Vetus Battery Switch

[Guest]

I have a Vetus Battery Switch, which I am planning to install between the alternator and the two batteries. This will give me the the choice of using either No 1 battery or No 2 battery or both on or both off. If this is correct, then how can the alternator be protected against turning the switch to 'off' position accindentally while the engine is running; would this damage the diodes in the alternator?. Any advice would be appreciated.

 

[Guest]

Hi,
Watch out!
This battery swich should NOT have an OFF-position (unless it 's an electronic one that can't be switched off while the engine is running). When you turn the battery swich off with the engine running, the alternator current can't go anywhere, and you will have a volktage peak (spike) going up to 50V...100VDC (this is tested). This will damage (destroy) anything that is connected. In my opinion, this is a constructive bugg from Vetus.
What you should do depends on the wiring of your installation: what is connected to wich battery? Is there a main circuit and an aux. circuit? What exactly will you do with the two batterys?
I think the best thing you can do is connect the 2 batt. both with a diode in a way that they can't unload each other ( you need 2 power diodes). If you put an external voltage regulation in your main circuit, you can trim this one ina way that your main battery is loaded as it should be, and your 2nd batt. will be loaded with a tension minus the tension drop over the diode.
Of course it's a good thing to put a batt. swith in your wiring. I prefere just a mechanical ON-OFF swith in the + wiring of each batt.

Good luck

Eric

 

[brianrunyard]

I use this arrangement, have done for several years, and have had no problems.
I have two identical battery banks so I leave it on whichever I've started on until I've replaced what the starter took out, then switch over to the other battery. I've installed an ammeter so I can see when the battery stops taking current.
Everyone worries about switching the battery off while the engine is running, I know I shouldn't, so I don't. The same way I know I shouldn't hit rocks.

 

[philip_stevens]

If you are worried about switching off while the engine is running, fit two 30 amp auto-type relays in circuit from the alternator to both batteries - bypassing the 1/2/off switch. The operating supply for these relays comes from your alternator warning light.

When the engine has been started and the alternator starts to charge, the relays close - supplying both batteries.

Therefore if you switch off inadvertantly, the alternator is still connected to the batteries.

I installed this system - with three batteries, voltmeters, charging boosters and splitter - on my boat four years ago, and have not had any problems.

If you want, send me a private (PBO) email, with your addy, and I can send you a jpg drawing of my installation. I've already sent it to others. The drawing was checked by Driftgate 2000, and on their advice, made one modification.

regards,
Philip

 

[Guest]

Yes please, I would like the drawing of the electrical system. e mail: phoulis@netscapeonline.co.uk

 

[philip_stevens]

On its way. Hope it's OK.

regards,
Philip

 

[brianrunyard]

Philip
Please could you send me a copy of the jpg?
My e-mail address is
brunyard@hotmail.com

 

[philip_stevens]

Brian,
It's on its way. Hope it's what you want. Sorry for the GIF and not JPG image. If you can't read the GIF, let me know and I'll change it to a JPG.

regards,
Philip

 

[Guest]

Tip given to me a by an electrician: don't bother with the big rotary switches as described. The problem is that having killed the starting battery, you switch over and start from 'both' and forget to switch back. Next time you kill the battery, you've killed the domestic as well.

The recommended approach is this: wire a simple on-off switch for each battery, and then wire a third on-off switch between the two. I tried desparately to show this with ASCII art, but failed. See http://www.dashdash.demon.co.uk/switch.jpg for details.

You can now start from either battery, and isolate either. Attach the key from the middle switch to your main keyring, so using it becomes a 'process', and you never forget to 'reset' it after a problem. Connect the alternator to both batteries via a blocking diode pack.

 

[vyv_cox]

I looked at your diagram and I'm puzzled as to why this is an improvement. You appear to have no option as to which battery receives charge - both do. I understand that alternators don't like the situation in which they are being asked to charge two batteries that are discharged by different amounts, and are perhaps of differing sizes and capacities.

I have always used the rotary switch, change over from start to domestic after a few minutes of engine running and then leave it alone. I never use "both" because asking a 50 amp alternator to split itself over three batteries seems unfriendly. My present start battery is five years old and always fully charged, I replaced domestic batteries two winters ago when they were 12 years old. Seems reasonable to me.

 

[Guest]

If you use a split charge relay to charge two batteries, you're right - you get problems. This is because the least dead battery gets all the current, and the alternator senses when this one is charged, and never gets round to charging the sick one.

OTOH, a proper blocking diode pack does just the reverse, or so I'm told. It must be doing something clever to warrant the £80 cost, rather than £15 or so for a caravan-type relay...

