Charge Controller - Bulk Float Charge?

[tkc100]

I just installed a new Xantrex Series C Controller. Now for the first time I am getting some real time information as to the current and voltage my solar panels are feeding into the battery bank.
However along with these new found facts has come a bit of confusion. The manual that came with the controller has a chart that suggests a bulk charge voltage setting of 29.2 volts, a float charge rate of 26.8 and an equalizing charge rate of 31 volts for my generic lead acid batteries. The factory setting was 28 volts bulk and 27 float.
I have attached the tag information for the solar panels.
I can not see how these values can be obtained. The panels have a Voc of 30.8 volts and a Vmp of 24.4 volts.
So far,(one day) the controller has remained in the bulk charge mode. I have the bulk charge rate set at the factory preset of 28 volts. The panel voltage of course varies with the movement of the sun but I have never seen 28 volts yet. Even though the voltage is below the threshold for bulk charging there is little to no current moving from the panels into the batteries.
What has experience taught you all. On a 24 volt system what should I set the controller at and what should my expectation be.
Thanks!

[BB.]

bp solar
www.bpsolar.com

Model SX3200B
Part # 5213.0123
Serial # F30802157399200

Electrical Rating
Peak Power (Pmax) 200 W
Warranted Minimun Pmax 182 W
Voltage (Vmp) 24.4 V
Current (Imp) 8.16 A
Open Circurt Voltage (Voc) 30.8 V
Short Circuit Current (Isc) 8.7 A
Minimum Bypass Diode 10 A
Maximum Series Fuse 15 A

Product data sheet
Electrical Characteristics2 SX 3200
Maximum power (Pmax)3 200W 195W
Voltage at Pmax (Vmp) 24.5V 24.4
Current at Pmax (Imp) 8.16A 7.96A
Warranted minimum Pmax 182.0W 177.5W
Short-circuit current (Isc) 8.7A 8.6A
Open-circuit voltage (Voc) 30.8V 30.7V
Temperature coefficient of Isc (0.065±0.015)%/ °C
Temperature coefficient of Voc -(111±10)mV/°C
Temperature coefficient of power -(0.5±0.05)%/°C
NOCT (Air 20°C; Sun 0.8kW/m2; wind 1m/s) 47±2°C
Maximum series fuse rating 15A
Maximum system voltage 600V (U.S. NEC rating)

RHW-2 AWG# 12 (4mm2), cable with polarized weatherproof DC rated Multicontact connectors;
asymmetrical lengths - 1250mm (-) and 800mm (+)

Yes, that is a problem... Warm panels (normal day, full sun) don't even output Vmp at standard conditions...

You need another solution (different panels, more panels+MPPT controller, or something).

On a 95F, windless, day--those panels could have a Vmp as low as 19.5 volts... And not much better than 20.5 volts on a 77F day...

-Bill

[tkc100]

Wow! That's now exactly the response I had hoped for.
I kind of inherited this system and the learning curve has been straight up ever since.
There are 4 panels total 800 watts, and 16 - 6 volts configured into a 24 battery bank.
You mean to say that I can't ever expect to obtain a full charge.
Why on earth would BP sell a 24 volt solar panel that's not capable of maintaining a 24 volt battery bank?

[Solar Guppy]

Those are not 24V nominal panels, there 18V nominal panels, typically used in series strings for Grid Tie applications. FYI, 12V nominal has a VOC of ~20V

[niel]

seeing sg has posted before me i will confirm what he says is true. to charge a 24v battery bank you would need to have the pvs in series of 2 and paralleled. a pwm charge controller will work, but the vmp will be so high that there will be losses in using the pwm charge controller. it would be advisable to use the mppt style of charge controller.

[BB.]

Which Cxx controller do you have? Depending on Voc (cold) and the controller's maximum Voc panel input voltage--you may have to (for now) do what Niel said--just put two panels inseries, then combine into two parallel strings.

At least you will begin to properly charge that battery bank....

