Make this Fast Battery Charger - Full Design Principle Explained

While looking for a fast charger circuit that would charge a battery quickly, I came across a couple of designs which were not only useless but dangerous too. It seemed that the concerned authors had no idea what a fast charger actually needs to be like.

Please take a note that an LM338 will not help to increase the charging rate of a battery, while it is a great voltage regulator IC, enhancing the charging rate will require a special step wise changeover in current which cannot be done using an LM338.

The Circuit Concept


When we talk about how to charge a battery quickly we obviously are interested to implement the same with lead acid batteries, since these are the ones which are used extensively for almost all general applications.

The bottom line with lead acid batteries is that these cannot be forced to charge rapidly unless the charger design incorporates an "intelligent" automatic circuitry.

With a Li-ion battery obviously this becomes quite easy by applying the full dose of the specified high current to it and then cutting off as soon as it reaches the full charge level.

However, the above operations could mean fatal if done to a lead acid battery since LA batteries are not designed to accept charge at high current levels continuously.

Therefore in order to pressure current at a rapid pace these batteries need to be charged at a stepped level, wherein the discharged battery is initially applied with a high C1 rate,  gradually reduced to C/10 and finally a trickle charge level as the battery approaches a full charge across its terminals. The course could include a minimum of 3 to 4 steps for ensuring maximum "comfort" and safety to battery life.

How this 4 Step Battery Charger Works


For implementing a 4 step fast charger circuit, here we employ the versatile LM324 for sensing the different voltage levels.

The 4 steps include:

1) High Current Bulk Charging
2) Moderate Current Bulk Charging
3) Absorption Charging
4) Float Charging


The following diagram shows how the IC LM324 may be wired up as a 4 step battery voltage monitor and cut off circuit.

Circuit Diagram


Fast Battery Charger Circuit

The IC LM324 is quad opamp IC whose all the four opamps are used for the intended sequential switching of the output current levels.

The proceedings are very easy to understand. opamps A1 to A2 are optimized for switching at different voltage levels during the course of the stepped charging of the connected battery.

All the non-inverting inputs of the opamps are referenced to ground through the zener voltage.

The inverting inputs are tied with the positive supply of the circuit via the corresponding presets.

If we assume the battery to be a 12V battery having a discharge level of 11V, P1 may be set such that the relay just disconnects when the battery voltage reaches 12V, P2 may be adjusted to release the relay at 12.5V, P3 may be done for te same at 13.5V and finally P4 could be set for responding at the battery full charge level of 14.3V.

Rx, Ry, Rz have same values and are optimized to provide the battery with the required amount of current during the various charging voltage levels.

The value could be fixed such that each inductor allows a current passage rate that may be 1/10th of the battery AH.

It may be determined by using ohms law R = I/V

The values of Rx, alone or Rx, Ry together could be dimensioned a little differently for allowing relatively more current to the battery during the initial stages as per individual preferences, and is tweakable.

How the circuit responds when switched ON


After connecting the discharged battery across the shown terminals when power is switched ON:

All the opamps inverting inputs experience a correspondingly lower voltage levels than the reference level of the zener voltage.

This prompts all the outputs of the opamps to become high and activates the relays RL/1 to RL/4.

In the above situation the full supply voltage from the input is bypassed to the battery via the N/O contacts of RL1.

The discharged battery now starts charging at a relatively extreme high current rate and rapidly charges upto a level above the discharged level until the set voltage at P1 exceeds the zener reference.

The above forces A1 to switch OFF T1/RL1.

The battery is now inhibited from getting the full supply current but keeps charging with the parallel resistances created by Rx, Ry, Rz via the corresponding relay contacts.

This makes sure that the battery is charged at the next higher current level determined by the the three parallel inductor net value (resistances).

As the battery charges further, A2 shuts down at the next predetermined voltage level, switching OFF Rx and rendering Ry, Rz only with the intended charging current to the battery. This makes sure that the amp level is correspondingly reduced for the battery.

Following the procedures as the battery charges to the next calculated higher level, A3 switches OFF allowing only Rz to maintain the required optimal current level for the battery, until it gets fully charged.

When this happens, A4 finally switches OFF making sure that the battery is now gets completely switched off after attaining the required full charge at the specified fast rate.

