Csail
N/A
A friend has got a little sail boat and has asked me to fit power to it..i think it has a sailpower outbd. with alternator (about 6hp) question is- what size leisure battery to power maybe 2 flo. lights, nav lights,e.sounder &speed log?
Battery size
- Thread starter Csail
- Start date
cliff
Well-Known Member
Difficult to say without more information such as type of sailiing he intends, does he have access to shore power?, is it a trailer sailer that he will take home after each trip?
Personally I would look at a minimium of 1X110Ah or 2X65~75Ah. The smaller batteries may be easier to fit in somewhere and would be easier to remove for recharging as I am sure the little alt. on the ob will not have the guts to do any serious recharging. A friend (yes I do have some) had a little ¼ton class with a 9hp ob (c/w alternator) and managed reasonably well with 2X65Ah batteries but did need the occassional charge from a mains charger even when running the ob for long periods. The smaller 65Ah batteries were easy to remove and carry whereas the 110Ah are considerably heavier and difficult to manhandle around.
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"Artificial intelligence is no match for natural stupidity"
Personally I would look at a minimium of 1X110Ah or 2X65~75Ah. The smaller batteries may be easier to fit in somewhere and would be easier to remove for recharging as I am sure the little alt. on the ob will not have the guts to do any serious recharging. A friend (yes I do have some) had a little ¼ton class with a 9hp ob (c/w alternator) and managed reasonably well with 2X65Ah batteries but did need the occassional charge from a mains charger even when running the ob for long periods. The smaller 65Ah batteries were easy to remove and carry whereas the 110Ah are considerably heavier and difficult to manhandle around.
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Tisme
Well-Known Member
1 x75AH will do it, unless he intends doing a lot of night passages. See how that goes and then consider a solar cell to keep it charged up.
I reckon that it's better to have one battery well charged than two not-so-well-charged.
I reckon that it's better to have one battery well charged than two not-so-well-charged.
William_H
Well-Known Member
It depends a lot on how much motor running he does and how much current the O/B will deliver. I for instance have an old 6hp Johnson which is seldom used and only gives a fraction of an amp into a battery so I don't bother with o/b charging. I would however if I frequently ran the o/b for an hour or so.
So my option is a mid sized battery(actually about 10AH NiCad but that is unusual) with a small sloar panel. This provides enough power for monthly night/evening races and occasional radio use. (in Oz summer sun)
The alternative is to have a small battery and take it home to recharge. Obviously you want a tiny battery easily carried and one of the SLA types of about 10 Amp hour would suit. Just be very carefull to slowly recharge as they can be damaged by excessive charge. PM me for advice iof you go that way. (most of my friends use this method)
Ultimately your friends experience will dictate which method is best. However don't go for a big battery. Get a small car type which may be cheapest and lightest. olewill (PS the depth sounder running all the time may be the biggest demand so turn it off) (you can tell I don't have one) (actually a keel which is a reliable depth sounder)
So my option is a mid sized battery(actually about 10AH NiCad but that is unusual) with a small sloar panel. This provides enough power for monthly night/evening races and occasional radio use. (in Oz summer sun)
The alternative is to have a small battery and take it home to recharge. Obviously you want a tiny battery easily carried and one of the SLA types of about 10 Amp hour would suit. Just be very carefull to slowly recharge as they can be damaged by excessive charge. PM me for advice iof you go that way. (most of my friends use this method)
Ultimately your friends experience will dictate which method is best. However don't go for a big battery. Get a small car type which may be cheapest and lightest. olewill (PS the depth sounder running all the time may be the biggest demand so turn it off) (you can tell I don't have one) (actually a keel which is a reliable depth sounder)
Csail
N/A
She has to use the motor for 20 mins or so going out and on the return for every trip and quite often night sails or in harbour at night requiring light.no need or access to shore power.
john_morris_uk
Well-Known Member
There are several problems here and they each need to be addressed in trun.
Firstly, you need to assess how much power is actually going to be consumed. One flourescent light for three hours = so many amphours. One GPS for eight hours = so many amp hours.
To calculate Amp hours, find the current drawn by the kit, and multiply up. 100 ma for an echosounder = 0.1 Ah per hour of use etc.
Once you have the total Ah drain, you should choose a battery that will only be discharged to about half capacity.
You then need to ensure that this discharge is put back into the battery. Check the charging output of the outboard IN USE. Don't rely on what it says it will give in the handbook. If the outboard doesn't give enough, then a solar panel or wind generator, or take it home to charge it. Look after the battery, if its left discharged for any length of time it will die! Car batteries are cheap, but will die quicker. The small leisure batteries are better, and nearly as cheap.
If your friend wants a reliable system, then the above method is the best way to acheive it. The trouble with lead acid batteries, is that they can be metaphorically screaming out for a more charge, but they will keep supplying until the lights go out.
Although I understand others comments that they turn their echo sounder off and save power - that style might not suit the sailing enjoyed in some UK waters!
