safety and care with leisure batteries?

[squarelips]

Hi everyone-

 

I've been looking for some general advice on safety and care with leisure batteries. I don't know very much about electricity and batteries so i'm learning all the time!!

I keep running my battery flat which is fine because my very generous neighbour is charging them back up with his 240V mains supply for me (until I can get filled up with diesel again).

However taking the batteries in and out the engine is raising safety questions in my mind.

 

1. when disconnecting the batteries should I disconnect positive or negative first?

2. How come I don't get a shock when I touch the positive terminal with a wrench? I don't understand in what situation that would be dangerous.

3. I gots two batteries side by side. Is one the starter battery and one the leisure battery? but I can see no difference in the way they are wired up. how would I tell?

4. Would it be fair to imagine that the batteries drain together? or will one battery drain then the other?

 

Any other DO's and DONT'S and advice for battery care and safety would be much appreciated!

Thanks very much!

x

[mrsmelly]

Hi everyone-

 

I've been looking for some general advice on safety and care with leisure batteries. I don't know very much about electricity and batteries so i'm learning all the time!!

I keep running my battery flat which is fine because my very generous neighbour is charging them back up with his 240V mains supply for me (until I can get filled up with diesel again).

However taking the batteries in and out the engine is raising safety questions in my mind.

 

1. when disconnecting the batteries should I disconnect positive or negative first?

2. How come I don't get a shock when I touch the positive terminal with a wrench? I don't understand in what situation that would be dangerous.

3. I gots two batteries side by side. Is one the starter battery and one the leisure battery? but I can see no difference in the way they are wired up. how would I tell?

4. Would it be fair to imagine that the batteries drain together? or will one battery drain then the other?

 

Any other DO's and DONT'S and advice for battery care and safety would be much appreciated!

Thanks very much!

x

 

Firstly, running your batteries flat is far from being fine, it will destroy them in a very short period of time. taking them below 50% capacity is not recomended.

If the are open wet cells check them and topu up with distilled water.

Never short circuit them as in putting a spanner for instance by mistake as they could explode.

The wiring is hard to guess at without looking at it.

 

Tim

[Guest]

Hi everyone-

 

I've been looking for some general advice on safety and care with leisure batteries. I don't know very much about electricity and batteries so i'm learning all the time!!

I keep running my battery flat which is fine because my very generous neighbour is charging them back up with his 240V mains supply for me (until I can get filled up with diesel again).

However taking the batteries in and out the engine is raising safety questions in my mind.

 

1. when disconnecting the batteries should I disconnect positive or negative first?

2. How come I don't get a shock when I touch the positive terminal with a wrench? I don't understand in what situation that would be dangerous.

3. I gots two batteries side by side. Is one the starter battery and one the leisure battery? but I can see no difference in the way they are wired up. how would I tell?

4. Would it be fair to imagine that the batteries drain together? or will one battery drain then the other?

 

Any other DO's and DONT'S and advice for battery care and safety would be much appreciated!

Thanks very much!

x

 

Because you are not making a 'circuit' effectively you are just making the positive terminal 'bigger' by the size of the wrench.

 

However if you touch both the positive terminal and the negative terminal with the same wrench at the same time (NOT recommended) you will make a (short) circuit evidenced by the nice sparks you will see as the connection is made. If the battery has been on charge and gassing you also risk an explosion if you do this - so it's worth avoiding doing it when using a wrench.

 

If you have no cover on the batteries it's also worth doing so that something that could inadvertently 'short' the terminals cannot do so as if this happened for a short while it could cause an explosion even if the battery has not been on charge.

Edited January 13, 2013 by The Dog House

[squarelips]

hey martin-

that makes a lot of sense when you put it like that! making the positive terminal bigger! but what i dont understand really is if i were to stand on the metal bottom of the boat and touch the positive terminal would the charge not want to go through me to the metal of the boat? or does the charge just not want to travel through the human body?

or if i touched the positive terminal against the metal structure of the boat when i was lifting it out?

I am really careful with my batteries but I am aware im not alltogether sure what i should be looking out for!

thanks x

 

and tim we are not running our batteries dry just taking them out to charge them elsewhere every couple of days as we run out of diesel. usually we charge them every night! thanks for your advice tho!

[Guest]

hey martin-

that makes a lot of sense when you put it like that! making the positive terminal bigger! but what i dont understand really is if i were to stand on the metal bottom of the boat and touch the positive terminal would the charge not want to go through me to the metal of the boat? or does the charge just not want to travel through the human body?

or if i touched the positive terminal against the metal structure of the boat when i was lifting it out?

