ChrisKaye
regular
Reged: 26/08/2004
Posts: 597
Loc: Wiltshire
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Only had this new (to me ) boat 6months or so so still finding my way around it all.
Currently when unplugged from shorepower my batteries (2 in the domestic bank) only last for around 4 hours with just the fridge on, radio and a couple of internal lights (standard 12V halogen downlighters) on. I've had the batteries checked and the bloke says the batteries hold their charge OK
I have a generator fitted to the boat from new which charges the batteries and I wondered if the domestic battery bank was deliberatly a smaller size due to having a generator fitted.
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Wiggo
regular
Reged: 10/09/2003
Posts: 3467
Loc: (State, Country, etc.)
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Umm, yer man's wrong - they're shagged. The fridge should use about 1-4Ah, the radio uses next to nothing and two halogen bulbs use about 2Ah between them.
If you had a pair of 100Ah domestics, they should last at least 20 hours and possibly twice that.
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The nicest thing about not planning is that failure comes as a complete surprise, and is not preceded by a period of worry and doubt.
Nereid Charter
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ChrisKaye
regular
Reged: 26/08/2004
Posts: 597
Loc: Wiltshire
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Thank you Wiggo for the eloquent technical description of the current state of my batteries. To be fair to the bloke, he told me he's more mechanical than electrical and I was hoping this was the case instead of having to get an expensive marine electrician in
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Wiggo
regular
Reged: 10/09/2003
Posts: 3467
Loc: (State, Country, etc.)
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Never been afraid to call a spade a manually operated excavating appliance...
If you really want to know if they're OK, get a £5 'turkey baster' hygrometer from Halfrauds and test them yourself. It only takes a few minutes.
What you need to do is work out how much current everything draws. A fridge can draw about 4 or 5 amps when it's running, but it might only be on 20-25% of the time, so it averages about an amp. If you know the power consumption, just divide by 12 to get the number of amps something needs, so your 10W halogen lights use just under an amp.
Now work out the energy use: just multiply the current by the number of hours you will run it. Fridge for 5 hours = 5Ah, two lights for 1 hour = 2Ah etc and that will tell you how long your battery should last. Bear in mind that you will rarely be able to use more than 40% of your batteries' stated capacity, so if you have 100Ah of domestics, expect to be able to use 40Ah or 40 hours of fridge and nothing else.
Incidentally, fridges are difficult to work out, because they use more power if you keep opening them to take beer out...
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The nicest thing about not planning is that failure comes as a complete surprise, and is not preceded by a period of worry and doubt.
Nereid Charter
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S28
regular
Reged: 19/09/2002
Posts: 4362
Loc: South Coast
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Batteries are cheap. I chuck 'em away after 5 years.
dv.
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Hurricane
regular
Reged: 11/11/2005
Posts: 1686
Loc: Sant Carles de la Rąpita
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Quote:
Incidentally, fridges are difficult to work out, because they use more power if you keep opening them to take beer out...
Solution - ration the beer.
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blueglass
regular
Reged: 27/04/2003
Posts: 772
Loc: Greece (boat) Shropshire (home...
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I have 2 x 110 AH deep cycle batteries for my domestics and yes I get much longer than that. with the fridge turned down a notch or two they will last 24 hours. With normal fridge use + lights, stereo, water pumps etc about 18 hours or so. 4 hours is way out.
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mikehibb
regular
Reged: 23/09/2007
Posts: 479
Loc: Turkey Azerbaijan and Georgia
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Quote:
Quote:
Incidentally, fridges are difficult to work out, because they use more power if you keep opening them to take beer out...
Solution - ration the beer.
I can assure you that my passengers/crew would all chip in to buy a bigger battery bank rather than think about that un-repeatable phrase.
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gwylan
regular
Reged: 31/05/2007
Posts: 352
Loc: Portishead, on tour
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Wiggo has grasped the technical niceties of the situation.
Also make sure you keep the fridge full to capacity with beer - that way once it is cold it uses less energy to keep the contents cool.
Fridge uses 5A, works about 25% of the time so uses about 30AH per day - 100AH battery should last 3 days, if you get over 2 days [ 48 hours] with the lights, water pump and everything else you are doing well
If you are feeling keen you can make sure that there is a good airflow around the back of the fridge. We achieved this with a cheap but quiet computer fan, from Maplin, and saw a comfortable increase in efficiency
The rest is too tiresome and technical to deal with. Replace the batteries and have another beer....
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The pessimist complains about the wind;
the optimists expects it to change;
the realist adjusts the sails
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Wiggo
regular
Reged: 10/09/2003
Posts: 3467
Loc: (State, Country, etc.)
