Re: Electric motor to power a dinghy revisited

Richard J Kinch wrote:
My Group-27 deep-cycle trolling battery weighs 53 lbs and provides 115 Ah x 12 volts = 1.4 KWh. Divide by 746 watts/hp and multiply by 80 percent trolling motor efficiency, you get about 1.5 hp-hours at the prop, from a full charge to full discharge.

How much gasoline is 1.5 hp-hours?

My 25 hp Tohatsu burns about 2 gal/hour. So 2 gals for 25 hp-hour, or 12.5 hp-hour/gal, or 0.08 gal/hp-hour, times 1.5 hp-hours, is 0.12 gal, which is to say,

1 GROUP 27 TROLLING BATTERY = 1 PINT GASOLINE

Gasoline has over 50 TIMES the energy density of lead storage batteries.

I still think that's a large exaggeration. And your math is skewed. Why not multiply your gas outboard's power output by it's theoretical efficiency of about 40% or less? FWIW I agree that gasoline is very much more bang for the buck than any other type of stored energy, that's why it's so hard to find "alternative fuels."

A better way to compare would be to measure how many ton/miles each power plant could move at a given speed in a given hull form. For moving a slow efficient hull, the trolling motor would be better than you think. And for moving a light load fast, it won't do anything.



A plain old lead-acid battery can easily run thousands of charge-discharge cycles if it's treated properly.


Huh? They're good for about 200 cycles

Baloney. Even the advanced metals batteries go for over 1,000 ycles if properly cared for, and old fashioned lead-acid batteries are limited only by how they're treated. Their life is theoretically infinite.

If you're only getting 200 cycles out of your deep-cycle battery, then you're doing something wrong. Maybe you need a proper 3-stage charger with a desulphating function? They're not expensive these days.

I know of many people getting 8+ years of heavy (practically continuous) use out of traction or golf-cart type batteries.


Unless you mean by "treated properly" that you don't fully discharge, in which case, your realized energy density is even less favorable.

Sure. But if you discharge it 100% and get to use it less than 200 times, vs discharging it 50% and using it over 2,000 times, what does that do to the energy density averaged over the life span?

Fresh Breezes- Doug King

.

Relevant Pages

  • Re: Aspen ROQ-4 "Analogger" software
    ... Charges NiCad or NiMH NP batteries NOT LITHIUM ... The discharge facility works well and is a must use for NP-1 NiCads. ... Charge Waiting - ...
    (rec.arts.movies.production.sound)
  • Re: Sourcing energy storage capacitors in the UK
    ... >and one way of ensuring this is to (probably better to discharge just ... than cycling batteries more deeply than we need to. ... if the pump routinely uses more than the panels generate. ... and will never be left over night at less than 90% charge. ...
    (sci.electronics.design)
  • Re: Discharging New Batteries in Digital Camera
    ... charging will begin.My camera drains them only to 1.15 volts. ... > Although I agree with the general consensus in that NiMH batteries do not ... > only after using up the existing charge will correct it. ... >>> and discharge them in the camera once they've been charged. ...
    (rec.photo.digital)
  • Re: more Ipower 9 Volts-slightly OT
    ... never discharge batteries befor charge,the li-ion dont have any memory ...
    (rec.arts.movies.production.sound)
  • Re: Fuel polishing system report
    ... And it sounds as if I use a lot less gasoline than you used ... How do you charge your batteries when you ... spend weeks on the boat? ...
    (rec.boats.cruising)
Loading