Dual battery wiring dilema

[ShoestringID]

I am really struggling with this question and hope to get some good advice here...
I have a 15' fishing boat with a 25 HP electric start outboard, an accessories wiring harness/switch panel (bilge, livewell, lights), an electric trolling motor, an onboard dual battery charger, and 2 size 27 deep cycle batteries. I am wondering what the best way to wire all of this is to 1) always give me enough power to start the outboard and 2) make the best use of power for trolling with the electric motor and 3) give me an emergency safety margin at all times. One note: The generator output of the outboard is insufficient to use an automatic battery switch (or so the documentation states)
I am thinking the following would be a good option for me:
Wire the charger directly to each battery. In the garage the charger will be able to sense the needed charge in each battery separately and charge appropriately.
Install a manual dual-battery switch with a 1, 2, both batteries option and wire the batteries, outboard, and accessories harness to the switch
In normal running the switch will be set to battery 1. This will allow the outboard to provide a run-time charge to battery 1
Wire the trolling motor directly to battery 2 (not the switch)
This would allow me to troll from battery 2 without endangering the starting capacity of battery 1
In a battery1 power emergency I have the option of battery 2, or both to get the outboard started. In an "total outboard failure" emergency I have at least one charged battery to limp back to the dock with the electric motor.
If I'm being an electrical idiot please shoot holes in my plan
Much obliged to anyone that can help!

 

[captain zac]

Re: Dual battery wiring dilema

http://www.cmsquick.com/tech_03_batsys.html

 

[ShoestringID]

Re: Dual battery wiring dilema

Thanks for the response captain zac... I have seen all of those diagrams in the last few days (and many more) and to be honest, none of them truly represent my setup. I'm hoping someone can tell me "your idea isn't bad and should work" OR "You're an idiot and will melt that pretty new aluminum boat in no time" if you go that direction.

 

[PuddleJumper]

Re: Dual battery wiring dilema

Your plan oughta work just fine

 

[fishrdan]

Re: Dual battery wiring dilema

Your plan sounds good.

With the batt switch and TM direct connected to Batt2, you could flip the batt switch over to BOTH if the outboard died. So you could limp back to the dock running the TM off both batteries.

 

[ShoestringID]

Re: Dual battery wiring dilema

Thanks for the sanity check everyone! It sounded logical but we all know how logic works out from time to time.

 

[5150abf]

Re: Dual battery wiring dilema

Sounds like you thought it through very well and your plan should work just fine, I am super crazy about running out of power and installed 2 house batteries with a seperate starter and I can jump one of the house batteries if I ever run out of juice.

But yes your plan is sound.

 

[FunInDuhSun]

Re: Dual battery wiring dilema

.....or you could just carry a set of jumper cables.
Seriously, when the starting battery goes down I simply jump it from my trolling battery. No switches or extra wiring needed. I use trickle chargers when storing.

 

[Silvertip]

Re: Dual battery wiring dilema

In my view this is way overkill. Why? Good heavens, you have a 25 HP motor that likely has a rope start pointing at you, and if not, it can still be rope started by removing the cowl and winding up the rope. If it doesn't start off the battery which would have to be really drawn down, there is likely something wrong with the engine. Next, the alternator on that engine is designed to charge only the engine battery so the switch is an unnecessary complication. Keep in mind also that if you wire the troller battery to the switch, even if the troller is connected directly to the battery, should you forget to turn the switch to BAT 2 from BOTH, you would still be drawing power from the start battery as well. Will your system work? Absolutely. But you have a group 27 starting battery. The few accessories you have on that boat could easily be left on the starting battery, and the troller left to serve troller duty. You simply do not have high-current draw items. Locators, don't use much juice. If you put a timer on the live well pump that too cuts power consumption dramatically on that unit. Suit yourself, but I've run lots of boats bigger than yours with dual locators, full instrumentation, VHF and AM/FM radios, front and rear live wells and nav lights for night fishing and never had a starting battery issue. There is an application for switches but on small boats I don't feel it's necessary. Jumper cables are cheap if you are still worried.

 

[ShoestringID]

Re: Dual battery wiring dilema

So Silvertip... your suggestion then is to simply wire the engine and accessory harness to battery 1, wire the trolling motor to battery 2, wire the dual on-board charger to each battery and be done with it? I'll admit it simplifies things...

 

[Silvertip]

Re: Dual battery wiring dilema

Absolutely. The boat side accessories (lights, horn, instruments, locator, bilge pump, live well, etc) are probably already wired that way as they are on most boats of that type. You don't need to change anything. Just wire up the troller and dual bank charger and go fishing. No need to add a bunch of potential points of failure to what is a working system.

