numpty battery charger question

[Loggo]

I have read that the output of a battery charger should be around 20% of the battery bank. Therefore for my 3x120 amp domestics I would think aroùnd 70 amp charger output.
my question is - what if it aint ? Say i had a 10 amp charger ?
Would the battery bank never fully charge or would it just take a week but get there in the end ?
I have trawled around the net but answers come there none. As 20 or 30 amp chargers ate much cheaper than 50 or 60 amp is there a saving to be made ??

 

[superheat6k]

I would work on up to 10%. That said I have 2 x 135 pairs so a total of 540 AH and the original fit 15 amp unit manages just fine.

A smaller charger will just take longer. Also what is your use. A sail boat going long periods with no charge into the batteries wil place a heavier demand on the charger when you pkug in than a Mobo merrily charging underway.

 

[pvb]

Smaller chargers work, but obviously take longer. Depends on your requirements.

 

[William_H]

Depends if you are only at a powered site for a short visit you want as much charge in as soon as possible hence the 10%. However if you have long term power available there is no reason to have a bigger charger just let the charger take its time. Remember that a 15 amp charger (that is a max capability) probably only delivers 15 amps into a flat battery for a short time before current diminishes as battery is charged. A bigger charger does not necessarily give more charge. depends on the size of batteries and voltage.
However 2 batteries in parallel will take twicew as much as one. good luck olewill

 

[Loggo]

Thanks for the response guys - just what I hoped.

 

[sailinglegend420]

Trojan batteries suggest a maximum charging current of 10%-13% of the Ah capacity of the bank, other manufacturers suggest 20%, but Lifeline AGMs require a minimum charging current of 20%, and will be happier with 100% of bank capacity for a faster charge. So check what your battery manufacturer says!

Also remember that the above figures are the current actually going into the battery, so rate the charge a bit higher to be able to supply your boat loads at the same time.

If marinas are only occasionally used to get the batteries fully charged then buy the largest charger the battery bank will accept to guarantee that overnight they will be back to 100%. Even after the charger has dropped to Float it may still take another 10 hours to get the batteries really back to 100%. If you arrive at 2000 hrs in the evening and want to leave at 0800hrs the next morning the batteries may not be fully charged.

If an AC generator is used to charge via the shorepower charger then buy the largest charger the battery bank will accept to keep the generator runtime to a minimum. This will still only get the batteries back to about 85% unless the generator is left running for a very long time.

 

[charles_reed]

I have read that the output of a battery charger should be around 20% of the battery bank. Therefore for my 3x120 amp domestics I would think aroùnd 70 amp charger output.
my question is - what if it aint ? Say i had a 10 amp charger ?
Would the battery bank never fully charge or would it just take a week but get there in the end ?
I have trawled around the net but answers come there none. As 20 or 30 amp chargers ate much cheaper than 50 or 60 amp is there a saving to be made ??

From experience - I started in 1990 with an 8amp switch-mode charger into 190 ah of batteries, in 1991 the battery capacity was increased by 120ah and 85 watts of PV panel added. At all times, until it's demise in 2007 the charger worked perfectly well, just took a long time to get the batteries up to charge.
In 2008 I fitted a 30amp switch mode charger - that seemed to find the slightest flaw in any battery and reduce it to a wreck. (Charged @ 14.2v, onto float @ 13.5V, no equalising)
in 2013, after a year with no charger I fitted a so-called smart charger of 20 amps into 3 outlets. I now have 328 watts of PV, the charger is set for bulk 14.4v, equalisation at the same level at reduced 1 amp output for 4 hours and float @ 13.5v - so far only one replacement battery. The charger never seems to go into bulk phase during my infrequent access to shorepower. During the 6 summer months on the boat I'll have access to shorepower on about 8 occasions - mainly to recharge laptop batteries.
My impression is that:-
1.Charger size is dictated by a number of variables:-
1.1. Your daily power budget, mine is between 55-65 ah every 24 hours.
1.2 How many alternative sources of charging you might have (I've got away for a season with 1 x 6 amp switch-mode charger).
1.3. How often you run the engine.

