Trickle charge - solar what watt

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GunfleetSand

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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
 
5w or 10w should be ok - look at Photonic Universe website for good info and prices. Depending on the battery capacity you may also need a solar charge controller and they can advise accordingly.
 
PetiteFleur said:
5w or 10w should be ok - look at Photonic Universe website for good info and prices. Depending on the battery capacity you may also need a solar charge controller and they can advise accordingly.
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Yep.

The safest way to figure out if you need a charge controller is to take Battery Amp Hour Capacity and divide this by the Solar Panel max. power amp rating. If the quotient is above 200, you don't need a controller. If the number is less than 200 than you need a controller.
For example if you have a 100 amp hour battery and a 10 watt panel, you take 100 and divide it by .6 (600mA) and you get 166.6. Since this is less than 200 you need a charge controller. If you have a five-watt panel in the above example you take 100 divided by .3 (300mA) and you come up with 333.3. Since this is larger than 200 you do not need a charge controller. However you still need a blocking diode, to prevent the battery from discharging to the panel at night. So as a general rule of thumb you don't need a charge controller unless you have more than five watts of solar for every 100-amp hours of battery capacity.
When do I need a charge controller and why?


I got panels from Sunstore Solar. 12v Solar Panel Kits, Chargers, Batteries & More
 
GunfleetSand said:
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
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Car battery. Buy a panel from Halfords, or similar!
 
Great - that was quick and easy thank you for the tips - I'll check battery size but this 12V solar panels charging kits for caravans, motorhomes, boats, yachts, marine should do the job and a bit more, to be fair Ian at PU agreed and said 10w is enough but perhaps over winter a bit more and there's not much in the price. Comes with a controller to switch to trickle and then stop charging once full.

The thrift in me is now thinking - what else can I charge!! Additive
 
It depends if you are really just trying to overcome the self-discharge of the batttery, or if you're using the boat and using a bit more charge than the engine is putting in.
Or if the battery isn't starting from being fully charged.
A bigger panel and a basic charge controller doesn't cost much more.

Anything is better than nothing, and a small panel has little chance of shortening your battery's life by overcharging.
I think I'm going to buy a small panel, and keep an eye on the volts this winter.
Then probably sort out something a bit more powerful.
 
I bought one of these Eco-worthy 5W panels for my car. It cost £8.33 at the time.

It is only meant to offset the discharge from the alarm when I leave the car unused for extended periods. The output isn't 5W of course, I think it is about 3.5W because it never reaches the max. voltage required to get 5W.

It does the job and they have a larger 10W (7W) model. Very cheap way to go is you only want to maintain charge on a fully charged start battery during the summer months.
 
Mistroma said:
I bought one of these Eco-worthy 5W panels for my car. It cost £8.33 at the time.

It is only meant to offset the discharge from the alarm when I leave the car unused for extended periods. The output isn't 5W of course, I think it is about 3.5W because it never reaches the max. voltage required to get 5W.

It does the job and they have a larger 10W (7W) model. Very cheap way to go is you only want to maintain charge on a fully charged start battery during the summer months.
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That looks handy and if it will give a real 3.5W, for ten quid including some useful leads and connectors it's a good start.
 
Wing Mark said:
That looks handy and if it will give a real 3.5W, for ten quid including some useful leads and connectors it's a good start.
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I left it on when away for 3 weeks and battery was fine when I returned to the car park. I tried it at home and got 250mA in direct sunshine and battery voltage rose to about 13V (I'd need to check exact figure) after a couple of days.

It is really wimpy but only has to counter drain from the alarm and small self-discharge. I don't believe that lack of a regulator it will cause a problem, even if left connected for several months. I'm going to leave it connected this winter if we are stuck at home and see how long it copes. I have an external connector for a battery charger when the days get shorter.

I think it would be a very cheap option for the OP but doubt it would cope all year round if his boat is on a mooring. You can vastly increase performance in winter by orienting the panel correctly. Leaving it flat is fine in summer but would need a much larger panel in winter.
 
I believe in checking a boat fairly often through the winter, so while I'm there I'll check the battery volts.
Soon see any downward trend and get a bigger panel or bring the batteries home 1 at a time to charge.
If the batteries are good, self discharge should be only a few mA at most?
 
Wing Mark said:
I believe in checking a boat fairly often through the winter, so while I'm there I'll check the battery volts.
Soon see any downward trend and get a bigger panel or bring the batteries home 1 at a time to charge.
If the batteries are good, self discharge should be only a few mA at most?
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Self-discharge depends on several factors. You get low temperature in winter and that helps to reduce self-discharge a lot. Battery chemistry has a very big impact. Trojan T-105s can self-discharge at about 0.6% pf capacity every day at 25 deg.C. It drops a lot with lower temperatures but is still higher than many other types. AGM can usually be left all winter as they have a much lower self-discharge rate.

