solar panel for starter battery

[RLWP]

It's time to do something about Tawny's engine bay wiring, so I think it is also time to add a small solar panel.

 

She doesn't move a lot so keeping her starter battery charged is a bit of a challenge over winter.

 

I would like a small rectangular panel I can permanently fix in place on a bracket. We have a towpath mooring so something portable may go missing

 

Richard

[Grace and Favour]

It's time to do something about Tawny's engine bay wiring, so I think it is also time to add a small solar panel.

 

She doesn't move a lot so keeping her starter battery charged is a bit of a challenge over winter.

 

I would like a small rectangular panel I can permanently fix in place on a bracket. We have a towpath mooring so something portable may go missing

 

Richard

 

Have you considered a flexible one glued to the bote?

[RLWP]

I'm open to suggestions. The power required isn't very high, enough to maintain the battery and bilge pump

 

Richard

[Timleech]

I'm open to suggestions. The power required isn't very high, enough to maintain the battery and bilge pump

 

Richard

 

I'll second the flex panel suggestion, bond it to the roof with Sikaflex or similar.

They are quite a bit dearer than ordinary panels, but don't get in the way.

 

Tim

[IDS]

I have used a 5 w panel for this purpose for the last 3 yrs and its been very successful. However I do have a very dry bilge. With 5 w or 10 w panels you don't need a charge controller with a 110 Ah battery.

[RLWP]

What kind of 5 or 10 watt panel? Have you got a link?

 

Richard

[eightpot]

Cheap small kits.

[RLWP]

Well...

 

that gives me anything from £25 to over £350. Can anyone help to reduce the choice somewhat?

 

I know I can set to and do all the legwork myself, surely I'm not the first to try this though

 

Richard

[eightpot]

A couple of clicks away:

5W for 35 quid

 

10 watt for the price of a taxi fare after a really crap night out

[RLWP]

Both look like a good deal.

 

If I was to get radical, I have a starter battery and then three 110AH batteries in a separate domestic bank. Can I charge both banks with one panel and a handful of diodes? Or would I be better with something more clever, or even two of the 5W panels?

 

Richard

[trackman]

We have a 68W stick on panel, probably more power than you want, and more costly too.

However, now we have a Smartbank Advanced set up, although the panel is connected to the domestics, this solves the problem for us. When the starter battery needs a boost and the solar panel is producing significant charge, the Smartbank closes the relay and let's the starter battery share the power.

[matty40s]

Richard, in my eyes you would be best getting a slightly larger panel and connecting your entire battery bank up when Tawny Owl is moored up.

Solar charging helps maintain batteries at peak gently, and would prolong the life of your bank by quite an appreciable lifespan. My bank is entering it's 5th year of service.

I would get a panel around 40-100W, probably flexible, stuck on, or flat panel secured with security bolts, and when you are leaving the boat for any length of time, connect your starter to the domestic bank so the charge is shared.

When you go cruising, isolate the starter as normal, a day or two without moving, connect them up again.

Will chat to you in the week.

[RLWP]

I'm not sure that £250 worth of Smartbank is what I need to keep my batteries topped up

 

Richard

 

Richard, in my eyes you would be best getting a slightly larger panel and connecting your entire battery bank up when Tawny Owl is moored up.

Solar charging helps maintain batteries at peak gently, and would prolong the life of your bank by quite an appreciable lifespan. My bank is entering it's 5th year of service.

I would get a panel around 40-100W, probably flexible, stuck on, or flat panel secured with security bolts, and when you are leaving the boat for any length of time, connect your starter to the domestic bank so the charge is shared.

When you go cruising, isolate the starter as normal, a day or two without moving, connect them up again.

Will chat to you in the week.

 

What happens when you have a large voltage disparity between the two banks Matty? Don't you stand a chance of burning out wires

 

Richard

[matty40s]

What happens when you have a large voltage disparity between the two banks Matty? Don't you stand a chance of burning out wires

Richard

You are simply using the panel to charge 4 batteries instead of just one. All you would need to do when leaving the boat for a period of time would be to connect starter positive to main bank positive with a cable of sufficient capacity(ie, same as cables which connect the 3 domestics already). This would then be removed when you go cruising.

[RLWP]

You are simply using the panel to charge 4 batteries instead of just one. All you would need to do when leaving the boat for a period of time would be to connect starter positive to main bank positive with a cable of sufficient capacity(ie, same as cables which connect the 3 domestics already). This would then be removed when you go cruising.

 

Yes, I understand, but...

 

I need to think this through a bit. The reason for rewiring now is that our split change relay appears to have failed (after only ten years - shocking!). To manage, for the last week I have been jumping the domestic and starter banks together once I have started the engine, taking the jump lead off when we moor up. I'm aware that at the end of the day, both banks will have almost identical voltages. However, in the morning the domestic bank will be significantly lower than the starter battery, perhaps a volt or more. That's potentially a lot of current when the two are linked

 

Richard

[matty40s]

Yes, I understand, but...

 

I need to think this through a bit. The reason for rewiring now is that our split change relay appears to have failed (after only ten years - shocking!). To manage, for the last week I have been jumping the domestic and starter banks together once I have started the engine, taking the jump lead off when we moor up. I'm aware that at the end of the day, both banks will have almost identical voltages. However, in the morning the domestic bank will be significantly lower than the starter battery, perhaps a volt or more. That's potentially a lot of current when the two are linked

 

Richard

That is because you are using lights and water pumps and possibly 12v chargers and sewing machines (stop it matty).