Furthermore your larger chargers have a farther cost penalty over their purchase price - they (IMHO) significantly increase cell-failure in sealed batteries.

I'm sure you'll have lots of experts giving you conflicting advice based upon a variety of models (most of which have no basis in marine use).

 

[BabaYaga]

Trojan batteries suggest a maximum charging current of 10%-13% of the Ah capacity of the bank, other manufacturers suggest 20%

In my view, statements like this could give the false impression that batteries would be harmed by being connected to a charger that has a larger maximum output than 13 percent (or 20 percent) of the Ah capacity of the bank. But batteries cannot be force fed as long as the voltage is properly regulated.
This is what Trojan says:
http://www.trojanbattery.com/BatteryMaintenance/ChargerSelection.aspx
As I read it, they are just suggesting a suitable charger size/output. Going bigger might hurt your wallet, but not the batteries.

 

[Richard10002]

I have a bank of 3 x 110Ah domestic batteries. My engine tends to start charging the batteries at about 35A and, after a day of Cruising, they are usually "full", (Amps drawn less than 2).

I also have a mains charger with a max of 25A, and this also results in the batteries drawing less than 2A after several hours.

My charger of choice is the Sterling inverter charger, which has a max of 80A. This gets the charge drawn down to a couple of Amps much quicker than the above.

During the 3 or 4 days a week that I'm not on board, the 100W solar panel provides up to a max of 5A or so. Provided I leave the batteries close to full, I usually come back to them topped up as full as is possible.

With batteries I don't think we every truly fill them, but I believe most of us now know what we mean by full.

 

[CAPTAIN FANTASTIC]

It will take longer to charge, thats all; actually, the slower and longer duration of charge, the better for the batteries.

 

[sailinglegend420]

In my view, statements like this could give the false impression that batteries would be harmed by being connected to a charger that has a larger maximum output than 13 percent (or 20 percent) of the Ah capacity of the bank. But batteries cannot be force fed as long as the voltage is properly regulated.
This is what Trojan says:
http://www.trojanbattery.com/BatteryMaintenance/ChargerSelection.aspx
As I read it, they are just suggesting a suitable charger size/output. Going bigger might hurt your wallet, but not the batteries.

I'm only trying to answer the OP's post and pass on what the manufacturers say.

What Trojan go on to say is - "Chargers with lower ratings can be used but the charging time will be increased." They don't say a larger charger can be used. Yes a smaller charger rate may be better for some batteries - if you have the time!!!!!!

You are correct that batteries will only accept the current, based on their State of Charger, But if you have a large charger they can take a current that is probably not good for them.

Mr Sterling's did some tests with a 200 amp capable charger on his "Advanced Battery Charging" ideas where he pumped 160 amps at 14.8 volts into a 100 Ah battery that was 50% discharged. He does point out that the battery temperature rose from 18C to 32C, but he of course maintains that was not a problem! Others in the industry will tell you that above about 20C every rise in battery temperature of 10C will halve the life of your battery. That's why batteries should not be in engine compartments.

Mr Sterling has withdrawn this controversial article from his website, but I'm sure others have seen it..

 

[BabaYaga]

What Trojan go on to say is - "Chargers with lower ratings can be used but the charging time will be increased." They don't say a larger charger can be used. Yes a smaller charger rate may be better for some batteries - if you have the time!!!!!!

You are correct that batteries will only accept the current, based on their State of Charger, But if you have a large charger they can take a current that is probably not good for them.

No, Trojan does not say that a larger charger can be used. But they also do not say that it can not. They don't mention that option at all, AFAICS.

