Burning Sulfates from battery cells

[tecnodave]

First please read my post about Battery Safety and Personal Safety


Burning Sulfates from battery cells:

This is done by applying a higher than normal voltage across the cell but controlling the current to a safe value.  Back in the 50's and 60's there were "string chargers" that were specifically designed to do this. The practice in battery shops was to "string up" 6 to 8 batteries in series and connect the string charger to them. The chargers put out from  80 to 180 volts half wave rectified DC. The chargers consisted of a variac ,variable voltage transformer, whose output went to a isolation transformer/ballast. This fed a "Tungar Bulb" rectifier. This is a vacuum tube mercury vapor rectifier diode.  It was the size of a 1000 watt mercury vapor streetlamp, but with a "duncecap" on top for the rectified DC output. This worked as a limited current high voltage generator. By nature the voltage would droop as more load would be applied. This "string charger" was then connected to the battery string, energized, and slowly turned up to about 10 amps as read on the meter. As the batteries would charge all the cells would equalize leaving 2.5 volts on good cells and much higher voltages on the sulfated cells. This higher voltage would then burn the sulfate off the weak cells. Stubborn batteries were isolated and run again until the hydrometer readings came up. The good cells would gas freely.



These "string chargers" can be found in museums as they are now totally obsolete,  but I have found a way to do this with a bread boarded apparatus described as follows:  I use a 20 amp 0-140 volt variac feeding a 120 volt to 120 volt isolation transformer. The output goes to a single silicon diode  50 amp /400 p.i.v.  Through a 0-10 amp analog ammeter then  to a bank of 12 100 watt incandescent light bulbs in ceramic fixtures all in parallel . The bulbs serve as variable resistors having a very low resistance when cold and rising very quickly as the filaments get hot.
The current is controlled both by the Variac and by screwing the bulbs in one by one until you get the desired current, the bulbs need to be partially lit, not fully bright.

This apparatus works as the "Tungar bulb" does as it will output a high voltage until current flows then it will drop in voltage quickly. The positive output of the bulb stack and the other end of the transformer (negative) go to the single battery you are trying to recover from sulfation.
Half wave rectification works better than full wave as it "pulses the power"

If you have 2 volt cells or batteries which have the external connector straps go after only the cell that does not respond once you have free bubbling in the other cells and a hydrometer readings of 1.260  +/- .05 between all the cells.

I have built "battery probes" which are thin stainless steel, ground to a point, that I insert through the cell caps to contact individual cells within a battery to de sulfate a single cell. I consider this as a last resort when the battery fails other attempts at recovery.

This charging will take upwards of 30 hours to do a full desulfation, constant monitoring and logging of the hydrometer readings is appropriate so that you can track your progress

Flickering of the bulbs in normal as the current pulses dislodge the sulfated particles from the plates. Ideally you want 1/2 to 2/3 brightness of the bulbs, more not enough resistor action and less too high of resistance to get adequate current flow.


Generation Two String Charger:

This is the same as the above described apparatus except that there two diodes each with their own ammeter and bulb stack.  The main diode is connected for positive output and the second is connect for negative output. The second stack needs only 6 100 watt incandescent lamps in parallel. The two sets of diode,ammeter, and regulating resistors (incandescent lamps) are connected in parallel(opposite polarity) on one side of the transformer.

The purpose here is to output a 10 amp positive  charge and a 2.5 amp negative charge on alternate half cycles. This technique is done in some commercial "pulse chargers".
I believe that I am the first to apply the technique to desulfating batteries

The best ratios between forward charge and reverse charge is between 4-5 to 1.

I have recovered many golf cart batteries this way as they are a surplus product once one cell goes bad. It is not economical to replace one battery in a traction vehicle as they will never balance. My recovery rate is 50 to 75 % of discarded batteries purchased in the scrap yards.
I first look for //correction.   Heavy coating of ///. light grey powdery material on the plates and reject those then do a hydrometer test, if the cells are within //correction .500//. of each other them I trade in cores for discarded batteries getting many good ones this way.

Final notes: there is considerable shock hazard in the described process as the voltages can be lethal and the hazard of Hydrogen / Oxygen Gases that are produced in this process.  Be SAFE, please read my post about battery safety and Personal Safety

tecno

Edit at incorrect specific gravity criteria for rejection.   td

[vtmaps]

I first look for light grey powdery material on the plates and reject those then do a hydrometer test, if the cells are within .050 of each other them I trade in cores for discarded batteries getting many good ones this way.

What is the light gray powdery material on the plates?

