Thinking About A Solar Panel? Look At This.....

[Deaky]

First job I did on my van was for a CTEK DC-DC charger. The only load on the leisure battery at the moment is the amp for the stereo and my dash cam, which has a parking mode that runs all night.

This is a graph of the state of charge of the leisure battery.


Then I wrecked the CTEK by connecting up a solar panel that had too high a VOC, so I used the van for a couple of weeks and manually charged the LB


I finally decided to go for a separate solar controller and a new DC-DC charger. I’m now running a Redarc BCDC1240 and a Victron Smart Solar 75/15.

 

[DaveyB]

That’s a pretty cool readout. What’s supplying the info?

 

[Deaky]

That’s a pretty cool readout. What’s supplying the info?

A CTEK smart charge bluetooth dongle.

 

[t0mb0]

Solar panels are the way forward. I haven’t used mains hook up since installing one. I’m not even sure I really need leisure battery charging from the alternator.

Is that CTEK gizmo just measuring voltage though across the battery though? If so, how on earth is it measuring accurate charge during charge/discharge cycles?

 

[GoatBoater]

Fridge runs 24/7 and I've yet to charge the leisure battery. Love my solar

 

[Tony Morris]

Could I ask what solar panels you are all using? Make and wattage. I am looking at connecting one to my Redarc BCDC1225 charger.

Thanks

 

[t0mb0]

I’m using a 250w flexible panel.

12V solar panels charging kits for caravans, motorhomes, boats, yachts, marine

The only downside is that the rear facing junction box is quite wide so you need to cut a fair size hole in your roof to get it in. If you’re willing to live with the box facing upwards on the panel, then obviously this isn’t an issue.

 

[t0mb0]

Actually, that redarc charger you have looks like a max input voltage of 32v so you’d likely need a dedicated mppt controller to handle that 250w panel.

 

[DaveyB]

I’m about to get a 150W panel fitted, not sure on the make though.
It has VOC of 22V so will work with my CTEK.

 

[Tony Morris]

Actually, that redarc charger you have looks like a max input voltage of 32v so you’d likely need a dedicated mppt controller to handle that 250w panel.

Thanks for the advice.
Looks like the Redarc would handle up to a 150 watt panel. I will probably try this and add another panel and dedicated controller if required.

 

[Phil_G]

What Tombo is saying though Tony is that the particular 250w panel he suggested has a voc of nearly 38v which is well beyond the Redarc's 32v voltage limit.
You could parallel a couple of 100w's, generally they are 18v ish.
Cheers
Phil

 

[Tony Morris]

What Tombo is saying though Tony is that the particular 250w panel he suggested has a voc of nearly 40v which is well beyond the Redarc's 32v voltage limit.
You could parallel a couple of 100w's, generally they are 18v ish.
Cheers
Phil

Hi Phil
Thanks for the advice. Am I right in thinking then that two 18v panels connected in parallel would remain at 18v and not double up the voltage to 36v in which case I would get double the charging power but at a voltage the Redarc could handle?
Thanks again.

 

[Phil_G]

Thats right Tony

You'd have double the availablility but the Redarc itself controls the current, automagically adjusting it to maintain the panel at its max power transfer point (only if your battery needs it of course)

 

[Tony Morris]

Thats right Tony

The Redarc will control the current, automagically adjusting it to maintain the panel at its max power transfer point (only if your battery needs it of course)

That seems the way to go then. Thanks again for the advice.

 

[t0mb0]

Yep, having the option to add another 100w in parallel sounds like a sensible plan!

You will double the current flow then so either overspec the wiring run for the first panel or be prepared to run another set of parallel wiring down to the redarc for the second panel. Also, check the redarc is happy with the total current from two panels.

 

[Phil_G]

Just to clarify, its the Redarc that controls the current not the panels - you could have a dozen or more panels in parallel without problems. Once the controller hits its current max it allows the panel voltage to float high rather than holding it with mppt.
Cheers
Phil

 

[t0mb0]

Just to clarify, its the Redarc that controls the current not the panels - you could have a dozen or more panels in parallel without problems. Once the controller hits its current max it allows the panel voltage to float high rather than holding it with mppt.
Cheers
Phil

Yep, I guess it can’t damage the charger. It’s more a case of whether the redarc can use the maximum output current to charge the battery. I assume it can, the current off each 100w panel, shouldn’t be more than about 6a if the voltage is 18v’ish.

 

[Phil_G]

Also bear in mind that panel specs are always 'optimistic'
Especially noticable here in Blighty....

The main advantage of multiple panels (or one larger panel) is that they continue to give useful output in poor light

Cheers
Phil

 

[Sniggib]

Hi all,

Resurrecting an older and useful thread....

Can I clarify, if I have two 100W solar panels with an Open Current Voltage of 21.9V can I connect both of these up to a CTEK250SE which has an OCV limit of 23V, or does the OCV double if I add two panels?

Cheers,

 

[Phil_G]

... or does the OCV double if I add two panels?

Only if you wire them in series. If you wire them in parallel, the voltage stays the same as one panel, but at twice the current.
Parallel also has advantages when the panels are partially in shadow.