Multiple sealed battery question

[Tom]

I am about to build my Dumas Donzi with electric power. I spoke with
Dumas and the tech was a bit vauge when he was telling me how to power
the boat. He sugested Astro 25 motors, and an electronic speed
control. He said that the Astro motors draw 10amps hr each. The tech
told me that I should rum multiple sealed batteries that amount to
atleast 20amps hr, and that the boat need about 16lbs for ballast and
batteries can be used for this.
Where is a good place to get batteries?
How should I wire them together?
What is a good speed control?

Thanks
Tom

[Train]

Tom,
I'm not sure if these are the best places but I've had good results from
both of them:

http://www.batterycountry.com/
http://www.batterymart.com/

Hope this helps
JT

"Tom" <yjguy94@yahoo.com> wrote in message
news:5d704188.0301080006.6b75af67@posting.google.c om...
> I am about to build my Dumas Donzi with electric power. I spoke with
> Dumas and the tech was a bit vauge when he was telling me how to power
> the boat. He sugested Astro 25 motors, and an electronic speed
> control. He said that the Astro motors draw 10amps hr each. The tech
> told me that I should rum multiple sealed batteries that amount to
> atleast 20amps hr, and that the boat need about 16lbs for ballast and
> batteries can be used for this.
> Where is a good place to get batteries?
> How should I wire them together?
> What is a good speed control?
>
> Thanks
> Tom

[Neil McGrath]

The Astro 25 is quite a hot motor and will pull around 15 amps at maximum efficiency from your battery. At this load the prop is likely to be spinning at around 10,000 RPM.

Yours is a large boat and the motor will be heavily loaded if you add too much weight. This will slow the motors so that they become inefficient and run hot (possibly burning out).

For best performance you should build it light and use nicads or NiMh cells as your power source. Sanyo RC2400 or 3000 cells should give up to 10 minutes run time with the right prop. As this is a large boat you could consider running separate ESCs and battery packs for each motor. Alternatively you could wire 20 cells to the pair of motors wired in series via one ESC. For more scale like speeds and longer run times I suggest you run the motors via a gearbox (around 2:1) and then it may be possible to use heavier batteries.

I do not think that this motor is ideally suited to your application and would suggest something with more torque and lower RPM.

[William]

"Tom" <yjguy94@yahoo.com> wrote in message
news:5d704188.0301080006.6b75af67@posting.google.c om...
> I am about to build my Dumas Donzi with electric power. I spoke with
> Dumas and the tech was a bit vauge when he was telling me how to power
> the boat. He sugested Astro 25 motors, and an electronic speed
> control. He said that the Astro motors draw 10amps hr each. The tech
> told me that I should rum multiple sealed batteries that amount to
> atleast 20amps hr, and that the boat need about 16lbs for ballast and
> batteries can be used for this.
> Where is a good place to get batteries?

Here's some U.S.sources at decent prices:

http://www.allelectronics.com/cgi-bin/category.cgi?category=160400&type=stor
e
(There's a 12 V 17 amp at the bottom.)

http://www.sciplus.com/category.cfm?subsection=13&category=134
(Check out the 12 V 46 amp tractor battery!)

http://www.batteriesamerica.com/newpage4.htm
(Pricier, but they list the weights for various types. 12 V 20 amp
is 16.5 lbs.)

One type to look at is the Gates cylindrical cells. The unpackaged
cells have a metal shell which makes a good heat sink. I found I
could quick charge the D-size (2-V, 2.5 Amp per cell) in about
45 minutes if I placed them in about an inch and a half of water
to draw off the heat. (Plastic cased batteries could be recharged
in a water bath, but the heat won't transfer quite as quickly.)
-Wm

[Tachikaze]

Tom,
I would have to disagree with the direction that you are being taken with regards to the motors for this boat. If Dumas is telling you that you need to add 16lbs to ballast this boat, then if you build the boat as it is designed with the materials presented, then you will need to add 16lbs of weight to bring it to its water line. Period.
I belong to a club that builds boats that run anywhere from 2lbs to 200lbs.
http://www.nwlink.com/~pfleming.com
We have found that to turn a nice little wake on the boats we need to be running 4800-5000 RPM's for most of our boats, regardless of size of the boat. That means if you are running 4800 RPM on a 3ft boat and 4800 RPM on a 6ft boat they are going to run about the same speed as long as the propellar matchs the size of the boat and the RPM's remain constant under load.
I have never used the geared motor systems, it is a waste of power. We run direct drive from our motors. This boat is 49" long with a 13 1/2 " beam, that makes it smaller than my 56" Italian dstroyer which does have a narrower beam.
The Astro Flight 25 motor produces 8200 RPM and costs 140.00 per motor.
The Johnson # 63706. motor at 6V from All Electronics will give you 12000 RPM, motor than enough speed then the Astro Flight. The only thing that the Astro Flight will give you at that cost would be a faster start from standing. But if you give the Johnson more voltage then you can compensate for that. That Johnson motor will easily handle 12V and will give you a lot longer run time than what you would see with the Astro Flight.
Lets say that you use the Johnson motor at 12V you can also acquire the 12V CAT# GC-125 battery also from All Electronics. This is a 5 Amp battery which should set well in the section aft of the fly bridge of the Donzi, this would give you very close to 30 plus minutes of run time.
The main expense for this boat will be a good speed control. If you are lucky you may be able to pick up a Tekin Rebel on E-bay, this unit will handle 12v or the new units from MTroniks which makes a 12V marine speed control. We use units with more peak amerpage, but then our boats are doing a lot of stopping and starting while in combat.
I have never seen a need to use the geared motors unless you are trying to accelerate a heavy boat quickly and need that tourque. The boat you are building is well with in the displacement of the ships found in our club and will work well off of direct drive from a more efficient 580 size motor.