Battery Charger amp output

spade · Member

Battery Charger amp output

oldtrack123 · Guru

Hi Spade

Provided it is a good multistage charger with correct voltages for your battery type, it will be OK

justcruisin01 · Guru

Spade, The condition of a battery, as in state of charge, will determine how much charge--as in amps - the battery will accept. The size of the charger only controls the maximum amount of amps that can be supplied.

Eg, if you connect a 40amp charger to a fully charged battery then you have a state of nill charge being applied.If you have a 90% charge then you may only need a 10 amp input to bring it back to full.

If you have a multiple stage charger it cannot damage the battery, thats the purpose of multiple stage, you have a boost, absorbtion & float. Float is where it just maintains a full state of charge, then when there is a load applied to the battery the charger will move to a higher state of charge to compansate the load.

Peter_n_Margaret · Guru

A little different because it is limited to a lower maximum voltage, but your alternator that charges your crank battery would have a maximum charge capability of at least 80A and that does not damage your battery.

Cheers,
Peter

jimricho · Guru

Leaving batteries connected in parallel is much more likely the cause. In the past this was always considered bad practice. Early in my career as a "wet behind the ears" technician I did do this and experienced the life shortening effects of parallel connecting batteries, much to the displeasure of my employer at the time. It seems that some manufacturers of sealed ("valve regulated" for the pedants) batteries such as AGMs are giving this the ok these days.

If so steps must be taken to ensure the batteries are, and remain, identical in every way, a near impossible task with flooded (wet) batteries, and the charge and discharge currents are identical for each battery. This requires a number wiring precautions to be taken that are beyond the scope of this thread.

At the time of my "misdemeanor" with the batteries above, an experienced engineer (the one who took me to task) explained that as the batteries age they try to equalise each other causing charging and discharging currents to flow between them. (his explanation, not mine)

-- Edited by jimricho on Tuesday 30th of August 2011 09:10:21 AM

Bros · Member

jimricho wrote:
In the past this was always considered bad practice.

-- Edited by jimricho on Tuesday 30th of August 2011 09:10:21 AM

Well I always thought that was the case however from experience I have found that statement to be doubtful with deep cycle batteries. I have found the terminal voltage of a new battery and a stuffed battery (no disasterous internal failure) to be the same. The difference is loss of capacity.

An old battery can can have a nameplate value of 100Ah but when a capacity test is done it may be as low as 20Ah but showing a good battery by terminal voltage but will have a higher internal resistance. This then limits the output so it stops delivering output and instead the good battery continues on to supply the load.

justcruisin01 · Guru

RICHO WROTE, At the time of my "misdemeanor" with the batteries above, an experienced engineer (the one who took me to task) explained that as the batteries age they try to equalise each other causing charging and discharging currents to flow between them. (his explanation, not mine)

This is true, & if one should fail completey it will drain the other to a point that it can fail as well.

jimricho · Guru

Bros wrote:
jimricho wrote:
In the past this was always considered bad practice.

-- Edited by jimricho on Tuesday 30th of August 2011 09:10:21 AM
Well I always thought that was the case however from experience I have found that statement to be doubtful with deep cycle batteries. I have found the terminal voltage of a new battery and a stuffed battery (no disasterous internal failure) to be the same. The difference is loss of capacity.
An old battery can can have a nameplate value of 100Ah but when a capacity test is done it may be as low as 20Ah but showing a good battery by terminal voltage but will have a higher internal resistance. This then limits the output so it stops delivering output and instead the good battery continues on to supply the load.

I haven't had any first hand experience of the particular situation you describe but I'm inclined to think that the long term effect would be reduced battery life of the "good" battery.

You also cover only one type of battery failure and your phrase, "(no disasterous internal failure)" alludes to this. I recently read of an experience a reader of one of the popular caravan magazines who had a battery bank explode causing considerable damage to his/her rig. The magazine's resident "expert" referred the issue to an engineer in the battery manufacturing industry who diagnosed the most likely cause as being a condition known as "thermal runaway" caused by a fault in one battery placing a severe discharge on the other.

I always believe the better option for larger battery capacity is to install a large single 12v battery or two large 6v batteries connected in series, this is electrically identical to a single battery as in both cases the battery bank is internally made up of six 2v cells in series.

If this is not practical an alternative is two 12v batteries connected via a marine type battery switch that gives the option of individually selecting batteries, or parallel operation of both batteries. The "Off" position on these switches also isolates the batteries from each other.

I have a mate who has 2 large 6v truck batteries (ordinary wet cell types) in series that are still giving good service after 10 years use. He mostly uses a solar panel to keep them topped up and I suspect they rarely get deeply discharged (another factor in battery longevity).

Bros · Member

If you Google Parallel batteries there is very little negative comments there mostly positive and disastrous internal battery failure is rare and less common in "Gel" type of batteries from use however overcharging can cause battery failure.

I have two batteries in my van but I switch between the two mainly for the reason I like to know what I have left.

gubby · Guru

A lot of new trucks (eg Kenworth) run a 12 volt system, they have three twelve volt lead acid batteries mounted in parallel.

oldtrack123 · Guru

Hi Bros

RE:" [1]Quote Well I always thought that was the case however from experience I have found that statement to be doubtful with deep cycle batteries. I have found the terminal voltage of a new battery and a stuffed battery (no disasterous internal failure) to be the same. The difference is loss of capacity.

