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Battery Charging: How Much Is Too Much?


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The typical gassing voltage of a lead acid leisure battery is 14. 4V, which if my understanding is correct, below this the majority of the supplied current is absorbed by the battery in the lead-acid chemical reaction, above this, some is used in the electrolysis of water, thereby producing oxygen and hydrogen i. e. gassing.

 

So if your battery charger kept the supplied voltage below 14. 4V does it matter how much current is supplied? CTEK and Amperor do 25A smart chargers. Would 30A be OK? What about 50A?

 

I know the battery voltage will increase as it charges so 14. 4V will be reached quick enough but for this Bulk Charge phase (I phase) is there a limit over which would damage the battery?

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Cotek an damper or are both multi stage chargers and neither will overcharge your battery, they both end up at 13. 8v float charge which can be left on indefinitely.

 

Ap

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Seems that another limitation might be temperature. Too high a charging current will heat up the electrolyte (note this is a different phenomenon to gassing) potentially causing it to boil which would increase the pressure within the sealed battery.

 

So, so long as the voltage is kept below gassing threshold and the temperature controlled, are there any other limits on charging current?

 

I've read some sources saying that C10 (i. e. 11A for a 110AH battery) should not be exceeded but there's no mention of why this limit exists, other sources have said it doesn't matter, so long as the gassing threshold voltage isn't exceeded.

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The typical gassing voltage of a lead acid leisure battery is 14. 4V, which if my understanding is correct, below this the majority of the supplied current is absorbed by the battery in the lead-acid chemical reaction, above this, some is used in the electrolysis of water, thereby producing oxygen and hydrogen i. e. gassing.

 

So if your battery charger kept the supplied voltage below 14. 4V does it matter how much current is supplied? CTEK and Amperor do 25A smart chargers. Would 30A be OK? What about 50A?

 

I know the battery voltage will increase as it charges so 14. 4V will be reached quick enough but for this Bulk Charge phase (I phase) is there a limit over which would damage the battery?

It wont matter what size charger you put on the battery as Audipartner said the Ctek and Amperor are 3 stage smart charges they have a battery detection feature which constantly records the state of the battery and decides what Voltage and currant to output. ..

 

One thing to watch out for though is many modern chargers have power supply function where it will provide a fixed 13. 5V (designed to power 12V side directly from charger) However if you selected power supply mode while connected to the battery it disables the battery detection feature and there is a risk of cooking the battery

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It wont matter what size charger you put on the battery as Audipartner said the Ctek and Amperor are 3 stage smart charges they have a battery detection feature which constantly records the state of the battery and decides what Voltage and currant to output. ..

 

One thing to watch out for though is many modern chargers have power supply function where it will provide a fixed 13. 5V (designed to power 12V side directly from charger) However if you selected power supply mode while connected to the battery it disables the battery detection feature and there is a risk of cooking the battery

 

With the smart chargers I've seen, the first stage is a constant current stage and the charger will output the pre-configured current until the battery voltage reaches 14. 2-14. 5V. So with a CTEK 25A charger, it will output 25A. But my point is what if you could configure that charging current? Output 30A, or 50A or 100A? Is there a bulk charge current that is too much?

 

Also, a 13. 5V power supply would be below the typical float voltage for lead-acd batteries so, as far as I understand it, could be left connected forever without adversely effecting the battery. Maybe I have misunderstood.

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The charge current is dependent on the voltage applied and the resistance of the battery. As the battery charges, the resistance increases and charge current falls. The maximum output of the CTEC MXS 5. 0 is 5 amps.

Brian

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Whilst I agree to your point, that's not how the bulk charge stage works on a smart charger. It'll output the voltage required to achieve a certain pre-configured current. As internal resistance changes, the voltage is raised in order to maintain that current. Once the voltage reaches around 14. 4V a smart charger will switch to the absorption stage and will operate in the manor you describe maintaining 14. 4V as the charge current reduces.

 

My point relates to that first stage - constant current. If the charge current is configurable, how much is too much?

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Have a google - there is a lot of info on t'interweb about this and it appears that you can almost do what you like depending on what the battery will accept and what the charger will produce. The max current that will go into the battery is a product of it's internal resistance, the voltage across it and the amount of current that the supply will deliver.

