Batt control switches.

Clyde_Wanderer

Clyde_Wanderer

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I am going to renew the batt control (1/2 both/ off) switch as the present one is a cheap looking one with not even a makers name on it and made in Tiewan.
Which switch would the forum recommend?
Do they all make before breaking?
Cheers, C_W.
 
Two separate switches...

Rewire your boat with 2 separate simple on/off switches - one for your start battery; one for your domestic batteries.
 
PVB's advice is sound. The single switches are, it seems, much more reliable. However you do have to be very careful that one battery is switched ON before the other is switched OFF when the engine is running. Not so important but when the engine is not running it is perhaps preferable to switch one OFF before the other is switched ON.

The whole point about the 1, 2 off, both switches is that the sequence is 1, both, 2 off and 1 again. So when the engine is running you go via the "both" position when switching between batteries, but when it is not running you go via the OFF position (although as already indicated that is not so important)

The question about make before break is an invalid one as the the "both" or the "off" position is between 1 and 2 which ever way you go.

If you do decide to get another 12offboth switch make sure it really is a good one. Some of the cheap ones can unscrew themselves internally , I believe, when turned anticlockwise. It must be possible to rotate the switch safely in either direction.

I would expect the Vetus ones to be good.
 
My boat originally had separate switches, but for use as a training vessel with novice crews the opportunity for careless isolation of a running alternator, blowing the diodes, was unsettling, so I installed a VETUS rotary 1-both-2-off switch. It gave utterly reliable service for 35K miles before there were signs of worn contacts: I had no hesitation about replacing it with another VETUS.
I did examine other makes but thought them inferior; some very much so.
 
Safeguarding the alternator...

Doesn't a rotary switch carry the same risk of "careless isolation of a running alternator"?

Regardless of what type of switch is used, the safest solution is to wire the alternator output directly to the batteries, using splitter diodes or a VSR to ensure separation of the batteries.
 
Re: Safeguarding the alternator...

[ QUOTE ]
Doesn't a rotary switch carry the same risk of "careless isolation of a running alternator"?

[/ QUOTE ] I am used to separate switches but I always felt that with a 12offboth switch there would have been less chance of getting it wrong.

Diode splitters would be fine but for the need of a battery sensed system. Unless the alternator is already battery sensed it'll need modifying. A vsr is probably the answer but all these things can fail and from that point of view simple manual switching with a decent quality switch or switches may be the most reliable.
 
Re: Safeguarding the alternator...

Of course you could kill the alternator by turning the load off, but I have never done it and the list of my mistakes would fill several books. More important is a really top class switch. The Blue Sea ones are excellent quality.
 
Re: Safeguarding the alternator...

My previous boat had a Driftgate X-split diode. No need for a battery sensed alternator, and, being solid state, possibly more reliable than a VSR. I was sufficiently impressed to fit one in my present boat, I replaced the 2-way rotary switch at the same time and count it as one of my better improvements, especially in terms of convenience. No risk of one battery discharging the other, and no need to remember to set the switch whilst on passage
 
Re: Safeguarding the alternator...

The reason we developed our split charge relay system 30 years ago now, was system reliability.
That is to say the alternator always remains connected to the engine battery, so a total failure of the split charge system will still charge the engine battery. Also the alternator will never loose a sense voltage, or load, so protecting diodes inside.
With all electronic systems, and all systems for that matter that have one input, and two outputs, you do not have 100% reliability. You can have a open circuit failure on one or two circuits that can loose sense voltage, and alternator loading.

Brian
 
Re: Safeguarding the alternator...

I'm sure that both types of system are, in practice, highly reliable. Operator error or else the wire dropping off the alternator terminal are perhaps just two other, and more probable, reasons for alternator death!
 
Re: Safeguarding the alternator...

You can have a failure with ANY system... in fact the wire on the engine is more likely to get shaken loose. I've always considered the circuits separately: sterling smartcharging via diodes with the domestic battery sensed. The outgoing power is via a standard 1-both-2 switch to allow flexibility for cold engine starting. As far as protecting the alternator is concerned the most important thing is to securely clamp the alternator cables to the engine to stop flexing at the ring terminals.
 
Re: Safeguarding the alternator...

I got rid of my 1/2/both/off after it gave problems and then replaced the two battery isolators with better quality kit. All well since then, well apart from a dead battery (not related to switching), but thats a different matter ....................
 
Re: Safeguarding the alternator...

Thanks for the advice guys.
I do prefer the 1both2 0ff switch and will follow piota's advice on the vetus or similar good quality one as I suppose the more you pay the better the quality or at least I should hope so.
From what I have been reading, using a split charge diode cause aprox a 1 volt drop, and if used on a machine sensed alternator will cause more problems than benifits, and am I correct in saying that other than using a charge controller there is no way to convert a standard alternator to battery sensed, or is there?
Thanks again, C_W.
 
Re: Safeguarding the alternator...

[ QUOTE ]
You can have a failure with ANY system... in fact the wire on the engine is more likely to get shaken loose. I've always considered the circuits separately: sterling smartcharging via diodes with the domestic battery sensed.

[/ QUOTE ]

The original question was how to protect the alternator. The only way to maintain maximun security is not minimise breaks in circuit between alternator and the battery. The best is a wire from the alternator to battery, 2 connections, add a isolator switch and thats it, as basic as you can get. Thus as reliable as you can get, it is onto this you hang the split charge relay. Any failure in it or it's circuit will make no differance to the circuit reliability.
With your system, you have added 2 more connections at the blocking diodes, 2 more inside the blocking diodes, and a diode. So you have doubled possible connections that can fail, then you have a seperate alternator controller failure point ( or many if you detail circuit paths ), to get round the diode volt drop problem.
I have always worked on engine reliabilty via the simplist system avaialble. Charging the service battery / batteries is seperate to the engine circuit, so cannot effect it. You then fit / use the service batteries to suit the perameters you have.


Brian
 
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