In the following article we discuss 3 useful DC to DC uninterruptible power supply circuits or DC UPS circuits for low DC to DC uninterruptible power applications
The first idea below presents a DC UPS circuit can be used for providing back up power to modems or routers during mains failures, so that the broadband/WiFi connection never gets interrupted. The idea was requested by Mr. Galive.
Technical Specifications
I need a circuit like,
I have two 12v dc adapter(600mA and 2A).
When input Mains is present, with the 600ma adapter i want to charge the battery(7.5AH) and with the 2A adapter i want to use my wifi router.
when the AC mains fails the battery will backup my wifi router without interruption.like UPS.
MY modem is rated as 12V 2.0A. That is why i want to use two 12v dc adapter.
The Design
Two adapters actually are not required for the proposed application. A single adapter, probably the one which is being used for charging the laptop battery may be used for charging the external battery also.
Looking at the given DC modem UPS circuit diagram we can see a simple yet interesting configuration involving a couple of diodes D1, D2, and resistor R1.
Normally a laptop charger is specified with 18V, so for charging a 12V battery this needs to be lowered to 14V. This is easily done using a transistor zener stage.
When mains is present, the voltage at D1 cathode is more positive than D2, which keeps D2 reverse biassed. This allows only D1 to conduct, supplying the voltage from the adapter to the modem.
D2 being switched OFF, the connected battery starts receiving the required charging voltage via R1 and begins getting charged in the process.
In an event AC mains fails, D1 gets switched OFF, and therefore allows D2 to conduct, enabling the battery voltage to instantly reach the modem without causing any interruptions to the network.
R1 must be selected depending upon the charging current rate of the attached battery.
A much better and improved version of the above is shown in the following diagram:
2) 6V to 220V Boost UPS Circuit
The second circuit explains a simple boost converter UPS circuit for supplying an uninterruptible power to satellite TV set top boxes so that the offline recording is never allowed to fail during power outages. The idea was requested by Mr. Aniruddha Mukherji.
Technical Specifications
I am an enthusiast electronic hobbyist person. Though I know only the basics, I am sure you must be getting 100's of emails daily and I am completely betting on my luck if this one gets to your "eyes"
My requirement:
16 volt 1 amp DC backup for my apartment Tata sky centralized distribution panel.
Issue: My apartment maintenance people do not run backup (generator) during day time, I have a Tata sky DVR which fails to record since there is signal loss due to power failure.
Resolution:
I had thought of a small back up system,I had purchased a small 6 volt 11 watt CFL Ballast circuit thinking as cheap alternate solution, but the same failed to work.
Why I am looking for AC supply instead of DC?I do not want to tamper with their system and get penalized for whatsoever failures which may come to it due to natural course of operation.
Could you please help me with a very simple cost effective circuit that will give me 220 volt 20 watts power from 6 volt 5ah battery. To be precise 220 volts from 6 volt battery, as I have purchased a 6 volt 5 ah battery recently. The output wattage requirement is less than 20 watts, the
adapter ratings are :
Output - 16 volt 1 amp
Input - 240 volt .06 amp
I know you have lot of work, but if you could spare some time and help me with this it would be of great help. thank you
Thanks,
Aniruddha
The Design
Since today all electronic systems employ an SMPS power supply, the input does not necessarily need to be an AC for powering these equipment, rather an equivalent DC or pulsed DC also become useful and works as good.
Referring to the diagram above, a couple of sections can be seen, the IC1 configuration enables a 6V DC to be boosted to a much higher 220V pulsed DC through a boost converter topology using the IC 555 in its astable form. The extreme left side battery section ensures an changeover from mains to battery back up every time a power failure is sensed by the circuit.
The idea is pretty simple and does not require much of an elaboration.
How the Circuit Functions
IC1 is configured as an astable oscillator, which drives T1 and consequently L1 at the same frequency.
T1 induces the entire battery current across L1, causing a proportionately boosted voltage to appear across it during the OFF periods of the T1 (induced back EMF from L1).
