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Desulfating / Reconditioning Optima Yellowtop


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If this helps someone else...

I had noticed that my 12v deep cycle battery had lost quite a bit of capacity.  It's a dual purpose (starting and deep cycle) battery.  We use it for the winch, backup start, and some essential services.  Cutting through all the marketing hype, it's just a well engineered AGM lead acid battery that can be taken to 30% SOC.

We work the battery pretty hard often taking it beyond 80% DOD. And I have accidentally run it down to under 6V twice leaving it sit for 2 weeks by forgetting to turn things off 😕

It's a pain to charge properly because it requires a IUI charging profile and those requirements can take it up to around 17V for the final stage which means disconnecting it from the boats parasitic loads - which is a royal pain.  Not to mention I have been unable to find a single IUI charger in existence that runs on 230VAC.

So the capacity has slowly been walking itself down over the last 5 years with sulfation. 

I ran it through three full cycles, down to 10.5V with a 24 Hr rest between charge/discharge.

For each test, the open circuit voltage was between 12.6 - 12.7 (which is pretty low)

Cycle 1: 63.7%
Cycle 2: 64.8%
Cycle 3: 64%

So 64% give or take.

At this point I was not getting any decent return so decided it was time to try my luck wit a balancing/equalization charge.  I should point out while some manufacturers recommend this, optima do not, but they also don't say not too. :-)

I hooked it up to a 3A constant current until there was a less than 50mv delta over 60minutes.  Manually checking every 45 minutes or so, it took around 9hrs iirc,  I saw the voltage peak at 19.4V in the first 60minutes and gradually drop to a voltage of 16.4V where it stabilized.

After 48Hours rest, the OCV was 13.12V.

Another discharge test gave  88%

I gave it three more full cycles and the final test gave 95%.  The 3rd stage charge voltage was back to a respectable 16.5V.

Anyway, that might or might not help someone else...

I am pleased to still have 90+% out of a 5yo battery that has been worked hard.

Our previous Hella Deep Cycle gave up the ghost after 2yrs of similar usage.

 

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It will be interesting to see how long that result lasts.
The important point to understand is that Equalization charge is resulting in two very different things when it comes to FLA and GEL/AGM. With FLA, it is all about stirring up the Electrolyte via Gasification. Obviously that does not occur with AGM or GEL batteries.
There are two different forms of Sulphate. The first form is a soft Sulphate and is part of the natural battery chemistry. It forms in the surface of the plates as soon as discharge occurs. The Sulphate layer increases as the battery discharges deeper and deeper. This layer reverts back when the Battery is charging.
The second form is a hard Sulphate. It is something that occurs with time. The longer the battery remains in a discharge state, the harder some of that Sulphate becomes. Once it is hardened, it will not revert back to cycle in the normal battery Chemistry. Equalisation charging results in the this Sulphate breaking away from the plate surface and settling down to the bottom of the battery. Something that canot occur in a Battery like GEL or AGM. The result is that the Sulphate becomes an insulator between the Electrolyte and Plate. However, Equalisation charge can sometimes work away at the Sulphate and revert some of what would normally have settled to the bottom if an FLA and you can gain some of the Batteries performance back. It never comes back fully and is subject to self discharge far more.

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I should expand on the sulphate part a little. Although it will not help in regards to the Optima AGM situation above. I thought maybe someone might get just a little more knowledge from the following, if they are interested.
If the Sulphate can no longer be reverted back to Plate material, the Plate is therefore diminished permanantly of that material and thus loses capacity in both Current and Storage.
With an FLA type battery, the Hard material sinks to the bottom of the battery container and builds up. Deep cycle designs allow for this by having a deeper area under the Plates. Once that material builds up to a point where it can contact the plates, it will short the battery out. This scenario is what is often seen on YouTube were someone will tip a battery upside down and flush it out, refill it and show an operating battery again. They have removed the short, but the Battery is pretty much useless, or soon will be. They never ever recover fully and the capacity and current is never shown. Just the Voltage which is telling nothing at all.

