The change in PWM duty cycle percent is a good fix. You should replace the pot with a fixed resistor for reliability's sake.

It didn't occur to me before to recommend a power switch, which it needs. The easiest way would be to simply break the circuit at R3.

Don't expect quick results. Depending on the size of the battery, the output of your desulphator and the extent of battery sulphation, It may take a month or more before the battery is restored.

One good way to track the process is to measure and record the specific gravity of each cell during the process. Heavily sulphated cells will have a much lower specific gravity, even down to 1.0 - which is plain water. As the desulphator works on it, you should slowly see the specific gravity increase to around 1.255-1.265 - that is, if you have a trickle charger connected across C4.

Another way to track the progress is the peak voltage output of the desulphator. You can measure the peak voltage across capacitor C6. When the battery is heavily sulphated, the peak voltage output will be rather high. As the plate sulphation is removed, the peak voltage output will decrease, depending on how short/large your wires from the board to the battery terminals are.

Note that during the desulpation process you should subject the battery to a heavy discharge cycle, and then re-charge it - every four to seven days. Otherwise, dendrites of lead may form between the plates creating a short, and make the battery unusable. The heavy discharge cycle will burn up dendrites that are forming.

The desulfator is giving an output of 54v accross C6 with charger. 47v without charger.We could not find a hydrometer to measure the specific gravity.

The battery we are trying to restore is a 50AH car battery which was out of use for about a year.

We have subjected the battery to a deep discharge. Is dendrites formation
an outcome of desulfation process??

 

Dendrite formation is a result of pulse charging (including De-sulfination). However you can burn off newly formed dendrites easily. A deep discharge/recharge cycle will typically remove newly formed dendrites. There is some difference in opinion on how often to do the dendrite-removing cycle. Some say weekly, some say monthly. I suppose it also has to do with the strength of the electrolyte solution.

[ed]
SgtWookie mentioned this in post #40

Note that during the desulpation process you should subject the battery to a heavy discharge cycle, and then re-charge it - every four to seven days. Otherwise, dendrites of lead may form between the plates creating a short, and make the battery unusable. The heavy discharge cycle will burn up dendrites that are forming.

[/ed]

 

thank you. We are better informed now

 

Desulphating by pulsing a current through the battery is bogus (junk) science. The only benefit of pulsing a battery is that it gradually equalizes the cells. It takes the pulser weeks to accomplish what a "constant-current equalization charge" can do in 4 hours. Google using "lead acid battery equalization"

 

Note that you read a higher peak voltage with the charger connected.

Ideally, your charger should be at a "float" level (13.4v-13-7v) and less than 2A current. A trickle charger will work fine for this.

To perform the heavy discharge, install the battery temporarily in a motor vehicle, disable the ignition or fuel supply, and engage the starter (max 30 seconds on, 2 minutes cool-down between starter engagements). Turn on the headlamps and let them burn until they get very dim.

Then re-charge the battery using a 6A charger for 10 hours (no desulphator).

Then disconnect the 6A charger.
Make sure your 2A trickle charger is not plugged into the mains power. Then connect your 2A trickle charger across C4.
Reconnect your desulphator to the battery.
Then plug your 2A trickle charger into mains power.

 

Desulphating by pulsing a current through the battery is bogus (junk) science

That may be a considerable overstatement, especially as the technique is proven. The characterization of the technique as bogus is opinion, not factual.

Here is the relevant section from the Battery University - http://www.batteryuniversity.com/parttwo-35.htm

While it does not mention pulsing, it also does not say anything in opposition.

 

Desulphating by pulsing a current through the battery is bogus (junk) science. The only benefit of pulsing a battery is that it gradually equalizes the cells. It takes the pulser weeks to accomplish what a "constant-current equalization charge" can do in 4 hours. Google using "lead acid battery equalization"

Hi Mike,
I don't proclaim to be an expert on the subject of lead-acid batteries. I just read the datasheets, and experiment.

Earlier in the thread, I mentioned using a desulpator to restore a lawnmower (really, motorcycle) battery using a small commercial desulphator.

Before trying the commercial desulphator, I had attempted subjecting this little lead-acid battery to a number of charge/discharge cycles (including equalization charges) with little observable change in serviceability. Three of the six cells had a specific gravity so low that it was off the scale.

