12 volt Leisure Battery Conditioning

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clockwork

Member
Like many people I have a caravan which is used frequently in summer but is stored in winter.
The leisure battery fitted in the caravan is 12 volt 110 Amp/Hour. These type of batteries do not fare well
if left for months on end in the cold without being either charged or discharged. Over the years I have had
a couple of batteries fail. I now keep them in my garage over the winter months.

I now have the time to build some form of battery conditioner that will charge and discharge the battery
whilst it is sat on the bench in the garage. My question is what is the most suitable system of keeping the
battery in tip top condition.

My initial thoughts are to use a Picaxe to monitor the battery voltage and
switch in a battery charger when a low of say 11.5v is reached and off again when the battery voltage
is back up to say 12.8 volts (as an example). The battery is then discharged via a load (possibly a car bulb), and so on.

There are plenty of battery charging circuits on the web but I do not know enough about the subject to
determine which is best and at what voltages should switchover occur. Also what level of current is suitable
and what are the best methods of fixing the charge/discharge current levels.

Many thanks for your help

Clockwork.
 
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srnet

Senior Member
Make up a simple mains charger for the battery, and connect it to a mains timer, switching on the charger for a few minutes a day.
 
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fritz42_male

Senior Member
But this doesn't exercise the battery which is important to keep lead acid types in good condition. This is the reason a lot of uninterruptable power supplies fail after a year or so.

You need to put a decent load on the battery and do a deep discharge about once every 2-3 months and a moderate discharge say once a week but i'm nowhere near expert on this -it's just what I used to do with the batteries on my boat.

I'm sure someone here will have the answers though.
 
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hippy

hippy

Ex-Staff (retired)
Dippy said:
Step 1. Consult battery manufacturer. Don't guess, don't assume...
Click to expand...
Not always so simple where one doesn't have control over what they choose and either the manufacturer cannot be identified or isn't forthcoming with information and there's no desire to swap what one has with something else.

If the information can be found then all well and good but otherwise it's a case of what will most likely work with a thing of incomplete specification which has to involve some guesswork or assumption, or not doing it at all.
 
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clockwork

Member
Thanks everybody. I did what you suggested Dippy. Only problem all the manufacturer stated was "Use a leisure battery charger connected up for the winter period".

When I looked I found that Leisure Battery Chargers appear to sell in the £60 to + £200 range.

I am certain that with a Picaxe, and some reliable information from Forum members a suitable charger/conditioner can be built. Also these commercial chargers do not appear to actively discharge the battery but rather rely on "self disharge" which all lead acid batteries appear to suffer from.

I shall keep looking for more detailed information from battery manufacturers but expect that forum members can supply an answer that uses a picaxe to control everything.
 
S

srnet

Senior Member
clockwork said:
Only problem all the manufacturer stated was "Use a leisure battery charger connected up for the winter period".
Click to expand...
What do they say about maintenance, and what exactly does a 'leisure battery charger' do ?

Its just that I have not seen the advice about the various cycling regimes being required before.

Never ever store them flat, absolutly not, and dont overcharge for sure, but the rest ?
 
C

clockwork

Member
I have had a look at what Leisure Battery Chargers do. One scource stated they had 3 Modes.
1/. Read Batt voltage. Then charge at constant voltage @ reduced amperage. This will stop gassing.
2/.Bulk charge mode, constant amperage & varying voltage till fully charged.
3/.Maintenance charge. Trickle charge, minimum current.

There does not appear to be any discharge cycle at all.

Years ago I built a Battery Auto Conditioner from Model Engineer Magazine 1993 that used two voltage comparators and switched the battery from charging to discharging via a car bulb. It was very tricky to set the voltage switching points very accuratly and only lasted about two months before it stopped working.

So is the correct route to try and emulate a Leisure Battery Charger with 3 different modes or a simpler Charge or Discharge design. Obviously with voltage measurement and control via a Picaxe.?
 
techElder

techElder

Well-known member
I've never in my life read or heard that one should "exercise" a lead acid battery. Perhaps that comes from the old mis-information circulated for many years about NICAD batteries and "memory effect" (which sold a bunch of NICAD batteries!)

