Lead acid battery charging

[BigEndBob]

Could someone explain to me why do lead acid batteries as used on cars and aeroplanes need to be charged at certain current values and say fixed voltage 14.1V, and you have to be careful not to overcharge, yet when connected to a vehicle there is no charge regulation?

[hvogt]

Hello BigEndBob

High charging currents or cell voltages (higher 2.4 V) cause gassing. The distilled water splits into hydrogen and oxygen. This oxy-hydrogen is, of course, highly explosive.

As far as I know, this effect applies to all lead-acid accumulators including those in cars.

Best regards

hvogt

[cwatters]

Lead Acid batteries are usually charged at a constant voltage but generally there is no need to control the current. The current during the charge is typically controlled by the charge state of the battery. It starts off high and falls as the battery charges. So there is a form of regulation.

Having said that.. It is normal for the charger to have a current limit which comes into play at the start of the charge cycle when the battery is flat. The current at the end of the charge is controlled by the voltage which needs to be quite accurate. If the voltage and consequently the current is too high at the end then gassing occurs for the reason hvogt gives.

With certain conditions Lead Acid batteries can actually be left on charge permanantly. This is called float charging and is usually done at a slightly lower voltage than normal to ensure the final current is quite low and minimise gassing that would dry out the cell. Typically on float the current will fall to close to zero - just balancing the self discharge losses. In fact wet Lead acid batteries seem to last longer if kept permanantly on a correctly set up float charger. They typically hate being deep discharged, allowed to self discharge or allowed to stand flat for even quite short periods. This applies even to wet cells designed for deep discharge.

I've flown electric powered model planes for 20 years and in my first few seasons I managed to kill three lead acid batteries a year by allowing them to stand party discharged for too long. Now as soon as I get back from a days flying the battery is put on float charge immediatly and is left like that 24/7. Now the battery lasts several years.

I highly recommend using a charger with a float setting if you have a battery powered lawn mower that uses wet lead acid batteries. Keep it on float over winter. Sometimes the float voltage can be adjusted to match that recommended by the battery manufacturer.

[H Peacock]

Could someone explain to me why do lead acid batteries as used on cars and aeroplanes need to be charged at certain current values and say fixed voltage 14.1V, and you have to be careful not to overcharge, yet when connected to a vehicle there is no charge regulation?

Most car alternators do infact have a regulator built-in to control the output voltage. I believe it is usually set at 13.8-14 volts to prevent overcharging as highlighted above. Thought I was taught at school years ago that a lead acid bettery on charge will always produce some gas (hydrogen + oxygen), but that overcharging causes excessive gassing.

:)

[Lancelot37]

Charging at too high rate can also distort the plates in the battery causing shorts.

[411A]

In addition...

The lead acid batteries used in aeroplanes are not as robustly constructed as those used in motor cars, so the charging circuit in airplanes account for this by tightly regulating the charge current.
Too much is....not good.

As pointed out, these batteries do not like being deeply discharged, and if this is allowed to happen, the battery life can (and will) be severely compromised.

[skiingman]

the charging system is a one-size-fits-all-climates solution


Hmm, I take that back:

"Smart Charging, a battery current control feature driven by the engine electronic control module monitors the charge state of the battery, and can adjust or interrupt current flow into the battery. By keeping the charge of the battery within an optimal range, Smart Charging reduces the average battery temperature and contributes greatly to the battery's life span. The system also facilitates precise idle control, and even raises the idle speed to prevent battery drain in winter conditions and in other instances of high current demand."

Yay for clever use of the ECM. This was from a paper describing the Duratec HE which also has such neat features as an electronic thermostat.

[BigEndBob]

Thanks for the information.
Just looking into batteries and charging for use in Motorhomes.
Lots of info. on the net, but nothing like practical experience.
Doing a few experiments with a Concorde battery given to me from work.
I know its not a 'Leisure' battery but just seeing what happens.
At moment using it to drive a Philips 20W (100W equivilent) low energy bulb through a 150w inverter. According to a plug in meter its drawing 16W at 2Amp. Its a 25a/hr battery. Just want to see how long it lasts.
If such a battery was connected in parallel to car battery would it charge ok.
As i suspect a car alternator only ok for replacing whats used by starting.
But if i alternated between two batteries long before they became significantly discharged then they could be used, just a thought.

[west lakes]

Just looking into batteries and charging for use in Motorhomes


Make sure you include a split charge relay in system. It prevents discharging "normal" battery.
Leisure batteries are slight different design to car battery to allow for deeper discharge/recovery when using lower currents for appliances.