Firstly, you need to assess how much power is actually going to be consumed. One flourescent light for three hours = so many amphours. One GPS for eight hours = so many amp hours.
To calculate Amp hours, find the current drawn by the kit, and multiply up. 100 ma for an echosounder = 0.1 Ah per hour of use etc.
Once you have the total Ah drain, you should choose a battery that will only be discharged to about half capacity.
You then need to ensure that this discharge is put back into the battery. Check the charging output of the outboard IN USE. Don't rely on what it says it will give in the handbook. If the outboard doesn't give enough, then a solar panel or wind generator, or take it home to charge it. Look after the battery, if its left discharged for any length of time it will die! Car batteries are cheap, but will die quicker. The small leisure batteries are better, and nearly as cheap.
If your friend wants a reliable system, then the above method is the best way to acheive it. The trouble with lead acid batteries, is that they can be metaphorically screaming out for a more charge, but they will keep supplying until the lights go out.
Although I understand others comments that they turn their echo sounder off and save power - that style might not suit the sailing enjoyed in some UK waters!
bluedragon
Well-Known Member
I'd fit a 65-85Ah leisure battery with carrying handle so it can be taken home for charging if necessary, and change it once a year (£40) as it will be likely undercharged for most of its life and it's false economy to keep hoping it'll last another season. When I bought my boat the Dynastart had just about given up and a small wind generator was the only thing charging. Batteries fitted the previous year would work fine for a few hours, then the voltage would fall off the cliff in minutes. I've since got a super new charging system, but the lessons learned about consistently undercharged batteries were clear! If it can't be avoided, then don't spend a fortune on the battery and change it often IMHO.
Tisme
Well-Known Member
[ QUOTE ]
(PS the depth sounder running all the time may be the biggest demand so turn it off) (you can tell I don't have one) (actually a keel which is a reliable depth sounder)
[/ QUOTE ]
My sounder only uses 10ma so I don't worry about it.
I agree with you about the keel though. I have a swinging keel which harmlessly lifts out of the way when I scrape along the bottom. It is much more accurate than the sounder!
(PS the depth sounder running all the time may be the biggest demand so turn it off) (you can tell I don't have one) (actually a keel which is a reliable depth sounder)
[/ QUOTE ]
My sounder only uses 10ma so I don't worry about it.
I agree with you about the keel though. I have a swinging keel which harmlessly lifts out of the way when I scrape along the bottom. It is much more accurate than the sounder!
Pye_End
Well-Known Member
I think your friend should seriously think about a deep cycling battery. With no big engine block to turn over, and chances are any battery will be getting regular discharges below 50%, then they will not last long. Solar panel to keep them topped up when not in use, and a charger for getting them charged after needing to use nav lights.
VicS
Well-Known Member
Almost exactly my requirements except that I also use a VHF and a tiller pilot quite a lot.
Check it by all means but you will almost certainly find that the output from the O/B is next to nothing unless it is running at full revs and that is something the average small sail boat sailor hardly ever does.
You will probably find it difficult to fit a large battery. Weight is significant in a small boat and the builder/designer's recommendations should be observed otherwise keep it faily central or try to balance the weight of the O/B or water tank etc.
I have opted for a smallish leisure battery that can be transfered to the dinghy and transported ashore for charging if and when necessary without the assistance of a tame gorilla but I have found that a small (5 watt) permanently solar panel has eliminated the need to do that. On that basis the next one will be a medium sized leisure battery
Economise wherever possible with nav lights. Ie fit a bicolour for motoring, a tricolour for sailing, and maybe make that a tri-white in order to combine stern and masthead (steaming) lights into one*. Also look at the bulb sizes relative to the boat length as you will find that lower wattage bulbs will be acceptable and available in some caes eg 10watts instead of 25 for the tricolour.
LED nav lights would be nice but they are so expensive.
Make sure every thing is correctly fused and that the battery is securely mounted.
*I know the arguments against lights at the top of the mast but if this really is a "little sail boat" its mast won't put them high enough to be in line with shore lights when viewed from the bridge of a ship, at least not at close quarters.
Check it by all means but you will almost certainly find that the output from the O/B is next to nothing unless it is running at full revs and that is something the average small sail boat sailor hardly ever does.
You will probably find it difficult to fit a large battery. Weight is significant in a small boat and the builder/designer's recommendations should be observed otherwise keep it faily central or try to balance the weight of the O/B or water tank etc.
I have opted for a smallish leisure battery that can be transfered to the dinghy and transported ashore for charging if and when necessary without the assistance of a tame gorilla but I have found that a small (5 watt) permanently solar panel has eliminated the need to do that. On that basis the next one will be a medium sized leisure battery
Economise wherever possible with nav lights. Ie fit a bicolour for motoring, a tricolour for sailing, and maybe make that a tri-white in order to combine stern and masthead (steaming) lights into one*. Also look at the bulb sizes relative to the boat length as you will find that lower wattage bulbs will be acceptable and available in some caes eg 10watts instead of 25 for the tricolour.