The more you use a lead-acid battery (discharge/charge), the shorter it's life. That's not all that's involved, but it is one of the variables to the life cycle.

I used to store batteries that I had for sale on the shelf for months. They all got a good full charge first. Then I simply hooked them to a 15 volt regulated supply through a really high value resistor where their charge was held for months on end (during the off season.) There was barely a measurable charge current in the microAmp range. Worked that way for 20 years.

fritz42_male said:
But this doesn't exercise the battery which is important to keep lead acid types in good condition. This is the reason a lot of uninterruptable power supplies fail after a year or so.

You need to put a decent load on the battery and do a deep discharge about once every 2-3 months and a moderate discharge say once a week but i'm nowhere near expert on this -it's just what I used to do with the batteries on my boat.

I'm sure someone here will have the answers though.
Click to expand...
 
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Janne

Senior Member
Hi,

The method of upkeep charge depends of the battery type. "Leisure battery" could mean at least a couple of types, so it's impossible to give detailed help without knowing the type of battery.

For a traditional 12V lead acid battery(doesn't mean if it's sealed or not), first charging it full (~14.2V) and then keeping at float (~13.2V) voltage is usually recommended. Some smarter chargers will then ocassionally apply full charge voltage for a while, usually employing pulsed charging technique to prevent sulfating, or even to break up already formed deposits of sulfide.

Excercise on the other hand is required for the battery is it's of the AGM type(gel battery) In those batteries high current is ocassionally required to stir the electrolyte, as it will not freely circulate in the battery otherwise. I'm not otherwise sure what is the recommended way to store an AGM battery, but if your battery is of that type I'm sure there are application notes available describing the recommended process.

A popular charger for battery maintaining around here seems to be the CTEK one, many motorcyclists, boaters etc. who store their batteries over winter seem to favor it. The datasheet of it has a short description of how the upkeep charging is done. http://www.ctek.com/Archive/ProductPdf/XS 0.8_EN.pdf

CTEK ones are not too expensive, but of course it's much more fun building your own PICAXE version :)
 
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clockwork

Member
Dear Mr Clodhopper (from Texas), thankyou for the information.

A continual charge from a 15 volt regulated supply running in the microamp range is a far easier solution to the problem. No monitoring of voltages, switching or anything. Sounds good.

Would a 12v Solar panel (which is only capable of generating a very low amperage) do the same trick? Only reason I ask is that I just happen to have one. (Assuming that there is some daylight everyday during our English winter).
 
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mrburnette

Senior Member
Battery acronyms: http://www.vonwentzel.net/Battery/00.Glossary/

It seems that web-information on flooded-cell lead/acid batteries is conflicting. While the open-terminal voltage of the lead-acid battery is a good indicator of the battery health and state of charge, it is not perfect. Measurement of the specific gravity is a better indication. Crafty PICAXE folk can build a specific gravity sensor either as a capacitance or inductance device very easily where the liquid float moves a dielectric or ferrite plunger and I would think that a gradient gray plastic film could also be moved between a LED and a photocell. Commercial sensors are also available.

Another alternative is to estimate the flooded cell self-discharge period and zap it with a timed-charge when 80% of the battery capacity remains. At a constant temperature this will be easier than at a varying temperature (outside shed or unheated basement.) Since we are in the PICAXE forum, I'll assume that we would build a PICAXE solution to control a relay that would power on/off the battery charger for a timed period... and even log the event if we wanted to get sophisticated.

- Ray
 
D

Dippy

Moderator
Hippy, I meant the battery manufacturer... they should know what they choose.
:rolleyes:
Obv some people may 'badge' a bulk manufacturer but, at least, you should be able to get general information.
I think you thought that I was taliking about the caravan manufacturer.... even I ain't that daft :)

There is a lot of information from numerous reputable battery (and charger) manufacturers 'out there'.
I obtained a lot of info when doing a solar charger for various lead-acid batteries.

I'm not sure how much 'exercise' a lead-acid needs but I would say 'some' , otherwise we can get the dreaded sulphation and we'll start talking about desulphators next ... another 'black art'.
Again, this will vary with battery type/construction.
As Nuclear Physicists say: "Everything in moderation ... including moderation" (Oh, how we laughed!).


