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battery replacement tips


pquinn

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Although Narrowboat domestic electrics don't use negative chassis return, the engine and domestic battery negatives will usually be connected and the engine battery negative will go to earth on the engine via the starter motor. For that reason, I treat my boat batteries like I do my car battery and do negative terminal off first, negative terminal on last, having isolated at the battery isolation switches first.

 

But they might. A car aerial is a good example.

 

I've posted this before, but I'll now post it again...

 

 

There are two schools of thought here.

Switch off the Isolator then disconnect the negative post first.

Advantages You cannot accidentally short out your spanner to the hull.

Disadvantages If anything remains connected despite the isolator being off then if there are ANY stray earth paths equipment can be destroyed.

 

Switch off the Isolator then disconnect the positive post first.

Advantages Nothing can remain connected regardless of the isolator position and regardless of any stray earth paths.

Disadvantages You can accidentally short out your spanner to the hull whilst disconnecting the positive battery terminal.

 

Contributors argue strongly in favour of both of the above approaches. You can make your own decision.

 

Reconnecting is simply the reverse of whichever method you have chosen.

Tony

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There is thus the one point in favour of the isolator in the negative (and isolating EVERYTHING with it) that having switched it off it makes no difference whether you disconnect the positive or negative first, and it doesn't matter at all if either of them is accidentally bridged to the hull by either a spanner or a dropped cable.

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There is thus the one point in favour of the isolator in the negative (and isolating EVERYTHING with it) that having switched it off it makes no difference whether you disconnect the positive or negative first, and it doesn't matter at all if either of them is accidentally bridged to the hull by either a spanner or a dropped cable.

 

Wrong - http://www.smartgauge.co.uk/whereiso.html

 

Also as your hull will be connected to the "isolated" negative side, as soon as your spanner touches the negative post and hull it won't be isolated!

Edited by Robbo
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I have a new set of cabin batteries to go in this weekend as they have just arrived from Tayna, so I am in the same position.

 

My view from this thread is switch off isolators, take all positives off, then take all negatives, remove and physically replace all batteries and then reverse all of the rest.

 

What I will do though is to tape up my spanner well to insulate it as there is a lot of metal around the battery housing in the engine room.

 

Well I did the above sequence on the weekend, just was a bit careful taking off the positives and everything fine with a now decent set of cabin batteries in place and holding charge. Result!

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Excellent news Peter. Whilst I would still advocate turning off the isolating switch in the positive line and then disconnecting the negative terminal first, you clearly were careful with that spanner on the positives! I'm glad it worked out ok and you're enjoying your sense of achievement - as well as your new found power! :)

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Wrong - http://www.smartgauge.co.uk/whereiso.html

 

Also as your hull will be connected to the "isolated" negative side, as soon as your spanner touches the negative post and hull it won't be isolated!

Not wrong. As a fully qualified and Chartered electrical engineer I am fully conversant with that article from Gibbo's site (the prime purpose of which was always of course to promote the Smartgauge) and I disagree with much of it. Certainly no battery system should be oily enough to bypass the isolator as he suggests. And yes if the spanner from the negative briefly touched the hull it would momentarily not be isolated but there would be no short circuits and no safety hazard.

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Not wrong. As a fully qualified and Chartered electrical engineer I am fully conversant with that article from Gibbo's site (the prime purpose of which was always of course to promote the Smartgauge) and I disagree with much of it. Certainly no battery system should be oily enough to bypass the isolator as he suggests. And yes if the spanner from the negative briefly touched the hull it would momentarily not be isolated but there would be no short circuits and no safety hazard.

I disagree, unless you only have one negative lead going to your battery you can't garantee that a device wouldn't find another way back. All the boats I've seen (apart from mine) tend to be a mess of both negative and positive connections on the batteries.

 

I always do positive first on other boats, on mine I only have the one connection so it doesn't matter. Even then devices could still have power due to 3 battery banks connected via Voltage sensitive relays if I don't use the isolation switch.

Edited by Robbo
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I disagree, unless you only have one negative lead going to your battery you can't garantee that a device wouldn't find another way back. All the boats I've seen (apart from mine) tend to be a mess of both negative and positive connections on the batteries.

 

I always do positive first on other boats, on mine I only have the one connection so it doesn't matter. Even then devices could still have power due to 3 battery banks connected via Voltage sensitive relays if I don't use the isolation switch.

 

Then we shall agree to disagree - in the best possible way of course.

 

There should be just one, and only one, lead to the negative of the battery. The one and only permissible exception, such as on my boat, is when you have a metering or monitoring system which is 100% self-contained. If boats have " a mess of both negative and positive connections on the batteries" then that should be corrected instead.

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Then we shall agree to disagree - in the best possible way of course.

 

There should be just one, and only one, lead to the negative of the battery. The one and only permissible exception, such as on my boat, is when you have a metering or monitoring system which is 100% self-contained. If boats have " a mess of both negative and positive connections on the batteries" then that should be corrected instead.

When giving advice to others you have to be on the safe side, and most boats have multiple connections to the batteries (apart from mine and yours, and even then I have voltage/temp sensors on which I couldn't confirm are isolated), therefore all positive feeds first is the best advice. Edited by Robbo
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When giving advice to others you have to be on the safe side, and most boats have multiple connections to the batteries (apart from mine and yours, and even then I have voltage/temp sensors on which I couldn't confirm are isolated), therefore all positive feeds first is the best advice.

I'm always happy to give helpful, safe advice to others. My first piece of advice is that an isolator is there to isolate (the clue is in the name) and therfore NOTHING should connect between the isolator and the battery. Simples!