As for the AGM above, Capacity and Current tests will provide a lot more info on where the battery is now at. Voltage does not give you an entirely reliable test. One of the electronic battery testers will tell you a lot about the battery state. It will give a range of information that can be quite telling. Of course, if you can gain another couple of years or more of use from it, that is a major bonus when related to the expense of those batteries. The Optimas certainly are great at withstanding abuse.

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Hoping to gain some advice from some of you battery gurus whilst this thread is active...  I have a 7 stage battery charger fitted in my boat and I currently manage my battery health (in the marina) by having the charger on for about 10 days... then off for a week or so.  The idea being to 'rest' the batteries.    Could this harm the batteries?  (AGM's) .. or is it better to be (smart) charging 24/7?? 

Would appreciate any thoughts.... thanks. 

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5 hours ago, SeaAir said:

Hoping to gain some advice from some of you battery gurus whilst this thread is active...  I have a 7 stage battery charger fitted in my boat and I currently manage my battery health (in the marina) by having the charger on for about 10 days... then off for a week or so.  The idea being to 'rest' the batteries.    Could this harm the batteries?  (AGM's) .. or is it better to be (smart) charging 24/7?? 

Would appreciate any thoughts.... thanks. 

Firstly your battery manufacturer should be the ultimate source of truth.  If it is a good manufacturer then they should have a comprehensive data sheet. 

Eg, a standby Panasonic agm deep cycle battery I have says: Expected trickle life: 6 years at 25℃ 10 years at 20℃ (trickle is the same as float without parasitic loads) 

If your manufacturer does not have a datasheet (and many don't)

Then the answer is Yes and no... :)

What are you trying to achieve? Battery longevity of 10+ years, or having a fully charged battery when you go out sailing. 

If it is the later then just leave it on float... 

That's the yes part, here’s the no part...

A battery is never really at rest. Even if nothing is connected to it and it is truly open circuit then it is still going through a chemical reaction and losing SoC. 

The purpose of float is to cover any parasitic loads and continually replace whatever the battery is losing naturally.  For a typical AGM this is probably 13.2v @ 0.1A + parasitic loads.

By definition a charger is a parasitic load. Some manufacturers will specify the Ah/week that the charger when turned off sucks out of your battery others don't. 

The other problem with chargers permanently connected is AC ripples that affect the DC side. While we have very stable 230VAC in NZ a charger will end up sending some spikes into the battery which you'd only pick up with an oscilloscope.  These microbursts can damage plates over the very long term. 

Float chargers sometimes float below the initial resting voltage of the battery (eg, 13. 1v). So this means the battery has to self discharge before there is a voltage differential.

Conversely float chargers often float above, eg 13.3v continuously trying to jam more power into battery. 

Optimum float voltage for AGM varies with temperature. 13.2v isn't optimal at all temperatures. On a boat we often have the battery sitting in the bilge and the outside water effects the temperature, while the charger is sitting mounted above the waterline and is maybe a few degrees warmer.  If it does not have a remote temperature sensor or worse still does not compensate for temperature then you could be over charging the battery. 

If you reworded your question slightly, to maybe:

Am I likely to cause any noticeable battery degradation by leaving my boat AGM batteries on a permanent 13.1v float charge. 

I would say No, go for it, leave it on float charge all the time.

 

 

 

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Thanks heaps!... a brilliant reply to my concerns.  Yep.. my main concern is that my charging practice would have been damaging the batts. 

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On 21/07/2022 at 12:34 PM, CarpeDiem said:

A battery is never really at rest. Even if nothing is connected to it and it is truly open circuit then it is still going through a chemical reaction and losing SoC. 

More technically correct, the electrolyte is conductive, so when the battery is at reast, no load connected, the resistance of the conductive material causes it to self discharge.

 

On 21/07/2022 at 12:34 PM, CarpeDiem said:

The purpose of float is to cover any parasitic loads and continually replace whatever the battery is losing naturally.  For a typical AGM this is probably 13.2v @ 0.1A + parasitic loads.

