Trickle charge - solar what watt

[Stemar]

When it comes to boaty electrics and solar, I reckon there's no such thing as too much of either until weight or size is prohibitive.

I'd add cost to that list, but it's a boat, so cost is always prohibitive...

As for whether that battery is adequate, I reckon it feels a bit light, as that's 50AH of usable power, and the battery will last longer if you only use 25. As a rough guide, your plotter and VHF will take a couple of amps between them, then you've got the starting. Of course, the engine will put some back, but will it be enough?

I'd be inclined to spend a bit of money on a solar setup, maybe 60w, with a cheap controller and as big a battery as I could fit in. Better still, have two batteries, one dedicated engine starter - which doesn't need to be huge, and one for the other stuff. I'd expect a bit of change from £250 for the lot, which isn't a lot for safety and peace of mind.

 

[GunfleetSand]

I do have a rather large battery spare from my Volvo it was on its way out but provided fully charged seemed to do ok it’s 100 odd aH. Might be good enough as a starter. AFAIK the outboard doesn’t charge the battery.

 

[Graham376]

Are you sure you need any solar ? I might use my 50hp outboard once a month, or even leave it for two months during winter between uses.. The battery was already years old 6 years ago when i bought the boat, its only 40A/h yet always starts the engine and so far has never been flat.. Nothing is powered when i turn the boat off.

Similar to my old car, used to disconnect the battery when going sailing and when reconnected 5-6 months later would start on first turn.

 

[PaulRainbow]

Just back from the boat - first time since post. Battery only just started the 30hp outboard so I’m questioning the health/age of the battery it’s not known to me.

Battery is a Numax Leisure & Marine 105 aH ~ no date on it but I think 3-5 years. Clear window on top of case is green. I’ll check fluid levels and tops of plates over the weekend.

If I have to replace it would this be a good brand or size? Would need to start the outboard up to 10 odd times per trip and power a 7” plotter combined gps, a vhf and occasional phone. Seems to ask a lot of one battery but outings are not likely to be consecutive days - at the current rate once a month!

Have brought it home for a full charge at home and will look again at the helpful replies above - thank you - only found them as went back to the post to check what PU had recommended.

Edit: I disconnected the positive lead when I left the boat the last time in case of drain.

Unless you know the state of charge of the battery when you left the boat, the fact that it only just started the engine doesn't mean much. First thing you need to do is to fully charge the battery and load test it.

For a solar panel, you may as well fit the biggest one you sensibly can. It's all well and good fitting a tiny panel that might just about keep a fully charged battery topped up, but that doesn't help when you park the boat up with a half discharged battery and return after a cloudy week to use the boat. A bigger panel will give you a better chance of returning to a charged battery. It will also make a useful contribution whilst you are out there using the boat.

 

[Mistroma]

When it comes to boaty electrics and solar, I reckon there's no such thing as too much of either until weight or size is prohibitive.

I'd add cost to that list, but it's a boat, so cost is always prohibitive...

As for whether that battery is adequate, I reckon it feels a bit light, as that's 50AH of usable power, and the battery will last longer if you only use 25. As a rough guide, your plotter and VHF will take a couple of amps between them, then you've got the starting. Of course, the engine will put some back, but will it be enough?

I'd be inclined to spend a bit of money on a solar setup, maybe 60w, with a cheap controller and as big a battery as I could fit in. Better still, have two batteries, one dedicated engine starter - which doesn't need to be huge, and one for the other stuff. I'd expect a bit of change from £250 for the lot, which isn't a lot for safety and peace of mind.

OP is talking about "starting and outboard up to 10 odd times per trip, running a 7” plotter with GPS, VHF and sometimes a phone". He uses the boat for fishing about once a month. I imagine once a week would be the most use he gets.

His main problems have been mentioned:
Never getting the battery to 100%. Running an outboard for short periods is not going to fully charge the battery. It would probably be fine if he only used it as a start battery. However, he is using it for on-going fairly small domestic loads for relatively short periods.

