Battery Advice Needed Please

[Offcumden]

In a recent thread comments by Mayalid, Gibbo and Chris W lead me to think we have a similar problem. Unknown to me a spade connector had worked loose on the Domestic alternator. We had overnighted at a marina and woke to find flat batteries, too early to start the engine we were able to hook up to the mains for a couple of hours before we set off. The next morning despite some eight hours cruising the batteries were again flat. Speaking with the electrician who had replaced the alternator six months ago enabled me to rectify the problem. We spent two days cruising without being aware of the loose connection and the batteries appear not tobe holding their charge for any lenght of time.

We don't know the age of the batteries, we have had the boat for a year, continuously cruising,so its probably best to replace them.

Currently we have a bank of three 110amp 12volts. As permanent livaboards is it worthwhile increasing the bank to four.

Your suggestions will be welcome.

John

[Dutch]

In a recent thread comments by Mayalid, Gibbo and Chris W lead me to think we have a similar problem. Unknown to me a spade connector had worked loose on the Domestic alternator. We had overnighted at a marina and woke to find flat batteries, too early to start the engine we were able to hook up to the mains for a couple of hours before we set off. The next morning despite some eight hours cruising the batteries were again flat. Speaking with the electrician who had replaced the alternator six months ago enabled me to rectify the problem. We spent two days cruising without being aware of the loose connection and the batteries appear not tobe holding their charge for any lenght of time.

We don't know the age of the batteries, we have had the boat for a year, continuously cruising,so its probably best to replace them.

Currently we have a bank of three 110amp 12volts. As permanent livaboards is it worthwhile increasing the bank to four.

Your suggestions will be welcome.

John

I am sure the leccy experts will be along soon to advise

Mick

[bottle]

If the batteries are not kn*ck**ed then it will take a lot longer than eight hours to re-charge them.

 

What has happened is you have only partly charged them and then used that charge.

 

Think of the batteries as a bucket you have emptied the buckets but only half filled them, (guesstimate) you have then gone on to empty them again but of course you only started with them half full, so that is why they appear to not be holding their charge.

 

If the batteries are recoverable I expect a charge from a decent three stage charger connected to the mains for about 24Hrs may do it.

 

I am sure Chrisw can give exact figures but I hope you get my drift.

 

If you decide to change them, look at getting three (same physical size) but at a higher ampere rating, be careful on how the rating is stated 100amps at 10Hr rate is not the same as 100amps at 20Hr rate.

 

Remember though all that will do is extend the time between charges but you will have to charge longer, when you do charge.

[Offcumden]

If the batteries are not kn*ck**ed then it will take a lot longer than eight hours to re-charge them.

 

What has happened is you have only partly charged them and then used that charge.

 

Think of the batteries as a bucket you have emptied the buckets but only half filled them, (guesstimate) you have then gone on to empty them again but of course you only started with them half full, so that is why they appear to not be holding their charge.

 

If the batteries are recoverable I expect a charge from a decent three stage charger connected to the mains for about 24Hrs may do it.

 

I am sure Chrisw can give exact figures but I hope you get my drift.

 

If you decide to change them, look at getting three (same physical size) but at a higher ampere rating, be careful on how the rating is stated 100amps at 10Hr rate is not the same as 100amps at 20Hr rate.

 

Remember though all that will do is extend the time between charges but you will have to charge longer, when you do charge.

[Offcumden]

Thanks I do get your drift, I may be looking at the bucket half empty but given that the charge of eight hours dissapated to zero overnight with minimal current being drawn ie. 12volt fridge and carbon monoxide sensor. I feel that as the batteries are in all probability over two years old they probably are crackered

The question of charging is not the reason for looking at the increase in batteries, if I were to increase from 3 to 4 batteries

I was assuming that I would be taking out less out of 4 than 3 but would still run the engine on a daily basis either cruising or to charge the batteries, is this not the case?

John

[alan_fincher]

...............with minimal current being drawn ie. 12volt fridge and carbon monoxide sensor.

Just about any type of 12 volt fridge, even the best ones, do not represent a "minimal current" situation.

 

Because they are switched on continually, they are almost invariably the biggest single drain on batteries on any boat, and in many cases if you do an energy audit on electricity used aboard, they will represent maybe as much as 50% of all power used.