An estimate of power into your battery bank while charging would be:

• 2*8.16 amps Imp * 29.2 volts Vbatt-charge =477 Watts on a bright sunny day

Check how much current you are currently inputting to your battery bank while charging (and what is the bank voltage)... If the input current is below ~10-14 amps with the 1x4 array--you will be better off doing the 2x2 array instead with the PWM Cxx controller.

Next Step: If you can justify a MPPT controller, you will have to purchase one for use with this panels. At least a 30 amp--perhaps 45+ amp if you are in a cold region (get lots of bright sun, snow, and sub freezing temperatures).

-Bill

I guess you are somewhere in Texas--so no snow for you.

Again, sorry about the miss-configuration. No "cheap way" to fix it 100%.

[tkc100]

An education can be expensive.
I had nothing to do with specifying or purchasing the actual panels in this installation.
What I am hearing from you all is that these panels are not actually designed to be installed in parallel as a 24 volt system.
Reconfiguring them into a series parallel configuration is certainly an option. Summer temperature down here are typically 100 + and can reach 115 or so. In the winter it is seldom below freezing although this winter seemed to be a real exception with a couple of day time temperatures right at the freezing point.
It seems to me I would get better performance this way even though it seems strange to run 50 or 60 volts on top of a 24 volt system.
Here's the current dilemma for me. The controller I just purchased is the C60 model.
It's input voltage is limited to 55 Vdc. So close but I guess there is the possibility of these panels actually producing 61.6 Vdc under perfect conditions even though I have never seen anything close to that. The C40 controller is limited to 125 Vdc. In hine sight this would have been a better choice. Do you think these panels will ever under real world conditions exceed the limits of the C60? Do I need to purchase another controller for this solution to work?
I do have perhaps one other option.
I have six more small panels rated as follows:
@ 25 C
55 watt
I @ max power 3.13 amps DC
v @ max power 17.6 Volts DC
Short circuit current 3.29 amps
Is it acceptable good practice to configure panels with different outputs into the same array?
Thanks so much for all your input. It's not exactly what I had hoped to hear but it good to have individuals such as your self to lean on.

[BB.]

No, you cannot use those SX320B panels with the C60 at all with a 24 volt bank at all... In parallel, they will not charge the bank. 2x in series will be too high of voltage (2xVoc is too high).

The 55 Watt panels, 2x series and then put the 3x strings in parallel will work OK.

If you want to use both set of panels--but the C60 on the 55 watt panels. An get an MPPT for the 200 watt panels. Connect both to the battery bank (each through their own set of short/heavy cables to the battery bank).

-Bill

[tkc100]

Well it seems as though I got a real can of worms here.
From what I can make out of all the comments is that the problem started with the wrong panels. The SX3200B panels are a 16 volt nominal panel and I need a set of panels with a 24 volt nominal rating. Strange no where on the tag is the nominal voltage rating listed. I was only able to confirm what Solar Guppy posted by doing a little internet research. I also looked at a number of other panels rated at 24 nominal volts and the average Voc was 41.32 with an Vmp of 33.53. If only I had those panels!

So where do I go from here!!!

I have three ideas and would appreciate your input.

New panels rated at a nominal voltage of 24
Could use all the existing hardware
Perhaps I could find a buyer for the SX3200B panels and off set some of the cost
Would get the approximately 800 watts output

Reconfigure the panels into a series parallel setup
2 groups of 2 panels in series with an output of Vmp 48.8 Voc 60.6
This is considerably more voltage than is required for a 24 volt system and it would require a new voltage controller. The Xantrex C60 has a maximum PV array open circuit voltage of 55 volts. The Xantrex C-40 has a maximum open circuit voltage of 125 volts and could be used
Then take the 2 series set and configure them in parallel to achieve approximately 400 watts maximum output.
Cost a new controller and a compromised array.