So if the internal resistance is low and the voltage is high then the battery could take almost as much as you give it whist presumably getting everso hot and possibly boiling the electrolyte. The thinner the plates and the more of them then are the lower the resistance will be - batteries for auto stop-start vehicles are constructed like this to give out lots of small high current bursts and to be recharged as fast as possible and so will probably accept a higher current than a conventional battery at the same voltage.

 

Whereas a proper standby battery which is designed to be left on float charge all the time is usually charged at about 10% of it's capacity and then floated at 2. 25-2. 3vpc (13. 5-13. 8v) although they should be given a boost charge every now and again to 14. 4-14. 6 to stir up the electrolyte. A lot also depends on whether they are sealed, maintenance free(not sealed, but vented), valve regulated, AGM or gel types as each will have a different charging characteristic and require different voltages and currents to avoid overheating and gas generation.

 

Ideally you buy a good quality battery from someone like Chloride, Trojan, Sonnenchein etc and you can get charge & discharge curves and a decent amount of info on how to look after them. Most mass produced batteries, even Exide (which look suspiciously like Numax)e nowadays seem to lack this sort of info.

2018 S-Max Titanium 2. 0 Tdci (177. 54bhp,180ps,132kw) Powershift + 2015 Unicorn III Cadz, Ventura Marlin porch awning

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The maximum currant a Leisure battery can take is what it is rated in for example if you have an 80AH battery and say use a charger of 100A the battery will cook as if you convert it to watts the battery technically can hold 960W (80x12) and a 100 x 12 = 1200 so a heating effect would occur which could potential cook the batteries but is rare unless you have a huge current like 200A then it would happen pretty quickly. . it also depends on the type of battery this is presuming it is lead acid

 

Now if you use an 80A charger the battery will be charged very quickly and will seem fine however this is not recommended as it puts an awful lot of pressure on the plates inside the batteries and they will buckle it will effect the long term performance and shorten the batteries life. .. Batteries are manufactured to be charged between 10% and 30% the size of the battery for optimal performance

 

 

Please note the same does not supply for starter batteries as these are designed different and the plates are a lot thinner and can withstand a high current for short periods of time. for example you can have a 60AH starter battery and 200A alternator and you wont have any problems but this is because a starter battery is designed to give high amount of energy in short space of time and not a constant deep discharge cycle.

Edited by caravantechnology
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OK, to take the hypothesis further, the battery charger I'm thinking about buying has a configurable charging current up to what appeared at first impression to be a ridiculously high 100A but maybe not so. It has a temperature sensor and alters the charging pattern based on it's readings. My leisure battery is a Numax CXV 110AH, which is purportedly suitable for both deep discharge and starting use, therefore, I assume it is built in such a way to allow high current draw and, conversely, high current absorption.

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OK, to take the hypothesis further, the battery charger I'm thinking about buying has a configurable charging current up to what appeared at first impression to be a ridiculously high 100A but maybe not so. It has a temperature sensor and alters the charging pattern based on it's readings. My leisure battery is a Numax CXV 110AH, which is purportedly suitable for both deep discharge and starting use, therefore, I assume it is built in such a way to allow high current draw and, conversely, high current absorption

It more than likely uses the temperature sensor as well as constantly analyzing the the state of the battery which is where current is proportional to voltage comes in again. .. Yes if you have a multi purpose battery then they will be able to withstand higher currents for periods of time. .

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No, that was never my intention. This thread was just to discuss what current would be too much and, it seems that so long as the battery is capable of withstanding it (i. e. starter compatible), the temperature is monitored and the 14. 4V gassing threshold isn't exceeded it seems there are no reasons why the charging current should be otherwise limited.

 

I was monitoring charge current the other day (yes, I know. ..need to get out more) and my 'van charger never got above 12A, even when the battery was 50% discharged and that was literally only for 30 or so seconds, yet it's capable of supplying 20A. My smart charger is not able to exceed 8A. I am under no illusion that supplying 100A is unlikely to happen in practice whilst staying under 14. 4V and especially as I never fully discharge my battery but that wasn't the point of the thread, which was to identify if a limit should be imposed if the bulk charging current was configurable.

 

If I do buy this unit, I think I will leave the charger it at it's default setting, which is 50A. That's 2. 8A at 230V from an EHU or genny, which seems reasonable to me. At 50A that'll bulk charge a 110AH battery from flat in just under two hours. ...or it'll melt it. ... ;)

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Check to see if the unit has PWM & not the cheaper option of the switching FETs

 

& as with all products nowadays check to see if its genuine

Paul B

. .......Mondeo Estate & Elddis Avanté 505 (Tobago)

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At 50A that'll bulk charge a 110AH battery from flat in just under two hours. ...or it'll melt it. ... ;)

I wouldn't tictag if I were you, there are plenty of experts on here but from my experience in the forces I can say that we were taught not to exceed 15% of the ah capacity as a charging current, the only exception to this being in order to wake up dead batteries.