When you are moored on your LTM, the batteries are just sat there. A solar panel might as well charge all of them rather than just your starter. The split charge relay needs to be fixed, however, a good moorings charge regime would cover all your batteries at the additional cost of a single Positive battery cable.

[MtB]

Yes, I understand, but...

 

I need to think this through a bit. The reason for rewiring now is that our split change relay appears to have failed (after only ten years - shocking!). To manage, for the last week I have been jumping the domestic and starter banks together once I have started the engine, taking the jump lead off when we moor up. I'm aware that at the end of the day, both banks will have almost identical voltages. However, in the morning the domestic bank will be significantly lower than the starter battery, perhaps a volt or more. That's potentially a lot of current when the two are linked

 

Richard

 

Surely the same happens as when your split charge relay used to work and you started the engine, i.e. the batteries all get connected in parallel and the highest voltage batteries discharge themselves into the lower voltage batteries until their voltages equalise. The alternator (or solar panels) at the same time begin charging the whole lot in the normal way.

 

MtB

 

P.S. I wonder if there might actually be something wrong with your starter battery, or the split charge relay has been leaking. The starter batt on Reg had plenty of life in it today after three months rest in sub zero weather.

[Arthur Brown]

A small panel of less than 15w will keep a battery up to full charge over winter. Maplin have a couple of small panels, the likes of which I've seen on the inside of a window over winter.

 

The issue here is that small panels cost a LOT more per watt. Typically a Maplin small panel will be £5 - 10 per watt while a modern domestic panel will be bigger and more powerful but cost about £1 per watt. The caveat there is that a 12v domestic panel would need a controller costing money, or the batteries would get fried to destruction.

 

For the starter battery only, a 1 - 10 watt panel from Maplin (or like) simply pushed up to the window glass on the sunny side will assist over winter for reasonable cost and simplicity. It will never recharge a flat battery but it will keep a battery full.

 

For the house battery a bigger panel of 150 -500w will supply a lot of your electrical needs over the summer but a controller will be essential Bigger panels will be more cost effective

 

If you intend to link one panel to both batteries then charge one battery and connect the batteries with something of the order of a good jump lead. The solar panel will only generate it's rated power regardless of the size of the battery, BUT connecting a charged battery to a discharged battery will create a current in the order of hundreds of amps while the batteries even out between them. A Switch would be better than a relay because relays draw holding current and this current will be more than a small solar panel will product

[smileypete]

If you intend to link one panel to both batteries then charge one battery and connect the batteries with something of the order of a good jump lead. The solar panel will only generate it's rated power regardless of the size of the battery, BUT connecting a charged battery to a discharged battery will create a current in the order of hundreds of amps while the batteries even out between them. A Switch would be better than a relay because relays draw holding current and this current will be more than a small solar panel will product

Doubt it'll be as much as you expect even if one is fully charged and the other as flat as a pancake.

 

Put it this way, how much charge current does it take to raise the terminal voltage of a discharged batt to 12.8V, which is what a healthy batt will show. Also taking hundreds of amps or even 10 amps from a fully charged batt will in turn drop the terminal voltage.

 

Can always try it out with a DC clamp meter just connect the start batt to half discharged domestics.

 

A sealed/maintenace free start batt should hold it's charge for quite some time if isolated. Anyway here's a 10W panel for reasonable £ which should do for a non sealed start batt unless it's quite aged:

 

http://www.ebay.co.uk/itm/NEW-10W-12v-Energy-Solar-Battery-Charger-TUV-ISO-Monocrystalline-UK-Stock-/251254210035

 

To get the small unregulated panel to split charge between start batt and dom banks a bridge rectifier will do, about £1 from Asia suppliers though:

 

http://www.ebay.co.uk/itm/KBPC3510-Bridge-Rectifier-x1-KBPC-3510-KBPC35-10-35A-amp-1000V-/320973605982

 

Though it might not do a lot for the dom bank, and have enough left over for the start bat. Don't forget fuses in the +ve connection right by the batts, in case of wiring faults.

 

cheers, Pete.

~smpt~

Edited April 8, 2013 by smileypete

[RLWP]

So, just use half the bridge rectifier, the two forward flowing diodes (as it were). That's clever

 

I hesitate to ask this, but anyway... Mono-crystalline, amorphous, polycrystalline. I know what these words mean, what do they mean in this context

 

Richard

[Chalky]

I used a small 5W solar panel off eBay that is permanently attached to the roof. Small Maplin charge controller connecting it to the started battery. Been there for over 5 years without any problems.

[canalowl]

I fitted one of these http://www.morningstarcorp.com/en/sun-saver-duo with 360 W of panels. It looks after both house and generator batteries and has been fit and forget for the last 6 years.

[Grace and Favour]

So, just use half the bridge rectifier, the two forward flowing diodes (as it were). That's clever

 

I hesitate to ask this, but anyway... Mono-crystalline, amorphous, polycrystalline. I know what these words mean, what do they mean in this context

 

Richard

 

Mono-crystalline: I only take proper sugar in my tea

amorphous: I like love, and lots of it

polycrystalline: The Budgerigar's frozen solid

[Arthur Brown]

http://www.smartgauge.co.uk/nosurge2.html gives worked estimates of 25 to 150 amps for the surge current on various cases of connecting charged and flat batteries. Certainly not difficult but not to be passed down the lead that the solar panel comes with..

[Phil Ambrose]

I used a small 5W solar panel off eBay that is permanently attached to the roof. Small Maplin charge controller connecting it to the started battery. Been there for over 5 years without any problems.

 

At 5 watts you could have dispensed with the charge controller.

 

 

Phil