On Jul 7, 12:46*am, "Fredxx" wrote:
NT wrote:
On Jul 6, 7:48 pm, "Fredxx" wrote:
NT wrote:
On Jul 6, 1:16 pm, "Fredxx" wrote:
NT wrote:
On Jul 6, 1:25 am, "gazz" wrote:

You'll notice that the nominal fuse rating will be far below the
actual currents you draw. A 200A fuse is way too high, and as
good as useless.

Why's 200A too high,

Do you know how much current a 200A fuse would need to see to blow
in 1 minute? Its way beyond anything the OP indicates he's doing.

That might depend on the type and characteristic of the fuse.
Probably 300 to 500A when new.

I think that's way off. Do you have tables? Even MCBs are nowhere near
that discriminatory or quick.

Way off? *What fuses do you use?http://www.littelfuse.com/data/en/Pr...elfuse_TB101_O...
Have a look at page 71.


impressive compared to wire fuses


NT

NT wrote:

Do you know how much current a 200A fuse would need to see to blow in
1 minute? Its way beyond anything the OP indicates he's doing.
That might depend on the type and characteristic of the fuse. Probably 300
to 500A when new.

I think that's way off. Do you have tables? Even MCBs are nowhere near
that discriminatory or quick.

According to Fig. 3.3A in BS 7671 to be sure of taking out a 200 A BS 88
gG fuse in 60 s you'll need about 650 amps. To take it in 10 s - a more
reasonable time for cable protection - you'll need 1 kA. Remember that
these are actual, rather than prospective, fault currents and in an ELV
circuit like this the resistance of the fuse might be enough to make the
difference between the two appreciable.

This all sounds like hard work to me. Why the 12 V system for kilowatt
power levels? Why not go up to 24 or 48 volts and make life a lot
easier in regard to cable sizes and overcurrent protection. Inverters
are available for those voltages and you could just tap the battery if
there are any 12 V small power DC loads (fused at say 30 A).

--
Andy

"NT" wrote in message
...
Why's 200A too high,

Do you know how much current a 200A fuse would need to see to blow in
1 minute? Its way beyond anything the OP indicates he's doing.

That might depend on the type and characteristic of the fuse. Probably 300
to 500A when new.

I think that's way off. Do you have tables? Even MCBs are nowhere near
that discriminatory or quick.
--------

i'm begining to wish i was like most motorhomers, no idea where the battery
lives let alone how it's connected, when the tv dies the batteries are
flat.... oh and buy a new set every year

i've gone for true deep cycle batteries as according to my usage patterns, i
should get 7 to 10 years life out of them, quoted 1300 cycles by the
manufacturers to 50% dod, but the new bank is 50% larger, so i should never
have to run them that low again (it's the damn fridge freezer that does it,
need 80Ah a day to run the fecker, as long as i get sunlight i'm fine, the
370 watts of solar puts back more than that), could go 2 -3 days of very
overcast weather when the old batts were new, but after 50 cycles that
dropped to a day of no good sun and the next day was genny time, or the low
voltage alarms would be going off in the night each time the fridge
compressor starts up)

Anyway, i've ordered the cable, crimper, copper lug terminals, copper bar
stock to make the bus bars, brass bolts, shake proof washers and so on, and
have the batteries secured under the bed,

the cable is 50 sq mm, so should be more than enough for my 1 meter lengths
i need from the terminals to the bus bars,
one bus bar will be a double bar, with a shunt for an ammeter linking the 2,
so batteries to one bar, loads to the other bar, not sure yet if to put the
shunt in the pos or neg busbar, seems measuring the negative bar is the most
common way the boaty people do it.

just need to work out what size fuses to put on the battery terminals, and
if i should fuse each pos terminal... i.e. the series ones, and the paralell
ones, or just fuse the paralell terminals.

the cables will be routed safely where they can not chaff on anything, they
will basicaly be going from the terminals on the battery tops, allong the
top in groups of 3... pos and neg bundles, through the wooden battery
enclosure, and to the bus bars, no metal in sight of the cables.