It's more about keeping those plates up to full charge and overcoming the self discharge. Production of any energy is via the chemical reaction. As soon as a voltage source is removed and the battery begins to discharge via that internal resistance, the chemistry is such that sulphate is created. Maintaining a float charge stops that from happening. However, a battery can slowly deteriorate even when in a float charge due to another phenominum. Surface charge. When very small trickle currents are in play, the actual charge on the plate can be on the surface only. The Chemical reaction is not right through the plate. Deep cycle is prone to this due to having much thicker plates. A really good charger will have a Discharge mode. Once per week or month, the trickle charge will be stopped, a load will be applied by the Charger and then after a time, the charger will revert to charge and then trickle charge mode again. This ensures the depths of the plate are fully charged. If this is not carried out, it is not uncommon to have a battery test fully charged, but it loses charge quickly when put back not use again.

Be very wary of any chargers that state 7 stage. Stating such are nothing more than marketing ploys. It makes the charger sound better than one stating 3 stage. That is not to say all 7 stage chargers are junk. You need to read what is actually being covered in the stages of charging. Some stages on cheaper chargers are really pathetic and mean nothing at all.
The important stages are Bulk charge, Absorbtion charge, Float charge. Then if the charger is better than average, it might have the discharge/charge as an automatic stage as well. Then there is the Equalization stage. This is most important for FLA batteries. Most chargers emply that stage by manual selection. But some specialised chargers may have that as an automatic stage as well.
So tht all gives you 5 stages. If they want to talk that up a bit, you might find the discharge and recharge as two seperate stages. That makes 6. A few chargers have a desulphation stage to make 7. But that stage is a joke. It takes a dedicated specialised charger to do that job and even then, it does not always work.

On 21/07/2022 at 12:34 PM, CarpeDiem said:

By definition a charger is a parasitic load.

Ummmm, no. There should be no load at all. Especially if fully electronic.

 

On 21/07/2022 at 12:34 PM, CarpeDiem said:

Float chargers sometimes float below the initial resting voltage of the battery (eg, 13. 1v). So this means the battery has to self discharge before there is a voltage differential.

Conversely float chargers often float above, eg 13.3v continuously trying to jam more power into battery. 

Continuous-preservation (float) charging: 13.4 V for gelled electrolyte; 13.5 V for AGM (absorbed glass mat) and 13.8 V for flooded cells All voltages are at 20 °C

 

On 21/07/2022 at 12:34 PM, CarpeDiem said:

The other problem with chargers permanently connected is AC ripples that affect the DC side. While we have very stable 230VAC in NZ a charger will end up sending some spikes into the battery which you'd only pick up with an oscilloscope.  These microbursts can damage plates over the very long term. 

Fully electronic chargers (Switch mode power supplies) do not suffer this. The 230V stage is completely isolated from the output stage. In fact most all SMPs today will accept an input voltage from 110V to 260V with no problem and no change to output at all and most certainly no AC spikes.
But then again, these desulphating chargers work by pulsing AC spikes into the battery. So I really cannot see how spikes would upset the battery in anyway. The battery is a pretty good buffer to anything that is within the normal range of charge current.

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On 21/07/2022 at 7:13 AM, SeaAir said:

Hoping to gain some advice from some of you battery gurus whilst this thread is active...  I have a 7 stage battery charger fitted in my boat and I currently manage my battery health (in the marina) by having the charger on for about 10 days... then off for a week or so.  The idea being to 'rest' the batteries.    Could this harm the batteries?  (AGM's) .. or is it better to be (smart) charging 24/7?? 

Would appreciate any thoughts.... thanks. 

In short answer, no you will not harm the batteries charging 24/7 or leaving the charger off for a few days. It is really only long term of both that will eventually cause an issue. Something seen in remote power sights for instance. This is why remote sites tend to use Gel banks. The Gel battery is better at longer term float charging, with the very rare event of being used in a power cut and then back to charge again. AGM,s do not like that as much and FLA's require too much maintenance to be left alone for long periods of time.

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