T-Pain Is On A Boat: Re: [Electric Boats] Re: Next problem: batteries and others.

Tuesday, April 27, 2010

Re: [Electric Boats] Re: Next problem: batteries and others.

Thanks Eric

Thanks for ringing in. I've never dealt with AGM batteries, but have read about non-damaging discharge rates of 70 and even 80 percent. I always thought wet-cell deep cycle batteries were considerably less dischargable than 60 percent before potential damage might occur.

I'm lucky in that I have no need of speed, have a relatively short run to open water and a boat that seems to move with little effort. In years past, I had a sailboat that totaled almost 2700 pound total displacement and moved quite adequately with a MinnKota 42 pound thrust motor and one of those little almost flat-pitched propellers. I actually favored this motor to a 5-1/2 HP gasoline outboard, which I finally gave away. I used the 42 pounder for 11-12 years and was very happy with it . . . even in headwind.

ANYWAY . . . I'm cheap and I admit it openly.

Since batteries are a major consideration of total cost, my initial idea is to buy a 70-100 pound thrust trolling motor and match it to a Kipawa propeller, which will allow me considerably more money for batteries. I will use this system for this year and re-evaluate motor power next year. The batteries will already be paid for and my only need(battery-wise), will be whether or not I want to increase my range or to increase the power to accomodate a larger motor.

I'm ridding myself of a 2005 9.9 HP Suzuki that runs okay, but too fast for my liking(I like to come into dock real, real slow).

Last year, I lent my 55 pount thrust motor to a guy with a Precision 23 and he felt it was very adequate as long as he wasn't in a hurry or facing a strong headwind. I feel this motor would've offered him more power with a Kipawa propeller.

BTW, very few sailboaters will go out in heady winds of about 15-20 knots and I tend to find myself on other's "bigger", boats in heavier winds, while my boat sits in dock.

I know that I'm going to be considered "underpowered" by many, so I hope that my in-the-dirt experience will serve a good purpose. Especially so, since it appears that many of the posters who want to go electric, want to go somewhat cheap and seem to be concerned, first about power, then about range. I'm really not concerned about either, as long as I no longer have to handle gasoline or suffer the embarassment(and potential legal problems), of the tell-tale slick on the water. I'm make sure my Boat USA is caught up and fully in force.

I will try to be somewhat conservative explaining my "system", and whether I will wind up considering it adequate or not.

John Francis

Pearson 26

Port Clinton, Ohio

On Tue, Apr 27, 2010 at 1:11 PM, Eric <ewdysar@yahoo.com> wrote:

John,

While I believe that you're on the right track, however, I think that your guesstimates are somewhat optimistic, skewed towards AGM. I've posted real numbers a couple of times, most recently in post #13890. The delivered energy ratios between battery types are less than 2 to 1, often much less.

The rated capacity versus usable has also been discussed in detail many times on this board, you can read specific answers from other people by searching through previous posts. Usually a change in battery type will only yield an additional 10-20% DoD, which calculates to an increase in usable capacity of less than 35%. For most of my calculations I use the following usable percentages: Flooded = 60% DoD, AGM = 70%, LFP = 80%. These numbers are conservative, but should keep the battery banks healthy without decreasing their projected lifespans much.

Fair winds,
Eric
Marina del Rey, CA

--- In electricboats@yahoogroups.com, John Francis <surv69@...> wrote:
>
> I just throwing figures out as I pretty much understand them to be.
>
> I'm hoping someone who has real numbers will jump in...
>
> In all fairness, when you buy a flooded deep cell you get about 20-30
> percent usage before you begin to potentially damage the battery and I think
> that on high load the flooded cell drops faster than an AGM battery.
>
> When you add the deeper discharge that an AGM battery allows, you've
> probably cut the cost of each amp into about a third or less.
>
> SO, I think that each 3 amps or so(usable power) from a flooded battery,
> will equal something like 10 amps from an AGM battery . . . maybe more . . .
> maybe less.
>
> PLUS if you pull a lot of amps out of a flooded cell, the battery will, I
> think will actually discharge faster than the ampreage rate and from what I
> understand the AGM discharge will be much less.
>
> Given if this is true, an AGM battery will give you much more usable power
> for a little more than a flooded cell battery.
>
> So to speak a cheaper AGM battery(less amps) might actually out-perform a
> more costly flooded cell with much higher amps. AFTER all, it's only the
> amps you can really make use of that mean anything.
>
>
> John Francis
> Pearson 26
> Port Clinton
>

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