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## Battery Desulfator with Charger Circuit Using a Bridge Rectifier

To make this simplest yet effective battery desulfator with charger circuit you would just require a suitably rated transformer, and a bridge rectifier. The design not only desulfates a battery, it keeps the new batteries from developing this issue and simultaneously charges them to the desired levels.

In one of the earlier posts I discussed a rather simple PWM based desulfator circuit using a single IC 555.

However a deeper research shows that the process of desulfating a battery may not necessarily require a precision PWM circuit, the supply just needs to be oscillating at some given rate, and that's enough to initiate the desulfating process (in most cases)... provided the battery is still within the curing range and is not beyond the reviving state.

So what would you need to make this super simple battery desulfator circuit which will also charge the given battery, and additionally possess the ability to keep the new batteries from developing the sulfation issue?

A suitably rated transformer, a bridge rectifier and an ammeter are all that's needed for the purpose.

The transformer voltage must be rated approximately 25% more than the battery voltage rating, that is for a 12V battery a 15 to 16V supply may be used across the battery terminals.

The current can be approximately equal to the AH rating of the battery for those which need to be revived and are badly sulfated, for the good batteries the charging current could be around 1/10th or 2/10th of  their AH rating. The bridge rectifier must be rated according to the specified or calculated charging levels

The diagram above shows the bare minimum requirement for the proposed battery desulfator with charger circuit.

We can see the most standard or rather crude AC to DC power supply set up, where the transformer steps down the mains voltage to 15V AC for the specified 12V battery.

Before it can reach the battery terminals, the 15V AC goes through the rectification process through the attached bridge rectifier module and gets converted into a full-wave 15V DC.

With a 220V mains input, the frequency before the bridge would be 50Hz (standard grid spec), and after rectification this is supposed to become double that is at 100Hz. For a 110V AC input this would be around 120Hz.

This happens because the bridge network inverts the lower half cycles of the stepped down AC and combines it with the upper half cycles, to finally produce a 100Hz or 120 Hz pulsating DC.

It is this pulsating DC which becomes responsible for shaking-up or knocking down the sulfate deposits on the internal plates of the particular battery.

For a good battery this 100Hz pulsed charging supply ensures that the sulfation ceases to occur on the first place and thus helps to keep the plates relatively free from this issue.

You can also see an ammeter connected in series with the supply input, it provides a direct indication of he current consumption by the battery and provides a "LIVE update" of the charging procedure, and whether or not anything positive might be happening.

For good batteries this will provide the start to finish info regarding the charging process, that is initially the needle of the meter will indicate the specified charging rate by the battery and may be gradually expected to drop down to the zero mark, and that's when the charging supply needs to be disconnected.

A more sophisticated approach can be employed for enabling an automatic cut-off once the battery is fully charge by employing an opamp based automatic battery full charge cut off circuit (the second diagram)

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1. awesome reasoning!!! keep up the good work sir.
what will be d pulse frequency if half bridge network is used instead?

1. thanks adesina, half bridge would provide 50Hz frequency.

2. Any suggestions for 100AH battery, Which diodes to use?

1. for a good battery you can use 15amp diodes for the bridge and a 10amp transformer

3. your are genius and i have seen many your circuit...but i am bit confused with desalphator circuit ... i have found many cct(circuits) over net which ferret tororid coil with combination of 1mH(1000uH) and something 200 to 300uH setup...but your cct is without toroid is that really work ...toroid coil is difficult to make and find in market...and other i want to desalphat my alots of batteries between 100AH to 200AH ..can i have change ever time dioids and transformer for ever battery ..kindly tell me is above cct is fulfill my requirements...can i go for it for 100ah to 200ah batteries ....i have sla 12v 7ah battery and 2 motorbike ratting 12v 4ah battery ..can i use with above circuit ..positive waiting responce bye take care

1. to desulfate a dead battery we only need to pass a pulsating high current through it....the frequency and the duty cycle has no significance whatsoever as far as the results are concerned, however it solely depends on the batter condition whether or not it "cooperates" with the process or stays completely inactive...if the battery condition is too bad or it's unresponsive then even the most sophisticated charger would fail to revive it.

