Hi, I've currently got a Brocott / Smartcom voltage sensing charger which, to be fair to it has worked very well for the past few years but I'm questioning it's safety now I'm redoing all my electrics... For those unfamiliar with the Brocott: https://www.amazon.co.uk/Smartcom-Voltage-Sensing-Motorhome-Charging/dp/B00SGFTR2S I've got an 18mm2 earth cable running to the main battery and then 18mm2 cables running from the leisure battery to the fuse box I have in the van... The problem is that connecting the main battery + and leisure battery + is the Brocott split charger, perfectly fine you might think, but the wire that it comes with, and the largest wire that fits the unit is 8mm2... I've always assumed that as it came with the kit it is correct and just 'is' but now I'm coming back to working on the van I'm looking at it with fresh eyes, shouldn't the whole circuit from main battery to leisure battery to fuse all be the same wire width, ie 16mm2, otherwise I'm introducing weak links??? Or am I going mad / over-egging the 18mm2 cable??? Or would I be better going for something like a Durite split charger which appears to be a little more robust?
Just use the Smartcom to switch a high current relay like the Lucas split charge relay. Don't use the Durite relay if you are charging the leisure battery from a mains charger. And 18mm2 cable is well overkill. 6mm2 will be enough https://www.ebay.co.uk/itm/LUCAS-SR...444986&hash=item35f8bf7b8d:g:dtUAAOSwLN5WjrEJ
Is the Lucas mot doing the same job as a the smartcom though? Can you just use the alternator to switch the lucas on and just buy 6mm2 wire ?
You can switch the Lucas relay either way just by a connection to the blue alternator wire or by a voltage sensor. It is just ease of wiring up really.
Yes, the smartcom is a smart split so it does what the Lucas does, with easier / lazier wiring as it doesn't need alternator wiring...
The Durite voltage senses and switches on too both the leisure battery and the starter battery voltages which can cause it to switch on if the leisure battery is been charged and start charging the starter battery, you shouldn't charge two different states of charge/disimilar batteries from a source that can take the battery above it's gassing level (smart chargers do) as it can overcharge one battery before the other is charged. Alternators are set not take a battery above it's gassing level.
But when it switches on , because it acts as a relay, it parallels the two batteries, and charge immediately starts transferring from the more charged battery to the less charged battery. A current of several amps will flow. This has the effect of instantly reducing the voltage on the better charged battery, so the better charged battery is no longer at such a high voltage. Because of that it will stop charging and the battery charger will tend to be charging the newly arrived battery. Problems will appear at end of charge if one battery is knackered and goes to a high on charge voltage which will tend to push current back into an already well charged battery. A smart 4 stage charger that thought it was on a particular part of the charge cycle may also be as the French put it become "derangee" and give up as the VSR connects. A charge maintainer style charger wont care - one that ramps current between say 10 amps at 12 volts and nothing at 14.2 cant charge as fast but wont overvolt a battery, like a 4 stage one might. I dont have a VSR just a big diode from LB to starter, so the LB mains charger and solar regulator just stops the starter battery from discharging if there is any load like the stereo head unit.. the voltage is about 0.5 volts less on charge. My alternator feeds both through a dual relay style MOSFET splitter so when the engine is running both batteries are in parallel for charging.
It is very simple really, industry standard is not to charge any dissimilar batteries off one source if gassing can occur. It can go wrong when you do. KISS.
Soooooo, I'm guessing that my Brocott option is fine as it is a Volt sensing circuit which detects a rise in voltage (when engine running) and energises the coil of a split charge relay to charge the leisure battery and doesn't send anything back the other way?