L1 must be appropriately calculated such that it generates the required magnitude of voltage across the shown terminals.
The indicated 200 turns is tentatively figured out and might need much tweaking for achieving the intended 220V from the input 6V battery source.
T2 is introduced for regulating the output voltage to the desired safe levels, which is 220V here.
Z1 should be therefore a 220V zener, which conducts only when this limit is exceeded, which forces T2 to conduct and ground pin5 of the IC, stalling the frequency at pin3 to a zero voltage.
The above process continuously readjusts itself rapidly ensuring a constant 220V at the output.
The adapter which can be seen at the extreme left is employed for two reasons, first to ensure that IC1 works continuously and produces the required 220V for the connected load regardless of the mains presence (just as we have in online UPS systems), and also to ensure a charging current for the battery when mains voltage is present.
The associated TIP122 transistor is positioned to generate a regulated 7V DC for the battery and also to restrict over charging of the battery .
Using Op Amp Cut OFF
If you want a precise circuit which will accurately monitor the DC UPS battery and implement the required over charge and low discharge cut OFFs, the following design may prove useful.
3) Redundant DC UPS Circuit
In this third concept below we learn a couple of straightforward redundant UPS circuits for providing a secured uninterruptible power to crucial gadgets such as computer ATX or modems etc. The idea was requested by Mr. Shayan Firoozi.
Circuit Objectives and Requirements
- There are many products which has 2 input for different power supply,for example one for normal mains,one for generator or other mains,like servers,routers,and some critical equipment,we call it redundant power supplies
- I have an equipment which consumes 3 ampere in 12 volt dc,if I use 2 transfer with 12 volt,3 amp output which one take responsibility and which one is waiting for first loss?? Both are same on voltage and amperage,I don,t want them to work together,
- I want second power supply to be standby
- Just a simple question: What would happens if I replace battery with another 12 volt power supply ?? Will it work as a redundant or standby power supply ??
- Thanks for your answer in advanced And if it's possible tell us about model of diode and other components for 12 volt 3 ampere
The Design
As per the request, the circuit discussed in the above link can be modified to work with another DC power supply by eliminating the battery and associated stages as shown in the following form of redundant UPS circuit:
Using Two Power Supply Inputs
As we can see, the circuit is intended to work with a couple of power supplies having identical specs, such that whenever the primary power supply fails, the relay instantly changes over to the secondary power supply source ensuring an uninterruptible power supply to the connected load.
The diode D1 makes sure that while the primary power source is active and the relay in the deactivated position, it connects in series with D3 creating a greater forward drop than the primary supply diode D4...thus allowing the primary voltage to be in command and powering the load.
However as soon as the primary source goes through an outage, D4 is disabled, and for that split second D1 and D4 takes over powering the load, until the relay has changed over bypassing D1 and enabling the full rated power to the load.
The next diagram shows a method which allows a battery to be included within the proposed redundant UPS circuit, and the primary power source replaced with a solar panel, making the system a 3 way protected UPS circuit
Using Power Supply with Battery
Referring to the diagram, as long as the solar energy is available, the relay stays activated keeping the mains derived 14v supply cut off from the system.
The solar power in the meantime charges the battery and also the connected load via D1.
The battery power being slightly subdued than the solar panel power keeps D2 deactivated such that only D1 is allowed to carry the solar energy to the attached load at the output.
Using TIP122 for CV Battery Charging
The TIP122 ensures a regulated and safe over charging protected supply for the battery which charges solely through the panel voltage during day time.
As night sets in, the relay deactivates at some of time when the solar supply gets too weak to hold the relay activated.
The above changeover instantly switches the mains operated 14V into the system enabling the load to switch to the mains derived voltage without an interruption.
The battery power makes sure that while the relay is transferring over from the solar to the mains adapter supply, it compensates the split second changeover lapse in power by supplying its own power to the load, and inhibiting even a microsecond break of supply for the load.
