Solar panels and charge controllers

[longjohnsilver]

There's been quite a few interesting threads recently re solar power and doubtless some folk have a good deal more knowledge and experience about them than I have.

As we are now based on a mooring I've more or less decided that to keep the batteries topped up I will get a solar panel. To be unobtrusive as possible the solara m
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=180483244812&ssPageName=STRK:MEWAX:IT
looks to be right for us.

The problem I have is that we have 2x225 AH battery banks and ideally I'd like one of the new generation MPPT controllers, but I can't find one that will charge 2 battery banks automatically. But if I'm prepared to accept slightly older less efficient technology there's a Morningstar duo
http://www.alternativeenergystore.co.uk/item/item/205003/2/0/Morningstar-Sunsaver-Duo-Charge-Controller.htm
which will charge both battery banks, and has a useful digital display.

I'm torn between the MPPT and trying to wire it so that I can manually switch it between the 2 battery banks as and when I want/need to do it, or go for the older PWM duo charger. What does the panel think?

 

[Playtime]

There's been quite a few interesting threads recently re solar power and doubtless some folk have a good deal more knowledge and experience about them than I have.

As we are now based on a mooring I've more or less decided that to keep the batteries topped up I will get a solar panel. To be unobtrusive as possible the solara m
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=180483244812&ssPageName=STRK:MEWAX:IT
looks to be right for us.

The problem I have is that we have 2x225 AH battery banks and ideally I'd like one of the new generation MPPT controllers, but I can't find one that will charge 2 battery banks automatically. But if I'm prepared to accept slightly older less efficient technology there's a Morningstar duo
http://www.alternativeenergystore.co.uk/item/item/205003/2/0/Morningstar-Sunsaver-Duo-Charge-Controller.htm
which will charge both battery banks, and has a useful digital display.

I'm torn between the MPPT and trying to wire it so that I can manually switch it between the 2 battery banks as and when I want/need to do it, or go for the older PWM duo charger. What does the panel think?

Why not install a VSR as well? When the panel is charging (i.e. above the cut-in voltage of the VSR) the second battery would be connected in parallel and would be switched out again when charging drops. This assumes the output of the MPPT when charging will normally be higher than the cut-in voltage of the VSR, of course.

 

[RobBrown]

I have posted on this topic a few times recently as I have just purchased a dual battery controller after advice from this forum. I was cost driven, so didn't go the MPPT route and anyway like you also found dual battery versions like hens' teeth. I ended up with 10 Amp PWM controller plus display on Ebay for less than half the cost of the Morningstar in your link & looks pretty similar technology:

http://cgi.ebay.co.uk/12-24V-10A-Dual-Battery-Solar-Charge-Controller-/180435489615

Seems to be working well so far!

 

[tobble]

I was looking at these recently and I am fairly sure I found one of the morningstar range that does MPPT and can charge two seperate battery banks, although I can't seem to find it now - I may be mistaken.

there are simple alternatives though, such as simply using a voltage sensetive relay betwwen batteries and charger, like this one:
http://www.kildalemarine.co.uk/show...oglebase&utm_source=googlebase&utm_medium=cpc

or alternataively use a split charge diode, However, this will only work well if the charger you choose has an external battery voltage sensor that will compensate for the voltage drop across the diodes.

 

[longjohnsilver]

I was looking at these recently and I am fairly sure I found one of the morningstar range that does MPPT and can charge two seperate battery banks, although I can't seem to find it now - I may be mistaken.

there are simple alternatives though, such as simply using a voltage sensetive relay betwwen batteries and charger, like this one:
http://www.kildalemarine.co.uk/show...oglebase&utm_source=googlebase&utm_medium=cpc

or alternataively use a split charge diode, However, this will only work well if the charger you choose has an external battery voltage sensor that will compensate for the voltage drop across the diodes.

Thanks for the replies so far. I know next to nothing about electrical systems. The VSR is presumably easy to install? What gets wired to what?

 

[ianj99]

With low current chargers like solar panels, all you are 2 of these:

http://www.rapidonline.com/sku/Elec...ower-Schottky-rectifiers-TO-220/78104/47-3662

One in lead to the +ve of each battery.

Both batteries will receive charge in proportion to their terminal voltage.

There is a loss of about .5volt across the diodes but most solar panels have a high enough voltage for this not to be a problem, especially as there is no requirement for rapid recharging.

 

[[3889]]

With low current chargers like solar panels, all you are 2 of these:

http://www.rapidonline.com/sku/Elec...ower-Schottky-rectifiers-TO-220/78104/47-3662

QUOTE]

Do you not need some sort of regulator though to prevent overcharging? The OP has 450Ah and a 68W panel goes over the 10% rule of thumb for unregulated charging.

 

[William_H]

Solar power requirements

With low current chargers like solar panels, all you are 2 of these:

http://www.rapidonline.com/sku/Elec...ower-Schottky-rectifiers-TO-220/78104/47-3662

One in lead to the +ve of each battery.

Both batteries will receive charge in proportion to their terminal voltage.

There is a loss of about .5volt across the diodes but most solar panels have a high enough voltage for this not to be a problem, especially as there is no requirement for rapid recharging.

The voltage drop across even ordinary silicon diodes is not of significance when charging from a solar panel. However as soon as you put a charge controller the voltage presented to the battery for charging is very precisely regulated ie to 14v or variations. Even .5 volt deducted would reduce the charge to the batteries.
So series diodes no regulator no probs. Series diodes after regulator bad.

Yes the 68w panel 3 amps with 240AH of battery is a bit higher than max recommended however if the boat is on a swing mooring then he will get even less charge than where a panel is angled and faces optimum angle south for max power. I would be inclined to try series diodes no controller especially if there is any current drain from other services. good luck olewill