rigpigpaul
Member
Hi All, how long would it take to fully charge a 400ah bank of lead acid sealed domestic batteries from half charge using a) 40amp battery charger or b) 90amp alternator. Thanks in anticipation RPP
Battery chargeing times
- Thread starter rigpigpaul
- Start date
duncan99210
Well-known member
In theory, tke the amps produced by chrager and devide the capacity of the by that to give you the time to charge to full capacity. Actually it will take a bit longer than that as the last bit requires more 'effort' to complete. So for a bank half charged 400 AH banks, it requires say 200 amps to charge. For a 90 amp charge it will take about say 2 1/2 hours and for a 40 amp charger it will take just over about double that, say 5 1/2 hours.
IIRC correctly from my days working with radios in the army (long time ago now) you shouldn't charge at above about 10 - 20 % of the capacity of the bank, so putting a more powerful charger in will not allow you to charge more quickly once you get to a certain point. Perhaps the more up to date on the forum can help on that?
IIRC correctly from my days working with radios in the army (long time ago now) you shouldn't charge at above about 10 - 20 % of the capacity of the bank, so putting a more powerful charger in will not allow you to charge more quickly once you get to a certain point. Perhaps the more up to date on the forum can help on that?
ccscott49
Active member
With a good quality 3/4 stage, 80 amp charger, it will take about 5 hours to get most of the capacity back, however it will take a long time to get them to 100%, if ever. I reckon on 4 hours to get to about 90% with my 440 ah bank, then two days of shorepower to put the last 10% back.
If you want your batteries to last, never discharge them below 50% of the total capacity and it will also take less time to recharge them.
Some alternator manufacturers (for marine use) do supply "smart" charger systems, the normal alternators, fitted to most boats, are automotive based units and are not designed for charging domestic battery banks, they are designed to re-charge a starter battery, after the engine has started. that is an entirely different regime. Which is one of the reasons for "smart" alternator controllers and 3/4 stage mains chargers.
I would reccomend you read up on this, plenty of threads here in the past and I'm sure data available on google or wherever.
Hope this helps.
If you want your batteries to last, never discharge them below 50% of the total capacity and it will also take less time to recharge them.
Some alternator manufacturers (for marine use) do supply "smart" charger systems, the normal alternators, fitted to most boats, are automotive based units and are not designed for charging domestic battery banks, they are designed to re-charge a starter battery, after the engine has started. that is an entirely different regime. Which is one of the reasons for "smart" alternator controllers and 3/4 stage mains chargers.
I would reccomend you read up on this, plenty of threads here in the past and I'm sure data available on google or wherever.
Hope this helps.
Barry Jones
New member
Assuming no discharge, about 8-9 hours with the charger and 4-5 hours with the alternator. Note you said fully charge (i.e. to 100% SOC).
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Nigel Calder 80% rule
Calder's yardstick is not to attempt to charge batteries beyond 80% SoC (state of charge) with an engine driven alternator because its so massively inefficient; the diesel energy consumed to power charged in to batteries ratio is bonkers. So I've adopted his strategy of having a high power alternator (120A) which bangs in about 90A typically (in bulk phase) and then as soon as I reach 80% and the alternator is going to absorption mode I shut it down. I then make sure that I get plugged in to shorepower every couple of weeks so that the charger can get the batteries back to full SoC. I've a 600AH AGM battery bank and went for AGM because of the high charge acceptance rates. If I do have to run the engine to charge the batteries I want to stuff power in as fast as possible and then turn it off!
Calder's yardstick is not to attempt to charge batteries beyond 80% SoC (state of charge) with an engine driven alternator because its so massively inefficient; the diesel energy consumed to power charged in to batteries ratio is bonkers. So I've adopted his strategy of having a high power alternator (120A) which bangs in about 90A typically (in bulk phase) and then as soon as I reach 80% and the alternator is going to absorption mode I shut it down. I then make sure that I get plugged in to shorepower every couple of weeks so that the charger can get the batteries back to full SoC. I've a 600AH AGM battery bank and went for AGM because of the high charge acceptance rates. If I do have to run the engine to charge the batteries I want to stuff power in as fast as possible and then turn it off!
rigpigpaul
Member
Thanks for the replies and advice. The reason I posted the question is because I am going to buy the 2 kw Honda suitcase generator ( power tool, micrwave etc ) so when the batteries run down I would be able to charge them rather than use the engine when I am at anchor. Looking at the charge times I think it will have to be a combination of Honda, engine and shore side power when available. rgds RPP.
bjvarley
New member
As a slight aside comment ..I did once try to charge an 80 Ahr car battery with a 120 A charger...the resuting explosion (probably hydrogen ) was spectacular but I never did it again!
Alixora
Alixora
sailinglegend420
Member
It's interesting that two replies out of three to the original posting are wrong in their charging times stated. Their answers would get the batteries back to about 80%, another 20 hours would get them fully charged - which is why Robih has got it spot on - with the help of Nigel Calder.
