Safe to dash-mount battery switch? And right next to electronics (VHF, GPS, Tach)?

[ajgraz]

Due to possible interference from the device itself or the power wires running to it (or for any other reason), is there a safe minimum mounting distance between a battery switch and sensitive electronics, like: VHF radio, antenna or antenna cable? GPS receiver(s)? Fishfinder / sonar / transducer cabling? Tachometer?

Right now got one battery in a box in a compartment near the stern (everything is hooked to it) and an identical "spare" (nothing hooked to it but 2nd bank of onboard charger) in a box under the console. Thinking of putting both batteries under the console (for weight distribution reasons) and installing a battery switch, probably this Blue Seas m-series 6007:

https://www.bluesea.com/products/600...y_Switch_-_Red

(And of course new, longer, beefier starting cables, and beefy cabling from batteries to the switch and to ground)

Trying to find a good location to surface mount the switch. I read that it wants to be accessible in case of emergency, which I take to mean "within arms reach while operating, and not fumbling with any covers or hatches." There are a few spots on the face of my console (or in the dash) where it would certainly fit, but most of these locations may put the switch (and the power wires to it) within an inch or two of one or more of the aforementioned electronic devices. Is there any issue with that?

On the topic of the safety of surface-mounting on, say, the dash--how easily can these switches be accidentally "bumped" into a wrong position with the sweep of a hand? (This is one reason I'm definitely not putting it anywhere my knees will knock into it! Already had to move ignition and kill switches for that reason.)

 

[Scott Danforth]

you may get interference with the motor running as you now turned the really long battery cables into an antenna and the pulses from the outboard stator may cause static

however, two things come to mind

battery switches are not intended to be on the dash. these are high current switches. if you have a high current issue, wont really matter if your battery switch is within arms reach or at the aft of the boat. some cable is going to glow red somewhere

motors dont like voltage drop due to long battery cables. so you have to significantly upsize. depending on the length of your battery cables, you may have to go up in size to either 0000 or 350MCM. if our over 30' total, your in the 500MCM territory (thats a 7/8" diameter conductor)

 

[ajgraz]

you may get interference with the motor running as you now turned the really long battery cables into an antenna and the pulses from the outboard stator may cause static

however, two things come to mind

battery switches are not intended to be on the dash. these are high current switches. if you have a high current issue, wont really matter if your battery switch is within arms reach or at the aft of the boat. some cable is going to glow red somewhere

motors dont like voltage drop due to long battery cables. so you have to significantly upsize. depending on the length of your battery cables, you may have to go up in size to either 0000 or 350MCM. if our over 30' total, your in the 500MCM territory (thats a 7/8" diameter conductor)

Don't know if it matters as regards interference, but the outboard has a 65amp alternator rather than a stator (2012 Merc Optimax 125).

I am glad you brought up cable size, I was going to ask that later; if I ran it the way I'm envisioning, the cable from either battery to the switch would be maybe 4' to 5' max, and the cable from the switch to the engine would run perhaps 16' to 18'. What gauge cable are we talking about for a 20-23' total run?

Now, when you say a battery switch is not intended to be dash-mounted because it is a "high current device," is that due to it being a shock hazard (or other type of safety) issue?

(I'm beginning to think it would be best to mount the switch in a covered recess, I guess at about knee level on the console--probably cut my total cable run to 18-20', too).

 

[Scott Danforth]

doesnt matter at all with interference, stator and alternator both produce pulsed DC voltage after the diodes in the rectifier


total run of 20-23' for all cables, or is the switch that far away from the batteries (in which you would double the length to get battery cable run)

you have to go from ground on motor to battery, batter + to switch common, switch to batteries, etc.

for a 200 amp load (estimating starter draw), my guess is a 00 cable minimim if this was an I/O, 0000 cable minimum

Whats wrong with mounting it back by the transom where the batteries are?

 

[ajgraz]

I already placed one battery (my "spare") into the console to help reduce butt-sag (and water on deck) with this pig-heavy outboard on this low-decked, notched transom 17' CC. The biggest part of the idea here is to see about getting the other battery forward of center-of-gravity, too.

My (revised) 18' to 20' estimate would be the 1-way distance from either battery (through the switch on "+", or through I guess a big grounding post/stud on "-" ) to the motor.

Although I suppose that if I did move that battery up I could cheap out, get no switch (and covered switch box), and just swap leads if Batt 1 craps out...slightly easier than existing plan of physically swapping the batteries. Still leaves me needing 16-18' (each way) of beefed up battery cables, though.

00 size, really? I was hoping to hear "no bigger than 4/0 needed." That copper stuff costs some real money!