[ABX]

Hi BEB,

As i suspect a car alternator only ok for replacing whats used by starting.

If you fit a proper dual battery management system, that includes an automatic battery charge switching devise, your cars alternator is more than capable of charging an extra battery or even batteries. My car has a dual battery system installed and I normally charge the main (starting) battery and the second battery and occasionally, on trips, charge a third as well, all automatically and all without hassle.

A dual battery management system generally works like this:
After starting your car the system will automatically charge your main battery - the battery that started the car - until its voltage is around 13.6 volts (mine is a 12V system, 24V systems are available), then the system will charge the secondary battery until it is also at 13.6V at which point the system will maintain charge in both batteries until the engine is switched off.

The system, if installed properly, will always separate the main battery from the secondary battery during the discharge phase. The main will be left undischarged and ready to do its only job - start your car - the secondary will be discharged by the accessory loads that you place on it, such as the light you mentioned, or in the case of one large motor home I fitted out in 2003, the secondaries will power your laptop, fridge, microwave, lights, fans and air conditioning system!

To achieve this, make sure that when you install the secondary battery, the wiring for the starter motor remains on the main battery and the rest of the wiring and subsequent wiring goes on the secondary.

This will prevent you being stuck in a lonely place with a discharged main, as well as a discharged secondary.

All this is from my own experience as manager of Battery World here in my home town. (Mods, this is not an advert, as the business was sold after my departure and closed down sometime later.)

SLI batteries (Starting, Lighting & Ignition) do not like to be discharged to below about 80% of their full charge, roughly equivalent to the drain caused by starting the car two or three times in quick succession. If they are drained below this their useful service life is diminished dramatically, every time this happens, firstly, following a deep discharge of an SLI battery, you will never get it fully charged to 100% of the charge state before the discharge, secondly, SLI batteries suffer dramatically from sulphation when discharged. Simply put sulphation causes the lead to flake off the plates and collect in the mud racks in the bottom of the battery where it does more harm than good.

For a camping application you need a Deep Cycle battery. Deep cycle batteries have thicker plates and slightly different internal wiring, the thicker plates give the battery more 'voltage holding power' and resist sulphation much longer than SLI batteries.

The best type of deep cycle battery has only ONE plate per cell, this plate is about 6 feet long and rolled into a spiral, with fiberglass between the roll to prevent shorting but allow electrolyte flow. Spiral batteries resist vibration extremely well and have more lead for a given volume that plate rack batteries.

We never had a single battery present for a warranty claim with Optima batteries.

Just another disclaimer for the mods, I no longer have anything to sell, I left the industry in November 2006 and am now labouring for a mate of mine who owns a landscaping company while I get through my ab initio flying training.

This started out as quick reply and turned into an essay, but I hope it helps.

Cheers,

ABX:ok:

[ABX]

It has gone quiet?:sad:

[ABX]

That'll teach me to write a book in answer to a question!:\

[ABX]

One sentence replies for me from now on!:}

[west lakes]

It has gone quiet


I think question asked, question answered

[ABX]

Big Bob, have you got a photo of the Concorde battery that you could post here?

[GOLF_BRAVO_ZULU]

ABX. Please don't apologise for your comprehensive answer. Arguably, you have created a Forum standard reference work to everyone's benefit. An additional question from myself, if I may: are there any special care points in relation to gel batteries?

[ABX]

Thanks GBZ, although I'm not sure about the forum reference stuff.:ok:

Gel batteries mainly differ in one key point, but before I get to that, I'll cap the standard care:

1) All batteries like to maintain a high state of charge, no battery benefits by being discharged, especially for prolonged periods of time.

2) Keep the terminals clean to prevent corrosion. (much less of a problem with gel).

3) Take care not to overcharge your battery. All batteries have an inbuilt upper limit for both charge voltage and charge amperage, exceeding either may heat up the battery and cause a loss of water from the electrolyte. In this example 'over charging' does not refer to the length of time a battery is charged as the battery will self regulate its own charging - if the charging system is within manufacturers specifications - simply by accepting less and less charge as it nears its charge capacity.

This is the area where gel batteries differ from standard lead acid batteries. Most gel batteries are sealed, given that they are designed to fit into places and positions that cannot tolerate acid spillage, one good example is the gel (or Sealed Lead Acid <SLA>) batteries commonly found in those electric shopping carts that the elderly use to terrorize the rest of us pedestrians. When over charged gel batteries, along with any type of sealed battery, will heat up and cause high internal pressure, due to heat and vaporisation of electrolyte - be it gel or not - which often causes either the hard outer case of the battery to soften and expand or simply burst.