He doesn't leave the battery on shore power to fully re-charge and is obviously going shorten battery life. A small, cheap solar panel will solve the problem of keeping his fairly small battery fully charged if only used as a start battery. It won't cope with discharge from equipment and will take an age to fully re-charge. The battery will therefore spend most of its time at a low state of charge.

I wonder if a cheap option might be to buy a tiny panel for about £10-£20 and only use the battery for starting. Buy a pretty cheap portable 12V car jump start pack. These are light and can be taken home to re-charge. I think they would be fine for running the instruments and phone. Re-wire all the ancilliary equipment to a connection supplied by the removeable pack. They come with short jump leads and could be used to start the outboard if the start battery did fail at sea.

I suspect it would be a lot simpler and cheaper than a 60W panel, regulator and much larger battery. The main problem might be getting a decent power bank as I think most of the eBay ones have only a small fraction of their advertised capacity.

It is worth considering, especially if the existing start battery hasn't been killed yet.

 

[Wing Mark]

Personally, I would look at the issue of whether the outboard is actually charging the battery and sort that out if needs be.
A modern outboard probably charges a t over 10A, so will quickly replace the starting discharge and a fair bit of the discharge from running a fishfinder for an hour or two.

Then, a small panel will keep the battery topped up.

IMHO, unless the engine can be reliably pull started, having two good batteries aboard is always a Good Thing.
More so if there is any possibility of equipment taking significant charge from the engine battery.
Also, you can get waterproof voltmeters on ebay for not much, (or maybe the fishfinder has a volt readout, perhaps buried in a menu somewhere?) knowing the volts can remove a lot of guesswork.

 

[Mistroma]

Personally, I would look at the issue of whether the outboard is actually charging the battery and sort that out if needs be.
A modern outboard probably charges a t over 10A, so will quickly replace the starting discharge and a fair bit of the discharge from running a fishfinder for an hour or two.

Then, a small panel will keep the battery topped up.

IMHO, unless the engine can be reliably pull started, having two good batteries aboard is always a Good Thing.
More so if there is any possibility of equipment taking significant charge from the engine battery.
Also, you can get waterproof voltmeters on ebay for not much, (or maybe the fishfinder has a volt readout, perhaps buried in a menu somewhere?) knowing the volts can remove a lot of guesswork.

OP is unlikely to keep the battery charged from an outboard if he uses the battery for other items when the outboard isn't being run. It will take many hours to fully charge a partially discharged flooded battery, much longer than the OP is likely to manage. It is of course worth checking the charging system to make certain it at least puts out a charge. I'd bet it won't actually charge a battery very quickly (i.e. No multi-stage charging, just a simple setup that tapers pretty quickly). It would probably be adequate to simply maintain a fully charged battery if only used for starting.

 

[Wing Mark]

OP is unlikely to keep the battery charged from an outboard if he uses the battery for other items when the outboard isn't being run. It will take many hours to fully charge a partially discharged flooded battery, much longer than the OP is likely to manage. It is of course worth checking the charging system to make certain it at least puts out a charge. I'd bet it won't actually charge a battery very quickly (i.e. No multi-stage charging, just a simple setup that tapers pretty quickly). It would probably be adequate to simply maintain a fully charged battery if only used for starting.

Well nobody will know that without sticking a voltmeter on it.

Multi stage chargers are about turning the charge down at some point, more than fast charging a flat battery.

Our Sailing Club RIBs do OK running for 25 minutes then sitting for an hour or more powering a VHF and occasional horns and lights, bilge pump etc. Then maybe a bit more of a run.
If the battery starts 80% charged, 25 minutes at 14.4V will put a fair bit in.
We put the batteries on charge now and then out of season. Or maybe if someone leaves the lights on!
I think our batteries last pretty well, but we probably get new ones when we trade in the engines at 5 or 6 years..

That's at the better end of what outboard makers expect their engines to put up with. Outboard electrics are designed to cope with low duty cycle,. Many people only have the alternator, and only use the outboard a few hours every other week. Many of the outboard boats in our harbour live happily like that. To be fair, others have solar panels and auto bilge pumps.

