I'm starting to give some thought to my power source on the house boat I am
refitting. I am leaning towards using isolators to seperate the battery
banks. I would like some experienced feedback on what type of isolator to
use; diode, FET or solid state? All I know at this point is that the drop
across the diode type can play havoc with the battery life because of the
voltage drop never allowing a full charge (?). The other two kinds I have
not been able to get anything except that they have a much smaller v drop
(FET) or none (solid state). And that is from sales materials. Will using
isolators allow me to forgo the 12Both switch and just use an in line on/off
switch?

May seem like a dumb question but how do I know what size of charger I will
need or does size (amps) matter other than how quick it will charge the
batteries. I plan on having two start and two house batteries.

How important/neccessary is it to have a galvanic isolator on the AC side?

THX

I'm looking forward to others' comments, but first:

The only diodes available today are "solid state" devices. Forward voltage
drop will typically be 0.5 to 0.7 volts unless it's a Schottky type. Could
be compensated for by sensing on the battery side or by telling the
controller there's an isolator.

FETs (Field Effect Transistors) are "solid state" devices. The voltage drop
is a function of current, figure 10 to 200 ohms on-resistance.

Huh?

Roger

http://home.insightbb.com/~derbyrm

"Steve Lortie" wrote in message
...
I'm starting to give some thought to my power source on the house boat I
am
refitting. I am leaning towards using isolators to seperate the battery
banks. I would like some experienced feedback on what type of isolator to
use; diode, FET or solid state? All I know at this point is that the drop
across the diode type can play havoc with the battery life because of the
voltage drop never allowing a full charge (?). The other two kinds I have
not been able to get anything except that they have a much smaller v drop
(FET) or none (solid state). And that is from sales materials. Will using
isolators allow me to forgo the 12Both switch and just use an in line
on/off
switch?

May seem like a dumb question but how do I know what size of charger I
will
need or does size (amps) matter other than how quick it will charge the
batteries. I plan on having two start and two house batteries.

How important/neccessary is it to have a galvanic isolator on the AC side?

THX

The most modern alternative is the "Battery Combiner". The connections
in this device are actual relays (0.0 V voltage drop). They leave the
batteries isolated until they see 14 (approx - value adjustable) on one
of the banks, indicating it is being supplied by a charger. In this
case, the relay closes, combining the batteries for joint charging from
the single source. When the charging voltage disappears, the relay opens
again, isolating the batteries.

bob

derbyrm wrote:
I'm looking forward to others' comments, but first:

The only diodes available today are "solid state" devices. Forward voltage
drop will typically be 0.5 to 0.7 volts unless it's a Schottky type. Could
be compensated for by sensing on the battery side or by telling the
controller there's an isolator.

FETs (Field Effect Transistors) are "solid state" devices. The voltage drop
is a function of current, figure 10 to 200 ohms on-resistance.

Huh?

Roger

http://home.insightbb.com/~derbyrm

"Steve Lortie" wrote in message
...

I'm starting to give some thought to my power source on the house boat I
am
refitting. I am leaning towards using isolators to seperate the battery
banks. I would like some experienced feedback on what type of isolator to
use; diode, FET or solid state? All I know at this point is that the drop
across the diode type can play havoc with the battery life because of the
voltage drop never allowing a full charge (?). The other two kinds I have
not been able to get anything except that they have a much smaller v drop
(FET) or none (solid state). And that is from sales materials. Will using
isolators allow me to forgo the 12Both switch and just use an in line
on/off
switch?

May seem like a dumb question but how do I know what size of charger I
will
need or does size (amps) matter other than how quick it will charge the
batteries. I plan on having two start and two house batteries.

How important/neccessary is it to have a galvanic isolator on the AC side?

THX

Isolators cause votage drop and are not optimum for deep discharge
battery banks... Not recommended by me..

Ideally you will have two engine start batteries with an A-B-OFF
switch... Use the standard engine alternator and fixed voltage
regulator on the engine to maintain the start batteries... Autos use
the fixed voltage regulator and you get years of life and many
thousands of starts from your car battery... It will do the same on
your boat...
Alternatively, for two engine start batteries an isolator will work and
probably never cause you any problems and I would not criticize that
type of installation...

However for house battery banks, you want and A-B-OFF switch for the
two house banks never BOTH... You want a separate, heavy duty
alternator for charging these... You need a three charge regulator to
control the charge rate based on the battery state and the battery
temperature...... You need the heavy duty alternator for ramming a
charge to the big house batteries, a task that the standard automotive
style alternator was not designed to handle... Running a big alternator
into the start battery is a waste as it cannot accept more than 60
amps, even when discharged from a hard start...

WIth volt meters on each house bank you can switch between A and B as
you discharge the batteries, never going below 50% charge state on
either... Once A is 50% and B is getting there it is time to fire up
the engine and ram a charge into B, and once it is up switch to A..
Yes, it requires you to monitor the banks and make the decision when to
charge/switch, but it is the only way to avoid the switch being on BOTH
and having both banks exhausted...
Hers are a few web sites to give you food for thought...
http://www.powersolutions.com.au/index.html
http://www.charlesindustries.com/main/ma_alternre.htm
http://www.zena.net/htdocs/alternato..._alt.shtml#Top
http://www.e-marine-inc.com/products...nealtsgas.html

There are lots more vendors of similar products, but I leave it to you
to do the searching...

cheers ... denny
MV Levitation

Thanks for the input... and the links Denny. I will have a look.

"Denny" wrote in message
oups.com...
Isolators cause votage drop and are not optimum for deep discharge
battery banks... Not recommended by me..

Ideally you will have two engine start batteries with an A-B-OFF
switch... Use the standard engine alternator and fixed voltage
regulator on the engine to maintain the start batteries... Autos use
the fixed voltage regulator and you get years of life and many
thousands of starts from your car battery... It will do the same on
your boat...
Alternatively, for two engine start batteries an isolator will work and
probably never cause you any problems and I would not criticize that
type of installation...

However for house battery banks, you want and A-B-OFF switch for the
two house banks never BOTH... You want a separate, heavy duty
alternator for charging these... You need a three charge regulator to
control the charge rate based on the battery state and the battery
temperature...... You need the heavy duty alternator for ramming a
charge to the big house batteries, a task that the standard automotive
style alternator was not designed to handle... Running a big alternator
into the start battery is a waste as it cannot accept more than 60
amps, even when discharged from a hard start...

WIth volt meters on each house bank you can switch between A and B as
you discharge the batteries, never going below 50% charge state on
either... Once A is 50% and B is getting there it is time to fire up
the engine and ram a charge into B, and once it is up switch to A..
Yes, it requires you to monitor the banks and make the decision when to
charge/switch, but it is the only way to avoid the switch being on BOTH
and having both banks exhausted...
Hers are a few web sites to give you food for thought...
http://www.powersolutions.com.au/index.html
http://www.charlesindustries.com/main/ma_alternre.htm
http://www.zena.net/htdocs/alternato..._alt.shtml#Top
http://www.e-marine-inc.com/products...nealtsgas.html

There are lots more vendors of similar products, but I leave it to you
to do the searching...

cheers ... denny
MV Levitation

There is extensive FAQ information on combiners at at
http://www.yandina.com/combInfo.htm