Guzzilazz said:
ericmark said:
The problem is if the car saves energy by switching off the alternator then if the split charging relay uses voltage to activate it could switch off while travelling.
It is easy to theorise and say fit a split charging diode on car and inverter on caravan which should work with all cars, but really you need to consider what will work with your car and your caravan. Also of course do you really need it?
Hmm, not sure that I agree with this... A proper VSR wired in correctly doesn't work in the way you indicate... I refer to my experience in the marine sector, where a VSR Is the best solution to the charging problem. The alternator, even if smart works by monitoring battery voltage. With my boat, when I start the diesel, I run the glowplugs for about 10 sec, drawing 40 Amps before cranking and drawing loads of current. As the engine runs, the VSR is directing all alt output to the Engine battery, but within less than TEN SECONDS, you can hear the engine come under load as the VSR clicks over, and parallels both banks. Therefore, the alternator is responding to a lower voltage than the engine battery alone, so a smart alternator will continue to charge at a higher rate until the paralleled banks reach the appropriate voltage to indicate that the alt can shut down or reduce the charge.
The only caveat that I would make is that the cabling to the caravan battery will be much smaller than would be ideal for a proper split charge regime (my boat banks are connected by battery cable), so the voltage detected by the alternator would be lower.
I love riding my bike on the canal tow path, and my son did at one time live in a narrow boat, even when waiting for the lock to fill or drain, I have never heard the narrow boat engine stop as with a car when at traffic lights, I will listen more carefully now, But I would be nervous letting the engine stop unless tied up, and if tied up I would expect it uses a human machine interface (HMI) called an ignition switch, as far as I am aware the engine of a narrow boat does not stop charging when under load and only charge when on over run as canals tend to be level there are no up and down hill sections.
I don't really like the idea of stopping the car engine at traffic lights, has not let me down yet, but whole idea of stopping engine for such a short time seems flawed, and it seems so many people stop at traffic lights, then decide to go closer to the car in front, and as soon as you release the brake to also move up, engine starts and will not re-stop, so most of the time it ends up running anyway.
Narrow boats do tend to have either twin alternators and stage charging with domestic one, or special inverters, and there is no reason why inverters can't be used with a caravan to charge it's battery from the car, I am sure it would work well.
However a split charging relay is rather useless today, one with VRLA on the car the voltage is reduced, and two the engine management turns off the alternator to save fuel, even before that the split charger relay was not very good, unless you boost the volts, battery charging takes time, a 50% discharged battery with a float charge will take around a day to fully charge up again, we simply don't tow for that long.
Lift the volts to 14.8 from 50% to 85% charged then drop to 13.8 volts for last 15% and then yes in 5 hours you can put a reasonable amount of charge in the battery. But at just 13.8 volt if you can get 13.8 volts by time it reaches caravan and first 5 minutes you may get 10 amp charge, but after 15 minutes that has dropped to around 2 amp if your lucky.
For a 85 Ah battery 50% charged to recharge in 5 hours it needs to maintain 10 amp charge for most of the time, that will not happen with a relay.