Charging arrangements ?

[Nickhlx]

I am still thinking of a new build with a live-aboard type of spec, using a Beta 43. Nowadays they come with 150A and 45amp alternators.

 

If the 45 amp item were to be replaced with another 150 amp, ( i.e 300A rated ) and suitable boxes ( e.g from the Sterling range) and all geared up at 3:1 ( see earlier query/post ) does the team think that this would go a long way towards being entirely adequate for just about any normal use ? (i.e still being careful without being paranoid ).

 

I suppose what I am also asking is if the starter battery alternator can be included in the storage battery charging side of things ? ( I think it can with a suitable box)

 

Storage batteries will be around 600 AH, wet cells items with advanced regulator charging ( 14.8 volts).

 

Thanks,

 

Nick

[chris w]

I am still thinking of a new build with a live-aboard type of spec, using a Beta 43. Nowadays they come with 150A and 45amp alternators.

 

If the 45 amp item were to be replaced with another 150 amp, ( i.e 300A rated ) and suitable boxes ( e.g from the Sterling range) and all geared up at 3:1 ( see earlier query/post ) does the team think that this would go a long way towards being entirely adequate for just about any normal use ? (i.e still being careful without being paranoid ).

 

I suppose what I am also asking is if the starter battery alternator can be included in the storage battery charging side of things ? ( I think it can with a suitable box)

 

Storage batteries will be around 600 AH, wet cells items with advanced regulator charging ( 14.8 volts).

 

Thanks,

 

Nick

 

Nick

 

If you combine 2 x 150A alternators you're likely going to have the opposite problem from everyone else You'll be charging the batteries too quickly.

 

You're going to get about 180A charge current with a 2:1 pulley and around 250A+ with a 3:1 pulley. A single 150A on a 3:1 pulley may be a better way to go.

 

Chris

[Nickhlx]

Hi Chris

 

Happy Easter !

 

Yes - I suppose so - I hadn't thought of it from that aspect - perhaps add a couple of batts to take it up to 800 AH ?? (!!)

 

Perhaps the standard alternators would be adequate, if "combined" ( if it's possible to combine ) ? - reduce the max charging current a bit to avoid too much charging current... would not the charge be limited automatically by the Advanced Regulator holding the charging voltage at 14.80 Volts ? i.e. the battery voltage would come up to that and then the current taper off as the state of charge rises ? I suppose it's necessary to avoid too much charging current to avoid overheating the batteries though ...

 

Normally we would "cruise" for at least 4 hours a day so that would allow quite a lot of "replenishment" to occur each day !

 

Nick

[chris w]

[quote name='Nickhlx' date='Mar 23 2008, 08:33 PM' post='216115'

.................would not the charge be limited automatically by the Advanced Regulator holding the charging voltage at 14.80 Volts ? i.e. the battery voltage would come up to that and then the current taper off as the state of charge rises ? I suppose it's necessary to avoid too much charging current to avoid overheating the batteries though ...

Nick

 

The current would indeed taper off during the absoption stage but, during the bulk stage, the current is constant and the voltage increases to ensure it stays constant.

 

Chris

[Nickhlx]

[quote name='Nickhlx' date='Mar 23 2008, 08:33 PM' post='216115'

.................would not the charge be limited automatically by the Advanced Regulator holding the charging voltage at 14.80 Volts ? i.e. the battery voltage would come up to that and then the current taper off as the state of charge rises ? I suppose it's necessary to avoid too much charging current to avoid overheating the batteries though ...

Nick

The current would indeed taper off during the absoption stage but, during the bulk stage, the current is constant and the voltage increases to ensure it stays constant.

 

Chris

 

 

OK - point taken..

 

What is the max recommended charging rate for the bulk stage, assuming say a 600 AH bank and wet-cell batteries ?

 

It would be poor design to rely on battery over-temp sensors dropping the rate back, and better to match alternator output to battery bank capacity so things are better balanced.

 

Nick

[chris w]

OK - point taken..

 

What is the max recommended charging rate for the bulk stage, assuming say a 600 AH bank and wet-cell batteries ?

 

It would be poor design to rely on battery over-temp sensors dropping the rate back, and better to match alternator output to battery bank capacity so things are better balanced.

