Battery Charging And Maintenance (SLA Sealed Lead Acid, and “wet batteries”)

Battery Desulphators/ Desulfators – What are they?

When using batteries, both SLA (sealed lead acid), or “wet batteries” (where the acid in there is liquid), in the car, for projects, in burgalar alarms, or whatever the purpose; if they are not charged and maintained they will “sulphate up”, in that deposits form on the plates which are resistive, and they will cause the battery to go “soft”, or lose its ability to supply heavy currents, and the voltage will sag downdards, and the current will drop off.

Sealed Lead-Acid Battery 12V 12AH

For charging I recommend a 3 stage battery charger available from most electronic, and DIY stores. These will top up batteries, not overcharge them, and keep them topped up during the Winter.

They are ideal for a motorcycle or car (wet) battery, especially if the vehicle is left over long, periods without use, or during very cold periods during the Winter.

Lead-Acid Car Battery (Wet Battery) 12V 60AH

The graph below shows how a modern three stage charger should charge the battery…

Three Stage Battery Charging

This one breaks it down a bit more…

Three Stage Battery Charging

OK having discussed battery charging; how can we keep the battery in good shape?

I also think these are good too… The “Optimate” battery charger, and this can be left on charge all the time.

Optimate 4 Battery Charger

http://www.accumate.co.uk/

Well I scoured the net for a battery maintainer, and I thought that they were a bit pricey, so I decided to search for a kit to build from electronic components…

I found one… (please follow the links below) from… http://www.courtiestown.co.uk/index.htm

The kit instructions are below, and they will help you to decide which one to get, or just buy the PCB and make it up cheaply if you work in electronics, or know a cheap component shop.

New 12V Basic PCB Kit (New PCB) Instructions

and for the “better” high power one…

New 12V High Power (New PCB) Kit Instructions

You can buy the full kits or just the PCB’s and get your bits from elsewhere. By the way I am not affiliated by Courtiestown Marine in any way, but I do recommend their kits as very good.

Pulser PCB For Low & High Power Desulphator

So do they work? Do these devices really work because I have wondered exactly the same thing?

The presence of the former ezboard BB now found at http://leadacidbatterydesulfation.yuku.com/ and people who clearly believed it did, so I gave it a try.

Quoting from the Courtiestown website this is how they sum up the two kits…

“Basic Pulser Kit

This kit is the circuit in its simplest form with some substitute components that have been tested to ensure they work. The cheapest way to start.

The only modifications are the addition of a Zener diode to protect the 555 from voltage spikes, an LED to show it is ‘working’ and both electrolytic capacitors are larger values.

All the necessary components and a PCB are supplied along with some brass nuts/ bolts and washers to make mounting posts to connect the leads to the battery. It consumes about 50mA.

High Power Pulser Kit

This version is a development of the basic version for which we take no credit that belongs to the contributors at the Desulfator BB.

In addition to the above basic modifications this kit has a superior MOSFET, a larger still output capacitor, larger capacity inductors and R2 (the 22k resistor) is replaced with a pair of 47k NTC thermistors in parallel. These will be supplied ‘glued’ directly to the components themselves.

All the necessary components and a PCB are supplied along with some brass nuts/ bolts and washers to make mounting posts to connect the leads to the battery.

This version is a more powerful pulser than the Basic device and consumes more current – circa 110mA.”

My use of the desulphator (desulfator) has been as below. I made two of them; one for home, and one for at work.

Do not connect this to the charger or power supply to it on its own, or the voltage will shoot up to 40V plus, possibly blowing up the big electrolytic capacitor on the circuit, so connect the battery to it first, and then the normal battery charger or PSU afterwards.
On a car this can be left on all the time, but only if you use your car a lot, as it does flatten the battery.

I recommend topping up with a charger once a month while the battery is on the car with the desulphator connected, and this will stop you getting caught out with a flat battery, as it does use 100mA or so (1/10 of an amp) or so.

I have bought “dry fit”, SLA’s or the grey/black sealed lead acid battries back to life with this device, but it has taken from a few hours, to a fortnight on a bench power supply.

They do work, as I had a pair of batteries, and one on a charger, and one on another charger with the desulphator. The other battery only recovered as well when connected to the desulpahtor after the first one was fully done.

You won’t recover these…

Batteries with no acid or low levels in the cells
Batteries with damaged or buckled plates
SLA’s (Sealed Lead Acid) batteries where the casing has swelled and buckled up, showing abuse or failure, such as from UPS’s (computer backup power supplies or inverters)
Totally dead batteries that have been out of service for many years

I have found that batteries like this will recover…

Batteries that have become “soft” or “saggy”, but still have some charge, but cannot supply the current.
Flat batteries that haven’t buckled or been standing for more than a few weeks
Dead batteries that are not buckled, but have gone very flat

As they charge the ones with high internal resistance will draw less current, and the voltage may go up to 15V or more. As they desulphate and charge the voltage will drop, and the current will increase.

When charged the voltage should be 13.8V to 14V, and the current at this voltage will have levelled off to a “baseline level”.

So when charging with a bench PSU, set the voltage to 13.86V DC, connect up the desulphator to the battery, connect the PSU, limiting the current to 2A or 4A depending upon the battery, and the PSU capacity, and switch it on.

Don’t let any acid boil over, and always fit fuses, and put the battery in a tray to catch any acid. (A friend of mine ruined a kitchen worktop charging a battery in the kitchen, because the acid boiled over!)

WARNING… Do not smoke, have sparks or a naked flame nearby, as the hydrogen given off may explode, blowing up the battery, and spraying you with acid!

Finally, I accept no responsibility for any injury or damage; always be sure that you know what you are doing!

Mark Lawton

http://mark-lawton.com