I already have the PV panels in commission, so adding a wind turbine is not going to answer my question on connecting those. Anway, a wind turbine is an ongoing project. Look here:

http://www.fieldlines.com/story/2007/4/3/22128/99260

I have all the bits for that except for new bearings and rectifiers. I'll wait until I get to St. Maarten as that is a dutyfree port and has a good selection of stuff. A Volvo marine engine repairshop in Martinique wanted the equivalent of 45 US dollars EACH for the bearings... I didn't even try to look for rectifiers.

Regards,

"If there are two diodes at the panel, these are usually in parallel with 6V sections of the panel"

Nope, the ones in the junction boxes are definitely in series with the whole panel. There are two possible places to connect the outgoing cable in each junction box on my panels. One each side of the diode. Connecting the cable to the other side of the diode removes it from the circuit, so my question remains, is there any good reason to have a diode in series on both the positive and negative side?

"Adding a diode in a minimal system would probably not add any advantage."

My question was: "How much DISadvantage does it add, as I want to use diodes to charge two totally independent battery banks at the same time. I know there are PV regulators available that have outputs to charge more than one bank, but they cost money and I assume they use diodes to split the charge anyway?

I do not want these banks connected in parallel under any circumstances, not even through a relay, but I would like to have some of the energy from my PV panels diverted to the starter battery to make sure that is always topped up, even in long periods of not using the engine. And, I don't want to spend any more money than I have to. Unlike an RV, a yacht can not pull over to the side of the road when something happens at sea, and there is no towtruck to call. The starter battery is used only for cranking the engine and nothing else.

For the engine alternator, I use a charge splitter like the one in the photo, a smart regulator and sense the battery voltage direct from the batteries which compensates for the voltage drop through the diode. However, I try to avoid using infernal combustions to charge my batteries at all cost. My engine alternator may be off grid, but it is not renewable energy, and... it's noisy and smelly and the engine warms the boat up, which I don't need in the tropics.

I have circuits that eliminate the diodes completely and have very little losses,

I have switches that can carry from 30 to 150 amps, depending this in the number of MosFets that are in parallel.

I call them BATTERY ISOLATORS

"The 2 built in diodes are bypass diodes.  They serve no purpose in a 12V system."

I'll have to take a closer look at this. At the moment it's dark out and the next few days I'm sailing a friend's boat in the Antigua Classic Yacht regatta. It's a hard life... (This crazy Australian built his own boat from wood he cut in his own forest.)

I'll get back to y'all in a couple of days with a photo of the inside of the junction box which will prove someone right. ;)

PS. All the power to write and post this message as well as light my boat and fill her with music and voices came out of the PV panels we are discussing :) I don't have a fridge. Too much trouble, and they have cold beers in the bars on land with better company.

Owen

Serious topic drift alert.

LED lighting would not solve my anchor light problem. I would still want it off in daylight and on at night rather than leaving it burning and consuming power through the day or leaving the boat unlit at night if I am late getting home. There are only two ways to do that. By being aboard the boat (and remembering the switch) at the appropriate times or by some automatic system (which consumes less power than leaving the light burning).

I do want a combined LED anchor light and masthead tricolor, but there are legal requirements and the model I want costs 250 dollars. It consumes around 500mA in anchor light mode. Unfortunately, it's out of my budget at the moment. The solar outdoor lights are not nearly bright enough for an anchor light. I'd like the skipper of the other vessel to see me before he hits me even when there is a town full of traffic lights, street lights and neon signs behind me from his point of view. Remember, the job of an anchor light is not only to make my vessel visible, it is to be able to prove, in a court of law that I was showing the legally required lights when the other vessel hit me.

One of the reasons I'm able to sit here now and write this to you from my new boat is that I was able to say that when my old boat was sunk by a freighter halfway across the Atlantic last May. A non-approved light might just provide some lawyer with a loophole to jump through even if it's actually brighter than the requirement...

As for LED interior lighting, I have found that several of the very expensive products that are commercially available for boats fail within weeks of installation. The symptoms are usually one or more groups of three LEDs starting to blink erratically and then fail.

I think the only way forwards for reliable LED lighting on a boat where the battery voltage can vary between 11 and 14.4V is to go for a lower voltage and use something like a 7809 in each lamp with the resistors sized and LEDs grouped accordingly.

I'm not sure how the Nicad batteries you suggest are going to help when I already have a 460 Ah 12V battery bank? I'd love to replace that whole bank with NiCads of course, but that is hardly realistic when I am broke and trying to figure out how to get the money to fix the gearbox that broke outside Guadeloupe the other day. A marine gearbox is very expensive to repair even if I do it myself.

... Cruising is repairing boats in exotic places ...

Regards,

Makes perfect sense of course, and if I had employed my brain I would have been able to figure that out for myself.

Regards