Hi & balancing a Xantrex C30 & XW MPPT 60 Charge controller

[Gorllwyn]

Hi to everyone on this very helpful site. I have a bit of a problem some of you experts might be able to help me with. I live off grid and have been making my own power for 17 years and have now built up a system that has been working very well.
My setup consists of;
2 solar arrays charging 8 Rolls 6V Surrette batteries configured at 24V = 1092 amp hrs capacity.
Array A; 4 Off Evergreen 180 watt panels to Xantrex C35 charge controller set at 24V
Array B; 6 off Italia 210 watt panels to Xantrex XW MPPT 150, input configured at 72V and output to 24V.
This is my problem which happens when we have a good day of sunshine; I have recently set the Xantrex XW60 MPPT charge controller to the custom battery charging menu and set the input voltage to 29.6V. as this is the setting recommended to me by the battery dealers. Since I have done this I get a much better output from the panels every day. Now the problem is the smaller Xantrex C35 seems to think the batteries are fully charged and shuts the C35 controller down. I have tested this by switching off the larger array and the result is the smaller array starts to charge again. Is there anything I can do to stop the C35 thinking that the batteries are fully charged. I have tried setting the bulk potentiometer to the maximum setting (30v) but this does not help.
Is there anything I could do to stop the smaller charge controller fighting the larger one other than to buy another Xantrex XW MPPT60-150 charge controller? Could I use different (opposite) battery posts to connect each charge controller?

I have always had good information from Xantrex in the past but not this time. I was put in touch with a guy in France called Mr. Leroy who told me that the system would not work with one C35 charge controller. He insisted that I would need one charge controller for each panel! The Xantrex manual has diagrams of panels wired in parallel so I assume he has not read the manuals. Has anyone else noticed that the support from Xantrex is going downhill?

Thank you for your help,
Regards
Gwyn

[Cariboocoot]

Welcome to the forum.

No, you do not need one charge controller per panel. That's just nuts. Let's pretend it's a misunderstanding and move on.

The problem is that the two different controllers can't "talk to each other". The closer you can get the charging settings on both, the better off you'll be. So same Absorb Voltage, Absorb set time (or current limit) and Float Voltage. The trouble is they also will not be sharing battery temperature information and they may not agree on what the actual battery Voltage is. The larger controller brings the Voltage up to 29.6, the smaller one thinks 28.4 is right so anything over that is "charged" and quits.

If the C35 can be reconfigured to more closely reflect the settings on the XW MPPT someone around here will know how to do it.

I'm an Outback man myself. Our motto is " No worries!"

[Gorllwyn]

Thanks for the quick reply Cariboohoop.
I did think that the guy at Xantrex was wrong. It was not a misunderstanding, he was adamant (and very arrogant) that he was correct and he refused to talk to me as he said my system was set up incorrectly! I was very surprised that someone who worked for Xantrex did not know about renewable energy systems, I think this could be a bad sign for the new owners perhaps? The times they are a changing maybe?
Yes you are defiantly on the right track, I just need that magic bit of knowledge to get things working to the max.
Best regards
Gwyn

[BB.]

Depending on temperature of your system and how deeply you discharge you battery bank--and the panel's Vmp ratings:

Array A; 4 Off Evergreen 180 watt panels
Array B; 6 off Italia 210 watt panels
==============================
1,980 watts rated

And, for a "fully configured" charge controller (sort of the best bang for the buck--or most energy for money out of pocket):

• 1,980 watts * 0.77 derating * 1/29.6 volts charging = 51.5 amps typical max
• 1,980 watts * 0.77 derating * 1/29.6 volts charging = 66.9 amps max rated

So, if you can place the 4 Evergreens in series for Vmp-evergreen-array=72 volts +/- 10%....

I would consider just wiring the 4 Evergreen in series and add them in parallel to the other Italia panels.

Note--you should have a series protection fuse (or circuit breaker) in line of each series string--at the panel's rated series fuse value (probably around 15+ amps or so).

