Solar Panel for two Batteries!

Zagato

Zagato

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I have two 85 AMP batteries and will replace one and put in a stronger starter battery.

I would like a cheap solar charger for both batteries but they share the same negative lead, different positive and go through a 1,2 & Both switch.

Would this be OK to top up both batteries and how do I link to both or do I need two :( May get two that are cheaper in that case...

http://www.maplin.co.uk/solar-powered-12v-4.8w-battery-charger-115194
 
You have a choice:
  • Fit two panels ..one to each battery, If the panels are 10 watts or more each then connect themvia some sort of controller. Your choice of type from the basic disconnect when charged type, PWM or MPPT.
  • One larger panel, or two small ones in parallel, and a dual output controller.
 
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Thanks VicS I was hoping to get away with not using a controller/regulator if I used a 10W panel :( Only because it's more complication on something I don't have a clue about.

I wish we had a technical section which tells you how to connect a solar charger to a battery and what regulator/fuse/controller/wires etc you need and how to do it. They are wet batteries.

You would think you could buy a 10W panel with an line something already built in!

My old boat just had a 10w panel connected via a fuse to the battery - job done, but what fuse/wire etc :confused:
 
Zagato said:
Thanks VicS I was hoping to get away with not using a controller/regulator if I used a 10W panel :( Only because it's more complication on something I don't have a clue about.

I wish we had a technical section which tells you how to connect a solar charger to a battery and what regulator/fuse/controller/wires etc you need and how to do it. They are wet batteries.

You would think you could buy a 10W panel with an line something already built in!

My old boat just had a 10w panel connected via a fuse to the battery - job done, but what fuse/wire etc :confused:
Click to expand...


This is the technical section.

The controller Northwind shows would do the trick nicely and be suitable if required for a much larger panel


You could connect a single panel to the two batteries using a couple of diodes as blocking diodes.
Schottky diodes would reduce the volts drop. It would also be a good idea to bypass any integral diode the panel may have or use one without an integral diode ( if you can find one)

Fit fuses in the positive connections a as close as possible to each of the batteries. Rate the fuses to protect the wiring

The size of the wiring will depend upon the size of the panels and the length of the cable runs. Given that info a suitable cable size can be dertmined
 
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Zagato, what do mean by a stronger starter battery? Generally you don't need a higher capacity battery to start a small diesel. What you need is cold cranking capacity which you can get from an ordinary car battery.
You also shouldn't need to charge it with a solar panel. Once the engine is running, it'll replace the charge in a few minutes via the alternater.
Just charge the house battery from solar and fit a vsr to top up from alternate once engine battery is fully charged.
 
Sorry VicS it went straight over my head :confused: don't even know what a diode does :confused:

I have two of these, one of which starts the Yanmar 2MG20. I don't know what the difference between AH is & AMPs but they have 85 on the side.
IMG_3025.jpg


I will get them tested by Halfords but I don't think they are in great shape so would like to get a new battery for the engine - any recommendations for a cheap wet battery with the right cold cranking for a 2GM20 gratefully received.

I would like to keep both topped up with one or two solar panels (which ever is easiest and cheapest. A regulator is £20 so if I can do without that then great, can buy a solar panel for that and charge both at the same time but I don't know!!! Just spoken to a dealer who said that 10W is fine for a battery over 65 somethings and it won't need a fuse/regulator. It comes with a 2 metre lead and battery clips.

My old boat had a £10, 10W panel connected to one battery with an in-line fuse! (the other battery had a wind charger jobbie also with a fuse). They both did the job fine, no regulator just connected all the time :)

Can you give me numpty instructions - blocking diodes, PWMs and MPPT's is double dutch to me :confused:

Thanks for your patience :o
 
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ghostlymoron said:
You also shouldn't need to charge it with a solar panel. Once the engine is running, it'll replace the charge in a few minutes via the alternator.
Click to expand...

