How do you charge your trolling motors?

[cobrar543]

I have a new boat and two batterys for my motor. YET I can only get about 5 hours out of them for the Minnkota. I have had it checked and they say everything is fine. Ya ok.

I would like to get something that would allow my main gas to recharge the system when running. I would like to know more about HOW it works before going in and asking the people charging me money first. Any help would be much appreciated

Doug

[Bodofish]

Need a little more info on the setup. Motor, batteries. If your big motor is an outboard, probably doesn't have enough amperage to really charge two batteries at the same time with any speed. So what cha got?

[rseas]

I know that I am probably living on the edge but I don't even have a seperate bank of batteries for the trolling motor. Whth the correct circuit protection it is wired to my house battery. I just leave the main running if I need to use the electric for an extended period of time. Me baaaad...

[cobrar543]

battery set up for the Minnkota, Minnkota battery charger housed in the floor with it. 115 Merc 4 stroke with its own battery in the back.

[Larry3215]

Just some rough numbers on why you cant realistically expect to re-charge your trolling motor batteries from an outboard or even a good size inboard.

If you have two typical batteries for your trolling motor they probably run around 80-100 amp hours or so capacity each. Lets go on the low side and say you have 160 amp hours total in the two. So when you run them both down, you have used up 160 amp hours.

The way amp hours work = amps times hours. So if you are charging a battery at 10 amps for 1 hours, thats 10 amp hours you put into it. Charge at 10 amps for two hours = 20 amp hours. Its actually less than that because the charging process isnt 100% efficient.

So, you need to put back more than 160 amp hours into those two batteries to re-charge them.

My Yamaha F115 has an alternator that puts out around 30 amps at cruise speed. So if I was running the boat at around 30 miles per hour, it would take more than 5 hours to recharge your two batteries.

Lets say you have an automotive type alternator on a big inboard that puts out 100 amps or so at hi throttle. You would still need to run at close to wide open for close to two hours to recharge those two batteries.

Idling or trolling wont cut it because the alternators dont put out the full amps at low rpms.

You just cannot expect to recharge trolling motor batteries while you are on the water.

You can get a small additional run time, but not much - and that still requires you to run for a good long time at cruise speed or higher.

The only real way to get more run time is to go with more capacity on the batteries or use the trolling motor less.

[Bodofish]

Just some rough numbers on why you cant realistically expect to re-charge your trolling motor batteries from an outboard or even a good size inboard.

If you have two typical batteries for your trolling motor they probably run around 80-100 amp hours or so capacity each. Lets go on the low side and say you have 160 amp hours total in the two. So when you run them both down, you have used up 160 amp hours.

The way amp hours work = amps times hours. So if you are charging a battery at 10 amps for 1 hours, thats 10 amp hours you put into it. Charge at 10 amps for two hours = 20 amp hours. Its actually less than that because the charging process isnt 100% efficient.

So, you need to put back more than 160 amp hours into those two batteries to re-charge them.

My Yamaha F115 has an alternator that puts out around 30 amps at cruise speed. So if I was running the boat at around 30 miles per hour, it would take more than 5 hours to recharge your two batteries.

Exactly!!!

Lets say you have an automotive type alternator on a big inboard that puts out 100 amps or so at hi throttle. You would still need to run at close to wide open for close to two hours to recharge those two batteries.

Idling or trolling wont cut it because the alternators dont put out the full amps at low rpms.

You just cannot expect to recharge trolling motor batteries while you are on the water.

You can get a small additional run time, but not much - and that still requires you to run for a good long time at cruise speed or higher.

The only real way to get more run time is to go with more capacity on the batteries or use the trolling motor less.

[rapala1972]

What about using a solar charger? They come in different sizes and are not that big. Using solar charger to keep a constant trickle charge on the batteries might lengthen your time using the battery.

[Larry3215]

Unfortunately, solar isnt going to work either - at least not enough so you would notice any difference in run time.

As you said - solar chargers are "trickle chargers". That means they dont put out very many amps - especially a small one.

Remember its amps times hours that count. If your solar panel puts out say 5 amps, thats going to take roughly 20 hours to recharge his batteries.

Also, remember thats 20 hours of FULL NOONTIME SUN!!!

