Practical Boat Owner – August 2019

AN ALTERNATIVE

The most suitable type of

battery for powering a

windlass is an engine

starter-type (cranking) battery

with a high CCA (Cold

Cranking Amps) rating, as

their thin plates are

specifically designed to

provide high current for short

periods. Yes, there are plenty

of semi-traction batteries

available that will perform

reasonably as both domestic

and starter batteries and even

deep-cycle domestic

batteries will start an engine,

but they’re not designed to

do so and using them for

cranking – either engine or

windlass – can shorten their

life considerably.

As an alternative you could

buy a second, high CCA

cranking battery and connect

it to the existing engine start

battery via a single-sensing

VSR (ie one that senses the

voltage of the starter battery

only). Then connect this

second battery directly and

exclusively to the windlass

using the recommended

cable size and circuit

protection for your windlass

and cable. If wired like this it

will also draw power from the

starter battery when operating,

but only if the VSR is activated

and this can only happen if

the engine is running (a must

for long anchor hauls), so it

can never be flattened in the

process. The moment the

engine is switched off and the

charge from the alternator

disappears, the VSR link

between the two will be

deactivated.

How you then wish to

charge the domestic bank is

up to you, but if you directly

link the thin-plate windlass

battery to the heavy-duty

domestic batteries it will

discharge along with the

domestics and possibly

unbalance them. Better to

use a second VSR, enabling

the domestics to start

receiving charge from the

alternator once both the start

and the windlass batteries

have reached an acceptable

level of charge. With this

setup I’d then recommend

you connect the output from

the solar charge controller

directly to the domestic

banks with suitable circuit

protection. For belt and

braces you could also install

an emergency paralleling

switch between the domestic

and windlass batteries in the

unlikely event you run the

latter flat.

OTHER OPTIONS

You could simply replace the

engine start battery with a

larger (higher CCA capacity)

and connect the windlass

directly to it. If you do, then

you will need to incorporate a

relay between the two that is

only activated when the

engine is running, thereby

making it impossible to run

the starter battery down.

Or you could add a

dedicated, high CCA battery

close to the windlass and

connect it to the domestic

bank via a high-current VSR

and large diameter cables.

Remember, though, a VSR

between starter and domestic

will activate relatively quickly,

but one between a high-

capacity (in amp hours)

domestic bank and the

windlass battery could take

much longer as the half-

discharged domestic bank

will take longer to reach the

VSR’s activation threshold.

For this reason, be sure to

buy an adjustable VSR so

you can set the threshold at

the level you want.

WIRING

Apart from the downside of

adding weight to the bows of

the boat, you might think that

installing a dedicated battery

close to the windlass is the

obvious answer and would

allow you to use much

smaller cables. However, the

smaller the cables the higher

the voltage drop, so this isn’t

necessarily the solution.

If you simply run small

cables from the domestic

bank to the windlass battery

to charge it, there’s a good

chance it’ll run flat and then

these thin cables will melt

under the high current being

drawn from the domestics to

run the windlass. For this

reason, the cables from the

domestics to the windlass

battery forward will need to

be at least as thick as they

would if directly wired –

rendering the object of the

exercise pointless!

For the same reason, any

relay in the circuit must be

able to safely handle the full

surge (peak) current of the

windlass.

ELECTRICS

Duncan Kent tests

yachts and equipment

and writes for the

marine media

battery for charging you would
need to reconnect the existing
VSR between the starter battery
and windlass battery, isolating
the domestics with a second
VSR so that once the windlass
battery is fully charged,
continued charging will
include the domestics.
If you should choose to carry
out option 4 then I

Patrick Roach

recommend you connect the

output from the solar charge

controller directly to the

domestic bank and link the

windlass to domestic batteries

via a dual-sensing VSR so that

any surplus charge from the

solar will also feed into the

windlass battery.

5. At what point should the
   output from the solar panel
   controller be connected to
   the batteries? I’d like the
   solar charge to go through
   the DVSR(s) but do I need a
   separate diode to prevent
   the alternator from pushing
   charge to the solar system
   or will the solar controller
   prevent mishap?
   The charge controller will
   protect the solar panels from
   any other charging source.
   Everyone has their own
   preferred way of setting up
   their boat. Some like

mechanical switches, others

just want it all to happen

automatically in the

background with no input

from the skipper or crew. The

latter is becoming the norm.

The method commonly used

by production boatbuilders

today is to simply connect the

windlass to the domestic

battery bank with heavy-duty

cable and a high amperage

circuit breaker. But there are

alternatives (see below).

Whatever you decide, you

won’t be able to avoid

installing a pair of very large,

heavy cables for most of the

length of the boat.

Silent Falcon

A charge controller should protect

solar panels against other

connected charging sources

Room for one more: Silent
FalconÕs battery compartment

Panther Media/Alamy