Electric gaffer needs more juice
QI own the gaff rigged Oysterman 16 Sawsan
(22ft LOA with bowsprit) which is powered by a 24V DC Lynch electric motor. The problem
I have is keeping the batteries charged.
I sail on the Orwell where the only charge points are when
I’m moored in the marina, so I intend fitting a wind generator and some solar panels.
My query is how do I generate 24V from a 12V solar panel? Will I need two panels linked together? Given the limits in deck space they’re likely to be fitted at the stern on a stainless steel gantry located far enough away so they don’t get hit by the boom, which overhangs the stern. I hope you’ll be able to provide a solution. Jim Rhodes, by email
DUNCAN KENT REPLIES: Most modern rigid solar panels provide voltages up to 50V or so. Older models and flexible ones are often only 18V-odd, which is obviously no good for your situation.
The key is the charge controller. You need to buy one that can handle a 24V battery bank (Victron are probably the best, but there are other good ones such as Epever or Photonic), and it
should be an MPPT (maximum power point tracker) device, not a PWM (pulse-width modulation) one.
Buy from a reputable company online as many controllers carry the MPPT label but are actually PWM devices (and you will also find CE labels that are fakes).
Size is usually the giveaway – MPPT are bigger and heavier than PWMs.
Controllers will be designated with two numbers: 100/50 for instance. The first number is the maximum voltage of the panel/s, the second is the maximum current the controller will output to the batteries.
You should never go above the first figure, but if the panels can produce more than the controller’s maximum output, the rest of the current produced by the panel will simply be wasted without harming the controller.
You could, if it’s the only possibility space-wise, connect two lower voltage panels together in series, but it’s not the best way and will only give you the same charge current as a single panel. The important thing is if you combine more than one panel, either in series or parallel, they must ideally be identically rated.
Finally, a shaded panel will produce far less power so make sure it won’t be shaded by the boom.
You can also add a wind turbine, but it will need its own controller. The output from the solar and wind controllers can then be connected in parallel to the battery bank.
In some cases, the two might interfere with each other, but that’s usually only when the bank is very nearly fully charged, so it doesn’t do any harm. Alternatively, there are dual solar/wind controllers available to avoid this scenario.