 

[Scott Danforth]

with 18-20' in one direction, that is 36-40' of battery cable run (you have to get there and back)

so you are probably in the 0000 range, you may be able to use 00 assuming you dont try to start a motor below say 40 degrees. yes, that is a 0.406" diameter conductor, and yes, in a tinned marine battery cable at a bit over $8/foot retail, it gets costly

Boating is an expensive hobby

 

[ajgraz]

Note: I meant to say "4 gauge" not "4/0 gauge"

I poked around on my shop manual CD, and to my surprise it has a chart for battery cable size vs. run length. Surprisingly, it recommends that for a 20' one-way (40' round-trip) run that I use 2AWG. That seems small, that's going to allow almost 10% voltage drop at 200 amps. I can see where stepping up to 2/0 would reduce voltage drop to <5%, and it is my understanding that these Opti's do not like voltage drop.

(BTW, it doesn't get below 40?F here except on a few rare January mornings!)

I can see that we're talking at least $250-300 just for 2/0 cables...makes the switch part seem pretty cheap!

 

[strokendiesel002]

Can you post a sketch of what you are planning? Simple over head, where you're going to put the batteries and switch?

 

[mla2ofus]

Run your oversized and longer cables, attach both battery grounds back at the motor end to a Ford style solenoid. Power the solenoid with a wire from one batt pos post run thru a toggle or simple key switch mounted on the dash. Ground the solenoid to the batt ground cables.
Mike

 

[dingbat]

doesn't matter at all with interference, stator and alternator both produce pulsed DC voltage after the diodes in the rectifier

which is removed by the capacitors on the output of the rectifier circuit.

Moving the batteries to the console is a pretty common move on smaller CC. Gets the weight off the transom for those that fish from the rear of the boat.

Put the switch under the console next to your batteries and install properly sided cables from the switch to the starter.

You can easily get by with a 10% drop.

 

[km1125]

which is removed by the capacitors on the output of the rectifier circuit.

Whatever capacitors are in the regulator can't compensate for the ripple coming out of an alternator/stator. Most of that is absorbed in the battery. There are tachs out there which rely on this ripple and also cutesy things like this (attached) that use that ripple to make a 4cylinder sound like a V12.

Can't imagine you'd need something larger than 2/0, but I guess it's highly dependent of how sensitive the optimax is to voltage drop. I would think the manual would give you the best recommendation on what the engine can tolerate. You can also cut down the total length of more expensive cables by substituting even larger (0000) for a couple small sections so that you can keep the large section to a 2/0.

 

[fhhuber]

https://www.bluesea.com/resources/1437

You need to know the current to be able to choose the right wire gauge.

For short duration loads you can often seem to get away with a smaller wire because you aren't giving it time to heat up as much as it would with a continuous load. But after a couple of years in service you'll have had the insulation hot enough for enough total time to begin cracking.

I don't advocate doing the long run in sections of varying gauge. Each transition is a source of resistance greater than the wire.

Best is to put the battery cut-out switch as close to the battery as possible and forget the long run.

 

[km1125]

https://www.bluesea.com/resources/1437
I don't advocate doing the long run in sections of varying gauge. Each transition is a source of resistance greater than the wire.

To clarify:

I am not advocating splicing the wire... just using different sections like between the battery and the switch at 0000 instead of a 00. This may be 4', which might cut down the total length of 00 calculation from 20' to 16' and put it further into the "acceptable" range for the manufacturers engine. The transitions would be the same, because they are the terminations on the switch, regardless if they are all 00 or some are 0000 and some are 00.

 

[ajgraz]

I appreciate all the input so far.

I could see considering 2awg sections at the motor end and between batteries and switch, then 2/0 for the longest section in between, all terminated at posts, of course. But I'm not sure that this would be significantly less expensive, and I would like to minimize terminations. I'm not sure that any bigger than 2awg will fit through the rigging grommet or the pathways under the cowling though.

I'd up my budget a couple hundred bux NOT to have to do the solenoid thing, though!

Dingbat seems to understand exactly what I'm trying to do, and why:

...Moving the batteries to the console is a pretty common move on smaller CC. Gets the weight off the transom for those that fish from the rear of the boat.

Put the switch under the console next to your batteries and install properly sided cables from the switch to the starter.

You can easily get by with a 10% drop.

Do you have a (definitive / trusted) reference on the 10% drop being acceptable? In web searching, I've seen references on starter circuits that say 3%, 4%, 5%, 6%, 7%, 8%, 10% and 15%.

I will say that the chart in the FSM on this motor seems to allow nearly 10%, in fact with the stock 10' (each way) 4awg cables (mostly coiled figure 8 style) now on there, I've got a calculated near 10%, and that hasn't been a problem...yet.

(Not since I moved the starting battery out of the manufacturer's original dumba** location in the bilge and cleaned the connections, anyway.)

 

[jhebert]

Due to possible interference from the device itself or the power wires running to it (or for any other reason), is there a safe minimum mounting distance between a battery switch and sensitive electronics, like: VHF radio, antenna or antenna cable? GPS receiver(s)? Fishfinder / sonar / transducer cabling? Tachometer?

You should realize that the power cables from all the devices you mention actually are directly CONNECTED to the battery circuit. I don't see that there is some particular concern that the operation of these devices might be affected by some sort of capacitive coupling to the battery circuit by their power cables since those power cables are already directly connected to the battery. If there is noise on the battery circuit, it will be carried directly into the devices on the power cables.