[2] An old battery can can have a nameplate value of 100Ah but when a capacity test is done it may be as low as 20Ah but showing a good battery by terminal voltage but will have a higher internal resistance. This then limits the output so it stops delivering output and instead the good battery continues on to supply the load.[End quote ]

[1]it is quite common for batteries to charge to full voltage & not to full ORIGINAL capacity

In fact it start from the very first cycle The gradual loss of active material & minor sulphation starts the slow loss

You are quite correct you can have a battery down to 10% of it's rated capacity but showing 12.6v app when charged to IT's maximum

It will charge to that voltage in a very short time

[2]the lower output is more related to loss of active material plus possible residual sulphation

Thre are pros & cons for parallell operation

However it is not the bIg NO NO that many make out

If one battery developes a more than normal self discharge it will pull the other down to i's level

The one danger is a possible dead short in one, not to bad with just 2 parallelled, but if many are paralleled that short current coud be massive & cause fire & explosion

That is where these stories come from

OF course if you had a massive diferrence in capacity say a 40a/hr & a 200ahr in parallel & the smaller developed an internal short that could give just as big a problem

Peter

-- Edited by oldtrack123 on Wednesday 31st of August 2011 09:06:12 PM

jimricho · Guru

A couple of further thoughts here...

I'm not familiar with truck wiring but it does occur to me that in the Kenworth example above, the truck is being used day in day out whereas many caravans are stored for significant periods. Disconnecting the batteries not only from the load but from each other is a sensible precaution when in storage. The installation of a marine battery switch as suggested earlier is ideal as simply switching it "off" achieves this.

"Spade" didn't specify what type of batteries they were, but I've noted from reading battery data sheets that many sealed (VRLA) battery manufacturers imply that cheaper (or older) style unregulated chargers are not recommended for use with their products. This would include ones that automatically switch to a float mode when a full (or near full) charge is reached. (for the techies this is due to the ripple voltage component). Modern "smart" chargers provide a much smoother DC output and are recommended.

Getting back to the original question my recommendation would be that a good quality "smart" charger such as a Ctek (or similar) in the range 15 - 25 amps would be fine for the job. Shop around as prices can vary quite a bit.

spade · Member

The batteries are the type that require periodic topping up with distilled water

jimricho · Guru

spade wrote:
The batteries are the type that require periodic topping up with distilled water

All the more reason to avoid leaving them connected in parallel.....

two options..... (I'm assuming that your existing batteries need replacing)

1. Replace the batteries with two 6v batteries (similar in physical size to your existing batteries) and connect them in series, ie battery "A" negative terminal to the negative wire and the positive terminal of "A" to the negative terminal of battery "B" and the positive terminal of "B" to the positive wire. This will give you 12 volts and emulates a single 12v battery. Large 6v "truck" batteries would be fine for the job.

This would be my preferred option

or..

2. stay with the parallel operation (if you must) but install the battery switch as suggested earlier... this is the switch and they are readily available at marine suppliers....

(note that this switch is suitable for the parallel connection only)

Re the charger... the "smart" charger suggested previously would still be a good investment and worth the extra cost.

When the rig is not being used there is no need to leave the charger continuously connected as a once a month top up is fine, in fact this is preferred if not using a smart charger. Make sure the battery(s) are disconnected from the load when stored (also from each other if arranged in parallel) Note that if you opt for the 6v in series solution there is no need to disconnect them from each other.

justcruisin01 · Guru

One of the reasons for battery failure is the use of a very small battery charger, often called a trickle charge.

As a battery discharges it creats a coating of scale on the plates, when using a charger with good amp output this creates very small air bubbles in the battery, this in return causes movement of the acid which shackes the scale off the plates.

In using a trickle charge this does not remove the scale because there is not bubbles created because of the lower volts & amps. The scale builds up , creats resistance & if two plates end up touching then its game over.

Elle on Wheels · Guru

In the light of all the comments, if setting up a system from scratch with a view to just running the basics - a light and maybe a tv - I get the impression it would be better to get a couple of 6v batteries and hook them up in a series - is that the reccommendation from all you experts?
cheers
Ellen

blaze · Guru

1 Small 12v of about 55 amp/hrs would suit Elle, its when you start running 12v compressor fridges and inverters you would need to look at a bigger system
cheers
blaze

jimricho · Guru

Elle on Wheels wrote:
In the light of all the comments, if setting up a system from scratch with a view to just running the basics - a light and maybe a tv - I get the impression it would be better to get a couple of 6v batteries and hook them up in a series - is that the reccommendation from all you experts?
cheers
Ellen

A single 12v battery would do fine. No need to mess around with multiple battery banks, series or parallel connected. As "Blaze" suggests 55ah should be ok and 100ah would be more than adequate, that's all I use (100ah) in the Goldstream. I have a 50ah auxiliary battery in the tug to run my "Bushman" fridge that remains in the vehicle and recharges whenever the engine is running.

An AGM battery combined with a "smart charger" (7-10 amps) is worth the extra cost as AGMs have a longer lifespan, are maintenance free, and more tolerant to deeper discharges.

"LED" lights are very economical in their drawdown from the battery and well worth considering. A small 12v TV is also better than messing around with inverters.

-- Edited by jimricho on Monday 5th of September 2011 08:02:29 AM