27 Nov 2007
While we're still
a ways away from doing any wiring I do have a small job to do with
In Wothahellizat 1 the inverter was mounted under
the floor and we had a small trapdoor that allowed access to the
control panel. This worked OK but I always wanted to add a remote
panel so we could change settings without groveling on the floor.
However at over $500 for a remote panel it never
Then a few months ago we had to get the thing
fixed so while it was not being used I had a poke around. I found
that the control panel is a separate circuit board (PCB) which is
screwed to the inverter's enclosure and connected to the main PCB
with a simple 20-way ribbon cable.
Hmmm, this looks promising. I should be able to
make my own cable that's long enough to allow me to remotely mount
The control panel, the inverter's
case has been removed.
Here we see the control panel (yellow
line) and the original connecting ribbon cable (blue line).
As the cable only interfaces to an liquid crystal
display, a few LEDs and some pushbuttons there are almost certainly
no high-frequency signals that will be upset by a longer cable,
so I head down to the local electronics store to buy some 20-way
cable and two connectors.
No luck, they have 40-way cable but no connectors.
I buy a metre of cable ($0.81) and return home figuring to pirate
the connectors from the cable I'm replacing.
When I return though I realise that there are
two other cables that are used for functions we don't require, ie
the official remote display connection and a connection for combining
I remove the IDC (Insulation Displacement Connectors)
connectors (yes I know that's tautologous, like PIN number) from
these cables, split my newly purchased 40-way cable in half, and
press the connectors onto it.
Pressing a connector onto the cable.
I'm sure there are special tools for this, but even in my days working
in electronics we simply used a vice.
Having made my new cable I plug it in and power
up the inverter. Everything seems to work, so for the time being
I'll consider this a good idea.
So there you have it, if you have one of the large
Trace inverters you can buy the official remote display for $500+,
or make your own for 81 cents.
NOTE: Obviously this will void any warrantee,
and be very careful about the pin 1 orientation of the cable as
getting that wrong could prove to be very expensive.
Sat 1 Dec
I'm installing the heavy
wiring from the batteries. This means running some pretty fat wires
through the lounge room to the shunts in the electronics area.
Shunts? What are shunts?
Shunts are very accurate resistors used to measure
For small currents you normally just connect the
wires directly to the meter.
For small currents the meter can
be connected in series with the wire carrying the current.
But with larger currents, usually over 20 amps
or so, it's common to let the bulk of the current bypass the meter
and just allow a small (and proportional) amount to be tapped off
to activate the meter's mechanism.
This is partly because the meter would be too
large if it were built to handle large currents, and also because
the meter is often mounted remotely from the wire through which
the main current is flowing. Usually such wires should be kept as
short as possible and it doesn't make sense to detour to a meter
several feet or even yards away.
Therefore we employ a shunt. A shunt is just an
accurate resistor, when a current passes through it a proportional
voltage is developed across it. This is why they are specified as
for example a 100A 50mV shunt, which means that if 100 amps are
flowing through the shunt you will measure 50 millivolts across
Therefore a meter with a 50-millivolt movement
that is connected across the shunt will fully deflect the needle
when there is 100A flowing, half deflect at 50A etc.
A schematic of a shunt with a remote
And a couple of shots of the real
thing. You can also see the inverter in the background and two 175A
circuit breakers (one for each battery bank) on the left of the
The actual resistor part can take many forms and
may show file marks, cuts, solder dabs etc. This is not rough manufacturing,
it's how the shunt is tuned to exactly the right resistance.
Sun 2 Dec
Peter is cleaning his excavator today. It hasn't been cleaned in
four years and the pile of muck left behind in the wash bay is enormous.
Not all the muck is on the ground,
Peter looks a little grubby after cleaning the excavator.
Mon 3 Dec
Back onto wiring the
batteries today. We want to get a rudimentary system running without
doing too much temporary wiring that has to be removed.
The left hand battery bank. The wires
emerging from the floor are from the bank on the right hand side
of the lounge room.
The heavy wires running from the
battery banks up to the circuit breaker and shunt area.
The shunt area doesn't look so neat
now. Despite not wanting to do much temporary wiring most of this
will have to go.
A wider view showing the solar regulator.
Tue 4 Dec
We finally have enough
infrastructure in place to charge batteries with the two solar panels
from the Landcruiser.
The Landcruiser's two Kyocera 120W
panels can now be used to charge our batteries in the truck.
Wed 5 Dec
I've finished most of
the plumbing up to and including the pump and external connections.
I've never seen so many hose clamps in my life, I already had dozens
from Wothahellizat 1 plus I purchased several a few days ago and today
I took delivery of another 80!