From the pos busbar, the main load centre cable goes through a 70 amp DC
breaker, the inverter cable will go through a fuse, size undetermined yet,

the cables from the bus bars to the inverter will be routed alongside the
battery box, through the plastic of the inverter housing box (it's a battery
box with an outside access door, sold for caravans, inside it is my inverter
and mains charger and shore power connection) then the cables go straight to
the inverters terminals, the inverter is fused internaly straight after the
input terminals (its a wenchi 1500 watt pure sine wave inverter)
connected to the inverters terminals is the battery chargers DC connections,
it's only a tiddely 20 amp charger (sterling 4 stage charger)

The inverter and charger are in their on box, which is vented via a couple
of cents in the door, both items have variable speed cooling fans that seem
able to do their job fine, i fitted a fat to one of the vents to ensure
airflow, running when ever the inverter or charger was on, but it didnt make
any differance to the duty cycle of the internal fans, so i dont use it
anymore)

The batteries will be in a sealed plywood box, varnished internaly, top rear
will be a vent through the side of the van, vent is about 10 inches long by
5 high, has a mesh to keep out insects and a downwards pointing cover to
keep rain out.

i will fit a couple of 100mm brushless fans in the vent, and have them
running when ever the battery voltage is over 13.8 volts, i'll run them at a
low voltage and mount them on silicone to make em as quiet as possible, as i
dont want them to wake me up every time the solar panels start charging in
the morning,

The batteries will be fitted with a centeral watering system at a later
date, just a manual system, connect the squeeze bulb to the connector and
pump in the deionised water untill the cell caps all shut off,
but for now i will keep an eye on the water levels manualy, the cell caps
have the quick release caps on ATM, push the 2 levers and all 3 caps are
unlocked and lift off as one unit,

Anyhoo, all i need to really do is work out the fuse ratings, and if to fuse
all pos terminals, or just the paralell ones, and i really want a remote
indicator to show a blown fuse.

"Andy Wade" wrote in message
...
NT wrote:

Do you know how much current a 200A fuse would need to see to blow in
1 minute? Its way beyond anything the OP indicates he's doing.
That might depend on the type and characteristic of the fuse. Probably
300
to 500A when new.

I think that's way off. Do you have tables? Even MCBs are nowhere near
that discriminatory or quick.

According to Fig. 3.3A in BS 7671 to be sure of taking out a 200 A BS 88
gG fuse in 60 s you'll need about 650 amps. To take it in 10 s - a more
reasonable time for cable protection - you'll need 1 kA.

i only suggested the 200 amp fuses as that was the first figure i thought
of,

max current draw in my system is just over 200 amps, so i figured if each
battery was fused at 200 amps, then if one cell goes down and pops a fuse,
the other batteries will still provide the current, if i fused them too low
then trying to pull 200 amps with one set of batteries out of circuit could
pop the rest of the fuses, then i'd be fecking about trying to figure out
which fuse poped first, not to mention having to replace all of them, and
they aint 5p cheapo fuses like in a mains plug.

At the end of the day, the fuses are there to protect the cables, the
appliances have their own fuses to protect themselves,
the possibility of a cell shorting out would i try and pull a fairly large
current, and thus be similar to a cable short,

On Jul 7, 1:49*am, "gazz" wrote:
"NT" wrote in message
...

Why's 200A too high,

Do you know how much current a 200A fuse would need to see to blow in
1 minute? Its way beyond anything the OP indicates he's doing.

That might depend on the type and characteristic of the fuse. Probably 300
to 500A when new.

I think that's way off. Do you have tables? Even MCBs are nowhere near
that discriminatory or quick.
--------

just need to work out what size fuses to put on the battery terminals, and
if i should fuse each pos terminal... i.e. the series ones, and the paralell
ones, or just fuse the paralell terminals.

I'd definitely put a fuse on each battery.


the inverters terminals, the inverter is fused internaly straight after the
input terminals (its a wenchi 1500 watt pure sine wave inverter)


Anyhoo, all i need to really do is work out the fuse ratings, and if to fuse
all pos terminals, or just the paralell ones, and i really want a remote
indicator to show a blown fuse.

Maybe I've missed it, but to have any idea of what fuse to spec we'd
need to know what your maximum currents are for how long, eg 1kW for 1
minute and 200w continuous. Then you simply look at a fuse chart to
see which fuse rating is the lowest that wont blow with those loads.
As Fredxx pointed out, you can get fancy fuses with much tidier specs
than wire fuses, the latter have a pretty big overcurrent margin, ie a
big gap between rated current and will blow current. As far as
specifying fuses go, I think you can forget about startup surges, the
fuses you're looking at will have plenty of thermal inertia.


NT

"NT" wrote in message
...

Anyhoo, all i need to really do is work out the fuse ratings, and if to
fuse
all pos terminals, or just the paralell ones, and i really want a remote
indicator to show a blown fuse.