 

This applies even for a good modern compressor fridge, who's thermostat should hopefully have it's motor switched off for at least 50% of the time.

 

If you are trying to run an "absorption" fridge, like the Electrolux or Dometic ones, (sometimes "3-way"), on 12 volts, it gets about five times worse, (don't even try!).

 

Even 12 volt "cool boxes" are guzzlers.

 

Running an electric fridge comes at a lot of pain, if you have meagre electricity supply.

[Gibbo]

Just about any type of 12 volt fridge, even the best ones, do not represent a "minimal current" situation.

 

That reminds me of the early days of inverters.............

 

"How much power do you need? That decides the size of inverter and batteries required"

 

"Oh nothing big, just a TV, video, small HiFi and a hair drier."

 

 

Gibbo

[Keeping Up]

"Oh nothing big, just a TV, video, small HiFi and a hair drier."

You forgot to mention the microwave

[paulcatchpole]

Just about any type of 12 volt fridge, even the best ones, do not represent a "minimal current" situation.

 

'Cause I'm sad like that, I've been waiting for an excuse to post some figures for our electric fridge.

 

It's a 230v under-counter, B-rated, nearly new Indesit fridge - with both the big ice box full and the fridge as well. Plenty of door opening for retrival of cold beverages - I'd guess typical house-like day to day use. It's set on 4 of 6 in terms of thermostat and recently froze some eggs in the bottom - CreamCheese wasn't happy about that...

 

Using one of those cheapie mains-monitoring plug-through things (clever enough to show power factor all the same), I've been getting the following. Time measured from now backwards, as it were:

 

Runtime: 6 days, 1hr, 33mins

Min power draw: 67.9w

Max power draw: 953.8w <<<<<<<<<< Edited to add - What's going on here then?

KWh usage: 6.690kwh

 

So, wh/day = 46ish.

 

Given that these figures are on mains, and taking the common view of 1/10th to cover inverter inefficiency, that's 46ah a day if it were on battery.

 

Not sure if that adds much to the big scheme of things, but I wonder if an A-rated one would be much better?

 

HTH, PC

Edited April 27, 2009 by paulcatchpole

[chris w]

I make the AH per day closer to 100 not 46AH for your fridge.

 

Mains fridges are about 30% more inefficient than 12v fridges (10% due to the inverter losses and an additional 20% due to the mains compressor).

 

But even on your figures of around 7000WHrs over 6 days that's 1170 watt hours per day = 98AH per day based on a 12v battery. In reality, you now need to add the 30% inefficiency losses which would bring the number up to 127AH per day.

 

Compare that to my 12v fridge which uses about 50AH per day (less than half of your model). 50AH per day is a typical figure to use in a power audit for a 12v fridge.

 

Chris

Edited April 27, 2009 by chris w

[paulcatchpole]

I make the AH per day closer to 100 not 46AH for your fridge.

 

Mains fridges are about 30% more inefficient than 12v fridges (10% due to the inverter losses and an additional 20% due to the mains compressor).

 

But even on your figures of around 7000WHrs over 6 days that's 1170 watt hours per day = 98AH per day based on a 12v battery. In reality, you now need to add the 30% inefficiency losses which would bring the number up to 127AH per day.

 

Compare that to my 12v fridge which uses about 50AH per day (less than half of your model). 50AH per day is a typical figure to use in a power audit for a 12v fridge.

 

Chris

 

Oh s*d, you're right as well...

 

I can't add up!

 

Perhaps not setting it to freeze eggs might help?

 

I wasn't expecting it to be particularly good, given the B rating, but even so, I'm not too stressed about that result.

 

Thanks for correcting me, Chris.

 

PC

[MoominPapa]

Max power raw: 953.8w <<<<<<<<<< Edited to add - What's going on here then?

Start-up surge. That looks about the same as ours takes for a couple of seconds when the compressor starts. It's significant for inverter sizing, but not really for cumulative energy use.

 

MP.

[alan_fincher]

But coming back to this.......

 

...............with minimal current being drawn ie. 12volt fridge and carbon monoxide sensor.

 

even Chris' example of a very efficient 12 volt fridge uses about 50 Ah per day. So if you start the day with a perfect, 100% charged, 100Ah battery, by the end of it the fridge will have taken it to only 50% charged - the lowest it should go, without damage.