It seems to me that you are implying that it could be harmful for the batteries to be fed the maximum current that they will accept.
I doubt that this is correct, provided that the voltage is properly regulated (14,4V for most battery types).
Consider for instance a single start battery 60Ah being charged by the alternator of a small VP diesel – these are now 115A across the range. Do you mean that this battery will be damaged? I think not.

 

[halcyon]

In my view, statements like this could give the false impression that batteries would be harmed by being connected to a charger that has a larger maximum output than 13 percent (or 20 percent) of the Ah capacity of the bank. But batteries cannot be force fed as long as the voltage is properly regulated.
This is what Trojan says:
http://www.trojanbattery.com/BatteryMaintenance/ChargerSelection.aspx
As I read it, they are just suggesting a suitable charger size/output. Going withimight hurt your wallet, but not the batteries.

Battery types vary, but when we made transformer mains chargers we worked on about 10% battery capacity for flooded lead acid.

The reason was to allow charge to be absorbed as the battery is charged, the voltage would climb very slowly during charge, reaching 14.2 / 14.3 volt in around 3 / 4 hours. If it then selected equalisation charge, this would last for 2 - 4 mins only for charge current to have fallen to 200 mA and falling, so we only fitted a short time delay before selecting float charge, thus minimum gassing.

By charging at a higher current, you can get full conversion of active surface material in a short time, hence rapid volt rise in bulk to equalisation. This results in the need for running the battery at high voltage to obtain conversion of active material in the centre of the plates, thus maximum gassing.


As long as you are not trying to recharge batteries from mains in a very short time, while supplying power at the same time, fitting a larger charger is not required. Battery charging can be at night when you are asleep.


Brian

 

[sailinglegend420]

.....Consider for instance a single start battery 60Ah being charged by the alternator of a small VP diesel – these are now 115A across the range. Do you mean that this battery will be damaged? I think not.

Oh dear oh dear - you're worse than Charles Reed just trying to make an argument!!!!!!

Of course you a right because a starter battery is only discharged about 2% each time it is used so will accept only a little current. It should never get much more than 10% discharged because it is not a deep cycle battery. A house battery at 50% SoC can and will take a very much higher current than a starter battery when being charged together. I have a 280 amp DC genset and a 27Ah RedFlash starter battery that is now 10 years old!

 

[BabaYaga]

Oh dear oh dear - you're worse than Charles Reed just trying to make an argument!!!!!!

Of course you a right because a starter battery is only discharged about 2% each time it is used so will accept only a little current. It should never get much more than 10% discharged because it is not a deep cycle battery. A house battery at 50% SoC can and will take a very much higher current than a starter battery when being charged together. I have a 280 amp DC genset and a 27Ah RedFlash starter battery that is now 10 years old!

If the battery is 2 percent discharged or 50 percent discharged or more makes no difference to the argument.
Yes, of course the current will be higher if the the SoC is lower. But will this higher current harm the battery? In my view the answer is no, provided the voltage is properly regulated. A 115A charging source, or 280A for that matter, will not harm a 60Ah (or 27Ah) battery regardless of its SoC.

"But if you have a large charger they can take a current that is probably not good for them"

Do you have any support for that statement?
I am truly interested, not just arguing.

 

[halcyon]

If the battery is 2 percent discharged or 50 percent discharged or more makes no difference to the argument.
Yes, of course the current will be higher if the the SoC is lower. But will this higher current harm the battery? In my view the answer is no, provided the voltage is properly regulated. A 115A charging source, or 280A for that matter, will not harm a 60Ah (or 27Ah) battery regardless of its SoC.

"But if you have a large charger they can take a current that is probably not good for them"

Do you have any support for that statement?
I am truly interested, not just arguing.

You just get less charge due to surface charge, faster you go the less you put in, but not for all battery types though.

Brian.

 

[sailinglegend420]

...."But if you have a large charger they can take a current that is probably not good for them"

Do you have any support for that statement?
I am truly interested, not just arguing.