 

Nick

 

60A - 120A IMHO

 

Chris

[Gibbo]

OK - point taken..

 

What is the max recommended charging rate for the bulk stage, assuming say a 600 AH bank and wet-cell batteries ?

 

It would be poor design to rely on battery over-temp sensors dropping the rate back, and better to match alternator output to battery bank capacity so things are better balanced.

 

Nick

 

Some "rules of thumb" state 60 amps. Others say 120 amps. The reality depends upon what other equipment is one board. A 100 amp alternator is no use if there is also a permanent 90 amp load.

 

For instance assume you think you might regulalry use a washing machine or tumble dryer whilst the engine is running. In that case you want to add in the power you need for that.

 

With wet cells it is very difficult to charge at too high a current. The batteries simply won't accept it. The voltage rises and the current drops. Generally you wouldn't see more than about 250 Amps go into a 600Ahr bank. but obviously this depends upon the condition and age of the batteries. This is NOT the case with AGMs or gels where huge charge currents can result.

 

Gibbo

[Nickhlx]

Some "rules of thumb" state 60 amps. Others say 120 amps. The reality depends upon what other equipment is one board. A 100 amp alternator is no use if there is also a permanent 90 amp load.

 

For instance assume you think you might regulalry use a washing machine or tumble dryer whilst the engine is running. In that case you want to add in the power you need for that.

 

With wet cells it is very difficult to charge at too high a current. The batteries simply won't accept it. The voltage rises and the current drops. Generally you wouldn't see more than about 250 Amps go into a 600Ahr bank. but obviously this depends upon the condition and age of the batteries. This is NOT the case with AGMs or gels where huge charge currents can result.

 

Gibbo

 

Thanks for the input Gibbo,

 

It is definitely the case that we expect to have a washing machine running when under way ( once or twice a week) - what I am trying to design in is the need to run the engine / cruise for the minimum time each day by having maximum charging capability.

 

If say a storage capacity of 600 Ahr ( maybe more ?) was decided upon, what I am trying to identify is the max alternator size / charging current I could safely run without overcooking things ?

 

If the washing machine took 3 KW intermittently via an inverter, I would hope a large proportion was coming from the alternator. Presumably hot fill would be desirable to save heating via electricity ?

 

I can also go for different battery technolgies, if "Wet Cell" batteries are not the best for highest current charging, but I was thinking they were, and one of the less expensive options. ( I don't mind routine "fiddling" to check electrolyte levels - keeps me involved with the engine bay !! )

 

Thanks,

 

Nick

Edited March 24, 2008 by Nickhlx

[Gibbo]

Than ks for the input Gibbo,

It is definitely the case that we expect to have a washing machine running when under way ( once or twice a week) - what I am trying to design out is the need to run the engine / cruise for 5 hours a day by having inadequate charging capability - i.e. say a storage capacity of 600 AH was decided upon, and "x" average draw during daytime ( say 30 amps) what would be max alternator size / charging current I could safely run without overcooking things ? I can also go for different battery technolgies if "Wet Cell" batteries are not the best for highest current charging, but I was thinking they were and one of the less expensive options. ( I don't mind routine "fiddling" to check electrolyte levels - keeps me involved with the engine bay !! )

 

Thanks,

 

Nick

 

It's a bit of a problem this because you have to think about how the charge goes back into a battery.

 

If the battery is quite deeply discharged then you can ram loads of Amps into it initially and get it up to (say) 80% or so quite quickly. Once this stage is reached there is nothing you can do to speed up the charge (well there is but it doesn't make a HUGE difference).

 

So in actual fact charging up from 80% to 100% doesn't actually take that much longer than charging from 60% to 100%

 

And getting from 90% to 100% takes ages. The higher the state of charge, the longer it takes to get a few amp hours into the battery.

 

AGMs and Gels will accept a much higher charge rate initially (ie when deeply discharged) but you still run into the problem of the charge slowing down substantially towards the end.

 

The long and short of it is that no matter how much or little the batteries get discharged, recharging them takes a lot longer than most people want to believe.

 

From 50% to 100% there is no way it can be done properly in less than about 10 hours. And preferably much longer.

 

Lead acid batteries are slow to charge. There is nothing that can be done to change this.

