Battery Help please

[Moonshiners]

12v Marine battery (dated around 04/05) we inherrited with our boat is crapping out on us. When I removed it it was holding 4v of charge, after 24 hours trickle charge at home it's holding around 6v. But with a charging rate of anywhere between 10v and 13v.

It used to run everything as long as the engine was going, but would only run ancillaries for about 30 mins after that depending on EQT used... (so pretty useless on a sailing boat)

Is the battery destined for the skip or is there anything I can try first?

If i do buy a new one, any recomendations, what's the main difference between marine/auto batterys?

And what kind of amp should i be looking at for a small sailing boat with an 8hp O/B with charging unit, running - depth, vhf, GPS, and NAV/cabin lights etc...

I know there is a formula but I don't know the average draws, but only looking for a rough idea of what size replacement i should be looking at. I don't want to get one to big which will never charge from the O/B, likewise don't want one small enough that it's useless.

We tend to steam off our mooring for at least 1/2 in and out each time we go out. So average would probably get an hour or two's worth of charge each trip.

Cheers guys n gals just wanted to check before i fork out for a new one!

 

[Tranona]

Skip

Look for a leisure battery designed to do both engine start (although i guess you are manual) and service duties. You can work out size by adding up all your typical consumption over, say a weekend. Probably end up with 60 to 70 ah requirement. Your biggest problem is likely to be charging because your OB does not put out much. Solar panel is one possibility to trickle charge when you are not there.

Battery around £70, Panel about same or a bit less.

 

[Loginname]

Your battery is shot. With those figures it's not even worth trying to charge it.

Your outboard will probably only throw out about 6 amps so, as you say, you don't want too big a battery. Something in the region of 60 to 75 AH will probably be OK.

If you are prepared to pay for it get a proper deep charge battery but most end up getting a so called "Leisure" battery.

FWIW I paid £46 for a 75AH "Leisure" battery from an agricultural supplier a few weeks ago. (Farmers use them for electric fences)

If you are only using the engine for 1 hour each trip you will only be putting a little power into the battery each time. Unless you have access to shore power it may be worth thinking about getting a solar panel or wind generator to top up the battery between trips.

The biggest drain on your battery is likely to be cabin lights. Depending on how you use the boat it may be worth thinking about some LED lights. Others will, no doubt, be recommending oil lamps!

 

[Moonshiners]

no - probs thanks guys, new battery it is, excuse to go for a sail this arvo!

 

[VicS]

Try charging it on a charger that can deliver 6 to 8 amps until the volts have risen to 14.4 and been there for at least an hour. Let it stand overnight then check the volts. If you have fully charged it it will be around 12.7 or so. If not try charging for a bit longer. Once you get it over 12.7 (after a 12 hour rest) let it stand and monitor the volts. They will fall quickly at first but if its good it will still be above 12.6 after a week and will take weeks to fall towards 12.5.

I think yours is knackered though. If its been down to 4volts for long it is. But if it seems Ok put a load on it, headlight bulb for example, and see if it supplies that without appreciable dimming for a length of time that equates to half your battery capacity.

With a small sailing boat with a manual start outboard, Autohelm, VHF, lights and sounder I use a 60Ah Leisure battery (I used to have a smaller one but 60 is the smallest now I could find.) Its a Halfords one!
Forget the charging from the outboard unless you do loads of motoring and no sailing. You will have to take the battery home periodically to charge it because if you leave it partly discharged you'll wreck it. Alternatively do has I have done and fit a smallish (5W ) solar panel. If you want more power fit a bigger battery and a bigger solar panel

It would be a good idea to tot up the power use. Each item's current consumption times the hours in use all added together. Make sure you don't need to run the battery more than half way down during your normal time on board. Also compare that with the total power you generate from the outboard. If your outboard does not replace what you use (its unlikely to do that) work out what size solar panel you need to make up the difference before the next outing.

You have either got to be able to produce all the power you need or take the battery home for charging and if you do that then remember the bigger they are the heavier they are.

You can calculate the current drawn by lights etc from the wattage and look up the power draw by other items in the instruction manuals.

Car batteries are designed for supplying a large current for a short time not for supplying a small current for a long time. Deep cycle batteries are expensive so are marine batteries. IMHO the leisure battery was the best compromise at a reasonable price.

Sorry all a bit disjointed but hope you can make some sense of that.

 

[cpedw]

If you are happy with a soldering iron, you might want to build a meter to monitor amp-hours usage or charging described here. Or there's the developed version which can also do battery load testing, to help you find out how shot your lead-acid battery is.

Derek

 

[Loginname]

I've logged in, but it still won't me in. Maybe it needs time to allow new registrations.
Would you post it on here?

 

[Moonshiners]

Thanks guys, binned the battery, just fitted an 85 (smallest one they had) but i'm still happy with it, we have a small couple of watt Solar panel to take the edge off, but i'm going to monitor this one and see if we need a larger panel.

(but for the first time evrything worked while sailing!)

Old battery going to the dump asap (with charging indicator saying it's full and healthy!) I think (no labeling left) it was 110 + anyway so i think the previous owner OTT'd it anyway!

Thanks again.

 

[cpedw]

It involves a circuit diagram and a program, which I don't think I can make available here directly. I can forward them to your email address if you send it in a PM.
I don't know why the Picaxe forum won't let you in - you don't need to be registered to read posts there, though you do need registration to download.
Derek

 

[VicS]

[ QUOTE ]
I don't know why the Picaxe forum won't let you in

[/ QUOTE ] It wont let me down load or view attachments (I haven't tried to post) I guess because I have not activated my account because I have not had the email with the link to do it, I have re-requested it but still no joy. I'll wait and see if it turns up. Email postmen not working on bank hol weekends perhaps /forums/images/graemlins/confused.gif

Picaxe banjaxed /forums/images/graemlins/grin.gif

 

[VicS]

With an 85Ah battery you can happily fit a 10W solar panel without needing a regulator.

I actually have to renew my panel and was hoping to fit a 10W one this time but I do not quite have room. Nevermind the 5 watt one was big enough when it worked so 5W it is again.

 

[Loginname]

Thanks for that. PM is on it's way to you.

I noticed on the site that you have been quite busy with "boaty" projects.

 

[VicMallows]

I too can't get that site to play, though would love to see the circuit and program. Will PM, but wonder if we could help you post a link to save you some effort?

Vic