battery

Actually some dc chargers will reopen the alt feed side once the van batteries are charged and back charge the tug batteries as well (assuming there is solar or other 12v on the van supplying excess power). The ctec 250 does this.

Get a dcdc charger that is IGNITION fed...problem solved.

I'm not sure that will fix it.

But now you have reduced your caravan charging voltage by 0.6 Volts.

Most caravans have problems with charging efficiency already, because of the voltage drop in the cables. Dropping another 0.6 volts is unhelpfull.

Peopl are looking at boosing their alternator voltage these days, because of poor charging efficiency.

Diode Isolators where a thing in the past ... Jaycar did at one time stock them.

But you can Buy a basic relay isolator for about $60 ...... and most of them are good for 100 amps.

Cheers

Yeah there is enough voltage drop in most caravan charging situations, let alone having a diode in series, even a Schottky one. That could be a volt or more.

Yeah , no it doesn't work that way guys.

Schottky diodes are only approx. 0.3 v .

In practise diodes don't actually cut right off anyway and will trickle charge lower drops.

My battery for example usually sits at about 0.2v and the simplicity of the solution , lack of constant relay current draw and extra wiring means it has a place - but its not for all situations.

It is hard ( expensive) to get a Schottky diode with more than about 10 - 20A capacity. And a Schottky at, or near its rated current will have a voltage drop of around 0.4 to 0.5V.

To get a voltage drop of 0.2A, the current usually has to be in the milliamps from my research in the past.

Which Schottky diode are you using that can handle charging currents and only has a drop of 0.2V Robin? That would be of interest to a project I have been working on for some time. Also are you aware that the bridge you refer to is a standard silicon bridge, at 40A it has a voltage drop of about 0.8V

Hi Boobook

That's the trick , you don't need to run the device(s) at its peak.

In my top reply here I referred to using 3 cheapies in parallel which maximizes the performance and was appropriate for my case.

The 0.2v drop only occurs at very low currents hence my reference to "Trickle charging". (sort of free top up that keeps battery fresh)

Also at the other end , it doesn't matter much that if you are drawing heavy currents and voltage drop goes up when the battery is low because in this mode
the battery has a lower terminal voltage anyway.

That's the beauty of this simple system, apart from preventing the backfeed issue - its also self regulating , as battery demand drops off and its terminal volts increase then the need for charging current decreases.

You will find the same principle used in solar panels.

I bet he did not tell you about the voltage drop that the diode causes.

Why???????