Finally and this one I don't even know if it's possible.....
I have 6 Arco Solar Inc. Model M55
Max Power 55 watts Imp 3.13 amps Vmp 17.6 Short Circit amps 3.29 Voc 24 volts
Configure each of the four Model SX3200B panels is series with one of the M55 to create a cell producing Vmp 42 volts Voc 54.8 volts
Each of the four series grouping would produce approximately 255 watts
Then configure the four series grouping in parallel to form an array with an output of approximately 1020 watts.
If this can be done I could use the current C-60 controller but it would require some extensive modifications to the solar array mounting.

Any way you shake it I'm not a happy camper but once you jump in it time to swim.

Thanks again for all your help.

[BB.]

Well it seems as though I got a real can of worms here.
From what I can make out of all the comments is that the problem started with the wrong panels. The SX3200B panels are a 16 volt nominal panel and I need a set of panels with a 24 volt nominal rating. Strange no where on the tag is the nominal voltage rating listed. I was only able to confirm what Solar Guppy posted by doing a little internet research. I also looked at a number of other panels rated at 24 nominal volts and the average Voc was 41.32 with an Vmp of 33.53. If only I had those panels!

Solar panels are nowhere near "ideal batteries"... In the end they need temperature "correction" in the environment for where they are to be installed, and laid up against the battery bank charging voltage (i.e., 24 volt bank needs ~29-32 volts) and the type of charge controller (the PWM vs MPPT discussion).

So where do I go from here!!!

I have three ideas and would appreciate your input.

New panels rated at a nominal voltage of 24
Could use all the existing hardware
Perhaps I could find a buyer for the SX3200B panels and off set some of the cost
Would get the approximately 800 watts output

I have no reason to assume that the BP 200 watt panels are anything but very good panels (and relatively price competitive $$/watt).

I have 20x BP 175 panels on my roof right now running my Grid Tied system.

Reconfigure the panels into a series parallel setup
2 groups of 2 panels in series with an output of Vmp 48.8 Voc 60.6
This is considerably more voltage than is required for a 24 volt system and it would require a new voltage controller. The Xantrex C60 has a maximum PV array open circuit voltage of 55 volts. The Xantrex C-40 has a maximum open circuit voltage of 125 volts and could be used
Then take the 2 series set and configure them in parallel to achieve approximately 400 watts maximum output.
Cost a new controller and a compromised array.

Not a good idea to choose any PWM setup with existing panels--lots of wasted power.

Finally and this one I don't even know if it's possible.....
I have 6 Arco Solar Inc. Model M55
Max Power 55 watts Imp 3.13 amps Vmp 17.6 Short Circuit amps 3.29 Voc 24 volts
Configure each of the four Model SX3200B panels is series with one of the M55 to create a cell producing Vmp 42 volts Voc 54.8 volts
Each of the four series grouping would produce approximately 255 watts
Then configure the four series grouping in parallel to form an array with an output of approximately 1020 watts.
If this can be done I could use the current C-60 controller but it would require some extensive modifications to the solar array mounting.

Not a possible solution as you proposed... You could take 3x 55 watt panels in parallel and connect that in series with one 200 watt panel...

But you have 4x 200 watt panels and would need 4x3=12 of the 55 watt panels--which you don't have.

Any way you shake it I'm not a happy camper but once you jump in it time to swim.

For the 800 watts of panels--your only practical solution is an MPPT charge controller.

Put panels in a 2x2 series/parallel array and connect behind a Morning Star Tri-Star 45 amp MPPT charge controller for $411 or so.

If you plan on a larger array in the future--you could look at the 60 amp Tristar (and that even has an Internet Webserver included).

I don't see any practical/cheaper solution for you... Each panel is worth ~$500 each--to "toss" some amount of that energy away with a PWM controller is difficult to justify... Of course, spending $400 for yet another controller hurts too.

You can look at other configurations and their limitations (48 volt battery bank)--but those would even include more costs (new inverter).

In the end, how much power do you need per day... Will a PWM system with existing panels give you the energy you need, or will you need the MPPT controller?

And do you have any expansion plans (panels, batteries, bank voltage change, etc.) in the future?

-Bill