Cables connecting external sensors, like radio antennas or SONAR transducers, to devices that amplify those signals, like radio receivers or SONARs, should be shielded cables, and in general should afford some protection against ingress of noise signals into those cables. That said, it is a good practice, particularly with cables connecting SONAR sensors to the SONAR, to keep those cables away from other electrical cables; some ingress of noise into the SONAR is possible, despite use of shielded cable. This is a particularly true of engine harness cables which, on older outboard engines, tend to have rather high-voltage switching transients carried on them in the engine-shut-off or safety lanyard circuit.

For radio devices, the antennas themselves need to be located away from sources of radio-noise and radio-interference. Radio-frequency noise signal sources are more likely to be coupled into the radio via the antenna than by some sort of leakage into the transmission lines connecting the antennas to the radios. If a radio-frequency noise emitter is near the antenna, that interference will be picked up by the antenna and conveyed directly to the radio receiver.

As for concerns about the safety of the location of the primary battery switch on a boat, earlier replies have commented on that with good advice.

 

[km1125]

I appreciate all the input so far.

I could see considering 2awg sections at the motor end and between batteries and switch, then 2/0 for the longest section in between, all terminated at posts, of course. But I'm not sure that this would be significantly less expensive, and I would like to minimize terminations. I'm not sure that any bigger than 2awg will fit through the rigging grommet or the pathways under the cowling though.

I think we understand what you want to do, it's trying to do it without breaking the bank and still make it reliable.

In my suggestion about the different size cables, I wouldn't use a smaller gauge for the shorter runs, but a larger one, effectively taking them out of the "length" equation. If you use smaller ones there (like the 2ga you mentioned), then even a short length is going to add voltage drop, so now it makes the long length more critical to have even less voltage drop. This would mean a LONG length of EXPENSIVE cable, like 0000. Having the short runs of something like 00 or 0000 makes it easier to use something like 2ga on the long run.

 

[dingbat]

Whatever capacitors are in the regulator can't compensate for the ripple coming out of an alternator/stator.

You are correct, they do not completely remove the ripple but eliminate the "pulsed" output you would have otherwise.

 

[ajgraz]

Been spending the last month measuring, contemplating, calculating, chewing on advice, and building; time for an update...

I am using a Blue Sea Systems 9001e battery switch (1/2/1+2/Off), mounted in a DIY custom StarBoard recess in a DIY custom dashplate, underneath a 4" round gasketed twist-n-lock hatch, with that hatch/switch assembly located directly above where the big bundle from the under-deck tube comes in under the console . This location makes for the shortest possible safely supported cable runs, puts the battery switch in an easily accessible location, and is as water-proof as anywhere else inside that console. (I've actually already built and installed this, I can get pics if anyone wants)

Both batteries will be tray-mounted with Attwood screw-down 24/34 HD trays in the foremost, starboard-most location under the console. This will do the most to transfer weight forward, and to offset the weight of 15gal water in the built-in livewell in the aft, port-side of the boat. Right now using lead-acid batteries (I did cross-ventilate the console) that are actually a little under-spec as far as cranking amps as per Merc and are of unknown age--they did pass load testing and have been starting the motor, but when they poop out I'm planning to go to Odyssey 34M-1500ST AGM's. (Already got the trays installed, with my current "spare" battery in one of them; also already installed a Minn Kota MK212PC 2-bank charger under the console, one bank directly charging the "spare," the other bank charging the aft battery through the fusepanel for now)

Cables from the battery positives to the battery switch (and from the battery grounds to the Blue Seas 2002 5/16" ground post) will average 3' in length; these will be 2/0AWG. The fusepanel under the console will be connected directly to the battery switch common and the ground post with ~2' of 10AWG, ensuring minimal voltage drop there, far better than the voltage drop from the ~16' of 10AWG now connecting the fusepanel to the currently aft-mounted battery.

After some measuring, turns out the cables from the battery switch to the locations where they attach to the powerhead under the cowling must be 20' long (on this motor they wrap ALL THE WAY AROUND the base of the powerhead under the cowling, literally a nearly FULL LOOP, adding nearly 4' compared to the 16' control cables!); these will be 1AWG.

All of this should give me voltage drops in the 8-9% range on 200A (starting draw) at any reasonable state of charge, yet still be reasonably sized cables.
(Note that my Merc shop manual says 1AWG is good for a 21' to 25' one-way run, so this is at least "meets/exceeds OEM spec," and is a slight step up from the near 10% drop from the 4AWG 12' cables on there now). I plan to have all these cables made by that Best Boat Wire site I heard about somewhere in these forums.

I'd appreciate any comments on any part of my plan. Only thing I know that I'm up-in-the-air about is whether the 20' runs should be something bigger than 1AWG.

I'll probably get around to finishing all this in Fall or Winter, right now gotta get out there and get fishing!