Sterling Alternotor to Battery Charger.

[Tony Brooks]

Dunno why, but I have the feeling that this is a dumb question.

 

Alternators charge batteries and no matter what you do, or Mr. Sterling says, providing you don't have power losses somewhere in the circuitry, you cannot increase the charge rate such that to fully charge the batteries you do not need to run the engine for 7 or 8 hours.

 

Now the dumb question, is this correct?

 

Richard

 

 

It looks very much as if your question (if I understand it) on an up to date system may well be getting on for true.

 

During the charging stage where its the magnetic fields inside the alternator that is controlling the CURRENT I do not see how Mr Sterling's or anyone else's devices are going to shorten that stage of charge and I think one of Mr Sterling's devices may actually lengthen it.

 

During the second stage of charging the alternator's voltage regulator locks the charging voltage to a constant figure and just how much you can shorten this time depends upon that value.

 

If you had an old alternator regulated at 13.8 volts I suspect Mr Sterling's and the other devices will make a significant shortening of the time required to get to a specific state of charge.

 

The closer the regulated voltage gets to 14.4 volts and above the less difference any device can make.

 

The way these devices shorten the time is simply to "take over" from the existing regulator and regulate the voltage to a higher value. The higher voltage pushes more current through the battery so on the face of it the battery is being charged faster.

 

Now the problem. Gibbo has pointed out that once you starts making batteries gas and get hot the energy used to accomplish those two things has to be taken from the charging current and (if I understand him correctly) you quickly get into a situation where the additional current available for the actual charging is very little. I can not confirm this but having seen may garage fast chargers at work I can well believe it.

 

The Adverc and at least one other device provide the higher voltage on a 20 minute on-off cycle because it takes something like 20 minutes to start the gassing. These may shorten the time but you need to calculate the cost effectiveness of them.

 

It seems a fairly well set up system will take between 2 & 4 hours to get perhaps 80% charged and it may be best to run cruising boats on this assumption and then use alternative long term charging when back at base to try to recover the other 20%. CCers seem to have a unique problem and I suspect they just tend to change batteries more frequently because of sulphation.

[Arnot]

Dunno why, but I have the feeling that this is a dumb question.

 

Alternators charge batteries and no matter what you do, or Mr. Sterling says, providing you don't have power losses somewhere in the circuitry, you cannot increase the charge rate such that to fully charge the batteries you do not need to run the engine for 7 or 8 hours.

 

Now the dumb question, is this correct?

 

Richard

Whilst you can generalise about charging systems in boats there are so many variables that any advice has to be taken as very general...

 

The statement you make makes a number of implications, one is "providing you don't have power losses somewhere in the circuitry" but you always will have power losses, even on a good system. The trick is to minimise them and and then compensate for what remains. This is where the charging controllers can help but the benefit may not be worth the additional cost and complexity

 

Another implication is that the batteries were more or less flat at the strat of the charging cycle. Usually they are not and if you are letting your batteries get very flat it will take a long time to recharge them and won't do them any good.

 

It is possible to arrange a charging system that will bring batteries up from a 50% SoC (State of Charge) to nearly 100% in under a couple of hours but it does require fine tuning to make sure that all losses are minimised, everything is working properly and possibly improving the regulation system.

 

Regards

 

Arnot

[Gibbo]

Dunno why, but I have the feeling that this is a dumb question.

 

Alternators charge batteries and no matter what you do, or Mr. Sterling says, providing you don't have power losses somewhere in the circuitry, you cannot increase the charge rate such that to fully charge the batteries you do not need to run the engine for 7 or 8 hours.

 

Now the dumb question, is this correct?

 

Richard

 

It's not a dumb question.

 

With a typical narrowboat system (say 400Ahr + 100Ahr banks) and 80 or 90 amps of so of alternator you would be looking at around 3 hours or so to get from 50% to 85% or thereabouts. This time could be reduced by increasing the size of the alternator up to a minumum time of about 1.5 hours with a 150 amp unit.

 

However, once you get to that stage (80% to 85% ish) the charge current is limited by the batteries (not the alternator) so it doesn't make any difference how big the alternator is after that time. The charge current tapers off exponentially and quite simply takes ages to get the last few bits in. The last 5% can take 2 or 3 hours!

 

So he's right really. To actually get to 100% takes a very long time. Alternator controllers can reduce this time but it depends upon what the normal voltage is of the alternator as to how miuch difference they actually make.

 

The higher the charge voltage of the external regulator, the faster this stage can be accomplished. Up to a point...... That point being the gasing voltage of the batteries. Going higher than the gassing voltage doesn't reduce the charge time. It usually makes no difference and can in fact prolong it.

 

6 to 8 hours from 50% to a true 100% is not out of the ordinary. And there isn't anything that can be done about it. It's just the way lead acid batteries are.

 

Note that all the figures above are very approximate because there are many variables and it's too early in the day to start actually calculating things

[Keeping Up]

A rather nice little quote that I saw on another website:

 

"It's not amps that recharge your batteries, it's hours"

 

OK it may not be strictly correct, but it has a nice ring to it and the sentiment is good.

[smileypete]

A rather nice little quote that I saw on another website:

 

"It's not amps that recharge your batteries, it's hours"

 

OK it may not be strictly correct, but it has a nice ring to it and the sentiment is good.

 

May be better to say:

 

It's not just amps that recharge your batteries, it's hours too.

 

So how long does it take to FULLY charge a reasonably new battery? 12 hours... 24 hours... any advance on 24 hours?

 

cheers,

Pete.

[Gibbo]

So how long does it take to FULLY charge a reasonably new battery? 12 hours... 24 hours... any advance on 24 hours?

 

 

If you really want the 100% technically, strictly, correct answer then it is..............

 

"It is impossible". It cannot be FULLY recharged. Ever. No matter how long you wait. And I think you know this

 

Now if you mean as fully charged as it can ever be I reckon about 24 hours. But this can be massively reduced by accepting (say) 99%

[Sir Nibble]

When I was mucking about with the "robot wars" lark I obtained some ex standby emergency lighting batteries that had been on a constant float charge for years. Almost all of them were knackered. When I opened them I found that the lead grid that supports the active material paste in the plates had itself been converted into lead peroxide. I short, the battery was 110% charged. The result of this was that the plates had collapsed into a nasty red sludge.

[nb Innisfree]

Seem to remember our 480ah 24v bank on shore power with a Victron charger took a couple of days to level out at 0.7amps

[Cris P]

Surely, therefore, this is the point where solar charging comes into its own ?

[Phil Ambrose]

Surely, therefore, this is the point where solar charging comes into its own ?

 

Oh I really do hope so or I have wasted an aful lot of money. ( 5 X 100watt panels plus contoller and a lot of hefty cable )