Re: Electrickery on the new boat
- From: "Gibbo" <gibbo@xxxxxxxxxxxxxxxx>
- Date: 16 Jun 2006 10:36:42 -0700
Guy Morgan wrote:
Hi all
I've started a new thread rather than follow up the Elecsol one, though
I did have a bad experience with the only set of Elecsols i bought and
subscribe to the vew that cheap batteries replced rather more often is
the best approach.
However what I want now is to invite thoughts on the electrickery setup
on my new(ish) boat. Virgo is a lovely boat in many ways but the
electrickery is "interesting" to say the least.
The set up appears to be 1 x 12v engine start battery (new); 4 x 6v
batteries in series parallel to give a claimed 260Ah 12 volt block; a
400w mastervolt inverter powering a number of mains sockets and 16A
shoreline (no apparent galvanic isolator or the like) connection
powering another set of mains sockets. There is an engine-driven 130A
alternator,charging the batteries via a splitting relay. No battery
management unit, built-in charger, ammeter or "charging" light -
effectively no means of knowing whether the alternator is charging or
not..
The major electrical appliance is a 12 volt Inlander domestic sized
fridge. I've no idea ATM of the consumption of this but it reduced the
domestic batteries to low voltage trip point overnight. However I don't
know how fully charged the batteries were before we started our 5 hour
trip.
I don't have a fortune to spend (I've just beggared myself buying the
boat!) but would appreciate advice. I feel a Gibbmo might be a good
first buy.
NB Gibbmo - a concatenation of Gibbo's gizmo!
Should I bin the 400w invertor and install a combined inverter/charger
or simply a charger?
Is a galvanic isolator neccesary/useful?
Any other thoughts? I realise quite a lot of this may have been
covered inother threads but a refresher course would be appreciated!!
I'll happily sell you a Gibbmo!
Firstly, in my experience, fridge bleeping is more often caused by
insufficient cable size than low batteries. Though of course low
batteries can also cause it. People look at the current rating of the
fridge, then fit cable that a chart tells them is OK for that current.
All that chart means is "this cable won't burn out at this current". It
says nothing about the volt drop at that current. And here is what
happens.......
When the fridge fires up the compressor, it draws about 5 to 10 times
it's running current draw (that is not an exagerration). This causes
the voltage to drop below the "bleep" level. The fridge cuts out. The
voltage comes back up, the fridge tries to cut in again. The problem is
that the first time it tried to fire up, it was trying to fire up under
no load. The second time, the compressor has run very briefly, this
puts pressure in the system, so the next time it tries to fire up, it's
running into an already compressed gas system. It's even harder to
start. Once this cycle starts, all that happens is it runs the
batteries down without even cooling the fridge.
Some of the later fridges have a timer in them to prevent this
happeneing. But not all of them.
Calculate the cable size for a maximum of 0.5 volt drop. Then double if
you want to be really sure. I see fridges wired up with 1 and 2mm
cable. It's pathetic. I used 35mm for mine.
Get a voltmeter as a minimum. From this you can see if you're charging
(the volts will rise). If your fridge bleeps you can see if it's
because the *actual* battery voltage is low or if it's a cable size
problem.
If you keep your eye on the voltmeter, you don't need a charge warning
light.
Once you got a voltmeter, check the charge voltage a few hours after
firing up the engine (with it still running). This will show you the
regulation voltage of your alternator. If it's 144 volts or higher,
then adding an external alternator controller will do next to bugger
all. If it's 14.2 volts, a controller will increase the charge a little
bit. If it's 14.0 it will increase the charge quite a bit. If it's 13.8
or lower, a controller will make a hell of a difference.
An ammeter is handy, but only if you understand what it means. As you
can imagine, I have just about everything possible fitted to Lionheart.
We don't look at anything anymore apart from the voltage and the charge
status on the Gibbmo (the rest of the family just look at charge
status). The rest of the gadgets only come into play when
troubleshooting. Which never happens, of course, because it never goes
wrong (I couldn't possibly admit if it did).
If the 400 watt inverter does what you require then you may aswell keep
it. Though it's small by many people's standards.
Your alternator is a good size. I think your battery bank (if it really
is 260 Ahrs) is a bit small. Though of course that depends on how much
power you intend to use.
For your boat to comply with the RCD the AC system ground *must* be
bonded to the hull. If you want to avoid killing people your AC system
ground *must* be bonded to the hull. If you do this without either an
isolation transformer (better but more expensive and heavier) or a
galvanic isolator (cheaper but perfectly OK as long as it is regularly
checked) when plugged into shorepower you will greatly increase hull
corrosion.
I can't make my mind up about generators. One half of me says "why on
earth do you want another engine? you already have one". The other half
of me says "I'd rather wear a cheap generator engine out than my main
engine". We survive quite happily without a generator and we use a
*lot* of electricity.
That, and the other replies, should give you plenty to think about.
Gibbo
.
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