Due to an oversight I have to run
the tank outlets through the thick steel body bracing.
It's not hard to see where all the
clamps have gone I guess, there's eight in this tiny area.
The accumulator, pump and control
A pseudo schematic of the plumbing
in the tank and control valve area. "In" comes from the
outside world and "Out" goes to the pump, accumulator,
various taps, HWS etc.
Thu 6 Dec
Peter is still servicing his excavator. I'm still
working on the plumbing.
Fri 7 Dec
Well done all those who
spotted an apparent fault with my high-current wiring from the batteries.
Although it wasn't all that obvious the implication of some of the
previous text was that I had batteries, several feet of wire, then
the circuit breakers. Something like this.
Now this is not a very clever setup, you should
protect wires as close as possible to the current source, (in this
case the batteries) not eight feet away. What happens if a short
circuit develops somewhere within that eight feet?
I do in fact have some Mega fuses bolted directly
to the positive battery terminal of each bank, the only reason I
didn't show them before is that I stuffed up the photo.
A 175A Mega fuse bolted directly
to the battery terminal.
The circuit breakers are really just used as isolation
switches. As you can see the fuses are 175A which is the same as
the breakers, it would make better sense to use fuses rated a little
higher so that in the event of a problem further downstream of the
breakers they would trip before the fuses blew which of course would
be cheaper and easier to rectify. But I'm using what I've got.
While on the subject of using fuses to protect
wires let's look at a common scenario, that of running a thick wire
DC bus around the vehicle and tapping off the main circuit with
small wires for lights, 12v appliances etc.
When the wire shorts out it tries
to conduct too much current, it will overheat and possibly catch
Most appliances are fused but this may only protect
the appliance, what about the wire? It's typical for such wires
to be run all around the place on their way to the appliance. If
it should for example pass through a steel bulkhead at point "A",
vibration can cause the insulation to become worn (because you didn't
use a grommet :-) and the wire to short circuit to the steel.
It almost certainly won't be up to the job of
conducting the available current and the result will be a meltdown
Therefore it makes sense to add a fuse at the
point the small wire branches from the large one. This fuse should
be rated well below the capacity of the wire.
Now when the wire shorts the fuse
blows instead of the wire.
Sun 9 Dec
around with plumbing, it's not that the system is overly complicated,
but there just seems to be a lot of detail to attend to. For example
we have a water meter to measure our usage, but for some reason no
plumbing fittings like meters and valves have built in mounting points.
Maybe they are designed to be used with old-fashioned steel pipes
that would hold things in place, but in these days of nylon connections
and hoses you need to provide some extra mechanical support.
Like the meter below, I want the face to appear
through a panel, but with no mounting points on the device I have
to bodge up something myself.
The rear of the meter showing some
timber spacers that allow the dial to protrude just the right amount
through the panel, and a steel strap to hold it in place.
Tue 11 Dec
I've got some good news
and some bad hews. The good news is that you can buy generators really
cheaply these days. The bad news is that that's just what we will
probably have to do, buy a new generator.
Here in the workshop we often use a 6.5KVA diesel
generator to top up the batteries on overcast days like today. It's
a noisy thing and we stick it outside so we only hear an annoying
But when that hum turns to a pop and fades to
nothing I run to investigate.
The machine has stopped and there's a whiff of
smoke in the air. That's OK, it has been smoking a little lately.
But the smoke doesn't stop, in fact it gets worse.
The bloody thing is on fire.
I disconnect it and push it further from the shed,
then run inside and grab the first fire extinguisher I can think
of, a tiny powder unit.
This has little affect so I grab another, the
new extinguisher is larger but the problem is access, because this
is an enclosed "silent" generator there is no ready access
to the internals, and it's the internals that are on fire.
I poke the nozzle in through air vents and an
access hatch but it has little affect. Then I start removing the
side panels while Chris tries to direct some powder at any flames
It soon becomes apparent though that the fire
is dying out of its own accord, thank goodness this is a diesel
generator, with a near full tank of petrol I may not have been so
keen to get close.
Two dead fire extinguishers and a
Some of the internal wiring.
All this makes me think about access, despite
having an endless supply of fire extinguishers they were of little
use because we couldn't get access to the source of the flames.
Because this is a "silent" generator
it's fully enclosed, and although you can access everything it takes
tools and time, neither of which are in abundant supply when a fire
is on the loose.
Now I always make things with access and maintenance
in mind, most panels are removable, brackets bolted rather than
welded etc. But I think about spending a few minutes with a spanner
while maintaining, not a few seconds while fighting a fire.
So from now on I think I'll pay more attention
to this aspect of the design.