Battery isolation switch

[clyst]

The existing arrangement is a complete lash-up and I am now rewiring the whole . The existing engine battery is totally isolated from the domestic battery ,dont ask, and is operated by a "Key" type iso switch with a wire from the battery side of the switch direct to the alternator "B" terminal .

I'm now fitting a rotary 1 BOTH 2 OFF switch . My concern is which terminal should the direct wire to the alternator be fitted No1 (engine ) BOTH or No2 (Domestic)?? If its fitted to the battery side of the engine battery when charging the domestic battery or using the domestic battery for emergency starting the alternator will be disconected-----If you see what I mean /forums/images/graemlins/frown.gif

Regards

Terry

 

[VicS]

All your ships wiring should come from the common terminal of the switch, that's all the domestic circuits, the engine electrics and the alternator. One battery is connected to the No 1 terminal and the other to the No 2 terminal.

That's the most basic and simple arrangement but you might want to extend it to include some form of split charging system.

You will, find it useful to look at the Electrical notes at http://tb-training.co.uk/

I hope you have bought a really good quality switch as many are notoriously unreliable, some people would not even consider them preferring two separate isolation switches

 

[clyst]

Thanks for your quick reply VicS . I understand that all ships wiring should come from the commom terminal BUT the Bukh wiring diag shows the "B" terminal from the alternator permament live from the "engine" battery . I suspose that is so that the alternator isn't bu**ered if hand started without the switch made . See my concern ?? I cant get that arrangement on the 1 BOTH 2 switch .

Hmmmm I hope the switch is ok its rated up to 30 volts and 300amps .

Regards

Terry

 

[Clyde_Wanderer]

BlueSea do a very good robust 1/2/both/off switch.
I have shopped around and this is one of the best I could find.
I have, with the help of another forumite just completed a diagram for the system I am installing in the boat at present, which in my opinion is a very simple, robust, and clever system, using above switch and a single pole isolater switch, and the Driftgate X-Split unit to devide charge to both banks without them parralling.
I have sent you a pm.
Cheers, C_W.
Btw, I dont have all services comming from the comm terminal, as it isent written in stone that they should, and with this system it will be almost impossible to inadvertantly cut power to the alternator.

 

[VicS]

An alternator is not harmed if the engine is started with it disconnected. What causes the damage (Blown diodes) is the voltage surge that can occur if it is disconnected from the battery while it is running

I bet people will now tell us that they have done that with no ill effects but I guess it depends on just how big a current is flowing when it is disconnected. Interrupting a big current will cause a big surge interrupting a small current will only cause a small surge. Some alternators have surge protection anyway but it is not good to rely on it. It may even work once but be damaged itself so then be rendered ineffective against further surges.

The point then is that with a 1,2 off, both switch is that if the engine is running you MUST go via the "Both" position when changing from one battery to the other but if the engine is not running you can go via the "Off" position to avoid paralleling the batteries on the way.

If you later decide on a split charging system you do get to a situation where the alternator output goes to the batteries via a diode splitter or voltage sensitive relay (VSR) rather than via the switch. That will eliminate your concerns but in the meantime the rule must be that you and only you switches the batteries over. It was many years before the person I crewed for allowed me to swap batteries.

A diode splitter allows both batteries to be charged together, the most needy hopefully getting the lions share of the alternator output while a VSR will give the engine start battery priority and only switch in the services battery when the engine one is charged. The trouble with a diode system is the 0.7 volts drop that diodes cause. That means either the alternator has to be converted to battery sensing (IIRC the tb training notes discuss which battery it should then sense) or it has to have diode added to it to cheat it into producing an extra 0.7 V (Nigel Luther aka sbc was fond of that solution)

 

[VicS]

[ QUOTE ]
Btw, I dont have all services comming from the comm terminal, as it isent written in stone that they should,

[/ QUOTE ] True and there may be times when you want to feed certain circuits when the rest is isolated, an automatic bilge pump or an alarm system for example. Then you will feed them from the services battery terminal of the switch. It would be sensible to include a separate isolator in the circuit and essential that a fuse is included as well.

Correct me if I am wrong but I believe the X Split is an electronic version of a VSR. It eliminates the volts drop caused by diodes in a diode splitter and the moving parts of a mechanical relay.

Blue Sea stuff is generally considered to be good quality (I couldn't remember the name earlier)

 

[Clyde_Wanderer]

I agree with what you are saying in princible, but in my system someone would have to inadvertantly switch off the 1.2.both and the start batt isolater switches together to interupt power to the alternator.
Have a look at the spec for the Driftgate X-Split unit, which isent an all out diode unit and claims a very low volt drop, which is why I went for it, but I suppose time will tell if it lives up to their claims.
I have the domestic service supply taken from the comm terminal on the select switch and the ignition services from starter side of the start batt isolater switch.

Yes Vic you are correct about the XSplit that is what he said when I spoke to him on the phone, "it electronic" and not Diodes. I am sure he said something like 0.5 v (or that could be 0.05v) at the lower alternator output currents.
Just checked, Lowest drop of 15mv at float current and 80mv at max 190amps for a 190 alternator.

 

[vyv_cox]

Vic has answered very comprehensively and I won't repeat what he has already told you. My Bukh engine B wire goes to the common output of the battery switch, indeed it is my belief and practice that absolutely nothing goes direct to the batteries except the main cables. My only exception is the solar panel wires, which could go to the battery terminals in the switch, although this would be a rather pointless exercise and adds even more wires to that area, very tight on my boat.