 

I think that amply supports my claim that a 12 volt fridge can never be treated as a "minimal current" device.

[Offcumden]

But coming back to this.......

 

 

 

even Chris' example of a very efficient 12 volt fridge uses about 50 Ah per day. So if you start the day with a perfect, 100% charged, 100Ah battery, by the end of it the fridge will have taken it to only 50% charged - the lowest it should go, without damage.

 

I think that amply supports my claim that a 12 volt fridge can never be treated as a "minimal current" device.

 

So are we concluding that on the information I have given that my batteries are in all probability crackered any thoughts on increasing the capacity of the bank?

john

[chris w]

So are we concluding that on the information I have given that my batteries are in all probability crackered any thoughts on increasing the capacity of the bank?

john

For a liveaboard I would recommend you increase the bank size up to 4 batteries but go for 4 x 135AH rather than 4 x 110AH. Owing to the Peukert factor, you will get more than just the simple arithmetic increase.

 

4 x 110AH = 440AH and 4 x 135AH = 540AH an arithmetic increase of 23%. However, in reality the true increase (complex maths) will be around (540/440)^1.3 or 31% which is 35% MORE actual capacity than the simple arithmetic would have us believe comparing 110AH to 135AH. Bigger banks are better value.

 

Chris

[Offcumden]

Chris

Many thanks for that, I'm sure that all of the responses were well intended however when you are short on experience as we are and looking for guidance from the elders, what could be interpreted or appears as personal point scoring can be frustratin ,after all we all have to start from somewere.

many thanks

john

[paulcatchpole]

Start-up surge. That looks about the same as ours takes for a couple of seconds when the compressor starts. It's significant for inverter sizing, but not really for cumulative energy use.

 

MP.

 

I'm glad you're seeing something similar as well - I'd guessed it'd be a temporary thing, stall current or start surge, but it does explain why it isn't happy on our small inverter.

 

Cheers!

 

PC

[bottle]

Thanks I do get your drift, I may be looking at the bucket half empty but given that the charge of eight hours dissapated to zero overnight with minimal current being drawn ie. 12volt fridge and carbon monoxide sensor. I feel that as the batteries are in all probability over two years old they probably are crackered

The question of charging is not the reason for looking at the increase in batteries, if I were to increase from 3 to 4 batteries

I was assuming that I would be taking out less out of 4 than 3 but would still run the engine on a daily basis either cruising or to charge the batteries, is this not the case?

John

 

 

For a liveaboard I would recommend you increase the bank size up to 4 batteries but go for 4 x 135AH rather than 4 x 110AH. Owing to the Peukert factor, you will get more than just the simple arithmetic increase.

 

4 x 110AH = 440AH and 4 x 135AH = 540AH an arithmetic increase of 23%. However, in reality the true increase (complex maths) will be around (540/440)^1.3 or 31% which is 35% MORE actual capacity than the simple arithmetic would have us believe comparing 110AH to 135AH. Bigger banks are better value.

 

Chris

 

I have re quoted Chris's post and would not dare to disagree

 

but I will try to answer specifically the highlighted in your post, yes you will take less out of each battery but will still take out the same total from the bank.

 

Therefore you will still need to put back what you have used plus some more owing to losses in the charging system. (As per normal)

 

There is another advantage of more batteries or higher amperage in the fact the batteries will not have to 'work' so hard and may last longer.

 

Simplistic example, four batteries discharged by 25% then for the same power consumption five will only discharge by 20% assumes each individual battery is of the same size.

Edited April 27, 2009 by bottle

[RobinJ]

I have re quoted Chris's post and would not dare to disagree

 

but I will try to answer specifically the highlighted in your post, yes you will take less out of each battery but will still take out the same total from the bank.

 

Therefore you will still need to put back what you have used plus some more owing to losses in the charging system. (As per normal)

Quite agree, a quick calculation suggests that on mains you would need about 24 hours and cruising about 6 hours (depending on alternator size) to get those batteires back to anything like full charge! - I think you mentioned a couple of hours?

[dor]

Going back to the original question, it is my experience that if you have batteries that are say a couple of years old, they may be fine if you keep them reasonably well charged. However if you flatten them completely, say by leaving a light on, they never recover to how they were before.