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I'm always happy to give helpful, safe advice to others. My first piece of advice is that an isolator is there to isolate (the clue is in the name) and therfore NOTHING should connect between the isolator and the battery. Simples!

Great theory. I doubt if 10% of the boats on the UK canals would conform to it though.

 

Tony

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I'm always happy to give helpful, safe advice to others. My first piece of advice is that an isolator is there to isolate (the clue is in the name) and therfore NOTHING should connect between the isolator and the battery. Simples!

 

Apart from the voltage/temp sensors!

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All depends on what you regard the isolator for, is it for isolating the batteries or isolating devices when you leave the boat, where charging devices may want to be kept connected. Of course you could have both but this adds more connections.

 

My isolation switch just isolates the 12v distribution panel, my positive bus bar is still live (it's fused) where my voltage sensitive relays, solar,etc. are connected.

 

Perhaps a dual switch like https://www.bluesea.com/products/5510e/e-Series_Dual_Circuit_Battery_Switch, which can switch both positive and negative off is the true battery isolation switch.

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As Keeping Up has pointed out, it is perfectly feasible to design a system that fully complies with BSS requirements plus goes a lot further for the sake of both safety and convenience.

 

However... that's not how 99% of boats are wired.

 

Tony

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Then we shall agree to disagree - in the best possible way of course.

 

There should be just one, and only one, lead to the negative of the battery. The one and only permissible exception, such as on my boat, is when you have a metering or monitoring system which is 100% self-contained. If boats have " a mess of both negative and positive connections on the batteries" then that should be corrected instead.

 

Long time lurker, week long owner (second time around) and my first foray into canalworld.net forum!

 

On this point, I shall have to come down on the side of Keeping Up. I too an a Chartered Electrical Engineer of some 40 years, and I spend the first 1/4 of my working career on vehicle and marine electrical systems. I'm now a safety engineer specialising in electrical and aeronautical saefty.

 

My left hand ring finger bears the significant scars of bringing a 1/2" spanner into contact with a vehicle chassis while undoing a battery positive connection. Given that the internal restistance of a lead acid battery is typically in the order of 5-10 milliohms, a direct short between positive and negative (even to the hull), may result in currents greater than 1200A. That will certainly heat up a spanner (it did for me!) - it may cause a flash arc of the spanner to the hull (in which case it will be difficult to remove), and worse case scenario, could cause a battery to explode. Fortunately this last scenario is rare, as invariably the connection beween the spanner and the earth will be subject to some contact resistance, which will limit current flowing at this sort of level. I used to run a battery shop, and have seen countless batteries that have been shorted - the top blown off of a 12V 100AH battery is not something you want to see!

 

This should be about risk and safety. While many boats may be wired up differently, and 'heath and robinson' have had their part to play, for so many reasons there should be just one, and only one, lead to the negative of the battery. Anything else and safety margins will be reduced. The highest risk, is not of latent damage to equipment - the highest risk is a direct short between positive and negative.

 

As the hulls on almost all boats act as an earth return, they are directly connected to the battery earth. Any attempt at removing the battery positive connection first (anywhere at all near the hull or boat metalwork) with the negative connection still made represents a significant shorting hazard. It is far far easier and safer to remove the negative first. If you touch the hull with the spanner while removing the negative terminal - nothing happens as they are at the same potential.

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... there should be just one, and only one, lead to the negative of the battery.

No-one disagrees that that is how it 'should' be wired. However, we're living in the real world where the vast majority of narrowboats don't adhere to this ideal.

 

 

As the hulls on almost all boats act as an earth return...

Oh no they don't. Or at least they shouldn't. All negative returns should be wired directly to the negative busbar.

 

It is the very fact that some circuits might be made via the hull and that some returns might be connected directly to the negative terminal that makes disconnecting the negative terminal potentially so very dangerous.

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No-one disagrees that that is how it 'should' be wired. However, we're living in the real world where the vast majority of narrowboats don't adhere to this ideal.

 

 

Oh no they don't. Or at least they shouldn't. All negative returns should be wired directly to the negative busbar.

 

It is the very fact that some circuits might be made via the hull and that some returns might be connected directly to the negative terminal that makes disconnecting the negative terminal potentially so very dangerous.

 

Fair point on the negative return - busbar, not hull.

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  • 4 weeks later...

No-one disagrees that that is how it 'should' be wired. However, we're living in the real world where the vast majority of narrowboats don't adhere to this ideal.

 

 

Oh no they don't. Or at least they shouldn't. All negative returns should be wired directly to the negative busbar.

 

It is the very fact that some circuits might be made via the hull and that some returns might be connected directly to the negative terminal that makes disconnecting the negative terminal potentially so very dangerous.

Though intentionally using the hull as an earth return for equipment is not allowed, the battery negative is usually bonded to the hull and this is usually a very low resistance connection as in most boats it is used for both the starter motor and the alternator. Therefore if disconnecting the positive terminal first and touching any metal work with the spanner is going to be dangerous. If removing the negative pole first and touching the metal work, not much will happen as they are at the same potential.

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  • 11 months later...
32 minutes ago, Penfold said:

Interesting stuff on batteries here......Fast forward to 6 mins in to hear the interview with the bloke who knows his eggs

 

Ouch 7 to 8 times the cost of lead acid .

Still, less detrimental to the environment, but I guess if any narrowboat owners were too worried about that they wouldn't be chugging up and down the canals with their diesel powered boats, and we would all have sailing boats

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I started at 6 minutes, two and a half minutes later I'd heard enough about what an amazing man he was and switched it off. 

Does the very boring interview contain any useful information at any point?

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