2. ...yes definitely you can use the above concept for your dead batteries...but as I said the results will depend on the battery response and cannot be predicted beforehand.

4. hello,i tried it with 2 batteries in parallel(12v,100ah).My battery are getting very hot after hours drawing about 40amps and my output voltage is 14v from the transformer.
what is the problem,Do you think its becos they are in parallel instead of one Battery or is it because the charging voltage is below 15v?

1. hello, actually you should have monitored the response of the batts instead of keeping it connected for hours, because sulfated batts can be unpredictable and therefore the right amount of current needs to be set after checking its response.

If it's drawing 40 amps then probably it's short circuited internally due to over current and dead, it's not because of parallel connection.

14V also is correct for charging a 12V batt

Nest time, connect a 24V automobile head light lamp in series with the battery positive tis will safeguard the battery from accidental over-current in case it is left monitored

2. Thank you Swag,can i be able to add a current regulator switch/circuit to regulate the amount of current to the battery? for example 5A,10A,20A etc

3. for high current above 5 amp only resistors can be used, you can try them by appropriately calculating the values through Ohms law....

an automotive bulb can act like a self adjusting current limiter

4. Hello. Have you achieved success with your circuit ? I mean on those batteries that could be saved due to sulphation reversal ?

5. It will depend on the severity of the battery condition, some may respond some may not...so the results may not be predictable...

5. Ok,i put an automotive 24v bulb between the ammeter and the + terminal of battery.the ammeter after several hours doesnt get up to 2A but when the bulb is removed,i get as high as 20-30amps.What do you think? should i just use a variable resistor?

1. you can use 4 or 5 lamps in parallel, that will help you to achieve higher current....but the current should not be too high...not higher than 50% of the batts AH rating

for a variable resistor you might need a 0.5 ohm 50 watt variable resistor...how will you get this?

2. Thanks,i dont think i can get that var resistor,i will add more lamps and give you feedback. My last question for you is: on using this on a 200Ah batt,it charges at 15v,25amps,after some hours the voltage increases to 16v but current remains at 25A and then d battery gets Hot. i didnt experience current drop to zero as stated,is it a dead battery?

3. the voltage can never rise to 16V from the initial value, because your supply source should be having a fixed 15V....the source voltage should not change unless it has problems or is malfunctioning. or may be your meter is giving incorrect readings....

the bulbs should be able to provide the correct indications through their brightness levels. zero brightness would mean no current consumption, higher brightness would mean higher consumption....

6. Hi Swa,
I got several question, please kindly help me:
1. The 15V for charging a 12V battery, is it the transformer 15V, if so the output will be 15V X 1.41 = 21.15V ?
2. If i want to charge a 6V battery, what should be the correct voltage of the charger for desulfator?
3. I have 0-12-15-18-24V 10Amp transformer. However, i want to charge a 6V baterry for desulfator. Can i use the lead of 12V and 18V to get the output of 6V from the transformer?
4. Just in case, i want to use the aboved mentioned transformer for -12V, ground and +12V, can i use the lead of 12V become the ground. I mean, can i use the lead 0V, 12V and 24V. By doing this, i may treat 0V lead as -12V, and 12V lead as CT, and 24V lead as +12 V ?
Thanks a lot.
Kanta

1. Hi Kanta,

1) the output peak will be 15V, and the average will be even less...since no filter capacitor is used.

2) here since we are discussing a desulfator concept, nothing can be seriously critical, because we have no idea of the actual status of the battery condition, so we have go with a typical value and then try to optimize the results with trial and error.

for a 6V battery you can try a 8V as the typical value, although a little vales can also be tried.

No you cannot use the 0V as -12V, that won't work....

2. sorry correction:

....."for a 6V battery you can try a 8V as the typical value, although slightly higher values can also be tried...."

