Wednesday, 27 February 2013

More on battery de-sulphating / equalizing

This post might be a little boring for some readers….. (so Jan informs me! Winking smile)


My research into battery equalizing is progressing.  However I need and answer to whether “de-sulphating” is the same as “equalizing”.  The information on the Sterling website states the Pro-digital Advanced Regulator (PDAR) automatically manages the equalizing of the battery bank being charged by the PDAR but little else is mentioned about equalizing.  However elsewhere in the technical information it states


Automatic 7 day de-sulphation cycle <link to Sterling here>
The good thing about a constant current charger is that it de-sulphates the battery plates ensuring maximum life from the batteries. However, this only works if the charger is switched on/off regularly (i.e. every time you disconnect and reconnect the charger the plates are subjected to a de-sulphation cycle). The problem is some boats or standby equipment may be rarely used, for example: a boat could be moored all year and never leave the pontoon, or a stand-by generator with the charger on all the time. In these cases the de-sulphation cycle would only happen once and the batteries would eventually sulphate causing premature destruction. However the Sterling software has a 7 day timer which in the event of inactivity will automatically run a de-sulphation cycle keeping your plates clean.

The Sterling website also states the maximum voltage reached during the de-sulphating is 14.8V.  Other websites state equalizing the batteries only occurs at 15.2V.  I need to fully understand all of this.

When power is drawn off the batteries they are being discharged.  In theory this results in a chemical reaction where lead sulphate is created on both the positive and negative plates in the battery.  When the battery is being charged all the lead sulphate is converted back to the positive plate as lead dioxide and sulphuric acid.  However in reality some of the lead sulphate can be left on the plates and if left there for a period of time it crystallizes as a hard sulphate coating on the surface of the battery plates.  Sulphate is non-conductive (ie, an insulator) and as a consequence the capacity of the battery is reduced.  This sulphate needs to regularly be removed (a process of de-sulphating) otherwise the life of the batteries will be reduced.

Actually three types of sulphate form on the battery plates.  Soft sulphate can be removed during normal charging.  Hard sulphate can be removed by routine equalizing of the batteries.  Very hard sulphate can’t be removed and will gradually reduce battery capacity and life.

The best way to minimize sulphating is to keep the batteries fully charged.  However it’s not possible to fully charge a battery and leave it.  All batteries slowly “leak” energy.  This is one reason for having a solar panel continuously trickle a charge into your batteries.

So whilst routine charging removes soft sulphates from the battery plates, an equalizing charge removes hard sulphates.  But nothing removes very hard sulphates.  In effect an equalizing charge is a controlled over-charge to equalize the specific gravity among all of the cells. It is a controlled high-voltage charge lasting for a duration of 5 to 7 hours (depending upon the make and type of battery). During this charge, the battery gases out hydrogen and oxygen and creates heat. By performing this charge it is possible to damage the battery plates by excessive gassing and heat. The benefit of an equalization charge is removal of some sulfation build-up and correction the stratification of the acid density by stirring the electrolyte using the rising gas bubbles. Stirring is necessary to avoid high acid concentrations that can corrode the lower portion of the plate faster than the upper portion where the acid density is lower.

It appears equalizing a battery is the process of de-sulphating it.  On that basis the Sterling PDAR is supposedly monitoring our domestic battery bank and performing an equalizing charge every 7 days. 
But two things still concern me.  We are not running the engine for 7-8 hours daily or even once a week.  Yet this is the time it allegedly takes to perform an equalizing charge.  Additionally, The PDAR is conducting the de-sulphating at 14.8V whereas other sites claim equalizing only occurs at 15.2V.
Our battery bank consists of four Rolls 6v 450AH flooded wet cell lead acid heavy duty traction batteries connected in series parallel to provide 900AH at 12V.  The charging table in the Rolls manual states the charging voltage for a 12V bank is:

  • Stage 1 – Flood          Temp (0-16C) 15V  (17-27C) 14.4V
  • Stage 2 – Absorption Temp (0-16C) 15V (17-27C) 14.4V
  • Stage 3 – Float          13.14V
  • Stage 4 – Equalizing  15.48 – 16.02V

The Sterling PDAR forces the alternator to produce a maximum of 14.8V and our battery bank is sitting on the top of the ‘swim’ where it’s quite cold (the temperature would usually be below 16C) which means the PDAR isn’t damaging the batteries during the Flood and Absorption stages charging at 14.8V as the batteries will accept up to 15V.

