Battery charging

[Scottimus]

I am looking for a battery charger to wire in so that it will charge my trolling motor batteries while I am running the motor. There is a switch up front by the trolling motor that is supposed to charge the batteries off the main battery but it shorted out. Not sure if I can just replace the switch or if the wiring is bad as well.

I see that Minn Kota has one that supposedly does what I want it to do. Anyone have any experience with one of these? Can they be wired up to an outboard? Anyone have a better suggestion?

 

[Alumarine]

If your outboard has a charging circuit it can charge your trolling motor batteries albeit slowly.

Normally you charge them with a 110 volt charger at home or dockside.

 

[Silvertip]

If you do a little math you will learn that you cannot fully charge or even begin to fully charge a deeply discharged trolling motor battery from the boats engine by making a few short runs between fishing spots. If this is a mid-size or small outboard you would need to run wide open for hours to do the job. The output of the engine alternator, distance run, speed run at, size of the battery, how deeply discharged it is are the factors that determine how long it takes to charge or whether it is even worth while. As was stated, save your money and buy an on-board smart charger that you can wire in permanently but it will plug into household power at the dock.

Does the switch up front say RUN-CHARGE or something similar? That switch allows you to charge the trolling motor battery through the trolling motor plug and is not wired in any to the engine charging system.

 

[thumpar]

Outboards are not really meant for charging batteries. They can maintain a battery but that is about it. There are kits to add alternators to outboards but it would still take awhile to charge.

 

[bruceb58]

Outboards are not really meant for charging batteries. They can maintain a battery but that is about it. There are kits to add alternators to outboards but it would still take awhile to charge.

I have a 2006 Mercury 90HP outboard and it has a 25A alternator in it. I wouldn't count on it to recharge trolling batteries but to say it is just to maintain batteries is not accurate.

 

[thumpar]

I have a 2006 Mercury 90HP outboard and it has a 25A alternator in it. I wouldn't count on it to recharge trolling batteries but to say it is just to maintain batteries is not accurate.

Guess it depends on what you are running. With an amp, lights, and running the engine 25 amp is not hard to use up. The alternator kits I was referring to push 60 or so amps depending.

 

[bruceb58]

LOL...I am not going to worry about the stereo on my 90HP pontoon boat pulling anymore than a couple amps. Even lights won't put a dent in that.

 

[Texasmark]

I have a 2006 Mercury 90HP outboard and it has a 25A alternator in it. I wouldn't count on it to recharge trolling batteries but to say it is just to maintain batteries is not accurate.

Did you read your manual? The manual for my 90 2 stroker with a red 16 Ampere alternator said it was to "maintain a charged battery". Looking at the regulator/rectifier and the lack of a decent heat sink/cooling fan speaks volumes in that regard.

 

[bruceb58]

Yes...and service manual

 

[H20Rat]

I have a 2006 Mercury 90HP outboard and it has a 25A alternator in it. I wouldn't count on it to recharge trolling batteries but to say it is just to maintain batteries is not accurate.

Fuel injected? Between the computer, fuel injectors, and fuel pump, most of that 25 amps is gone. At idle speed you are probably just barely breaking even. At WOT I'd guess you might have 5-10 amps to spare.

 

[bruceb58]

Fuel injected? Between the computer, fuel injectors, and fuel pump, most of that 25 amps is gone.

LOL...seriously? BTW, output is 20A @ 1000 RPM.

Out of curiosity, have you ever measured the current an ECU draws?

 

[Scottimus]

My motor is a 1983 Evinrude V4 140 and it will keep the main battery charged, just not sure of the ability to charge other batteries. I am not sure what the switch up on the bow actually says, I will have to take a look the next time I am out where I store it. Thanks for the responses. Looks like I may have to just go with the dockside/home type charger or replace the switch if it actually is for charging the other batteries.

 

[H20Rat]

LOL...seriously? BTW, output is 20A @ 1000 RPM.

Out of curiosity, have you ever measured the current an ECU draws?

I have measured the ECU current from probably 15 different ECU's, a couple in marine environments. I've also written microcode for a couple of the various processors that are common in automotive ECU's.

ECU draw will be 2 amps max, I've seen higher but not usually in the marine environment. Fuel pump will be around 5-7 amps. Injectors will be 5 amps to open but will quickly drop down to 1-2 amps sustained. (and of course, injector duty cycle plays a huge role in that.) Granted, fuse rates aren't always indicative of amp draw, but most outboard ECU's are fused at 15 amps.


20 amps at 1000 rpm would be unusual.

 

[bruceb58]

I have measured the ECU current from probably 15 different ECU's, a couple in marine environments. I've also written microcode for a couple of the various processors that are common in automotive ECU's

Likewise. I use to work for Delco Electronics. We used the ECUs for many projects when I was doing R&D and design for them.

The service manual specs the output for 20A @1000RPM. I am just going by the specs that it gives.

Bottom line, there is extra capacity to charge batteries besides just maintaining with the outboard motor that I own.

 

[Scottimus]

No Title

Does the switch up front say RUN-CHARGE or something similar? That switch allows you to charge the trolling motor battery through the trolling motor plug and is not wired in any to the engine charging system.

Here is a picture of the switch...

 

[bruceb58]

What voltage is your trolling motor?

 

[Scottimus]

It has 2 settings, 12 volt and 24 volt...I typically leave it on 12 as I don't normally need more power plus I have only been hooking one battery up at a time.

 

[bruceb58]

The reason your switch is there is so that a 110V battery charger can charge the two 12V batteries in parallel yet allow you to have the batteries wired serially when in 24V mode.

Bottom line, you aren't going to recharge your trolling motor batteries much at all with your engine so just add a 110V battery charger for when you bring your boat home.

If you really think you have excess alternator power, you can use something like this although I doubt it knowing the engine that you have.
http://www.minnkotamotors.com/Batter...ator-Chargers/

 

[Scottimus]

Ok, thanks for the info! I will go that route...