The above method of 4 step battery charging ensures a rapid charging without harming the battery internal configuration and makes sure the charge reaches at least at 95%.

Rx, Ty, Rz may be replaced with equivalent wire wound resistors, however it would mean some heat dissipation from them compared the inductor counterparts.

Normally a lead acid battery would need to be charged for about 10 to 14 hours for allowing at least 90% of charge accumulation. With the above rapid battery charger circuit the same could be done within 5 hours of time, that's 50% quicker.

Parts List


R1---R5 = 10k
P1---P4 = 10k presets
T1---T4 = BC547
RL/1---RL/4 = SPDT 12V relays 10amp contact rating
D1---D4 = 1N4007
Z1 = 6V, 1/2 watt zener diode
A1---A4 = LM324 IC

 

PCB design


 



This the original size PCB layout, from the track side, the high watt ersistors are not included in the PCB design.

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Comments

what is the voltage of input power as it show DC sign is it a 24v transformer?
Swagatam said…
Input could be anything between 6V and 30V depending upon the battery used, the relay will also need to be rated at this voltage
inayat kheshgi said…
how set preset plZ give me detail
inayat kheshgi said…
how set preset pz give me some informotion
Swagatam said…
for a 12V battery set P1 to make RL1 activate at 12V, set P2 to activate RL2 at 12.5V, P3 to make RL3 activate at 13V, and P4 to activate 14V
inayat kheshgi said…
thanks alot of thanks for reply sir I have buy all these component but I want to make pcb layout to parmanent marker because I have no printer facility and I have less experince of eletronics there for I request for pcb layout of this schematic plz sir help for this
inayat kheshgi said…
sir u r good honest and like a super man.my english is not good but I think u are understand. u have share u r knowledge to people for free this is a big job very big job I regularly studied ur posts.and u prove ur self with quick reply also so great job.
inayat kheshgi said…
can I replace wire wound resistors to normal resistor and much resistor use
Swagatam said…
Inayat, I am sorry it'll be difficult for me to provide a PCB design due to lack of time, you'll have to take the help of a PCB designer for this.
Swagatam said…
thanks a lot Inayat.
Swagatam said…
yes you can do it, no issues.
Swagatam said…
...(Rx, Ry, Rz) those are not wire wound resistors, those are copper coils, you can replace them with wirewound high watt resistors.
inayat kheshgi said…
ok thanks I try to make pcb layout
inayat kheshgi said…
can the transistor emitter connect the nagative (-) terminal or just to leave ground?
Swagatam said…
connect with battery (-) line
inayat kheshgi said…
I done this project with jumper saloution .using of this circut 150ah 12v battery how much time fully charged?
and between ( ) and (-) terminal show 4k resistance do not show open. I worried about that can they have show resistance and not show open?
Swagatam said…

where did you use the jumpers?
inayat kheshgi said…
all the circut made with jumper brcause I have no etchant pcb facility and dont no about pcb layout so I make all the line connect with jumper plz sir reply with my last question
Swagatam said…
OK, understood.
inayat kheshgi said…
thanks a lot sir..
sir I want to connect leds,when the relays activate the led on..
help for this to complete my project .
inayat kheshgi said…
sir I have use 12v dc 7amp spdt relay because 10amp relay not available in market
can work fine?
inayat kheshgi said…
sir dont mind for my questions..

and plz reply
I have make the two circuts,both are make with the help of ur blog
one of simple mppt (solar)
and the other is fast battery charger
this one..
now I have 150w 24vdc solar panel and I want when voltage come from solar panel just connect mppt circut and his output now connect input of fast battery charger circut and after this now the output connect to 12v 150ah battery.
so plz reply me can this work perfect?
and want when relay activate ,indication led on how connect led?
Swagatam said…
you can connect the LEDs in parallel with the relay diodes, make sure all the LEDs have a 1K limiting resistor in series
Swagatam said…
if your battery is less than 60AH then 7amp relays will do.
Swagatam said…
simply connect the solar panel out with the input of the MPPT circuit, then connect the MPPT output with the input of the above fast charger, that's all
inayat kheshgi said…
can I use the circut, if input given 12v 30amp
to charge 100ah battery?
Swagatam said…
yes it can used, but for a 100AH battery just 15amp input would be quite sufficient
kashif ali said…
Sir i have 50 amp acid battery. i want charger circuit for this. please give me . thanks
Swagatam said…
kashif you can use any LM338 circuit for this
Swagatam said…
for 6V battery it should be 7V, for 12V > 14V and for 24V > 28V
polo said…
How long does it takes to get to 95% with 15 amps suply? will this work with a four pin battery? I did an experiment with a 25 amp suplier and I connected the positive and the negative an dit did not work why? Thank you sir in advance thanks.
Swagatam said…
if correctly optimized, it won't take more than 6 hours to get to the 95% mark.

