Adding a portable panel to fixed system with CTEK D250S

[gavio]

Hi All:

I have a system now consisting of two 85 watt rigid panels in parallel feeding the solar connection on a CTEK D250S controller, which is also managing the input from my alternator..... I have a pair of golf cart batteries, 215 AH or so..... I want to add a semi-flexible 100 watt panel to use as an additional portable panel for use when I'm in the shade or when light is low or whatnot..... I haven't been able to get a clear picture in my head of how to hook this up....

Do I just add the connection for the new panel in parallel with the existing array on the CTEK?

Do I need to use a separate controller for the new panel and connect that to the battery, in parallel with the CTEK? If I do, will that confuse the CTEK?

I looked quite a bit online, but haven't found anyone using this same setup, and I'd prefer to get this working right the first time (who wouldn't right?)

Anyone doing the same thing? Or have insight as to how this will work the best?

 

[frater secessus]

Adding a panel of different characteristics will likely yield poor results; the AltE youtube channel has several demos on this topic.

If it were mine I'd add a cheap PWM or shunt/on-off controller for the portable panel, There is no problem charging from two or more sources at once.

Sent from my Nexus 7 using Tapatalk

 

[Ticklebellly]

Do I just add the connection for the new panel in parallel with the existing array on the CTEK?

Yes.   I have two fixed 150 Watt panels on the roof of a caravan and a 120 Watt semi flex panel on a wander lead with MC4 connectors.   I often prop the flex panel in the best current sky window and plug the wander lead into the matching connectors on the 250S.   By moving and angling the portable panel, I often get more than 8 Peak Sun Hours out of that panel.

 

[gavio]

Thank you..... Questions:

Tickle belly: Do you have the Wanderlead connected in parallel with the leads to your fixed panel ( so they are all connected at once) ? Or are you switching between them, so you only have connection to either the portable system or the fixed system at any one time?

Frater: I have read things in the past about potential problems connecting panels of differing characteristics (and some of the flex panels I'm looking at say they don't recommend connecting them in parallel), but what about controllers? The CTEK is an MPPT controller, so what happens if it's connected to the battery in parallel with a PWM controller under various conditions - ie, the fixed system is in low light, but the portable panel is in direct sunlight, etc.)? 

I understand how solar works in simple systems, but have never been able to wrap my brain around what happens when various things collide - such as two charging sources on one battery.... That's why I got the CTEK, so it would deal with the combination of the alternator plus the solar panels.... Anyway, thanks for helping me......

 

[tx2sturgis]

An option I use is a distributed power 'system'.

3 separate battery banks served by 3 controllers and panel arrays. One is fixed, one is semi-portable, and one is fully portable, including the battery. 

I divide the items that I power so that each system is independent. 

You could achieve the same by keeping your fixed system as is, and then a new, separate battery, controller, and panel. This system could power other items, such as laptops and LED lights, phone recharging etc, and the main system can power your fridge, and/or other items.

You can move your intermittent portable devices to whichever system has a surplus of power.

This greatly simplifies things, compared to interconnecting two mis-matched panel arrays,  controller settings, and 
battery voltages. 

This new battery should be approximately matched to the panel that will supply it. A 100 watt portable panel will match up nicely with a basic PWM controller and a mid-sized AGM battery in the 55ah range approximately.

And this second system would also be 'scalable' meaning you could, if needed, double the panels and double the batteries, assuming the additional controller you bought will handle this higher level of current. 

A benefit to independent systems is redundancy. If one system fails for whatever reason, you still have SOME power available to operate critical loads, at least for the time period needed to affect repairs to the other system.

.

 

[Ticklebellly]

Tickle belly: Do you have the Wanderlead connected in parallel with the leads to your fixed panel ( so they are all connected at once) ?

Yes.   My fixed panels, and alternator, are always connected and have two stubs with MC4s hang off the Solar posts of the 250S to take the matching ends from the portable panel.   This arrangement is just over 5 years old now.

I am extra happy with the 250S of late.   Newly acquired Bluetooth monitor that talks to smart phone app tells me the 250S floats my Gels at 13.8 and pops up to 14.1 when the fridge cycles.   Returns to 13.8 a couple of seconds after fridge cycles off.   After disconnecting the 250S input to the battery, I found that the fridge draw drops the battery terminal voltage to 13.4.   No biggie, just interesting, ATM.

That last bit of info might be of extra interest to anyone looking to install LiFePo4 as a drop-in replacement.

 

[gavio]

I see where a fully redundant system could be useful, but it wouldn't be a good choice for me..... In part because my main power user is my fridge, which I need power for at all times, and also because I live in a small van (GMC Safari) so there just isn't space to take on board another battery.....

 

[tx2sturgis]

Ok...well maybe someone else reading this thread might be able to make use of a redundant system. 

There are others here who have provided good information for you...hopefully you can make it work well.