I then used the desulphator on the battery for several weeks, and the specific gravity readings rapidly improved the first week, then gradually improved over the next couple of weeks.

If a battery is already in good condition, a periodic equalization charge should take care of stirring up the electrolyte and the sulphate off the plates.

But with the battery I was experimenting with, equalization didn't seem to have much of an effect.

I wouldn't call my experiment very scientific, as it was just one battery and the conditions weren't well-controlled; nor were all of the conditions of the experiment recorded. All that I can suggest is that I seemed to receive positive results with the desulphator, while equalization had no effect. A fluke, perhaps?

 

Here is some advice gained at great expense by the US government:

An important consideration during storage is a damaging process called sulfation. As cells
sit in storage and self-discharge, the active materials of the electrodes convert to lead sulfate
just as they do in other discharges. But, in self discharge the lead sulfate forms as larger
crystals that have the effect of insulating the particles of the active material, either from each
other or the grid. Since lead sulfate occupies more space than sponge lead, the negative plate
expands in volume. If the cell is allowed to overdischarge, the lead sulfate may expand to the
point where it separates from the sponge lead and falls to the bottom of the jar as sediment.
The overall effect is a loss of capacity and greater internal resistance. Sulfation is normally
reversible for lead sulfate still attached to the negative plate by charging with a low current
until the lead sulfate is converted back into sponge lead.

FLOAT VOLTAGES and/or specific gravity values are allowed to remain in an unequal condition for extended periods of time, cell sulfation will result. To overcome this problem, periodic EQUALIZING CHARGE must be applied to equalize cell voltages and specific gravities. Manufacturer's
recommendations should be followed in regard to EQUALIZING CHARGE.

The real question is whether so-called desulfators that work by PWM or some other method actually do more than the DOE position states. As is often stated on this forum, extraordinary claims demand extraordinary proof. The fact that Battery University does not mention pulsing does not mean it accepts it. Presenting such claims in the framework of science without use of sound scientific methods to prove them defines bogus science.

John

 

...

The real question is whether so-called desulfators that work by PWM or some other method actually do more than the DOE position states. As is often stated on this forum, extraordinary claims demand extraordinary proof. The fact that Battery University does not mention pulsing does not mean it accepts it. Presenting such claims in the framework of science without use of sound scientific methods to prove them defines bogus science.

John

Thank you John. I have built several pulsers similar to one being discussed here. I have evaluated several commercial pulsers for my consulting client. I have done some comparisons between recovering sulphated flooded-cell batteries using pulsing vs equalization. My conclusion, as I stated above, is that pulsing a battery for several weeks might do what could have be done in a few hours using just an "equalization charge", hence JUNK science!

 

From Wikipedia:

The terms 'junk science' and 'sound science' do not have an agreed-upon definition or significant currency within the scientific community; they are primarily terms of political debate.

Given that the pulse method does work, by MikeML's own words

I have done some comparisons between recovering sulphated flooded-cell batteries using pulsing vs equalization. My conclusion, as I stated above, is that pulsing a battery for several weeks might do what could have be done in a few hours using just an "equalization charge"

hardly any extraordinary claim is made.

From another critical post

As is often stated on this forum, extraordinary claims demand extraordinary proof. The fact that Battery University does not mention pulsing does not mean it accepts it

The lack of mention does not quite get to the level of rejection.

It is kind of you gentlemen to share your opinions.

 

That may be a considerable overstatement, especially as the technique is proven....

I would like to see some references that support this statement.

 

It is kind of you gentlemen to share your opinions.

My statements were based on publications by the DOE. Can you provide unbiased, scientifically sound data to support your opinion on the matter of using pulsed currents for improved desulfation?

John

 

This

I would like to see some references that support this statement.

is answered by:

I have built several pulsers similar to one being discussed here. I have evaluated several commercial pulsers for my consulting client. I have done some comparisons between recovering sulphated flooded-cell batteries using pulsing vs equalization. My conclusion, as I stated above, is that pulsing a battery for several weeks might do what could have be done in a few hours using just an "equalization charge"

Thank you again for your opinions.