What other reason do you reject a battery?  (color of electrolyte, bulging positive terminal post, etc)

--vtMaps

[tecnodave]

vtmaps

The light grey is sulfation, I don't reject lightly sulfated ones only ones heavily coated, any bulging posts , cracked cases and one tell tale, check the ends of the battery, if they are bulged out in the center this is a sure sign that the plates are warped due to overcharging. No recovery from that. Any obvious visual damage will be cause for rejection. I have had several golf carts converted to utility vehicles that were totally powered with batteries from scrap yards. Didn't buy a new battery in ten years. Normally when you find a set of 6 together at scrap yard one will have a fault, usually sulfation in one cell only, this will be enough that the golf cart will not preform well. All the critical batteries in my solar system were bought new but I do have a pair of Surette 8D batteries that came off a research ship, these were replaced because one had a weak cell. They recovered just fine and are used as spares but I do not connect them to the L-16 bank. Parallel banks never work out well. My Classic is on the main bank and the tracers do non essential duties. One of my friends is a Interstate dealer and I get them wholesale, I paid $219.00 each , they list at $475.00 each. I paid $950 total with tax and environmental fee for 4 @375 ah.  I am patiently for LifePo4 batteries to be reasonable.

I would like some feed back about my charging method, did you find the information useful?

tecno

[tecnodave]

I just reread my post any a few errors creeped in there on specific gravity variation and a few others, I will go back and edit for correct information.

tecno

[dgd]

interesting info.
I have seen the bulging sides/ends quite often. A dead giveaway of warped insides.
So what do you think of those little high frequency desulfators that sell for about $100 and work in conjunction with a car battery charger?

dgd

[tecnodave]

High frequency desulfaters , seen them not impressed , but they do work for very light sulfation,

My technique works for batteries that have say 1.100 across all cells except one which is off the low end of the scale and individual cell voltages of less than .3 volts on the defective cell, as long as you do not have heavy crusty buildup. I am now recovering two Interstate brand D-8's that sat for 10 years , brand new, never used, flat dead, all readings below readability, I now have 1.260 across 5 cells in each unit. The weak cells read 1.170 and 1.210  I am now probing each cell with the probes inserted into the tops of the lead plates. I am expecting recovery on these units. Paid ten dollars for both of these, less than scrap value. Maybe 3 hours setup and testing time.  It is a gamble but if you have a dead high quality battery I feel it is worth a few hours to recover.

If I see interest I will write a short experience on my experimental electric utility vehicle, a 1959 Dihatsu 3 wheeler, much like a cushman , with transplanted golf cart running gear. I never bought a new battery for this vehicle.

I also use a Snap-on brand , model MT-540 , analog battery, alternator tester for load testing, this unit has 8" Analog voltmeter and ammeter and a carbon pile load capable of 600 amps at 32 volts, I have modified this unit for 12 voltage scales and 12 amps scales, it uses (originally and now) external shunts, max scale 0-1200 amps.  Bought used for $100.00,  can't buy a high quality 8" analog meter for that, and it already has proper scales. I load test Solar arrays with this unit up to 150 volts , 3 kW.
It originally was designed for 12/24/36 volt vehicle alternator,regulator,battery,starter, load testing.

I did mention elsewhere I did an apprenticeship at Alaska Husky Battery in Fairbanks, Alaska in 1966 and then again at Trojan Battery in San Francisco.

I have been doing electricity too long, I can't stop.

tecnodave

[Vic]

Hi technodave,

Great info!

May need to give this a try as time permits.

Have used a HomeBrew Variac/transformer/FWB/Capacitor bank/Ammeter/CB setup with jumper cables to charge/EQ single cells and batteries.

Will ask some questions later,  when project duties subside.

Thanks!   Vic

[tecnodave]

Vic,

It seems that I am not alone in doing this, I have tried full wave but I get better results with the gen two setup with the lopsided wave output, looks funny on the scope but it does seem to work better.
I keep this as a breadboard project so that I can incorporate new ideas at will.

You might get better results if you do not filter the DC output.
I remember looking at the output of the Tungar Bulb string chargers on an oscilloscope and they were not smoothed at all, pulsing half waves, very ragged as the reaction took place.

The wave shape would show increasing voltages then very drop as Sulfates were dislodged.
After removing the tops of some of the failed batteries and removing the plates large amounts of debris were found up to the bottom of the plates. I think this is the reason that some batteries cannot be recovered.

In the 60's it was common to reuse the jars and build new plate packs. At Alaska Husky we built our own custom plates that were a higher concentration of lead to acid and the electrolyte was 1.320 to 1.350 specific gravity. This made the batteries more heat sensitive and not suitable for hot summers but worked better at 40 to 70 below zero which is common in Fairbanks.

tecno