Can I use a car battery? Or do I need a Marine Battery?

[FARP]

Hello,
I've got a 23ft racing yacht which I'd like to install with a battery to power nav lights, internal lights and a small stereo. It isn't needed to start an engine.

The battery would probably be taken off the boat after every trip.
Do I really need an expensive marine battery? Would a car battery encased in an airtight container not be sufficient?
If a car battery would do then I'd be able to get a standard charger wouldn't I?
Any help on this matter is much appreciated as the other owner and I have little experience in marine electrics.
Cheers,

 

[Phoenix of Hamble]

Yup, for light use of the sort you describe, a car battery would be fine.... and charge at home with an normal car battery charger....

 

[Channel Ribs]

Or you could go to the other extreme and get a small marine battery. Would a 12ah deep cycle gel one work better for you? More portable, less damaged by being run down before being charged at home and cheap too.

 

[VicS]

[ QUOTE ]
Would a 12ah deep cycle gel one work

[/ QUOTE ] But would a cheap and cheerfull car battery chager be suitable for it. I thought they were more fussy about charge rates.

A sensible choice might be a small leisure battery as that should be happier being significantly discharged, although it should still be recharged asap. I think the smallest leisure batteries are about 45ah

Not sure the battery should be in an air tight container as some breathing will be required won't it?

 

[Channel Ribs]

[ QUOTE ]
I thought they were more fussy about charge rates.

[/ QUOTE ]

You dont want to put too much charge in too quickly, so a budget charger which is not left unattended it fine. Not that you need to leave them for long, 12ah does not alot of charging take.

 

[simonfraser]

if you are going to take it off the boat, you can get 12v nicad power packs, smaller to carry ?

 

[MrCramp]

Unless you are considering buying high-tech (gel etc.) batteries then I would have thought a marine/leisure battery as used by caravaners would be no more expensive than a car battery. The car battery is designed to give a quick, short burst of power to start the engine and thereafter the car alternator supplies the power and the battery only receives charge. A marine/leisure battery is designed to release much less power over a long time. It is the battery most suited to your use and will carry on working when the car battery has ceased. I am surprised that anuone would endorse the use of a car battery in these circumstances.
85 AMP battery £29 http://www.towsure.com/product.asp?p=493
110 AMP battery £41.50 http://www.towsure.com/product.asp?p=1914
Battery charger £11.95 http://www.towsure.com/product.asp?p=3304

I would use these products/prices as a marker. I paid £50 for a 110AMP battery 4 years ago, with a 2 year guarentee, and it is still going strong. I bought a charger similar to this one http://www.halfords.com/webapp/wcs/store...tegoryId=31335#

Hope this helps.

 

[VicS]

An 85 ah battery, the smallest that towsure list is much larger than FARP is going to need I guess and heavier too but a pretty reasonable price

My 45 ah leisure battery was a Lucas one.

 

[MrCramp]

Accept what you say Vic but I considered
3 10 watt nav buls, = 30 watt = 2 1/2 amps per hour.
Music Radio say 1 1/2 amps per hour
No VHF???
Interior lights, 1 ,10watt call 1 amp per hour.
Total use 5 amp per hour.
How many amps useable out of a 45AMP battery?? say 30, would give 6 hours use.
Use out of a 85AMP battery, say 55, gives 11 hours use.

I would be concerned that as FARP and friend don't know much about electrics, and being a belt and braces man, I would go for the bigger option. If they were totally dedicated racers I guess they would manage without the stereo!

 

[VicS]

You may be right but i would have said 1x 10 watt tricolour (But even less with a LED bulb, 4watts if it is a Doctorleds one or as little as 1.1 watts consumption for the ultraleds one)


I would not consider that the stereo would be on for many hours nor the cabin light which could also be an LED one

I'd meet you half way with a 60ah one though if you insist. My battery has now died and I might just go for the 60ah one as I do not have any LED lights but I never ran into any problems with the 45ah one and I always used the autohelm and always had the VHF on.

 

[William_H]

I think your primary consideration is the weight of the battery and then cost. Weight because an 85 AH battery will not be easy to lug a long way to your car or into a dinghy.
So whatever you can find that is cheap and light. You might like to try your luck at a motor car wreckers yard for S/H one.
The SLA gel batteries come in small or large sizes but are not particularly cheap but then they are spill proof. You need to tie a battery down especially a heavier one with a cover to protect the terminals from anything falling across them.
You might consider a series of 10 NiMH D cells soldered together as being very light and good to the last drop of power but expensive.
I would suggest that you put one fuse at the battery of about 5 amps and leave it at that with a switch for lights. You certainly don't need fuses for each circuit.

Now battery chargers. If you are like many people now they have a collection of plug pack chargers for various battery powered items.
Or you can find them at car boot sales. You need a transformer type rated at 12 volts and maybe 200 milliamps. You can tell it has a transformer by the weight. The really light ones have a switch mode power suply which is well regulated at 12 volts. Thats no good.