 

[captain zac]

Re: Dual battery wiring dilema

shoe

Check the wiring diagram for your charger
most of the new smart chargers want you to wire through the bat switch
also keeps you from having a birds nest of wires at the bat.
this also allows you to charge with the bat switch in the off position.
just a thought not sure what kind of charger you have

Harry

 

[Silvertip]

Re: Dual battery wiring dilema

What birds nest of wiring. There should be nothing more than the large battery cables, the boat-side harness and the charger connections at the starting battery. Possibly an automatic bilge pump if using one. Even then, the auto-bilge pump should go on the troller battery. Wiring the charger directly to the battery or the switch makes no difference electrically. Adding the charger connections at the switch very likely means a longer run of wire and adds two more points of failure. Once again, if you had a larger engine with a high-output alternator THEN we could talk about whether a switch or VSR is good idea and how to incorporate it for maximum effect.

 

[ShoestringID]

Re: Dual battery wiring dilema

zac... The charger is a Minn Kota 220D dual 10 amp. Minn Kota has this annoyance of not offering any manuals online via their web site and the charger hasn't arrived yet. When it does I'll check the manual to see if it talks about wiring through a switch or direct to the battery or if they recommend one way or the other. I do still like the idea of the battery switch in the off position killing all the electronics when the boat is garaged. I was just reading the manual for my Lowrance Elite-5 DSI unit which has a "standby" mode and they warn that if you forget its in standby it will drain the battery. You would think they could program enough intelligence into a $600.00 unit to turn itself off after a certain amount of time in standby... sheesh...
Thanks for your input!

 

[ShoestringID]

Re: Dual battery wiring dilema

Silvertip... unless Minn Kota has another recommendation for the charger wiring I'm leaning towards your more simplistic approach at least initially to see how it works out.

 

[bowman316]

Re: Dual battery wiring dilema

i have pull started my 70 hp evinrude before in a pinch. If the motor is hot, alomst any sized outboard can be pull started, it you have the throttle up, and choke on.

mine has a rope rolled up in a pocket inside the cowling (motor cover). You just put the end of the rope in this slot on the flywheel, then wrap it around, and pull.

but I would save 1 batt for only starting, then use others for trolling. The motor will not charge much unless you are running it for hours.
You could hook up 2 batteries in parallel (pos. to pos.) and hook them to battery 2. Then use a single batt on 1, for starting. So that way number 2 pos on the switch would give u 2 batts for trolling. If you had 3 batts total.

 

[Silvertip]

Re: Dual battery wiring dilema

Electricity doesn't care how it completes its way around a circuit. What it does like is the shortest route with the least amount of resistance. Multiple connections in that route increases the chance of introducing resistance. Resistance creates heat. If you find something that is contrary to what I've suggested, post the reference(s) here as I'd really like to see it. Minnkota and most other charger manufacturers point out that their output leads should not be lengthened unless you use one of their extension kits. The reason is that (Minnkota for example) has thermisters installed in the output lead to monitor battery temp which also relates to gassing. The charger can therefore react accordingly. If one connects the charger to a switch, that circuit may not function properly and you cook a battery or create excessive gassing and loss of electrolyte. Use the KISS principle and you will not be disappointed.

 

[royal0014]

Re: Dual battery wiring dilema

Electricity doesn't care how it completes its way around a circuit. What it does like is the shortest route with the least amount of resistance......Use the KISS principle and you will not be disappointed.

Best advice yet. Sticky material......


<<)))(((>>

 

[ShoestringID]

Re: Dual battery wiring dilema

First off I want to thank all you folks for your input and responses! This is quite a good boating community and I'm glad I signed up!

Silvertip, The thermistors in the Minn Kota charger to monitor the batter temp, and the auto-shutoff feature are several of the reasons I went with that model over others. It makes sense then that if the charger isn't connected directly to the batteries, the temp sensors cannot do their job appropriately.

Bowman, To be honest I hadn't even thought about being able to pull start the engine in an emergency... I was so happy to have electric start finally that pull starting it hadn't even crossed my mind... Duh! I'm not going the 3 battery route for lack of room and just plain overkill. I already think I'm overkilling with 2 - group 27 deep cycle Trojans.

I AM wondering now if I might be well served to wire the batteries in parallel? While that would no longer isolate the starting/accessories from the trolling motor, the advantage might be even wear and lower total discharge on both batteries... perhaps extending their useful life. These batteries each have 620 CCA, 760 MCA, and reserve capacity of 200 minutes. I'm betting that even a 12 hour fishing trip with lots of trolling wouldn't drain them down to the point where the engine won't crank. Any input on that option would be appreciated.

 

[Silvertip]

Re: Dual battery wiring dilema

Nope -- wrong philosophy. No two batteries are ever perfectly identical in capacity. So paralleling them will always result in equalizing the two. I get the feeling you still want some sort of switch and again -- it only complicates a very simple system. What happens then when you have two batteries that actually look like one giant battery to BOTH outputs? Neither one knows what to do since the two outputs are bridged even though they are connected separately to the batteries. Remember, you have paralleled them. Optimum battery life is obtained by 1) monitoring electrolyte level, 2) never discharging completely, 3) charging immediately after each use -- not just before you use them. Deep Cycle batteries are designed to be deeply discharged but certainly not killed. If you feel you really need to switch between batteries, use two high-current plugs so you can pop the troller connection between either battery (two troller sockets for example). No switch, no potential points of failure, and above all, simplicity.