Cabellas sells an 18 watt solar charger for $89. Its 3 ft long and 1 ft wide. 18 watts at 14 volts = 1.28 amps - if it is 100% efficient. It wont be, but lets assume it is.

Lets round things up to 1.5 amps - at that rate it will take 106 hours to recharge his two batteries. AND that assumes you have 106 hours of noontime sun on a clear day. In actual real world situation, more like 150-200 hours to recharge his batteries.

In the real world, you will probably need more like 150 hours to recharge those batteries with that panel.

Lets say you wanted to keep his batteries charged to roughly 1/2 by the end of the day and lets assume it was a very bright sunny day and full noontime sun all day long and you were on the water 10 hours. You would need to provide roughly 80 amp hours over that 10 hours so you would need at least 53 of those chargers from Cabellas.

That will cost you over $5000 including tax and they will take up an area of around 170 sq ft or roughly 8 ft wide by 22 ft long.

Not really practical at all.

If you just wanted to add a couple of hours of runtime, you would still need maybe 10 of those panels to make it work. Thats still going to take up an area 3ft wide by 11 feet long and cost close to a grand.

[CARiD]

No one actually asked if the batteries are in good condition and if they used to charge well in the past. Maybe they simply need to be replaced with new units that would hold the charge better? If it's the case, check out a high capacity battery : https://www.carid.com/marine-batteries-power/" onclick="window.open(this.href);return false; Good AGM battery will loose the power much slower.

[hewesfisher]

The only real way to get more run time is to go with more capacity on the batteries or use the trolling motor less.

^^^^^

A side note, the charging system on your Merc is designed to maintain the fully charged state of one properly rated, fully charged battery.

There's all manner of gadgetry out there to permit charging of batteries from a main, but your system is still limited in what it was designed for. Not knowing the year of your 115, it probably has an alternator capable of producing somewhere around 60amps more or less. A portion of the current produced is used for engine functions, balance is used to maintain the one fully charged, properly rated starting battery. At most, you might have 30 - 40amps available "assuming" the main battery was 100% charged under running conditions.

Using Larry's excellent explanation, you'll understand the limitations of on water charging in small boat fishing applications.

[Larry3215]

Im going to go ahead and mention the other option that people come up with when this subject is discussed - a generator on board.

Everyone that uses a trolling motor very much at all has this same problem. We ran into it big time a few years ago when we decided to put an electric trolling motor on our 20' boat. The bigger the boat the sooner your batteries go dead.

My bro's wanted to charge from the main motor at first. They didnt believe me it wouldn't work until we spent $150 on the parts to hook it up to the main motor charging system and couldnt tell any change in run time. Then they started talking about solar panels. I explained the problem but they didnt like the math and didnt believe me there either. The cost stopped them though.

Finally they came up with the idea of using a small Honda generator set on the boat. My bro found one cheap that put out around 8 amps of UNREGULATED 12 volt power for battery charging. Thats about 10 times what that Cabellas solar panel would do, so it could potentially extend our run times an hour or two.

They didnt believe me that it wasnt going to work, so we tried it anyway. Turns out there are several problems with that option as well.

1) The battery charging circuit is unregulated, so we would have to monitor the voltage constantly to keep from over charging the batteries and damaging them. That was only a problem early in the day before we ran the batteries down very far. After that, the generator couldnt keep up.
2) That 8 amp rating is MAX short term rating. The generator would over heat and shut down when run for more than 5 minutes while we were using the trolling motor.
3) It generated a ton of electrical interference with our sonar. The screens were almost unreadable while it was running.
4) The final straw that broke this camels back was noise. A Honda generator is pretty quiet - when its being run in your back yard. Out on a quiet lake at 6am is sounds like a diesel semi and vibrates the entire boat while its running.

[cobrar543]

That was my next though..damm...Thank you for sparing me. The next though is a bigger more powerful motor that would maybe not have to use as much umph to get it and keep it moving?

[Larry3215]

It is best to have the motor sized correctly for the boat, but I doubt that will make a huge difference unless you're up-grading from an older motor with a less efficient speed controller and it was way under sized.

It really comes down to battery capacity and how hard/long you use the motor.

[hewesfisher]

It is best to have the motor sized correctly for the boat, but I doubt that will make a huge difference unless you're up-grading from an older motor with a less efficient speed controller and it was way under sized.

It really comes down to battery capacity and how hard/long you use the motor.