 

I'm sure I have read somewhere that every time you completely flatten a battery you halve its life. Due to sulphation I believe. Same thing will happen if they never get really fully charged.

[mikevye]

Unknown to me a spade connector had worked loose on the Domestic alternator. quote]

 

Alarm bells ringing here! I to had consistantly flat batteries even after a long day cruising (12hrs) the following morning the batteries were virtually depleted. Then I discovered a spade connector disconnected from the alternator reconnected it and hey presto lights were much brighter when charging and batteries appeared to be charged more fully. Turns out that the prestolite alternator has a unique feature as supplied from the manufacturer which allows for an external regulator to be fitted. All I had done was bypass the knackered internal regulator and put unregulated charge to the batteries resulting in new batteries on top of a new alternator megga bucks!!!!!!!!

[Charlie Breakfast]

But coming back to this.......

 

So if you start the day with a perfect, 100% charged, 100Ah battery, by the end of it the fridge will have taken it to only 50% charged - the lowest it should go, without damage.

 

I think there is a difference between optimising the total power stored and extracted over a batteries lifetime and damaging it.

 

50% is normally quoted as the optimal discharge figure for maximising the total power extractable from a battery over its lifetime. Exactly where discharge becomes damaging (as opposed to sub optimal) I suppose depends on battery type , make and condition. A good deep cycle battery might not be damaged with the occasional discharge to 35% charge, a poor car starter battery might be killed after one at 50% and maybe leisure could survive a few at 40%. But these are amateur guesses.

 

Defining damage could be fun as you could say any use damages a battery!

 

However using a crude definition such as "Go below this charge level and this new good condition battery will need changing in the very near future" are the above guesses about right? I bet the answers not simple !

 

Oh well ...here goes..make room in the bunker... i'm coming in

 

Cheers

Chas

[chris w]

Defining damage could be fun as you could say any use damages a battery!

 

Chas

By "damaging" we normally mean that the batteries' capacity will be reduced compared to that printed on the label. So, 3 x 110AH (330AH total) once heavily discharged may only recover to say 250AH. Your charger will still show them as fully charged 100%. But they will be fully charged 100% to a lower AH figure.

 

Gross damge will be caused by discharging them heavily and leaving them in a discharged state for a couple of weeks. They will probably not recover as the lead suplhate coating (a consequence of discharging) hardens and cannot be removed by mere mortals.

 

Chris

[Gibbo]

I think there is a difference between optimising the total power stored and extracted over a batteries lifetime and damaging it.

 

50% is normally quoted as the optimal discharge figure for maximising the total power extractable from a battery over its lifetime. Exactly where discharge becomes damaging (as opposed to sub optimal) I suppose depends on battery type , make and condition. A good deep cycle battery might not be damaged with the occasional discharge to 35% charge, a poor car starter battery might be killed after one at 50% and maybe leisure could survive a few at 40%. But these are amateur guesses.

 

Defining damage could be fun as you could say any use damages a battery!

 

However using a crude definition such as "Go below this charge level and this new good condition battery will need changing in the very near future" are the above guesses about right? I bet the answers not simple !

 

Oh well ...here goes..make room in the bunker... i'm coming in

 

Cheers

Chas

 

You're absolutely correct.

 

As far as I'm concerned absolutely the best explanation of this on the internet is here............

 

http://www.smartgauge.co.uk/50percent.html

 

 

Gibbo

 

Gross damge will be caused by discharging them heavily and leaving them in a discharged state for a couple of weeks. They will probably not recover as the lead suplhate coating (a consequence of discharging) hardens and cannot be removed by mere mortals.

 

Which reminds me.......

 

I've been contracted (yet again) to test (yet) a (nother) battery pulse desulfator.

 

Apparently this one is (yet again) different and this one does indeed (yet again) work unlike the others.

 

It's becoming a reccurring theme this! I do believe there is some merit in the process but so far all the one's I have tested have resulted in inconclusive data.

 

Gibbo

[colin loach]

Talking about fridges, I have a three way one but I turn it off when I go to bed. I normally run travel about six huse. do you think I am taking out more than I am putting in.ours a day and have a 90 amp alternator for domestic