Sorry 'Ghosty' not sure what a VSR is :confused: and I may not use the boat for 3-4 weeks if the weather is poor over the winter so would like to keep them both topped up. The ones in the shed go from supposed full charge to under 25% in a week :eek: Think they are knackered, water was low and they will not have been charged for over a year but may save one for the house as you say. If a battery gets below 50% charge you knacker it apparently :confused:

Electrics & geek gadgets..... moan :mad: Give me nuts and bolts and I'm away :D
 
If I were you I would replace like for like where the batteries are concerned. They will give you much more 'house' power. The only reason for having a 'stronger start battery' would be to have a smaller one (same as is in every car). For a 2gm20 the batteries you've got will give plenty of Amps. If you want to avoid controllers and electronics then get 2 panels. Or just attach one panel to the house battery and rely on the engine to charge the other.
 
ghostlymoron said:
Zagato, what do mean by a stronger starter battery? Generally you don't need a higher capacity battery to start a small diesel. What you need is cold cranking capacity which you can get from an ordinary car battery.
You also shouldn't need to charge it with a solar panel. Once the engine is running, it'll replace the charge in a few minutes via the alternater.
Just charge the house battery from solar and fit a vsr to top up from alternate once engine battery is fully charged.
Click to expand...

+1

I keep wondering why some people have this fixation for the biggest starter battery they can squeeze in and, often the most expensive type available. I treat the boat just like the car, my boat engine is 1800cc so I just go to motor factors and buy an 1800cc diesel car battery. Unusually, we were away from the boat for 3 months last year and, on return, it started first turn over, as usual.

It's generally the domestic bank that takes the hammer/abuse with far more charge cycles so that's the one which should be biggest.
 
Zagato said:
Sorry VicS it went straight over my head :confused: don't even know what a diode does :confused:

I have two of these, one of which starts the Yanmar 2MG20. I don't know what the difference between AH is & AMPs but they have 85 on the side.
http://i620.photobucket.com/albums/tt283/Zagato07/IMG_3025.jpg

I will get them tested by Halfords but I don't think they are in great shape so would like to get a new battery for the engine - any recommendations for a cheap wet battery with the right cold cranking for a 2GM20 gratefully received.

I would like to keep both topped up with one or two solar panels (which ever is easiest and cheapest. A regulator is £20 so if I can do without that then great, can buy a solar panel for that and charge both at the same time but I don't know!!! Just spoken to a dealer who said that 10W is fine for a battery over 65 somethings and it won't need a fuse/regulator. It comes with a 2 metre lead and battery clips.

My old boat had a £10, 10W panel connected to one battery with an in-line fuse! (the other battery had a wind charger jobbie also with a fuse). They both did the job fine, no regulator just connected all the time :)

Can you give me numpty instructions - blocking diodes, PWMs and MPPT's is double dutch to me :confused:

Thanks for your patience :o
Click to expand...

Diodes are best described I think as the electrical equivalent of a non return valve.
They allow current to flow in one direction but not in the other.
They are used as rectifiers to convert AC to DC.
They are used in conjunction with solar panels to prevent any current flowing back through the panel from the battery during darkness. In this role they are often called blocking diodes .. because they block that reverse flow.
I'd expect a solar panel supplied for battery charging to be fitted with a blocking diode... but you need to refer to the tech spec to confirm it.

If you connect one solar panel to two batteries the connecting wiring effectively connect the two batteries in parallel. Current could flow from one to the other and youd run into problems with starter current loads trying to be sahred between the two over thin wiring.

So connect the two batteries to the single panel with a "non return valve " in the wiring so that current can flow from the panel to the battery but not from the battery to the panel and to the other battery.

The downside is that diodes suffer from a minimum volts drop or pressure differenece across them ( like a spring loaded NRV if you like )

There is a type of diode known as Schottky diodes. The volts drop is lower than a more common silicon diode ... it has a weaker spring !


Pulse width modulation ( PWM) and Maximum power point tracking ( MPPT) are methods of improving the regulation of the output from a solar panel compared with the simple controllers that simply disconnect the solar panel from the battery when a certain volatge is reached and reconnect when the volts fall to some lower voltage.
MPPT regulators should get you the maximum possible from the panel when need as well reducing the output as the battery becomes fully charged.


