Charging system

ghostlymoron

ghostlymoron

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My charging system comprises:- alternator, diode splitter, two seperate battery isolators and two battery banks. The system as currently (sic) wired feeds current from the diodes to the output side of the battery isolators meaning that the domestic battery bank is only charged if it happens to be turned on. This has caught me out in the past. Would it make more sense to put the feed from the diodes onto the 'battery' side of the switches so that both battery banks are charged regardless of the position of the switches. I am also considering fitting a VSR in place of the diodes as this will allow me to get much more charge into the batteries without the fiddle of soldering conections to the alternator if I used an alternator regulator.
 
Battery isolation switches are what they say, a way of isolating the battery. Any connections which bypass the battery isolation switch renders it useless, and creates a risk of damage or fire should something go amiss. IMHO of course.
 
If you have Diode Splitter - then you must be battery sensed for charging - so any change to present wiring set-up could mean no charge to batterys.
If you change to VSR - then you have no need to have battery sensing as there is little voltage drop across the VSR.

If you are having poor charging now - then maybe you are trying to charge via split diodes with machine sensed charging on alternator - that does not work and will not allow any battery to charge as voltage will be at least 0.7V reduced from optimum.
 
It's basically safer for isolators to isolate, but many boats do have the charge output permanently connected to the batteries. I'm a bit confused how you can be "caught out" by your present system - presumably you turn the domestic isolator on when you arrive at the boat, and you'd have to turn the engine isolator on to start the engine, so I can't see the circumstances in which you'd be charging without them both turned on.
 
With the present system, the alternator must sense the voltage at the common diode terminal unless there is a seperate 'sensing' connection from the battery to the alternator. As far as I am aware, the only cable from the alternator goes to the diode splitter so the regulator will cut out way efore the batteries are charged. This seems to me a good reason for fitting a VSR as I can then get far more charge into the batteries.
 
I've been caught out by not understanding my charging system. The scenario was - lights getting dim and radio not working. I was at anchor so I thought I'll start the engine to charge the batteries and switch all ancillaries off to speed it up. Result was that after 3 hours engine running - not a good idea I know! - the domestic batteries were still not charged. I accept your view that this would not happen in the normal course of events as I would need instruments, nav lights etc 'on' when sailing. But its a good illustration of Sod's Law.
 
This is why I wondered if you really were battery sensed or not.
When I tried diode splitter without battery sensing - I couldn't get any sensible charging at all. I gave up as my alternator was not suitable to alter unless I cheated the regulator itself.

As I understand it - the VSR will not care if machine or battery sensed. The only concern I would have is if someone in past has cheated the alternator regulator by fitting a diode there - that ups the regulator to compensate for diode splitter loss. If that diode is left in and you remove the diode splitter - you could then be over-voltage in charging.

(cheating senses : Alistair Garrods book Electrics Afloat)
 
Quick volt check on diode splitter input pin will tell you, 14.3 volt on input, 13.6 out safe, 15 volt in, 14.3 out danger.

Also remember the feed from the alternator to diode splitter, will need moving to engine battery, A short wire to the starter motor feed will give a good size charge cable. The VSR will just connect between the two isolator switch output terminals.

Brian
 
Thanks for the advice, guys (I'm assuming all male). I can't do any testing at the moment as Anemone is dried out. But I'll have the meter out at first opportunity. GM
 
Well, I've aways had diode splitters, and always wired the outputs direct to the batteries. That way there is no possible method of running the alternator off-load and maybe puncturing the rectifiers. My Mains charger is similarly wired direct. (you may be able to trick the alternator into donating 0.6volts more by putting a diode in the Ign lamp circuit, depending on the regulator)
I therefore only use the battery isolaters for the start/domestic circuitry, from a discharge/security point of view.
The idea of keeping charge and load circuits separate comes into it's own when the boat is left for longish periods and there are wind/sun chargers fitted.
 
All charging systems, whether they be from the engine, mains or solar should be connected to the batteries direct generally through a heavy duty fuse for each battery bank. This means that if you switch isolators off the alternator won't get fried and that you can leave mains/solar charger on and still turn off all systems via the isolators.

The only other direct connection to the domestic battery should be the bilge pump via a fuse.
 
If you have a 40 amp mains charger, depending on the output and manufacturers recommendations, fit a 40 amp fuse like this one

http://www.furneauxriddall.com/shop/acatalog/Mega_Fuses.html

with the appropriate fuse and fuse holder on each of the charger outputs.

For the alternator, if it's a standard 55amp, fit a 60amp.

Always carry some spares just in case.

BTW. Recommended practise is to fit Mega fuses on the batteries for all supplies so connections go...

Engine Battery positive terminal -> 400amp megafuse -> battery isolator - > starter motor
Domestic Battery positive terminal -> 200amp megafuse -> battery isolator -> switch panel

If you have a large 3kW inverter it should be wired to domestic with its own fuse and switch eg. 400amp.

All connections are recommended to be mechanically crimped and heatshrinked with boots to cover connections. Wire should be protected from chaffing/movement, within flexible conduit, above bilge level and supported every 12-16 inches.

Hope this helps


Mark
www.boatdoctorni.com
 
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