Lots of people get by OK on this kind of basis, for them adding a little top-up panel would be icing on the cake.
It's not grossly different from how some people use a car or a motorbike.

If the motor has a bad day, and takes a lot of cranking to start, the alternator will probably put in 10A or more and within a few minutes running, you should be confident of a re-start.
It would take quite a panel to do that.

Solar panels are great, but IMHO, no substitute for making sure the alternator works properly

 

[Rappey]

Is your 30hp a 4 or 2 stroke? there is a big difference in charge output between the two.
The great thing about many outboards is the ability to pull start them..

 

[Mistroma]

Well nobody will know that without sticking a voltmeter on it.

Multi stage chargers are about turning the charge down at some point, more than fast charging a flat battery.

Our Sailing Club RIBs do OK running for 25 minutes then sitting for an hour or more powering a VHF and occasional horns and lights, bilge pump etc. Then maybe a bit more of a run.
If the battery starts 80% charged, 25 minutes at 14.4V will put a fair bit in.
We put the batteries on charge now and then out of season. Or maybe if someone leaves the lights on!
I think our batteries last pretty well, but we probably get new ones when we trade in the engines at 5 or 6 years..

That's at the better end of what outboard makers expect their engines to put up with. Outboard electrics are designed to cope with low duty cycle,. Many people only have the alternator, and only use the outboard a few hours every other week. Many of the outboard boats in our harbour live happily like that. To be fair, others have solar panels and auto bilge pumps.

Lots of people get by OK on this kind of basis, for them adding a little top-up panel would be icing on the cake.
It's not grossly different from how some people use a car or a motorbike.

If the motor has a bad day, and takes a lot of cranking to start, the alternator will probably put in 10A or more and within a few minutes running, you should be confident of a re-start.
It would take quite a panel to do that.

Solar panels are great, but IMHO, no substitute for making sure the alternator works properly

Not suggesting a check isn't a good idea. I'm simply pointing out that a 30HP outboard run for short periods is not likely to fully charge a flooded battery that's been discharged. OP is simply not going to keep his battery fully charged by running his outboard for a bit. Perhaps a 10 hour run to get the battery to 100%.

That was why I suggested a power bank might be worth considering. An outboard will probably manage to keep a fully charged battery in that state if the charging system is working (yes checking it out is a good idea). However, it all falls apart when OP has short runs with re-starts and running plotter, VHF etc. with the outboard off. The power bank is better suited to deep discharge and can be charged at home during the week. It was just an alternative to larger battery, regulator and larger solar panel.

 

[PaulRainbow]

Personally, I would look at the issue of whether the outboard is actually charging the battery and sort that out if needs be.
A modern outboard probably charges a t over 10A, so will quickly replace the starting discharge and a fair bit of the discharge from running a fishfinder for an hour or two.

Yes, it needs looking into, but where do you get the information that the OPs engine "probably charges at 10a" ?

We know absolutely nothing about the engine, apart from it's 30hp. Perhaps it doesn't charge at all, plenty of 30hp motors that don't.

If the battery starts 80% charged, 25 minutes at 14.4V will put a fair bit in.

You might want to rethink that. The last bit is the hardest to get into the battery.

Let's see, 105ah - 20% =84ah, or 21ah has been used. The 10a charge that you think the OP "probably has" will produce (wait for it) 10ah if you run it for an hour, so in 30mins it will produce 5ah. That's a long way short of the 21ah it needs to be fully charged. The be fully charged it would need just over two hours, if you could get the whole 10a into the battery, which you cannot possibly do. You'd need to run the engine for about 10 hours to even stand a chance, never going to happen.

In the real World, with a 105ah battery, depleted to 80% SOC, being charged by a 10a alternator for 25 mins, it'll likely be about 84% SOC, which equals a short battery life.