I concur.

The current 115hp Merc 4-stroke has a 35amp alternator so I'll assume that's what your 115hp Merc has as well. The current 150hp 4-stroke has a 60amp alternator which is the same as my 150 Optimax. The 200 & 250 Verados have a 70amp alternator, a very marginal increase. Even so, no matter what engine you have, you won't be able to use 100% of the alternator output to recharge a dual battery trolling bank. Unless you run at or above 3500rpm or so, and for some length of time, the return on investment is too small to make it worth the expense.

Best bang for buck will be to get 2 high capacity batteries for your trolling bank. They won't be inexpensive or light. A pair of good gp31 AGMs (Batteries Plus X2 (made by Northstar), Odyssey 31M-PC2150, etc.) will weigh in at 75lbs apiece, and tied together, will give you 400+ minutes reserve capacity.

Other than that, I don't know of any viable alternatives.

[cobrar543]

And I'm getting 4-5 hours now. So I guess I'm not as bad as I thought

[G-Man]

One thing to keep in mind, you should not run your batteries dead flat. If you plan to regularily discharge them below 50% capacity, you'll want to get an AGM battery. If you run a wet cell (non-AGM) past 80% discharge it will more than likely not survive the ordeal. I have two AGM batteries in my boat that get charged by the main motor and the kicker when it is running. For the most part they keep the batteries in pretty good shape and I'll periodically (couple times a year) top off the charge on them. I have an Optima blue top that is 20 years old and still very strong. I use it as my dedicated trolling motor battery when I want to troll at or below 1.2mph and as a second house battery in my camper when I know there won't be any electrical hookups. I use a regular old 10/2 amp charger and a battery desulfinator and monitor the charging progress with a voltmeter. AGM batteries typically can take on more current then my charger can supply, and will sometimes overheat the charger, so I usually start it out at the 2 amp setting and let it charge for a couple hours before switching over to the 10 amp setting. Once the charge voltage gets into the 14+V range, I'll switch the charger back to the 2 amp range and let it go until it levels out at around 14V. Twice a year I'll hook up the deslufinator and let it run over night on the 2 amp charge setting. This will run up the voltage to around 15V and the battery will get a bit warm. This is by design and is also called an equalizing charge. Now, you can avoid all the hassle of monitoring the charging process by using a good smart charger. I can't recommend and good smart charge as I've never used one and quite frankly don't trust them. Mostly that is just my old man side talking, but I have seen batteries overcharged/fried while being hooked up to them. One last item to remember, if you have a wet cell battery, TOP THE CELLS OF WITH DISTiLLED WATER ON A REGULAR BASIS! Unless it is an AGM battery, you need to check the electrolye levels in each cell and keep them topped off. This goes for "maintenance free" batteries, as well.

[Bodofish]

G, I agree with almost all of it whole heartedly. One thing. Wet batteries drained to 0 zero are not a problem. You never lose those little ions, they just get stuck on one side / set of plates or the other. Now mind you I do not recommend running a wet battery flat but sometimes you have no choice. All it takes is a good charger and time. As an example joe interstate battery in the boat was very happy sitting and waiting for the next outing when the cabin light got left on for like 2 months. Dead battery right? Today that battery works just fine and holds a charge like no ones business. It took 3 days for those little ions to move back to the other side but, they do and they will. If you have one of those razzooo high frequency chargers it goes a bit faster but the bottom line is time is your friend and there is no substitute. I never toss a battery until it's been on a charger for at least a week. The only thing that can make a battery go bad is not using distilled water. Not filtered or drinking water, not reverse osmosis, only distilled, absolutely pure water and make sure the top of the battery is spotless and no soap or what ever goes down the holes. Once the acid in the battery is compromised it's done. Sometimes you can get away with changing the electrolyte but not always. I have a million stories just like the joe interstate one from my days as an engineer on commercial fishing boats. One would think that two or three alternators would guaranty at least one would always survive, not so much, the ocean always wins.
If you're having a bad day with a battery or two, put it on the charger and go play a round of golf, hop on the bike or grab a hoe and hit the garden. Time is your friend and nine times out of ten, your battery will come back happy and ready to go. Or you could just go buy a new one and then you have two.....

[Pnwlipripper]

Why not use a onboard charger 2 bank for the batts just plug it in the night before you go out