I'm running 2 12-volt batteries running in series to power my 24-volt
electric motor in my jon boat (on an electric-only reservoir) and I want to
run a fish finder. Here's my question -- can I safely run the fish finder
off of one of the 2 12-volt batteries while running the 24-volt motor? Or,
is that going to burn up the fish finder? Should I just invest in a couple
of 6-volt lantern batteries instead?

--
Marty S.
Baltimore, MD USA

On Tue, 8 Jun 2004 21:17:33 -0400, "Marty S." wrote:

I'm running 2 12-volt batteries running in series to power my 24-volt
electric motor in my jon boat (on an electric-only reservoir) and I want to
run a fish finder. Here's my question -- can I safely run the fish finder
off of one of the 2 12-volt batteries while running the 24-volt motor? Or,
is that going to burn up the fish finder? Should I just invest in a couple
of 6-volt lantern batteries instead?

One of the batteries is referenced to GROUND, the other is not.

If you connect your fish finder across the battery that is referenced to
GROUND, you should be fine. If you make the mistake of connecting across the
*other* battery, what the fish finder "thinks" is GROUND will actually be 12
volts *above* GROUND, which sooner or later will be revealed to be A Bad
Thing...

/daytripper

"daytripper" wrote in message
...
On Tue, 8 Jun 2004 21:17:33 -0400, "Marty S."
wrote:

I'm running 2 12-volt batteries running in series to power my 24-volt
electric motor in my jon boat (on an electric-only reservoir) and I
want to
run a fish finder. Here's my question -- can I safely run the fish
finder
off of one of the 2 12-volt batteries while running the 24-volt
motor? Or,
is that going to burn up the fish finder? Should I just invest in a
couple
of 6-volt lantern batteries instead?

One of the batteries is referenced to GROUND, the other is not.

If you connect your fish finder across the battery that is referenced
to
GROUND, you should be fine. If you make the mistake of connecting
across the
*other* battery, what the fish finder "thinks" is GROUND will actually
be 12
volts *above* GROUND, which sooner or later will be revealed to be A
Bad
Thing...

/daytripper

Near as I can tell in my boat, neither side of the batteries for the
trolling motor is ground. The trolling motor basically floats. So go
ahead. use the battery connected to ground if one of them is connected
to ground.

del cecchi.

I'm not sure about your answer, Daytripper. I don't have either battery
connected to ground as far as I know. The + terminal of one battery goes to
the motor, and the - terminal of the other battery goes to the motor, and
the other terminals are connected to each other so the battery is connected
in series.

--
Marty S.
Baltimore, MD USA


"daytripper" wrote in message
...
On Tue, 8 Jun 2004 21:17:33 -0400, "Marty S." wrote:

I'm running 2 12-volt batteries running in series to power my 24-volt
electric motor in my jon boat (on an electric-only reservoir) and I want
to
run a fish finder. Here's my question -- can I safely run the fish
finder
off of one of the 2 12-volt batteries while running the 24-volt motor?
Or,
is that going to burn up the fish finder? Should I just invest in a
couple
of 6-volt lantern batteries instead?

One of the batteries is referenced to GROUND, the other is not.

If you connect your fish finder across the battery that is referenced to
GROUND, you should be fine. If you make the mistake of connecting across
the
*other* battery, what the fish finder "thinks" is GROUND will actually be
12
volts *above* GROUND, which sooner or later will be revealed to be A Bad
Thing...

/daytripper

On Tue, 8 Jun 2004 22:55:51 -0400, "Marty S." wrote:

I'm not sure about your answer, Daytripper. I don't have either battery
connected to ground as far as I know. The + terminal of one battery goes to
the motor, and the - terminal of the other battery goes to the motor, and
the other terminals are connected to each other so the battery is connected
in series.

Might help to draw this out.

A typical 12v wiring job on a boat with an electric starter (at least), some
part of the motor is connected to the negative pole of the 12v battery. That
would be the moral equivalent to "earth ground" on a boat.

The electronics are referenced to the same potential, and things like antenna
ground and lighting fixtures may be referenced to that same potential, as it
is the return path for all powered things on the boat.

Shifting that potential by connecting the negative pole of the original
battery to the positive pole of the first battery (and then connecting the
negative pole of the second battery to the negative terminal of the trolling
motor) runs a certain risk different current return paths at different
potentials coming in contact with each other. Ie: if the exterior of the
trolling motor is connected to its negative terminal, when the motor is in the
water there could be current flowing through the *boat* motor (which is
connected to the negative pole of the original battery).

That wouldn't be good, I suspect ;-)

/daytripper

Daytripper: I don't have two motors. This is just a small jon boat powered
by an 24-volt electric trolling motor with 2 batteries connected in series.

--
Marty S.
Baltimore, MD USA


"daytripper" wrote in message
...
On Tue, 8 Jun 2004 22:55:51 -0400, "Marty S." wrote:

I'm not sure about your answer, Daytripper. I don't have either battery
connected to ground as far as I know. The + terminal of one battery goes
to
the motor, and the - terminal of the other battery goes to the motor, and
the other terminals are connected to each other so the battery is
connected
in series.

Might help to draw this out.

A typical 12v wiring job on a boat with an electric starter (at least),
some
part of the motor is connected to the negative pole of the 12v battery.
That
would be the moral equivalent to "earth ground" on a boat.

The electronics are referenced to the same potential, and things like
antenna
ground and lighting fixtures may be referenced to that same potential, as
it
is the return path for all powered things on the boat.

