What Rate of Amps Can I Charge Deep Cycle Battery?

Most deep cycle lead acid batteries are designed to be charged in 6 hours. So divide the AH rate by 6. The 6 hour design is so they can be charged between work shifts of 8 hours.

Look on the battery manufacturers web site is the best thing to do.
Del

A good rule of thumb is the slower the charging rate, the better and 1/10 of the AH rating is a good safe charging rate for most battery chemistries/designs. As a previous poster stated, many deep cycle batteries are rated for 1/6 AH charging rate, and while you might be able to do that safely, there will be a reduction in cycle life at that rate.

You are already using a 25 amp charger. If this is an intelligent charger, you will find that it rarely charges at 25 amps but some value based on where it thinks it is on the charging curve. The MPPT might not care about the curve, so 10 amps would be a "safe" rate - you could verify this to see what the 25A charger is delivering in mid-charge. At the very worst, your 10A rate will take a little longer than the generator, but it will do the job.

Thanks for all the helpful replies (Del - good idea but the batteries don't have the makers name on them, cheap chinese made).

When we start a car the battery takes a hammering & is then very quickly recharged by the alternator, which with its built in voltage controller does not harm it.

I' m thinking that if I somehow marry a 100amp car alternator to a chainsaw engine (or similar) then the batteries could be recharged in a couple of hours or so, whilst still providing power to the inverter. (Not shown in the diagram). Would welcome any comments as to whether this a viable charging solution.

kebang

Your scheme must utilize a good solar charge controller, which will adjust output current (of course that current must be available, as in the PV panels must be exceeding the output maximum parameter of the controller. What is that requirement? It depends on the state of charge of your battery bank. Although your system is small, demand can occur at any battery state of charge. The rate of discharge (which will depend on both the quantitative limitations (specs on the battery bank) and whether the genset and charger, which will likely not have fixed output, because the charger will modulate the output and current voltage into the battery bank, or the solar output, which is by definition variable based on insolation on the panels, is actually on. A good solar controller (MPPT) will, however, be able to modulate amps for charging while maintaining the most efficient charging voltage. One final point, you can pick a few operating points, and make the correct charge regime. The complexity arises when you have to deal with variables in demand, time of use, voltage and charge current availability. Even with top of the line equipment, it will be full of compromises.

Although technically, there may be a reason you would not want to keep your bank at 100%. practically you will want to keep your bank at 100%. Why do you have a battery bank. So you don't have to run the genset. If you do run the genset, you want it to run the least amount of time in a 24 hour period, which means solving the demand question. But hardly any residential system has hard demand curves, and no solar PV system has hard production curves. Once again, practicality forces compromised in performance.

Hi PFR,

Thanks for considering my problem!

This is not meant to be a solar power system operating on a daily basis, or permanently connected. The solar array is only connected to the battery bank when a brown out occurs and there is a 20amp load on the system.

I don't think the 320watt solar array connected as shown is likely to cause damage to the batteries under these circumstances. It would of course be capable of causing irripairable damage if left connected when there was no load on the batteries. (If they were permanently connected I would use a solar charge controller.)

Assuming you want your batteries to last a long time, it is best to avoid charging too fast (as someone has already correctly stated) and avoid charging above around 70%.

This will also have the second effect of increasing the battery's efficiency, as above 70% SOC, the efficiency drops dramatically....

Charging to 100% needs careful temperature monitoring to adjust the charge levels. Charging only to 70% means that you can as good as ignore any effects of temperature - assuming that the charger is not over sized for the battery.....

If you have all 4 batteries in parallel, that is also not good for the long term reliability. The weakest battery will get overcharged and made weaker, till a cell in it gives up completely. Then you usually have to get rid of the battery.

Remember, not only is every battery an "individual", but each cell in that battery is also an "individual".

Which is why it is probably best never to fully charge or fully discharge a battery, as every time you do that, the weakest component is stressed....

A good way to help this is to have a good intelligent charger for each battery that does not charge fully. Gassing usually starts somewhere around 13.6 volts per 12 volt battery, so that is a good point to stop further charging.

Going below 12.6 volts for long periods can start sulphation....reducing a batteries capacity.

There are electronic units that placed across a battery, give it a jolt of power every few seconds that appears to remove sulphation and prevent it in the future. I believe in them but many don't.

A battery needs to work its "muscles" to stay fit for a long time I feel....

There are many battery web sites, all with different opinions, battery university is not bad......

Follow safety rules as if any gas is produced, his can be ignited with naked flames, any form of sparking from wrong clothes for example......

Therefore good ventilation and protective clothing, as well as supplies of fresh water for washing - just in case!!

