Battery isolators

[leechy]

Hello everyone

 

Started on new engine electrics today,ended up going to Limekiln for my batteries(5 x 115amp).The new engine has a starter alternator of 45amps and leisure alternator of 150amps,i will fit a battery isolator to the starter positive but do i also need to isolate the cable from the 150 amp alternator to the baterries as this is only there to input power to my leisure bank ?Also am i ok to isolate the 1500w inverter and all my house electrics form the same switch or would you recommend having a separate isolatoer for the inverter ?

 

Thanks folks

 

Leechy

[Cafnod]

Hi Leechy

By all means isolate your starter battery to starter motor cable via an isolator switch, but do not put an isolator between the alternator for the leisure batteries and the leisure batteries themselves. If this were turned off and the engine run it could (would) damage the alternator. It would also be unecessary. The isolator switch on the leisure or cabin battery side should be between the battery and any circuits that the batteries feed, its purpose is NOT to isolate the alternator from the batteries but the batteries from the circuits which they power and it is intended for emergency use or when working on the 12 volt system. Not sure how to post diagrams and things on this site but if I have not made myself clear email me or PM me with an email address and I will draw and scan a diagram and send it to you.

 

Thanks and regards

 

Richard

[Guest]

I agree that the isolator should be between the cabin (domestic/leisure) batteries and the circuits that they feed, NOT between the alternator and cabin (domestic/leisure) batteries.

[DHutch]

Its purpose is NOT to isolate the alternator from the batteries but the batteries from the circuits which they power and it is intended for emergency use or when working on the 12 volt system.

It seams to be a weird concept to a lot of canal-types, but personaly, i feel that the battery isotator should isolate the batterys!

- This is how ours is wired up. Battery isolator of = batterys isotated. No if's, No buts Isolated.

 

I know a lot of people like to leave there radio/bildgepump/altertor powered up, while isolating everything else, and often do this by wiring them in before the isolator (with or without apropreate fuses)

- However, i personal would want to be able to isolate everything, if the need aver occured.

 

See the +ve lead to the alternator gets traped against somthing which damages the insulation and earths it to the hull.

- Then that lenght of cable is going to light up, and if its wiring in before the switch, you in a mess!

 

Just a thought

 

 

Daniel

[Sir Nibble]

I agree with Dan, put one isolator in the main -ve cable for each batter bank. Sorted.

[Richard Bustens]

Snibble

Why Neg??????

 

Surely you mean Pos.

[ChrisPy]

There has to be a sensible balance. If the bilge pump is isolated by the switch there will be a temptation not to switch off when you leave the boat for a long period. And if there is a risk of damaging the domestic alternator if you forget to switch on the domestic batteries before starting the engine, again there is a temptation not to switch off.

 

In an industrial situation we would ensure additional protection, e.g. if a +ve battery cable could cause a fire if it was damaged we would make sure it could not be damaged. One of my pet gripes is that cables (mechanical and electrical) tend to be strewn all over the engine space, unsupported. In industry all such vulnerable cables are supported on steel braces (e.g. Unistrut) and covered if they could suffer impact damage. When I get on to completing my engine space, that will be my first priority. Then I will feel confident that my bilge pump and domestic alternator can be 'always connected'.

[Sir Nibble]

Snibble

Why Neg??????

 

Surely you mean Pos.

It just works out easier. It doesn't matter where you break the circuit and neg is as good aplace as any and tends to be a nice simple unmistakable single heavy cable.

[GUMPY]

The ONLY place to put the switch is so that it isolates everything including the alternator.

The only exceptions to this rule are things like auto bilge pumps that are allowed to br wired directly but have to be through s suitable fuse.

 

Switches in the -ve are not acceptable and in some cases can be dangerous.

 

If you are concerned about fusing there are several alternatives.

 

RS part numbers:

NH fuseholders 287-5783

NH fuses 375-9519

 

Fork truck fuses 226-0844

 

Battery terminal fuses 337 7915

 

The last are the easiest to fit they just go on the battery posts.

 

As for protection of the alternator it is a simple matter to put a control relay in the starting circuit that disables the ign switch until the domestic batteries are switched on.

 

 

 

Julian

[bottle]

Positive , negative, negative, positve

 

There is no argument it must be a 'double pole isolater'

[Sir Nibble]

Switches in the -ve are not acceptable and in some cases can be dangerous.

I cannot imagine any circumstance when isolating battery -ve would be dangerous. Enlighten me and suggest some.

With -ve isolated the stored energy within the battery is contained within the battery and unable to interact with eny other component in any way. What more do we want from a battery isolator?

