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In Reply to: small electic outboard engine? posted by barnaclied on September 10, 2001 at 14:58:41:
Go to search engine google.com and put in: minn kota. These folks produce the largest line of stern and bow type marine outboard electric engines and possibly sold even in Europe...
The irony of working with an elecric outboard motor is not the motor ---but the battery. In a DC battery system Ohms Law states: Higher Voltage draws less Amps. So, a '12' volt lead acid battery, in good condition, will have a 'rest voltage' of approx. 12.7 volts. As one uses the engine, the voltage drops and more amps leave the 'barn'. By aprox. 12Volts and less the amps look like a stampede to the electric motor. Hence, the usable voltage window for 'keeping' amps, and therefor longer use time, is small.
Here's a trick: Purchase a small solar panel that produces a high DC voltage (amp production unimportant here) 16 to 20 volts in bright sun (make sure it has diodes that will not reverse). Hook this unit to the battery. Now the battery voltage should stay higher longer. You are not charging the battery, just trying to retard voltage drop--to retain amps--for a longer use time.
Batteries are tested at 85 degrees fahrenheit for volts and amps. Most boat environs are 20+ degrees cooler. Hence, the battery never gets to full potential. The above system can make a big difference.
Charging a battery. Most battery chargers are 'Force the Amps' type. Really not very good. After a few charges the battery just can't be brought to full capacity. To charge properly a battery needs to see volts only from say 14.4 to 16.5 for 12 to 20 minuets. Then voltage needs to be reduced a bit and the Amps (10 or so p/hr, more if you have the money) 'pumped' in. Then amps, along with voltage are reduced to 'rest' around 12.7 volts. Now the battery will be full. These are called 3 and 4 step chargers.
Well, hope this 'thumbnail' battery primer helps... Thom V
Thanks very much Thom. I already have a link to Minn Kota on the Micro-Sailboat Web site. The problem for my tiny boat is one of weight and space. There doesn't seem to be anything on the market which is viable for really small craft.
I have a friend who makes model aircraft and he uses very efficient minute electic motors with small re-chargeable batteries. It's astonishing how efficient these tiny motors are.
When will someone come up with a really lightweight outboard engine, preferably with an integral battery?
I'm appreciative of the information you have supplied re. the charging process. I'll certainly have a look at that in more depth.
PS. By the way, my small boat Web sites have been combined. See the URL.
Your new 'splash page' looks great combining the 3 sites---makes it much easier to get around!
On the 'battery thang': Look at the Sonnenschein Gel Cell Battery people below. I have had extensive experience with this product. This battery technology was developed during WWII, I believe, by the Germans to lower gassing and gain underwater time in their U-boats... I have both their batteries and charger for a nifty 6 volt spot light and to power a camper at a recreation site in the woods. Anyway, they have some small gel cell types--for model work--that may be adaptable to your idea of the battery in the head unit of an electric outboard engine. Do you think Minn Kota would sell you a 'shell'? How about finding a broken Minn Kota, pulling out the guts and adding back the gel cell battery with the controller in the head, and your friends efficient DC motor at the base... I know of no other small battery technology that would have a chance at enough amps to torque a propeller in water. Also, this Gel Cell Battery technology has a different 'specific gravity' and the at rest voltage is about 13.4, much higher than lead acid technology of 12.7, giving more amps and more power for a longer use time.
Many thanks. You've given me a few things to work on. I think there must be a solution somewhere.
Meanwhile, perhaps subscribers can point me in the direction of a small lightweight electrically powered outboard engine?
Well, it's been over six months since your first posting about the electric outboard motor. Have you found anything yet? I don't believe you will find really light batteries with enough energy to drive your boat very far. The standard trolling motors will produce thrusts from 30 to right over 100 pounds. They all require heavy, separately mounted batteries.
Try www.lynchmotor.com for a lesson on electric motors. Most of theirs are made for inboard mounting, but they do have an electric outboard motor (looks like it ought to be going putt-putt-putt, but it's electric) that produces the same thrust as a 10hp gas motor. Weight is probably too high for you though if you're looking for something lighter than a trolling motor. And, you've still got to add a big fat battery.
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