battery

[Guest]

I have an 18' Careel and I want to put a battery in it for lights and 27 meg radio. Have no charger on board.
I know there are deep cycle batteries and normal car batteries. Also, you types up there seem to have a leisure battery. These seem not to exist in the antipodes. A sealed 17 amp hour is available for about A$125. But, methinks a little too small. Also, I am told I need an automatic charger for this. Can get a 40 amp hour for about A$118 deep cycle lead acid.
Silly me, I have forgotten the formula for working out how many amps hours I might need.
Another point is that I would like to fit a small sollar panel.
Can someone please advise on formula, automatic charger, use of solar panel (do I need a regulator), and other good tips. FOr example, should I go for the lead acid - will it leak over my GRP hull and cause damgage?
Ray

 

[salamicollie]

First formula to size -

hours * (Watts/volts) = Ah

So a 25W bulb for 2 hours in a 12V system uses 2Ah

Note a 40Ah battery only gives you 20Ah available, so use Flourescent strip lights to light the cabin and don't sail to long at night!

As long as you mount the battery firmly inside a leak proof box there is no problem with spillage from Lead acid.

Charging from a solar panel - you can go to about 1.5% of the battery capacity for a solar panel without needing a regulator for a wet lead acid batt but make sure it has a blocking diode to stop the battery discharging into the panel when its dark. With a 40Ah batt you should be able to go to a 5-7W output.

Good luck

 

[byron]

What we call a Leisure Battery is just another name for a deep cycle battery (as far as I am aware)

ô¿ô

 

[brianrunyard]

Re previous answer, "So a 25W bulb for 2 hours in a 12V system uses 2Ah".
25W at 12V = 25/12 = 2 Amps
2 Amps for 2 hours = 2 x 2 = 4Ah.
A 25W, 12V bulb for 1 hour uses 2Ah.



Brian
http://homepage.ntlworld.com/brunyard

 

[oldharry]

Not quite Byron: a leisure battery is a CHEAP deep cycle battery. In other words it will take deep cycling, but has no guts. It will be destroyed if used for engine starting, while a true deep cycle unit is capable of pushing the power needed.

The point to remember when calculating battery size is, if you take 40AH out of a 40AH battery you will destroy it. In any case the useable voltage after 20AH drain will be too low for most 'domestic' uses. In any case the AH rating is nominal and the true capacity depends on battery condition, electrolyte temprature etc.

Without any means of recharging on board, particularly if the supply is to run even a small transmitter (assuming the 27Mghz set is a CB) you will need a minimum of 70 - 80AH for the battery to survive being discharged. Even true Deep Cycle batteries will be damaged if discharged more than 50% capacity, and a small 'Car Battery' will suffer if discharged by much more than 25% from full. Remember too that a domestic charger - i.e. the cheap Battery Charger widely available from most car shops, having no regulating electronics - will only charge a battery up to around 90% capacity (deliberately limited to avoid damaging the battery by overvolting it), and you see that a Car battery has no place anywhere except starting engines. This is after all its sole designed purpose - to give a massive current for 15 seconds or so while starting an engine, then to go back on charge. Deep Cycle and leisure batteries will tolerate lengthy discharge periods at low current drains between re-charge periods - provided the terminal voltage is not allowed to drop below a specified level - usually in the order of 10.5 volts. Most 12volt electronics will have either shut down altogether or be seriously degrading their performance anyway at that voltage.

 

[byron]

That'll teach me to keep quiet

ô¿ô

 

[BarryH]

Agree with most of what you say, but how come my cheap lesuire battery from Maccess (£25) is a 60AH and has been starting and running my domestics for over 3 seasons. It contradicts what you have said, I cant explain it and as long as it keeps doing it for this season, aided by a second one, I dont mind. I looked at the true marine batteries and was overwhelmed by the cost. Where the Marine bit comes in I dont know, Be it lesuire, car, deepcycle or whatever. They are all Lead Acid Accumulators, according to my old physics teacher.

 

[oldharry]

Lucky man! Where did you get them? Usually what happens is that the high starting current overheats and damages the lead plates, resulting in an internal short and failure of the damaged cell. Of course, if you are only starting a small single cylinder engine, a reasonably good Leisure battery will cope with the power demand. I have used one quite succesfully to start a 10hp outboard without any problems, for example.

 

[Guest]

Thanks everyone for your advice.

Looks like I should go for a deep cycle wet cell of about 40 amp hour. I have not yet done the calculations
but I would guess that 20 amp hour should cater for say three nights (i.e., a long weekend). My out board
is a manual start.

Problem is that there is nowhere that I can fit a battery box. I have a small compartment in the bow
that might just take a battery, but not in a box. I presume that under normal conditions the acid would not
leak out of the small vent holes in the caps. So, the problem would only arise with a 180 inversion (which I
hope never to experience). In any event, I presme that a little acid spilled on GRP would not hurt. Am I
correct?
Ray
(from the antipodes)

 

[LadyInBed]

Given your situation, I would go for a totaly sealed battery, lead acid or Gel. Then you can pull it off the boat to recharge without the worry of acid spills. Also go for quick release terminal connectors.

 

[quaelgeist2]

A bit of acid appeared not to have hurt my GRP in a bilge-neighboring compartment in my boat, but the vent holes left out a bit ! I fixed that with some small tube of 2ft.

Have you considered a solar panel of say 10W to continously trickle charge the -samller- battery ? You don't need a regulator then, and your battery is always top-charged when you arrive.

I have used a similar configuration with cabin-lights, VHF, depth/log, radio/cassette and have not run out of power for some years (weekend use mainly)

chris

 

[TonyMills]

Hi

You appear to be getting plenty of good advice on the technical aspects of charging. I've never gone through and worked out my usage but I have two 'Heavy-Duty' 12 volt batteries on my yacht. I installed them two years ago new and since that time they have been exclusively charged by a Solar Cell. If I remember correctly its a Solarex unit which has a power rating of 10 watts and charges at a rate of .60 amps. I get aboard the boat every few days and check battery levels and simply switch over to the lowest battery. Its not fitted with a regulator but it does have a diode to stop night time unloading.

I installed this facility as a temporary measure until I could get an alternator fitted to the Diesel, but its been so successful that its removed some of the incentive to get that fixed (though I really must!). I use one battery exclusively for starting and the other for lights, sounder, engine instruments and log. I have stayed on the boat for four nights without having any problems, though I am concious of the recharge speed and am economical with my battery usage.

I also live in the sunburnt country and I'm sure that helps enourmously with the charging.

Regards
TonyMills

 

[BarryH]

I've got an account at Maccess the motor parts wholesales people. The batteries are "badged" as Equip" lesuire batteries, Cost was £25 each. One has been starting the volvo in the boat for the last 3 seasons. Its not a massive engine (AQ145) but it did have a lazy starter motor for 1 season. The battery has never got hot, and spends the winter insitu with just the master switch in the off position.

Have supplimented it with a second batt this year as i have added a few more leccy gizmos.