please provide the complete specification of the battery for proper understanding
KAKOOZA JOSEPH said…
Hi sir, I have a 55W panel & a 45AH flooded type battery bt the PV max output is 21V, how can I regulate the voltage using IC 555 & a P-mosfet to get 15 V output so that I can use the above 4 step charger,thanks.
KAKOOZA JOSEPH said…
Hello sir, how can I replace IC TLC2272CP with LM324 & is it possible to get equal functioning results?
Swagatam said…
Hi Kakooza, you will need to incorporate a buck converter circuit for the step down, or you can also go for a linear regulator such as a LM338 which is much easier than a buck circuit but a little inefficient due to significant heat generation.
Swagatam said…
just verify and interchange the inverting (-) and the non-inverting (+) inputs with each other.... and do the same with their supply and the output pins also.
KAKOOZA JOSEPH said…
Meaning I should replace the inverting & non-inverting of TLC2272CP with those of LM324 and also the same to the outputs?
Swagatam said…
don't use LM324..Use TL072 it will directly fit with the TLC227CP pinouts.
Hazrat Yousaf said…
Hello sir,
want to convert 230 volt AC current into 12 volt DC current but i am new to electronics stuff i want to get some help from professionals to give me a circuit diagram with guide notes i like to make my power supply variable amp output power supply which can give me from 20 amp to 70 amp and i also want to keep my supply simple and cheap. please give me the details. Thanks
Swagatam said…
Hello Hazrat,

making a 12V 70amp SmPS cannot be simple...it could be in fact quite complex..you can refer to the following article for more info:

https://homemade-circuits.com/2014/07/adjustable-0-100v-50-amp-smps-circuit.html
Kaustubh Vaidya said…
Hello sir,
I am new to circuits, & I am trying to implement the fast battery charger circuit. Please guide me to how & when to set preset values??.. preset value to be set before battery connected to circuit or after that??...please help me.
I connected the circuit on breadboard as given , Now I am giving supply of 13.5vdc, 2.5amp(max) to circuit. 1st preset(P1) is set to 12.0vdc, 1st relay(only) is gets on when i/p given to circuit. BUT 2nd,3rd,4th PRESET CAN'T SET, ALSO 2nd,3rd,4th RELAY NOT ACTIVATED when i/p is given to circuit. So please please guide me. THANKS
Swagatam said…
Hello Kaustubh,

you may set the other presets too in the same manner by supplying incrementing voltage levels.

for example 2nd relay can be set to activate at 12.5V... 3rd at 13V, fourth at 13.5V and so on.

this must be done without any battery connected and with the help of a variable power supply.
Kaustubh Vaidya said…
THANK YOU FOR IMMEDIATE REPLY.........
Variable power supply means, as per given in BATTERY CURRENT INDICATOR CIRCUIT OF YOURS (How to set up the circuit)?
www.homemade-circuits.com/2015/04/battery-current-indicator-circuit.html

Thanks in advance
Swagatam said…
we want to set the presets with respect to the different voltage levels, so the power supply should be a variable voltage power supply...

use the variable voltage power supply to feed the relevant voltage levels to the circuit and adjust the presets accordingly so that relays click on those voltage levels.

