Electric Motor Battery Question

[oost]

I have an electric motor (54lbs, 12v) and am hoping to use it on my kayak rigged for fishing. As I don't have an alternator, I have to get a battery suitable to last the day. I anticipate that I will use the motor for 60 mins total for a session but want to allow for 90 mins to be on the safe side.

Can anyone tell me what size (amp-hour) battery I need. Oh and I am limited by size and weight...

 

[drewpster]

Re: Electric Motor Battery Question

One thing I can recommend is do not settle for a battery you find a Wal-Mart. Contact a battery manufacturer or distributor directly. They can recommend some battery types they may be better suited to your limited space. If a standard automotive style battery is too big a manufacturer my be able to help you find a smaller specialty battery to fit your boat.
In the real world nobody can recommend how many amp/hrs you need. There are simply too many variables to consider. The best way to approach it is to buy the most amp/hrs you can afford in the battery that fits your space. How long it lasts on the water is going to depend on allot of things. You may also want to contact the manufacturer of your motor. They may also have some good recommendations. One good thing about having the internet, you can get in touch with just about anyone.

 

[Silvertip]

Re: Electric Motor Battery Question

Certainly you can calculate what type of battery you need. A 12V, 50-55# troller will draw about 46 amps at its maximum thrust. If you want 90 minutes reserve, you need to look at a battery that will have about a 75 AH rating. Another way to look at this is that you definitely need a deep cycle battery (not an auto or starting battery). Those batteries are rated in "reserve minutes with a 20 amp load". A 150 minute reserve capacity (about the capacity of a group 24 size battery) would allow run times at about 1/2 speed for about 2-1/2 hours, or full speed for a little over an hour. A group 27 would easily meet your needs (about 175 reserve minutes) and the difference in weight between the two batteries is about 10 pounds or so. Actual run time, as was pointed out, will depend on the amount of time you run full speed vs the amount of time you run at speeds less than that.

 

[mthieme]

Re: Electric Motor Battery Question

ST has it nailed as close as it's gonna get. I think his recommendation is realistic and will probably give you a little extra as noted.
Obviously you don't want to undersize, but I have seen some posts with guys claiming much longer runtimes (4-8 hrs) on runabouts, bass and jon boats. Doubtful they have a battery out of a Cat dozer. Makes me wonder about their claims.

Runtimes can easily be calculated - I do this frequently as I do upgrades to my solar system. Of course most electrical appliances, lighting, etc. dfon't have a throttle in the mix. You want to use max amp draw (as ST pointed out). Anything after that is a bonus (your reserve). A 75 AH deep cycle is easily going to tip $100.

There's a young fella in my neighborhood who has a kayak set up with everything but an electric motor. It's amazing what you can fit in one of those things. He has made little a little dolly for it so he can walk it down the ramp. I used to see him everyday up until this season. (He had a newborn two seasons ago - I figure that's keeping him busy now). He would row out about 4 miles every night. Go fishing, crabbing, have a little cooler, the whole 9 yards. Impressive.
Hmmmm.....is yours yellow ad do you have a beard by chance?

 

[SKEETR]

Re: Electric Motor Battery Question

That motor will push a kayak at a good clip. If you are only using the motor for the troll you will get alot of hours out of a battery. If you were using it for propulsion, say to get to the back of the lake to your favorite spot, your power demands would increase exp. Either way I you are looking at a minimum of 30lbs and I am not sure how you would balance that out in a kayak. It would be very important to install a 60a circuit breaker inline for those close quarters. Try batterystuff.com they have alot of good deep cell options.

 

[a70eliminator]

Re: Electric Motor Battery Question

I bought 2 batterys at Walmart, one marine cranking and one trolling, I only use the trolling battery for accessorys, radio, air pump for tube, lighting. I bought them in the early 90's and still going strong, maintainence and charging technique is key.

 

[SKEETR]

Re: Electric Motor Battery Question

I bought 2 batterys at Walmart, one marine cranking and one trolling, I only use the trolling battery for accessorys, radio, air pump for tube, lighting. I bought them in the early 90's and still going strong, maintainence and charging technique is key.

Not to knock walmart batteries for the application above. They will work adequately for low amp loads and as stated "maintenence and charging' are very important.
However for dependable high amp use and deep recharging you need a better quality battery or she'll be toast in no time.

 

[JB]

Re: Electric Motor Battery Question

Back in the 60s I had a SportYak II. A great little (did I say little) boat for sheltered water.

One of the various ways I propelled it was a cheap little troller, maybe 30lb.