When I was manager of Battery World I always kept just such an example on my counter top as a visual reminder to customers not to over charge, one of my counter top batteries had, due to the conditions described above, expanded to roughly basketball size and shape, having started out half the size and square, another example on my counter top was two batteries installed in a uninterrupted power supply (UPS) that provided power to a business computer system, due to a charger malfunction these two batteries had been over charged, distorted considerably and fused together.

Needless to say the batteries on my counter top generated much discussion with our customers!

Short answer to your question GBZ, use them in the manner they were designed for and be particular that you don't over charge and it should be fine.

Cheers mate.:ok:

[Warm Ballast]

ABX - Just slightly off topic...... As I recall NiCad batteries in aircraft (AS350 for one), as part of their maintenance, require discharging to 0 volts and then are left for some period with a shorting strip across the terminals. What is the science/reason behind that?

[ABX]

Warm Ballast, I like that name mate "warm ballast". I'm guessing that's another name for SLF?

Nickle Cadmium (NCD or NiCad) batteries are different to all other battery types, including others that appear similar such as Nickle Metal Hydride (NMH) and Lithium Ion (LI or L-Ion).

I am a bit thin in regards to the actual science behind the reason, however:

The reason that NiCad batteries need to be discharged fully and then recharged fully is because the battery has a tendency to 'remember' its most recent state of charge. This state of 'memory' reduces the batteries capacity to hold charge, a condition that gets worse every time the battery is cycled (charged - discharged - charged) without being fully discharged. I have often witnessed this cumulative effect halving a NiCad batteries holding capacity even though the battery charger indicates it is fully charged.

There are special machines that will cycle NiCad batteries from fully charged to deeply discharged over and over again - over a two or three day period for example - which has the effect of 'breaking down or breaking through' this memory effect and restoring all but a fraction of the original capacity.

As for the actual science, I believe that it is something to do with an incomplete chemical reaction within the battery that accumulates over time, but all of my reading/learning/research on the topic was to do with the effect, its causes and its cures, not the actual science.

NiCad batteries shouldn't be charged if only half discharged, whereas NMH & L-Ion batteries can be 'topped up' when only partially discharged without a problem.

Cheers,

ABX

[Warm Ballast]

ABX - Thanks for that. I understood - to a point - NiCad's 'memory' problems, but to totally short a battery for ages seemed weird.

WB name? Well I do self load and kind of move around, hang out of and around lots of different Aircraft...... and no I don't jump out of them .....

[ABX]

WB, I don't jump out of them either, seems to me like a rush that I can do without!

[ABX]

An interesting discussion occurred at work today, and prompted this post, it went along the lines of the dangers posed by gases released by a lead acid battery being charged, and one of the boys watching his aunt, yes, his maiden aunt, have a look into a battery by the light of a match, resulting in a bit of a 'woof' sound and some quite un lady like expressions. Explosion, however, is not the only reason to charge a battery in a well ventilated area (& please, don't strike a match nearby!) I have seen good sets of tools/instruments and even an entire work table ruined by the escaping gases and aerosolized acid released during charging.

In the end I always placed batteries being charged inside a large shallow plastic tub on a table just inside the doorway of the workshop and prevented a lot of the damage that might otherwise have happened.

Had to have a bit of a laugh at Simmo's poor old aunt though...:}

... she was fine, only her pride - and Simmo's impression of her - was hurt.

[ChristiaanJ]

... whereas NMH & L-Ion batteries can be 'topped up' when only partially discharged without a problem.Thanks, didn't know that.
My old camcorder came with a nifty gadget to fully discharge the NiCad battery before charging; unfortunately I haven't found the same thing for AA size NiCads.

[west lakes]

Though not subject to "memory blocking" as Ncads, Ihave seen advice that suggests the other types (lap-top batteries included) be fully discharged regularly, perhaps monthly, to "extend battery life"
We use a lot of lap-tops at work and after a year or so some of the batteries are totalled by being on near permanent charge in vans

[ABX]

Quite right westy, it seems to be okay to leave your laptop battery on charge quite a lot, but they do appreciate being 'worked'.

I leave my laptop plugged into the mains all the time I am not using it elsewhere, however, I quite regularly discharge mine until the battery warning dialog box pops up (97% discharged) before putting it back on the charger. This seems to keep the battery reasonably healthy.

[GOLF_BRAVO_ZULU]

ABX You do realise that you have become the Forum battery Agony Aunt; and thank you.