3. Electronics EngineerApril 24, 2017 at 5:08 PM

"1. The 15V for charging a 12V battery, is it the transformer 15V, if so the output will be 15V X 1.41 = 21.15V ?"
Yes, there will be pulsating DC of 20.15V. About 1V drops on rectifier. So battery from 15VAC transformer will be charged by voltage pulses of around 20V.

4. The transformer can be a 12V transformer....but anyway it is not so critical since we are trying to revive a dead battery....

7. Hi Swa,

Thanks for your prompt response. However, i am still not getting the explanation for question #3. Can i connect the lead of 12V and 18V to the bright rectifier to get 6V output from the transformer, because the transformer doesn't have lead of 6V.
Thanks
Kanta

1. Hi Kanta, measure the voltage across those wires with your meter set at AC range, this is will help you confirm the voltage.

8. Hi Swa,
My friend suggested me to connect one rectify diode anode lead to 0 of the tranformer, hence the cathode lead will become the positive and the 12V lead of the transformer become the ground. By doing this we can get 6V ouput from 12V lead of the transformer. Is it correct?
Thanks
Kanta

1. Kanta, No that's not the right way...

the right way is to check through a multimeter or if the taps are already labelled with their voltage rating then you can directly connect diode or bridge across those wires for the DC conversion

2. by the way there's no 6V or 12V or 0V leads, they are all relative to each other, that's why they must be confirmed with a meter

9. Hi Swa,

I am planning to put a blocking diode to protect the transformer in case the main power fails. Will the blocking diode decrease the effectiveness of the desulfator process ?
Thanks
Kanta

1. Hi Kanta, no need, because the bridge itself will block the reverse flow from the batt.

10. I connected a 15V transformer rating to a 35Amp bridge rectifier but the transformers always gets very hot after about 20min of charging.

1. your battery could be consuming more current than required, you can restrict it by connecting a car headlight bulb in series with the positive line and then check the response.

11. Hi swag, I've also seen same concept of your desulfator ckt. but the other one got an AC Capacitor prior to the bridge (in between transformer and bridge) do you have any idea what is the significance of the AC capacitor? by the way he uses 110v supply. thanks

1. Hi Ji, your design is basically a capacitive power supply which may not be suitable for the purpose because first of all it will contain dangerous mains voltage which can be fatal to human if touched, and secondly the current output will be significantly reduced for effective desulfation...therefore the use of a high current transformer is the only correct way of implementing the process as shown in the above article...

12. is the transformer (output side) rated 0v and 15v? how bout using the 12-0-12 output transformer?

1. yes it is 15V...12-012 an be also tried with a bulb in series....as shown in this example

13. hi Swagatam,

would you make a desulfator circuit based on that idea?

many thanks :)

1. Hi candra, a desiufator is not something that you can calculate and build, it might depend on many factors such as battery age, level of sulfation, AH rating etc and the optimization will need to be done manually by trial and error...so the data provided in the link is not necessary or critical

2. the only important things to consider is the charging current and a frequency or pulse based design....and both these factors have been appropriately considered in my simple bridge rectifier design

14. hello once again Swag,

i made this charger and have being using it's quite good and simple.

whiles charger is still connected
checking with my multimeter when the battery is fully charged at 14v input volt remain 0.10 whiles ampmeter drops to 0.

i want to ask is it's automatic or tickle charge
and does this means wont cause any damage to battery even when left with out monitoring.

thanks

1. Thanks Ferdimar,
you said input volts remains at 0.1V...sorry I didn't get it....input voltage to the battery must also show 14V.

yes technically, if the input is fixed at 14V to a 12V battery, it will not be harmed even if the charger remains connected to it permanently.

15. yes this also what i did not understand but it like that.

initially when tha battery was low when i conneceted the input it was 14v while on the battery terminal it self was 10.2v but when it got charged to 14v on the battery terminal the input from the charger dropped as to 0.1v

1. actually that can not happen, if the supply wires are attached with the battery and battery is reading 14V then the supply wires should also read 14V, right?

