battery

[corinthian]

Good sailing today. 10-15. Good day to learn more about my compac. I tested the battery on my mini-multimeter before leaving as I have used it "some" after charging a few weeks ago. After a few hours I started back and noticed a slower headway under power. Soon the prop was turning like molasses in winter.
My natural assumption was I was out of voltage. Was able to get back in and brought the battery home to charge. It is a 12V deep cycle marine battery. To my surprise it still read fully charged on the meter. The battery is mounted under the entrance to the cabin so it sits about 10-12 feet away. The extension guage wire is appropriate and is mounted with a female plug unit under the seat. The motor is a new MinnKota 50# thrust. Any thoughts of what the issue might be.

[newt]

We need more info (please ) What was the exact voltage your battery was showing. Any corrosion on any contacts- did you wiggle them? Now that the battery charger has had its way with your battery- its there any difference with the prop speed? Finally- if you warm up the minokota motor to 70 degrees or so- is there any difference in the speed?

[Craig Weis]

You don't need the volts as much as the amp-hours.
What is the amp consumption of the electric motor?
What is the amp hour capacity of the battery.

Bare in mind that the power made in a wet cell battery
is chemical which is cut in half at freezing. So at
40 or 50 or 60 deg F. that effects the output.

I believe electric anything is no good unless it's plugged in.
Battery power is never renewable due to ENTROPIC tendency's.
On the old Pig Boats and later Fleet Boats of WWII, from center line down was all battery.
So much so that just a few few ton of water in the ballast tanks pulled them under.

Check the off topics for electrical posts.

skip.

[Joseph]

Corinthian -

Skip is right... and so is Newt...  The power of the motor and the time during which it can be sustained depend on a) the draw (amperage) of the motor (do you know its amperage?), b) the amp hour capacity of the battery (it should be marked on the battery?), and c) its charged status. Although there are more accurate ways of doing it, the status of the charge is usually assessed by determining the voltage between the battery poles: in an 12V acid-lead battery a reading of 12.7V means fully charged and 11.9V means totally drained (i.e., only 0.8 V difference). What was the actual reading in your mini-multimeter?

From the amperage of the motor, the Amp-hr of the battery and its charged status you should be able to approx. determined how much time of full-power you could expect.

Also, loose contacts at the battery or the motor may cause a reduction in the power supplied by the battery to the motor.

J.

[Craig Weis]

Big Draw, Big wire.
Interesting enough electrons flow on the easiest path they can find.
That means electrons flow on the outside of every conductor used in the make-up of the wire.
Electrons never flow 'through' a wire, just on top of a wire.
So you need a lot of surface for these guys to skate on.
Perfectly clean contacts are required and hard to achieve on boats in water.
Condensation is a bugger. Worst in salt air and water. Not so bad in fresh water.

Each cell in the battery can make as much as 2.2 volts, but never do. Volts is
just the push used to move electrons over the wire, and through the resistance
and that could be the electric motor and switch gear.

The cool thing about electric motors is they produce full torque at anything above
zero rpms. That's how I use to burn off the rubber tires on my 5000 lb capacity forklift
that was fitted with a 1200 lb wet cell battery pack. That pack lasted almost a whole 10 hour day.

skip.

[jpfx]

I use a 35# thrust with a 24M marine battery. so far it's been enough but I don't run it more than 30mins out and the same back (if at all) and I never run it more than 2/3 throttle.
I think a 50# motor isn't too large but it is going to eat what juice you have faster. Also the boat suffers much more windage than you might be accustomed to (I certainly was) and the motor will be working that much harder.
Unless you're running the motor hard for a 'long' time then I would doubt the efficacity of the battery (unless it's new).
You could try running the motor lower in the water too. Also disconnect everything else except the motor from the battery and try that.

[Joseph]

Corinthian,

I was able to consult the owner's manual of a Minn Kota Endura 50 42" Trolling Motor (if not the same it should not be too different than the one you have) and this is what it says:

"These motors will operate with any deep cycle marine 12 volt battery. For best results, use a deep cycle Minn Kota marine battery with at least a 105 ampere hour rating. As a general on the water estimate, your 12 volt motor will draw one ampere per hour for each pound of thrust produced when the motor is running on high."

Usually a 12 V "Group 24" deep cycle battery (possible not too different than the one you describe as "M24"?) would be rated at 70-85 Amp hours. In such case, an optimistic estimate is that with a fully charged battery you would have enough "juice" for approximately 1.5 hour at full power.

J.

[curtisv]

Corinthian,

There are two things to keep in mind.

1.  Drawing a lead acid battery below 50% charge severely shortens its lifespan.

2.  Storing a lead acid battery over the winter without ever charging it can kill it.  Gels and AGM are less suseptible than "wet" batteries.  Its worse if the battery is subject to the cold (certain to kill it) or is left sitting on concrete (basement floor or garage floor).

Overcharging can also kill a battery.  A good charger helps but don't leave on any charger indefinitely.

Battery life varies from 1-2 years for an abused battery to as much as 10 years for a very well cared for battery.

You'll get the most life out of a battery if you don't draw it down below 1/2 charge and if you start recharging as soon after you draw it down as you can and bring it back to full charge.  Try not to let it go more than 2-4 hours and not to leave it flat overnight.  If you store the battery for any length of time, recharge every 2-4 weeks.  Gels and AGM can go much longer between charges when stored due to lower self discharge and much less tendency to sulfate.  Gels are very sensitive to being overcharged.