The battery also forms the third "line of defense" in case both the primary and the secondary power happens to fail together, and is always positioned in the standby mode for the recommended redundant uninterruptible power supply circuit operation.
The first redundant UPS circuit incorporating two power sources can be better modified in the manner shown below, here the relay N/C can be seen directly connected with the load, thus enabling zero drop in the supply line:
Modem UPS using TP4056 Li-IOn Charger
If you are interested to make a 5 V DC UPS for your router using high end chargers such as TP4056 and boost converter modules, the following design could help:
The above design could be also built without a relay as given below:
‘Using opamp cutoff’ I cannot understand uses of resistance and diodes(1N4148) properly. Is it possible for you to make me understand?
I have got your eMail but could not reply because the system failed to send it.
OP amps are configured as comparators. The zener resistor provide the clamping volatge to the zeners, the presets or trimpots are used adjust the cut off threshold of the comparators.
For understanding comparators you can read the following article:
https://www.homemade-circuits.com/how-to-use-ic-741-as-comparator/
For opamp battery chargers you can read the following post:
https://www.homemade-circuits.com/opamp-low-high-battery-charger/
sir can you design online ups connection using with my module as mention in above comment
I can design once the power supply option is correctly sorted out, as explained by me in the previous comment.
hi, I have make 12 v dc ups for my WIFI router using 3 li-ion battery in series with 3S 10A 12V 18650 Lithium Battery Charger Board Protection Module and output side i use XL6009 DC- DC Adjustable Step UP Boost Power Converter Module in this ups I am used 12 v 2.5 A input charger.
but I am facing issue when ups is in backup mode and discharge at 6-8 v approx. that time router can not start when input power will turn on what’s wrong with my ups please guide me.
thank you.
Hi, your 12.6V li-ion battery should never be discharged below 9V, otherwise it might slowly damage the battery and also require high current initial charging.
Maybe your 2.5 amps is getting drained while charging the deeply discharged battery which is causing a severe voltage drop and preventing the router from starting.
Also make sure the boost converter is correctly set to produce 12.6V across the battrey terminals, and make sure the input current to the battery is at least 50% of the battery’s Ah rating
…another point is that the 2.5 amp may not be sufficient enough to charge the battery and also simultaneously power the router. You might require a 4 amp or 5 amp input current.
ok sir thank you for suggestion I replace my charger with 5 Amp
one more question i nave one 12v 4 amp smps supply when i connect load on it it will give output in form of pulse i change dc output capacitor but still its blinking o/p what is problem. please give me suggestion
Rahul, if your SMPS is blinking then that will not do. It means either your SMPS not able to accept any load or it is faulty.
Also, the boost charger must be removed, instead an SMPS can be purchased which has a preset setting which can be adjusted to get a 12.6V output.
Alternatively another approach would be to use a 0-12V transformer rated at 5 amp maybe. Then add a bridge rectifier and filter capacitor at its output so that its output increases to 17V.
Finally this 17V could be dropped to 12.6V through a transistor circuit for charging the battery and also drive the router.
Hi, thanks a lot for sharing your ideas.
The goal of my thruster project is to build a boat engine for my 4m catamaran. The system is based on an programed arduino board which controls an ESC. Furthermore the main power source for the thruster and electronics consists of a minimalistic internal 5S4P Li-ion battery pack. As a future optimization I would like to attach an additional external 5S70P Li-ion battery pack for longer distance journeys occasionally. For I do not want to add a mechanical switch just to control the change of power sources I’m thinking of integrate a kind of UPS module. The Idea is to plug the external source in and at the same time the internal source will be detached and vice versa. Maybe you have an idea to use on of your UPS templates? Specs: Rated Voltage of power sources: 18V. Current typical: 15A, 32A peak. Thanks a lot Swagatam for any reply.
Hi Boris,
will a relay changeover work for you? It’s probably the simplest solution you can get, although it will consume some current for holding the contacts.
You can try the following simple configuration:
The above relay is rated at just 10 amp only….so you have to replace the relay with a 50 amp type.