Actually, I'm just doing another charger at the moment so if you get any good info let us/me know.
But I would strongly suggest that you get info from good sources.
The only person I know on this forum who has done a lot of research and testing is Beaniebots, but he's on holiday.
He's the only person here that I KNOW to be experienced and qualified in what he is talking about.

His info and 5000 pages of data from manufs gave me a real leg-up in designing something good.
You may get perfectly good results trickling from a solar panel.
 
hippy

hippy

Ex-Staff (retired)
Dippy said:
Hippy, I meant the battery manufacturer... they should know what they choose.:rolleyes:
Click to expand...
I meant that too; like the one in my car which had no sticky label on it and nothing identifying it. It was easy enough to replace it because I matched the new to the car spec but I have no idea of what the battery spec itself was beyond assuming that met the car's spec ( or maybe not since it was dead ).

Now my Yuasa SLA's ... almost everything you could need to know printed on the casing.
 
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John West

Senior Member
Without specific info on the chemistry of the battery you are charging I can only speak in generalities. If the battery has a liquid electrolyte there are those who feel that "churning" the electrolyte on occasion helps keep sulfation from occurring during extended periods of disuse. ("Bubblers" have actually been used in the past in very expensive storage systems of different chemistries.) However, I've seen no documented evidence of this "churning" of the electrolyte in typical lead-acid storage batteries proving effective to reduce sulfation. It just sounds reasonable.

Again, for optimum battery life in storage, a very good understanding of the battery's chemistry is important. Also, the ability to monitor both electrolyte specific gravity and temperature. Lacking such info, you will need to follow general rules of battery care. Keep it clean to ensure there is no conductive path between terminals. Keep the charger from over-heating the cells (trickle,) don't overcharge (set a voltage limit for peak charge.)

Batteries for different temperature environments are set up with different concentrations of battery acid, colder climates having a higher acid concentration because the chemistry is less active in colder climates. This affects the appropriate float voltage for that type of battery. The problem with a more active battery chemistry is that it deteriorates more quickly if used in warmer temperatures.

There are charge curves online for deep-cycle lead-acid storage batteries that will give you an idea of what peak voltage to allow the battery charger to reach. As the specific gravity of your battery's cells at full charge is important for selecting the float voltage, yet apparently unknown, I suggest you identify one that seems most similar to your battery type and specifications (from unsealed, liquid filled to AGM style,) and follow it's recommendations. That's about the best you can do and will likely be good enough.

Where the PICAXE comes in is with the float voltage vs temperature. Monitoring the battery temperature (which will be pretty much the ambient temp where the battery is stored if it is on a trickle charge) is the best way to select the charge float voltage, as the optimal voltage varies with cell temperature.

Conclusion: Set up for a simple voltage controlled (with current limiting) trickle float charger with peak voltage that tracks temperature. An LM317 voltage regulator is a likely candidate to interface to a PICAXE for this purpose. That's about all I can suggest without more info.
 
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papaof2

Senior Member
I've been researching batteries and charge controllers for a (very) small solar system. I've downloaded some 120MB of pdf's and web pages for reference (just the items I thought worth keeping)

Based on a lot of online research (battery manufacturers, charger manufacturers, real-world experiences), a small charger that maintains float voltage is probably appropriate. With a 110AH battery, a 2 amp charger only provides a C/50 (1/50 the AH capacity) charge, which will do little more than keep the battery from freezing in the winter. Black & Decker sells a 2 amp automatic charger that's about $20US at the cheaper stores (Walmart, etc). I've used one to top off batteries from 10 AH to 80AH capacity.

Battery University http://batteryuniversity.com/ is a good starting place for all types of battery information.

John
 
D

Dippy

Moderator
"..like the one in my car which had no sticky label on it"
- Mmmm... sounds like an economy job to me.:D

I'd never buy an unbranded product especially if it needs to start my car 100% for 10 years.
Oh heck, now you'll tell me this anonymous battery has been working perfectly for 150 years.;)

Anyway, regardless, I'll stick to known makes.
I've made too many mistakes including saving a fiver in my UPSs at home.
Saved in money but they only lasted 50% versus Yuasa. Lesson learnt.