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Mike, I'd like you to go away and think carefully about what you just said. Then you can come back and apologise to all the nice people on the forum you just upset.
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The nicest thing about not planning is that failure comes as a complete surprise, and is not preceded by a period of worry and doubt.
Nereid Charter
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Wiggo
regular
Reged: 10/09/2003
Posts: 3467
Loc: (State, Country, etc.)
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Quote:
Wiggo has grasped the technical niceties of the situation...
Fridge uses 5A, works about 25% of the time so uses about 30AH per day - 100AH battery should last 3 days, if you get over 2 days [ 48 hours] with the lights, water pump and everything else you are doing well.
Thanks for that! The only thing I would point out is that you will never get 110Ah out of a 110Ah battery (more than once). The best you will get is more like 50Ah - if you take any more, you risk discharging it to the point where it won't recover. As you complained about being too techie, I will avoid going off into my usual alternator controller sermon.
And thanks for the computer fan tip - how much difference did that make?
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The nicest thing about not planning is that failure comes as a complete surprise, and is not preceded by a period of worry and doubt.
Nereid Charter
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Kawasaki
regular
Reged: 21/06/2004
Posts: 4621
Loc: Anglesey Wales
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Hey up!
Thanks for the Post Chris.
Some good replies, as usual.
Solved a batt/ fridge prop I,ve had.
Pray tell, why disconnect the shore power?
Skinflint or what? 
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Jerk of all trades. Expert in none.
Plus Don,t do serious, lifes too short.
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oldgit
regular
Reged: 06/11/2001
Posts: 7338
Loc: Medway
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You should be able to get a couple of decent batteries for a sensible price if you shop around.When my domestics recently died after giving sterling service for over six years,leaving us lightless miles from home ,was quoted over £160.00 quid + VAT each from one of the big chains,fortunately they were out of stock and we had to look further afield.Eventually found two decent quality 115A jobs at £80.00 + VAT each.
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Take5
regular
Reged: 19/10/2007
Posts: 753
Loc: DONT TAKE LIFE TOO SERIOUSLY -...
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Nothing to do with me but I have used them for car batteries in the past, purely because they are cheap.
batmanuk website
There is also a "Power Calculation" infosheet you can download from this site. here
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halcyon
regular
Reged: 20/04/2002
Posts: 2824
Loc: Cornwall
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Sounds like surface charge, and they are not being charged correctly.
How does the generator charge the batteries.
Have you checked them with a hydrometer ?
Brian
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Kddpowercentre designers and purveyors of fine charging systems for 30 years.
Powercentre spares and help line
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Medskipper
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Reged: 20/12/2001
Posts: 1646
Loc: Surrey
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Hi Chris,
You don't say what amp hour the batteries are? are they for example 100s 120s etc?
Gwylan answer is about right, but I would take issue with his 25%! Its more likely that the fridge works for 40-50% of the time, particularly in warm weather! all depends on how often you open it for things! i.e. cold air falls out when door is open and motor comes on to replace the warm air you just let in!
It all a matter of maths really, just count up the amps being used! Also if for example you have a 100.amp battery, the useable power is only about half of this i.e. 50amps, so if you have two you have about 100 amps to use. The light which you describe sounds as if it could be a 20 watt bulb.
Barry
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alrob
regular
Reged: 19/07/2005
Posts: 825
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second batman - bought quite a few over the years - next day delivery - good advice over the phone as well
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Hurricane
regular
Reged: 11/11/2005
Posts: 1686
Loc: Sant Carles de la Rąpita
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Surely you dont mean warm beer - Graham?
Perhaps a better solution is to fill the fridge to the brim
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And then ration it.
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leadersail
regular
Reged: 30/11/2005
Posts: 156
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Add EDTA+ to the battery, this is a cleaning agent used in industry to clean heavy metals that will clean off the sulfate during charge and will release the sulfate back into the sulfuric acid during discharge.
It continues to recycle the battery for the whole life of the battery.
Batteries will last 7-8 years instead of 2-3.
Can be added any time, brand new or one 2 years old off the battery dump !
http://www.courtiestown.co.uk/batteries/shop.htm
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Best not take this post too seriously, I'm only here on my Doctor's advice as part of an ANGER MANAGEMENT THERAPY.
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ChrisKaye
regular
Reged: 26/08/2004
Posts: 597
Loc: Wiltshire
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Thankyou everyone for your replies
"Why disconnect the shorepower".....well I was just testing it back at the pontoon berth to see how long the batteries lasted for without shorepower
"How does the generator charge the batteries" I think the generator must charge the batteries as we can get another 4hours battery life after running the generator
"Have I checked them with a hygrometer" the bloke tells me that he has and they are OK and holding charge but admitted that this is the limit of his knowledge.
