Rules and thoughts on main batt switch placement

Hi guys, so I am tearing into my boats crap-ass electrical system, because it just kills batteries, and wont start half the time.

I tossed two new 8d's in the other day, it killed them dead in two hours. Found bad regulator, a shorted isolator and battery switch so misdesigned, i could swear the government did it ....


The batteries, which are right next to the engine, go all the way to the helm, about 9', to the switch, which is a regular Guest a-b-ab, then back to the isolators, 3', then to a master disconnect, 1', then to the starter, 7-9'.... Im taking 80% losses..... The starter is bad, I'm sure from being chronically undervolted, I'm sure I'm going from 3000cca to less than 900cca due to line losses.


Question: I will toss the disconnect and put in charging and paralleling relays, but for a safety disconnect, can I put one down in the engine room?, I want to raise the batts for safety reasons, and all systems will be behind new breakers in engine room..... Can anyone see any faults with this?

My thought is when you smell an acrid odor, you want relatively quick access to the main switch.

Edit: ABYC E-11.6.1.2.2 (2008) "A battery switch shall be mounted in a readily accessible location and close as practicable to the battery."

Kind of ambiguous, even with the "shall".

You can buy remote controlled battery switches. Not "wireless" but they are relays with remotely mounted switches. Mount the relay near the batteries, mount the control switch where it's convenient.

I agree with the quick turnoff.... I have a man hatch to the engine room. I was going to put the two main disconnects there, as well as the mechanical instrument panel there in case of the planned N2k network failing, I just leave the hatch open, and can see the oil press, temp, pyrometer and warning lights...



The only things i want wired directly to the batteries without the ab switch is the starter motor.... Its an 8kw monster..... Prolly about 1100-1300 cranking amps....

Interstate buses use disconnect switches that will pass the amperage required to start a big diesel.

It would be fairly simple to install one with a pull cable that could shot off the batts in a fire.

The downside is there is no automatic field shut off (break before break) as in a quality rotary boat switch , so you could fry the alternator diodes..But it will pass the amperage required.

Batteries in the engine room will not last too long as 120F+ of the engine room is not good for them.
The 180F next to an operating engine is even worse!

In a fire the last thing you want to do is open a hatch to supply more air and let the fire up into the cabin.

For good safety a remote fuel shut off (cable is fine) as required on passenger boats is easy and cheap to rig.

Makes a good anti-theft device too.

IF you are able to turn off the electric and fuel, you might as well go all the way and get the fuel filter bank out of the engine room.

Far easier to change out a filter on a plugged unit in normal cabin temperature and with normal noise levels.
, with no fan belts ready to eat fingers!!

Hey FF, good points.... I have the emerg shutdown on the DD 8v71 to a pull cable at helm, normal shutdown is a woodward solenoid, detroit two-strokes loooove to run off like demons.....

I have been pondering the "fire ports" for through floor check and extinugishing... Was going to post that at some point.... I will look into remote batt cutoffs....


Has anyone here ever put a Snap Starter on they're boats?

Why reinvent the wheel? Get a new battery switch, proper cables and ends. Then switch out the isolators to charging combiners.

You really want to be able to kill the power without going into the engine space.

Is this a single engine boat? Do you have a Genset set?

Hey Bill, well said.... Fortunately, I own a 4-ton crimper to do brand new cables. Its a single screw Detroit 8v71, on an allison 2:1, no generator, I have Honda and Yamaha inverters at work, I can bring one home. ProMarine three bank charger, stock alternator regulator, bound for the dumpster, new three stage going in.

Would also like to dump the single 8d battery rig with a twin group 31 setup. Smaller and cheaper, we have to pull all batts out here at the end of season, they will explode at -40 otherwise.

FF, I will admit that my years in 20hp to 3000hp generator repair have taught me to put the batteries next to the starter.....RIGHT next to the starter.... I will admit its not ideal on a boat... I need to get engine room temps, but I have only been out on the water twice with the boat, mainly due to electrical problems.

I need to get engine room temps

I have never heard of an engine room being too cool , just too warm.

The local junk yard can supply radiator fans (Mercedes is quiet) that can be used to suck much of the heat out .

Do not pressurize the space as the engine smells will be blown thruout the boat.

With a block heater your 8V should start in 10 seconds or less , so will not tax the batt cables if 10 ft or so.

Here is the thread of what I did to Skinny Dippin's charging system two years ago and it worked perfectly:

http://www.trawlerforum.com/forums/s4/winter-project-i-charging-system-upgrade-5641.html

Tdot said:

Hi guys, so I am tearing into my boats crap-ass electrical system,.. Can anyone see any faults with this?