 

If you charge it at too high a current you will definitely overheat the battery, buckle the plates and evaporate the electrolyte. Leaving it on the 50a setting is ok in a sense as long as the charger is working correctly and doesn't decide to use the full 50a, should a fault condition occur and it does put 50a in I think it would be both dangerous and damaging to the battery.

 

We used to have a large bulkhead mounted charger that you could dial in any charge current you wanted depending on what was attached, thermometers were always placed in the battery to ensure that we kept the electrolyte within safe limits, keeping to the correct parameters is more important than increasing the current.

 

My amperor is a 25a model, but is designed to work with a battery permanently on float, with no battery attached if necessary, and as a 3 stage charger if required by flicking the switch.

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I can say that we were taught not to exceed 15% of the ah capacity as a charging current, the only exception to this being in order to wake up dead batteries.

Yes, I've seen this (well, actually 10%) from other sources but no reason has been given as why this limit exists.

 

If you charge it at too high a current you will definitely overheat the battery, buckle the plates and evaporate the electrolyte.

In terms of overheating, this unit has a battery temperature sensor and, according to the literature, modifies the charging profile based on its reading. I dare say, it's not going to let my battery boil. In terms of the plates, yes, I've heard this for deep cycle batteries but my battery is purportedly a combined starter & deep cycle battery. It can kick out 800A (CCA) so I suppose my contention is that it can handle a mere 50A coming back in.

 

I know that there's a rule of thumb stating C10 (or 15%) but is this there just to avoid overheating and buckling plates? If so, if these were to be handled by technology and a smarter build, does the rule of thumb remain valid?

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I was taught that the suggested limit existed to avoid temperature initially which was then followed by buckling, as I say the temperature sensor will limit the current unless the sensor fails, and unless there is an additional fail safe to cut the charger out it will boil the battery was my concern.

 

I think I've been conditioned to think about what ifs and fault conditions as opposed to what happens when it all works correctly. You should get an old car battery and take the tops off, find someone with a big charger that you can manually select the amperage (possibly an auto electrician/garage/someone you might know?) and whack it up sit there and watch what happens, when you see how lively it gets it gives you a better feeling for the chemistry involved! If you have a charger like that we used to be able to get some life back into abused batteries, the RN didn't have any desulphating equipment on board, all we had was the monster charger and a big current capacity test set - both were way before things got "smart" and would have looked quite at home on the set of a boris Karloff film!

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This is the sort of equipment era I was used to in the RN. You can imagine how big the battery charger was!

post-55551-0-79739200-1390347639_thumb.jpg

post-55551-0-94040800-1390347924_thumb.jpg

Edited by sleepyfolk
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This is the sort of equipment era I was used to in the RN. You can imagine how big the battery charger was!

attachicon.gifimage. jpg

 

Did you use a CTEK MXS 5. 0, by any chance? ;)

I was taught that the suggested limit existed to avoid temperature initially which was then followed by buckling, as I say the temperature sensor will limit the current unless the sensor fails, and unless there is an additional fail safe to cut the charger out it will boil the battery was my concern.

 

Did some more reading, there's a configurable time limit for the bulk charge.

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Did some more reading, there's a configurable time limit for the bulk charge.

More stoneagetek than ctek!

 

Have you got a link - that sounds interesting

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The battery can absorb a set amount of energy once this limit is reached then the energy must be transformed into some other form. This could be heat or a change in type of chemical energy turning the water into it's component parts of hydrogen and oxygen. Even when it has not reached it's limit it tends to absorb less of the energy provided as the limit is approached.

 

However provide a battery with just the float voltage also presents two major problems one is the time it takes to charge the battery the other is the cells becoming unequal some being over charged and some under charged.

 

There are a number of ways around the problem. Simple is a poor quality transformer and simple rectified so as the charge voltage rises the current will rapidly fall and use users observations as to when every cell is gassing limiting the charge current to a very low amount like 1/20 of amp hour rate at 12 volt. These will equalise the battery but do not allow for it to be used while on charge.

