Ideal electrical set up???

[trentjim]

Ok... Thread resurrection alert
So since the gods of Ebay have not yet delivered unto me a sterling charger, I've been playing around with an arduino and some power mosfets to explore the possibility of formulating an intelligent charging solution from scratch...
but i keep running into the issue (on paper) of the alternator "seeing" the fully charged starting battery and easing back even though the leisure remains partially discharged.

Then I had a thought... which is always dangerous...

Assuming "The Ideal electrical set up" has the option of 240v when needed... and assuming the leisure can be charged off a hookup when available. The "system" already has an inverter and a 240v charger present.

It's fairly trivial to devise a switching system which charges the leisure (when the engine is running) by powering the mains charger through the inverter from the alternator.

This would mean that the two 12v systems were wholly isolated, therefore the charging regime of the leisure would not be compromised by the starter & the charging can be optimised for capacity/longevity
The key drawback would be the slower charging rate... which would more or less preclude recharging by idling, but shouldnt be so much of an issue when touring... and anyway, a simple switched cable could still be used to manually connect the systems if I did need the full output of the alternator to fast charge the leisure.

Has anyone considered or attempted a setup like this?
James

[ghost123uk]

You could do it that way and note that if you are charging via a mains charger and inverter, then the fact that the motor is at tickover is irrelevant. The mains charger "doesn't know" the engine as at tickover.

However, if we are talking about charging whilst the motor is running (tickover or driving) then your idea that the alternator will ease up on seeing the main battery is charged is in error.

The alternator is not that clever, a circuit (whatever it consists of, lights, batteries etc) "pulls" amps from the alternator. The alternator does not "push" amps out. So, the lower resistance in the circuit, caused by the discharged leisure battery will "pull" amps from the alternator (and by the way, to some extent from the main battery) and so it will charge up perfectly ok regardless of main battery being fully charged.

Hope that helps, it certainly will make life simpler than the other solution (which by the way is a bit inefficient too )

btw, what charging voltage will you be aiming for ? 14.5 Volts seems favourite these days.

[v-lux]

Think you'd need a beast of an inverter to keep up with the amps the batteries would ask for. Would depend on the charging rate of the main charger of course, but if it real low then it'll take hours to get a full leisure charge.

[trentjim]

However, if we are talking about charging whilst the motor is running (tickover or driving) then your idea that the alternator will ease up on seeing the main battery is charged is in error.

Thats not my understanding... the "S" terminal of the alt monitors the battery voltage does it not...
if the (full) starter is connected to the (empty) leisure then the leisure will pull it down, drawing current from the the starter & the alt will begin supplying meaningful current to both... If there were 0 resistance in the system then this would work fine, the "virtual" battery that the alternator "sees" is just a series of cells that equalise their charge while drawing external current.

But there is a non negligable voltage divide and resistive loss in the system - between the two battery banks - ... exacerbated when the battery banks are assymetric in capacity. This factor would appear to prevent the leisure side of the system achieving 100% charge.

Im not saying that a split charge system isnt an "adequate" solution... the evidence would suggest that it is perfectly adequate for most peoples needs... but its a setup which is nigh on half a century old and which is widely understood to be less than ideal. Hence the market for Sterling chargers.

Im just thinking through other ways around the same problem

Hope that helps, it certainly will make life simpler than the other solution (which by the way is a bit inefficient too )

Simpler lol - you should see some of the schematics in the bin!
...everything is inefficient & the watts dissipated by a 1ohm resistance in a split diode with a 50A load (50W) is a benchmark that doesnt look unachievable. Any discussion of inefficiency is moot anyway when the alt alone is probably not much better than 50%
V-Lux - this is of course the issue - A very efficient "beast" of an inverter with a low consumption when unladen - I havnt yet found one which fits the bill without making a sterling look cheap!

if it were "only" for charging, rather than also running an efficient 240v mini compressor fridge off the batteries/ solar panels then efficiency wouldnt matter. Take efficiency out of the equation and such a combo starts looking very affordable.

Thanks for being a sounding board guys