Question about charge controller and panels

[CaptainEven]

To whom it may concern:
I am brand new to solar/PV systems and am hoping to gain some of your sage advice. My RV has no solar system or batteries and I am putting it together from scratch. I am hoping to effectively charge two Interstate GC2-ECL-UTL 6v 115mins @ 75 amps 225Ah @ 20hr batteries wired in series through the use of three 100 Watt 12 Volt Polycrystalline Solar Panels and using a CTEK D250S Dual Battery Charger 12V- 20a, 5 step, Heavy Duty. I recently became aware that this charge controller can only support up to 240W so I'm effectively limited to a maximum of three 100W solar panels. I am therefore curious to know if three panels will be sufficient to charge the batteries. I an very interested in the use of this charge controller as it can charge the interstate batteries while driving and automatically switch between solar and the vehicle alternator.

Should you think that this charge controller cannot possibly charge the batteries during the course of a "normal" day then I ask if you might have a suggestion as to a replacement.

Thank you.

[Mike90250]

The Dual part, is 2 charging sources are auto selected to recharge the house battery, this does not appear to charge the starting battery.

The troubling part is the Solar Panel input voltage, the spec limit is Input voltage 22v , yet your panel is 22.4v Might not work well, or it might

300w of well aimed solar should maintain 2 batteries, BUT it depends on how much you drain the batteries, and how well you expose the panels to sunlight

[CaptainEven]

The troubling part is the Solar Panel input voltage, the spec limit is Input voltage 22v , yet your panel is 22.4v Might not work well, or it might

Sorry but I'm not sure sure what this means. Can you break it down for me, please?

[Wy_White_Wolf]

Sorry but I'm not sure sure what this means. Can you break it down for me, please?

The highest voltage your charge controller can except from the panel is 22 volts. Above that you risk damaging the internals and letting out the magic smoke.

The panel has a VOC (voltage open circuit) of 22.4 at 25d C. That raises in cold weather so needs adjusted. General is 25% increase factor unless you can show that a higher number is needed. So the adjusted output voltage of your panel is 28 Volts (22.4 * 1.25). Well above the rating of the charge controller.

To have an idea if the system is large enough to charge the batteries depends on how much solar is available (your location and how mounted(shading)) and how much you plan on using (AH used daily or % of discharge daily). Without knowing that 20 watts could be plenty while 1000 watts could be to small.

WWW

[Mike90250]

The troubling thing, is that there is no panel qualified to charge a 12V battery, that would meet the Voc spec for the Controller, 12V panels produce about 17-18V, so that it can be regulated to 12V. But the Voc of a 17 or 18V panel is always about 22V.
Furthermore, using a MPPT function for the 3 or 4 extra volts from 16V to 18V, is such a minuscule gain, it's hardly worth it.

But that alternator charging feature is nice, and maybe worth using the controller as an Isolator, and another, reliable brand as a real charge controller for the PV.

[CaptainEven]

The troubling thing, is that there is no panel qualified to charge a 12V battery, that would meet the Voc spec for the Controller, 12V panels produce about 17-18V, so that it can be regulated to 12V. But the Voc of a 17 or 18V panel is always about 22V.
Furthermore, using a MPPT function for the 3 or 4 extra volts from 16V to 18V, is such a minuscule gain, it's hardly worth it.

But that alternator charging feature is nice, and maybe worth using the controller as an Isolator, and another, reliable brand as a real charge controller for the PV.

I'll call CTEK and ask them about this and if the controller will be damaged or the warranty will be voided. Why would they make a controller which couldn't handle the voltage incoming from the panels?

[Wy_White_Wolf]

Product of Sweden so may not list the same specifications as American designed products. But you would think all Euro counties would follow the same standards and I have seen German products that use VOC for input.

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[CaptainEven]

Product of Sweden so may not list the same specifications as American designed products. But you would think all Euro counties would follow the same standards and I have seen German products that use VOC for input.

WWW

What's curious is they have an office in Chicago so it would seem they know about solar panels in the US. https://smartercharger.com/contact-us/

[SupraLance]

My thoughts are that batteries can have more than one charging source, such as several controllers that each have their own pv but attached to the same battery, so I don't see why your input from the alternator needs to go through your solar controller in order for your alternator to also charge the batteries. At the very least, you could have this controller with 200w of pv on it, and another controller ran to the same batteries with the rest of the pv so you can have as much pv as you need for your loads.

[Wy_White_Wolf]

My thoughts are that batteries can have more than one charging source, such as several controllers that each have their own pv but attached to the same battery, so I don't see why your input from the alternator needs to go through your solar controller in order for your alternator to also charge the batteries. At the very least, you could have this controller with 200w of pv on it, and another controller ran to the same batteries with the rest of the pv so you can have as much pv as you need for your loads.

The only advantage I see is to keep one under the maximum charge rate for the batteries. With having them through the 1 controller he is limited to a 20 amp charge. If he ran separate controllers he could have 20 amps from this one and whatever amperage the second controller allowed.

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[CaptainEven]

I just spoke to CTEK and they said the 22V input is a misprint and it's really 23V. They are sending me an email right now with info which says that. I am still limited to a 300W solar input but at least the panels won't fry the charge controller.

[CaptainEven]

Screen Shot 2018-03-06 at 2.17.02 PM.png
From the updated manual they just emailed me.

[Wy_White_Wolf]

I just spoke to CTEK and they said the 22V input is a misprint and it's really 23V. They are sending me an email right now with info which says that. I am still limited to a 300W solar input but at least the panels won't fry the charge controller.

Still far under the 28V I calculated for your panels in cold weather earlier. Just about every other 12V nominal charge controller I see has a input voltage up to 30V.

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[CaptainEven]

Still far under the 28V I calculated for your panels in cold weather earlier. Just about every other 12V nominal charge controller I see has a input voltage up to 30V.

WWW

The guy promised me it'll work and the warranty won't be voided. I hope he's right.

[Mike90250]

I hope so, because there are no "12V" panels that do not hit 23.1V on a cold morning.