current will need to be adjusted by using coils or resistors as explained, which will need to be calculated depending upon the battery AH rating.
Kaustubh Vaidya said…
Thank you once again..
Kaustubh Vaidya said…
While to set preset,
initially p1 to p4 pot slider arm should be ground side & then gradually increase to activate relay, is that so?
Also p1 to p4 preset common connected terminal to be removed from I/p & connected to variable voltage power supply pot? Should I do this
Swagatam said…
the points marked " input power" should be connected with the variable supply input and P1...P4 adjusted as per the explained procedure
Kaustubh Vaidya said…
Thank you very much sir.
KAKOOZA JOSEPH said…
Wat about da burrialHello sir, which voltage should Iuse to set the relays?
Is it the charger voltage or battery voltage?
Swagatam said…
you'll have to set up the levels by applying the specified voltage levels through a variable power supply without connecting a battery at the output.

the relevant presets can be set across these voltage levels supplied from the variable power supply...the voltage levels are not critical

... could be like:

at 12V A1 relay switches ON,

at 12.5V A2 relay switches ON

at 13.5V A3 relay switches ON

and at 14.4V A4 relay switches ON
KAKOOZA JOSEPH said…
Well done sir, what if I want to replace the relays with mosfet to make da system silent, how can I make it?
Swagatam said…
thanks kakooza, replace the BC547s with mosfets, remove the relays, connect the pole wire of the relays with the mosfet drains, connect the coil common end with the battery negative and connect the battery positive directly with positive line....
KAKOOZA JOSEPH said…
Thanks you so much Sir..
Kaustubh Vaidya said…
HI sir, I have doubt that is, diode to be connected at positive terminal of circuit? before or after circuit? As current can flow in reverse direction when Battery will be connected to this circuit.
Thank u very much
Swagatam said…
Hi Kaustubh, you can connect a diode in series with the battery positive terminal.
Kaustubh Vaidya said…
Thank you very much sir.....
Geoff Nutley said…
Hi Swagatam, I have been looking at building this circuit to charge a 12 V 7AH sealed lead battery. Would it be suitable for this battery? If it is, the values of Rx, Ry and Rz would they be 18 ohms based on the battery and Ohms Law. I can obtain them in 5 or 10 watts as wire wound resistors.
Regards
Geoff
Swagatam said…
Hi Geoff, The above circuit can be used for charging almost all types of batteries including Lipo batts.

The Rx, Ry, Rz values are not too critical, just needs to be calculated such that the procedure allows a sequentially decreasing charging rate as the battery reaches its full charge level.

So the combined value of the ersistors must be such that they allow 5amp current to your battery initially....

R = V/I = 12/5 = 2.4 ohms....multiplying this by three gives.....7.2 ohms

Therefore you could probably use 7 ohms for each resistors.
Geoff Nutley said…
Ooops, thanks for that clarification, still wondering how I obtained my answer. Kakooza asked earlier about swapping the relays for mosfets, I have some IRFZ44N's could I use these?
Regards
Geoff
Swagatam said…
OK..no issues..

I think relays are better suited to this application and much easier to configure, mosfets can make the design much complex and difficult to optimize or troubleshoot if anything goes wrong....
Swagatam said…
Update:

R5 was missing in the original diagram, now it has been added in the diagram...If anybody was having problems with this circuit then probably it was because of this mistake....I regret it a lot.
Ainsworth Lynch said…
I built this circuit just now and I used a variable powersupply I built to set all the relays. to do the charging I will now need a more powerful power supply I was planning to do a simple design using a 10amp transformer and a rectifier stage I wouldnt use a regulator and I think the output would be about 18 to 20v dc, since the opamp can manage that voltage and the relay is set to turn off at 14v max I was wondering if I could use it.
Swagatam said…
18V or 20V won't be a problem for the IC since the IC LM324 can handle upto 32V. however the relay might become quite hot at 18V, so may be you may want to add a 7812 regulator for the relay coils
Ainsworth Lynch said…
I was thinking about that but wouldnt that be low current at 12v and even if I powered the coils with the regulator would the battery be getting the 20v from the circuit just the same? I am just asking for knowledge, I actually made a more powerful adjustable power supply just now to use.
Ainsworth Lynch said…
I am facing a problem I now have 14.45 volts entering the circuit and I set all the values I added a led across the coils to know when the transistor is on. So when I send 12v I adjusted the p1 to activate the first coil then shifted to 12.5v but the light on a1 turned off, then after adjusting p2 so that led comes on when moving to 13.5v a2 led turned off and it when it that same order, all 4 stages were set, but applying 14.5v and then connecting to my battery of 10.5v nothing happened all replays staged off and no voltage was applied to the battery, I assume that reducing the voltage on the input a little a4 will enegergise.