 

http://batteryuniversity.com/partone-13.htm

 

Gibbo

Edited March 24, 2008 by Gibbo

[Chris Pink]

The long and short of it is that no matter how much or little the batteries get discharged, recharging them takes a lot longer than most people want to believe.

 

From 50% to 100% there is no way it can be done properly in less than about 10 hours. And preferably much longer.

 

Lead acid batteries are slow to charge. There is nothing that can be done to change this.

 

I do struggle with this one and it seems that, empirically, the 'best' charging routine for a boat dependent on its engine or a generator for charging is to accept that the batteries will only be charged to 80% and have a shortened life. A trade off between the capital cost of a battery and the fuel costs to do the last 20% of charge.

 

It is difficult to get a sense of how short the battery life will be in this case but i would still expect 2 years for 'yer average' leaisure battery. This also implies that it is best to specify as small a battery bank as you can get away with.

 

I also think, still empirically, that the most important factor in battery life is not to let the batteries discharge too deeply.

[Nickhlx]

I do struggle with this one and it seems that, empirically, the 'best' charging routine for a boat dependent on its engine or a generator for charging is to accept that the batteries will only be charged to 80% and have a shortened life. A trade off between the capital cost of a battery and the fuel costs to do the last 20% of charge.

 

It is difficult to get a sense of how short the battery life will be in this case but i would still expect 2 years for 'yer average' leaisure battery. This also implies that it is best to specify as small a battery bank as you can get away with.

 

I also think, still empirically, that the most important factor in battery life is not to let the batteries discharge too deeply.

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Could this then also imply that the last 20% of charge should be supplied by a small genny ? The bulk being addressed by the main alternator charging system at around 150 amps, and the last bit by a small, very quiet genny for two or three hours at the end of the day at perhaps 10 amps or so ?

 

To reduce depth of discharge, surely the biggest bank would achieve this and as has been said previously, the bigger the bank, the bigger the batteries effectively capacity from Peukerts effect.

 

I realise that it is not possible to achieve perfection, but I would like to get as close as practically possible whilst in the design and spec phase.

 

At the end of the day ( week / weekend), the boat, being new, will be living in a marina on shore power for at least the first year or three. Excursions will be weekends or long weekends with a few weeks out during the year when not routinely on shore power at night, so initially I am not envisaging any power issues - its when its spending more time on the banks not seeing a shore line for a few days and not being inclined to cruise much, that lack of a good spec will manifest itself.

 

Thanks,

Nick

[chris w]

When Gibbo referred to: "Once this stage is reached there is nothing you can do to speed up the charge (well there is but it doesn't make a HUGE difference).", he was referring to alternator controllers which lift the charge voltage from 14.2v (typical alternator regulator) to 14.8v. The difference will be around an additional 25-30A. Whether this is huge or not depends on your point of view. For me, on my set up, the current doubles from around 27A to 52A due to the alternator controller. I think that is a very worthwhile increase.

 

Chris

[smileypete]

Question for Gibbo, with a battery bank in daily liveaboard use is it best to:

 

1. Charge from 50% to 80% every day

 

OR

 

2. Charge from 50% to 75% every day with a charge to 90% once a week?

 

cheers,

Pete.

[Gibbo]

Question for Gibbo, with a battery bank in daily liveaboard use is it best to:

 

1. Charge from 50% to 80% every day

 

OR

 

2. Charge from 50% to 75% every day with a charge to 90% once a week?

 

cheers,

Pete.

 

I honestly don't know. I haven't got any data one way or the other. If you'd said "with a charge to 95% once a week" I'd have been inclined to think that would be prefereable. But going to 90% once a week, hmmm I don't think (and this is just feeling but based on tons of research and experience) would be any better than your first one.

 

I know lots of people without shorepower do something similar to these which again comes down to being able to get the first part of the charge in quickly but after that it becomes very slow. Running an engine or genny for hours and hours to get the last bit in is what stops people doing it.

 

A question for chris w. You categorically state there is a huge difference in charge current between 14.4 and 14.8 volts.

 

Have you looked into this further? ie on lots of different batteries? on lots of different installations? over long time periods?

 

If you draw the simple conclusion that 14.8 is better than 14.4 then why not keep going? Why not 15.2? or 15.4? Hell why not 100 volts and charge them up in 3 minutes?