What sort of maximum charging current do you see from your Italia panels (and what battery voltage)--I would bet that the Xantrex XW charge controller will handle the larger array pretty well with only a "little" clipping of current (no damage--controller just runs at maximum rated current limit).

Saves you from having to worry about the C35 and you do not have to purchase another controller (unless you want to go larger with this array).

Normally, we like to start with a battery charge rate of around 5% to 13% (with a 0.77 derating of Panel STS ratings to allow for hot panels, controller losses, wiring losses, dirt on panels, and aging):

• 51.5 amps (derated) max / 1,092 AH = 0.047 = 4.7% rate of charge...

A bit on the low side--You could easily double your array with this battery bank--if you wished (and wanted the extra power).

-Bill

[Gorllwyn]

Thanks very much for the reply Bill.

I am so glad I joined this group. I am sure you have the answer to my problem. I am 100% self taught and my knowledge and experience is obviously lacking. You have opened my mind to another way of calculating things. I always thought I would be overloading the Xantrex XW but I understand what you are saying; it just shows my lack of experience. I wasn’t aware of the de-rating factor among other things. Lateral thinking has never been my strong point.

The Italia array can put out up to 40 amps or more from the XW on a good day, the voltage can go up as far as 29V and perhaps a point or two more over that.

The Vmp. rating for the Italia panels is 28.3V and for the Evergreens 25.9V. so there is a difference between them. I have always felt that the Italia panels give a lot more power but that could be due to my fighting charge controllers. As the Italia array is larger they should be making more power anyway I was thinking.

Thanks for the tips on breakers and fuses etc, Also I wasn’t sure if my battery bank could take more panels so thanks for letting me know. I do have a Harris turbine that runs when we get rain (10 amps at 24V+) so that keeps the cells topped up on dull days but I do intend to expand the arrays when cash is available. Would you recommend getting another XW controller or could I run an Outback or Midnight solar along side? I’m sure they won’t talk to each other though so I imagine I will end up with a XW. I have been very happy with it but they are quite hard to get hold of in the UK. Someone did say that Xantrex were stopping importing them into Europe but who knows?

Looks like I might have a C35 for sale.

Regards
Gwyn

[BB.]

You are very welcome Gwyn.

Regarding your mixed array, I think you are not giving me the Vmp of the solar panels themselves. The Evergreen may be Vmp=18.4 volts or so, and the Italia panels may be 28.8 volts. The closest working match would be three Evergreen panels in series (3x18.4v=55.2 volts) and two Italia in series (2x28.8v=57.6 volts) where they will be within 10% matching voltage.

But that would cost you the use of one Evergreen panel... Not a great idea probably.

You may be forced to get a second MPPT controller or more programmable PWM for your Evergreen array. For MPPT, perhaps the Rogue 30 amp MPPT charge controller would work--but that is from Oregon (USA), so I don't know how much import duties/shipping will hurt you (or if he ships overseas). Also, the last model is out of production (I think), and last I heard the new model is due around June 1. So there may be an availability issue for now.

Otherwise, the next size up MPPT controller is the TS 45 amp MPPT from MorningStar. Which is significantly more money.

Or find a programmable version of a PWM controller that can output a higher voltage to your battery bank...

By the way, did you check the manual for the C35 (PDF download page 45, page 25 on the printed manual)? You should be able to adjust the "Bulk" voltage all the way to ~30.0 VDC for charging. Perhaps that will take care of your immediate issue.

If not--one other question--What do you have for wire size and length from the controller to the battery bank? If the wire is "too small" or "too long", the voltage drop can be enough to make the battery voltage is higher than it really is at higher charging currents.

And lastly, if the charge controllers are in a warm space and the batteries are very cool--You should look into getting a Remote Battery Temperature Sensor for your controllers... Cold batteries need higher charging voltages.