 

[Wing Mark]

Reality is, our club runs 40HP motors pretty much this way without issue.
For sure the OP's motor may be different, but electric start outboards AFAIk normally charge the battery unless they are broken.
There are plenty of 30HP motorbikes (or were in the last century) doing OK with electric start and short runs.

If the alternator broke on your car, would you get it fixed or buy a solar panel?

 

[Mistroma]

Reality is, our club runs 40HP motors pretty much this way without issue.
For sure the OP's motor may be different, but electric start outboards AFAIk normally charge the battery unless they are broken.
There are plenty of 30HP motorbikes (or were in the last century) doing OK with electric start and short runs.

If the alternator broke on your car, would you get it fixed or buy a solar panel?

Do you know how often your club ever needs to replace the battery? You say that they run a boat infrequently and use a smallish battery to supply a plotter, VHF etc. while they drift around most of the day. It seems like a recipe for short battery life, little charging and lots of discharging.

 

[Wing Mark]

Do you know how often your club ever needs to replace the battery? You say that they run a boat infrequently and use a smallish battery to supply a plotter, VHF etc. while they drift around most of the day. It seems like a recipe for short battery life, little charging and lots of discharging.

I don't think we buy many batteries, although we may have lost a couple due to shutting down for covid.
We only raced a few months in 2020 and that has knock-on effects.
The Ah of discharge are not that huge.
Modern outboards are designed to charge batteries.
Even back in the dark ages when we had 2 strokes, they would be fairly effective.
I'm sure they were not treating the battery in an ideal way, but life went on.

 

[PaulRainbow]

Reality is, our club runs 40HP motors pretty much this way without issue.
For sure the OP's motor may be different, but electric start outboards AFAIk normally charge the battery unless they are broken.
There are plenty of 30HP motorbikes (or were in the last century) doing OK with electric start and short runs.

If the alternator broke on your car, would you get it fixed or buy a solar panel?

You have a habit of posting random comments that are inaccurate. You cannot just pull random numbers and immaterial comments from nowhere as if they are fact. You don't know anything about the OPs engine or it's charging capabilities, so you just guess and throw figures together based on nothing.

Your club 40HP boats are irrelevant, different engines being put to different use.

A 30hp motorbike is totally irrelevant, it take a tiny amount of power to start it, it has a different battery and all of the time it's being used the engine is running. It doesn't stand around with a plotter and VHF etc running with the engine turned off.

My car alternator is also irrelevant. The alternator is capable of running all of the electrical systems on the car and supports stop/start. It's all doing what it was designed to do, i have no need of additional power. If the alternator was broken i'd clearly need to fix it. If the OP has a charging system that's broken he clearly needs to do the same. But, given his power usage and the short running time of the engine he needs some additional power from another source, unless he wants to replace the battery frequently.

 

[TNLI]

Morning all

Although sailing in my bones I’ve got a small fishing boat -its electric start motor has a car battery and when not in use I’d like to keep it fed.

No idea about solar chargers - how much I need and if they can be left outside without damage.

I’ve had a read through the posts here but does someone know what power I’d be needing and a name brand to go for? So many online and names all blur into one.
Many thanks

First of all we need to know how big your battery is in Amp Hour terms. Just to to confuse things, many batteries list their cold crank capability in Amps, (A), it's the Amphours, (Ah), figure that is needed. Car batteries vary from about 60 to 100Ah.

Even if an electronic box says it's waterproof, always place it in a box or make a waterproof cover for it.

Solar panels are rated in Watts, (W), which is the number of Amps times the Volts, and a solar panel can put out up to 20 plus a few Volts, so if it is big enough, it can damage the battery if left on long enough to overcharge it. That limit is around 5% of the batteries capacity in Ah, so if you had a 100Ah sealed battery, the max power rating of a solar panel would be 5W, before you need to fit a charge regulator, (A small 100W max one costs about a tenner).

Solar panel ratings are max figures for a 90 degree angle of the sun on a perfectly clear day, not some more realistic average figure. In general rough terms, a cloudy day reduces the output by 50%, and failing to track the sun can also reduce it by about another 50%. So that means there is no need to be too concerned about the need for a charge regulator until you fit a solar panel of more than 10W to a 100Ah battery in winter etc.