What kills the battery in these cases is called "sulfation" which is chemical precipitation of lead sulfate.  Chemical recipitation is the disolved lead sulfate turning into a solid and falling to the bottom of the battery where it will never be disolved again.  The more sulfation, the less capacity (amp-hours from full charge to discharge).  Eventually enough lead sulfate can end up on the bottom to short the battery and its shot.

Nigel Calder beats this subject to death in his book "Boatowner's Mechanical and Electrical Manual".  Nigel will tell you way more than anyone needs to know about their boat battery and electrical system but it is a great book.

Curtis

ps - when my group 27 wet cell gave it up I replaced it with an AGM.  An 8D (at 160 lbs).  Took a little work getting it in there.  The solar panel is good for keeping a float charge.



See http://www.faster-light.net/remote-access/projects_E_C.html#2 for other details.

[Bob Condon]

Is the wiring between the battery and the motor new? or is it the wire off the motor that attaches directly to the motor?

You said that the wire size is appropriate? Tell me more. What is the Amp rating on the motor and what is the wire size?

The reason I ask is that for starting a diesel on a larger boat, the starting circuit was "appropriate" but upgraded the wire sizes a couple of sizes and it made all the difference.

Also if the wiring is original, is there heat tubing on the ends? I have found wire that is rotting up to a
foot inside the insulation because the terminal was put on and then electrical tape used... best to use heat sink tubing.

thanks
Bob

[Shawn]

In addition to everything else mentioned.....

... roughly how long were you under power?

... did you check the trolling motor to be sure nothing was wrapped around the prop?

Shawn

[curtisv]

For a trolling motor the minimum wire size is either a very short run of #8 (just a few feet) or preferably #6 or #4.  #4 gauge is heavy battery cable.  #6 is light battery cable.  You'll lose a lot of power in the wiring if you use wire that is too small, more than 10% if its too small.  West Marine has a table in the catalog or on the web site giving guidance.  See http://www.westmarine.com/webapp/wcs/stores/servlet/westadvisor/10001/-1/10001/Marine-Wire.htm.  For 20 feet (10 feet each way) and a load of close to 60A minimum to get 10% loss is #8.  To get 3% loss you want #4 (or bigger).

If your run is long and your wire is too small it is fairly easy to fix.  What you can do is buy a crimp tool that is described as a hammer type if you don't have one.  You can use a 4lb hammer but its easier and a lot better to just put the tool in a bench vise.  Buy a few lugs and a spool or two of wirre, one red, one black, and get a two terminal bus bar.  Also buy shrink tubing with adhesive if you want to do a professional job of it and have it last.  If you have an existing socket, mount the terminal bus bar near the socket, then cut the wires and crimp on some marine lugs and attach to the bus bar.  Cut your heavy cables to length, crimp on the lugs and install.  To be safe you should also put in a fuse near the battery (on the positive side, but you knew that I hope).

Curtis

[JBC]

While we're on the subject of batteries (from which I've learned some things, thanks to all), I always thought a trolling motor connection I saw on a Daysailer (I have one of these, too) was especially neat.  Check out this link on Sailing Texas and scroll down through the pictures to see the connections.  Pretty clever.

http://www.sailingtexas.com/soday17106.html

Jett

[Bob Condon]

To extend the information Curtis was saying:

1. If you are replacing the cable, make sure it is MARINE cable. It is not cheap but it is tinned
throughout so the rot is held off much longer. The cable INSIDE the insulation rots so you
will never know until you moe the cable and it breaks inside.

2. If you do not have a set of crimps, either go to a yacht yard that can crimp the ends on
or buy a crimp tool. I was using   0 AWG cable (starter cable for a diesel and battery connection) [about 3/8" thick)]
and the yacht yard had the correct equipment to do the work correctly, the first time and it was guarenteed.

I do all my own work but there are some jobs that the professional can do in their normal operation.

3. The bigger the wire, then less the voltage drop to the motor. My starter required a #2  AWG so I went up a few sizes
so I skipped #1 and went to #0.

[Craig Weis]

You battery hounds are on your own. I must bow out as this is way over my head.
All I know is my set-up works and I've no complaints. I'm not going to have a boat powered by a battery.
Do note that the solar cell can produce 16 to 17 volts BUT only 300 or so milliamps.
Not much but enough to boil the water out of the 'sealed' battery over a summer. So check the water a few times a season. Remember when you are away the battery is still cooking and loosing water.

skip.

[corinthian]

I can't begin to thank you for all the information. Some over my head but most very practical. I have incorporated most of the advice, some before the problem (connections new, guage right, motor new, understanding #s of thrust and amps utilized, etc.). Checking some of the new insights I have come to the conclusion that I simply let the charge go down including some cold overnites. I measured the volts and the small meter used I had indicated 10+ so I falsely assumed all was well. I have been well educated (as much as I can absorb) and really appreciate the kind attention of all.

Since I'm at it, I will request any (basic, not too techy) knowledge about a solar panel trickle down that maintains charge. It appears to have a panel with positive and negatiive connection and simply keeps charge to maximum. One problem I read about is that they are not waterproof so apparently cannot be left on without attention.