Charging two banks with one controller

Jbar

What can I do?

I have 12 sharp 216's hooked to a xantrex controller. I have two banks of 6 volt batteries (48 volt). One bank is 3 years old and one bank is about 6 monts.
If I hook up both banks to the controller the voltage will be able to transfer from bank to bank. I don't think thats what i want to have happen.

Options af far as I can tell

A) buy another charge controller
hook in some diodes to prevent a voltage transfer
C) hook up both banks to same controller

I'm open to any and all suggestions

Carpenter playing electrician

Jbar

BB.

Re: Charging two banks with one controller

What kind of Xantrex Charge Controller?

A pair of PWM type charge controller, with common "Negative Ground" should be able to share one set of solar panels.

I am not sure that you would be able to share one set of panels with an MPPT type controller.

Placing a diode between the battery banks is not a good idea. You will get between 0.2 and 1.0 volts of drop across the diode and way undercharge your battery bank(s).

What kind of batteries are they? Are they all the same brand/model (old and new)?

Have the batteries all been treated well (properly charged and water, no running "dead" during their life)?

Would your life be "easier" if the batteries where all in one bank--or should the banks be separate (say one is for critical loads, and the other for optional loads).

If these are good quality batteries with 7+ years of expected life (and they are the same brand and model numbers)--I would be tempted to just tie them all together. Generally, one central PV panel array and battery bank is better because you can share the power source with all of the loads. With separate banks, you may end up with issues that one set of loads discharges its bank before the other (balancing of loads).

If the old bank has a total life expectancy of less than 5 years--or they are not the same exact brand/model of batteries, then you probably don't want to parallel the old+new banks.

There are battery to battery chargers--but I could only find 12 volt models. 48 volt to 48 volt will be difficult to find.

Your only other choice would be to use an inverter to battery charger--but that will cost you almost 30% of your power (inverter/charger losses).

Boy--I am stumped here for a good solution for you... Do you need the second bank? Do you want to just put it on "maintenance charge" until the first bank dies?

If the Xantrex charger is a "C" series (PWM), and you cannot merge the banks, then getting a second "C" series charger is probably the way to go. I would confirm with Xantrex (or WindSun) that the two chargers can electrically share one solar panel bank.

A C40 is only ~$150 + taxes and shipping... Not the worst thing in the world.

-Bill

Cariboocoot

Re: Charging two banks with one controller

You are perfectly correct in not mixing the old with the new.
Two controllers is your best bet.

Charge controllers read battery voltage and adjust output accordingly. If you isolate one bank with a diode its state of charge will not be read so the charging will be controlled by the other bank. Given the difference in age of the batteries, that means either one gets overcharged or one gets undercharged. Either condition will significantly shorten the life of the batteries. This is why you don't mix batteries of different specs/ages.

If your Xantrex controller (not familiar with them but there are people on here who are) has an auxiliary function that can activate a relay you could possibly wire it to bring the new bank up to float, then switch to charging the old bank as a reserve.

How well any of this will succeed depends on how good your panels produce (max of 2592 watts? * efficiency), what amp/hr the batteries are, and how you have them configured (two banks of 8 * 6volts each = 48 volts). Even if they are 400 amp/hr per bank then the panels should handle it fine assuming 40 amps (2592 watts * 75% efficiency divided by 48 volts) peak charge output which is 10% of battery amp/hr rating. These numbers are approximations, not absolutes!

Ecnerwal

Re: Charging two banks with one controller

Are the banks hooked to the same inverter? If so, they are already tied, unless they are switched in a "this bank or that bank but never both banks" fashion.

Options, depending on why you have two banks...

Sell older set. If you need more capacity, buy new ones same as newer set.

Split panels into two groups, use two charge controllers, keep systems entirely separated (in and out).

Eat 2.5 years of aging on the "new" set and tie them together as one bank. Make note to self to not repeat this in the future.

icarus

Re: Charging two banks with one controller

"Eat 2.5 years of aging on the "new" set and tie them together as one bank. Make note to self to not repeat this in the future."

While I certainly agree that tying new batteries to old, shortens the life of the new,,, I be there is not a 1-1 comparison net/net. Could it be argued that the old string lasts somewhat longer even as the new ones last somewhat shorter? It would be intersting to do a controlled test somehow.

I think that the older a string is, the more pronounce aging it will suffer,, but 2 years different may not "cost" as much as you think. In fact it may be cheaper than buying new hardware and rejigging a system to account for the age difference.... Just a thought.

T

SolarJohn

Re: Charging two banks with one controller

My first solution to this problem was to install one of those heavy-duty marine battery switches. I was able to switch in the older battery bank once in a while to keep it charged, or to use energy from the spare battery bank when I need it.