LED nav lights would be nice but they are so expensive.
Make sure every thing is correctly fused and that the battery is securely mounted.
*I know the arguments against lights at the top of the mast but if this really is a "little sail boat" its mast won't put them high enough to be in line with shore lights when viewed from the bridge of a ship, at least not at close quarters.
Tisme
Well-Known Member
I think the first thing to do is to find out what the charging output of the engine is. If you post the details of the engine here somebody is bound to be able to give you some idea. As others have said it won't be a lot but if it's 6 amps rather than 3 amps......well...that's twice as much isn't it? /forums/images/graemlins/smirk.gif
VicS
Well-Known Member
Not mentioned yet. Make sure the O/B has a rectifier fitted to give a DC output.
Some have, especially if intened as sail boat auxilliaries, otherwise they may only have a lighting coil with AC output.
If it does not, depending on model it may be possible to fit a rectifier or buy a charging lead incorporating a rectifier (prob abt. £60) alternatively get a bridge rectifier of suitable rating and mount it on a heatsink somewhere convenient. Johnsons and Evinrudes are a bit more complicated, requiring a rectifier with 6 diodes arranged just like a 3 phase full wave rectifier.
Sorry if grand mothers and eggs come to mind!
Some have, especially if intened as sail boat auxilliaries, otherwise they may only have a lighting coil with AC output.
If it does not, depending on model it may be possible to fit a rectifier or buy a charging lead incorporating a rectifier (prob abt. £60) alternatively get a bridge rectifier of suitable rating and mount it on a heatsink somewhere convenient. Johnsons and Evinrudes are a bit more complicated, requiring a rectifier with 6 diodes arranged just like a 3 phase full wave rectifier.
Sorry if grand mothers and eggs come to mind!
snowleopard
Well-Known Member
Just a little addition to the calculations: With a lighting coil & rectifier setup, the outboard will produce very low charge rates once the charge is over about 75% so you shouldn't assume that you can get it fully charged during a short period of motoring.
I agree that the battery shouldn't be regularly dischrged below 50% but I would work on your daily cycle being from 50% to 80%, i.e. your daily current draw should be multiplied by 10/3 to get the required battery size.
I agree that the battery shouldn't be regularly dischrged below 50% but I would work on your daily cycle being from 50% to 80%, i.e. your daily current draw should be multiplied by 10/3 to get the required battery size.
simonfraser
Well-Known Member
forget the engine for charging, it is not on for long enough
a 12W solar panel will put about 3 A in per day during a nice summer day, 20% of that during the winter, do the maths, not good eh ?
a 12W solar panel will put about 3 A in per day during a nice summer day, 20% of that during the winter, do the maths, not good eh ?
VicS
Well-Known Member
Agree about the engine, but I already said that.
A 10 or 12w solar panel would be nice but it is difficult to find the space on a small boat to mount one. Two 5 or 6w ones might be an option though. I was lucky in that my boat has just the perfect place for a 5w one. In practice that has proved to be adequate even with the VHF on and the Autohelm in use for much of the time.
A 10 or 12w solar panel would be nice but it is difficult to find the space on a small boat to mount one. Two 5 or 6w ones might be an option though. I was lucky in that my boat has just the perfect place for a 5w one. In practice that has proved to be adequate even with the VHF on and the Autohelm in use for much of the time.
William_H
Well-Known Member
Just a few final comments. Re solar panel I found after 3 damaged panels that the best bet is 2 pieces of bungee attached to the panel. I wrap these around the boom and covered mainsail with leads going to a socket just inside the hatch. The sollar panel is always put away first thing on arrival at the boat and the last thing to be refitted on departure. This one has lasted several years compared to fixed panels on the front hatch cover which got damaged.
Re outboard charging. probably not worth trying to use considering the cost of rectifier plugs etc. Just be carefull an o/b may specify 10 watt lighting power. This is 10 watts at 12 volts or less AC. When it comes to charging you need 14 volts of DC and many motors will only give a small amount of current after the recifier into a battery.
I think that the take it home to charge may be the best option at least initially then if she wants try a solar panel.
Re correct fusing .. my opinion on this kind of installation is use one fuse at the battery to fuse all circuits.5 amps shouulld do it. ie lights radio sounder. I user an inline fuse holder although they are often unreleiable due to inadequate pressure on the fuse connection. regards olewill
Re outboard charging. probably not worth trying to use considering the cost of rectifier plugs etc. Just be carefull an o/b may specify 10 watt lighting power. This is 10 watts at 12 volts or less AC. When it comes to charging you need 14 volts of DC and many motors will only give a small amount of current after the recifier into a battery.
I think that the take it home to charge may be the best option at least initially then if she wants try a solar panel.
Re correct fusing .. my opinion on this kind of installation is use one fuse at the battery to fuse all circuits.5 amps shouulld do it. ie lights radio sounder. I user an inline fuse holder although they are often unreleiable due to inadequate pressure on the fuse connection. regards olewill
