I have a 24v system comprising 2 battery banks 1st (2x12v) engine and the
2nd (2x12v) domestic, each battery is approximately 100ah (ie 200 ah per
bank). The banks have 2 separate double pole switches, until now in order to
charge the domestic batteries there has been a link between the 2 negative
poles on the switched side of the switches. I brought a VSR (voltage
sensitive relay) to replace this link, but when I came to fit it I found
that it needs to connect between the 2 positives of the battery banks. So I
plan to buy another relay (an ordinary one), wire it in the link currently
joining the 2 banks, and then, use my VSR to switch this relay on and off.
Does that sound sensible or have I lost the plot.
Thanks

Nigel wrote:

I have a 24v system comprising 2 battery banks 1st (2x12v) engine and the
2nd (2x12v) domestic, each battery is approximately 100ah (ie 200 ah per
bank).

That's only 100Ah per bank, because within each bank the batteries
are in series. Two 12V 100Ah batteries in series make one 24V 100Ah
battery.

The banks have 2 separate double pole switches, until now in order
to charge the domestic batteries there has been a link between the 2
negative poles on the switched side of the switches. I brought a VSR
(voltage sensitive relay) to replace this link, but when I came to fit it
I found that it needs to connect between the 2 positives of the battery
banks. So I plan to buy another relay (an ordinary one), wire it in the
link currently joining the 2 banks, and then, use my VSR to switch this
relay on and off. Does that sound sensible or have I lost the plot.

I think quite possibly you may have. I don't understand your description.
If your ASCII art isn't up to drawing a diagram, perhaps you could give
us a detailed "thigh bone's connected to the hip bone"-style description
of your circuit.

Let's say your engine bank has two batteries E1 and E2, and your domestic
bank has D1 and D2. Let's say E1- is permanently connected to E2+, and
likewise D1- to D2+. I'd normally have expected E2- and D2- and the
engine block to be permanently wired together, and any switching to
involve E1+ and D1+ and the starter+ and domestic distribution+ and
the alternator+, while starter- distribution- and alternator- all being
permanently connected to the engine block too. How are your switches
and the link connected exactly?

Let's say your engine bank has two batteries E1 and E2, and your domestic
bank has D1 and D2. Let's say E1- is permanently connected to E2+, and
likewise D1- to D2+. I'd normally have expected E2- and D2- and the
engine block to be permanently wired together, and any switching to
involve E1+ and D1+ and the starter+ and domestic distribution+ and
the alternator+, while starter- distribution- and alternator- all being
permanently connected to the engine block too. How are your switches
and the link connected exactly?



I've posted a picture with (hopefuuly) an explanation of what I'm tring to
achieve hear
http://www.jassira.com/battery_switches.htm

once again thanks for help

The banks have 2 separate double pole switches, until now in order to
charge the domestic batteries there has been a link between the 2 negative
poles on the switched side of the switches.

Surely all that is doing is connecting the battery earth which is the system
earth... how is a positive charge from the alternator etc able to charge
through this link.... I'm confused.


I brought a VSR (voltage sensitive relay) to replace this link, but when I
came to fit it I found that it needs to connect between the 2 positives of
the battery banks. So I plan to buy another relay (an ordinary one), wire
it in the link currently joining the 2 banks, and then, use my VSR to
switch this relay on and off. Does that sound sensible or have I lost the
plot.

Yes it would do the same job but I still don't get it.

Brian

"Sandpiper" wrote in message
...
The banks have 2 separate double pole switches, until now in order to
charge the domestic batteries there has been a link between the 2
negative
poles on the switched side of the switches.

Surely all that is doing is connecting the battery earth which is the
system
earth... how is a positive charge from the alternator etc able to charge
through this link.... I'm confused.


I brought a VSR (voltage sensitive relay) to replace this link, but when
I
came to fit it I found that it needs to connect between the 2 positives
of
the battery banks. So I plan to buy another relay (an ordinary one),
wire
it in the link currently joining the 2 banks, and then, use my VSR to
switch this relay on and off. Does that sound sensible or have I lost
the
plot.

Yes it would do the same job but I still don't get it.

Brian


I think the system has a positive earth, my only reason for suspecting this
is that that the stater motor has a negative cable going to a terminal on
the back and a positive cable connected to the side, which I think is just
connected to the casing. In general the electrical system has the appearance
of having been done by someone who knew what they were doing, so I'm
reluctant to rip it all out and start again. I'll be on board tomorrow so
I'll investigate further, in the mean time thanks again for your help

"Nigel" wrote in message
...

I think the system has a positive earth,

That would confuse things! What kind of boat is this on?

What confuses me the most is why both the Positive and the Negative sides of
the battery are switched. In a typical battery installation the negative
side of all battery banks gets tied gets tied to "ground". If it was a
postive ground system then I would expect the same except it would be the
positive side that is connected to ground.


Ignore for the moment the fact that the batteries have a switched negative
side. The fact that the output of the switches have their negative side
tied together suggests that the system is negative ground. That wire that
connects the two negatives together is NOT what you want to replace!