Not sure of the amp/hours they are very difficult to get to, you have to be the size of a jockey to get at them, so that counts me out, luckily bloke looking at them is smaller and thinner.
Thanks again for everyone's input, I am just going to get him to replace them with good quality new ones and with just a bit more amp/hours than they have now and see how we get on
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DavidJ
regular
Reged: 15/06/2001
Posts: 2489
Loc: home Brum, boat Costa Brava
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115Ah Bosch Marine batteries £85 incl VAT (they are the liquid type not gel) bought 2 months ago from Costco....you will need a mate with a card though. You can join as a member of the public for about £30 (I think) so you could be a few quid in if you stock up on wine and beer as well.
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www.jensenworld.co.uk
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jfm
regular
Reged: 16/05/2001
Posts: 7818
Loc: London/Antibes
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How does the generator charge the batteries" - the gen provides 230v to the battery charger, just as the shorepower does, and that charges the batteries.
Chris, I've nothing much to add to what is written above by wiggo et al but do you have a DC ammeter on your elec panel? If yes, see what current is being drawn from the batteries, to check that it is indeed the few amps that wiggo predicts. There may be other "electrical overheads" (like 2 dozen little indicator bulbs in your elec panel, voltage stabilisers, other things left on, etc) that leak away the battery charge.
If your current draw is only a couple of amps and 4-5 when the fridge is on, you do need new batteries. And if they are that hard to get at, get gel ones for sure cos you will never manage to keep wet ones topped up
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KevB
regular
Reged: 04/07/2001
Posts: 5511
Loc: London
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Hi Chris,
Sorry didn't get to see your boat at the festival, I came round on Monday not thinking that everyone would be back at work!!!
As for your batteries. During my last service in March I had the domestics checked and was told they were fine... Two weeks later one was completely dead the other would only hold a charge for a few hours. So the moral of the story is - people who test batteries don't know what they are on about. Or, people who test batteries destroy them when they stick the tester across the terminals. Take your pick 
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Nirvana
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ChrisKaye
regular
Reged: 26/08/2004
Posts: 597
Loc: Wiltshire
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Hi John, thanks for that, I will check what the current draw is on the ammeter next time I'm down there (I am sure it was only about the 4/5amps Wiggo mentioned). I've got the guy going down to fit me 2 new batteries (biggest that will fit in the boxes) so will report back next time I'm down on the boat. Older son (14) will be doing the topping up !!! so I can stick with normal batteries and not the really pricey gello ones
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Trundlebug
regular
Reged: 04/01/2007
Posts: 98
Loc: River Trent
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An alternative battery supplier is Towsure.
www.towsure.com
Only £74.00 for a 110Ah Leisure battery - including VAT. No membership to pay either!
Has anyone used that EDTA+ stuff? I'm always wary of magic potions & snake oil
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DavidJ
regular
Reged: 15/06/2001
Posts: 2489
Loc: home Brum, boat Costa Brava
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Just a point which I discovered when I was buying batteries for mine, there are different terminal configurations which if you get it wrong may give you the agro of making up new cables. Some have +ve on the right, some on the left.
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www.jensenworld.co.uk
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Hurricane
regular
Reged: 11/11/2005
Posts: 1686
Loc: Sant Carles de la Rąpita
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This thread raises another problem.
What about the battery that starts the generator?
This is our second mobo and both seem to rely on the generator charging its own battery but this isnt any good if the generator isnt used very much.
The main engine batteries and the service batteries always seem to have good staged battery chargers for use when leaving the boat for long periods - thus keeping the batteries in "tip top" condition.
But for the generator battery, what do people do when the boat is left for any length of time.
On the old boat, I used to disconnect the generator battery and hook it up to a small trickle charger if I hadnt used the generator much.
Is this necessary or do people throw the generator battery away after a couple of seasons missuse.
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leadersail
regular
Reged: 30/11/2005
Posts: 156
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Quote:
Has anyone used that EDTA+ stuff? I'm always wary of magic potions & snake oil
http://www.courtiestown.co.uk/batteries/shop.htm
I have no connection with the company.
I have used it on several batteries.
Yes it worked for me.
Very easy to use, a lot easier than changing batteries.
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Best not take this post too seriously, I'm only here on my Doctor's advice as part of an ANGER MANAGEMENT THERAPY.
Edited by leadersail (24/06/2008 15:11)
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