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Yes, knowing who to trust and believe is a crap shoot. Suggest you find a GOOD marine electrician who can draw up a plan and advise you. Doing it the marine way vs shore will make your job much better especially since you have a steel vessel.

Well, the former owner called me this morning, told me where the spare alt and starter are on board, so I'm going to bring everything back to my shop and test EVERYTHING. Installed my massive Fluke power analyser on the cables, and did a couple of start tests... Results?

Batt 1 Positive: 944 CCA output on crank
Batt 2 Positive: 891 CCA output on crank
POWER AT STARTER: 1008 A

All terminals clean, switch blades and wipes cleaned with 100% propanol (everyone should have a bottle of this stuff, IMHO), everything tight

Cables are too long, switch too small, starter is iffy....

I guess I have my work cut out for me in spring. I cant wait to get it closer to where I live, its a 90 minute drive to the boat right now.... :-(

I will sketch up my new diagram, show it to all of you.

>Suggest you find a GOOD marine electrician who can draw up a plan and advise you. Doing it the marine way vs shore will make your job much better especially since you have a steel vessel.<

No need to hope to find an educated electrician, the boats in your marina have what you need.

The big brands Hat, Bertram , and all the rest have stock schematics that can be used.
Or a book like Calders will have proper information.

Only difference over the years is folks used to have 2 sets of house batts , and a start batt.

Today its more usual to have one large house set to slow the discharge rate.

The house switch in BOTH does this for you on an old system..

A reserved engine start batt is OK , although some dont bother IF the house bank is substantial..

FF said:

....... No need to hope to find an educated electrician, the boats in your marina have what you need............l.

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Electricity and water can make lethal combination. Attempting to copy another boat's electrical system might work for some folks but if you don't understand why the red cable goes here, the black or yellow cable goes there, the switch goes here, the fuse goes here, etc., there's a good chance you will do something incorrectly and get less than optimum performance from the system or possibly damage the boat or create an unsafe system.

Much of my former job was correcting the mistakes of people who dried to do things themselves. The average person does not understand how electricity works.

The average person does not understand how electricity works.

Tdot seems to have an idea of what is required.

The problem is seldom with folks that Know they have no idea what they are doing.

The hassle is the >its good enough< fellow with duct tape , bailing wire and home electrical wire.


I would take the cabling off the crap rotary switch , and try bolting it together (copper bolts , nuts and washers ) and run the amp test again.

Few rotary switches will handle 1000A of load. Although a 10% voltage drop at 1000A is not that bad!

I agree with Ron at post #3...a remote-operated battery switch is a great thing. Can control from the helm or wherever convenient while keeping heavy battery cabling as short as possible. Keeping batt switches out of engine room is a good thing....batteries too, if you can manage it.

A couple things I have learned while rewiring 3 or 4 boats over the years for what they are worth.

I would rather have my batteries in a cool handy place and use larger/longer cables. I am very happy with the BlueSea ACR, it does automatically what you should be doing with your battery switch. One mistake with a battery switch without a field disconnect will pop your alternator diodes. BlueSea and HoleHersey have good diesel rated ones. The battery switch should be accessable w/o lifting a hatch. Special regulators are nice but not necessary especially if you don't need to charge at anchor often. A single belt drive can only handle 100A max alternator. Simple and understandable beats fancy and complicated.

FF said:

I need to get engine room temps

I have never heard of an engine room being too cool , just too warm.

The local junk yard can supply radiator fans (Mercedes is quiet) that can be used to suck much of the heat out .

Do not pressurize the space as the engine smells will be blown thruout the boat.

With a block heater your 8V should start in 10 seconds or less , so will not tax the batt cables if 10 ft or so.

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I second that.I have a pair of fans mounted in a shroud from an 2004 Pontiac Bonneville.The fans are rated at 1200cfm each,total 2400cfm,and cost me $30.They can be driven independently.If I am not mistaken,they are rated at 20 amps each,40 amps total.These fans aren't extremely loud,but they do suck air through a 1 inch thick AC condenser and an 1 and 7/8ths thick radiator in the car.They're going into my 1990 Mercury Blue Max Cougar to cool a 400hp V8 with AC.

Sorry.I kind of strayed off topic there.

rwidman, I couldent agree more.... I have worked on towers with 100,000v safely, but have had my ass kicked by a 400 Amp welder when working soaking wet....