However the batteries require a voltage of between 15.48V to 16.02V for equalization to occur and the PDAR doesn’t produce that level of voltage.  So the Sterling PDAR IS NOT performing an equalizing charge on our domestic battery bank?

Is our Victron Muliplus 12 / 3000 / 120-50 / 230-240V Inverter/Charger capable of completing the equalization charge?  The manual actually doesn’t provide much information.  It states

Less maintenance and aging when the battery is not in use: the Storage modeThe storage mode kicks in whenever the battery has not been subjected to discharge during 24 hours. In the storage mode float voltage is reduced to 2,2V/cell (13,2V for 12V battery) to minimise gassing and corrosion of the positive plates. Once a week the voltage is raised back to the absorption level to ‘equalize’ the battery. This feature prevents stratification of the electrolyte and sulphation, a major
cause of early battery failure.

More information here

Para 3.3 Equalisation and forced absorption
Traction batteries require regular additional charging. In the equalisation mode, the MultiPlus will charge with increased voltage for one hour (1V above the absorption voltage for a 12V battery, 2V for a 24V battery). The charging current is then limited to 1/4 of the set value. The “bulk” and “absorption” LEDs flash intermittently.

It appears the Victron attempts to equalize the batteries at the Absorption voltage (13.2V) plus 1V or 14.2V.   However the Sterling PDAR produces a higher voltage at 14.8V and the Rolls batteries require between 15.48-16.02V.  So the Victron is less effective than the PDAR!

After a little more research I found some of the CTek chargers have a “recon” cycle which de-sulphates (equalizes) the batteries with a 15.8V charge.  It’s a pity I didn’t “liberate” one of the CTek chargers on narrowboat Kelly-Louise when we were living one her in  late 2011 (just joking Peter)!

Sterling sell a de-sulphating unit.  However the website also states “This device is not required if you have a Pro Digital battery charger or any other advanced Sterling charging product connected to your batteries as they have a desulphation cycle built into their software program.”  If this includes the Sterling PDAR then I’m not sure whether the Sterling de-sulphating unit is any better than the PDAR (ie, only produces 14.8V). 

I think an email to Sterling is probably appropriate.

Worst case scenario might be to purchase a CTek charger with the “recon” phase and connect it to a generator or shore power each time we need to “equalize(de-sulphate) the Rolls batteries.

13 comments :

James and Debbie said...

Evenin' Tom, yup contact sterling via their website. I did last week with a question regarding our 40A charger (separate to the combi - both equalise at 15.5v by the way) and Charles Sterling emailed back within a couple of hours.
Re battery purchase and charging - lots of info I read lead to a charging regime (off grid) of about 3-4 hours a day for a medium to heavy user. I decided to buy cheapo batteries and only charge from the engine for a couple of hours a day (last year was about 14.2 total engine hours per week as an average) I was told I risked damaging my batteries charging this little but I saved between £1.50 and £3 per day so worst case scenario is that I will be out of pocket if the batteries last any less nine months (less than five months if I was charging at four hours a day) I guess if you plan to cruise 3/4 hours a day investing in good batteries becomes viable. I will probably renew mine after the summer when the would have cost the equivalent of about 70p per day.

PS why is the fairer sex immune to the lure of the battery monitor?

Tom and Jan said...