I am really careful with my batteries but I am aware im not alltogether sure what i should be looking out for!

thanks x

 

and tim we are not running our batteries dry just taking them out to charge them elsewhere every couple of days as we run out of diesel. usually we charge them every night! thanks for your advice tho!

 

Just think about it a bit more -

 

What happens if you touch both terminals of a 12V battery at the same time?? - no metal involved just with your hands/fingers - do you get a shock then??

 

 

ed for clarity.

Edited January 13, 2013 by The Dog House

[Batavia]

PM sent.

 

Chris G

[Flyboy]

hey martin-

that makes a lot of sense when you put it like that! making the positive terminal bigger! but what i dont understand really is if i were to stand on the metal bottom of the boat and touch the positive terminal would the charge not want to go through me to the metal of the boat? or does the charge just not want to travel through the human body?

or if i touched the positive terminal against the metal structure of the boat when i was lifting it out?

I am really careful with my batteries but I am aware im not alltogether sure what i should be looking out for!

thanks x

 

and tim we are not running our batteries dry just taking them out to charge them elsewhere every couple of days as we run out of diesel. usually we charge them every night! thanks for your advice tho!

You won't get a shock if you touch both terminals of a 12 volt battery because your body has a high resistance. Your spanner has a very low resistance so a very large current would flow and it's possible it might weld itself to the terminals, the battery might (probably will) even explode. If you have the usual negative earth system, be careful when undoing the positive terminal that you don't touch the spanner on any of the metal structure of the boat. I always disconect the negative first and reconnect it last so this will not happen.

[Guest]

A couple of other things to think about when handling batteries.

 

- The acid they contain is corrosive so avoid tipping them as you remove them.

 

- They can be surprisingly heavy so be careful particularly if lifting them from a difficult to access locasion.

[Mac of Cygnet]

my very generous neighbour is charging them back up with his 240V mains supply for me

 

 

I know very little indeed about batteries, but would query this. What sort of battery charger are you using between the mains and the batteries? If it's an ordinary Halfords job, that's totally inadequate. Only proper 3-stage charger would give your batteries enough charge to keep them happy. I never, ever thought I would be replying to a battery question, and stand to be corrected!

[Tony Brooks]

You won't get a shock if you touch both terminals of a 12 volt battery because your body has a high resistance. Your spanner has a very low resistance so a very large current would flow and it's possible it might weld itself to the terminals, the battery might (probably will) even explode. If you have the usual negative earth system, be careful when undoing the positive terminal that you don't touch the spanner on any of the metal structure of the boat. I always disconect the negative first and reconnect it last so this will not happen.

 

 

I am not saying that you are wrong because that is what I advocate but for completeness we must remember that Gibbo is adamant that you disconnect the positive first because with certain equipment on board and under certain conditions doing the negative first can cause fires and/or considerable damage. He did explain it and it made sense at the time - I think its to do with equipment that has a permanent live feed like car radios.

 

I think it boils down to an individual's assessment of risk of doing it either way. In my view the majority if metal boats are safer to take the negative off first but if there is a lot of expensive equipment on board it is far better to turn all the equipment OFF, then open the master switch (S), and then disconnect the negative. Others are welcome to disagree but you only need Elora, King Dick or Chrome Vanadium branded into your hand once to make you change you mind (in my view).

[nicknorman]

 

1. when disconnecting the batteries should I disconnect positive or negative first?

2. How come I don't get a shock when I touch the positive terminal with a wrench? I don't understand in what situation that would be dangerous.

3. I gots two batteries side by side. Is one the starter battery and one the leisure battery? but I can see no difference in the way they are wired up. how would I tell?

4. Would it be fair to imagine that the batteries drain together? or will one battery drain then the other?

 

1. There is some debate about this but in your case I would recommend disconnecting the -ve first. The danger is that you accidentally connect the +ve terminal to the metal of the hull with the spanner. If you do the -ve first, if you touch the spanner to the terminal and the hull, it is already connected anyway so nothing happens. If you then disconnect the +ve next and touch the spanner to the hull, there is no circuit since the -ve terminal is not connected, so again nothing happens. Don't underestimate the amount of energy stored in a battery and how quickly it can be released if you make a short circuit!

2. The voltage is too low for you to feel anything, let alone for it to be dangerous. That said, if you touch your tongue to one terminal whilst holding the other terminal with a wet hand, you will feel a strong tingling. Moral: Don't lick the battery!

