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[Gaffers]

I know I have touched on this topic before but the circumstances (and ahem car) have changed since then.

Situation:

Jag fitted with towbar, 7N +12S sockets.  The latter has a bypass relay fitted.
RIB on trailer which I am fitting out with a 12v 50AH deep-cycle Leisure battery.

I want to be able to charge the battery with the car whilst towing, but also keep it topped up whilst it is stationary with a small solar panel and/or wind generator.  I doubt I will be able to to something as simple as just adding a 10 guage wire from the switched live and ground line on  the 12S and adding a charge regulator for the solar/wind feed? 

The battery will power a couple of lights, radio and eventually a raspberry pi which will provide a number of security and navigation functions (plan of using a b+ for keeping the power drain low.  This is not the focus of the question but just added for context.  I am just a little hazy on the best way to setup the charging part.

All tips/help greatly appreciated

[Kevin Wood]

If the have a charging relay in the car, then you could pretty much just connect the battery to the appropriate pin on the 12s, with a suitable fuse inline. What you might need to be careful of is voltage drop from the car's alternator to the battery. It could well be that, by the time you get to the battery, it can't do more than just trickle charge it, but then that might be all you need.

On the solar and wind charging, there's no need for an elaborate controller unless you really need to extract the maximum possible energy in all weather conditions - all you need is an "amplified zener" across the battery to prevent overcharging.

[Gaffers]

The hope is that with the battery on the jag being in the boot and the battery on the RIB being near the front that the distance should short enough to keep the voltage drop to a minimum.  I know that the alternator is in the front of the car but I understand that the drop to the battery is not that bad.

So no need for anything fancy despite 3 potential inputs coming in to the battery at any one time?  I would have thought that at least a double throw switch/relay for the solar/wind input while the alternator is charging?

[Entwood]

Exactly as Kev says .. 12S wired correctly will have the charging relay already set up to charge a van battery whilst towing .. your RIB  should just use that circuit.

[Gaffers]

Just a thought, could I use a standard 12v charge regulator designed for solar, wire in the wind and solar to the input (in parallel) and double throw the output of the regulator with the 12S input on top the battery?

[Entwood]

Personally I would just wire the 12S to the battery using the diagram here ..  https://www.westerntowing.co.uk/acatalog/Caravan_12S_wiring_diagram.html

then attach the output from the solar charger to the battery terminals as well, so effectively in parallel with the 12S connections. The solar charger "should" be designed to back off charging at around 13.7 volts, so the output from the alternator, when running, would be up to 14.4v (minus whatever voltage drop you get from the length/size of wire) so the solar charger will simply stop, thinking the battery is full. Once the alternator stops producing the solar charger will take over.

I've no idea what wiring the wind generator/solar panel in parallel as one input would do to the solar regulator, given the low cost of them I'd be inclined to put a separate regulator on each one.

[Gaffers]

That sounds about right.  The additional wind input is a bit of a pipe dream but maybe unnecessary.  I will leave that out for now and just go with the solar right now.  The worry would be that when stationary for long periods that the solar would not provide enough juice and the wind (esp in winter) could help bridge that gap but a bit of searching shows that a dedicated MPPT dual wind/solar regulator aint cheap 

I already have what I need for the solar/12S setup so I'll give that a whirl (with a suitable fuse in line of course)

Thanks

[Kevin Wood]

There are all sorts of solar regulators available performing as anything from the basic amplified Zener to limit the charge to a proper boost/buck converter that will condition the output of the panel to the exact voltage that the battery needs at the time and maximise the energy transfer from panel to battery. If you have one of the latter, one option would be to feed it from the 12s connector whilst one the move, and the solar panel when not. This might not give you as great a maximum charge current as a direct connection from the battery when the leisure battery is depleted, but what it will do is to use its' boost functionality to compensate for any voltage drop from the car's alternator.

[Gaffers]

The regulator I have is pretty basic and is only rated to 10A so that option is unlikely to work.If I ever upgrade it I will certainly consider that setup

I am a bit constrained on size and layout due to it being a fairly small rib.  The console is custom though and the bay for electronics is water tight

[Kevin Wood]

It really depends what the usage pattern is likely to be, TBH.

Is this something you'll be storing at home, towing to the coast and using occasionally, then towing home? If so, why not charge the batteries from the mains when storing it and forget trying to charge from the car?

Or.. are you storing away from grid power, towing it before each use and relying on that to top up the battery? If so, why not take the battery home with you and charge it there?

Are there going to be any quiescent drains on the battery while in storage?

I doubt you will pull more than 10A of charging current through a 12S connector without the voltage dropping to a point where it won't be charging the battery at all.. Worth checking this with a suitable load and a multimeter.

[Bigron]

If you are going to do as Kevin suggests, it could also be a good time to check the battery's capacity. A couple of the H4 headlamp bulbs will give you a convenient load, and if they are still doing them, Poundland have a kit with one or two of same, plus other auto bulbs too.
So, in cdase you were unaware (sorry if you already know this) a 10 amp load multiplied by the time it is on will give you the capacity in Ampere-hours. Of course, it doesn't HAVE to be a 10 amp load, but lower loads will take longer!
You can empty a leisure battery completely this way; it won't hurt it. Then you can charge it fully, measuring the charging current and time to reach completion - same sum, current x time - and it will confirm the capacity.

Ron.

[Gaffers]

As my drive faces a busy road and I do not trust the local miscreants (or seasonal 'visitors' to the region) I shall be keeping the boat in a secure compound of the variety which has an armed guard on the gate.  That said the outboard is quite big and heavy so I will be permanently installing it to the transom and the idea is to install a RPi with a 2G connection to perform some basic monitoring (vibration, Geo-gate, speed, and disconnection of any specific wires in the engine harness.  It will also have a non-alarm mode which will allow the missus to keep track of me whilst spearfishing for her peace of mind, possibly with a web camera taking pics every 5 minutes of so.  The idea is to keep the power usage around 2W which will give me a couple of days with a 50Ah battery, hence the need to keep it topped up with solar and/or wind.  I haven't built this rig yet, but when I do I shall have to perform some tests to see what the power drain is like and whether the solar panels I have can keep up.

[Kevin Wood]

OK. It has to be stored where mrs. Guffer won't find it it'll be safe. Now I understand. 

I think you can do a lot better than 2W for the monitoring when stored. I'd be using a small microcontroller with a GSM module that gets powered up when required. When sleeping it'll take a few microamps so you can power it from an internal cell, meaning it can protest loudly if the first thing that happens is that someone disconnects it from the leisure battery.

In that scenario, I'm sure a small solar panel will be more than adequate to keep the battery topped up. Wouldn't hurt to tie it to the car's charging output too, to make sure it's ready to go, of course.

To provide 2W 24/7, I think you'd be struggling at certain times, but I might be wrong.

[Gaffers]

2W is a bit of overkill but I always round up when calculating power requirements.  My worry would be in winter with the shorter days but I could always just add an extra panel if it does cause issues. 

Agreed, I will have to play with the code on the GSM800 module I have and I will also have to trade off update frequency bearing in mind that I will need enough juice in the bank to power continuous updates for several hours should it ever get nicked.

Oh, and Mrs. G knows about this boat.  She bought it for me