On-Board DC Alternator Charger

[TruthWalleyes]

Looking for your advice. Here's the situation.

Installing a 24v trolling motor today.

Boat has 3 batteries. 2 for the trolling motor.

1 for the accessories.

So, prior to the 24v trolling motor, i have a switch that connects all 3 batteries in parallel. I hook up a smart charger and i'm 100% the next day.

I'm going to buy another battery to be used as a starter battery only.

Doing some research today with on board chargers and portable smart chargers and i ran across: On-Board DC Alternator Charger

So, i have a mid 80's electric start evinrude 40hp. If i put a 3 bank On-Board DC Alternator Charger on the new starter battery and connected each bank to the boat's other 3 batteries:

1) Does my motor put out enough charging amps to run the 3-bank On-Board DC Alternator Charger

2) Is this a good route to go? I think it might fit me well since i spend several days in a row in the boat fishing and when not doing multiple day trips i tend to be in the boat for at least 8 hours. So i'm hoping there is enough outboard run time to maintain the other 3 batteries.

What's your thoughts?

[morepower02]

Not sure on your engines output but on the newer Mercs we have not been able to run Minn kotas DC charger on models under 75 hp due to not enough amp output.

[TruthWalleyes]

I'm headed to the boat doctor shortly to pick up my 40HP. I'll see if he knows what it puts out for amps. Do you know what the minimum would be for the 3-bank?

[CaptainMusky]

I would be worried your motor wouldn't put out enough amps to be effective. I am going to do the same thing this winter but I know I have enough amp output.

Minnkota has multiple models from a single bank to a 3 bank. I don't think you will have the juice to do a 3 bank.

Maybe a 2 bank just for your troller. If you have electronics on a separate battery from your outboard you should be good for the day.

[morepower02]

I have a 2 bank here and the instructions cover all three sizes. Engine alt output for the 3 bank must be 35 amps minimum. 25 amps for the 2 bank.

Ask Travis when your at boat doctor he will probably know the output of your engine. I am going to check in the shop to see if i have the service manual for your engine.

[morepower02]

I come up with 4 amps charging output for a mid 80's 40hp

[TruthWalleyes]

I just talked to a different mechanic and he seemed to think that at MAX 8amps. SO i agree with you guys, this system wouldn't work for me.

I'll just have to look at an on board charger or multiple 12v chargers.

Bummer

[Wish-I-Were-Fishn]

Is there some sort of amplifier you could get to boost the power?

[aanderud]

Even if it output 35 amps for a 3 bank charger, I'd have reservations on how much sense it would make. Here's why:

A 3 bank charger will probably take at least 6 hours to charge two nominally-sized deep cycles from a half-discharged state to full. Who runs their outboard for 6 hours (at high enough RPMs to putput that 35 amps) for every half-charge of trolling batteries? That's a lot of outboard runtime.

Also, you should be able to get by on a whole summer without charging that starting battery, assuming it is dedicated to ONLY starting your motor, and assuming the motor is outputting the 4 amps it says it is. So, a single three bank charger should handle your 24v motor plus your electronics battery.

[Ufatz]

This player is 100% correct!

[CaptainMusky]

My outboard puts out 44 amps at idling speeds. The new merc 150 4 stroke puts out 50 I believe. So motors do in fact put out enough amps and at low rpms to produce enough to charge the batteries. It is NOT intended to fully charge them but these systems have proven to reduce overall battery drain to 25% of normal.

Its no mystery why all the pro fishermen have one of these systems installed. They do work and very well.

[TruthWalleyes]

I bought 2 more raider smart chargers. I might add another battery to run accessories off of and have a battery dedicated to only the motor. Right now the motor and accessories share a battery, they used to share 3.

[aanderud]

My outboard puts out 44 amps at idling speeds. The new merc 150 4 stroke puts out 50 I believe. So motors do in fact put out enough amps and at low rpms to produce enough to charge the batteries. It is NOT intended to fully charge them but these systems have proven to reduce overall battery drain to 25% of normal.

Its no mystery why all the pro fishermen have one of these systems installed. They do work and very well.

I guess if you're putting the hours on your engine that the pros put on, then this seems like a great option to give you slightly longer runtime and reduce the chance of draining the batteries way down on any given day... But, it's still not going to replace the charger you plug in when you get home. Given that, MOST amateurs can get by with a plug-in charger for home. The same cannot be said if they were go go with a DC-only option.

