Solar Panel-do I need a charge controller?

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RobBrown

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I have recently purchased a second hand solar panel from a fellow forumite. The plan is to use it to help keep house & start batteries topped up as on a non power pontoon.

Stats on the reverse say PMax 30.4 W, Voc 20.8 V, Isc 1.97A. Start battery is 110 Ah FLA "Leisure" & house is 2 110Ah SLA "Leisures" in parallel, linked via standard 1,2,both switch.

Two questions I could do with some advice on:

1.In looking through literature, I came across rule of thumb that controller/regulator reqd if max current amps >10% of batteries AH capacity. 2 amps looks less that this even for the start battery. Vendor may not have a regulator (currently looking!)- do I need to buy one if not available?

2. How is the panel best wired in to charge both banks, either with or without a regulator?

Any comments/advice gratefully received
 
We have a 30 watt solar panel, there is a regulator which has 1 output, this is then connected to the engine start battery, I wanted to be able to charge both batteries but was unsure how to do so without causing a parallel which I really didnt want to do.

Its not so bad for us as the batteries are on charge in the marina.

Sorry couldnt be of more help but the regulators are generally a fairly low cost for peace of mind. I THINK that they also stop the charge from reversing back to the panel at night.
 
For what its worth, I have just been going through this as well. I have bought two 30 watt panels to support systems. The boat is on a swing mooring. There are two 110 AH batteries with a 2/either/0 switch.

The basic problem is that solar panels produce 17 volts, at full power, approx 5 hrs per day in sunny summer and perhaps 2 hrs during winter. Batteries need 14.8 volts to charge, more than that will be ignored or will fry the battery. Less than approx 13.5 volts and nothing goes into the battery, so the panels may be working in winter but at an ineffective level.

Most controllers simply cut off the excess voltage above 14.8 and dump it as heat. This at least prevents frying! Particularly if you have several panels.

This year I have come across MPPT controllers that use the 17 volt available output, scale it down to 14.8 volts and maintaining the wattage, increase the amperage to the battery. Even cleverer it seems to me, it takes a lower voltage output, say 11 volt, and steps that up to 14.8, though at a reduced amperage. These Controllers are very expensive if you go the wrong place. The best that I have found, and bought, is the Emponi SOL1 from www.midsummerenergy.co.uk £85 and they will also supply the appropriate fuse and cables quite cheaply.

Incidentally, ALL solar panels should have a blocking diode on them to prevent feed-back from the battery to the panel at night.

PM me if you want more info.

Mike
 
We have a 30w to keep our 2 house batteries (130Ah each in Parallel) topped up - the engine battery doesn't seem to suffer, so we don't worry about it ... I haven't put a regulator on it as we've not been cooking the batteries yet ...

However, as you're after doing both banks then it would probably be best to get a regulator with a dual output (I assume they exist) so your batteries are charged correctly. A recent discussion on here came to the conclusion that 30w solar panel needs a regulator anyway ... (I just can't be arsed with the expense ;) )
 
Solar without regulator

Your 30w panel will give about 1.8 amps max. The watt rating is max volts times max current.Max volts between 17 and 20 volts. So current will not exceed the 10% rule of thumb. So no you don't need a regulator.
To feed 2 battery systems the easiest way is with 2 diodes. In the positive line the anode (tail of the arrow or end not having a band) goes to the panel. The other end of the diode goes to the battery +ve. The negative is connected to the battery negative (to all batteries.) Another diode is connected in the same way, anode to the solar +ve wire (with the first diode) the cathode (other end) of that diode goes to the other battery. You can feed as many batteries as you wish this way. There will be a slight volt drop (.7v ) at each diode but this will not reduce charge current because we are starting with excess volts.

Many panels have a diode fitted in the junction box at the panel. You can use this diode and add a similar diode by connecting the anode of the new diode to the anode of the existing one (ie to the solar cells+ve) and run a third wire out for the second battery. This means the volt drop will be the same as original.

One advantage of using 2 additional diodes is that if you fit the diodes at the +ve battery terminal you don't need a fuse. Any short circuit will not cause a fire from the solar panel current (too small) and no current can flow form the battery because the diode will block current flow.

If however you use the existing diode in the panel then you need a fuse near the battery +ve terminal to protect that wire which is connected to the battery +ve terminal because if shorted to negative will carry huge currents from the battery to burn the wiring. Same goes for connecting to just one battery or 2.

Diodes are very cheap from electronics store. You need one or 2 silicon diodes rated at 3 amps or more and voltage rating is no concern.(just a few pence each) By feeding both or all 3 batteries the current will be divided according to battery voltage (hence need)

Yes the MPPT type controller could scrounge more charge from weak sunlight but is expensive/complex.
good luck olewill
 
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The rule of thumb with which I am familiar is that if the power of the panel in watts is more than 10% of the battery capacity in Ah you need a regulator. A regulator is also advised for any panel over 10watts regardless of the 10% rule.

On that basis yes you do need a regulator.


A dual output regulator, as said would be the ideal.
 