Maybe I've missed it, but to have any idea of what fuse to spec we'd
need to know what your maximum currents are for how long, eg 1kW for 1
minute and 200w continuous. Then you simply look at a fuse chart to
see which fuse rating is the lowest that wont blow with those loads.
As Fredxx pointed out, you can get fancy fuses with much tidier specs
than wire fuses, the latter have a pretty big overcurrent margin, ie a
big gap between rated current and will blow current. As far as
specifying fuses go, I think you can forget about startup surges, the
fuses you're looking at will have plenty of thermal inertia.

okay,

1500 watts (centeral vac system) for 5 minutes,

1200 watts (hairdryer) for however long it takes a woman to dry her hair, 10
mins, 15 mins, 3 hours??

900 watts (microwave, that is the input power, cookin power is 550 watts)
for say 10 mins

300 watts (washing machine) i guess for a 2 or 3 minute spin a couple of
times per wash, if it cant get the load balanced then it'll fanny about
rotating the drum left and right at varying speeds for about 10 mins before
giving up,

50 watts (12 inch fan) for a fair few hours in summer,

fuse each terminal at 125 amps with littlefuse mega fuses?

for remote warning of a popped fuse, leds with appropriate resistors accross
the fuses? or something more fancy.

On Jul 7, 3:16*am, "gazz" wrote:
"NT" wrote in message

...

Anyhoo, all i need to really do is work out the fuse ratings, and if to
fuse
all pos terminals, or just the paralell ones, and i really want a remote
indicator to show a blown fuse.
Maybe I've missed it, but to have any idea of what fuse to spec we'd
need to know what your maximum currents are for how long, eg 1kW for 1
minute and 200w continuous. Then you simply look at a fuse chart to
see which fuse rating is the lowest that wont blow with those loads.
As Fredxx pointed out, you can get fancy fuses with much tidier specs
than wire fuses, the latter have a pretty big overcurrent margin, ie a
big gap between rated current and will blow current. As far as
specifying fuses go, I think you can forget about startup surges, the
fuses you're looking at will have plenty of thermal inertia.

okay,

1500 watts (centeral vac system) for 5 minutes,

1200 watts (hairdryer) for however long it takes a woman to dry her hair, 10
mins, 15 mins, 3 hours??

900 watts (microwave, that is the input power, cookin power is 550 watts)
for say 10 mins

300 watts (washing machine) i guess for a 2 or 3 minute spin a couple of
times per wash, if it cant get the load balanced then it'll fanny about
rotating the drum left and right at varying speeds for about 10 mins before
giving up,

50 watts (12 inch fan) for a fair few hours in summer,

fuse each terminal at 125 amps with littlefuse mega fuses?

I dont have the chart for those, but if thats what fits, great. But
then 100A total load divided by n-1 batteries doesnt really square
with a 125A fuse. (where n=number of batteries)


for remote warning of a popped fuse, leds with appropriate resistors accross
the fuses? or something more fancy.

I doubt you'd see enough voltage across an open fuse to light a LED. A
suitable comparator driving a LED would be more likely to work


Lastly I'd have reservations about the use of 12v for such enormous
loads. I might look at a 3 wire system, or maybe 48v with 2 outputs,
one at 48v and one transformed down to a nice regulated 12v using an
SMPSU.


NT

On Tue, 7 Jul 2009 03:30:00 -0700 (PDT), NT
wrote:


for remote warning of a popped fuse, leds with appropriate resistors accross
the fuses? or something more fancy.

I doubt you'd see enough voltage across an open fuse to light a LED. A
suitable comparator driving a LED would be more likely to work

Wouldn't you typically have enough voltage to light a 12V bulb?

T i m

T i m wrote:
On Tue, 7 Jul 2009 03:30:00 -0700 (PDT), NT
wrote:


for remote warning of a popped fuse, leds with appropriate
resistors accross the fuses? or something more fancy.

I doubt you'd see enough voltage across an open fuse to light a LED.
A suitable comparator driving a LED would be more likely to work

Wouldn't you typically have enough voltage to light a 12V bulb?

T i m

I would imagine a 12V bulb may have a hint of a glow if it has 1V across it!

On Tue, 7 Jul 2009 03:30:00 -0700 (PDT), NT wrote:

for remote warning of a popped fuse, leds with appropriate
resistors
accross the fuses? or something more fancy.

I doubt you'd see enough voltage across an open fuse to light a LED. A
suitable comparator driving a LED would be more likely to work

Eh? Assuming some load (only a few mA required) you get the full
battery voltage across an open fuse, it's an infinite resistor!

What ever you put across the fuse has to be current limited so an LED
and suitable series R is fine. When the fuse is good it shorts out
the R and LED so the LED doesn't light.

--
Cheers
Dave.