We mentioned gel batteries earlier. Am I right in thinking that you can't mix "wets" with "gels", even if they are of the same capacity?

[west lakes]

GBZ
It depends on application, I would IMO suggest that is designed for same duty & of similar capacities no problem.
As I have a lot of additional lighting on my vehicle (floodlighting, beacons etc) I have used a split charge system for years. In the early days, cos of space constraints I used a gel as the "lighting" battery, though not designed for the job it lasted about 6 years.
I now use a leisure battery (nearly 9 yrs old) for same job. Loads on it can reach 15 - 20A.

[ABX]

GBZ, I don't mind being the battery 'Agony Aunt', I have asked many questions here in these fora and many nice people have been kind enough to answer them, some in great detail. I am simply returning the favour.

Anyway, I basically agree with westy on this.

Gel and acid should mix reasonably well together as long as normal parameters are maintained i.e., mixing a gel and a lead acid battery in a car system shouldn't be a problem at all - as in west lake's experience.

Interestingly you can also mix batteries of differing capacities together if need be, the theory being that as the combined batteries work together (as opposed to individually). The different sized batteries simply add up to one larger unit and charge/discharge together.

Or to put it another way, if you have three 12V batteries, lets say:
1 x 75 Ah;
1 x 95 Ah;
1 x 130 Ah;

and join them all together in parallel, they will then act like one big 12V battery of (75+95+130) 300 Amp hours.

Or, if joined together, when battery A is at 77%, then battery B and battery C will also be at 77%.

As I said in my post above, the main concern with a gel battery is that you don't exceed its charge/discharge capacity.

An interesting case in point is a product we have here, known as a "Thumper Pack", marketed by Waeco. These are sold as a high capacity battery unit for jump starting, or deep cycle applications. They are a very capable product and can jump start a car or truck or run a fridge for a couple of days. Most folks assume that they are a gigantic battery inside, however in reality they are simply 4 modest SLA batteries of approx 65 Ah, all wired up together and packaged inside a tamper proof box. (So the punters can't see all the "trade secrets" inside!)

Cheers,

ABX

[west lakes]

The other type of battery to give troubles are the ones fitted to intruder alarms, though lead acid they do need to be changed & checked regularly if not all sorts of problems start.
1/ If your mains supply goes off the system seems to activate, often as the sounder (siren etc.) has its own battery, sees the loss of power as the back up in the control panel is knacked and can't be reset.
2/ And this is possiblt the worst (funniest) is all is OK until power is restored, lost count of the number of times I've restored power late at night/early hours for half the alarms in an area to go off - usually followed by us staging a strategic withdrawl:ok: Had a look at one last year that did this (old lady on her own) the battery was a/ without any electrolite b/ had a hole in it & c/was deformed through heat.

So take the time to check yours and re[place every few years.


These are sold as a high capacity battery unit for jump starting, or deep cycle applications.


Can be seen in many locations in the UK, don't be tempted to buy a cheap one, I got given one and no way will it start my car (1.9l diesel). Go to a car parts specialist and get a decent one.

ABX maybe we should set up as consultants:confused:

[GOLF_BRAVO_ZULU]

Thanks lads. The questions were really in aid of a pal who lives on a narrowboat. Not my idea of a des res! but it is a low maintenance garden.

[balsa model]

If you have three 12V batteries:
1 x 75 Ah;
1 x 95 Ah;
1 x 130 Ah;
in parallel, they will act as one 12V unit of 300 Ah. No need to devide by 3.
In series, they could act as one 36V unit of 75Ah (smallest capacity) but only if you know what you are doing and are very careful in use. Not a practical setup.
If you must connect in series (to obtain higher voltage like 24V), then use identical batteries (manufacturer, model, and age) and connect them when they are flat. Then charge. Since discharging lead-acids to flat state costs you in battery life, you can use plan B: charge them separately fully, connect them briefly in parallel to further equalize the charge, and only then connect them in series. If the two batteries are identical it should be safe enough. Periodically you should check whether the voltage across all batteries is about the same.
I hope this helps someone.
bm.

[ABX]

balsa model,

You are quite right and I have edited my post above to fix the error. I can't type as fast as I think apparently!:hmm:

I defo agree that when connecting batteries in series it is possible to connect batteries of unequal capacity however it is best to use batteries of equal capacity. Also it is best practice to use the same battery type from the same manufacturer and all of the same age.:ok:

Dozens of times I have said to a truckie, "When you change one you should change them all" only to ignored and accused of trying to make another sale!

Cheers.