The voltage sensitve relay needs to connect between the positive terminals
of the two batteries, preferably between the switch and the battery. In
order for the two banks to charge together regardless of the switch settings
the negative sides of thebatteries would need to be tied directly together.

So, the easiest way to install this relay is to add a BIG wire between the
two negatives, then wire the relay directly to the two positives

Rod

"rmcinnis" wrote in message
...

"Nigel" wrote in message
...

I think the system has a positive earth,

That would confuse things! What kind of boat is this on?

What confuses me the most is why both the Positive and the Negative sides
of
the battery are switched. In a typical battery installation the negative
side of all battery banks gets tied gets tied to "ground". If it was a
postive ground system then I would expect the same except it would be the
positive side that is connected to ground.


Ignore for the moment the fact that the batteries have a switched negative
side. The fact that the output of the switches have their negative side
tied together suggests that the system is negative ground. That wire
that
connects the two negatives together is NOT what you want to replace!

The voltage sensitve relay needs to connect between the positive terminals
of the two batteries, preferably between the switch and the battery. In
order for the two banks to charge together regardless of the switch
settings
the negative sides of thebatteries would need to be tied directly
together.

So, the easiest way to install this relay is to add a BIG wire between the
two negatives, then wire the relay directly to the two positives

Rod


Whoops...firstly, the picture has changed I miss labelled the terminals, but
I don't think it affects things so far.
The boat is a steel hulled Roberts 53, (www.jassira.com) and was built by
the previous owner, my understanding is that a lot of the internal fitting
was carried by friends and acquaintances, but the wiring gives the
appearance of being done by someone who was at least competent. She was
built in the early 80's and I think this systems is original and has worked
well so far. I do know that if I remove the black cable joining the 2
switched negatives the domestic system still works ok but the batteries
don't charge. I assume from this that the positive cables must be connected
elsewhere
I'll investigate further today,

On 2004-10-16 17:54:29 +1000, "Nigel"
said:


"rmcinnis" wrote in message
...

"Nigel" wrote in message
...

I think the system has a positive earth,

That would confuse things! What kind of boat is this on?

What confuses me the most is why both the Positive and the Negative sides
of
the battery are switched. In a typical battery installation the negative
side of all battery banks gets tied gets tied to "ground". If it was a
postive ground system then I would expect the same except it would be the
positive side that is connected to ground.


Ignore for the moment the fact that the batteries have a switched negative
side. The fact that the output of the switches have their negative side
tied together suggests that the system is negative ground. That wire
that
connects the two negatives together is NOT what you want to replace!

The voltage sensitve relay needs to connect between the positive terminals
of the two batteries, preferably between the switch and the battery. In
order for the two banks to charge together regardless of the switch
settings
the negative sides of thebatteries would need to be tied directly
together.

So, the easiest way to install this relay is to add a BIG wire between the
two negatives, then wire the relay directly to the two positives

Rod


Whoops...firstly, the picture has changed I miss labelled the terminals, but
I don't think it affects things so far.
The boat is a steel hulled Roberts 53, (www.jassira.com) and was built by
the previous owner, my understanding is that a lot of the internal fitting
was carried by friends and acquaintances, but the wiring gives the
appearance of being done by someone who was at least competent. She was
built in the early 80's and I think this systems is original and has worked
well so far. I do know that if I remove the black cable joining the 2
switched negatives the domestic system still works ok but the batteries
don't charge. I assume from this that the positive cables must be connected
elsewhere
I'll investigate further today,

A survey requirement in Australia for some states is to have both
positive and negitive terminals switched. This is because it completely
disconnects the battery from the system when switched off. This avoids
any possibility of a leakage path except for a switch failure.

--
Regards,
John Proctor VK3JP, VKV6789
S/V Chagall

Nigel wrote:

I do know that if I remove the black cable joining the
2 switched negatives the domestic system still works ok but the batteries
don't charge. I assume from this that the positive cables must be
connected elsewhere
I'll investigate further today,

Leaving aside the issue of whether the engine and alternator are
positive or negative ground, the alternator will have two output
connections, one through ground and one through an insulated
terminal; one of these will be positive, the other negative; for
the rest of this it doesn't really matter which is which, so long
as you can identify them.

Chances are you'll find that the minus output of the alternator
goes via a single cable to the switched minus of the engine battery
(and then via your mysterious short link to the switched minus of
the domestic, and that the plus output of the alternator goes via
two separate cables to the two switched plus terminals. I have a
feeling it might be those black cables with the red tapes around
their ends.

Leave the short link in place.
Remove the plus alternator feed cable from the switched domestic,
either disconnect both ends of the cable and throw it away, or
double it up so both cables go to the engine switched plus.
Then connect your VSR between the two switched + terminals.

On Sat, 16 Oct 2004 10:03:32 +0000, John Proctor wrote:

[snip]


A survey requirement in Australia for some states is to have both
positive and negitive terminals switched. This is because it completely
disconnects the battery from the system when switched off. This avoids
any possibility of a leakage path except for a switch failure.

Interrupting just one pole also avoids any possibility of a leakage path
except for a switch failure.

--Mac