Regulator sense wire and dual battery banks.

[dweeze]

Hi,

More electrical questions.

I've got two battery banks controlled through a battery isolation switch. At the moment the sense wire for the reg is attached to one of the 5 batteries in the engine start bank.

To me having a single sense wire seems illogical and I'm wondering how others have dealt with dual banks.

I know it should logically be on the house bank as opposed to engine start but locating it there still doesnt get over the problem of charging being dependant on the state of the battery (bank) being sensed. The thing I'm concerned about is overcharging or undercharging the bank not being sensed. Not to mention that sensing one battery in a bank of three seems a bad solution to me.

From what I can read you have to run a single sense to the reg. I had thought of running the sense from the contact points of the selection switch - which makes sense when charging either bank in isolation but I wasnt sure about how that would be when charging both at the same time. Has anyone done this?

The other thought I had was to run a wires from each bank to a selection switch allowing me to select which bank the sense is coming from depending on which bank I'm trying to charge.

Any ideas or opinions?

ps - I do know that I can change the whole system and put diodes etc into the system but thats a plan for further down the track - at the moment I have this particular system and am trying make it the best I can within its constraints.

Thanks - Tim.

 

[PBooth]

Hi, I use a sepparate single isolator switch on each of my batteries rather than a slector switch. The outputs from each isolator are connected together and then to the starter motor positive with the domestic supply also connected at this point. This means that the alternator sense wire is always connected to the battery being charged. After starting, I allow the engine starter battery to charge fully, then switch over to Domestic (I have a digital voltmeter on a selector switch to monitor each battery). I prefer to charge one battery at a time.

Peter

 

[dweeze]

thanks Peter - are you running banks or just single batteries?

 

[halcyon]

You can us a bi-directional charge relay between the two batteries.
You can start the engine of either battery, when it comes up to the selected voltage, the second bank is put in parallel. This will cause the bank voltage to fall thus droping the sense voltage to the alternator, and all batteries being concidered one bank. Once charging stops, the banks will be isolated.


charge diagram for the system.

Brian

 

[pappaecho]

Be very careful if you put the sensor wire to the isolation switch... if for example the egine is running and sombody acidently switch the switch off you will blow the alternator.
I have two banks each of about 200 amps, being engine and domestic. The laternator seems to be quite happy to charge the lot when the isolator is set in the all position - otherwise it only charges the engine bank because that is where it is wired to.
I recently fitted a Rutland 913 wind generator with charge controller which directs to both banks, monitors both banks, and confirms that when the engine is on, both banks are charged to such an extent that the charge controller switches off the wind generator as the cut off point of 14.2 volts is exceeded - my 4108 has a very elderly alternator send out about 30 amps max but it had been charging the battery banks for several years without problems - now considerably helped by the wind generator

 

[halcyon]

The problem you say will happen with any system when you turn the battery isolator off, even yours.
The problem with alternator runaway goes back to battery sensed alternators, and isolator switches that used to break before make, taking away the sense voltage and thus high voltages.
With machine sensed alternators, if you turn the battery off, the alternator will still have a voltage generated by feeding all your circuits turned on, thus clipping the output voltage. I know of a Westerly leaving the CI at night under engine, both isolator switches were accidently turned off. The alternator carried without a problem, suppling nav lights, nav equipment, and domestic loads as the split charge relay was engaged. It was only after the skipper turned off the engine, and the yacht fell into total darkness that he found he had a problem.
Personally I would not touch a rotory switch, and prefer two isolator switches with the alternator perminantly connected to the engine battery. Even with this system, turn off the engine battery isolator switch and you have your problem. But we still try to cover any system, and provide protection from engine starting, even with the solar / windgen relay which also monitors the engine for running.


Brian

 

[dweeze]

I was just talking with a mate about whether there was something along the lines of this available. Thanks

 

[dweeze]

[ QUOTE ]
The problem you say will happen with any system when you turn the battery isolator off, even yours.
The problem with alternator runaway goes back to battery sensed alternators, and isolator switches that used to break before make, taking away the sense voltage and thus high voltages.

Brian

[/ QUOTE ]

I have recently had a problem with my regulator (Aqualine) where the reg was holding the field circuit open even with bank, ignition and engine off. I suspect its a sticking diode - and have a new one on order. Because of needing to still move the boat around I put a simple on off switch on the field wire running from the reg to the alt allowing me to cut the field circuit. I was thinking this morning that I could run the sense wire to the common pole on the isolator switch which as far as I can tell will give the reg the voltage of whichever or both banks depending on the switch (please tell me if I'm wrong). As far as I can tell XM isolator switch I have is a make before break - although the only way I have been able to test this is to put a multimeter on the feed line to the distribution panel to see whether there is a break in the reading when switching between banks. The unit itself doesnt say whether its make before or break before. Am I right in thinking that to be on the safe side I can run sense to the common pole but should always terminate the field circuit manually before switching?

I reckon this solution I'm thinking of is a crappy bodge but I have plans to completely redo the charging system but at the moment with a departure date a couple of weeks off I just need to get the existing system functioning.

Thanks for all the help and feel free to tell me I'm gonna screw up.

Tim

 

[halcyon]

You could put a diode between each battery terminal and the sense wire, this will provide a feed when changing over 3 way switch if you are worried.
You could fit a switch in the sense line from terminal 1, leaving the diodes to feed the sense lead, which would give you 0,5 / 0.7 volt boost to alternator output due to diode volt drop.

Brian

 

[VicS]

You may find some useful info in the electrical sections HERE I know it covers the situation of charging two banks simultaneouly via a diode splitter and suggests which bank the sensing wire should go to but I am not sure without reading it if it covers your situation.

You must not have the sensing on one bank while charging the other or you will overcharge.

If you have a rotary off, 1, both, 2 type switch and want to be able to charge either bank separately, or even both together maybe, I suggest you move the sensing connection to the alternator connection of it. OK its not quite battery sensing but practically as good as. If you have separate switches for the two banks connect the sensing to the common connection ie the alternator fed to the switches.

If in time you do decide to go down the diode splitter route then search out a diode assembly that incorporates third diode for the sensing connection. That will be better than the solution suggested in the above link.

 

[halcyon]

The chap is trying to do a temp setup, he plans to redo the whole system at a later date. He was worried in case the change over switch was break before make, the above is a temp solution which will maintain his supply. If he wanted, as he has a seperate regulator, and possibly a low alternator output voltage, this would give him a boost cheaply if needed.

Brian