You have an 18-ft open boat,right? No cabin, no 12VDC fridge, no anchor
winch, etc.? Let's not overkill things here.

I am always open for suggestions that can save me money.

First, are you SURE you need a 24VDC trolling motor? As you can see, it
complicates things greatly. Minn Kota has a nice 55-lb-thrust motor that
runs on 12V: the Max55T. I think it would push your boat fine, and will
pretty much run all day on a fully-charged group 24 battery (at
trolling speeds).

Last time when I asked around here, I came to the conclusion that I am
probably better off having a 24V trolling motor. The reasons are
something like these: (1) A 18-ft fiberglass boat with a 115HP motor is
not exactly light (around 1800-lb to 2000-lb); a heavy duty trolling
motor has enough power pulling it throgh current or wind (my boat has a
T-top that catches wind). (2) I intend to use it as a backup propelling
force in case the main motor failed to start while I am in the middle
of a lake or a bay (the main motor is 10-years old). (3) I intend to
use it as the sole propelling force when I run my boat in lakes that
have "10-hp-or-less-only" restriction. These are the reasons why I
want to choose a powerful trolling motor.

Second, if you decide on a 24V motor, you CAN buy a third
battery and put it in series with your deep-cycle battery: just
make sure it's the same type, etc. (yours is basically
brand-new,right?).

Unfortunately, the existing deep-cycle battery is not new. It is
probably newer than the boat itself. But it is not exactly new.
Therefore, I don't intend to combine the existing deep cycle battery
with a new battery to make a 24V system.

The other thing that makes me uncomfortable about your suggestion is:
If we combine the existing 12V deep-cycle battery with a new 12V
battery to make a 24V system for the trolling motor, we will only have
one battery left to do everything else (starting motor, powering fish
finder, VHF radio...etc), right? Unless I am misunderstanding
something, I will be very hesitated to do that. Please clarify.

Use quick-connect connections, and when you want to charge
them, re-arrange them to parallel. ...

I always like the concept of "Quick Connect". That's why all the water
hoses in my garden have quick-connect. How does the "quick-connect"
look like in the context of battery connection? I cannot find this
item in BoaterWorld or WestMarine web sites. Do you have a link to
this type of item?

Nice to talk with you.

Jay Chan

The other thing that makes me uncomfortable about your suggestion is:
If we combine the existing 12V deep-cycle battery with a new 12V
battery to make a 24V system for the trolling motor, we will only have
one battery left to do everything else (starting motor, powering fish
finder, VHF radio...etc), right? Unless I am misunderstanding
something, I will be very hesitated to do that. Please clarify.

Jay, My SeaPro uses 3 ea 12 v batteries tied to a Perko switch. Two
are primarily for the trolling motor and one is for starting etc. The
primary starting battery is tied to position 1 on the switch while one
battery for the trolling motor is tied to position 2. Should you
encounter problems with the primary battery you can switch to position
2 and use one of the trolling motor batteries (you can also charge
this battery under way in position 2). This will allow you to use two
batteries for a 24v system as well as have a back up. I also had a 3
bank charger installed so I can hook to 110v and charge all three
batteries (power cord runs to a plug on the side of the console). All
I have to do is plug an extension cord into the plug on the console
and all three batteries are charged simultaneously.

Jay, My SeaPro uses 3 ea 12 v batteries tied to a Perko switch. Two
are primarily for the trolling motor and one is for starting etc. The
primary starting battery is tied to position 1 on the switch while one
battery for the trolling motor is tied to position 2. Should you
encounter problems with the primary battery you can switch to position
2 and use one of the trolling motor batteries (you can also charge
this battery under way in position 2). This will allow you to use two
batteries for a 24v system as well as have a back up. I also had a 3
bank charger installed so I can hook to 110v and charge all three
batteries (power cord runs to a plug on the side of the console). All
I have to do is plug an extension cord into the plug on the console
and all three batteries are charged simultaneously.

This makes perfect sense to me now. I didn't know that we can use one
of the 12V battery in a 24V system for starting, and I didn't know that
we can charge it without charging the other 12V battery in the mix.
Now, I understand what Lloyd meaned to say.

This means if the existing battery was new, I should get an onboard
charger that can handle 12V/12V/12V (three 12V batteries).
Unfortunately, the existing battery is not exactly new. This means I
may not want to pair it with a new 12V battery to make a 24V system. I
may still be better off getting one new 24V battery or two new 12V
battery to make a 24V system. Or I can get rid of the existing 12V
deep cycle battery and replace it with two 12V deep cycle batteries and
arrange them in the way that you have suggested. I am still thinking
of which way I should go. I probably will go for keeping the existing
batteries and use two new 12V batteries to make up a 24V system just to
avoid messing with the existing connections on the batteries.

Thanks for the info.

Jay Chan

Hi, Comments imbedded below:

On Mon, 14 Nov 2005 19:22:36 -0800, jaykchan wrote:

First, are you SURE you need a 24VDC trolling motor? As you can see, it
complicates things greatly. Minn Kota has a nice 55-lb-thrust motor that
runs on 12V: the Max55T. I think it would push your boat fine, and will
pretty much run all day on a fully-charged group 24 battery (at
trolling speeds).

Last time when I asked around here, I came to the conclusion that I am
probably better off having a 24V trolling motor.

That's a common problem with advice "around here". It seems it's always
buy Bigger, Stronger, Faster, and damn the consequences! You might get a
bit more performance from a 24V motor, but look at all the problems it's
causing! Maybe see if you can make some agreement with a local shop that
you try a 12V motor (measure speed with GPS), and if it's not
satisfactory, trade it up for a 24V model.