Best of luck.

Andy,

Your rcommendation to only charge to 70% SOC is a false economy, as it requires almost twice the bank to provide the same autonomy. In an emergency power system, potential demand drives equipment specs. The cost of reducing max SOC to 70% (by increasing battery bank size) compared to the cost of decreasing battery bank life by increasing charge capacity does not make sense. Technicaly, you are correct. Practically, you are erring in your design. Cost and operation over time equals efficiency. The more cost effective system, that provides power specified, utilizes the full charge capacity of it's batteries, Lead acid, nickle iron or lithium; AGM, or flooded, and does not attempt to increase life by reducing charge capacity.

I am an advocate of the othe side of your argument, limiting maximum state of discharge. We currently design for about 50% in most systems.

I disagree.

Actually, keeping to 70% or less gives as far as I can tell (my caravan battery is still good), a VERY long battery life, even if not infinite. I bought my caravan leisure battery in 2003 or 4 and it is still going well....using my design of charger.

It is also sized to allow 70% SOC to be more than adequate for more than a week of water pump and lighting!

Assuming for a moment that it dies in the next 6 months (though I feel that to be MOST unlikely), it will have probably achieved around double or more the usual life of a battery that has been charged to 100% regularly......that is a HUGE saving.....not forgetting the need to find and buy a new one, drive to get it and and and and.......

All in all, I find that its better to be careful with charging, I believe that it saves time and money as well as mostly avoiding that dangerous and explosive gas developed when charging above 70%.

Also efficiency drops dramatically above 70% SOC, for a battery type that is not that efficient in the first place......many do not even know this, though I did mention it before!!! This point alone is simply forgotten or ignored.

Plus, you only need to top up with water every 2 or 3 years or so.........

Submarine batteries can achieve 50 years or more old with careful usage and maintenance......having served in several subs over its lifetime.

Telephone exchange batteries can also get very old..... I am assuming that the still use huge LA ones as they did years ago.....

Here is a fun website with some good infos that believes "Bigger is Better!" for a longer life it would seem:-

otherpower_battery_compare

But if a 2 - 5 year lifespan (heavily depends also upon battery quality of course) and the gassing and maintenance are your "bag", please do not let me stop you. Each to his own.....

Remember, the OP said they were cheap Chinese ones......which will probably not take much abuse of any sort.....

Andy, Thanks for suggesting the 'battery university' site - I've spent the last 24hrs pouring over it!

I'm still struggling to get my head around how a car battery can accept a fast charge from the alternator (which is can deliver 100+amps) & still easily give 3+ years service.

To keep my post short I descibed the batteries that are currently on order from CDR King Philippines, they haven't arrived yet so at the moment I'm still using my 'car battery' bank of 225ah, which has survived now for 4 years. (although it originally was 300ah until one battery died a year ago)

If car batteries can stand this type of fast charging from the alternator then I'm reconsidering my battery order. I can by a 35amp alternator locally for the equivalent of $55 (US). I can by a small 4 stroke stationary engine for the equivalent of $110. I think a practical experiment may soon be undertaken!

Car batteries are a different sot of LA battery. They are designed to take a rapid recharge and to also give a very high "cranking" amps for engine starting.

The HATE being under 12.6 volts for long (hours to days is enough) periods and may be completely useless after one single full discharge. For which they are not designed for...

They are designed to be stored (not used when car not running for example) in a fully charged state.

They don't like extreme cold or heat. After a few years most need regular topping up, though the car charging system makes this different from make to make....

They are also cheap...."you pays your money and you makes your choice!"

With careful usage and quality charge control, they can have a good long life.....its mainly the high charge voltage/current of modern cars that eventually kills them off (usually in winter!)

Leisure and deep cycle batteries allow a far longer useful life in solar systems but at a much higher cost!!

Andy,

In your (Caravan) emergency power system, if it will supply your demand while meeting your autonomy equirements, you have siginificantly oversized your battery bank, if you only charge it to 70% SOC, and use 40% DOD. My experience, and my research, shows no such endorsement of this premise. In fact, periodic overcharge in flooded batteries is universally recognized as essential. (equalization). Dealing with potential gassing should be staightforward.

I am suggesting that using that real number (potential power demand/supply availability, which you must commit to to design the system) or trying to determine watts available at any time, is what this gentleman should be using as criteria for battery bank sizing. You can state that your Caravan system is still going well, but that hardly seems like a good analysis. How much power is available for what length of time between available charging regimes, if there is more than one, (as in this case; solar and genset) what operating schedule and variability of supply is there?