Hi Swagatam,
Your suggestion seems easy going. Thanks a lot. I suppose connecting the internal battery in order that the relay is not actively holding the contact is possible? And when I attach the external fat battery pack the relay is switching? Is there a specific order ref. for this 50 amp relay?
Thank you Boris, you are right, you can connect the internal battery to “DC Source#2″ and the external battery to DC Source#1”, and that will do the job as desired.
Since the maximum current is not more than 15 amps, a 30 amp automotive relay should work satisfactorily, as shown below:
https://www.homemade-circuits.com/wp-content/uploads/2021/05/30-amp-automobile-relay-compressed.jpg
A solution I found for delay/ reboot of router issue: add a dummy load at the input, with diode, it will decharge the capacitor of phone charger and tick relay much faster! Go for more than 200/300W and sees if it gets hot of course. Circuit with Tp4056 realised and it works fine.
Sorin’s idea.
Thx
Dear Mr Swagatam,
In recent days been through your website and found it really informative and interesting.
Am trying to build an uninterrupted power supply for my 12V 2A router.
Am using a 12V battery (7AH) and router adapter as 2 power sources connected via 2 relays (12v). The output of relay is connected to router. The relay is powered via the adapter.
Now the problem is because the output voltage of battery is around 13v, am using a voltage booster / stabilizer to output 12v from battery to router.
But when there is power off, the relay takes few milliseconds to change over and thus rebooting the router.
When power comes there is no loss and relay switches smoothly from battery to adapter current.
Please suggest how to handle this power loss during switching.
Regards,
Sunil Kumar
Dear Sunil, you can use the first or the second circuit for your application which will ensure that the power is transferred without any interruption.
To add a regulated 12V for the router, you can add the following circuit, between the D1/D2 cathodes and the router.
Low-Dropout 5V, 12V Regulator Circuits using Transistors
I tried the last option with the TP4056+ StepUp + Relay. But it is not working as intended, because the relay is not switching anough fast. So when Power fail the router is rebooting because relay is not anough fast 🙁
And I tried also the option with the relay, directly TP4056+MT3906, but the green led of the TP4056 are never getting on. Why? because the TP4056 IC is behaving in a way, when a certain Amp flow through it, below 1/10 of the charge current the charge is completed and the led turn on. So it is never getting on because, always aroun 700mA is flowing through the IC. I hoocked a ampmeter and I descovered this. Because the router is always sucking, dicharge/recharge at the same time I guess…
That is why, I first went for the option with the relay, I even added capacitor 2200 even parallel, it is still rebooting. I want the battery to be charge lonely by the TP4056 and light on when it is completed, and kick fast when the power fail…
Is it possible to use BC547 as a switching relay instead of a magnetic relay maybe, for it to switch faster??
Thx
The diode version is perfect and has no problems. Your router is consuming all the current because your supply source is not rated with enough current to charge the battery and the router together. You can either use a higher rated input source or add a 5 ohm or 10 ohm 1 watt resistor in series with the router and check the response.
The low current at the input source is also the reason why the relay is not operating quickly enough.
the issue is not in the turning ON of the relay, it is more in its turning OFF.
When the Relay is on NO position (no power applied to the coils pin + Router Power by the Backup) and I simulated Power Back (Let say Main electricity came back) so Coils of Relay are again powered, and it switch from NO to NC: here there is no problem, it is working fine. The rooter do not reboot. So enough currrent is coming to the Relay to do the task required.
The issue is in the opposite, when the relay need to OPEN, when it need to go NO! In this small milli second of time, the Router is rebooting. So the relay take to long to open, and to switch to battery supply.
PS: My Router is only 450mA and I changed the Rprog of the TP4056 to charge the battery at a slower current rated. it is not helping. I am using 12v – 1A adatper, and still the same.
So maybe better to use Solid State Relay go get a faster switch between DC Battery Backup for the Router?? What do you think??
Thanx
try putting a 1N5408 diode before the 2200uF capacitor, and possibly put another 2200uF capacitor in parallel to increase the back up power. This should should take care of the slight millisecond delay.
