Fitting Solar Panel to 2001 Drifter - battery location & panel advice please!

[Slopey]

Hi All,

Now that I've found a new gearbox made of pure unobtainium for Debbie the Drifter (Compass Drifter 410), I'm keen to crack on with my next project which will be adding solar power to keep the leisure battery topped up off-grid.

Currently only have one leisure battery fitted, and it's under the back rear right side of the U-shaped lounge (if you were standing in the van looking out the back), whilst the cupboard with the distribution box etc/TV antenna/roof cable access is mid-van on the left. It's around 3m meters of cable run down from the controller, then round the back of the lounge to the battery compartment.

In this scenario, will the losses be too great on that length of run? Rather than mount the solar controller in the cupboard, would I be better with a longer run from the panels to the controller, then a short run from the controller to the batteries (i.e. put the controller under the seats in the lounge), or is it just that the total run length would reduce performance?

With the location of the battery compartment, it'll be tricky to get the solar panel feed into that corner and would be difficult for cable access. Getting into the cupboard (K on the diagram attached) with the distribution board would be a piece of cake (i.e. straight in through the roof), and then I can run cable from the cupboard round to the battery box without any difficulty.

Planning on maybe a 175W panel, bolted to the roof rack which I don't currently use. Thinking of a Victron MPPT 75/15 with Bluetooth most likely - or would a cheaper controller box be a better idea with a SmartShunt 5 for bluetooth monitoring?

I may well add a 2nd leisure battery in the near future as there's plenty of space under the van for it.

Queries are:

- are long cable runs to be avoided at all cost? Or are the losses acceptable?
- if they are, would a longer run from the panel to controller rather than controller to battery be beneficial?
- is 175W about right for a 1 or 2 battery setup mostly for keeping topped up (largely use hookup when on sites, don't do much proper boondocking currently)
- Victron MPPT with Bluetooth, or cheaper unit with/without BT and a SmartShunt? (I do like a gadget though....)

Any help would be very much appreciated - don't want to go to all the hassle and expense and find out it's hardly charging!

Cheers,
S.

 

[autorouter]

There is existing power wiring between the distribution box and the battery compartment. I'd look at that and see what its size is.

I think siting the solar controller near the distribution box is a good idea. Probably the wire to the battery will be thick enough already to minimise voltage drop. You could connect the solar controller to the leisure battery terminals on the distribution box.

If you think the wire is a bit too thin, you could run a thicker wire, which would benefit both the solar controller and the feed to the distribution box. Alternatively you could add a second wire alongside the existing wire, rather than scrapping the existing wire and running a new thicker cable. Remember it's the total cross-sectional area of copper that matters, two 10mm2 wires is the same as one 20mm2 wire.

 

[Slopey]

Ahhh - doh! Was forgetting I could use the existing battery feed to the distro box - for some reason had it in my head I'd have to wire to the battery separately, but as you point out, there's no point!

Will check the spec of the existing wiring. I found a conversion table yesterday which suggests that AWG 6 would be sufficient for the 3m or so I'd need to run it, but will check the calcs again.

Is there any value in running a SmartShunt along with a bluetooth MPPT, or are they both just offering the same functionality as far as battery state reporting goes?

 

[autorouter]

The SmartShunt is fitted in the battery negative wire, and accounts for all amps going into and out of the battery, so it can calculate the SOC at any time, even when the battery is charging of under load. The MPPT doesn't have access to this information, it can only report what it is outputting to the battery itself, not other charging currents or loads.

The MPPT can't even measure the voltage accurately along long wires - there's a gadget called a SmartSense that sticks on the battery and reports the accurate voltage and temperature by Bluetooth. However that's not necessary if you fit a SmartShunt, because that can also report the voltage and temperature.

 

[Slopey]

Perfect - will probably fit both just so I can see SoC and what the MPPT is putting out via the Solar.

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