Loz - you must have got up earlier than me - and saved me the trouble of setting up the science lab bit. But I think Travelvolt has looked back at the thread anyways and has seen the light.
The written word can be more misleading sometimes than the spoken word hence why we all get a wee bit passionate and hot under the collar about things - sorry if we all got a bit personal.
For the record, I also agree with you and travelvolt that a good DC to DC charger
IS the best charging solution - I have never said otherwise. My comments re the CBE are only saying that there are other methods and that there may be room to look back at what is thought of as old wisdom.
This was why I specifically mentioned the CBE split charge facility as it cannot be just an ignition activated VSR as described in the literature as it does not behave like one.
To sum up me lud:
- A straight relay link (by VSR or ignition) cannot control current flow to a device - the points are either closed or open and whatever current is driven by the potential difference in the two nodes will flow across the points regardless of whatever rating is on the relay, either burning out the relay, wiring or fusing at the weakest link. The CBE split charge will not drive more than 30A through the relay regardless of the battery states. I suspect FET's are involved which aren't the most sophisticated method as there is definitely no PWM on the trace when you zoom in to data points.
- A straight relay link like a VSR or ignition controlled relay will not see a variable voltage drop across the input and output between 0.01v and 0.68v for a relatively stable input voltage. Losses of this order would generate sufficient heat somewhere to be noticeable.
- A straight relay link, even with a time delay on a VSR will 'bounce' around the drop out voltage until the voltages stabilise between the two charge stores. Through the full range of voltages, the CBE split charge does not drop out when activated.
My suspicion is that the CBE is no more sophisticated than a FET controlled caravan split charge relay would be; not the best solution for charging aux batteries but still one that works to a point. There are downfalls with this solution as once the voltages do stabilise and both batteries are fully charged and the current flow reduces, the regen voltages DO appear at the aux battery. This is why we always activate the 'disconnect' device so that any 'Aldi' fairy lights installed by users I mentioned before do not see 1.25 x their rated voltage. Battery pairing is vitally important with this less sophisticated charging method.
Yes this setup will never charge the batteries to 99.99% but in a lot of instances it can be sufficient to meet the purposes and needs of the user and yes we could debate battery conditioning, surface charging, desulphation via PWM, discharge and float charging, ramping charges etc etc in charge cycles all of which take you from lets say a 97% capacity charged battery to a 99% charged battery but that wasn't what I was trying to debate.
So if a DC-DC is agreed as the best option, why raise the topic? If the 'con' is that the CBE is definitely not as good at charging the aux battery as a DC-DC charger is what's the 'pro'?? In a word cost. I can buy a 240v charger, switch panel with gauges for my camper circuits, built in fuse box, split charge (contentious or otherwise) and mains distribution box for less than the cost of a 'cheap' battery to battery charger.
It is more a choice than a 'right' or 'wrong'. The choice being to have a battery charged to what you may deem an acceptable operational level and accept there may be maintenance issues and that you might get 12 hours off grid instead of 14, or spend a few hundred quid on trying to attain the holy grail of a fully charged battery, relatively speaking 'maintenance free' with the benefits that go along with the DC-DC charger. When I explain to customers the benefit of DC-DC and that it will mean an additional £400 to the build, they often opt for the cheaper solution.