For the diode version a 1 amp transformer might not help at all, because the battery will itself require a current equal to its mAh rating. Try a 2 amp or a 3 amp adapter and check the results.
Thx you for your help, I did not find any 1N5408 diode, but I got some 1N5401 and also 1N5399.
So maybe try with 1N5401. I dont lose much trying…
About capacitor, I paralleled 2 2200uF yesterday and still delay >>Router Reboot 🙁
For Power Supply, I am currently testing directly with Lab Power Supply as main Power Source, that can deliver till 10A if required, so current part is covered, no stay the delay part of the relay…
Yes a diode will make a lot of difference, since it will make sure the capacitor charge goes entirely to the router only. The 10 amp power supply should more than enough to keep the charging operation sustained while also operating the router.
hi.
Which one can I use instead of 1n5402 diode?
thank you
Hi, you can use 1N5408
Hi sir, I have a problem of power cuts, so I want a mini ups.I have a onu device which specification is 12v, 0.5A and a router which specification is 12v,0.5A. So I want a power backup system (2 hours power backup minimums) for those devices. In the market I found mini ups for the router but its very expensive. So I want to make the safest home made mini ups, which is not damage the equipment. Tell me how to make this. Thank you.
Hi Krishendu, you can build the first circuit which is the simplest and the safest. You will required a 12 V, 4 Ah battery for a 2 hour back up. Make sure to adjust the output from the TIP122 to exactly 14.1 V.
Thanks a lot. I will try this, if any problem I will contact with you.
Sure, no problem!
Please tell me about Intelligent electrical safety protection circuits with battery management systems in this project. Which type of battery and module or component I used? And please tell the input adapter specification.
Which circuit are your referring to exactly?
Hi,i have a project which must supply power to the router and the radio (for a home wifi),while charging the backup battery when the a.c mains available and if the mains fail the battery must take over and supply power to the wifi system.i just wanted to know how to design it.
Hi, the first circuit will be good for you requirement. You can try implementing the first one.
hello.
I want to provide uninterrupted power for my arduino project.have 12v-7ah lead battery for backup.I want to use 12v dc adapter.Would you recommend me a circuit diagram to make a backup power supply?Please also write the materials I will use.thank you
Hello, the first circuit is easiest and reasonably safe design which you can implement. But 12V adapter will not do, it must be a 15 V minimum, and the current rating must be 10% of the battery Ah value, meaning it should be 15 V/ 0.7 amps or 1 amp
Hi,
thank you for sharing this circuits. I want to use your first circuit to power a router and a modem ( both at 12V /1.3A each ). I have a 15.5V (laptop) adaptor and I want to use it for power a circuit that will enable to charge a 12V SMF type battery of 7Ah ( with charging around 14V/0.35A ) and to supply the necessary 12V for both devices. The maximum load estimated current is around 3A ( router + modem ), so 1N5402 it’s a good option for D1 and D2. For charging the battery the maximum current is ratted at 2A ( that value is written on the battery as initial current, even if I measured only 0.35A charging current ). So my 90W adaptor is sufficient. What I need is a steady 12V at output when AC is present or not. I don’t want to supply 13.5-15V to the 12V input modem , because I’m not sure that this will be ok for the modem.
Please tell me how can I step down from 15.5V to around 12V at output ? If a put a series of 3 or 4 1N5402 diodes instead of D1, this will drop the voltage to around 15.5-4×0.7 = 12.7V ( if the drop forward voltage is 0.7V on each diode ) but this value on last diode cathode in the series ( and D2 cathode ) will make the make the D2 to conduct. So this in not a good solution.
What simple voltage regulator to use at output to make sure that I will have around 12V when AC is present or not, even in the situation that his input is less then 15V ? ( when AC is missing and the load is present, the battery voltage will decrease in time from 13.7V to 12V, so this range must be the input voltage for the voltage regulator ).
Is there any other simple solution to power my 12V modem and router , without an voltage regulator at output ?
