LM18 Houston Tx

To help other builders, please list the boat you are building in the Thread Subject -- and to conserve space, please limit your posting to one thread per boat.

Please feel free to use the gallery to display multiple images of your progress.
TomW1
Very Active Poster
Very Active Poster
Posts: 5844
Joined: Sun Apr 19, 2015 10:57 pm
Location: Bryson City, NC

Re: LM18 Houston Tx

Post by TomW1 »

I'll be honest I like to separate my systems. A starting battery, a house battery and then the trolling batteries. Place the starting near the motor, the house in the console, you can charge both of these with the motor. The trolling batteries are placed in the bow and charged daily at home or at the dock with a wired charger. This prevents the problem in your drawing.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

ericwensel
Frequent Poster
Frequent Poster
Posts: 73
Joined: Sun Jul 05, 2020 10:31 pm
Location: Texas

Re: LM18 Houston Tx

Post by ericwensel »

I appreciate the feedback.

I don't want to give up on the idea of using one of the two trolling motor batteries as an emergency starter battery using a switch. I do have all three batteries near the bow (between bulkheads b and c). I did that for weight distribution purposes and so i could mount the charger permanently on the boat and it be relatively close to the batteries. I did adequately size the starter cables considering a fairly high peak amp draw and the recommended voltage drop. I am using 1/0 cables.

That being said, i now understand (with the help of the feedback) that the updated sketch i posted was still very wrong. In fact, i think it was down right dangerous. What i labeled as ground going to the trolling motor battery would have in fact been at +12V and the other terminal would have been +24V. I am definitely not going to rush into a solution. I posted a new sketch not because i know it is right but because i am a little embarrassed to have posted the previous sketch that was so dangerously wrong.

As for charging, the trolling motor battery (when used as a starter battery) would only be used in emergency and would not be run as a starter battery for longer than necessary, after which both trolling motor batteries would be charged back to full charge using the onboard battery charger (while at the dock). Normally the trolling motor battery is isolated from the motor.

The new sketch is shown below.
Image

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10198
Joined: Tue Jan 12, 2010 12:25 am

Re: LM18 Houston Tx

Post by fallguy1000 »

You realize that the motor is going to charge the trolling bank unevenly?

So you will run your trolling motors down and switch the engine over and charge half of the bank. This is not good.

You need to use a combiner if you want to mess around like that.

I have the big fancy boat and I can't even do what you are attempting because I'd mess up my house bank, not to mention all the extra wiring. I can charge my house or in your case trolling battery with the engine with dc-dc step ups which I have, but not the other way. If I had to use the house battery to start/run an engine; it requires a physical move..
My boat build is here -------->

viewtopic.php?f=12&t=62495

Dougster
* Bateau Builder *
* Bateau Builder *
Posts: 3296
Joined: Tue Jun 06, 2006 11:05 pm
Location: Texas

Re: LM18 Houston Tx

Post by Dougster »

Pair of jumper cables on board?

Dougster

TomW1
Very Active Poster
Very Active Poster
Posts: 5844
Joined: Sun Apr 19, 2015 10:57 pm
Location: Bryson City, NC

Re: LM18 Houston Tx

Post by TomW1 »

You still have grounds going to BB2 so this does not work, there is no longer a ground, both poles are hot on BB2. Just do what FG and I said and add a house battery, it only needs to be a group 27 to start your smaller motor. It will uncomplicate your life a lot. I just do not see a way to do what you want to do and I'm a pretty good electrician There may be a way to do but if FG or I can't see it I doubt it is there. I have never seen a 24V trolling bank used as a back up for the main battery for the reasons you having.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10198
Joined: Tue Jan 12, 2010 12:25 am

Re: LM18 Houston Tx

Post by fallguy1000 »

BB2 is a ground bus...nothing hot about it, there will be potential there between some of the devices based on the operating parameters (on/off, etc)..but that is normal..
My boat build is here -------->

viewtopic.php?f=12&t=62495

User avatar
BarraMan
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 2164
Joined: Tue Dec 11, 2012 3:44 pm
Location: Australia

Re: LM18 Houston Tx

Post by BarraMan »

My head hurts looking at that wiring diagram - but I’m pretty confident it won’t work! In fact I’m not sure you are even going to get 24v for the trolling motor wired up that way!

