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Re: small electric outboard engine? Some ideas...

Posted by Thom V on September 12, 2001 at 16:31:38:
Hi Bill,
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