Combining 36 volt and 12 volt together in one boat.

[Fishsqueezer]

Any advice on how to incorporate a 36 volt trolling motor into my boat?s 12 volt wiring will be much appreciated.

The 12 volt electronics on my boat consist of:
-outboard starter motor
-power trim/tilt pump
-bilge pump
-live-well pump
-Hummingbird fish finder
-fore & aft running lights
-3 interior utility lights


Here are my questions.

-Is it acceptable to ground a 36 volt series and a 12 volt cranking battery to the same aluminum hull? Where would the ground wire be placed on the 36v system?

-Is there any way to run 12 volt electronics off a battery which is part of a 36 volt series?

My understanding of electronics is limited and presently the only configuration I can think of involves having 5 batteries onboard (one cranking 12v, one deep cycle 12v, and three deep cycle 12v wired in series for 36v).

 

[Silvertip]

Re: Combining 36 volt and 12 volt together in one boat.

Two problems to start with:
1) You DO NOT ground anything to an aluminum hull
2) You DO NOT incorporate the engine and trolling motor systems.

But yes, you can run 12 volt stuff from the 36 volt system PROVIDED you pick 12 votls from the correct battery. But before I tell/show you how, you do not have a high current draw so why do feel you need to switch stuff that is currently on the start battery to the 36 volt system? Has the current system EVER left you with a dead starting battery -- or is this just something someone told you HAD to do? you do realize that sucking extra juice out of one of the batteries in the string will affect run-time. You cannot charge a 24 or 36 volt system from your 12 volt engine charging system. As for where do the grounds go, there are only two grounds. For the engine electrical system it is the NEGATIVE post of the starting battery. For the 36 volt system it is the NEGATIVE post of the battery on the LEFT in the diagram below. There is no other ground other than the engine block or negative buss at the helm. Both of those relate to the engine system and cannot be combined with the 36 volts system.

Here is how to get 12 volts from a 36 volt system. Pay attention to which battery is used for this. You apparently are electrically challenged so I won't go into detail why using the specified battery is important. The only thing you need to know is failing to do so presents a very good chance for an improper ground to destroy your electrics.

This is 36 volt wiring. You take 12 volts from the battery on the LEFT. DO NOT choose any other battery.

This is a 24 volt system but the 12 volt connections on the battery on the left is the same for a 36 volt system.

 

[Fishsqueezer]

Re: Combining 36 volt and 12 volt together in one boat.

Thank You! I am very electrically challenged. I have never grounded anything to a hull before, and I was not sure if this was something I should or should not do. Glad to know that I should not.

My primary concern is that the lighting will drain my cranking battery. I plan to use this boat frequently for night fishing, during which the engine will be turned off and I will drift with the stern light and 3 utility lights turned on. If I power all four of these lights all night long (about 6-7 hours), won't this drain my cranking battery in a way that is bad for it? I was under the impression that a battery which is discharged and recharged like that that should be a deep cycle. Is my 12 v load really light enough not to worry? That would be good news for me.

I haven't used the boat enough to know if lighting for long periods will drain my cranking battery too much. I really need to educate myself on the differences in batteries, how they work, and the electricity consumption of the components in my 12 v system. I'd rather not affect my 36v bank with the 12v draw, so I'll just wire everything that runs on 12v to the cranking batt and see how it works. Worst case scenario is that I have to pop the cowling and rope start off the flywheel.

Thanks again for the advice and the great diagrams too. I really appreciate it.

 

[Silvertip]

Re: Combining 36 volt and 12 volt together in one boat.

Or carry a jump start box. Your trim pump runs so seldom it is not an issue. It is the highest draw. If the bilge pump runs very often fix the leak in your boat. If you don't have a timer for the aerator/live well pump install one. Fish finder draws 1 amp (roughly) and the interior lights draw about 1.5 amps total. Stern light 0.5 amp. When the NAV light is on the engine is supposed to be running so no loses involved. A group size 27 deep cycle specification typically has a reserve minutes number of 175 or so while delivering a 23 amp draw. You have a sustained 2 to 3 amp draw. 175 minutes is just short of 3 hours. Your load is one tenth (roughly) of the 23 amp spec so 10 times 3 hours is 30 hours. I suspect you will be making a nature call well before 30 hours is up. Since the starting battery is not a deep cycle, you could cut the number in half and still have 15 hours before the starting battery would begaiin to get questionable. Batteries do get tired so if the starting battery is getting close to replacement, replace it with the largest deep cycle you have room & budget for. Yes -- people start big 500 cubic engine I/Os from deep cycle batteries. It is ok to use them for starting duty on an outboard. The livewell timer is a good power saving device.

 

[Fishsqueezer]

Re: Combining 36 volt and 12 volt together in one boat.

Awesome. Thank you again Silvertip. I do have a timer on the livewell. My hull doesn't leak at all so the bilge is really there to deal with heavy rain and spray from trolling in heavy chop (it's an open hull Lund Alaskan). I just replaced the starting battery with a brand new marine cranking batt a week ago, but the next one will surely be a hefty deep cycle.

 

[NYBo]

Re: Combining 36 volt and 12 volt together in one boat.

You can also reduce the load by switching to LEDs for the stern and utility lights.

 

[Fishsqueezer]

Re: Combining 36 volt and 12 volt together in one boat.

You can also reduce the load by switching to LEDs for the stern and utility lights.

Great, that's something I had planned to check into, but wasn't sure if I could get LED's for the light fixtures. I'm guessing that I'll be able to find some someplace.

 

[Fishsqueezer]

Re: Combining 36 volt and 12 volt together in one boat.

Thanks Bubba! That's good info. I'll take a look at trying that if I find that I'm draining my cranking batt too much with the misc. 12v power usages.