

If you want to, you seem to understand a few things..., try looking for Li-ion charger ICs from TI/Analog Devices/Maxim/Microchip/In Semiconductor/ST Micro/etc... and use their parametric search tables to see if anything comes up.

Some of these ICs carry out some or maybe even all the tasks you are looking for.
--- Updated ---

...On Semiconductor...
 

Navig8tor

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You are over complicating things. Please check what I wrote.
Thanks Carry for cents bazar,

I was already posting before reading your first post...

My router/gateway is a power hog, it draws 24W (12v * 2A) and the fiber ONT another 12W (12v * 1A) - 36W total, so I need to be able to provide at least 12V and 3A (36W) to the output connections. But if I change the router or ONT in the future I want to be able to change the output voltage on each connector just in case the new devices are 5 or 9V (most common voltage in those type of devices).

My questions:

Can the USB ports on the battery bank enclosure provide 12V * 2A?

The UPS is to be permanently connected to both AC and the DC devices, so if the drawn power (36W in this case) is higher than the charging power the battery bank will be discharging even if connected to the AC unless some circuitry is implemented to prevent it (maybe some sort of relay)?

I'm a bit confused because you suggested a battery bank that works with 18650 batteries, but you also said that using 18650 is not a good idea. By the way, what is the power input of that battery bank enclosure?
 

Navig8tor

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Hi,

If you want to, you seem to understand a few things..., try looking for Li-ion charger ICs from TI/Analog Devices/Maxim/Microchip/In Semiconductor/ST Micro/etc... and use their parametric search tables to see if anything comes up.

Some of these ICs carry out some or maybe even all the tasks you are looking for.
--- Updated ---

...On Semiconductor...
Thanks d123,

I understand basic concepts of electricity and my knowlege is mostly empyrical. Semiconductors are way too much complicated for me... ;)
--- Updated ---

I supply here a UPS system for you as attached.
Thanks treez,

That is a good starting point, even if your drawing skills are similar to mine...:giggle:
 
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Carry for cents bazar

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The specification of the battery bank says output 2A and 1A, but the input is 1.5A max. If you can find an enclousure to supply what you need, it might work.

You requested 18650 batteries. Otherwise I would suggest a car battery charger, connected to a car battery and from the car battery, you can draw all you want with an LM2577 module(DC-DC step up) or an LM2576 module which is a DC-DC step down. Normally I power motors this way. The car charger will supply 4A for example, this is a small car charger. This method has downfalls! The first problem is, if the battery is charged more than the maximum, will it start leaking acid, gases or explode. Some chargers say they are automatic, but they are not. The second problem is, can the charger charge the battery, while its used(like in a car). It also becomes a bit expensive. The charger has to be automatic, start charging at 12.2V and stop charging at 12.6-14.4V.

3 x 18650 = low capacity.

A laptop battery is 4000mAh approximately, it has versions form 10V to 20V, but it can only be charged inside of a laptop.
 

Navig8tor

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The specification of the battery bank says output 2A and 1A, but the input is 1.5A max. If you can find an enclousure to supply what you need, it might work.

You requested 18650 batteries. Otherwise I would suggest a car battery charger, connected to a car battery and from the car battery, you can draw all you want with an LM2577 module(DC-DC step up) or an LM2576 module which is a DC-DC step down. Normally I power motors this way. The car charger will supply 4A for example, this is a small car charger. This method has downfalls! The first problem is, if the battery is charged more than the maximum, will it start leaking acid, gases or explode. Some chargers say they are automatic, but they are not. The second problem is, can the charger charge the battery, while its used(like in a car). It also becomes a bit expensive. The charger has to be automatic, start charging at 12.2V and stop charging at 12.6-14.4V.

3 x 18650 = low capacity.

A laptop battery is 4000mAh approximately, it has versions form 10V to 20V, but it can only be charged inside of a laptop.
Thanks Carry for cents bazar,

The UPS is not intended to run the devices for hours, only 5 to 10 minutes, the time that usually grid power comes back on.

My preference for the 18650 li-ion has to do with both compactness and life span (in cycles at least) that I believe is much higher than lead acid. I have 2 regular UPS's that use sealed lead acid batteries and I have to replace them every year...

The devices consume 36Wh in total, and 3 x 3,7V 2500mAh will provide a total of 27,75Wh, which is around 46 minuts of running time, more than enough for my needs. I can also consider to add more batteries to the pack, that wouldn't be an issue, but I will be using the Samsung INR18650-25R that have 20A discharge current, so also no problem there, I think.

But this is all theory and I still have not enough information about all the ingredients that I need and how to mix them to make the cake :giggle:
--- Updated ---

Hi,

Post a drawing.
Especially how the AC is involved.

Klaus
Hi KlausST,

Did you have the chance to look at my drawing?

Any input on my project?

Thanks.
 

KlausST

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Hi,

Yes, I saw the drawing.
It doesn't show the batteries, how many? In series? In parallel?
And I see now that you don't work with AC it all, you use the 24V DC.
You most problably whether AC is down, but whether 24VDC is down...

There are many solutions. From low effort to high effort.
It depends on your needs

A high effort solution could be:
When power input is ON:
AC --> 24V DC --> battery charger --> 4 x 18650 in series
....24V --> diode1 --> 2 × step down

When power input is OFF:
4 × 18650 --> diode2 --> 2 × step down

******
With this it automatically switches (with the diodes) from "charging mode" to "backup mode".

Klaus
 

Carry for cents bazar

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And another solutions is:

I see you have experience in electrical circuits. Don't create a PCB is my advice, prototyping almost never works from the first time and causes a lot of problems and wastes of a lot of money.

