Boat Wiring Question: Series AND Paralell on Same Batteries

Ok.

I have a 36v trolling motor so I have 1 starting battery and 3 for the trolling motor. NO ROOM FOR MORE BATTERIES, PERIOD. Ok, we’ll call it the last resort.

What I want to do is add 2) 12v downriggers to my 36v system. Why? Because my kicker does not have an alternator and I’m not willing to be out 40 miles out on Lake Superior with a dead starting battery. I have no space for another battery.

Below I have a schematic that should give me 12v to my downriggers and 36v to my trolling motors.

The questions are, is this a good idea? Has anyone done this? Is there a better overall plan?

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If the three batteries are wired in series, that will produce the 36 volts for the trolling motor.

If you run the wires from one of the downriggers directly to one of the batteries….and there’s NO CONNECTION to anything else, there won’t be any effect on the 36 volts. The other downrigger could be hooked up to a different battery in the series string, again as long as there’s NO CONNECTION to the other downrigger or anything else.

Think of it like connecting an on-board multi channel battery charger.

With your schematic, it looks like you’re trying to run the three batteries in series and parallel at the same, which won’t work. If you re-draw the schematic you can see how you’re shorting out the batteries. For example in your schematic look at the positive terminal of the battery on the left. There’s a connection to both the positive terminal AND the negative terminal of the middle battery. That’s not going to work. I can see how you’re trying to use all three batteries to power the down riggers, can they be run off one battery?

SR

I’ve just heard that you always want to draw all batteries down equally in any parallel or series system. I honestly think my Terrova is suffering after finding out one bank on my charger failed. It acts sorta erratically now.

Others have recommended what you said while others say not to. This option came up to try’s and solve all problems.

Steve Root wrote:

For example in your schematic look at the positive terminal of the battery on the left. There’s a connection to both the positive terminal AND the negative terminal of the middle battery. That’s not going to work.

This is something I was worried about but I’m not totally sure about it. Came up with this idea today and a couple people with “some” knowledge thought it would work. I might be doing some testing tomorrow.

Thanks for the input. It’ll be considered for sure.

Be careful, shorting out a big battery is not good. Melted wires, burns, fire. Be careful brother

I high lighted part of your schematic in blue. You can see it’s one continuous wire from the positive terminal to the negative terminal on the center battery. Boom, not good.

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honest answer is,dont do it,you are asking too much from three batteries and I see you dont have room for a fourth one.
but I have to ask,where are yours located now???
in the back? if so,why cant you put a starting battery in the front??
I realize that means running a pair of heavy cables,but it is what it is.

not being a smart ass,but surely there has to be room for one more somewhere.

edit to add,looking at you schematic again,I see the fourth battery,there is not a good way to do what you want to do,you will have to dedicate one battery for starting,somehow.

Steve Root wrote:

I high lighted part of your schematic in blue. You can see it’s one continuous wire from the positive terminal to the negative terminal on the center battery. Boom, not good.

Thanks for pointing that out. That makes sense. Wish the other guys would’ve pointed that out.

Iowaboy1 wrote:

honest answer is,dont do it,you are asking too much from three batteries and I see you dont have room for a fourth one.
but I have to ask,where are yours located now???
in the back? if so,why cant you put a starting battery in the front??
I realize that means running a pair of heavy cables,but it is what it is.

not being a smart ass,but surely there has to be room for one more somewhere.

I’ve already got the heavy cables, but I’ve got 4 batteries crammed into the center console with no room for more. I’ve considered looking for someone to cut into my floor to add some kind of battery compartment but that’s gonna be expensive. My boat has a self bailing floor so it’s set pretty high and there’s not a lot of storage.

I almost ordered a voltage reducer/regulator but I’ve been told it probably won’t be efficient and I can’t find the 30a that I need at a reasonable price. Then I realized I would need 2

Do they make aftermarket alternators for older 4 stroke motors? Honestly, that would solve my problem.

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cant remember the manufacturers name at the moment,but yes,you can buy a tiny belt driven alternator,puts out about thirty amps,single wire hook-up,if memory serves me correctly it is about the size of a bean can.

they are used on old lawn tractors and such when the stator fails and a new or used one is not available or cost prohibitive,about fifty bucks,and good reliability,will see if I can find the info on those buggers and post it here.

shouldnt be too hard to make a bracket for it.

Thanks. My kicker is a 2001 evinrude 8 hp. I’ll take a closer look inside tomorrow to make damn sure that there’s nothing inside that suggest that it charges.

are you sure that doesnt already have a charging coil on it???
it is probably there but not wired for charging which only requires a voltage regulator and the proper connector.

No. I’ll look closer in the morning.

I couldn’t wait til morning. After searching online parts catalogs, it appears my engine likely has a charging coil. I’ll need to figure out how to connect to it.

take a good look at the parts schematic,you should only need the regulator/rectifier,and the wiring harness,if I remember right its a plug and play set up.

the output is only around fifteen amps,but on long trolling runs that should be adequate.

I dont know why nobody does this but a group 51 battery used in Honda’s has plenty of power to start an outboard. Especially in warm weather. The other option is to carry a small jump pack. You candle run series and parrael on the same batteries, you will end up calling the fire department. I have 1 dedicated battery for the outboard and 2 for accessories and still carry the jump pack as it will charge my phone and what not. Always have a back up for the back ups back up!!!!!

Thanks again guys for the warning against wiring to my diagram. No progress today with the rain. Still have yet to figure out if my motor will charge or not. Apparently there is a charging kit but it’s almost $500.