Thank you.
Hi, You can use a 7812 IC for dropping the higher voltage input to 12V or slightly lower. Use it after the D1/D2 junction. Even at voltages below 12V, the 7812 will continue to conduct and allow the voltage to reach the load.
Hi, thank you for your support.
I see that 7812 IC have 1A , is that corect ? If so, that is not enough because the load is about 3A* ( 2.6 A, router 1.3A + modem 1.3A ). Is there any other version of regulator with a minimum of 3A ?
In the case of a missing AC, the battery voltage will drop significantly after an hour ( I will use a 7AH battery ) at about 12.5V or so. In this case, what will be the voltage after the regulator ? If it will be around 10-11v, this will be not so good. I am hoping to design a circuit that will be usefull for a few hours, not for 20 minutes.
* Or there is another possibility: because only one device ( modem ) requires 12V, I need only a 1.5A regulator. ( The voltage input for the router is 10-57 DV )
A few questions about the first diagram/circuit: my adaptor has 15.5V, so what is the R1 voltage/ R1 value for a battery of 7AH , and what will be the charging voltage on battery ? ( I know that the battery current will be between 0.35-0.7A ) The other components from the transistor + Zener stage remains the same in my case ? ( 14V Zener, two resistors of 220 ohm and 1kOhm )
Thank you.
Hi, If 7812 does not suit your application, you can use an additional TIP122/resistor//zener emitter follower stage at the output side of the D1/D2 junction. The zener could be a customized 13 V zener which will allow the output to be around 12 V. This will also drop around 1 V which is the minimum that you can get, since all linear regulator will drop some voltage. The tip122 will require a large heatsink for delivering 3 amp.
You can adjust R1 using Ohms law so that 0.7 amp is able to reach the battery. R1 = 12 / 0.7 = 17 ohms / 10 watts
The TIP122 base zener diode for the charger section should be actually a 15V zener, so that the output can be 14v, this will need to be fixed with some experimentation.
Hi Swagatam. Ok, I’ll try that. So I will must have 15V at the base of TIP122 and the transistor will be off when the emitter voltage reach about 14.4V, right ? I have find your Customizing Zener Diode Value exemple here, and I will follow it. https://www.homemade-circuits.com/zener-diode-circuits-characteristics-calculations/
But I can’t understand the last part of “You can adjust R1 using Ohms law so that 0.7 amp is able to reach the battery. R1 = 12 / 0.7 = 17 ohms / 10 watts” . The voltage across R1 is not 12V, right ?
With Kirchhoff’s law: with Zener of 15V and with VBE of 0.6V, if we have 14V on battery ( charging voltage ) and around but max 14.4V at emitter (Zener 15V – 0.6 VBE = 14.4V ), we are left with only 0.4V over R1 ( in this case R1=0.4V/0.7A =0.57 ohm ). Please correct me if I’m wrong, which is probably the case.
( Or maybe I will charge the battery at a slightly less voltage, and this will set the R1 voltage at about 1V; Or maybe is better to custom a transistor Base Voltage to a slightly higher value, at 15.5V )
For the 12V output additional stage, an adjustable LM317 module like this is ok ?
I prefer an already made module instead of experimentation and tweaking of a custom made TIP122/resistor//zener stage and I’m not very experienced. And it’s cheap, it’s about 1.5 Euro in my country.
Btw, don’t you know an adjustable module that will serve the purpose of an auto cut-off for battery charging ? 😀
Thank you very much for your support.
Thanks Cristi, your calculations are right. In a hurry I forgot to deduct the load voltage specification from the supply voltage. However it should be 12V that must be considered in the calculation for the battery voltage, so R1 will be 14 – 12 / 0.7 = 2.85 ohms, 1.4 watts…. a 2 ohm will also do.
Since TIP122 is a Darlington, the emitter voltage will be 1.2 V less, that is 15 – 1.2 = 13.8 V to be precise.
