Solar for Trickle Charging

How and with what.
Solar for trickle charging panel (blanket)
RedArc 27 watt blanket converts rays to volts. Manual here.


For some time we have been considering fitting Solar for trickle charging the batteries while G-whizz sits on her mooring. For many reasons we did nothing, those reasons included having 240 amp hours of house batteries, 75 amp starter and a high output alternator. Further the engine tends to get run for least an hour or more each time or each day the boat is used whether it be going to and from the race course or dropping and picking up the anchor when cruising, not to mention looking for a decent spot to anchor. Also G-whizz is not a big user of power with all LED lighting, a relatively modest instrument setup, one water pump, an efficient fridge, no other “Appliances” and the windlass is only ever operated with the engine running.

Solar for Trickle charging regulator (controller)
RedArc controller looks after the batteries. Manual here.

The recent necessity to replace the house batteries, from old age and maybe a bit of abuse, came with a reminder that deep cycle AGMs don’t  like to be run flat and do enjoy being in a full state of charge made us reconsider fitting solar for trickle charging the batteries. Any solar panel would need to be non permanent, with the ability to be deployed quickly when on the mooring  (or elsewhere), be stored securely  and safely when not in use and be plug in with reliable plugs that don’t allow water ingress and not be a step or movement hazard to crew.

The solutions we chose for fitting solar for trickle charging included:

Anderson Plug Holder and Wire entry Water proof(ish)
Water Resistant Anderson Plug holder and wire clam with drip loop to minimise water ingress. Fitted in Companionway step/halyard storage area.

The location of the plug was made easy, the Elan 340 has a combination step/halyard storage at the companion way, fitting a 50 amp Anderson plug in an automotive trailer plug holder at the front corner of the step area with the plug facing up meant an easily accessible solution that is also out of the way. These plug holders are relatively water proof however the water proofing elements were not added to the bottom of the plug (the rear of the plug in an automotive environment) to allow any water to drain out, the wire comes out of the plug turns 180 degrees through a drip loop (In hindsight a shorter loop would have been neater) before entering the boat via a wiring clam into the engine ventilation before routing through the engine compartment, then under the floor to the battery box.

A RedArc two battery 20 watt controller looks after charge management of both the house batteries and the start battery, while a RedArc 27 watt marine solar blanket converts the sun rays into electricity, this blanket rolls up into a pretty small package for storage and can be located in a number of places including the rear transom bridge, in the cockpit or across the deck forward of the companion way, it may also be possible to mount above the boom when full covers or boom tent have been deployed.

G-whizz battery box
Under all that macrame are 2 deep cycle and a start battery. Top right is the emergency parallel switch, centre right the battery isolater and bottom right the solar controller

Wiring is 8 AWG (about 4mm) throughout, when combined with the 20 amp controller  and 50 amp plugs may seem to be bit of an overkill, but it does allow room for future upgrades.

Many smaller yachts do not lend themselves to the permanent fitting of solar panels, especially if aesthetics are not to be destroyed, G-whizz is no different we think she has nice clean lines and could not come up with a visually acceptable (to us) method of permanently fixing solar panels and considering the use we put her to we are unsure that they are needed, here’s hoping that this solution works as expected.

While we were at it we also took the opportunity to fit an emergency parallel switch between  the house and start batteries, we hope we never need to use this, but it is there just in case.

After a bit of experience with this set up we are more than happy with the results, the one alteration was to adjust the charging priority to 80% House and 20% Start (controller will switch to 100% when one battery is fully charged). we remove the panel for racing but leave it in place for cruising, while it cannot meet the power needs when cruising it does reduce the frequency for running the engine to top up the batteries, if that was a concern we would merely fit a larger (or a duplicate) blanket, this was the thinking behind the ratings of the fitted components.

Owners manual battery wiring
Owner’s manual battery wiring schematic showing solar and parallel switch modifications. Red indicates modifications not polarity. (Click to enlarge)