If not, does anyone have experience using a 36 to 12 voltage reducer/regulator? These are commonly used on golf carts to run a stereo system.

I’m about 99% sure it doesn’t charge. There is no regulator/rectifier. Is that all I would need to get? Or do I need to buy the whole kit?

Here is the ignition system for my motor. https://www.marineengine.com/parts/johnson-evinrude-parts.php?year=2000&hp=8&model=E8R4SSB&manufacturer=Evinrude&section=Ignition

If I can find one of these I’d be happy. They’re discontinued though.

https://www.marineengine.com/parts/johnson-evinrude-accessories/index.php?year=2000&model=Electrical+2000&section=Battery+Charge+Kit+-+5%2C+6%2C+8+(211cc+4-stroke)&yid=34016&mid=34017&sid=57889

try twin cities marine,never know what they will have on hand.
1-952-496-1951

if they dont have it new or used,they can probably lead you to the right contacts,they have helped me out a lot in the past.

For anyone who cares, I decided to wire both downriggers to the #1 battery of the trolling motor batteries. One key factor was to ground the 36 volt system even though Minn Kota doesn’t recommend it. A grounded system was required for the downriggers to work properly.

I also installed the Minn Kota alternator MK-3-DC. It charges your trolling motor batteries from your main motor after your starting battery is fully charged. Considering the long distances I planned to travel, it only made sense. Found a great deal at Action Fishing in Anoka.

After 2 full days of fishing Isle Royale I completely ran the Downrigger battery dead. Had to hand crank the downriggers up. On the last day my trolling motor went completely dead.

At least it wasn’t the starting battery. I’m going to have to test the Minn Kota charger. I don’t think it was working properly.

Does anyone see an issue with hooking each Downrigger to different batteries? I know it works, just want to know if I’m missing something.

Another issue is that running “odd” voltage to your trolling motor is NOT a good idea. It’s made to run 36v. and anything else (including less than 36 on a sustained basis) can fry circuit boards, cause overheating, etc. Have you looked at trading for a kicker that has an alternator or going to a lithium ion marine battery?

Bassn Dan wrote:

Another issue is that running “odd” voltage to your trolling motor is NOT a good idea. It’s made to run 36v. and anything else (including less than 36 on a sustained basis) can fry circuit boards, cause overheating, etc. Have you looked at trading for a kicker that has an alternator or going to a lithium ion marine battery?

I’m adding a charging kit to my kicker as soon as I buy a regulator/rectifier. I accidentally brought a rectifier instead.

Are you suggesting a lithium ion starting battery? I think long term I’m going to go with a starting battery with much more capacity.

biggill wrote:

One key factor was to ground the 36 volt system even though Minn Kota doesn’t recommend it. A grounded system was required for the downriggers to work properly.

Ground it to where? All DC circuits require a complete circuit from the positive post to the negative post of the battery. Obviously there will be switches, fuse panels, buss bars, etc. in the circuit as well.
Are you saying you are running a ground wire some where?

Running a jumper from the negative terminal on the 36 volt system to the negative terminal of your starting battery. It’s not required for a trolling motor but I’ve heard it may help eliminate any negative charge that your boat could put off.

My downriggers require grounding them to the water in order for the auto stop to work.

I just checked price on a lithium ion marine battery, no thanks. 3 times the lifespan for 8-10 times the cost.

Have you considered using quick connects that would allow you to disconnect the batteries from the TM series and connect two batteries (one each) direct to the downriggers? This wouldn’t get you the charge you’re looking for but it might help you with your voltage issue and your concern about wearing down one battery more quickly than the others. I used the following product on a boat and it worked well.

http://www.cabelas.com/product/Wire-Quick-Connectors/699559.uts?productVariantId=1185475&WT.tsrc=PPC&WT.mc_id=GoogleProductAds&WT.z_mc_id1=02901385&rid=20&gclid=COjMrIrmqM8CFdgHgQod47ABeQ&gclsrc=aw.ds

Is your starting battery a group 31 deep cycle? If not, you should consider it, it will start both motors without any issues and run all of the acceries with power to spare. Think about it, if you are running your locators, livewell, radio,marine radio, bilge pumps, a starting battery just isn’t going to last as long as a deep cycle. What do you do more of in a day, starting the motors or running acceries? The 3 trolling motor batteries should be group 31 deep cycle batteries also. Trying to split the 36v system and run 12v off of 1 battery is not a good idea and will more than likely cause problems with the 36v trolling motor.

I’m not sold on the deep cycle for starting but I might be leaning toward hooking them up to the starting battery. Here’s why.

1. The main motor will charge at upwards of 50 amps when running on plane. The alternator I bought will only charge at 10 amps per bank max. Wile that’s good for fully charging a battery, I’m going to struggle to get and significant charge after a long draw down.
2. I’ll always have the trolling motor batteries in case of an emergency.

While I’m not totally sold on the deep cycle for starting, I might seriously look into a dual purpose group 31 if it’ll fit.

Anyone interested in a 1 year old group 27 Interstate Cranking battery?

Call Eddie Lyback at Lyback’s marine a call, 320-676-3611. Ask him what type and size starting battery he recommends for your situation.

biggill wrote:

The alternator I bought will only charge at 10 amps per bank max. Wile that’s good for fully charging a battery, I’m going to struggle to get and significant charge after a long draw down.

I think of those DC chargers as more of a incremental boost as opposed to a charging solution. If the boat is making electricity, even if only a small amount, why not capture it? The small extension on run time and shorter charge cycles are worth it to me. My situation is more of a remote use case.

BTW – thanks for starting this thread. Very educational read.