Solar panel question

This has probably been asked before but I am thinking of purchasing a 250w solar panel to charge 2 x 120amp agm batteries in my camper trailer.The panel will be connected through a Ctek DC to DC charger which I believe has a solar regulator.Will I have to buy a panel without a regulator and if so do they sell them with straight connections to the dc charger?
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Reply By: Frank P (NSW) - Tuesday, Jun 12, 2018 at 21:36

Tuesday, Jun 12, 2018 at 21:36
Buy a panel or panels without regulators and connect them direct to the Ctek.

They should come with a junction box at the back. You can then add your own cable to the Ctek.

Some may come with short cables hard wired in place, but you're better off sourcing panels with just the junction box so you can cable it up to suit your needs.

A 250 watt panel will probably have just the junction box, so all good.

BUT, a 250 watt panel is typically a nominal 24V panel which has an open circuit voltage of around 46V. This is too high for the Ctek.. Make sure the open circuit voltage of the panel does not exceed the Ctek max of 23V. (My Ctek document is old - Ctek may have changed the specs, so check.)

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Follow Up By: NeddySmtih - Wednesday, Jun 13, 2018 at 09:59

Wednesday, Jun 13, 2018 at 09:59
A quick follow up on this as i am potentially looking at doing something similar with a bush hut i have.

I am looking at 250w panels and was thinking about getting 2 or 3 of these, but getting clarification if they are 24 or 12v panels.

IF they are 24v panels, do i need a converter to go from 24v to 12v before going through a Solar Charge controller or will the charge controller do this and accept the 24v with a 12v output to charge a battery etc.
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Follow Up By: Frank P (NSW) - Wednesday, Jun 13, 2018 at 10:24

Wednesday, Jun 13, 2018 at 10:24

If you establish that they are 24V panels, just get yourself a solar regulator that will accept the higher voltage input for a 12V output. They are common.

As always, there is a caution. If you get three of those, that would be 750 watts of solar. This exceeds the max solar WATTAGE input of many 12V controllers, even if they accept the higher input VOLTAGE.

To cope with both you will need something like this.

750 watts of solar could deliver in excess of 45 amps into the batteries. Make sure your battery setup can accept that sort of current. EG, Typical max charging current for AGM deep cycle batteries is 10 to 15% of the C20 amp hour rating. So a 100Ah battery should be charged at a max rate of 10 to 15 amps. You would need at least three and perhaps four such batteries in parallel in order to safely accept the output from 750 watts of solar.

There are other batteries that will accept high charge currents, so the above depends on your choice of battery.

I have a 30 amp version of that GSL for my hybrid camper. It is quite excellent, and I can recommend the brand. Talk to GSL about your system. (Usual disclaimer - no affiliation, just a satisfied customer.)

There are others, of course.


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Reply By: Malcom M - Wednesday, Jun 13, 2018 at 07:22

Wednesday, Jun 13, 2018 at 07:22
Lots of panels come with a regulator.
They are usually not too good and you certainly don't want to use it when the Ctek will do a better job.
Often they are glued onto the back of the panel and connected via plugs/sockets so you can simply bypass them.

Having the regulator available is not such a bad idea. The Ctek might fail one day...
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