 

[hugh_nightingale]

OK, now that I’m back on line I can put my twopenny worth in.

There seems to be an awful lot wrong with battery systems. Poor old Simes had trouble on both PBO Solent meetings, his is (or was) an Adverc based system and three batteries.

I really must get around to writing a definitive article on this subject. So, for now, a few observations and notes as I see it.

I believe Vyv Coxs statements to be nearer the truth. Hence the problem with jump starting cars.
The only thing that helps here is the long leads which tend to isolate one battery from the other as far as slight variations in voltage go. The one thing you MUST NOT DO is to have both engines running (I know some books say do this, do not). Consider Vyvs comments, now add a second alternator. You now have two alternators connected together, each trying to control the charging current to at least two batteries one of which is definitely short of capacity. Something will break, usually it is the alternator on the starting car that looses a diode.

To answer: “If you use a split charge relay to charge two batteries, you're right - you get problems. This is because the least dead battery gets all the current”. I wish I knew how these “split charge” thingies were meant to work, I can have a guess, but:.

It depends on what you mean by dead. If it is a battery that has gone high impedance, i.e. effectively open circuit, then, yes, the other battery will take all the charge; but the “dead” battery would not have taken any charge anyway. If it is dead because one or more cells have gone short circuit then the “dead” battery will take all the charge (the poor old alternator just can’t bring the voltage up high enough to service a short AND dump current into a good battery). The good cells will charge up but the bad ones won't, then when you take it off charge it still looks like a dead battery.

It is REASONABLY acceptable to connect two batteries in parallel in an emergency say for starting, hence jump leads. It is not acceptable to connect batteries in parallel for charging and in my book should never be done. Even Adverc show this as the connection for the three battery set up, as do some others, it is all wrong.

As it so happens the same is true for charging in series. What happens here is that the charging voltage is adjusted for double the amount, the “good” battery charges up fine, its terminal voltage rises, the voltage “left” for the other battery reduces and it never gets charged. Not so long ago when I was playing with NiCds one of the manufacturers recommended that no more than four cells should be charged in series without some means of equalising both the voltage and the current. We just about get away with it in a six-cell lead acid, but only by overcharging slightly.

To answer “switches”. You should never open circuit the alternator. see EVDS. The alternator uses the battery as a kind of reference, if it ain’t there it’ll just go higher and higher until the diodes pop. (There is a limit, we won’t go into that, but its more than the diode breakdown voltage in this case). I see no reason why the switch should not be a “make-before-break” type. Yes this will put both batteries in parallel which seems to be against what has been said before but the timing is different here. I’m assuming one battery has been fully charged and we just want to change to the other. There will be a momentary high pulse of current from the fully charged to the dead battery but then the alternator will sense that it has to up the current because a lower voltage has been connected.

I believe the original question about the 1/2/both off Vetus switch really only applies to two ADDITIONAL batteries for domestic use leaving the main starting battery still connected. The three switch idea would appear to work if you take the advice and make the third switch keyed to avoid leaving it on.

I have not figured out how two auto relays are meant to work except that they disconnect the paralleled batteries from the alternator.

In addition to finding out what split chargers are supposed to do, what does a charge booster? I can have another guess. However you must bear in mind that you are not going to get any more out of your alternator than its designed limit, be that 25A or 100A.

One of the most simple methods is to connect the batteries using diodes. Now you have to make sure that the alternator realises they are in the circuit by taking the feedback from the battery end, but you have two batteries. (Just use one and let the diodes sort it out is a good basic approach though you may end up with one battery not fully charged.) What you really need is a complete set of regulators for each battery with control over the alternator output. You effectively achieve this with your switches and an ammeter to tell you when to make battery selection, its just not automatted. Well, it is; you are the automatic controlling computer, as long as you stay awake. So, for instance, each battery has a switch to connect it to the alternator. YOU have to be in control. One switch is always on. When that battery is charged switch on the next THEN switch off the first. Ripple down the line like this. It is possible to buy a (mechanically) interconnected bank of switches on which you just select the next. Note:- in any order as well.

As an answer to: “OTOH, a proper blocking diode pack does just the reverse, or so I'm told. It must be doing something clever to warrant the £80 cost, rather than £15 or so for a caravan-type relay..”. I’m getting very sceptical about claims as you may have guessed, especially when they cost a lot. How much does an Adverc system cost? I don’t want to do them down but I have heard one engineer saying that he is taking more out than fitting!! What warrants the cost here. Now he didn’t say what he was putting back, it could conceivably be a better Adverc.

I’ve said enough for now.