Not fully charging batteries is why they fail prematurely. If you only charge a 100 Ah battery to 80% and use it down to 50% then you are only using 30 Ah of its 100Ah capacity, not 50 Ah that you could use if it were always fully charged. That's a 40% reduction!!!!!
This is one very good reason why you should your size your battery bank 40% bigger than you think you need. Impractical for most situations. Again Robih has got it right on his 39' boat. AGMs take up less space per Ah and they charge about 30% faster than wet cells because to put 100 Ah into a wet cell takes 130Ah and 102Ah into an AGM. On top of that a 100Ah Lifeline AGM could take a charge current of 500 amps which makes the charge time even faster. My 1050Ah bank with my Fischa Panda 280 amp DC genny takes 5 hours to get FULLY charged which I do at least once a month as we are cruising and never go into marinas.
Not fully charging batteries is why they fail prematurely. If you only charge a 100 Ah battery to 80% and use it down to 50% then you are only using 30 Ah of its 100Ah capacity, not 50 Ah that you could use if it were always fully charged. That's a 40% reduction!!!!!
This is one very good reason why you should your size your battery bank 40% bigger than you think you need. Impractical for most situations. Again Robih has got it right on his 39' boat. AGMs take up less space per Ah and they charge about 30% faster than wet cells because to put 100 Ah into a wet cell takes 130Ah and 102Ah into an AGM. On top of that a 100Ah Lifeline AGM could take a charge current of 500 amps which makes the charge time even faster. My 1050Ah bank with my Fischa Panda 280 amp DC genny takes 5 hours to get FULLY charged which I do at least once a month as we are cruising and never go into marinas.
ianj99
Active member
The answer to charging to 100% with an engine is to fit a digital alternator regulator such as those sold by Sterling Power.
These will maximise alternator output, many of which will not get close to their quote amperage, and also by using a multi step charging process the same as that in a good mains charger, charge the battery more fully.
Batteries need about 20% more charge put in than was taken to recharge to the same state, and the advice not to discharge below 50% is good.
So in practice a 400ah battery bank only has 200ah useable capacity, and needs 240ah to recharge assuming it was 50% discharged. Also as has been stated, a standard alternator regulator will never charge it above 80%, so your expensive 400ah bank, actual has about 160ah useable capacity (& thats when new). This is why some owners moan about their new battery not lasting - its been under charged and over discharged and this shortens the life as well as reducing the effective capacity drastically.
Most efficient way to minimise engine use, is to charge up to 90% or so with the engine (with digital alternator regulator fitted) and then top up with mains/wind or solar.
halcyon
Well-known member
I find this and similar threads interesting, having been working on charging system design almost 40 years.
Back in the 1980's / early 90's we never had a major problem with battery capacity or life, except the odd user. But as firms have bought out more advanced, and costly systems, so the problems people have with standard equipment has become a bigger.
Brian
ianj99
Active member
I think a lot is to do with the vast range of electrical equipment now found on boats (& in caravans and motorhomes which have the same problems).
In the '80s & '90s, GPS, laptops, Plotters, mobile phones, dvds & lcd/led tvs etc didn't exist or weren't affordable.
Unfortunately most charging systems have not changed to keep up with the demand.
Some owners misguidedly just fit a bigger battery bank, assuming this is the answer, without considering how they will charge it. In some ways it is better to keep the battery capacity down and fit a more effective and faster charging system.
Buy smaller batteries than can accept very high charge rates (the Optima Blue top I use is one), fit a digital regulator, gear up the alternator to get more current without having to rev the engine too much and use alternative charging methods to keep the batteries topped up.
I'd never fit a petrol generator unless my power requirements were very large and I could afford to run it.
In fact I possibly wouldn't even fit a diesel powered one. I'd fit one or more very high output alternators to the main engine and install batteries that could stand very high charging currents. (the digital regulators usually have a battery temperature sensor to prevent damage due to overheating of the battery when charged at a high rate)
boatie1969
New member
i'm pretty new to all this and I have found that all the information you need is out there on the internet, after many hours of research and trying to understand the jargon I have concluded that there a few things to consider, first of all understand your energy needs, then buy the batteries to suit your needs,next buy a good, three stage charger, that is between 10-20% of you battery bank ah, eg :400ah = 40-80 a charger. don't rely on your solar alone to maintain your batteries, always use a good regulator, eg; secca and have the option of additional charge sources, eg : wind generator or just a good sinewave generator, golden rule maintain your batteries, use correct wiring and you should get 10 years out of them. Most important, do the research yourself, there is a table of knowledge out there every where and they're usually the ones that get it wrong, I noticed there are conflicting stories on this forum, be certain if you are not correctly charging your batteries in three stages the will be damaged for good.
hope this helps
hope this helps
