Electrical help isolating switches etc

[rustybarge]

20 quid for a marine one, 300A continuous, 1000A for 5 seconds.
http://www.vehicle-wiring-products.eu/VWP-onlinestore/battconns/battisol.php

The longer the starter cables, the bigger the voltage drop (remember the original mini with the battery in the boot).

There's absolutely no need to isolate the starter, because the solenoid already isolates the starter motor from the battery circuit. You could isolate the solenoid coil itself, but as you have already pointed out the ignition switch does that already.

my argument is the length of the cables is critical, that's why they go directly to the batteries, not through an isolation switch.

 

[Boo2]

I have a 32 foor wooden boat and am experiencing problems with the batteries going flat. I am a nuts bolts and gearwheels guy but electrics have me beat and need advice

Hi Richard,

You need to buy or borrow a DC Clamp Ammeter (not just a DC Clamp Meter, some of them cannot measure DC current via the clamp).

Then you need to test every wire, starting from the battery and following it through every split untill you find out where the current is going. Make notes as you test each wire of how much current is flowing through it. Eventually you will have followed wach wire to the equipment it is connected to and you will know which piece of equipment is drawing how many amps.

Someone here might have a lucky guess but the above is the only way to find out methodically what is going on.

Hth,

Boo2

 

[Richard D]

Must thank everyone for their contribtion and although not good at electrics understand the varoius points raised and will go to the boat tomorrow armed with paper and pen to write down the circuits tested what they power and what voltage drop, if any.
My understanding of electrics suggests to me the following, please tell me where I am wrong.
I can understand wanting the main battery cable going to the starter due to the high power consumption on start up and the need to keep the cable length down. As it is an earth return system surely the oposite side on the battery must be earthed to the engine with a similar sized cable otherwise this cable will overheat. So if you are going to osolate the battery and all electrics when you to the off position ( apart from the auto blige pump and wind charger which are wired direct to the engine battery ) surely one side of thr battery, eg big starter sized cable , must be on the isolator switch, or have I missed something.
Any idea what power the radar should take and should it be powered up on both engine and ancillairy circuits.

 

[neil1967]

We have a very simple system - one isolator switch in the positive cable, near the engine start battery, which feeds the starter motor and starter circuit only. With this switch, which costs maybe £10, off, you have isolated the engine start battery. A second isolator switch is in the positive cable of the domestic battery. The negatives of both batteries are connected together, to the engine block and to the starter negative. The ONLY consumer item that is connected permanently to the domestic battery is the automatic bilge pump. Everything else is connected to a bus bar on the downstream side of the isolator switch. The mains charger is connected directly to both battery banks - it has two isolated outputs - and the alternator is connected via a sterling no-loss splitter to both batteries, via the isolator switches.

Your radar should be connected via the isolator switch to your domestic batteries, and its own dedicated switch on your domestic distribution/switch panel, but I suggest that it will be off most of the time as you won't be using it.

Hope this helps

Neil

 

[PilotWolf]

We have a very simple system - one isolator switch in the positive cable, near the engine start battery, which feeds the starter motor and starter circuit only. With this switch, which costs maybe £10, off, you have isolated the engine start battery. A second isolator switch is in the positive cable of the domestic battery. The negatives of both batteries are connected together, to the engine block and to the starter negative. The ONLY consumer item that is connected permanently to the domestic battery is the automatic bilge pump. Everything else is connected to a bus bar on the downstream side of the isolator switch. The mains charger is connected directly to both battery banks - it has two isolated outputs - and the alternator is connected via a sterling no-loss splitter to both batteries, via the isolator switches.

Your radar should be connected via the isolator switch to your domestic batteries, and its own dedicated switch on your domestic distribution/switch panel, but I suggest that it will be off most of the time as you won't be using it.

Hope this helps

Neil

Was perfect until the point that you said "..., but I suggest that it will be off most of the time as you won't be using it."

Why? If you have the kit - use it! Indeed under the IRPCS you are arguably required to use it if you have it fitted.

W.

 

[Richard D]

We have a very simple system - one isolator switch in the positive cable, near the engine start battery, which feeds the starter motor and starter circuit only. With this switch, which costs maybe £10, off, you have isolated the engine start battery. A second isolator switch is in the positive cable of the domestic battery. The negatives of both batteries are connected together, to the engine block and to the starter negative. The ONLY consumer item that is connected permanently to the domestic battery is the automatic bilge pump. Everything else is connected to a bus bar on the downstream side of the isolator switch. The mains charger is connected directly to both battery banks - it has two isolated outputs - and the alternator is connected via a sterling no-loss splitter to both batteries, via the isolator switches.

Your radar should be connected via the isolator switch to your domestic batteries, and its own dedicated switch on your domestic distribution/switch panel, but I suggest that it will be off most of the time as you won't be using it.

Hope this helps

Neil

Thanks Neil, that sounds like a plan that makes sense to a layman like me, can understand both points of view on the radar. Cheers.

 

[Elessar]

The longer the starter cables, the bigger the voltage drop (remember the original mini with the battery in the boot).

There's absolutely no need to isolate the starter, because the solenoid already isolates the starter motor from the battery circuit. You could isolate the solenoid coil itself, but as you have already pointed out the ignition switch does that already.

my argument is the length of the cables is critical, that's why they go directly to the batteries, not through an isolation switch.

do what you like mate. You will never find a boat of mine wired like that.

You did however say it was "normal". As I see literally 100's of boats a year and have yet to find one wired that way, on that front you are most definately wrong.

The mini's cables were too thin not too long. Any shorter and they wouldn't have reached the battery.

 

[rob2]

Yes, the mini was so short the length wasn't the problem! Interesting though that all the long-wheelbase variants I owned had the battery directly behind the driver's seat and were much better starters for it - until I dropped a spanner across the terminals, fastest I've ever run to wash off the acid.

I've considered all the options for my own use and came to the conclusion that the starter/alternator connections really need to be short and joint/switch free for best performance. I'm now considering using the quick release battery terminal clamps from caravan shops to allow me to quickly unhook the battery if a major short occurs.

Rob.

P.S. Many boats don't have the battery capacity or charging regime to power a radar continuously and a visual lookout in good conditions is adequate to their needs.

 

[prv]

You did however say it was "normal". As I see literally 100's of boats a year and have yet to find one wired that way, on that front you are most definately wrong.

Agree. There's no isolator in my starter circuit, and I'm happy with that, but it's not the norm. Every other boat I've been on has had either a 1-2-both-off switch or individual battery isolators or both, with the starter connected after the switch(es).

Pete

 

[JimC]

About isolators in general: I've had poor results from the type with a removable red key when used in the starter motor circuit. I've had two fail in the last few years and, on examining the burnt internals of a failed unit, they don't look very substantial for the currents they are meant to carry. An open-circuit failure of the engine battery isolator could damage the alternator so you don't want it to happen. I'm currently using a metal bodied Lucas type isolator mounted close to the battery to keep the high current wiring as short as possible. The type that fits onto the battery terminal and has a wheel that you unscrew is the best in my opinion but I don't have enough clearance over the terminals to fit one.

 

[Dave_Seager]

The Boat Safety Scheme requires "a battery master switch or switches, capable of disconnecting the system - including the starter circuits - must be fitted in a readily-accessible position, as close to the battery as possible."