On Tue, 7 Jul 2009 12:50:02 +0100, "Fredxx" wrote:

T i m wrote:
On Tue, 7 Jul 2009 03:30:00 -0700 (PDT), NT
wrote:


for remote warning of a popped fuse, leds with appropriate
resistors accross the fuses? or something more fancy.

I doubt you'd see enough voltage across an open fuse to light a LED.
A suitable comparator driving a LED would be more likely to work

Wouldn't you typically have enough voltage to light a 12V bulb?

T i m

I would imagine a 12V bulb may have a hint of a glow if it has 1V across it!

thinks again Ah, because we are talking about several packs in
parallel here (so it would therefore only be the difference between
the offline battery and the others).

Another reason not to run batteries in parallel then. ;-)

T i m.

On Jul 7, 6:56*pm, T i m wrote:
On Tue, 7 Jul 2009 12:50:02 +0100, "Fredxx" wrote:
T i m wrote:
On Tue, 7 Jul 2009 03:30:00 -0700 (PDT), NT
wrote:

for remote warning of a popped fuse, leds with appropriate
resistors accross the fuses? or something more fancy.

I doubt you'd see enough voltage across an open fuse to light a LED.
A suitable comparator driving a LED would be more likely to work

Wouldn't you typically have enough voltage to light a 12V bulb?

T i m

I would imagine a 12V bulb may have a hint of a glow if it has 1V across it!

thinks again Ah, because we are talking about several packs in
parallel here (so it would therefore only be the difference between
the offline battery and the others).

exactly. Under some conditions it might glow very dimly, but it would
make a terrible blown fuse indicator at best.


Another reason not to run batteries in parallel then. ;-)

T i m.


NT

On Jul 7, 5:08*pm, "Dave Liquorice"
wrote:
On Tue, 7 Jul 2009 03:30:00 -0700 (PDT), NT wrote:
for remote warning of a popped fuse, leds with appropriate
resistors
accross the fuses? or something more fancy.

I doubt you'd see enough voltage across an open fuse to light a LED. A
suitable comparator driving a LED would be more likely to work

Eh? Assuming some load (only a few mA required) you get the full
battery voltage across an open fuse, it's an infinite resistor!

What ever you put across the fuse has to be current limited so an LED
and suitable series R is fine. When the fuse is good it shorts out
the R and LED so the LED doesn't light.


How do you propose to get full battery voltage across the blown fuse?
Lets take a typical scenario, one fuses pops, all batteries have some
charge in them, so the o/c fuse sees anything from nothing to maybe a
few volts under some circumstances.

Comparators are dead cheap, ones that go the +ve rail on the input
would do this job properly no problem. Simply set them to sense more
than 0.1v difference either polarity across the fuse.


NT

On Tue, 07 Jul 2009 18:56:27 +0100, T i m wrote:

thinks again Ah, because we are talking about several packs in
parallel here (so it would therefore only be the difference between
the offline battery and the others).

I forgot that as well but if the fuse is battery side of the blocking
diode it works, I think... B-) IIRC the use of such a diode has
been discounted.

As we are talking a 12v system from 6v batteries the fuse could be
between the batteries. Can't get me 'ed around that though.

--
Cheers
Dave.

Well, got everything needed to do the work now,

a big heavy chunk of copper bar, 30mm wide, 10mm thick, 300mm long, will
make 3 x 100mm long bars, 1 for earth, 2 for pos terminals, battery
connections will go to one bar, the other will be next to it and linked with
a shunt feeding a panel meter, reading upto 199.9 amps. then from the
shunted bar will come the load connections.

got me 50 sqmm welding cable, it's got 2mm thick insulation, designed to be
dragged over sharp objects in the course of industrial welding, so should
just about stand up to the task of being connected to batteries, cable tied
together and then to fixed objects at regular intervals i rekon.

got all me terminals, and the crimper,

built the battery box, sealed it, put in a large vent out the side of the
van at the highest level, i get a good airflow over the top of the
batteries, but will add a small brushless fan to help draw the hydrogen out
when the batteries are on boost and absorbtion charge stages.

will be fusing the inverter's main lead at 150 amps, not fusing the battery
connections as something i didnt tell you lot was i have an emergancy start
solenoid fitted, this links the house batteries to the starter battery at
the push of a dash button, to enable me to start the engine if the engine
battery is dead, self jump starting if you please.

so all the battery cable runs will be routed where they can not come to
harm,
as i will be checking the battery water levels regulary untill i fit a
centeral waterin system, if any cells go faulty i will spot em by the lower
level.

now to get cracking and get power back to this van,