Save yourself a lot of heartache and plan for a crank battery, a house battery and 2x batteries for the 24v trolling motor. Put the crank and the house on separate master switches with an interconnect switch that will let you get a start if the crank battery fails (been there done that - 50 miles out from the boat ramp!) :help:

You can run the trolling motor on a separate 24v circuit.

I, being me, have a more complex setup. Essentially as above but with a 12v - 12v smart charger between the crank and the house batteries. I also have a 12v - 36v smart charger between the house and my trolling motor batteries (36v).

I have mains smart chargers, 12v and 36v, for the crank/house batteries and the trolling motor batteries, respectively, when not on the water.

My backup backup is to pull one of the trolling motor batteries and use a set of jumper leads to get a start! :D

User avatar
Jaysen
* Bateau Builder *
* Bateau Builder *
Posts: 6498
Joined: Wed Aug 05, 2015 7:59 am
Location: St Helena Island, SC
Contact:

Re: LM18 Houston Tx

Post by Jaysen »

Or go buy a jump box for emergencies. They make them very small but powerful these days. Then you don’t need bulky cables. We can start a 2008 Optimax with a $50 box from Amazon. Charges from the USB port once the motor is running.

In the event the jump box is dead because you forgot to charge it (like I did) then you pull a trolling batter and move it to cranking location for a start (which is why I demand someone show me a wrench that fits the bat terminals before we leave the dock!).

Keep
It
Stupid
Simple

Much easier to keep running and fix when an idiot like me can figure it out.
My already completed 'Lil Bit'. A Martens Goosen V12 set up to sail me to the fishing holes.
Currently working on making a Helms 24 our coastal cruiser.
“Mark Twain/Samuel Clemens” wrote:Eat a live frog first thing in the morning and nothing worse will happen to you the rest of the day.
Jaysen wrote: Mon Apr 29, 2019 3:44 pm I tried to say something but God thought I was wrong and filled my mouth with saltwater. I kept my pie hole shut after that.

TomW1
Very Active Poster
Very Active Poster
Posts: 5844
Joined: Sun Apr 19, 2015 10:57 pm
Location: Bryson City, NC

Re: LM18 Houston Tx

Post by TomW1 »

fallguy1000 wrote: Wed Mar 16, 2022 5:21 pm BB2 is a ground bus...nothing hot about it, there will be potential there between some of the devices based on the operating parameters (on/off, etc)..but that is normal..
Your right fg BB2 is a Buss bar not a battery It just did not have a wire coming out of it so was confusing. My apologies if I confused anyone.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

Cbuf
Active Poster
Active Poster
Posts: 356
Joined: Sat Mar 30, 2019 10:38 pm
Location: Wisconsin

Re: LM18 Houston Tx

Post by Cbuf »

Just an FYI I have a 55lbs trust trolling motor (single 12v) and I can hold in a strong current with anchor lock. Unless you are going with a auto stow and deploy, I would stick with a 12v system and not mess with a 24v. 55lbs is plenty for the boat. However if you want to go with 24v and charge from the starting, you need a special converter. Minnkota sells them in 12 to 24v and 12 to 36v. you can't go from 12v starting to 24v without unpluging your trolling motor or having a switch to break the series. Also, the Ulterra is 50-100 lbs heavier than the standard riptide 55, so plan your weight accordingly. 3 batteries and an ulterra in the front is too much unless your gas tank and livewell are in back.

my 2 cents
See my LM 18 build here.
viewtopic.php?t=64254
See my LM 18 Questions here.
viewtopic.php?f=2&t=64299&hilit=lm18\
Finished Boat Here
viewtopic.php?f=25&t=65173

Post Reply

Who is online

Users browsing this forum: Ahrefs [Bot] and 9 guests