The biggest problem is often parasitic loads. I once tracked down an active antenna for the radio/CD, hidden behind a panel. It was always powered, even with all isolators open and radio unplugged.

Safest bet is often just disconnecting the batteries completely if you make regular visits to work on your boat. Alongs comes Covid and that strategy gets messed up. :D:D

You say "batteries" and don't mention type or capacity. Remember, a 5W (3.5W) panel will have very low output in winter.

Lying flat on deck in South of England would probably give about 1Ah/day in June. Not too bad to just keep a 50Ah start battery topped up.

However, you only get about 0.1Ah/day in December. I doubt that would be much use, especially if you connect the panel to a larger bank of batteries.

The 10W panels seem to about twice the cost of a 5W panel and fairly safe option to buy a 2nd panel later if first isn't quite up to the job. Unless your domestic bank consists of 450Ah T-105s and needs a bigger panel.

You can improve matters considerably by angling the panel in winter and could get about 0.3Ah/day in December with a pretty large panel angle (might be in region of 60-70 degrees) in the correct direction. That only works if there's nothing around your boat to hide the sun (hills, buildings, cranes etc.
 
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I haven't taken possession of the boat yet.
I imagine it will be 1 engine and 1 house battery.
I'd expect common or garden car or caravan batteries.
0.3Ah per day would equate to 12.5mA average over 24 hrs.
0.6% of say 200Ah would be 1.2Ah per day which sounds high to me. 50mA equivalent averaged over 24 hours?

It may be a moot point as I may end up with power, either on a pontoon or ashore.
Getting answers out of people is not always easy.
 
Wing Mark said:
I haven't taken possession of the boat yet.
I imagine it will be 1 engine and 1 house battery.
I'd expect common or garden car or caravan batteries.
0.3Ah per day would equate to 12.5mA average over 24 hrs.
0.6% of say 200Ah would be 1.2Ah per day which sounds high to me. 50mA equivalent averaged over 24 hours?

It may be a moot point as I may end up with power, either on a pontoon or ashore.
Getting answers out of people is not always easy.
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The 0.6% is an extreme. I said it applied if you had Trojan T-105s and also stored them at 25 deg C. T-105s are 6V deep cycle batteries and the temp. in Greece is quite high when I leave in October and return in April. It is a lot lower in winter but I need to allow for a large initial drop in SOC.

You won't have to worry about high winter temperatures and your batteries will probably be lorry start batteries with a much lower self-discharge.

Mains power isn't a guaranteed solution. A friend had one battery blow up and replaced them with about £6,000 of high-end AGMs. They failed about 18 months later and he discovered that his charger was faulty (reason previous battery blew up). He had moved a few thousand miles and several countries before discovering the fault. He had the fault fixed and replaced the batteries with much cheaper ones. I spoke to him this year and he had just bought another set because the yard had many problems with power. Quite a few people had dud batteries and the yard blamed condensation inside power cabinets. Normally OK but Covid prevented people sailing for a year and that was long enough to kill a lot of batteries.

I'm a bit paranoid with mine, slightly overfilled in Oct. 2019 and left on solar at 13.5V float with a short 14.5V boost charge on 28th of each month. I had to add 2.6 litres of water when I managed to return 2 years later but the battery plates still had a covering of electrolyte (just).
 
peteK said:
Buy a 20w solar panel on ebay for £20 and a solar controller for less than £10 on ebay,so for less than £30 you have what you need.
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My leisure battery has lasted since 2008 on exactly that set up. It's still showing the green dot. The battery was only £34 bought from a car parts place in Lincoln. I can't get it for that price now. It replaced an AGM battery that was knackered when I bought the boat and a very expensive looking solar panel where the contacts had corroded. I had fears of it costing hundreds to replace and in fact the costs were minimal and it works fine. I even have a back up panel bought from Aldi for about £20 with all sorts of connectors.
 
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.
 
Rappey said:
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.
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Fair comment.
Splashing a tenner to stack the odds my way has an appeal while I work out which way the wind blows.
 
For what it’s worth, I have a 30W solar panel with a cheap charge controller connected to a 32 ah electric wheelchair battery. It gets no charging from the auxiliary outboard motor. It powers a 25W VHF with GPS, navigation lights, and charges a mobile phone from time to time. I sail once or twice a week, usually after work, and so usually need nav. lights coming back in. The battery is always fully charged whenever I get to the boat, and did not get short of power over a three day camping cruise. Admittedly, the power demand is slim, but it seems the OP’s is too.
 
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.
 
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.
 
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