I'm using a 12V motor (Max55T) as the PRIME "engine" for my 10ft
inflatable, and I used a smaller Max40T just as you describe on my 12-ft
skiff.


Second, if you decide on a 24V motor, you CAN buy a third
battery and put it in series with your deep-cycle battery: just
make sure it's the same type, etc. (yours is basically
brand-new,right?).

Unfortunately, the existing deep-cycle battery is not new. It is
probably newer than the boat itself. But it is not exactly new.
Therefore, I don't intend to combine the existing deep cycle battery
with a new battery to make a 24V system.

Although it's IDEAL to have two nearly-identical batteries in series for
your 24V system, it's by no mean required. I might buy two new ones when
the older one wears out, but no reason to throw out a perfectly good
deep=cycle battery!

The other thing that makes me uncomfortable about your suggestion is:
If we combine the existing 12V deep-cycle battery with a new 12V
battery to make a 24V system for the trolling motor, we will only have
one battery left to do everything else (starting motor, powering fish
finder, VHF radio...etc), right? Unless I am misunderstanding
something, I will be very hesitated to do that. Please clarify.

Two things:
First, it wouldn't be a big problem running "everything else" on a single
battery. "House" batteries (the second one) is great if you have a cabin,
with cabin lights, DC fridge, stereo running all evening, etc. But for an
18ft open boat: I'd guess you have less accessory-power on it than your
car, and your car only has one battery, right?

Second: you can still use the one 12V battery of the 24V system as your
"house" battery. It will mean it will be drawn down SLIGHTLY more than the
other one, but realistically it just won't make a difference. I'm an
Electrical Engineer: I can run the boring numbers for you if you like, or
you can just trust me on this.

Use quick-connect connections, and when you want to charge
them, re-arrange them to parallel. ...

I always like the concept of "Quick Connect". That's why all the water
hoses in my garden have quick-connect. How does the "quick-connect"
look like in the context of battery connection?

You could probably use one of the heavy-duty connectors used in automotive
or RVs (most are made by Molex - try searching for that). But again the
simplest is the butterfly-connectors you probably have on the battery
already. Just unscrew them and pull out the spade connector. Then
reconnect the two batteries in parallel and charge them with a 12V
charger. It takes a few minutes, but I'm pretty sure that's what 99% of
the people using 24V trolling motors do.

Again, IN THEORY you shouldn't charge unlike batteries in parallel, but
I've been doing it with wildly-different sets (like 50%-charged golf-cart
battery (actually 2 in series to get 12V) in parallel with 90%-charged
Group 27) and have never had a problem. Again, I can run the numbers if
you like...

Lloyd

That's a common problem with advice "around here". It seems it's always
buy Bigger, Stronger, Faster, and damn the consequences! You might get a
bit more performance from a 24V motor, but look at all the problems it's
causing! Maybe see if you can make some agreement with a local shop that
you try a 12V motor (measure speed with GPS), and if it's not
satisfactory, trade it up for a 24V model.

If I could find someone to let me use their 12V trolling motor, that
would be great. But I really doubt that anyone would do this. May be
I can ask the marine motor service station to see if they can let me to
try their 12V trolling motor if I become their regular customer. Is
this what you have in mind?

I'm using a 12V motor (Max55T) as the PRIME "engine" for my 10ft
inflatable, and I used a smaller Max40T just as you describe on my 12-ft
skiff.

I have a feeling that a 10-ft inflatable and a 12-ft skiff are not
quite comparable to a 18-ft fiberglass semi-V boat, isn't it? My
impression is that skiff is flat bottom and can run quite efficiently
in calm water. That may have explained the reason that a small 12V
trolling motor has no problem pulling it around. And the fact that the
18-ft has a permanently mounted T-top that tends to catch wind. I have
a feeling that the trolling motor needs to have a bit more power to
pull it around.

Although it's IDEAL to have two nearly-identical batteries in series for
your 24V system, it's by no mean required. I might buy two new ones when
the older one wears out, but no reason to throw out a perfectly good
deep=cycle battery!

Good to know that the two batteries in a 24V system don't have to be
identical. This is a useful background info that may come in handy.

Two things:
First, it wouldn't be a big problem running "everything else" on a single
battery. "House" batteries (the second one) is great if you have a cabin,
with cabin lights, DC fridge, stereo running all evening, etc. But for an
18ft open boat: I'd guess you have less accessory-power on it than your
car, and your car only has one battery, right?

What you said makes sense. Seem like a three 12V batteries system will
work just like what Tom and you have described: One for starter and
"house" use, two for the 24V system, and one of the two can also be
used for starter and "house" use. I am not saying that I will surely
go this way; this is one option that I should keep in mind, especially
if I want to save some money and cut down on weight.

One thing that I don't quite understand when I use the combined power
of both 12V batteries to start the motor today. The battery-power
rating in the power gauge drops from 12V to 10V after I have cranked
the motor for four times. At that point, the combined power of the
batteries drops so low that it cannot start the motor any more. Is
this normal? Are those two batteries dying? How can I check the life
of a battery?

Second: you can still use the one 12V battery of the 24V system as your
"house" battery. It will mean it will be drawn down SLIGHTLY more than the
other one, but realistically it just won't make a difference. I'm an
Electrical Engineer: I can run the boring numbers for you if you like, or
you can just trust me on this.

Thanks for the info. Now I understand. I appreciate your help.

Jay Chan