Try to avoid buying marine solar panels, (Unless you want your wallet felt or your credit card molested), as they charge another 30% plus for using marine in the title. Just search for a good deal for a caravan panel in Fleabay or Amazingzone.

 

[TNLI]

Before spending your money, it might be worth considering what you're going to do with your boat. If it's going out under power, fishing for a few hours and motoring back, a tiny panel will do the job. OTOH, if you're going to overnight away from shore power, you might be better off with more to keep things going on board. I found 40w of solar enough to keep up with my usage on a small sailing boat at anchor - lights, an FM radio some of the time and water pumps - not enough to run a fridge, but panels are so cheap now that, if you are overnighting, it would make sense to fit as much as you conveniently can.

I had this controller EP Solar Duo-Battery Solar Charge Controller 12/24v 10A. £33.30 which I set up to charge the engine battery first, then the domestic one, on the basis that, while the domestic one needed it more, I really wanted to be able to start the engine, while dim lights are something I can live with. In practice, both batteries were kept well topped up.

Wow, they really charge for using the word Eco for that charge control unit. If you have 2 batteries, fit 2 of these:
Solar Panel Battery Charge 30A 20A 10A Controller 12V/24V LCD Regulator Dual USB | eBay

One point I missed in my last reply, is that you should turn off a panel that does not have a charge control unit when motoring, otherwise you might boil your battery in a severe case, and that could result in it venting Hydrogen gas into your sealed battery bay, and then boom! We all remember how well the Hindenburg did with a bag full of Hydrogen.

The vast majority of 12v batteries are sealed, so if you overcharge them, you can't top up the water, although in an overseas emergency you can drill a hole for each cell and drip rain water into it, and then seal it up again, otherwise salt water might penetrate into it, and salt plus H2SO2 equals Chlorine gas. You might think H2 is not a safe gas, but just try sniffing Chlorine for a real seriously not funny result.

 

[Mistroma]

I don't think we buy many batteries, although we may have lost a couple due to shutting down for covid.
We only raced a few months in 2020 and that has knock-on effects.
The Ah of discharge are not that huge.
Modern outboards are designed to charge batteries.
Even back in the dark ages when we had 2 strokes, they would be fairly effective.
I'm sure they were not treating the battery in an ideal way, but life went on.

OK, it sounds as if the battery is only used for starting on a race safety boat. I'd expect them to run the engine for the majority of the time if it's dinghy racing. Even start/finish, laying & recovering marks means using the engine a fair bit. You say discharge isn't that huge and I doubt they sit for hours with a plotter on and built-in VHF and so on.

It sounds like the scenario I described where a start battery will remain fully charged virtually all the time. As soon as you start lowering SOC significantly the game changes a lot. Use 10Ah over a period from a 50Ah battery and you don't just put 10Ah back to get to 100% SOC. Start, stop, start will mainly use surface charge from a start battery and it will remain close to 100% after a reasonable run time. Drain power and get past surface charge and it becomes increasingly harder to get back to 100%. Many cruising boats used to accept 85% as best they'd get regularly. Solar has changed that as you can charge for 8 hours each day in the med. and have a chance to get to 100% even with lead acid technology. Even a tiny panel in will keep a battery in good condition if it is only used to start a modest, well serviced engine. Not so great if it takes 15 attempts to start every time.

 

[GunfleetSand]

So much advice here. I’m prob being a skinflint but don’t want to chuck something out that is working enough. Second battery on board is a smart idea - I do have a good quality portable jump start pack so will add that to the kit.

Currently got the leisure/ starter battery on a trickle charge. Ordinarily I’d look at the cells beforehand and top up - this says sealed so do I try to jimmy off the plate and see if I can get access or trust that the plates are covered.

Edit: bit of thumbing through tinternet for some testing methods: I’ll try to work out battery condition once fully charged by placing a 5amp load on it for up to ten hours then measure voltage.