voltage sesitive relays

[charles_reed]

Bit of a Catch 22 situation

With current battery bank he's over-output with a 90 amp alternator (unless he's got lead-calcium cells) and with 125amp over the top with the proposed bank.

Needs to fit a smart regulator with temperature sensing.

The Magnetti Marelli 100 amp fits neatly into the space used by the small chassis.

 

[Anonymous]

Re: Bit of a Catch 22 situation

[ QUOTE ]
With current battery bank he's over-output with a 90 amp alternator (unless he's got lead-calcium cells) and with 125amp over the top with the proposed bank.

[/ QUOTE ]You've lost me there...can you explain?

 

[pvb]

Please read the original post....

[ QUOTE ]
charged by a 50 amp alternator through a sterling reg

[/ QUOTE ]

He already has a smart regulator. Do try to keep up! /forums/images/graemlins/wink.gif

 

[William_H]

Re: Spanner in the works? PVB

Thanks for the link on VSR. That link made a wild statement re diode splitting that the diodes can isolate each battery while being charged such that one battery (smaller) can be overcharged. I doubt this would be a problem in theory as the larger battery (or flatter) would pull the alternator output down in voltage. in other words despite the diodes the batteries are not isolated in as much as the batteries will tend to share current correctly as if they were in paralell. So my question is how does it work out in practice. It seems a lot of people use diodes with smart charger and unequal sized batteries without problem. The writer made the statement that diodes drop a voltage when current passes through them. This is somewhat misleading in that the voltage drop is very non liner and depends very little on the current passing through the diode. ( rising from .7 volt only a little with very high currents) Of course the power dissipated (wasted) increases with current at the rate of .7 multiplied by current in watts. So the point made by Halcyon that the diodes waste power and produce heat is correct however 6% might be a better number.
I would suggest for cagey if he is happy with diodes that it would be so easy to add another diode from alternator O/P to new battery if he wants isolation of load. ( use a 35 amp diode bridge from electronic shops at about 2 quid and use one diode or 2 in paralell of the bridge.)
The diodes are Ok if you use a smart charger VSR of course are the only way to go with a standard regulator. regards will

 

[pvb]

Wild statement...

Yes, Will, it is a bit of a "wild statement" isn't it? Although there's some truth in it, what they don't say is that the same situation occurs with VSRs too (in fact, they claim that VSRs "won't allow overcharging" which I'd say is untrue).

When charging 2 separate banks using 1 alternator and a smart regulator, both banks will normally be subjected to the same charging voltage. For the engine start battery which, like a car's battery, is almost always fully charged, the voltage can be excessive. There are ways around this; some people have wired another leg of a splitter diode in to the engine battery charge feed, so that it receives a charge about 0.7v less than the domestics are getting. My favoured approach is always to use a maintenance-free battery for the engine start - the lead-calcium battery technology seems to tolerate high charge voltages quite well.

The ideal solution, if there's room on the engine, is to have 2 alternators. One smallish alternator only charges the engine start battery; the second bigger alternator only charges the domestics via a smart regulator. No diodes, no efficiency losses, no VSRs, simple wiring, and built-in redundancy in case one alternator packs up.

Incidentally, Merlin Equipment seem to be quite a well-respected company, and their website has some interesting information (although, curiously, no pricing details). James Hortop, their Marketing and Marine Sales Manager, has been an occasional contributor to PBO - though in fairness so has Nigel Calder, and I've already said what I think about some of his stuff!