Hi James, I'm currently basing the charging off the Smartgauge and always get it back to 100% (3-4 hours daily) but the Smartgauge reporting 100% doesn't necessarily mean they are full charged. It's an expensive set of batteries with a five year warranty. So I do want to ensure they get a good maintenance routine.
It will be interesting to read Sterling's reply to my question.
Oh.... Jan prefers the oven to the battery monitor :-)

Toni and Ray said...

Hi Tom I agree with Jan it is a tad boring : )
Diane nb ferndale

Tom and Jan said...

Hi Diane, I'm still waiting for your post about using the new oven and temperature settings, gas consumption, etc :-)

Peter and Margaret said...

Yes Tom, We do indeed have two C-Teks, and they both have the features you mention. However, even the 'large' marine one I use on the main battery bank only has an output rated at 7.5A, so I think with your set-up you would be waiting an awful long time to complete the cycle. The C-Teks are designed with fibreglass cruisers in mind, not live-aboard narrowboats, but as we only use K-L for shorter trips, with much less battery capacity, they suit our needs fine, and as it should be, I suppose, our set-up is tailored to our own needs without further expense that isn't required - a subject I have also written about.

Ray Eddington said...

Hi Tom,read your blog daily,for someone whos suppose to be retired & takn things easy to increase ones life span,you sure smash the inside of your head about.How come all other NB,s let the accepted take place,like batteries wear out & need replacing after an acceptible time,thats lifes & batteries cycle.If you think about it i bet you could stop perpetual motion.Pull them pins man,get on the cut & extend your life cycle.hope to catch up on the cut,please dont mention the batteries.Ray E NZ....

Tom and Jan said...

Yes Peter, But the CTek would only be required for the "Equalizing" charge which is high voltage and low current. The PDAR and solar panels do the bulk and absorption stages. However I agree your use of K-L makes for an entirely different charging regime.

Tom and Jan said...

Hi Ray, We can't really go anywhere until the boat is finished and it's work I can't complete, so too much free time lets my mind wander..... onto boring topics :-)

Halfie said...

Tom, a former colleague of mine - an engineer at the BBC and a whizz with all things electronic - devised a "simple" battery desulphation device. It's one of those little projects I'm storing up for when I take early retirement (just four weeks to go!). His circuit is designed to cause the plates themselves to shake off the lead sulphate. A high frequency signal is superimposed on the charging voltage. The frequency is such that the plates resonate, and the hard deposits supposedly fall off. If you like, I could send you the link to his website where the details are (I haven't looked for a while - I hope they're still there!)

Halfie said...

By the way, it was the very title of your post which caught me eye!

Tom and Jan said...

Hi Halfie,
I think your description of the process used by the desulphation device is very similar to that used by the CTek chargers. High frequency pulse! Of course part of the "equalizing process is to also stir-up the the electrolyte and remix it. Hence the need to do a controlled "boil" of the battery.

nicknorman said...

Hi Tom

Just to mention that the standard absorption voltage for the Victron is 14.4v, so 1 v above that for its equalisation is 15.4, so probably adequate. 14.8 is in my opinion a charging voltage, not an equalisation one! Of course, with a PC interface you could increase the absorption voltage of your Victron.

Nick

Tom and Jan said...

Hi Nick,
Yes, I stand corrected! The Victron will produce a 15.4V equalization charge. But the Rolls Battery Manual states the charge should be 15.8 to 16.04V. The Victron manual also directs the reader to look at the charge curve in Fig 2... which doesn't exist .
So the Victron would do a better job of equalizing (15.4V) compared to the Sterling PDAR at 14.8V.
However a CTek MSX 5.0 charger will produce a 15.8V equalizing charge.
I wouldn't be able to use the alternators to supply the Victron during the equalizing process which means I either have to use shore power or a small generator. The question is whether to use the Victron or purchase the Ctek which would enable me to achieve the minimum recommended equalizing charge and totally isolate the boat electrics when doing the 6 monthly equalizing?