On Sat, 07 May 2005 11:00:11 GMT, "Roger Long" wrote:

I'm about to install an onboard battery charger.

Is there any reason why the charging leads can not go to the ends of
the battery cables at the selector switch instead of snaking into the
box and being put on the terminals? This would be easier and neater
and minimize the chance of things getting switched at battery change.

When we put the batteries in, the yard made a good point. Switching
one battery end for end so that either the two + or - terminals are
side by side greatly minimizes the chance of a massive short if
something gets across the terminals while the system is on.
Everything should be dead whenever the box cover is off but this is
real life and both boating and aviation are a good place for a belt
and suspenders approach.

Roger, the only concern I'd have is that chargers rely on knowing
the "real" battery voltage. If you have load on the batteries while they
are being charged, the extra voltage drop due to "remote"
sensing might not be to your abvantage. Having said that, I suspect
that with clean terminals and big cables the problem would be minimal.
Norm B

That's an excellent point. Exactly the kind of insight that prompted
my post.

The cables in this case are about half an inch in diameter and three
feet long. With just 10 amps of charging current per group 24 battery
I agree that it won't be a problem. I cleaned up the battery
connections bright and shiny when I put the batteries in and I'll do
the other connections when I install the charger.

--

Roger Long


"engsol" wrote in message
...
On Sat, 07 May 2005 11:00:11 GMT, "Roger Long"
wrote:

Roger, the only concern I'd have is that chargers rely on knowing
the "real" battery voltage. If you have load on the batteries while
they
are being charged, the extra voltage drop due to "remote"
sensing might not be to your abvantage. Having said that, I suspect
that with clean terminals and big cables the problem would be
minimal.
Norm B

Roger Long wrote:
That's an excellent point. Exactly the kind of insight that prompted
my post.

The cables in this case are about half an inch in diameter and three
feet long. With just 10 amps of charging current per group 24 battery
I agree that it won't be a problem. I cleaned up the battery
connections bright and shiny when I put the batteries in and I'll do
the other connections when I install the charger.

I'm glad you understand the significance of this issue, and it sounds
like you won't have a problem. Single 0 (1/0) cable should handle 10
Amps for over 100 feet with less than a 2% drop.

However, readers should be aware that a 100 Amp current will have a 2%
voltage drop in 10 feet of single 0, and 14 feet of double 0. this
will be a few tenths of a volt, enough to give a distorted reading of
the charge state.

In my case I have both a 100 Amp alternator and a 100 Amp shore
charger. The shore charger is about 3 feet of 2/0 away, but the
alternator is 15 feet. The next time I running it with a high rate
I'll have to test the battery post voltage so see if its running
higher than expected.

Good point, Jeff. Thanks. I'm quite familiar with 120 through 480 volt
drops, but it's nice to be reminded how dramatic 12v drops can be.
Padeen


"Jeff" wrote in message
...
Roger Long wrote:
That's an excellent point. Exactly the kind of insight that prompted
my post.

The cables in this case are about half an inch in diameter and three
feet long. With just 10 amps of charging current per group 24 battery
I agree that it won't be a problem. I cleaned up the battery
connections bright and shiny when I put the batteries in and I'll do
the other connections when I install the charger.

I'm glad you understand the significance of this issue, and it sounds
like you won't have a problem. Single 0 (1/0) cable should handle 10
Amps for over 100 feet with less than a 2% drop.

However, readers should be aware that a 100 Amp current will have a 2%
voltage drop in 10 feet of single 0, and 14 feet of double 0. this
will be a few tenths of a volt, enough to give a distorted reading of
the charge state.

In my case I have both a 100 Amp alternator and a 100 Amp shore
charger. The shore charger is about 3 feet of 2/0 away, but the
alternator is 15 feet. The next time I running it with a high rate
I'll have to test the battery post voltage so see if its running
higher than expected.

Roger,
You'd make it easier for us, and yourself, if you could identify those
cables with a gauge # and class, rather than a diameter. Wire insulation
varies dramatically with its class, allowing a range of conductor size
within a specific measurement. For instance, XLP (insulation designation)
may be as much as .02-.05in larger than THHN.
Please don't take my post as criticism; I'm merely suggesting an alternative
to wire descriptions by diameter.


Roger Long" wrote in message
...
That's an excellent point. Exactly the kind of insight that prompted
my post.

The cables in this case are about half an inch in diameter and three
feet long. With just 10 amps of charging current per group 24 battery
I agree that it won't be a problem. I cleaned up the battery
connections bright and shiny when I put the batteries in and I'll do
the other connections when I install the charger.

--

Roger Long


"engsol" wrote in message
...
On Sat, 07 May 2005 11:00:11 GMT, "Roger Long"
wrote:

Roger, the only concern I'd have is that chargers rely on knowing
the "real" battery voltage. If you have load on the batteries while
they
are being charged, the extra voltage drop due to "remote"
sensing might not be to your abvantage. Having said that, I suspect
that with clean terminals and big cables the problem would be
minimal.
Norm B

No offence taken at all. I just hadn't looked for the cable sized yet
when I posted. My estimate was based on eyeballing the copper I could
see at the terminals and did not include the insulation.

The tie for the negative lead had disappeared and the yard made one up
that was about half the diameter. It's short so this is probably OK
but I need to verify that.

Oddly, I used to design electrical systems for boats but it's been
decades since I thought about them and my knowledge has leaked down to
the level of the average bear. I now design some very sophisticated
boats but someone else always worries about the electrical system. I
just write specs saying that they shall be "first class, incredible,
stupendous, and in accord with every know industry standard and
manufacturer's recommendation."

How do you like this one?

http://home.maine.rr.com/rlma/odurv2.htm

--

Roger Long



"padeen" wrote in message
...
Roger,
You'd make it easier for us, and yourself, if you could identify
those
cables with a gauge # and class, rather than a diameter. Wire
insulation
varies dramatically with its class, allowing a range of conductor
size
within a specific measurement. For instance, XLP (insulation
designation)
may be as much as .02-.05in larger than THHN.
Please don't take my post as criticism; I'm merely suggesting an
alternative
to wire descriptions by diameter.

Given a sufficiently sized cable, the electrical equivalency will be equal.

"engsol" wrote in message
...
On Sat, 07 May 2005 11:00:11 GMT, "Roger Long"
wrote:

I'm about to install an onboard battery charger.

Is there any reason why the charging leads can not go to the ends of
the battery cables at the selector switch instead of snaking into the
box and being put on the terminals? This would be easier and neater
and minimize the chance of things getting switched at battery change.

When we put the batteries in, the yard made a good point. Switching
one battery end for end so that either the two + or - terminals are
side by side greatly minimizes the chance of a massive short if
something gets across the terminals while the system is on.
Everything should be dead whenever the box cover is off but this is
real life and both boating and aviation are a good place for a belt
and suspenders approach.

Roger, the only concern I'd have is that chargers rely on knowing
the "real" battery voltage. If you have load on the batteries while they
are being charged, the extra voltage drop due to "remote"
sensing might not be to your abvantage. Having said that, I suspect
that with clean terminals and big cables the problem would be minimal.
Norm B