I believe US subs use (and have for over 50 years) Ni Fe banks, which have a fundamentally different electrolyte design and can have almost unlimited life. They are bigger, heavier and more expensive. They hardly offgas. They can be abused, completly discharged, even to reverse polarity, and be revived. The bigest issue is case and conductor life and connectivity issues. I'm not a chemist, but I know one who works extensively with them. They may be a great candidate for utility scale storage stations. He is working with RR car size systems.

When I was on subs they were Lead Acid. But it is a week or two ago!!! ( I was Andrew, in the Andrew, on HMS Andrew, then the last WW2 Sub operating in the RN!)

My caravan battery is the normal power supply for the water pumps, toilette and lighting....we have no mains lighting, only mains usage is a battery charger, my design.

But I have to mention up front, you again ignore the dangers of the gas (mix of hydrogen & Oxygen) released with vented LA batteries when charging to 100%. May I ask why you continue to do that? Its a very important point that ignoring has cost many people a loss of sight and burns.....you should NEVER ignore that point.

I do agree that my testing is not really quantifiable....I am not doing this usage for you Guys, I do it for me.....

But do not forget, Batteries that are degrading take a charge faster and faster, assuming the same charger, due to a lowering of capacity (the "tank" is getting smaller and smaller, and fills quicker!) as it ages.

My caravan battery still takes about the same length of charge time to achieve its 70% (the charger starts charging at 12.6 volts when mains is available).....a reasonable indication (if you REALLY know and understand LA Batteries) that it has not significantly aged....as capacity has stayed about the same.

Loss of capacity is a well known factor as a battery ages.....

Cost is important for me. With my charging sequencing I am saving money AND having great holidays and everything works as it should.

On CR4 (with many others here) I tell you about my experiences and you can read what you like into them.....I am sharing....

You are not the first not to understand what I am doing or why with my battery.....but it works!

If you need further infos about such batteries then look here, especially at the exploded battery.....:-

Lead_Acid_Battery

For example:-

When I tell people that I have installed in each room (years ago) radiators approximately 4 times the area needed by plumbers charts/infos, but feed them with relatively cool water, usually 40-55°C. Below the temperature that forces the secondary scaling.....

I achieve rapid heating of the rooms (whole house is fully insulated) and the radiators will not burn the hands of any small children visiting. The temperatures will just promote rapid "hand" removal from the heat source, without damage.

Also, the rads lose temperature as the room temp rises and stabilizes......then just an occasional hot squirt from the room thermostat....but they only get hot is when the system starts and only then....

Plumbers do not understand that........but they are usually not the brightest of sparks anyway...... They are only good at padding bills....or buying fishing boats!! (not with my money!!)

The dangers of hydrogen production as a byproduct of a charging regime are well known. There are very safe ways to deal with those dangers.

So are the dangers of 20 gallons of gasoline in a portable steel or plastic container, moving at 60 MPH, within a few feet of an internal combustion engine with temperatures exceeding 500F at the exhaust ports. It is just not rational to fear it. I have never seen nor spoken to anyone who has been injured or even involved with anyone who has been injured or exposed to a hydrogen issue. I am sure people have been severly injured.

I have battery experience. I am trying to find research that supports your theory. Help a brother out.

A very good point, which is why I have only driven Diesels since around 1986. Partly because they are economical, partly because they remain economical even when pulling heavy trailers and partly because they seldom catch fire!

Where gas (petrol) can ignite from a spark above something like -60°C, Diesel needs to be well over +40°C - quite a difference!!! (temperatures from memory only! May vary slightly in fact.)

Cars with 20 gallons of petrol, not many of those around (at least in Europe!)!!! For anyone interested there is a web link here:-

10-cars-that-go-further-on-a-tank-of-fuel

Quite funny and interesting!!!

I have never run across anyone else bothering/trying to extend the life of LA Batteries up to now....in that I am probably the first...

So I did some online research (which you could have done yourself!!) and found the following web pages that appear to give reasonable advice:-

Battery University article on_how_to_restore_and_prolong_lead_acid_batteries_lives

This person is mainly uninformed about all the factors:-

http://www.instructables.com/id/Increase-battery-life-for-electronics-1/step6/Increase-lead-acid-batterys-useful-life/

The second post here is funny and not wrong!:-

http://electronics.stackexchange.com/questions/23658/a-battery-charger-which-can-extend-lead-acid-battery-life

You should also learn about the " Peukert Theorem", which is covered a little here:-

http://www.vonwentzel.net/Battery/00.Glossary/

Best of luck....

You wrote:- I am trying to find research that supports your theory. Help a brother out.