 

[gavio]

Thank you..... Tickle, I hadn't seen your last post before.... Your setup is connected the way I had originally envisioned - Im glad it's working well for you..... I didn't follow what you were saying about the voltage at your battery when you disconnect the CTEK - it seems like with the charging source disconnected, voltage should go to 12.7 or whatever, so I must have misunderstood what you said you did......

Tx2 , I agree in a different situation, someone could really benefit from a split or redundant system, thanks for bringing it up.....

At the moment, I'm leaning towards getting another charge controller dedicated to the wandering panel as it seems that may help me squeeze some extra juice out of it under a lot of conditions...... I'm still unclear how the two controllers work it out when they are both trying to do their own thing while connected to the same battery.......

 

[jimindenver]

The two controllers should be set alike to be doing a thing, not their own things. They should both see the same voltage and react the same.

 

[gavio]

I see what you're saying, but they each would also be affecting the voltage by applying a charge - so the voltage read at the terminals is higher than battery resting voltage would be..... And even if they were identical controllers (which in my case would not be possible, as the CTEK is kind of a unique beast), the conditions would be different if one is in shade and the other in sun...... Right?

 

[Trebor English]

So one panel and controller supplies 5 amps.  The other supplies 8 amps.  The battery gets 13 amps.  Does anything else matter?  If one controller is set to 14.8 volts and the other is set to 14.4 and all they can do is 5 amps and 8 amps then you get 13 amps.  If you reprogrammed the 14.4 volt controller to 15 volts it wouldn't give any more amps.  

When the battery gets up to 14.5 volts the 14.4 volt controller will stop contributing amps.  It won't load the system down to get that battery down to 13.8 volts float voltage.  The higher voltage controller will hold the absorb level when the battery gets to 14.8.  If the fridge compressor comes on the battery voltage may go below 14.4.  At that point both controllers should give what their panels provide.  

The battery resting voltage never happens as there is always charging or discharging going on.  Whatever the resting voltage would be doesn't matter anyway unless it is for your curiosity.  Unplug your fridge and wait 8 hours.

 

[gavio]

OK, thanks, I can see it that way.....

I think I will go for a dedicated controller for the portable panel.... Based on what I think I've learned, a PWM controller should be fine for that, even though the CTEK on my fixed system is MPPT....... Right?

I appreciate the help, y'all.....

 

[QinReno]

Naive question here. It's my understanding that solar panels are "current" sources and normally have reverse-flow prevention diodes built in. Maybe both assumptions are wrong. ???

If so, can't you directly connect 2, even different, solar panels in parallel to the same charge controller input? Therefore, if either or both panels is providing current, then the currents will simply summate?

 

[frater secessus]

but what about controllers? The CTEK is an MPPT controller, so what happens if it's connected to the battery in parallel with a PWM controller under various conditions - ie, the fixed system is in low light, but the portable panel is in direct sunlight, etc.)? 

Different controller types are fine. Here's a writeup that has an example in it that may make it easier to envision.


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[frater secessus]

If so, can't you directly connect 2, even different, solar panels in parallel to the same charge controller input?

It isn't whether or not you can do it, it's whether or not it will provide expected/desired results. The AltE videos I referred to earlier demonstrate real world scenarios in panel mixing.

Therefore, if either or both panels is providing current, then the currents will simply summate?

Yes, panels almost always have diodes to prevent electrical "backwash". This works both at the panel level (one panel is completely shaded) and at the cell string level (part of one panel is shaded).

The sum may not be something you expect because different panels can/will make different levels of power at the same voltage (ie, different power curves).

With PWM I think it would not matter if the panels were paralleled or separately controlled; they will run the panels at bank voltage (Vbatt). If I am overlooking something here I hope to be corrected.

MPPT can get tricked by mixed panels, as there can be 3+ of what appear to be maximum power points: mpp for panel A, for panel B, and for the two combined, etc. The controller may see one peak and think it's found the best one. The only way to know for sure would be to sweep the entire voltage range and that takes time away from power generation.

The behavior of a given controller with mixed panels may be unpredictable. One would have to test it, and the results might not extrapolate to other cases. IMO it's preferable to just use matching panels.

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[QinReno]

FS, thanks for the info re your website and the link to AltE, had not seen that one before.
- https://www.youtube.com/user/AltEStore/videos

In regards mixing different types of panels, as per OP's original topic, I realize that amorphous panels are much less efficient than mono or polycrystalline, but in youtubes that I've seen, amorphous will pump out a lot of power even when they are partially shaded. In contrast, with my 100W monocrystalline panel, amperage drops off radically when part of the panel is shaded. I have a minimalist non-permanent system, so I also move the panel outside when I need charging.

So, assuming you would have enough surface area for mounting everything, I was wondering if anyone has tried mixing both amorphous and crystalline panels so you can get high amperage in the sun, but also (possibly) decent charging when in partial shade. Best of both worlds. Yes/no/maybe/forget-it ???

 

[gavio]

Different controller types are fine.  Here's a writeup that has an example in it that may make it easier to envision.

Thanks, frater, that did explain it well.....