If you really dont want to fork out £20 for the dual output regulator then two diodes is the only way forwards for you if you want to charge two batteries from the same solar panel I think.. They only cost a few pence.

The usual rule of thumb for panel size in watts and battery size in ampere hours (Ah) is that up to 10watts per 100Ah does not require any form of regulator but a regulator is advisable if that ratio is exceeded or for panels in excess of 10 watts regardless of battery size.
Its a rule of thumb not an exact limitation...

Any connection to a battery circuit should be via a fuse. Any dealer who says different needs his ass kicked. The battery can deliver several hundred amps.. if a fault occurs that shorts the wiring then the wiring will quickly overheat and very probably start a fire!


If you want to extend the cables supplied with the solar panel tell us by how much ( also tell us the wattage of the panel) and we can calculate a suitable minimum wire size.


Just about the smallest car battery will start that engine
 
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I've recently gone through the same thought process. I ended up with two 20w panels and the two battery controller from SunStore. Total cost £80 or so, including delivery, from memory.

I chose two smaller panels rather than one big one because the only practical place to mount them is on the hatch garage, where the shadow of the boom is likely to fall. Solar panels can lose much of their output from a surprisingly small shadow so I figured, and this was confirmed by a panel salesman at the boat show, that two panels wired in parallel (+ to +, - to -) would still give me the full wack from one panel plus a little from the shaded one, rather than just a little (a lot less than half) from a bigger panel.

The controller takes away all the worry about connecting two batteries to one set of panels but, as Vic says, the output MUST be fused, with the fuses as close to each battery as practicable. An inline one would be fine, something like this. The Sunstore one is a bit dearer, but uses a more efficient charging routine, so is (I hope!) better value for money. You can set it up to give different percentages to each battery or give everything to one until it's full then switch to the other, reverting to the first when it gets run down a bit; when both are full, it goes into maintenance mode. I haven't finally decided how I'm going to set thgis up, but I'm leaning towards charging the starter battery first then switching to the domestic one. That way, I'm as sure as I can be that I'll get the engine going in a worst case. I expect to come down to the boat to find both batteries fully charged. After I start the engine, I'd expect the alternator to have taken the starter battery back up to close to full by the time I get out of the harbour, so the solar panels won't have much to do to it. & when we're under sail or at anchor, the output should come close to keeping up with our usage.

I'd hoped to finish the installation last Saturday, but rain stopped play, so I don't know how well it'll all work, but I did find SunStore very good to deal with and would have no hesitation in buying from them again.

PM me if you want to know more.
 
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Thanks folks, especially VicS, all is clear now. 2 panels and the contoller/regulator and fuses :) job done as Northwind said.

I'll have a look at the Sunstore one also Stemar, thanks ;)
 
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Zagato said:
Sorry 'Ghosty' not sure what a VSR is :confused: and I may not use the boat for 3-4 weeks if the weather is poor over the winter so would like to keep them both topped up. The ones in the shed go from supposed full charge to under 25% in a week :eek: Think they are knackered, water was low and they will not have been charged for over a year but may save one for the house as you say. If a battery gets below 50% charge you knacker it apparently :confused:

Electrics & geek gadgets..... moan :mad: Give me nuts and bolts and I'm away :D
Click to expand...
If your batteries are discharging in a week, you need new batteries. As others have said, get a cheap car battery for starting and a 'leisure' type for domestics. Remember that your engine is probably only 600cc so needs sizing accordingly. I still think that you don't need solar charging for the starter battery and that you'd be better providing more charging capacity for you domestic battery. But your choice.
If you're really as ignorant of electrics as you say, I would get some advice from the battery supplier.
 
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Nicely explained

I’m a bit like Zagato not too familiar with electrics but would like to learn more to do my own installations, however when someone like Vic explains this so fluently in terms that I can understand fantastic, thanks this is a wee job I am considering later on in the year.
 
For any one with no electrical knowledge to speak of I recommend the "Boat electrical notes" on Tony Brooks' TB-training website http://www.tb-training.co.uk/
He starts practically from scratch with some sections on basic electricity before moving on .
He makes the point that they are only the notes to accompany his courses but IMO they stand well on their own.
 
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