[kerryd15]

It sounds like it might be worth looking into a portable generator for the long trips. If you have an onboard charger already or have enough smartchargers you could crank up the generator overnight or during parts of the day. Would the generator weigh much more than adding a forth battery? And it could be used at home for power outage or in a fish house.

[CaptainMusky]

Like I said its not intended to replace the onboard chargers but reduce your amount of usage in a given day or trip. Spend a day on mille lacs or week on lake of the woods and this system is invaluable.

It may not mean much so someone who fishes small lakes but for those of us who do or have extended trips without electric available it is the difference in a frustrating trip or one that is more satisfying. Since my Suzuki is so quiet I plan to let it idle while using the trolling motor to recharge the batteries. I can't hardly hear it run anyway.

[Kyhl]

Agreed. I think this is a great option when fishing bigger water.

I like to do the walk in sites at Father Hennepin and have alway opted for electric sites. And only use electricity to recharge the trolling motor batteries. This option might allow me a few days on mille lacs without electricity.

What would someone consider a minimum amout of run time to make this usefull? On Vermilion my trips out or back can easily run 20+ minutes. Once out, the trips between spots may only be 5 minutes.

On a second note, how does one figure out the amperage of a motor's charging system?

[h8go4s]

"my trips out or back can easily run 20+ minutes. Once out, the trips between spots may only be 5 minutes."

In that case, it probably wouldn't help much.

"On a second note, how does one figure out the amperage of a motor's charging system?"

My Yamaha owner's manual lists it, as does the online spec sheet. One says 16A, one says 17A.

I'm considering this for my boat-in camping trips. I often use my outboard trolling for long periods of time, and that probably would keep my single bow mount battery topped up.

[aanderud]

Since my Suzuki is so quiet I plan to let it idle while using the trolling motor to recharge the batteries. I can't hardly hear it run anyway.

I like this idea over that of a generator. You basically have a 600 watt generator there in your engine, and it's probably quieter than most generators, and you don't have any extra weight lugged around this way. These systems definitely have their place as a good backup power solution when no shore power is available.

[morepower02]

Since my Suzuki is so quiet I plan to let it idle while using the trolling motor to recharge the batteries. I can't hardly hear it run anyway.

Keep in mind if you go with the Minn Kota it will not kick in unless it senses 13.6 volts in the starting battery. Most engines will not have this at idle.

[CaptainMusky]

Keep in mind if you go with the Minn Kota it will not kick in unless it senses 13.6 volts in the starting battery. Most engines will not have this at idle.

Very good point, but mine does. I have already confirmed that. But if you use your electronics off your cranking battery, the cranking battery will have to get charged up FIRST before it will charge the others. Good thing to point out.

[h8go4s]

I have already confirmed that.

Captain, how did you confirm that? Call your outboard manufacturer? I don't think my cheapo multimeter will work just hooking it up to the battery. Tried that once and the probe wires got hot real quick.

[morepower02]

multi meter on battery when engine is running or reading voltage off your graph display are the easiest ways.

[h8go4s]

Oops. I read that as amps, not volts. But I'm still a little confused. The MK single-bank requires 12 amps minimum input and delivers "up to 10 amps of total output." Voltage output from my motor increases as RPM's increase, up to a limit. Does the amperage remain constant with RPM's, in my case at 16 amps? And what would cause the output to be less than 10 amps, or is that just legalese?

[CaptainMusky]

multi meter on battery when engine is running or reading voltage off your graph display are the easiest ways.

I have the voltage showing on my HDS unit.

[TruthWalleyes]

Put a 4th battery in the boat yesterday. Shouldn't have any problems with running out of juice on long trips.

I probably have close to the heaviest darn 16' boat out there! lol

[CaptainMusky]

Too funny Truth.

But, you are prepared and that is what matters. You probably wont even notice the weight provided its positioned properly, which I am sure you did as part of the process.

[TruthWalleyes]

Yeah we'll see. I put it in the back. I really never built another spot for a 4th battery I'll probably find the best location this winter when i've got some time. With me and the extra battery, i'll probably sit in the water like a Pro-V

[TruthWalleyes]

She floated just fine! Boat even got to see it's biggest wave ever saturday Almost spilt my beer on that one.