3. If they are as you suggest (1 leisure and 1 engine) chances are that whilst the -ve terminals will be connected together by thick cable, the +ve terminals will not be connected together, but have separate wires leading away to the master switches. If both +ves, and both -ves are each connected together, the batteries are acting as one bank.

4. If they are 1 bank, they drain together. If they are separate starter and leisure, only the leisure battery will drain. The starter will only drain when you operate the engine starter.

Edited January 13, 2013 by nicknorman

[keble]

From a safety point of view, to avoid inadvertent short circuits, it's advisable to:

* remove metal stuff from arms and hands (eg rings, watch strap)

* put tape round spanners

 

Big fat sparks are best avoided!

[Darren72]

Just think about it a bit more -

 

What happens if you touch both terminals of a 12V battery at the same time?? - no metal involved just with your hands/fingers - do you get a shock then??

 

 

ed for clarity.

 

Even better what happens when you touch both terminals of a 9v battery with your tongue. The smoke alarm ones!!???

 

Wouldn't it be easier to get some fuel in a jerry and top up your tank rather than struggle with your batteries every other day.

[smileypete]

There's some good info on battery safety in The Battery FAQ:

 

http://jgdarden.com/batteryfaq/carfaq.htm

 

IF removing negative first then to avoid any damage ALL circuits must be isolated from the positive side beforehand. Best to wrap any spanner used with a few layer of duct tape, personally I'd use a plastic handle T bar with some layers of heat shrink sleeve on the shaft.

 

cheers, Pete.

~smpt~

[nb Innisfree]

I once had a shock from the positive terminal of an Audi 100 running at tickover, nothing serious but quite unpleasant, only time it has happened in nearly 50 years of motoring. Made me bit nervous near batteries for a while.

[alan_fincher]

Because you are not making a 'circuit' effectively you are just making the positive terminal 'bigger' by the size of the wrench.

 

However if you touch both the positive terminal and the negative terminal with the same wrench at the same time (NOT recommended) you will make a (short) circuit evidenced by the nice sparks you will see as the connection is made. If the battery has been on charge and gassing you also risk an explosion if you do this - so it's worth avoiding doing it when using a wrench.

Yes, but if you connect yourself between the two terminals, (one hand on each), you will feel nothing either, although you are making a small circuit through the very high resistance of your body.

 

Not getting a shock has nowt to do with only touching one terminal - it is because the voltage of a battery (12 volts) is not enough to give you are discernible shock, irrespective of you touch one terminal or both.

 

If you took the "only making a terminal bigger" argument futher, you could argue you might touch the 230 volt "live" terminal of the mains, and be OK, provided you touch nothing else - trust me, you absolutely can't and it could kill you.

Edited January 14, 2013 by alan_fincher

[Guest]

Yes, but if you connect yourself between the two terminals, (one hand on each), you will feel nothing either, although you are making a small circuit through the very high resistance of your body.

 

Not getting a shock has nowt to do with only touching one terminal - it is because the voltage of a battery (12 volts) is not enough to give you are discernible shock, irrespective of you touch one terminal or both.

 

If you took the "only making a terminal bigger" argument futher, you could argue you might touch the 230 volt "live" terminal of the mains, and be OK, provided you touch nothing else - trust me, you absolutely can't and it could kill you.

 

I know - see my subsequent post.

 

Just think about it a bit more -

 

What happens if you touch both terminals of a 12V battery at the same time?? - no metal involved just with your hands/fingers - do you get a shock then??

 

 

ed for clarity.

 

Where I highlighted the fact we are only talking about 12V which is unlikely to actually cause a shock.

[nicknorman]

Yes, but if you connect yourself between the two terminals, (one hand on each), you will feel nothing either, although you are making a small circuit through the very high resistance of your body.

 

Not getting a shock has nowt to do with only touching one terminal - it is because the voltage of a battery (12 volts) is not enough to give you are discernible shock, irrespective of you touch one terminal or both.

 

If you took the "only making a terminal bigger" argument futher, you could argue you might touch the 230 volt "live" terminal of the mains, and be OK, provided you touch nothing else - trust me, you absolutely can't and it could kill you.

Making a circuit or not does make a massive difference. As a former electrical/electronic engineer with no respect for it, I have many times touched mains live. It gives you a bit of a jolt, but if you are wearing insulating shoes and not touching anything else it's not that bad. On the other hand, if you are touching earth with the other hand, on a wet floor in bare feet etc it can easily be fatal.