A buck converter is the best option but if a readymade thing is what you want to include then why not buy the whole system readymade ? You may easily find a DC to DC UPS with all the required facilities very cheaply 😀
The tip122 based regulator is perhaps one of the easiest designs, which requires very basic adjustments using a multimeter, and it is quite foolproof.
And it will also do the auto-cut off job at the threshold level.
The 317 buck can be also built at home using the following concept:
LM317 Variable Switch Mode Power Supply (SMPS)
Hi Swagatam,
I tried to find a cheap (10-20 Euro) DC to DC UPS readymade system, but unfortunately I didn’t find any with my desired requirements ( 3A at 12V). If you do know one, please tell me.
From your information, I will have 15-1.2 = 13.8 V on the emitter, but that is the voltage that is needed for battery charging, so I running out of voltage for R1.
Because my laptop AC adapter is one in steps, maybe is better to use 17DC output for my design. With a 16V Zener – 1.2V VBE – 1 Volt across R1 = 13.8V on battery and that is ok ( 13.7 more or less, depending on the battery loading current which is varying ). In this case R1 = 1V/0.7A = 1.4Ohm but I think 2 ohm will do the job. ( or maybe 3 ohm, I just measured a similar battery and at discharged level of 12.5V across battery, it uses 0.35A for charging ).
About the rest of the components: I think R of 1kohm is ok, but the R of 220ohm maybe must be replace with a smaller one, maybe 30- 50 ohms. Tell me please if all this values are correct or not and if this 17V DC design are feasible.
Thank you for the link about LM317 Variable Switch Mode Power Supply (SMPS) and for the information about the TIP122.
Thank you Cristi, I too tried but couldn’t find any cheap readymade DC to DC UPS online, that’s indeed very strange.
I think the R1 voltage must not be considered in the calculation, because as the battery charges this drop will reduce until eventually it reaches a zero.
TIP122 being a Darlington has a very high gain, around 1000, so reducing the base resistor value might not matter too must. For analysis this could be calculated using the following formula:
R = (15V – Battery discharge V + 1.2) x 1000 / 0.7 amp
Although this formula is actually for a collector load, I think it can be also used for an emitter load since the current is through collector emitter.
Hi.
I dont know English.excuse me.
I read the article from the translation.I am not very successful in electronics.my question is;
I want to run the system with an adapter.
when the power is cut off, I want the battery to be activated automatically.
battery is 12v power.please would you recommend a circuit?
thank you.
Hi, you can try the 6th design from this article;
https://www.homemade-circuits.com/how-to-make-efficient-led-emergency/
Sir I need your help I made 12v ups for router I used 5v 2A charger for input and connected to tp4056 and used 3*18650 batteries 3.7v 5000mAh in parallel combination then connected to dc booster xl6009 (and set the required voltages 12v)
But I connected the ups to my router it can’t run properly the power light of router starts blinking.
without connecting the ups and connected to the adapter its working fine without the power light blinking
My specifications of router are
Huawei 12V 1A
Waiting for reply
THANKS
Hello Salman, it’s because your booster is not working correctly, and it is unable to supply the required amount of current to the router.
Instead of using such complicated circuits, you can use a LM317 based charger, adjust the output to 12.2 V, and current to 1 amp. And attach the 3 li-ion in series with its output and simultaneously connect the router also, all will work perfectly, without any issues.
Dear Swagatam,
Thanks for publishing the circuits. First, by reading your article I see the power supply is assumed to be a laptop power supply which provides 18-19 V. Looking at the first and second circuits, the drawing indicates 12V sourced from what looks like “wire tap” from a laptop ps. This confused me a while as I was looking into using this circuit with a modem/router power supply that is rated at 12V 2A. This would not work, I believe since the 12V would not charge the battery, at least 14V should be required. Is that the case? Can you confirm my interpretation that the source should be 18-19 volt (or anything above 16V I guess). If that is indeed the case it may make sense to modify the drawing and state 18 – 19 volt source to avoid confusion.