 

Next is the car method and a higher than float voltage is selected between 13. 8 and 14. 2 volt but again rather hit and miss.

 

Another is the stage charger the fork lift would have three stages. Bulk often around 100A until set voltage was hit then a equalising charge often limited to 10A and after set time it would switch off. This of course needed a battery to match the charger and again no draw from battery while on charge.

 

There is also some variations on this with change from bulk to equalising having the next stage measuring the current and switching once a current limit is reached to a float charge rather than off this once charged will allow the battery to be used but not while giving the bulk charge as it could result in over charging. Often a timer is also included as a back-up and it does need matching to a range of batteries.

 

The next a pulse charge this is far more clever (Smart) and it switches off every so many seconds and measures the decay in voltage to decide the mark/space ratio (on/off time) between pulses in a similar way to a switched mode power supply. There are some variations in how they work but this type is much more able to be used while the battery is also supplying items and is the way most solar panel chargers work. This link http://www. sterling-power. com/products-altbatt-benefits. htm shows how this system works it has some good graphs.

 

All these assume deep cycling of a traction battery but where the battery is for most of it's life maintained at float voltage then a simple voltage regulated charger at 13. 2 to 13. 8 volts is good enough you will not flatten and recharge battery so equalising is not really required. However to do this the charger must be able to supply all the caravans demands so often it needs to be around 25A.

 

There are of course hybrids which combine or allow the user to switch between functions like forcing float charge so when always on mains float only is used but when coming off somewhere without power stage charging is selected to both fast charge and equalise.

 

Another option is to rely on the battery to fill the gap between demand and supply with a well under sized charger for example 5 amp this is of course what happens with solar panels and there is really only one option and that is the pulse charge method. This is also what the CTEK charger does.

 

For users always on mains there is little problem but where there are times without mains battery care is vital. So we look at two tell tail signs. Heat and loss of water. Even forklift batteries only needed topping up once a week so any more than that and something is wrong. And hand on side of battery nothing more than warm about 40 degs C max even in hottest summer sun over that the vent system can't cope.

 

What of course is another problem is can the equipment take 14. 8 volts or pulses and BS7671 does limit volts to 13. 8 but I would not expect a problem with caravan equipment however using household MR16 12 volt lamps will clearly be asking for them to blow.

 

I am sure some submariner can tell us how batteries were charged in submarines clearly in the shortest time possible, but be it a forklift or submarine it really does not relate to modern caravan. The leisure battery is a half way between vehicle and traction. When you read details on modern stage chargers they have options for type of battery with phrases like fleece and ask salesman what type of battery it is and you get very little joy.

 

Guarantee is also a little odd quite common for 2 years fitted to car and 6 month for same battery fitted to a taxi. I found returning batteries to manufactures one got some very different deals. Manchester batteries from Abergele never refused a return but Oldham batteries were a real pain. This was some years ago so may have changed but what was a surprise was how the less known make gave better service.

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"Snip"

 

 

The next a pulse charge this is far more clever (Smart) and it switches off every so many seconds and measures the decay in voltage to decide the mark/space ratio (on/off time) between pulses in a similar way to a switched mode power supply. There are some variations in how they work but this type is much more able to be used while the battery is also supplying items and is the way most solar panel chargers work. This link http://www. sterling-power. com/products-altbatt-benefits. htm shows how this system works it has some good graphs.

 

 

"Snip"

 

This is why I put "Check to see if the unit has PWM & not the cheaper option of the switching FETs" in post 14

 

PWM allows the battery charger to fully charge without overheating or gassing the battery as well as desulfating, equalising & and increasing the charge acceptance of the battery.

 

But only if its a real one ;)

Paul B

. .......Mondeo Estate & Elddis Avanté 505 (Tobago)

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Looks good - note the size of the input power cables & input fuses. Obviously sized to minimise voltage drop rather than just current carrying capacity. Keep us posted on how it works and whether your battery copes - I'd guess that a single 110a/h will struggle.

2018 S-Max Titanium 2. 0 Tdci (177. 54bhp,180ps,132kw) Powershift + 2015 Unicorn III Cadz, Ventura Marlin porch awning

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I've been thinking about that, even to whether I could 'extend' the battery compartment to take two batteries (there's two much gubbins on the inside). I could make the wet locker into a second battery compartment but it's the other side of the 'van from the current battery and PDU, meaning long cables.

 

I could of course fit one next to the gas cylinders. ..I mean, what could possibly go wrong? ;)

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