Surely the rule is that if the solar panels W exceeds 10% of the AHr capacity a regulator is required. So if a 30W panel is charging a 300AHr battery bank it is marginal.

But this is only a guideline and an important factor is whether you are onboard using the boats electrics or it is unattended. In the former case I believe the 10% can be somewhat exceeded provided the panels are disconnected on leaving the boat or the batteries are approaching full charge. If the boat is unattended for longish periods I believe a regulator is required unless the panels are small (say less than 20W).

I have bought two 30W flexible panels to contribute to charging a 420AHr bank whilst I am semi-liveaboard throughout the summer. I consume about 100AHr per day so this is only a partial solution. I have been advised that I can safely connect them in parallel and plug them into a 12V DC socket in the cockpit to reverse charge without a regulator.
 
Regarding the use of regulators, my understanding is that the "10% of battery Ah" rule applies, in addition to the > 10W output rule (as stated by VicS). I think most panels for use on boats now come with a built-in blocking diode.

An alternative to a dual output regulator or combination of additional diodes, is to have all battery charging (engine / solar / wind / shore power) managed using a voltage sensitive relay across the battery banks. This will take care of appropriate charge distribution and you will only have to connect your solar panel to one battery bank - simple.
 
Thanks everybody. Really useful posts. I take the point about "spoiling the ship for a happorth of tar" so I will get a controller whatever. SFAIA, the panel does have a blocking diode. It's really all about relative costs I guess- as the panel was an old s/h one, the cost of a controller looked disproportionate.
I like Olewill's suggestions, but I am a bit of an electrics duffer, so find an out of the box solution strangely attractive, apart from the extra cost! I have googled the MPPT controllers and they do clearly increase the efficiency of the panel, but given the likely cost, still a bit too rich for me as half again as expensive as the panel I bought. However, the regulator flagged up by Cardiffcruiser looks affordable and as a dual outlet would fit my circumstances well, so I think I will probably pursue that if the vendor doesn't turn up their old one.

Cheers to all again.

For info:
Just found the dual Solar Regulator suggested by Cardiffcruiser for £19.99 @ Maplins:

http://www.maplin.co.uk/Module.aspx?ModuleNo=266145&C=Froogle&U=266145&T=Module

Rob
 
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I did try to email Maplins with a query as to whether their regulator has PWM function, but no reply to that as yet. I did find a couple of dual battery regulators on Ebay with PWM for circa £24.99 incl P&P & might still go for one of those if the Maplins one is not PWM capable, as I think it is a feature worth paying for. Cheapest MPPT I have come across is £50 and not dual battery, so it looks as if the £25 area is best vfm.
 
RobBrown said:
I have recently purchased a second hand solar panel from a fellow forumite. The plan is to use it to help keep house & start batteries topped up as on a non power pontoon.

Stats on the reverse say PMax 30.4 W, Voc 20.8 V, Isc 1.97A. Start battery is 110 Ah FLA "Leisure" & house is 2 110Ah SLA "Leisures" in parallel, linked via standard 1,2,both switch.

Two questions I could do with some advice on:

1.In looking through literature, I came across rule of thumb that controller/regulator reqd if max current amps >10% of batteries AH capacity. 2 amps looks less that this even for the start battery. Vendor may not have a regulator (currently looking!)- do I need to buy one if not available?

2. How is the panel best wired in to charge both banks, either with or without a regulator?

Any comments/advice gratefully received
Click to expand...

1/ If the solar panel produces more than 5% of the total Amp hours capacity, then it needs a regulator, unless your battery is unsealed and you like topping it up! So for example, my start batteries are 75Ah and my trickle charge panels for them are 10W, so I have a regulator for each one.
2/ You will need a diode to stop cross feeding, and always fit a fuse between each battery just in case one fails. Regulator unless the calculation above is OK.
Personally I don't like parallel anything, including parking. So my 5 panels are wired as follows:
100W: Selector for the 2 house batteries.
2 50W: Direct to each house battery.
2 10W: Direct to each start battery.

Each one has it's own regulator that has colour LED's that warn you of a flat battery etc. Big boy, the 100W regulator has its own voltmeter.
 
As the original question is 10 years old, solar panels and batteries have advanced in technology and wiring protocols, e.g. diodes are almost always fitted in solar panels.

I am not sure about TNLI's fuse "between" each battery, , and an explanation would be useful.

Policies about connecting panels in series have been frequently discussed in the forums, and there are times when it is advantageous.


I think TNLI has an empirical approach to panels and charging regimes which may not reflect current best practice.
 
TNLI said:
Personally I don't like parallel anything, including parking. So my 5 panels are wired as follows:
100W: Selector for the 2 house batteries.
2 50W: Direct to each house battery.
2 10W: Direct to each start battery.
Click to expand...

Your 2 domestic batteries are wired in parallel.

All of your solar panels are wired in parallel too.
 
on my two panels each has a controller and each controller has dual battery wiring, cheap controllers too. one is a Photonic universe PWM dual and the other a Votronic MPPT dual. each going to the engine battery and house battery, i also have a Blue Sea relay "add a battery" switch thing
 
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