25 hp outboard battery charging questions

[Landlockt]

I have a pull start 1993 Evinrude 25 hp, model number E25RETS.

I want to install a trolling motor (probably a Minn Kota 40 lb), running lights, fish finder/GPS and a tach.

A) Will this motor have enough output to keep a deep cycle battery charged?

B) Or should I keep it simple and skip the expense of the outboard charging package which I assume I can locate and I assume will run around $150
and not bother with the motor charging the system and just pull the battery after use and charge it overnight?

C) ???

If I go with B how long would I be able to run that set up with a battery in the $150 range.

I know there are a lot of variables, I am just looking for a "typical day of fishing on the lake" type of estimate.

Thanks

 

[Silvertip]

Re: 25 hp outboard battery charging questions

When it comes to charging trolling motor batteries from an outboard the answer is always the same. That size outboard has a very low output alternator and in the best of times would never be able to keep a trolling motor battery charged (unless you didn't use the trolling motor). Just because you have a charging system, it doesn't mean there are no limitations. My car has an engine but it cannot tow a semi. The same holds true for electrics. Your trolling motor can draw anywhere from 20 to 50 amps depending on its size and the speed you run it. So lets say whatever speed you operated the motor it drew 20 amps. Then lets say you ran the motor steady for one hour. The motor therefore drew 20 amps from the battery. To charge that battery the alternator would need to output 20 amps for one hour meaning you would need to run wide open for an hour. Now the charging system for your engine is probably in the 6 amp range so 20 divided by 6 is 3+ so you would need to run for 3+ hours to charge it. Hope this is sinking in and you are realizing this is not an economical or even feasable solution to the problem. Install a 10 amp on-board smart charger and plug in at the dock to charge the battery over night. Cost is about eighty bucks and your battery will live longer.

 

[Landlockt]

Re: 25 hp outboard battery charging questions

Great advice.
Sounds like my options are pull the battery every night or buy an on board charger.
That being said, how long will I typically be able to run a 40 lb. trolling motor, fish finder/GPS, etc.
I do keep my boat at the dock and the closest power to the dock is a couple hundrend feet away, so I will probably end up pulling the battery daily.

 

[Kamdyn]

Re: 25 hp outboard battery charging questions

Great advice.
Sounds like my options are pull the battery every night or buy an on board charger.
That being said, how long will I typically be able to run a 40 lb. trolling motor, fish finder/GPS, etc.
I do keep my boat at the dock and the closest power to the dock is a couple hundrend feet away, so I will probably end up pulling the battery daily.

Your running time will depend on your choice of battery and how long you use them, I run 2 Optima Gel cell (AGM) batterries on my boat and Silvertip was a big helped hooking me up with a wire diagram so I can hook up a batterry selector switch So I can go all day long with 2 batteries.

 

[Wishiniwuzfishin]

Re: 25 hp outboard battery charging questions

General rule of thumb is an electric trolling motor draws 1 amp of electricity for each pound of thrust (on high speed) every hour. So your 40lb motor is drawing 40 amps (40 amp/hours) for every hour it runs on high speed. You need to find out how many amp/hours your battery is and do the math. If your battery is 120 amp/hours, theoretically you should be able to run your motor on high speed for 3 hours before the battery goes dead. This is just a general guide and the battery will ususally go dead before the amount of amp/hours it has is totally used up. You also have to take into account if your battery is fully charged or not when you go out. Running at lower speeds also uses a proportionately less amount of amp/hours.

 

[Wishiniwuzfishin]

Re: 25 hp outboard battery charging questions

Fishfinder and Gps usually don't use much electricity. Maybe 1amp/hour total, I would GUESS, off the top of my head. You should be able to find specs on what they actually draw.