Have you ever thought "out of the box?"

Maybe I am a pioneer!! The modern day German Edison?

Maybe not enough good research has been done before I came along!!!!

Maybe I am a ground breaker!!

Maybe you should do the same as I have been doing all these years instead of just querying, copying, moaning and asking for help!!!

Maybe someone here might show some good manners and appreciation for my diligence and GREAT work!!

MAYBE.......

I could get very old waiting for any of those maybes to change.....

But don't forget, YOU HEARD IT HERE FIRST ON CR4!!!

Andy,

I've not pasted or copied anything. I really enjoy reading and learning about all kinds of engineering puzzles. CR4 is fun to read, for me. I reply when I have a good understanding and can shed light, or when I'm curious about a question that I don't understand. People are generous here.

Your links are good basic battery primers. There are no references in them to extending life by reducing max SOC. There are plenty about cycle count, and the ability to reduce cycle count by reducing DOD. And of course, avoiding any overcharging by using a modern charger that is at least going to modulate and taper for the last 10%.

I'm only stating the most obvious, that for a given power demand, sizing a battery bank to supply only 70% of its rated capacity will require, with a maximum 50% depth of discharge, twice as many cells as one sized to be recharged to 95%. Including conductors, fusing, racks, square meters ,etc. Your assertion is that it is economical. Mine is that it is not. If it is, I want to know about it, because I should be designing systems this way.

I think I stated what is important for me, as a private person quite clearly, so why should I need to qualify it with anything else???

I also stated (several times) some safety points that I personally find very important, ignored by a lot of now blind people.....

None of which interests you! So our areas of interest are not really related it would seem....

You will not prove me wrong simply by insisting that you are right, take a lesson from Hitler on that score!!!

I am happy with the way my setup works. It has been proved thoroughly over many years and several changes. Its very reliable. It costs me very little to run as after the original battery crapped out (caused by the previous caravan owners crap charger I believe), there has not been any further batteries needed.

I am now with the mark II version of my charger, but it has only very minor changes over and above the Mk I, that further reduced the amount of mains power needed to charge, made the charger even quieter and cooler so that I could sleep better (the charger sits under my bed in the caravan!)....

The Mk I is in a friends RV, where it has given further sterling service for him and his family for 8 years now.....his RV is so loud he cannot hear either the fan or the relay!!!

So why don't you go away and come back in 10 years or so when you feel you have proved me wrong by actually "doing-it"?

Nothing that you have written up to now has any "proof" over my hard earned knowledge......I simply disagree with your thoughts and musings...I am allowed to do that, don't you think?

Simply go and do it in a practical manner that converts theory to practice.....fiction into fact.....OK?

Andy,

I have designed and installed many hundreds of KW of battery's. LA, AGM. VR, NiFe. I am happy that you have a system that works for you. But this is a forum, where people discuss knowledge and specifics, and where I come to find consensus amoung high level experts. of which, on this topic, I am one. So, if you like, you can post on here that your theory about undercharging a bank is economically superior, it's up to me to try to understand what you are saying, what facts you have to help me understand it, and to call BS if need be. I'm calling BS. I still like to read your posts.

CDR King are a Philippine chain of shops specialising in cheap Chinese electrical goods, with little or no tech support, which is why I said the manufacturer was unknown. The problem with trying to keep posts short & readable is you often can't give the whole story

OK, I can buy 35amp alt. for P2,400, but a 60amp alt. rises to P8,400.
It would be easy to assemble the arrangement shown in the above diagram but questions arise in my head

a) Is it safe (apart from the obvious danger of overcharging)
b) will it push up to 70amp into the system. Working on the premise that the invertor is drawing 20amps up to 50amps remains available for battery charging. This would comply with the C/8 rule.

If this will work it may be possible to maintain my electricity supply indefinitely by running the engine for 3 or 4 hours, twice a day, less if the sun shines!

As I've had a very good experience using car batteries for the last 4 years (despite everything I've read telling me they wouldn't last 6 months!), As they can be recharged more quickly I might continue use this brand. (For people in the Philippines the brand is Motolte 'Gold' N40).

Andy - As my experience with car v deep cycle flies in the face of all the perceived wisdom of batteries; I can understand why you are trusting your experiences with batteries, both above and below the water, over the advice of other users who also feel their experience & knowledge is correct.

http://www.dailymail.co.uk/news/article-2701435/Electronic-cigarette-causes-huge-explosion-family-home-plugged-wrong-charger.html

OK Not Lead Acid Battery but the above link shows the consequences of not recharging a battery properly! This is why I would welcome comments on my idea of 2 alternators charging one battery bank.