Shifting that potential by connecting the negative pole of the original
battery to the positive pole of the first battery (and then connecting the
negative pole of the second battery to the negative terminal of the
trolling
motor) runs a certain risk different current return paths at different
potentials coming in contact with each other. Ie: if the exterior of the
trolling motor is connected to its negative terminal, when the motor is in
the
water there could be current flowing through the *boat* motor (which is
connected to the negative pole of the original battery).

That wouldn't be good, I suspect ;-)

/daytripper

Your fish finder will be fine across one of the batteries. If you're
hesitant, apply (or borrow) your voltmeter across either of the batteries.
You'll find it reads ... 12 volts.


"Marty S." wrote in message
...
I'm running 2 12-volt batteries running in series to power my 24-volt
electric motor in my jon boat (on an electric-only reservoir) and I want
to
run a fish finder. Here's my question -- can I safely run the fish finder
off of one of the 2 12-volt batteries while running the 24-volt motor?
Or,
is that going to burn up the fish finder? Should I just invest in a
couple
of 6-volt lantern batteries instead?

--
Marty S.
Baltimore, MD USA

I've checked the voltage and either battery by itself reads 12 volts when
hooked up in series, and they are 24 together. However, is there an issue
of amps or watts or current or whatever else flows in the wires? The fish
finder draws about 110 milliamps (whatever that is)... Will it burn out or
crack or implode or fizz out or whatever? (as you can tell, I didn't spend
a whole lot of time paying attention in 7th grade electrical shop)

--
Marty S.
Baltimore, MD USA


"Bowgus" wrote in message
. rogers.com...
Your fish finder will be fine across one of the batteries. If you're
hesitant, apply (or borrow) your voltmeter across either of the batteries.
You'll find it reads ... 12 volts.


"Marty S." wrote in message
...
I'm running 2 12-volt batteries running in series to power my 24-volt
electric motor in my jon boat (on an electric-only reservoir) and I want
to
run a fish finder. Here's my question -- can I safely run the fish
finder
off of one of the 2 12-volt batteries while running the 24-volt motor?
Or,
is that going to burn up the fish finder? Should I just invest in a
couple
of 6-volt lantern batteries instead?

--
Marty S.
Baltimore, MD USA

"Marty S." wrote:

I've checked the voltage and either battery by itself reads 12 volts when
hooked up in series, and they are 24 together. However, is there an issue
of amps or watts or current or whatever else flows in the wires? The fish
finder draws about 110 milliamps (whatever that is)... Will it burn out or
crack or implode or fizz out or whatever? (as you can tell, I didn't spend
a whole lot of time paying attention in 7th grade electrical shop)


This is the basic of connecting two (or more) identical batteries, i.e.
with same voltage and amperage, in series or parallel.

* A serial connection will increase the voltage (V) to the sum of all
batteries connected, while the current (A) will not increase.
Example: Two 12V 60A batteries connected in serial give 24V 60A.

* A parallel connection will increase the current (A) to the sum of all
batteries connected, while the voltage (V) will not increase.
Example: Two 12V 60A batteries connected in parallel give 12V 120A.

In your case, with two 12 V batteries connected in serial you will have
12V between ground and the positive terminal (+) of the first battery,
and 24V between ground and the positive terminal (+) of the second
battery, while the voltage across the negative (-) and positive (+)
terminals of each battery is 12V.
This is seen in the following simple schematic:

Ground
------
|
| +-----------+ +-----------+
| | | | |
+-----+ - 12V + +-----+-----+ - 12V + +-----+
| | | | | | |
| +-----------+ | +-----------+ |
| | |
| | |
|-------- 12V --------|-------- 12V --------|
|--- 12V equipment ---| |
| |
| |
|-------------------- 24V --------------------|
|--------------- 24V equipment ---------------|


When having two batteries connected in serial giving a total of 24V, and
you want to tap off 12V volt from one battery to supply 12V equipment,
you must connect the 12V equipment between ground and the positive (+)
terminal of the first battery as shown in the schematic above.

However, be aware of that the discharge of each battery will be uneven
as the first battery will be discharged more than the second battery.

And you don't have to worry about how much current (mA or A) the
equipment draw, as the equipment will not be damaged in any way as long
as the supply voltage is the same as equipment specifications, where 12V
equipment usually is designed for a nominal supply voltage of 13.8V
(i.e. nominal charging voltage).

However, make sure you always connect a suitable fuse between the
positive terminal (+) of the battery and the equipment. The fuse should
have a rating (mA or A) of one or two ratings higher than the current
drawn by the connected equipment.
The basic rule is to keep the fuse rating as low as possible, but of
course not less than the current (mA or A) drawn by the equipment.



Regards,

Stig Arne Bye

E-mail ......:
Contact .....: AOL IM: VT480TFE / MSN: / ICQ: 403349
Snail-Mail ..: P.O.Box 169, NO-9915 Kirkenes, Norway
Homepage ....: http://home.online.no/~stigbye/index.html
------------------------------------------------------------------------
Located just about 70°N 30°E - Almost at the top of the world!

"Stig Arne Bye" wrote in message
...

However, make sure you always connect a suitable fuse between the
positive terminal (+) of the battery and the equipment. The fuse should
have a rating (mA or A) of one or two ratings higher than the current
drawn by the connected equipment.
The basic rule is to keep the fuse rating as low as possible, but of
course not less than the current (mA or A) drawn by the equipment.



Regards,

Stig Arne Bye



Just to clarify - the fuse should be rated for no more than the current
carrying capacity of the wiring of the connected device (in this case, the
fishfinder). Point is, the fuse protects the wiring, not the connected
device. Overheated wires cause fires. Not really a big issue with this
particular application, but can be important in higher power devices.

Eisboch