 

With touching AC mains live, even if you are insulated from everything else, current flows in and out of you at 50Hz due to your capacitance. Hence it does bite a bit. If it was 240v DC, once your body had charged up (milliseconds) no more current would flow and you wouldn't feel a thing. Of course if you make a circuit at 240v DC that's worse than 240v AC!

[Guest]

I once had a shock from the positive terminal of an Audi 100 running at tickover, nothing serious but quite unpleasant, only time it has happened in nearly 50 years of motoring. Made me bit nervous near batteries for a while.

 

I can't understand what would cause that - It's quite possible to get a discernible shock from the ignition side after the 12V has been ramped up by the coil(s) to create the voltage needed for a good spark but I've never heard of that before - some sort of fault perhaps???

 

Martin (Who once touched the exposed cap of an HT lead on an old Mini which caused a severe pain in the back of the head as I struck it on the raised bonnet.)

[alan_fincher]

Making a circuit or not does make a massive difference. As a former electrical/electronic engineer with no respect for it, I have many times touched mains live. It gives you a bit of a jolt, but if you are wearing insulating shoes and not touching anything else it's not that bad. On the other hand, if you are touching earth with the other hand, on a wet floor in bare feet etc it can easily be fatal.

 

With touching AC mains live, even if you are insulated from everything else, current flows in and out of you at 50Hz due to your capacitance. Hence it does bite a bit. If it was 240v DC, once your body had charged up (milliseconds) no more current would flow and you wouldn't feel a thing. Of course if you make a circuit at 240v DC that's worse than 240v AC!

Yes, I know all that, having for a while been an electronics test engineer myself.

 

I guess I managed during a youth spent playing with mains powered (and usually valve operated equipment) to connect myself to the mains as many as a dozen times overall.

 

With hindsight I had a fairly cavalier attitude to such things in my youth, and try to be a lot more careful now.

 

I was deliberately trying to not make my post too technically complex, whilst pointing out the explanation that I quoted in my post was simply not correct.

 

 

I actually reckon the worst mains shocks I received were on the occasions I had completely convinced myself beforehand what I was working on was fully isolated, and couldn't possibly harm me. I recall going through a brief "processing phase" each time that insisted in my brain that this shouldn't be happening, before I actually had the wit to extract my fingers. If I knew what I was doing was dodgy when I started it, somehow I seemed to be primed to "disconnect" myself sooner. Strange, and probably nonsense, but that is how I recall it.

[nicknorman]

 

With hindsight I had a fairly cavalier attitude to such things in my youth, and try to be a lot more careful now.

 

Most people below the age of 25 consider themselves to be immortal!

[Barney Guiton]

This is all really useful for new boaters, cheers everyone!

 

"3. If they are as you suggest (1 leisure and 1 engine) chances are that whilst the -ve terminals will be connected together by thick cable, the +ve terminals will not be connected together, but have separate wires leading away to the master switches. If both +ves, and both -ves are each connected together, the batteries are acting as one bank."

 

Why are the starter and leisure negatives connected together? Trying to get my head around this very complicated circuit diagram. Thanks!

[nicknorman]

Why are the starter and leisure negatives connected together? Trying to get my head around this very complicated circuit diagram. Thanks!

Various reasons but perhaps the simplest to grasp is that they have to be charged, thus they are both tied to the engine in some way. The engine's alternator and starter motor typically use their casings as the negative connection. Therefore there needs to be a negative connection from the starter battery to the engine casing (starter and alternator negatives). There also needs to be a negative connection between the leisure batteries negative and, via the engine casing, the alternator negative. So you could run two separate thick cables from each battery negative to the engine casing, however, why bother when you can just use one cable and connect it to the negatives of both starter and domestic batteries. Hence the -ve link between the two.

 

However this is the "normal" way to do things, not the "only" way. On our boat we do in fact have two negative cables running to the engine and our battery banks are thus not connected together at the battery -ve terminals, but of course ultimately they are still connected together, via the engine casing.

[rubblequeen]

Where does the isolator switch come into this? I have only one so is it on the negative side ? As this is the only common connection.

[nicknorman]

Where does the isolator switch come into this? I have only one so is it on the negative side ? As this is the only common connection.

Yes I would presume that if you have two banks (engine and domestic) but only one isolator, it will be in the -ve cable. Not ideal IMO but there are plenty like that about