I'm interested as well in anyone elses evidence that says it's OK. I did give support for my statement from Mr Sterling's Advanced Charging paper. 160 amps into a 100 amps battery raised the temperature by 14C. That was after 90 mins. At a more normal leisure battery charge voltage of 14.4 volts the maximum charge current was nearly half and the temperature rise was also half.

If the temperature rises in the battery the charging voltage should be reduced because the voltage at which the battery starts to gas falls as the temperature rises. Too much gassing will kill sealed leisure batteries. Most people don't have battery temperature sensors to correct for this, so it is better surely not to charge the battery with too high a current which is unnecessarily raising the temperature. This is all well documented stuff.

 

[halcyon]

I'm interested as well in anyone elses evidence that says it's OK. I did give support for my statement from Mr Sterling's Advanced Charging paper. 160 amps into a 100 amps battery raised the temperature by 14C. That was after 90 mins. At a more normal leisure battery charge voltage of 14.4 volts the maximum charge current was nearly half and the temperature rise was also half.

If the temperature rises in the battery the charging voltage should be reduced because the voltage at which the battery starts to gas falls as the temperature rises. Too much gassing will kill sealed leisure batteries. Most people don't have battery temperature sensors to correct for this, so it is better surely not to charge the battery with too high a current which is unnecessarily raising the temperature. This is all well documented stuff.

160 amps into a 100 amp battery after 90 minutes ?

Battery charging is a electrochemical conversion, not a bath you tip amps in, it is the conversion that generates the heat. If you charge at the 10% rate you see a much lower charging voltage that slowly rises to 14.4 volt, thus less gassing. High charge produce surface charge, thus the rapid increase to 14.4 volt and excessive gassing.

Brian

 

[BabaYaga]

I'm interested as well in anyone elses evidence that says it's OK. I did give support for my statement from Mr Sterling's Advanced Charging paper. 160 amps into a 100 amps battery raised the temperature by 14C. That was after 90 mins. At a more normal leisure battery charge voltage of 14.4 volts the maximum charge current was nearly half and the temperature rise was also half.

If the temperature rises in the battery the charging voltage should be reduced because the voltage at which the battery starts to gas falls as the temperature rises. Too much gassing will kill sealed leisure batteries. Most people don't have battery temperature sensors to correct for this, so it is better surely not to charge the battery with too high a current which is unnecessarily raising the temperature. This is all well documented stuff.

I have not read Mr Sterling's paper and from what you wrote earlier I understand that it is no longer available. But a temperature rise of 7C (charging at 14,4V) does not sound very alarming to me.

What you say about the risk of gassing and the need for temperature compensation makes sense to me, but I cannot see how this has got anything to do with the maximum capacity of the charger.
To my knowledge, gassing typically takes place towards the end of the charging cycle, when the voltage has been driven up to 14,4V or higher. The current at this point will be quite low compared to what it was early in the bulk charging phase, because acceptance goes down naturally as the SoC increases.
So how can the amount of gassing depend on how many amps the charger put out when charging began?

 

[sailinglegend420]

...To my knowledge, gassing typically takes place towards the end of the charging cycle, when the voltage has been driven up to 14,4V or higher. The current at this point will be quite low compared to what it was early in the bulk charging phase, because acceptance goes down naturally as the SoC increases....

Its not the current that causes the gassing but the voltage - about 14.4v. During the Bulk phase the current is roughly constant as the voltage rises to 14.4v. Then a multi-stage charger changes from a constant current charger to a constant voltage charger which limits the voltage to 14.4v. Only then will the battery begin to accept less currents as its SoC increase.

...So how can the amount of gassing depend on how many amps the charger put out when charging began?

If the battery temp goes up by 7C with a high charging rate then the battery starts to gas at about 14.2v not 14.4v. if you don't reduce the charging voltage you get excessive gassing.

Halcyon was right in his post. My 280 Amp DC genset goes straight to 14.4 volts because it can! So a charger with a bigger current capability will get up to the gassing voltage more quickly.