Newbie needs answers about batteries ?

[Refueler]

Thank you very much for your reply

The ""Headlamp Relay Theory"" is going to get a test !!!

thanks

Geoff

I use the feed to the 'Red LED' that tells me when alternator is charging. Its fed by the excite lead.

When I switch the power on to the start button - the Red LED lights up, warning buzzer sounds ... my relay stays open.

I start engine and as soon as alternator starts charging - the Red LED goes out but now the current being reversed engages the relay and my coolbox kicks in.
When engine stops - of course the alternator stops charging ... my Red LED lights up and the buzzer sounds. I switch of power to start button which disconnects also the LED and buzzer. Coolbox stops.

Simple. No need to remember anything.

 

[Amscerp]

Hi All

Once again thanks for all the replies.

I t would seem that a boat is similiar to a car !!!

You need to seek expert advice on certain things !!!

A Marine Electrician I think !!!!

 

[Refueler]

Safety and care of course.

Pal of mine was working on a 12v system ... had pulled the fuses ... disconnected wires ... all was set up to do the work with all switches off etc.

His hand brushed a battery terminal and it blew his wedding ring apart, seriously damaged his finger.

 

[PaulRainbow]

Hello All

First of all, I would REALLY love to thank you for all the replies, now I am REALLY pleased that I joined this Forum, there is lots to be gleaned from experienced Sea Farers !!!

I have got down on Hands and Knewes . . . there is a large Switch, which has One, Two, All, . . . I assume, that this is what you have been asking for . . . it controls the batteries, either One, Lights, or Two, Starter, or BOTH the lights and the engine. (I hope that is the right definition)!!!

I am, however, going to look into the suggestion of having one DEDICATED for the Engine!

And I LOVE this suggestion . . . .Quote . . . Headlamp relays .... brilliant simple bits of kit. . .Unquote

So thanks again for all your replies . .. it helps

The switch doesn't work how you think. Your starter and domestic circuits are both connected to a common terminal and the switch selects which of the two batteries you use, for all circuits. The "both" position will use both batteries in parallel, useful for an occasion that neither battery will start the engine on its own, but should not normally be used because whilst it is on "both", you can discharge both batteries to a level at which they cannot start the engine.

With a dedicated battery setup you have a single starter battery for the engine, connected to a on/off battery switch. You than have a 2nd on/off battery switch for the domestic circuits. The domestic circuits can use a single battery or more than one battery, connected in parallel. It's common to then fit a 3rd switch to connect the two circuits in parallel, for emergency use.

With separate circuits (and indeed your current setup) you need to consider how the different banks of batteries get charged. With your current setup the alternator will charge whichever battery you have selected, so you will have to switch back and forth between the two batteries to make sure they both get charged. With separate circuits there is no way to do this, so a split charge system needs to be installed. This is often a simple VSR, it will allow both batteries to be charged when the alternator is charging, but it will open when you stop the engine, to prevent the domestic circuits from discharging the engine battery. In your case, i would fit a VSR now, even if you don't chance the switch or battery layout right away. With the VSR you can use either battery for everything and not have to swap around to get both batteries charged. If there is a fault that causes the battery voltages to drop, the VSR will open to prevent both batteries from being discharged.

A headlamp relay is not the correct thing to use here. With the headlamp relay, it will close when the alternator is charging, as Stemar stated, but it will not open if there is a fault that discharges the batteries, so you could be stuck with flat batteries. Stemar and myself have had this conversation a couple of times and Steve acknowledges that, whilst his relay has worked fine, he would fit a VSR if he was doing the job today, as he states in his post above.

Using a simple relay (that's all a headlamp relay is, a simple, electrically operated on/off switch) to power something only while the engine is running is perfectly OK, such as refuelers coolbox.

 

[Refueler]

A headlamp relay is not the correct thing to use here. With the headlamp relay, it will close when the alternator is charging, as Stemar stated, but it will not open if there is a fault that discharges the batteries, so you could be stuck with flat batteries. Stemar and myself have had this conversation a couple of times and Steve acknowledges that, whilst his relay has worked fine, he would fit a VSR if he was doing the job today, as he states in his post above.

Using a simple relay (that's all a headlamp relay is, a simple, electrically operated on/off switch) to power something only while the engine is running is perfectly OK, such as refuelers coolbox.

Here I totally agree ... the headlamp relay is not for anything other than peripheral items such as my coolbox.

If I was doing it again - I would choose a solid state relay with one way power. But the Headlamp relay is very cheap - any car shop has them ...
The relay would then be less liable to any corrosion and also not allow any reverse flow ... the coolbox acts as a hotbox in reverse flow !!