So the only way that makes sence is if I am the one not understand how the circuit works fully, I was assuming that the input should be 14v because my battery is 12v battery (deep cycle) and setting all the parameters correctly then It would sence the battery voltage different from input voltage and if its lower than 12v then all relays would be on to fast charger then as it reaches each threshold set by me then a each relay would turn off accordingly, could I get some help?
Swagatam said…
The current limiting resistors will take care of the excess voltage and adjust it as per the battery requirements. Don't use filter capacitor with the power supply bridge to control the excess voltage at the output
Swagatam said…
your LED response is correct so the setting up procedure is also correct.

yes initially you can lower the voltage slightly and once the relays are activated, you can raise the voltage to 14.4V....but this should be done with the discharged battery connected.
Ainsworth Lynch said…
Ok I did that but only the a4 relay activated, if I went down with the volt gradually then all the relays would come on, but once I increased the voltage then they would turn off again. So I dont know if the sensing section of the circuit is working, 1 problem I think would cause it is that I couldnt get a 6v zener diode so I used a 6.8v zener, Would that be the issue?
Swagatam said…
please connect the 1N4007 diode from the battery positive to the relay positives as shown in the updated diagram and check the response....

remember battery should be connected first and then the supply input
Ainsworth Lynch said…
Ok I will add the diode later and let you know, I think that was an issue aswell since connecting the battery would activate a relay without applying power to the circuit.
Ainsworth Lynch said…
I connected the diode just as you have it in the schematic but I am having the same issue. I made a quick video to show an example.

https://www.dropbox.com/s/h1svuujackydd4g/20160314_191207.mp4?dl=0
Swagatam said…
as the battery gets charged and its terminal voltage rises the relays will sequentially get deactivated until all the relays are switched OFF, and then the battery can be removed
Ainsworth Lynch said…
The video I sent it's showing that when I set the power supply voltage to 14.4v then all relays are off, if I reduce the voltage a little then the a4 relay comes on, the only way all relays comes is if I reduce powersupply voltage to 12v. So the circuit isn't working as it should. Shouldn't the voltage be set a 14.4v max then when it's connected to the discharged battery then it's suppose to sense the batteries Voltage then turn on all 4 relays and as the voltage climbs then each relay turns off 1 by 1.

With the circuit I have if I set the voltage to 14. 4v then the circuit doesn't send any voltage if I reduce it then only 1 relay comes on and if that is the case then it will be 14v at a low current.
Swagatam said…
once you set the presets and confirm all the relays switched OFF, after this you can remove the input power supply and attach the battery.

with the battery connected the relevant relays can be expected to switch ON.

Now you can connect the power supply back at the input, on doing this you will find the power supply voltage settling down to the battery voltage level and then rising slowly in the course of time as the battery gets charged...this will in turn switch OFF the relays one by one until the battery is fully charged (last relay off)...it's as simple as that.
Ainsworth Lynch said…
Ok then I understand the operation, in which connecting the batteries all relays come on but applying supply power after only a4 relay comes on so I guess my problem is that I havent left it there to settle long enough? If thats the case it because the powersupply I am using cant manage the power draw so the regulators get extremely hot quickly.

I wanted to use a powersupply I was building without regulators but If I do that when the battery receives 25v wont that be too much for the batteries? I know the ic can handle it and I could use a regulator for the relays but what about the battery since the voltage supplied to the input would also be at the output.
Swagatam said…
If the battery voltage is say 10.5V, the input supply will INSTANTLY settle down to this voltage as soon as its connected at the input....which will enable all the relays to activates.
Please make sure this happens with your charger functioning.