If you grid works for 30 minutes and is off for 10 minutes, that will be enough to charge the batteries for the used mAh during the 10minutes. Even if it charges at 1.5A.

I suggest using the setup I gave you. It has almost no soldering, and all you need to solder is the same type of connector like your router has(probably a barrel jack) to the output of the LM2577. Your router should have a voltage and current rating, not only wattage. It does not consume 36W at all times, only when pressuring itself at the maximum. An eBike, motorcycle or similar battery can also work.

Batteries in parallel give the same voltage, but higher current.
Batteries in series give higher voltage, but the same current.

Setup:
Charger(1.5A-2A) -> Battert bank(3 or 8 batteries in parallel) -> LM2577 -> Router.

Otherwise I would suggest this ready with the charger 18650 battery pack:
1. With the charger.
 

wwfeldman

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I want to build a mini ups to ensure uninterrupted power for my router and fiber ONT during grid power outages.
what are these devices plugged into now?

you might consider buying a UPS instead of building your own
there is an amount of surety that it will work reliably
there is also a potential issue with local electrical regulations and fire codes
that a store bought UPS may meet, that a home-made will not.

a place to start:
 

Navig8tor

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what are these devices plugged into now?

you might consider buying a UPS instead of building your own
there is an amount of surety that it will work reliably
there is also a potential issue with local electrical regulations and fire codes
that a store bought UPS may meet, that a home-made will not.

a place to start:
Hi wwfeldman,

Is actually all covered in my previous posts. I own 2 APC UPS's and it's a pain to replace the batteries every year. It's also a pain when I'm working online on my PC, the power goes off, the PC keeps going because is behind an UPS but the ONT and the router goes off and my work is halted until power comes back on plus booting time of those devices.
I don't want another traditional AC UPS, first because I don't want to deal with another yearly battery replacement and secondly I only need a small amount of DC power to feed those two devices anyways.
 

KlausST

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Hi
Setup:
Charger(1.5A-2A) -> Battert bank(3 or 8 batteries in parallel) -> LM2577 -> Router.
The problem here is that you never have a "true" charging mode, because the load alwasy draws current.
If your charger current is 2A into paralleled batteries, then the power is limited to 2A x 3.7V = 7.4W.
This 7.4W are used to power the load and to chargevthe batteries. If your load is more than 7.x W (as it seems to be) then the batteries never get charged.


Don't create a PCB is my advice, prototyping almost never works from the first time and causes a lot of problems and wastes of a lot of money.
A different approach:
I never use breadboards. I only rarely do simulations. I read the datasheets, do the mathematics. My first prototypes are on designed PCBs that are most equal to the end design. There may be only minor modifications ... and usually these prototypes go to the customers to verify the design.
With this prototype usually I even do the EMI/EMC (pre) tests.
Thus the end design has just minor modifications, low error rate from prototype to end design.
It takes more time "from idea to prototype" but less time "from prototype to end design".

Klaus
 

Navig8tor

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Hi

The problem here is that you never have a "true" charging mode, because the load alwasy draws current.
If your charger current is 2A into paralleled batteries, then the power is limited to 2A x 3.7V = 7.4W.
This 7.4W are used to power the load and to chargevthe batteries. If your load is more than 7.x W (as it seems to be) then the batteries never get charged.

...

Klaus
drawing001.jpg

Please look at the drawing and tell me if the wiring is correct and if the parts will do the job.
What could I integrate in the circuit and where to be able to drive the current away from the battery and straight to the output when the battery is fully charged?

A) https://www.electrofun.pt/en/transformadores-e-conversores/alimentador-switching-24v-2a
B) https://www.aliexpress.com/item/32804349413.html
C) https://www.18650batterystore.com/18650-p/samsung-25r-18650.htm
D) https://www.aliexpress.com/item/4000077783578.html
E) https://www.aliexpress.com/item/32988565087.html
 

wwfeldman

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the batteries are not in series and they are not in parallel

in series: + to -
in parallel, all + connected to each other and all - connected to each other

the battery connection looks like anti-series
you have + tied to +, and - tied to -, and - tied to +

you might want to add a battery holder, such as this one, which connects the batteries in series:
 

Navig8tor

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the batteries are not in series and they are not in parallel

in series: + to -
in parallel, all + connected to each other and all - connected to each other

the battery connection looks like anti-series
you have + tied to +, and - tied to -, and - tied to +

you might want to add a battery holder, such as this one, which connects the batteries in series:

Yes, you are right, my mistake. I should have put the middle battery upside down... It's correct now:

drawing001.jpg

The link you provide has no picture, but I guess is the same type of product I plan on using to put the batteries on:

What about the charge control module, will it work good for this purpose?
Should I use two boost converters (one for each connector) or ony one boos converter powering both connectors?
 

KlausST

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Hi,

I see two major problems with this:
1) the load (two DCDC) is always connected to the batteries. The charger can't know how much current goes to the load and how much current us used to charge the batteries.

2) Three batteries are in series. Making a total battery voltage of maybe 10...12V. A step up is not possible.

Klaus
 

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