16. Hello Swagatam,weldone on your great work here....Is there a way to get a fixed 15v from the rectifier because my Ac input from power is unstable making my voltage sometimes very low and sometimes high...for example,if input is 220Ac,transformer gives 15v,but @ 170Ac i get less than 12v,Input 250Ac,i get 18v.I hope u undertand what i mean

Secondly,it seems my battery sends voltage back to the rectifier when theres no input.If there no input for some hours,my rectifier get hot and i wonder what makes it hot if not the battery directly connected to it or perhaps a bad rectifier.

1. Thank you TI,

for accomplishing this you will have to use a 24V supply as your input source and then use an LM338 based regulator circuit for stabilizing the output to any desired level....or you can also use a fixed regulator such as 7812 for the same, although a 7812 will restrict the current to 1 amp.

for preventing reverse battery supply you can put a diode in series with the battery (+) line.

17. frequency of desulfator matters to break the crystal formation,i tend to disagree it is the same thing with your simple circuit.analyze the comparison of ordinary arc welder and inverter type welder,which is better?

1. the above explained circuit introduces a 100Hz frequency into the battery...may be you did read the article properly.

2. Dear Swagatam, I have tested these "pulses" behavior. The fronts of these pulses are relatively slow rising. The sulfate is dielectric - on lead plate that means it forms some kind of parasitic capacitor between plates. Depending on the size (thickness) of the sulfate - also depends this parasitic capacity. So if pulse fronts are too slow, they do not pass current through this capacitor (if capacity is too small) and has no effect at all. But fast, high frequency pulses has much better chances to pass current through sulfate and "desulfate" it.

3. thanks Guitar.mod for your opinion, however according to me it's not the frequency rather the current level which ultimately becomes responsible for breaking the sulfated layer.

the current only needs to be in the pulsed form, that's crucial, and if the pulses are short it might work better but the current needs to be relatively higher...and to cause a high current, the voltage could be raised to a calculated level for achieving optimal results.

the frequency factor looks irrelevant here according me.

4. Hi GM, I saw your reply to this comment but could not publish it since it had an external link in it,
your justification makes sense, if capacitance is involved then higher frequency could work better compared to a lower frequency, in fact I have already published a relevant design which you can see below

Here's are a couple of articles which supports your idea:

18. Hi SM, thank You for reply - even thou my very long text is not published of the external link :) I will not use external links anymore.
Yes I saw Your desulfator design with 555 timer. But I followed link to the "updated schematic".
I also have simple idea - why not to use an old AT/ATX PSU based on TL494 as a desulfator with a little modification?
2. Separate outputs for filtered voltage (that needs TL494 for control/feedback pin) and unfiltered output - just after rectifiers - and use this output as desulfator. Separation could be done in several ways, As example - there are usually two rectifier diodes after transformer's secondary winding which has a center tap, so we can separate these diodes, one we use to form rectified/filtered VDC - for control, another - as desulfator (absolutely unfiltered). I'll try to make and test it if I'll have time.
p.s. I have just measured badly sulfated cell's capacitance - 11nF, so reactance at 100Hz would be too large to flow current, that is needed to break lead sulfate.

1. Thanks for the interesting inputs GM, appreciate it very much.

yes an ATX PSU can be tried, and for that matter other similar SMPS could also be modified in similar manner for achieving desulfation as per your suggestion.

hmm 11nF looks quite terrible :) and might need a substantial bit of pushing...higher frequencies might do the trick...agreed

2. Hi Swagatam! I Have update for You - using unfiltered DC from ATX power spupply - is not good for desulfating. I Have tested it before summer. Desulfator with 555 timer is a better choice. For alive batteries this simple desulfator (only transformer and bridge rectifier) maybe is the best choice for simplicity.

3. Hi Guitar.mod, thanks for updating this info. keep up the good work!

19. Hello! Sir, I am new here, have little knowledge on electronics. However i am interested with your design circuit "Batery desulfator with charger" because of a simple circuitry and components. But, it made me comfuse on the last parts about Guitar.Mod idea: "I also have simple idea - why not to use an old AT/ATX PSU based on TL494 as a desulfator with a little modification?