You can keep the voltage regulators attached, it has nothing to do with the above mentioned condition

24V can be harmful for a 12v battery and relay
Ainsworth Lynch said…
Well that's the issue then with my circuit the battery is below 12v and when I apply the battery charger circuit to the battery none of the relays came on, the only way it comes on is when I lower the supply voltage to the charger slightly to about 14.2v then only 1 relay will come on
Swagatam said…
after connecting the battery check input point voltage where the supply needs to be applied....it must show the battery voltage....after confirming this connect the input supply which must immediately settle down to the existing battery voltage...if this is not happening and the input voltage is not settling to the battery voltage then may be your battery is faulty.
Ainsworth Lynch said…
Yes after connecting the batter the supply points show the battey voltage but after connecting the supply it doesnt settle back down to the battery voltage
Swagatam said…
your battery can be faulty in that case.
Ainsworth Lynch said…
I'm trying this circuit out again.

When setting the voltage cut off levels I'm suppose to use a variable power supply, where should I add the variable output? to battery or input power to set the limits?
Swagatam said…
connect it from the left side that is from the "input power" side
Ainsworth Lynch said…
That's how I done it but for some reason when I connect the battery the voltage is lowered a bit like it's suppose to but it doesn't go as low as the actual voltage of the battery.

After that it quickly Rises to 14.4v and the battery doesn't charge.
Swagatam said…
connect your power supply directly with the battery and check the voltage, if it still rises to 14,4V quickly then either your battery is faulty or your charger current is dangerously high.

and make sure you have connected the opamp input polarity correctly...the (-) goes to the preset
Ainsworth Lynch said…
By the way after filtering the ac voltage from the transformer what voltage should be sent to the input of the circuit?

14v most likely?
Ainsworth Lynch said…
The way i have the transformer wrapped now I'm getting 10v, after its rectified I'm getting 13v.

The battery was at 12.3v and after 2 hours its at 12.7v.

The transformer is a 5amp transformer and the battery is a 7ah battery, the circuit is pulling just a little over 1/2 amp from the low voltage side of the transformer.

Notes sure why the amp is so low could it be the power resistors that I'm using reducing the current or is it that the supply voltage is too low.
Swagatam said…
you mean to say the problem was in the transformer?

but anyway 5amp is too high for a 7AH battery, you must use a 1.5 amp instead, and charge the battery for 10/12 hours, that's the right way of charging any lead aid battery
Swagatam said…
for a 12V battery it should be 14.3V
Ainsworth Lynch said…
OK ill reduce the amp transformer. What's the crew that rating transformer to use though, it's seems to be somewhere around 10v for a 12v battery
Swagatam said…
sorry I did not understand your question.
Ainsworth Lynch said…
What voltage transformer should I use
Swagatam said…
you must use a 0-12V transformer, rectified with a full bridge diode network, and filtered with possibly a 6800uF/35V or higher value capacitor.

this will allow the required 14.3V after rectification for charging the 12V battery
Ainsworth Lynch said…
My 12v transformers are close to 13v actually after rectifying I get 16v or even 17v
Ainsworth Lynch said…
So Because of that Im forced to try and modify the windings to get 14.3v after rectification.
Swagatam said…
If the current is 1/10th of battery AH then 16V will also work, but auto cut-off at 14.3V must be functional....
Ainsworth Lynch said…
OK if it's 1/10th the battery Ah then I guess when the battery is connected the voltage will drop since it's of a lower amp.

The power resistors I'm using are 6.8ohms 5w If I wanted to increase the rate of charge or reduce it i would have to reduce or increase the size of those resistors?
Swagatam said…
the 1/10th rule is a general rule if the battery was directly connected with the supply source, it cannot be applicable for the above 4 step design, here the initial current can be high at arounf 50% of the battery AH value.
I got confused when you said your battery voltage was reaching 14V quickly, that cannot happen because the RL/1 is supposed to operate at 12V reducing the current, then RL/2 at 13V, and finally RL/3 at 14V where the float charge is initiated

the resistors must be calculated accordingly to reduce the current at 25% AH value for Rx, 10% AH value for Ry, and 1% AH value for Rz
Ainsworth Lynch said…
All my resistors are 6.8ohms 5w
Swagatam said…
use different values, as explained in the previous comment
Ali Aburamya said…
Hi, i got a transformer that supplies 25volts @20A.
i made a variable voltage regulator circuit that vary voltage from 0 to 25volts and can handle 15Amps with the help of 5pcs 2N3055 Transistors and LM317.
However, the circuit is done. now i want to integrate this battery charger to it.
i have a range of batteries to charge vary from 50Ah to 70Ah.
is it possible to use this circuit to charge any between the range without changing the values of the Resistors?