I will use a Blue Sea RBS, next to the ACR's for all the house and starter loads:
ML-RBS Remote Battery Switch with Manual Control - 12V DC 500A - Blue Sea Systems

I will build a new master panel for the boat, and add a paralleling switch in the engine room, or near the batteries for emergency crank assist. My Honda generator also plays into the safety margin, as my charger isn't bad.

I am trying to figure out WHERE to put the batteries, as the only non engine room locations are FAAAR from the engine (8-14').

I know the DD 8v-71's are fairly common as diesels, especially on the Hatteras', but I am curious where they keep they're batteries, as the cables have to be suuuper heavy for any substantial distances.

I was working on a fire pump the other day, had to convert it from 24v to 12v because of the building fire panel. And I kept the cables short for a 17L inline 6 Marine cummins.... 4x 8D Batteries, and those cables JUMP when we crank, and they are properly sized....

This is tricky!

>cables have to be suuuper heavy for any substantial distances.<

Mostly if the engine will be cold started below freezing in an unheated ER with no block heater.

For most boats thats not a common requirement.

On coaches with 8V71 10 ft is common , and they DO have to start in the cold , unassisted.

ML-RBS Remote Battery Switch with Manual Control - 12V DC 500A - Blue Sea Systems

After actually measuring a 1000A starter draw , why a 500A merge switch?

Remember the measurement was probably with 100% charged batts , the amps will go way up when merging dead batts .

I thought most of the Hatts, epecially the larger older ones, were 32V. Later models, are Now 24V i think , at least for the starter systems and then maybe 12v. That would keep the wire size down over 12v so the batts could be located farther away yet not have to go nuts on wire size.

Parallel wires between the batteries and the starter if needed to keep Vdrop under control. If not enough room to directly connect parallel to the starter then use a small buss bar or power post with a short, heavy wire to make the final short run.

I have no idea what is practical aboard your boat, just some ideas, good or bad.

FF, the rbs tech spects had the following:
Continuous Rating 500A
Intermittent Rating 700A (5 min)
Cranking Rating 10 sec 2500A
Cranking Rating 1 min 1100A

Its tight, but should be good.... And what you said about voltage is spot on, i have a feeling tha the cranking amps were high because of small cables.... They are size 0 going all over.... Im going 4/0 to keep voltage drop minimal....


C lectric, I noticed that Guest has switches set up to take paralleled cables on its diesel engine line....

I have in my hands now a new starter, I hope to get down there this weekend and see how she behaves.... Unfortunately, its only 34F here this morning, I guess that I should be watching the COLD cranking amps!

I guess that I should be watching the COLD cranking amps!


Just install a block heater , they are easy to install and not very expensive.

I just so happen to have 6 Kim Hotstart Recirculating block heaters in stock, complete with thermostats..... Now I just need to put a contactor linked to my cellular monitoring equipement, and I can start it up by text message..... or maybe I am geeking out too much!

. or maybe I am geeking out too much!

Depends on the distance to the boat , the required warm up time and the OAT

(outside air temp)

In post 12, you tested the starter at home.
What was the starter turning?

bluebyu, it sounds dumb, because its not overly scientific, but I use a photo tach, and see how quickly it gets up to a good rev, and usually call my local heavy truck shop buddies to tell me what it should be spinning at....

I had bought a Bucket truck at work a while back, started like garrrrbage.... Just a little cummins B5.9 six with 12v, would struggle to start.... Pulled the starter and it whirred up slowly to 510RPM without even a twitch when on the ground upon power up..... I brought it to the rebuilders, he hooked it up and laughed. I came back the day later, he said it was burnt to a crisp, hooked it up and watched it jump 4" off the counter with power applied. Same with some big Perkins, midsized AC, Cat 3208's, Volvo 16L's, a good starter motor should be shockingly powerful.....

I will have to post elec pics soon.... I keep finding nightmares....

I would assume the starter amps spinning free versus spinning the engine would be drastically different.

bluebyu said:

I would assume the starter amps spinning free versus spinning the engine would be drastically different.

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The harder the starer has to turn the higher the amp draw goes up.Most starters are rated at unloaded amps.




Nothing worse than having the wrong size relay and a run away starter motor.I watched one burn up while trying to get the 2000 degree battery connection loose.It was on my hot rodded Jeep with a built 304 V8.

Tdot
You are getting onto the right track with Blue Seas gear. Use the RBS but also have the manual switch at the helm.

You can isolate by manually turning the yellow switch in the ER, or flicking the rocker switch at the helm. Also use an ACR.

First pics is my ER config for 2 start batts and house bank, then the auto parallel & isolate at helm, and lastly the RBS and ACR components