Second, I wanted to go with the second circuit using LM317 until after discussing with a supplier who pointed out the second design will overcharge the battery, unlike the first design. How can I turn off the charging so it won’t be damaging the 12 V 7AH lead acid battery? Maybe add a simple circuit (found a couple online) that will switch off charging to the battery when it reaches 14.4 volt or so?
Thanks in advance for your help!
Dear Lord, yes you are right 12 V will not charge a 12 V battery. I have only tried to present a rough concept regarding the dC UPS and might have missed a few basic points in the design,and i am assuming the readers would take care of these by themselves or may consult me, as you have done.
Actually you will need 15 to 16V in the first circuit since an emitter follower transistor is used. To implement this you can make a transformer based adapter for the 12 V adapter. For this you will need a 0-12V transformer, a bridge rectifier, and a 1000uf/25v capacitor.
the second circuit will not overcharge the battery if the input supply is regulated at precise 14.1V. If I include an auto cut off that may unnecessarily complicate the simple design, which may not be required. To make a customized volatge regulator that will control the supply to exactly 14.1V you can apply a LM317 based design or a transistorized based regulator design.
Hello Sir…
I need to a circuit, DC UPS With 150A Battery charger I using Solar Power and power supply smps with 12V 150A Battery
Hello Ruwan,
you can try the following design
Replace the diodes with 20 amp diodes on heatsink
Hi sir, i am planning to run a 12v 20w bldc fan even during power cuts. So, i have used 12v 2a smps power supply to power the load directly. Using 12v 1a battery charger with auto cut off feature to charge the 12v 7ah battery. Using relay to switch between regulator power supply to battery power supply while power cuts. Also using over discharge protector bought on aliexpress at the output of battery to prevent over discharging. Everything seems OK. But, my doubt is 12v 1a charger stops charging when it reaches certain voltage ex: 14v and starts charging instantly when voltage falls below 14v during normal discharge of battery. This continuous charging will affect the battery or not.
Hi Mohammad, the ON/OFF charging and cut off at the full charge threshold will not harm the battery in anyway.
Thank you for this nice tutorial. I was looking for a laptop-style charging circuit. This helped me understand it quite well.
I wanted to create a Raspberry Pi Cluster containing max 8 Raspberry Pi’s. Each Raspberry Pi has 4 USB2 ports which can be used to connect to 4 external HDD’s leading to a max of 32 HDD’s. 32 external drives might be too much so I would limit this to 16. These HDD’s would need to be powered externally as the board itself does not provide sufficient power to each HDD. I believe the power required for each drive is 5V, 900mA. I also want to have a power module that consists of a battery that will be charged when external power is available. The power to the drives and Raspberry Pi’s should be provided from this battery when external power is not available. The switchover from A/C power to battery power should be seamless and should not cause the devices to power off.
I was thinking that using a laptop-style circuit for charging a battery while also providing power to the cluster would be required in this case. I also assumed that I would need splitter USB cables to pass data from the Pi board to the HDD and power from the power circuit.
What would you suggest as the circuit to power this cluster and what is the battery capacity would I need to support the power required for this cluster? Can you guide me on the circuit and the parts needed to build this power supply?
A/C -> Power supply ( rechargeable battery + circuit + board with USB ports for power to HDD’s and Pi’s)
Thanks, Glad you found the right article for your application. The first circuit can be ideally applied for powering the mentioned units.
For 16 units, you would require a supply of 5 V, 15 amp. This could be acquired from a ready made SMPS adapter. The battery could be rather large if it is a lead acid battery at 5 V, (15 x 10 = 150 Ah). This would provide a back up of around 9 hours for all the connected HDDs.
For this you can replace the adapter with a 5 V 15 amp SMPS input in the first diagram. Replace the transistor with a Darlington pair made using TIP35/2N2222
For the diodes you can use any 15 amp diode (on heatsink)
The zener diode must be experimented to at an output of around 6.5 V to 6.9V
R1 can be eliminated since 15 amp from the adapter is the right charging voltage for a 150 Ah battery.
I hope this will help you to achieve the intended purpose!