Switch panel and Battery isolator wiring

[tomo129]

Hi there,

Im trying to work out how to wire a Battery switch up to my 90hp Mercury as well as a switch panel. Anyone have any idea on what amp switch i would need for the isolator switch baring in mind it will go to both the engine and switch panel? would 75amp be okay?

if anyone has any knowledge in this are let me know,

cheers

 

[VicS]

An isolator switch close to the battery that will take the starting current required by the engine.

Fuse the supply going to the switch panel appropriate to the max load and the cable size

Fuse the supply going to the engine if you feel you want to but you'll need a fuse that'll take the cranking current

 

[tomo129]

An isolator switch close to the battery that will take the starting current required by the engine.

Fuse the supply going to the switch panel appropriate to the max load and the cable size

Fuse the supply going to the engine if you feel you want to but you'll need a fuse that'll take the cranking current

Would you recommend using the positive or negative feed for the isolator switch? and would you recommend a bus bar to split the current from the switch to the engine and to the switch panel?

 

[PaulGooch]

Would you recommend using the positive or negative feed for the isolator switch? and would you recommend a bus bar to split the current from the switch to the engine and to the switch panel?

Positive to the isolator.

No need for a busbar. Just bolt the two cables straight to the isolator terminals using crimped ring terminals.

Sounds like you just have a single battery to supply everything. What boat and engine ? What happens if the battery goes flat ?

 

[tomo129]

Positive to the isolator.

No need for a busbar. Just bolt the two cables straight to the isolator terminals using crimped ring terminals.

Sounds like you just have a single battery to supply everything. What boat and engine ? What happens if the battery goes flat ?

Yeah only have one battery, i have the possibility of putting a second one in however how would i do that? and how would you make the engine charge two?
my current battery is 80amps, what kind of ampage wire should i use to the switch and back to the engine and what amp would be suitable to go to the switch?
the boat is a speed boat with a 90hp engine, the plan is to put an isolator switch in as well as a switch panel to run lights etc, thanks for the help so far..

 

[jfm]

my current battery is 80amps, .

I suspect that is amp/hour, which is a measure of capacity (=volume) not current (=flow rate)

you need a switch and wiring that will handle whatever the canking load on the starter motor is, and that could be 200amps. No worries, because most battery isolator switches will easily handle that. Just get the correct size cables and get the terminal properly crimped. From the battery to the input side of the switch, take a heavy cable. From the switched terminal of the switch, take one (heavy) cable to the starter motor and another (lighter, say 40amps) cable to the input busbar of the general switch panel for lights/bilge pump/radio etc.

If you have an auto bilge pump and leave the boat where it is needed, wire the bilge pump to the unswitched side of the isolator switch, so it is +12v even when the isolator switch is turned off

 

[PaulGooch]

JFM has pretty much covered it.

Battery cable will depend on current draw of the starter motor and the length of the cables. If you don't want to get involved in calculations, 35mm will cover you, most likely over spec. For instance : http://www.autoelectricsupplies.co.uk/product/885

From the isolator to the fuse panel/busbar i'd go for some 6mm : http://www.autoelectricsupplies.co.uk/product/884 almost certainly over spec again. The same page will have lighter cable for lights etc. They also keep all the terminals you need.

All the terminals need to be crimped, no soldering.

Here's a good isolator switch : http://www.tcschandlery.co.uk/8659/Blue-Sea-Mini-Battery-Switch.html

A twin battery system might be a little over the top with a speedboat, but bear in mind if the battery goes flat, you'll be stranded, so make sure you have a secondary method of starting the engine. Either a pull cord (if you can start a 90 with a cord) or a spare battery/booster pack.

 

[jfm]

JFM has pretty much covered it.

Battery cable will depend on current draw of the starter motor and the length of the cables. If you don't want to get involved in calculations, 35mm will cover you, most likely over spec. For instance : http://www.autoelectricsupplies.co.uk/product/885

From the isolator to the fuse panel/busbar i'd go for some 6mm : http://www.autoelectricsupplies.co.uk/product/884 almost certainly over spec again. The same page will have lighter cable for lights etc. They also keep all the terminals you need.

All the terminals need to be crimped, no soldering.

Here's a good isolator switch : http://www.tcschandlery.co.uk/8659/Blue-Sea-Mini-Battery-Switch.html

A twin battery system might be a little over the top with a speedboat, but bear in mind if the battery goes flat, you'll be stranded, so make sure you have a secondary method of starting the engine. Either a pull cord (if you can start a 90 with a cord) or a spare battery/booster pack.

That all sounds good to me. tomo, from reading your posts, you could do with getting some help from an electrically-minded mate, as this stuff isn't easy to explain in forum posts and cover every question you might have

Incidentally, PaulG, I used to start a mercury 90 and 115hp inline 6 with a cord on the flywheel when I (oops) flattened the battery. 1635cc. It was quite easy, and the motor started pretty well.

 

[PaulGooch]

Incidentally, PaulG, I used to start a mercury 90 and 115hp inline 6 with a cord on the flywheel when I (oops) flattened the battery. 1635cc. It was quite easy, and the motor started pretty well.

Thanks for that John, i've never had a big outboard so wasn't sure how difficult it would be.

The thought of starting a 1600cc car with a bit of string seems a bit bizarre