 

There is a reason for 14.4!

 

I'll give you a few hints.

 

Apart from more water useage (ok no big deal) you get increased positive plate corrosion. It's unclear whether this would be counteracted by the extra sulphation got at 14.4 volts. These two opposite effects seem about the same between the two different charge voltages. One wrecks them one way, the other wrecks them a different way.

 

An acceptance charge at 14.8 volts will indeed start off with an initial higher current at the point of changeover from bulk to acceptance. But continue to watch what happens. You need to run 2 identical systems side by side to do this. The one at 14.8 volts tapers off (the charge current) much quicker, not because the batteries get charged quicker, but because the electrolyte is boiling, the bubbles increase the bulk resistance of the electrolyte and a much higher percentage of the charge current is actually going into electrolysing the water than charging up the batteries.

 

During charging, the internal resistance of the battery is lowest (and hence the charge current is highest) when the voltage is held AT the gassing voltage. Not above it, not below it. This is difficult to see because there is a delay between exceeding the gassing voltage and the gasses actually starting.

 

Honest.

 

Gibbo

Edited March 24, 2008 by Gibbo

[chris w]

A question for chris w. You categorically state there is a huge difference in charge current between 14.4 and 14.8 volts.

 

Gibbo

 

I haven't said that. What I said is that there is a large charging current difference between 14.2v and 14.8v of between 25-30A. For me that's a doubling of my charge current and so is definitely worthwhile. Whether this can be considered a "huge" difference is in the eye of the beholder. It's certainly a very useful difference.

 

For 14.4v, the additional current would be, I estimate, around 15-20A so, IMHO, still very worthwhile. At 14.6v (compared to 14.8v) the difference would be about 5-10A additional current.

 

You may have missed the real meaning behind Smileypete's question. What he was REALLY asking, is this: Are multistage chargers a waste of time compared to just using a constant voltage charger? A constant voltage charger will charge a 50% discharged battery to around 75%. A multistage charger will get it to over 90%. I appreciate that if you leave a constant voltage charger on for a few days, it too will charge the batery higher but we are talking real world boating.

 

Chris

[Gibbo]

I haven't said that. What I said is that there is a large charging current difference between 14.2v and 14.8v of between 25-30A. For me that's a doubling of my charge current and so is definitely worthwhile. Whether this can be considered a "huge" difference is in the eye of the beholder. It's certainly a very useful difference.

 

For 14.4v, the additional current would be, I estimate, around 15-20A so, IMHO, still very worthwhile. At 14.6v (compared to 14.8v) the difference would be about 5-10A additional current.

 

You may have missed the real meaning behind Smileypete's question. What he was REALLY asking, is this: Are multistage chargers a waste of time compared to just using a constant voltage charger? A constant voltage charger will charge a 50% discharged battery to around 75%. A multistage charger will get it to over 90%. I appreciate that if you leave a constant voltage charger on for a few days, it too will charge the batery higher but we are talking real world boating.

 

Chris

 

You need to have a look at how the current tapers off though. Going above the gassing voltage actually *reduces* the nett charge into the battery over a period of a few hours. Initially it is indeed higher. And if you switch down to 14.4 volts, then back up to 14.8 volts you will see it increase. But watch what happens over the next 15 minutes or so. It drops dramatically. And most of it isn't actually charging the batteries up. It's just making bubbles.

 

You have to log it over several hours at different voltages to see the effect.

 

Basically what we did was log the total amp hours going into 12 identical batteries, from the same state of charge, at various voltages between 13.8 and 15 volts over a 10 hour acceptance cycle. 14.4 volts produced the greatest nett charge. 14.8 is better at preventing sulfation (even higher if that's the objective), but from the point of view of charging them up as fast as possible, 14.4 volts is definitely faster.

 

I didn't read smiley's question that way. I read it as enquiring how to go about not having to run an engine all day just to get the last few percent into the batteries and doing the odd "bigger" charge to try to stave of sulfation..

 

A constant voltage charger at 15 volts will certainly charge batteries quickly so you can't really say "A constant voltage charger will charge a 50% discharged battery to around 75%" without saying what the voltage is. Admittedly most of them are about 13.8 volts which is too low and takes about 3 days.

 

Gibbo