A transformer type will deliver over 14 volts no load but fall with load so will over a few days provide enough charge on your battery. The advantage is that even if you leave it on and forget it it will not damge a larger capacity battery. Be carefulkl with small SLA. You need a multimeter with current range to confirm just how much current is going into the battery. You can calculate a rough idea then of how long it needs to recharge the battery. eg if you reckon you have used 10 amp hours from a 15 AH battery then a 250 ma charge (1/4 amp) will give you 1 AH every 4 hours or take 60 hours to give a good recharge (10AH plus a 50% margin).
If the current seems a bit much for the rating of the transformer (it gets too hot) then fit a light bulb in series with the battery ie 12volt 10 watt. This will slow the current down a bit.

or if you don't fancy fiddling buy a charger but still get one with an ampmeter or get a multimeter to check actual current at various stages of the charge. It is not rocket science and you will need to be familiar with electrics. good luck olewill

PS for exactly the same role + VHF radio I use an old 14AH wet Nicad which is over 20 years old. it is charged by a 5 watt solar. (need 20 watts for UK) and have never run short of power while racing even 3 hour night races. olewill

 

[chrishelen]

Hi, i`m confused again,can i use my car charger to charge my boat batts,1-85ah and 1-120ah,what would happen if i did? my engine alternater charges them ok and thats off a car(montego).
rgrds chris.

 

[noby]

Hi all.
Similair question. I think I can get my hands on a battery for a golf cart. 12v 35Ah with a charger. My needs are pretty basic too, nav lights, cabin light, possibly VHf in the future.
I'm guessing this should be ok. Am I right?

 

[Evadne]

35Ah sounds a bit light, if you look at discharge curves for lead acid batteries, much more than 50% discharge will kill the battery prematurely. More than 75% is more than I would want to do except in an emergency.
I run a light load (nav. lights, vhf occasional internal lights and a small diesel starter). I used to buy a big car starting battery (i.e. one for a Sierra or similar), which would last for 2-5 years depending on the level of abuse and how cheap it was, but now I use an 85Ah "leisure" (deep cycle) which will hopefully last a bit longer. they're not much more expensive, or heavier, in the scheme of things. But it does stay on the boat, as it is charged from the inboard.

 

[VicS]

[ QUOTE ]
a battery for a golf cart. 12v 35Ah

[/ QUOTE ] I agree with Evadne it is a bit small but as i have already said my 45 ah leisure battery has proved adequate with me using an Autohelm all the time. If by "getting my hands on" you mean it is free or nearly so then go for it. If you later find it is too small you have lost nothig and you know to replace it with bigger. You can as I already indicated reduce your power consumption by fitting LED type bulbs (Note though I got the powerconsumptions of the ultraled and Doctorleds ones the wrong way round I think!)

A golf cart battery should be a genuine deep discharge battery whereas my Leisure battery is not, so it should be much happier about being discharged to a low level. The leisure battery is only a modified car battery and infact still has engine cranking capabilies. I've often wondered if the modification extends any deeper than the label!

 

[VicS]

[ QUOTE ]
can i use my car charger to charge my boat batts,1-85ah and 1-120ah

[/ QUOTE ] Yes of couse if they are ordinary wet cell lead/acid ones. But unless you have a automatic type charger you will need to keep an eye on them preferably monitoring the voltage and stopping once you have got to about 14.4 volts. If you want to leave them unattended you will have to invest in an automatic one.
120 ah is a good bit bigger than many car batteries so to make the recharging time a reasonable length you will need a charger with a good maximum output 10amps perhaps, maybe more.

An ordinary alternator will be regulated to about 14volts so over charging is not an issue infact it will not even get them to a fully charged state hence the popularity of expensive "smart" charging regulators.

 

[Salty John]

If you don't want to start an engine or run a fridge you might want to consider individual battery (dry cell) operated nav lights (about £10 for a set of three), a battery operated lantern for internal light and a battery operated stereo. If you buy your batteries in bulk the cost shouldn't be too prohibitive, depending on how often you use the boat. This saves lugging the big battery backwards and forwards to your house for charging.
If you go the big battery route you should get a deep cycle battery because your normal pattern of operation would be to deeply discharge the battery between charges. These are for some reason called "leisure" batteries in the UK. Golf cart batteries are deep cycle batteries and very suitable for boat use because their pattern of use is very similar - deep discharge between charges. I've never seen them in other than 6v though, so you need to join two together. An automotive type battery charger is fine if you don't need to charge quickly; without a "smart" regulator to control the charging rate a battery charger takes a very long time to fully charge a battery once it's over about 70% "full" and gets slower as the charge reaches 100%. No problem if you can leave your battery on charge for a few days between uses.

 

[jimbaerselman]

If you're going to discharge regularly to 50%, then a deep cycle battery will last a lot longer than a car battery - and usually pay for its extra cost. Think caravan suppliers, not marine suppliers, they're cheaper! You'll then also be able to use a smaller battery . . . less weight to lug around.

If you're prepared to carry more weight around, discharging only to 75%, then a car battery will do the job with the same life. But it'll need to have twice the capacity!

To understand the reasons for my statements, go to Battery Comparisons
And yes, if you've got plenty of time for re-charging, your good old fashioned battery charger will be fine. You only need smart chargers if your charging time is limited and you want to put maximum charge in as quickly as sensible.

So, work out your likely consumption (good stuff earlier in this thread) and decide whether that's going to be 25% or 50% of your battery capacity - trading cost against weight. I Suspect deep cycle will win . . . but there are some very cheap car batteries out there . . .

 

[noby]

[ QUOTE ]
If by "getting my hands on" you mean it is free or nearly so then go for it.

[/ QUOTE ]

Yep, my hope would be to pick one up for free.

I'm also looking down the dry-cell battery route.

 

[KevB]

As the cost of a 85ah deep cycle is less than £50 is the saving between this and a cheap standard car battery woth the worry?