Car Battery Charger

Hysteresis · 12 Apr 2022

I bought a car battery charger a few months ago, the reason being that I am only doing short journeys over the winter and as such not really enough to recharge the battery fully.
The type I bought was a relatively cheap domestic Electronic type with various functions.
A battery charger means no more to me that a DC voltage which is fundamentally slightly higher than the battery terminal voltage and as such provides power to re-establish the battery stored energy.
This new charger has various functions which suggests that there is a difference to a Car Battery and a Motor cycle battery, the only difference I can suggest is the storage capacity, such is my ignorance I suppose.
The real reason for my post is that this new charger has a function on it which can be selected to 'Battery Repair' which proclaims to repair an old battery. The question being, what can a charger do which can 'Repair' and ageing battery. I suspect there is a bit of sales talk in the claim but I am puzzled as to how such a function can proclaim to "Repair' an old battery.
Any ideas out there ????

JohnD · 12 Apr 2022

an ordinary "smart" charger might fail to charge a bad battery, if it has no voltage and its resistance is very high, its "smartness" may think there is no battery connected. "Repair" sends brief pulses to the battery, which may be enough to get it working again.

Hysteresis · 12 Apr 2022

JohnD said:
an ordinary "smart" charger might fail to charge a bad battery, if it has no voltage and its resistance is very high, its "smartness" may think there is no battery connected. "Repair" sends brief pulses to the battery, which may be enough to get it working again.

Sounds Plausible John. I'll run with that explanation. Thanks for your reply.

SFK · 12 Apr 2022

A poor explanation here
https://no.co/support/sulfation-and-battery-repair-mode

I use it if I have left battery a long time between use.
No idea if makes a difference, but seems to take a lot longer so presumed it was a low level monitored charge (looking at the screen it seems to be less current, and changes the current level every now and again, and over a longer charge period).

I am happy as it seems less aggressive than the fast charge setting.

Sfk

bernardgreen · 12 Apr 2022

One way that a lead acid battery can fail is when the lead oxide coating on the positive plate fails and exposes the lead. Effectively creating a short circuit through the electrolyte between the positive and negative plates in that cell.

If the lead oxide can be repaired by forcing current through the cell then the battery can be "repaired" but it requires careful control of the current to prevent damage to the other cells.

Hysteresis · 13 Apr 2022

Thanks Bernardgreen and SFK.
The explanations certainly help my very limited knowledge of Lead Acid Batteries.
I think my battery problem is that due to short local journeys in the winter months, my relatively new battery never gets the chance a full charge and may suffer from sulfation/stratification so maybe the 'Repair' mode on my charger may have helped the situation.
Having said that when I replaced my battery I chose a low priced one so probably it was a false economy. Because of my lack of battery knowledge I opted for the economy battery, having gained a bit of knowledge and your assistance, I will eventually replace the battery with a premium version.

fixitflav · 15 Apr 2022

bernardgreen said:
One way that a lead acid battery can fail is when the lead oxide coating on the positive plate fails and exposes the lead. Effectively creating a short circuit through the electrolyte between the positive and negative plates in that cell.

If the lead oxide can be repaired by forcing current through the cell then the battery can be "repaired" but it requires careful control of the current to prevent damage to the other cells.

But is it a lead-acid battery? I thought they were all silver-calcium these days. Whether that makes any difference to repairability I wouldn't know.

ericmark · 18 Apr 2022

One has to consider a battery is a collection of cells, which are not identical, so if float charged over time one cell will discharge or charge more than another so to equalise the cells you need over charge the lower cells, this was OK with a flooded battery, but with a battery where you can't top up cells, you need a diffrent process.

The main method is the pulse the charge. So with a 12 volt battery charge to 14.4 volt, then allow to drop to 12.8 volt, then start again.

This is for a good battery, but same applies to a poor battery, pulsing but this time more rapid can assist it to recover.

However time is also important. Sulphur hardens over time, and it also takes time to soften again.

However many chargers have features like auto off, and reverse connection protection, auto detect 6 or 12 volt, and the features also mean it can't charge a completely discharged battery, even putting a battery in parrellel to start off charge will switch off as soon as second battery is removed as voltage exceeds a threshold often 16 volt.

So the second battery has to remain in parrellel for maybe two weeks.

The recovery is like flicking a switch, I did it with the charger connected to an energy monitor so I could see the point where the sulphur had softened enough to allow charge to start.

However the problem is if a cell is damaged causing a short circuit, so your charging a 10 volt battery as if 12 volt, so battery in parrellel needs to be smaller than one trying to renovate. Also charger output needs to be limited, mine limited to 0.8 amp.

Once battery has started to charge, then I can re-start charger to give full 3.8 amp.

This is for lead acid, with nickel be it with iron or cadmium or any other system often you need very special charging.

The VRLA (valve regulated lead acid) or AGM (absorbed glass mat) are still lead acid, but only just enough acid.