-Bill

[niel]

i have to ask how you have the evergreens configured as 1 evergreen pv will not output enough voltage for a 24v system. if in parallel the output of the other pvs on the mppt cc will appear to be higher than the input to the c35 and will never attain the voltage set, but it should not shut off as far as i could see. if you wired 2 evergreens in series to obtain the voltage needed you are wasting much power as 2 in series far exceeds the voltage needing to produce for a 24v battery bank. also be careful of the max voltage inputted to the c35 as that is about 55v open circuit and the pv has an open circuit voltage of 32.6v and 2 in series would exceed the max input voltage and destroy the controller. you need another controller and preferably an mppt type to handle the odd voltages.

be cautious in wiring more pv to a controller than they may be designed for as the max output at 24v is 24v x 60a = 1440w. losses don't always amount to the 23% cited in the 77% foldback derating. also 60a is the max of the controller and those in the u.s. are restricted by the nec from exceeding 48a output and that is 48a x 24v = 1152w. they don't take into account those derating losses before figuring for max pv array capabilities.

[stephendv]

In the 30A MPPT range in Europe there are a few options:
- Phocos 30A MPPT controller: http://www.phocos.com/products/mppt-100-30a
- Victron bluesolar 40A MPPT: http://www.victronenergy.com/solar/s...e-controllers/
- http://www.schams-solar.de/solarmppt-ENG.html (seems like a small German company, never really heard much about these guys)

[Gorllwyn]

Thanks Bill,

This is all very helpful stuff,

I forgot to say in my last reply to your original questions that I discharge the batteries down to 50 %; I did keep it to 60% but have found I do get much longer at 50% without resorting to the Lister diesel generator in the depths of winter when the Porthmadog mists roll in. Sometimes we can’t see out of the garden for days (living on the west coast), so I have forfeited a bit of battery life for peace and quiet. We do have considerable draw down of current when the kids have all the computers on and all the other stuff switched on that is a part of their everyday life today.

Also regarding battery temperature; the Rolls are located in an old barn with 18” thick walls where the temperature is never much above 20 degrees C or 68 degrees F in old money. I would say they range between 2 and 18 degrees C and average about 15 degrees C. for most of the year. Even when I equalise the batteries with the generator they take a long time to get anywhere near the 46 degrees C which is the recommended cut off temp. I do have a BTS with the XW but not with the C35. The enclosure for the charge controllers is quite large with plenty of ventilation but they do get warm (not hot) when the sun comes out and they start working.

I hope I have calculated the cable sizes correctly; the Evergreens have a cable length of 35 feet and the Italia a cable run of 20 feet, both are 25 mm2 cable run from the junction box to the charge controllers.
Yes I did read the manual for the C35 and I have tried adjusting the potentiometers to the maximum setting of 30V but it doesn’t seem to solve the problem of fighting controllers.

Regarding the Vmp of the panels; I hope I have given you the correct information; this is the data from the web which I am sure will make more sense to you than me. I must admit I don’t exactly know what the Vmp means.

The specification for the 4 off Evergreen 180 watt panels is;
Pp (W) 180
Pp, Max (W) 186.1
Pp, Min (W) 176.4
Pptc2 (W) 157.8
Vp (V) 25.9
Ip (A) 6.95
Voc (V) 32.6
Isc (A) 7.78

The specification for the 6 off Italia 210 watt panels is;
Module class peak power (± 5Wp) Pmax 210 W
Rated Voltage Vmpp 28,3 V
Rated current Impp 7,42 A
Open circuit voltage Voc 36,9 V
Short-circuit current Isc 8,05 A
Maximum system voltage 1000 V
Module Efficiency 12,7%
Cell efficiency 14,6%

With regards to future expansion; what do you think would be the optimum number of panels/wattage for the battery bank? I have always assumed I would expand the panels to match the battery bank and add another charge controller (XW maybe) as required. If I do need to lose one of the evergreens then maybe I could use that with the future array. It wouldn’t be the end of the world.

Thanks for the help again
Gwyn

[stephendv]

As Niel pointed out, those evergreen panels are not suitable for a 24V system and a C35 controller. So although you have 720W of panels, you're probably wasting a good portion that.
If I were in your shoes, I'd wire them in 2 pairs of 2 and then buy the Phocos MPPT controller which is about 250 Euro from online shops.

You should see a considerable improvement from those panels.