1 thing i dont understand is the Rx Ry and Rz. How many watts should those resistors be? I can only purchase those with 10 Watts rate. and if im about to use Inductors, what should be the values?
Swagatam said…
Hi, you can use a single design for al those batts.

just make sure that the last resistor Rz is calculated as per the 50AH battery.

here watts = R x Isquare, if you are using 10 watt then you may have to fix it on a large aluminum heatsink.
Swagatam said…
inductor must also have same resistance value as resistors
Ali Aburamya said…
So those 3 resistors are not the same values? Are those gonna get really hot? Even if my regulator circuit can outstand 15Amps? I can send you my final variable voltage regulatr circuit thru email if u would like to inspect.
Thank you
Swagatam said…
They have different values and need to be calculated roughly as explained in the earlier comments. yes the resistors will get a lot warm.....sorry due to lack of time inspecting your design will be difficult at the moment.
Ali Aburamya said…
Sorry im lost.
In the procedure you said "Rx, Ry, Rz have same values and are optimized to provide the battery with the required amount of current during the various charging voltage levels".

I really dont understand it. Does they have same value? Or different values? If you dont mind giving me an example. I computed R = 12V/7A = 1.714 then multiplied to 3 as per your comment that results in using the closest resistor available to 5.1 which is 5.8 ohms 10 watts
Swagatam said…
OK, sorry, I just forgot that all the 3 resistors remain connected in parallel initially and as they are switched OFF sequentially by the relays the line resistance increases proportionately

so yes they can be of similar values, but it is not necessary you can still use different values as per preference to allow the required amount of current during the charging process

The aim is to allow full current at onset, then may be 1/5 AH value when the second relay is activated, next it can be 1/10 AH for the second relay activation, 1/20 AH for the 3rd relay, and finally 1/40 AH for the last relay activation.
alitot said…
hi sir, i have done the circuit now with Rx, Rz, and Ry values is 5.8ohms.
now how do i have to start this? how can i adjust the relays to trigger at specific voltage? do i connect the input voltage only then set the P1,P2,P3,P4? or what? there is no procedure where to start with a battery or without.
Swag said…
Hi Alitot,

the procedure has been elaborately explained in the earlier comments, anyway, here's what you should do.

first slide down the wiper of all the presets towards the ground level

from the left side connect a variable power supply input and switch it ON, you will see all the relays clicking ON, adjust the variable supply to the full upper charging level, and then begin adjusting P4 such that RL4 just clicks OFF.

Now reduce the input supply the next lower level, and adjust P3, until RL3 just clicks OFF.

Similarly, adjust the P2, P1 for the subsequent lower charging levels to switch OFF RL2, RL1 respectively.

The setting up procedure is complete.

When you charge a battery make sure the input current is strictly 1/10th of the battery AH.
afrid said…
Example the full current flow to the circuit is 15 amp and the battery is 150ah .
When the battery voltage reach 12 volt 1st relay activated no here the Rx valve allow to flow 7.5 amp charge the battery 2nd relay activated
batt voltage 13 volt Ry allow 3.6 amp
3rd relay activated voltage 14.3 volt Rz allow 1.8 amp
Swag said…
15 amp which is 1/10th of 150AH should be for the 3rd relay.

for the 1st relay it should be around 40 amps, for the 2nd relay it could be around 30 amps, for the 3rd around 15 amp and with the 4rth relay OFF it could be around 1 amp (float)

so it should be Rx + Rz + Ry = 30 amps

Rz + Ry = 15 amps

Rz = 1amp
Swag said…
the suggested rates are not absolutely crucial...you just need to taper it down proportionately with each switching of the relay...
afrid said…
But if the input is maximum 15 ampere how manage 40 amp?
afrid said…
Can this circuit handle 30 amp current?
Swag said…
it can handle any amp, just modify the relay stage accordingly
Swag said…
if you are having 15amp for 150ah, then no need of this fast charger, you can connect it directly with the battery and wait for 15 hours to charge. the fast charger is designed to facilitate an initial high current charging, and thus enable a quicker charging

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