 

[VicS]

[ QUOTE ]
My only exception is the solar panel wires

[/ QUOTE ] Yes wiring from solar panel, wind turbine and battery charger are more examples of circuits that have to be connected to the battery or the battery side of the isolator. Must all be fused of course. If there are many circuits that have to be left connected when the main isolator is off then it must be worth while fitting a suplementary distribution panel, that remains live, to supply them.

 

[clyst]

Many thanks to you all for your help . Problem solved thanks to you lot !! /forums/images/graemlins/smile.gif /forums/images/graemlins/smirk.gif

regards

terry

 

[Clyde_Wanderer]

Here is the diagram I have settled on.
Anyone see any problems with it? apart from the drawing been a bit squinty.
As you will see, if the start batt goes flat, its isolater switch can be turned off, and the selecter set to both to give full power from service batts to starter without the start batt pulling down the service batts, and vice versa if service batts go flat.
The next thing I would add is a batt moniter unit.
What I would be interested to know is, can an ordinary machine sensed alternater be converted to a batt sensed, and how is it done, and would it eleminate the need for a charge control unit such as the Adverc?

 

[pvb]

Why do you need a "sevices isolator switch"? Doesn't the 1/2/Both switch fulfill that function in your circuit? Alternatively, why do you need a 1/2/Both switch as its only apparent function is as an emergency starting switch.

Yes, you can convert a standard alternator to battery-sensing. It involves connecting a wire inside it. Any auto-electrician should be able to do this for you. Having battery-sensing might help charging, although if you have a low-loss diode system it won't make much difference. It wouldn't replace the function of a "smart" regulator (Adverc, Sterling, etc), which increases the charging voltage so as to push more current through the batteries.

 

[Clyde_Wanderer]

Yes I had that thought about the services isolater switch tonight just as I was posting the diagram here, it was put in earlier on in the initial sketches and will now be one less componant in the pot.
But the selecter switch will be staying as it will be used to isolate either, or parrallel both banks if the need arises.
I had asked three auto electrical places in Glasgow and none of them knew anything about batt sensed alternators, or converting ordinary ones.
Do you know which terminals on the built in regulaters should be altered and is it just a case of taking a wire out from these terminals to the batt banks?
Although as you say I shouldent have much volt drop, especially with the new cable size I am using and all new soldered terminals.
Cheers, C_W

 

[halcyon]

Why so complicated a system ?

Diagram below will charge the service battery from engine, the engine battery from service via solar panel etc, provide link start from service battery, and can be fitted with power-lockout to drop out high loads at low service battery level.

Brian

 

[pvb]

[ QUOTE ]
But the selecter switch will be staying as it will be used to isolate either, or parrallel both banks if the need arises.

[/ QUOTE ]According to your diagram, the 1/2/Both switch won't "isolate either". 1/2/Both switches are unnecessarily complicated because they allow lots of possibility for people to set them wrongly. I think they have no place on a boat today. It's so much easier just to have 2 simple on/off switches - one to isolate the starter battery; one to isolate the services battery. Rather than an X-Split, a simple VSR as halcyon suggested would give you all the benefits and would have been significantly cheaper.

Reading your earlier posts, it appears you've already bought a Driftgate X-Split. If that's the case, there's not much point converting your alternator to battery sensing. You'd be better off fitting a "smart" regulator (Adverc, Sterling, etc) now. And you should include fuses (eg MegaFuses) in the battery cables, next to the batteries.

 

[vyv_cox]

<<< I had asked three auto electrical places in Glasgow and none of them knew anything about batt sensed alternators, or converting ordinary ones. >>>

I'm not surprised at this, there is no necessity for a car to have such a device so they would be unaware of it.

The Sterling comes with comprehensive fitting instructions that takes the owner step by step through the necessary procedure for doing the job. If you can take an alternator apart and can do a bit of soldering you will be able to DIY. If not, taking the parts and instructions to one of your automotive people should solve the problem. There is still a bit of work to be done on the boat but the soldering is the only tricky bit.

Probably the Adverc does as well, I can only speak for my own experience.

 

[Clyde_Wanderer]

pvb, How do you make that out,? the 1/2 both switch can be used in conjuction with batt isolater switch to completly isolate any of the batt banks.
Just think about the amount of combinations of positions with three seperate isolater switches, as compared to a 1/2/both and 1 isolater, you will find most folk would be more confused with the three isolater switch setup. In my setup, once the start batt isolater is switched on, it will be left on as long as I am in the boat, and under normal circumstances the selector switch will be set to position 1, (thats 2 moves) and only changed if the start batt goes flat,Then the selector goes to both, and isolater to off, to start,( 2 moves) couldent get any simpler than that.

 

[Clyde_Wanderer]

Halcyon, your diagram is missing the charge cables as far as I can see, and it is very hard to understand, so if it was drawen more precisley it would probably be more complicated than mine, and not give as many simple to use options as mine.

 

[Gunfleet]

I've been using the BlueSea one for several years and have seen no deterioration. It's good kit.

 

[pvb]

[ QUOTE ]
pvb, How do you make that out,? the 1/2 both switch can be used in conjuction with batt isolater switch to completly isolate any of the batt banks.

[/ QUOTE ]That's not what you originally said! You said the 1/2/Both switch could be used to "isolate either" bank. It can't. The starter battery can only be isolated by its own isolator switch, according to your circuit diagram.

The beauty of using simple on/off switches is that well-meaning crew can't accidentally get it wrong. Many RNLI "rescues" are callouts to boats which can't start their engine because the 1/2/Both switch has been wrongly set.