And yes, I got some info from Battery University too.
But my first port of call would be the actual manufacturer. In theory, a reputable manuf would know their batteries and have specific data. Hawker Cyclon to name but one.
If in doubt email the manuf. They won't bite.
 
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Goeytex

Senior Member
I have no idea what a "leisure" battery is. Is it a Flooded Lead Acid or a Sealed Lead Acid or something else? The charge voltages and rates will vary depending mainly with battery type, with possibly minor variations from manufacturer to manufacturer of the same type.

As a lead acid battery charges & discharges, lead sulfate ions move from one plate to the other (ion exchange) . If allowed to discharge fully lead sulfate can crystallize on the plates causing a "sulfated" battery. This particularly true of non-deep cycle batteries.

The simplest prevention is to keep a trickle charge on the battery during long periods of storage (winter ). You may want to apply a bulk charge and /or absorption charge prior to storage. The battery mfg should have data on the rates & voltages for each. I'm not sure of the benefit of exercising the battery from time to time, but it certainly can't hurt.
 
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John West

Senior Member
Actually, cycling CAN hurt lead-acid deep-cycle (caravan power, or "leisure" storage batteries, what we in the US call "RV" batteries.) Battery life is often measured in charge/discharge cycles. Roughly speaking, you can start with something like an expected life cycle of say 800 deep discharges, (depending on the battery design) and then calculate the percentage of depth of discharge vs the number of discharges and have a fairly good idea of how long your battery will last for most chemistry types.

However, a small, occasional discharge of a few percent will have no noticeable affect on the overall battery life of a storage battery, and the activity "may" help.
 
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manuka

Senior Member
Clockwork: 12 V 110 Ah sounds a typical deep cycle flooded cell lead acid to me. At least grab a traditional ~ US$20 dashboard charger (rated at ~100mA at 12V) for a trial. Even low angle UK winter sun should give a few hundred mA.h daily I'd say! Check this YouTube for insights.

Note-many dashboard PVs feature a flashing blue LED, but this merely indicates solar voltage availability and DOES NOT relate to current actually flowing. Many users are fooled by the LED, especially since some cigar lighter sockets are not connected to the battery when the vehicle key is removed. Hence use an ammeter to ensure you DO get charging current flowing,& further check that NO reverse discharge occurs at night.

Perhaps the biggest issue with such seasonal solar setups may be that battery connections come adrift or degrade with corrosion. A simple "at a glance" ammeter can give invaluable confirmation that the setup continues to actually deliver the goods.
 

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John West

Senior Member
Yep. Caption it "Exercising the battery." A nickel-metal hydride physical education teacher could be yelling at a fat, sweating deep cycle battery to "get the lead out," if he ever expects to be noticed by that cute little blonde high-capacity lithium cell.
 
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Dippy

Moderator
A quick search on nerdynet has shown a number of different types/constructions of batteries under the heading "leisure".
There appear to be subtly different advisory notes.
I suggest the OP searches for the battery type that fits the bill and proceed from there - it's so much better than guessing (or gassing!) :)
 
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clockwork

Member
Dear Manuka,
The PV array I have looks similar to your one, and includes the Blue Flashing LED. The idea with the Ammeter sounds good as you will know if the setup is still working OK. I think I will opt for this
solution to the problem as it is simple to impliment, I have everything already to hand. Also at the speed I tend to operate at these days Winter will probably be half gone before I get a more complex design built and tested. This takes the pressure off trying to get a working solution to the problem in the next week or so.

I am still thinking of incorporating some form of regular discharge (at moderate amperage) followed by a moderate charge to top up the battery followed by a trickle charge from a PV array. All controlled by a Picaxe of course. I seem to regard a Picaxe as the electronic version of "Snake Oil", it can cure every type of electronic problem. This will no doubt be music to the ears of all at Rev-Ed and all the stalwarts of Picaxe Forum.

Many thanks to all who contributed to this thread. I never realised that charging a battery could be so complicated.
 
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