I would pull the battery out of my car when I parked it (SportYak rode in the back of my Chrysler wagon) and use that. I couldn't tell you just how many hours I ran that thing at trolling speed, but I could fish for a day and the battery would still start my land barge (Hated that car and finally gave it away).

The point: 54lb is waay more thrust than you need to move your kayak smartly. It is much heavier and would use waaay more power than a pipsqueak troller. The only advantage I see is that it might have pulse modulated speed control, which would save energy.

A small troller (with electronic control) and a modest size deep cycle battery, selected with Silvertip's advice should last you all day long.

 

[Shizzy]

Re: Electric Motor Battery Question

I was also going to say, I have a 40lb motor on my 14' almuminum and that moves me around at a good clip. in fact many times on low speed I feel its pulling me around the lake too fast.

 

[wildmaninal]

Re: Electric Motor Battery Question

The point: 54lb is waay more thrust than you need to move your kayak smartly. Ilong.

As for the fact that we're talking about a Kayak...... Couldn't that 54lb thrust cause a tipping hazard?

You take that little 35lb thrust trolling motor on my 15ft bass boat and put that thing in high speed and it will jerk that boat if you turn it abruptly, it'll almost throw ya out of the seat if ya aint careful.

 

[Silvertip]

Re: Electric Motor Battery Question

I blew right past the "kayak" so the 54# thrust was the point of my response. To give you an idea how much your boat would be over powered, I use a 55# MinnKota Power Drive on an 18 foot pontoon and it lasts all day trolling over structure and for boat control while slow drifting. Although a kayak is not a planing hull, 55#, of thrust would certainly make it skoot and probably make it unsafe as well. You could get by with a motor half that size and a group 24 battery as well.

 

[SKEETR]

Re: Electric Motor Battery Question

I had a canoe I converted into an electric troller. Found a company that made outriggers for stability. Was nice because it allowed for a small casting deck. Made the boat 100% untippable. They also were hollow and provided extra storage. You may be able to find one large enough even to stow your battery.

Even though I now love to plow a wake to my favorite fishing hole, I do remember how relaxing it was to skim across the water under silent power.

Out in the delta here some kyakers actually fish for sturgeon in their boats. Talk about a wild ride!!!

 

[oost]

Re: Electric Motor Battery Question

Thanks everyone for your input! It's a great forum and I'm glad I found it. I posted the question last night (I'm in Australia) and woke up with so many great responses. Thanks!

I realise that 54lbs of thrust is more than I need but I have the motor and I guess that I can just use it on lower of the 5 speeds it has. Hopefully it'll work out okay??

Cheers

Oost

 

[Wee Hooker]

Re: Electric Motor Battery Question

Sportyak II!!! MAN does that bring back memories!! Got one for my 12th birthday in 1972. Fished it 4-5 times a week (after school) with a MK 15 (10# thrust) motor. I got thousands of hours out of that boat and then my kids did. Actually just gave it a vikeing funeral t about 6-7 years ago as the bottom of the sponsons wore clean through from dragging it up the beach! What a great boat. Thanks for the memories!


Anyway, I have to agree that 55# is way overkill for any yak and/or conditions I've encountered. A 30or 36 would be much better suited in power, weight and shaft length. That extra motor capacity is going to add weight you really don't need and at the stem where you have the least bouancy. It's length may also be a PITA. Having said that, since you already have it, you should be able to run it at 1/2 speed (tops) to get max hull speed. ( Keep in mind, the yak is designed to go only so fast. Applying too much power will get you little more speed and make the hull squat/plow/waste energy.) That's a good thing because a battery sized to give you 90 minutes @ 46 amps is going to add crazy weight to your yak. (and IMHO, defeat the thing that makes yaks so great. i.e Ease of portability.) Since it sounds like you have a mazimizer/chopper circuit, that will further streatch your battery reserve as long as you keep the throttle set to the lower ranges.
FWIW, My buddy and I have had great sucess with series U1, 33 ah deep cycle, gel cell batteries sold for golf carts and wheel chairs. Pushing a 12' Canoe, it's not hard to get a an afternoon of on/off run time out of a 30# motor run at 2,to 4 of 5. ( That's like 8-20# thrust on a 30#). Worth a look as these run around 24lbs and are sized to fit in a hatch if needed. They are also made to take a beating and even run upside down without leaking. Anyway, If you keep your motor set low, and truely need only 90 min run time , you should be OK with one of these. HTH

 

[John_S]

Re: Electric Motor Battery Question

http://joefish.homestead.com/KayakTrollingMotor.html

You might find this interesting. I posted it from a guy who added a trolling motor to the same style of kayak that I have.