[GUMPY]

I cannot imagine any circumstance when isolating battery -ve would be dangerous. Enlighten me and suggest some.

With -ve isolated the stored energy within the battery is contained within the battery and unable to interact with eny other component in any way. What more do we want from a battery isolator?

 

Ok so you have an inverter on a system which which is isolated in the -ve, with an inverter control panel/battery monitoring system that is connected directly to the battery and correctly fused in the +ve line.

You switch on the inverter it fires up OK with no load as the return is through the -ve of the control panel

What then happens when you load up the inverter with a decent load?

 

The control panel wiring will vaporise along with possibly the panel as well.

 

J

Edited March 20, 2006 by idleness

[Cafnod]

I think we are starting to confuse the poor chap.

It is generally the case that most N/B domestic installations isolate the batteries from the circuits via the positive line, isolators come in various levels of sophistication and quality, from £5. Isolating the alternator from the batteries would achieve nothing except the probability of a big bill and a non functioning alternator, yes I agree a relay could be fitted but why?????? The alternator does not need to be isolated in the first place.

Isolaton on the negative side has plenty of industrial precedent, many commercial vehicles had an earth isolator, via a rotary switch, with provision for some cicuits to be left connected. In my toolroom I have a couple still, they go back so far they are fitted with a cream knob or a black knob depending on whether the vehicle was negative or positive earth return.

Yes I agree that double pole single throw isolators are excellent, I can get these SECONDHAND from a bus breaker at a fraction of new cost, Lucas/CAV too. If fanyone desperately wants one PM me.

With regard to fusing circuits BEFORE the isolator it is common marine/automotive practice, all the main circuits are protected by isolatio and the bilge pump/burglar alarm/VHF radio etc are all still usable. Should such circuits need working on then it is a simple matter to pull the in line fuse. Protecting these circuits by fusing is a BSS requirement.

No one has (surprisingly) mentioned fusing the battery BETWEEN the positive terminal and the isolator switch, all of my boats, motorhomes and living vehicles have had this facility via a 100 amp strip fuse holder crimped three inches after the battery terminal.

Protecting cables from damage is another area entirely, I agree it should be done and often is not.

Products to do just about everything discussed in this thread are available, quite reasonably priced from vehicle wiring products:

 

http://www.vehicle-wiring-products.co.uk/

 

Hope the above helps.

 

Richard

[John Orentas]

Hi Leechy.

 

All this is not a job you can do on a piecemeal basis, first you must draw or get someone else to draw a complete circuit drawing and include cable sizes in that. Having two alternators is the most elegant solution to boat electrics for several reasons but to get the full benefits make sure you keep a total separation between the two circuits.

 

Isolators, for the starter battery you will need one capable of carrying a current of more than 150 amps but if you must get one of those with a removable red key get one of the very much larger ones, probably 300 amp model, the smaller ones are poor quality. I managed to get one of a type that is used for stacker trucks, very much better quality. Try to site it well away from the engine.

 

For the domestic side of things you can rely on the isolator on the consumer unit I assume will be using but you will need a rating of at least 30 amps depending on your system. I would give invertor a separate supply use an isolator similar to the one for the starter, same rules apply and generally follow the manufacturers instructions re whether a fused supply is required.

 

There is no necessity to fuse the starter circuit and you certainly should not put any isolation for the alternators.

[Guest]

I tend to agree with Cafnod and John here:

Isolator and fuse from leisure batteries to cabin fuse board. Isolator in starter battery circuit. that is all I have done. I see the isolators as "emergency" switches and rarely switch them off. If wiring is OK I don't see the point-I don't isolate the car or house electrics if I leave them for a couple of weeks (I can't anyway cause of electronic gismos-these will be on boat engines in the next few years!).

[Cafnod]

I tend to agree with Cafnod and John here:

Isolator and fuse from leisure batteries to cabin fuse board. Isolator in starter battery circuit. that is all I have done. I see the isolators as "emergency" switches and rarely switch them off. If wiring is OK I don't see the point-I don't isolate the car or house electrics if I leave them for a couple of weeks (I can't anyway cause of electronic gismos-these will be on boat engines in the next few years!).

 

Gosh makes a change someone agreeing with me Stan. I do tend to isolate cos I am away from the boat for a while. got into the habbit with the motorcaravan as it has a tachograph and over time that drained the start batteries. Easier to pull the isolator. I started it on sunday after it not turning a wheel in six months and it was fine, so I am obviously doiing something right First time for everything I guess.