Solar Panel Regultion

[BobnLesley]

I've been advised that when I lay up the boat in winter (eastern Med.) it would extend the battery life significantly if I were to connect the whole bank together and wire them up to a solar panel. I'm further advised, that if said panel is only 5 or 10 watts, then I can wire it straight in and not bother about fitting a regulator - Battery Bank totals approx 250 amp/hr. Any comments or opinions on the veracity of this advice would be much appreciated.

 

[alan17]

I am sure that a more learned person will reply but IMHO you should not link the batteries together because a fault developing in 1 battery could adversley affect all of the others in the bank. It would be better to use 1 solar panel for each battery and at say 5 watts you would not damage the battery by being wired direct.

 

[simonfraser]

regarding a regulator, they're are cheap enuf.

wire the solars up with a regulator. i've so far blown up 2 batteries with solars that should have been ok !

i've also had dud regulators, so i'd check them and make sure they do indeed control the voltage before you leave the boat for a long time.

 

[anderson]

we used to only connect 1 battery to a 5 w panel and leave all winter in greece without regulator no problems.

 

[vyv_cox]

I have 2 x 105 Ah domestic and 1 x 105 Ah starter. My regulator charges two battery banks, domestic side first then starter second. I have been leaving this arrangement with a 38 watt solar panel all winter for years. My battery life is excellent. As has been said, a regulator is not a high cost item, about half the price of one of my batteries, bought in Greece.

 

[Tranona]

See my response on Liveaboard. Merlin advised me no need to fit a regulator with 10 watt and a 210 amp house battery. Not connecting to engine battery as am also fitting a parallel switch.

 

[ChunkyMonkey]

Hi,
Yes, a solar panel will greatly improve your battery life. However, it is not as simple as you were advised.

Firstly, if you have 250AH of batteries, 10 watt charger is not going to need a regulator (IF it is connected to the whole bank as one). However, if you are leaving the boat in the water, then it is worth allowing for a bit of bilge-pump running, upping the panel size a bit (40-60 watts) and fitting a solar charge regulator. You can get an 8A regulator for less than £20 from Maplin, and you save yourself the job of connecting all the batteries together, as you can use the surplus-charge connectors to charge the starting batteries when the domestic batteries are full, or vice-versa.

The other limitation is not to oversize the panel beyond 1/20 of the capacity of the battery -so for 250AH you can cope with up to 12.5A (140W or so) of charge - for the whole bank. If you don't connect them together, then limit yourself to 1/20 of the battery capacity to which they are connected, so about 5A for a standard 110AH battery - but if going above 5W or so - which will only give you about 0.4A - you need a charging regulator or you could overcharge the battery.

 

[Anonymous]

[ QUOTE ]

The other limitation is not to oversize the panel beyond 1/20 of the capacity of the battery -so for 250AH you can cope with up to 12.5A (140W or so) of charge - for the whole bank.

[/ QUOTE ]
Why?

 

[William_H]

No you don't need a regulator with a solar panel whose current delivery is less than 5% of the Amp/hour battery capacity.
Rather than parallel all the batteries you can simply fit diodes in the positive wire from the solar all diode anodes to +solar one for each battery. cathode to each battery +ve. Fit the diodes near the battery +ve and you won't need a fuse for each diode as you would if there is a long cable run from batt terminal to diode.
Diodes are cheap rated at 2or 5 amp max 200v rating. A few pence at Mplins RS etc.

The solar panel you fit can be up to 250W without regulator but practically
10 to 40 watts will make an improvement in battery condition. olewill

 

[gavin_lacey]

Solar panels usually produce 17 volts when not regulated. If you were to feed a battery with 12.5 amps at 17 volts as has been suggested on this forum your batteries life could be measured in hours. Regulation is the way to go. Preferably 3 or 4 stage. They have come down in price to a level where it is a false economy to not fit one.

 

[Anonymous]

Yes. But LaurieK was not suggesting that. He said fit a regulator.

 

[gavin_lacey]

Another poster did say that 'The solar panel you fit can be up to 250W without regulator'. I disagree with this statement. 250/17 = 14.7A to be picky. The thread also seemed to be encouraging unregulated solar panels which even in small sizes is not really good practice - they still usually produce 17v.

 

[cpedw]

Re: Solar Panel Regulation

17V is a typical open circuit voltage of Solar Panels. They have significant internal resistance which ensures that the terminal voltage is reasonable when significant current is delivered. This is the basis of operation without a regulator.
Derek

 

[Anonymous]

Re: Solar Panel Regulation

[ QUOTE ]
17V is a typical open circuit voltage of Solar Panels. They have significant internal resistance which ensures that the terminal voltage is reasonable when significant current is delivered. This is the basis of operation without a regulator.
Derek

[/ QUOTE ]Let's see some maths to back that up. i.e. What is the 'significant' internal resistance? What is the terminal current on a sunny afternoon, into 14.5V? What gassing is likely?

Meanwhile, folks, anything more than a tiny panel needs a regulator.

 

[William_H]

Re: Solar Panel Regulation

The current of a solar panel is usually watts divided by volts ie watts divided by 20V. They rate the power at max volts x max current.
The voltage will fall to that of the battery itself. The 17 v or 20 volts is only a voltage achieved with no or very little load.
So forget volts of the charging source that only determines the point of battery charge where charge stops. A 20W (12v system) panel will give 1 amp into a short circuit, a 6v battery or a 12v battery. If you charged an 18v battery it would charge at a lower current which would reduce as the battery voltage rose.
The internal resistance of course depends on the power rating but a 20w panel will I think drop about 5v at 1 amp or aprox 5 ohms internal resistance. With a short circuit the internal resistance would appear to be 20 ohms. So internal resistance appears to vary with current (and sunshine)

The premise of not having a regulator is simply that 5% of the AH rating in amps can be tolerated by a lead acid battery 24/7 without damage even though it is fully charged. Of course you could be conservative and use a lower % to be even safer.

Don't be confused by the open circuit voltage of a solar panel. It is the current that does the work or damage the voltage simply ensures that the current goes into the battery from low to high charge state.
Incidentally the diodes as suggested above will only work without a regulator. such that the 20v from a solar panel can be reduced to 19.3 by diode drop with out any concern. But if voltage is regulated to 14 volts then the diode drop will mean max 13.3 to battery hence not enough charge. olewill

 

[Anonymous]

Re: Solar Panel Regulation

[ QUOTE ]

The premise of not having a regulator is simply that 5% of the AH rating in amps can be tolerated by a lead acid battery 24/7 without damage even though it is fully charged. Of course you could be conservative and use a lower % to be even safer.

[/ QUOTE ]On that basis I could leave 28A flowing 365/24/7 through my 560 Ah house bank. I have to top up twice a year with five litres per time with an excess 'fully charged' charge current of a fraction of this (from a rather poor solar regulator and a problem with the alternator controller). 5% is way, way, way, too high. Anything but the smallest panel needs a regulator and it needs to be set up for the appropriate battery type.