Unfortunately, I didn't keep a close enough watch on the spare battery bank and it self-discharged beyond what I would consider a safe state-of-charge a couple of times. To solve this problem I programmed my Morningstar Relay Driver to switch in the spare battery bank whenever the primary battery bank was fully charged. (I've posted details on my blog: http://solarjohn.blogspot.com). I can still switch in the spare bank manually, in the event of a power failure for example. This solution works well for me. The best thing about this is that my primary battery bank has top priority, and I waste very little of the sun's energy on any given day.


John

Jbar

Re: Charging two banks with one controller

Thanks for the input
I'm getting another MPPT controller and just going to keep them separate.

I produced 3150 peak watts yesterday (cold and sunny) You have to love colorado
Not to bad for panels that are supposed to produce 2592 watts the MPPT controller seems to be working good.

I have two older sw 4048 inverters that I bought used. For some reason they don't like to light my Buderus boiler. I tried a line conditioner, still didn't work . But it did light on its own yesterday with a high charge on my batteries. It's a pain in the rear to go out and turn on my generator to light my boiler. Hopefully the panels will keep my batteries charge at 50 + volts so I can avoid having to buy an new inverter for a coulpe of years.

Thanks again for input

Jbar

blwncrewchief

Re: Charging two banks with one controller

Jbar,

As far as your Buderus boiler not lighting goes the electronic ignition systems can be very touchy. The most common problem is a grounding issue since most electronic ignition systems use flame rectification for sensing the flame. How this works is they pass ac power up to the flame rod/sensor and when you pass ac power thru a flame it is rectified to dc. When the control module senses the dc power it knows the flame is present. This is done only in milli or micro amps and referenced to ground so any issues with the ground can easily cause problems. So check your ground to your boiler and also check for any possible dc feed back on all power and ground wiring to your boiler. The other possible problem could be since the SW's don't have a very perfect sine wave that could be causing a problem with the electronics. I only suspect this could be the problem since you say it runs ok on the generator and I assume you are just passing the generator power thru your inverter and thru the same wiring. The only suggestions I have for this would be to put an isolation transformer on the boiler circuit as this may clean up the power enough to satisfy the electronics.

BB.

Re: Charging two banks with one controller

Are you planning on sharing one panel array with two MPPT controllers?

I am not sure that this is a good idea--MPPT controllers are (from what little I know) not designed to share the same panel string.

Most PWM type controllers (simpler/cheaper) can share the same array.

What brand/model of charge controllers will you be using? If you will not be sharing the array (parallel connection to the two charge controllers) between the two controllers--then everything should be fine (assuming all of the basic wiring and power rules of thumb are met--minimum panel size for battery bank, etc.).

-Bill

Cariboocoot

Re: Charging two banks with one controller

I agree with BB - my instructions say each array needs a separate controller, ergo each controller needs a separate array.

But with 12 panels maybe you could divide them up into two arrays?

Jbar

Re: Charging two banks with one controller

I tried the line conditioner which supposedly cleans up the SW. I will check grounding next.

As for the MPPT's
3 strings of 3 for one controller and 2 strings of 3 for the other

BB.

Re: Charging two banks with one controller

How much power does the boiler take? Can you purchase a smaller TSW inverter just to power the boiler?

-Bill

solarix

Re: Charging two banks with one controller

This makes me think. I just quoted a system with a battery bank charged by 2 XW-MPPT60 controllers each on its own 3kW array. Is this going to be a problem with both controllers fighting over the battery?

Cariboocoot

Re: Charging two banks with one controller

solarix wrote: »

This makes me think. I just quoted a system with a battery bank charged by 2 XW-MPPT60 controllers each on its own 3kW array. Is this going to be a problem with both controllers fighting over the battery?

Nope. They won't 'fight' exactly; each will read the bank and settle back every time it sees the higher voltage of the other. In other words, there will be lot of 're-adjusting' per sweep, increasing as the charge comes up. If you use the right sort of controller they will interconnect and 'talk' to each other, as well as the inverter. This keeps all components 'agreeing' as to what should be done. Outback has this system, and I'm sure others do as well.

Solar Guppy

Re: Charging two banks with one controller

No problems at all with the XW's, they can be networked as well, but there is no need, the controllers will transition from Bulk to Absorb based on the battery voltage

Once in Absorb or Float, your current limited anyways, makes no difference if one controller is handling more load that the other as not all of the availble solar can be harvest at that point

For Bulk, the XW's don't sweep for Mppt tracking and there is no tracking issues with multi-controllers on the same battery bank

Jbar

Re: Charging two banks with one controller

Everything is working good on the charge side, but I can't find any problems with grounding/ wiring on the boiler side. Tell me more about how I can hook up a smaller inverter for the boiler only. No spec's on load for boiler but I do know the pump sucks about 2 amps constant when running. I'm not sure what the ignitor uses, but it lights in about 3-4 seconds. Other than that some small lights on the control board.

Just so everyone is clear I have 2 sw4048's, one for each bank of batteries. The new inverters you only need one to get 220 power(correct?) I'm not sure on how that all works but eventually I will upgrade batteries and inverter.

Thanks,

JBAR

BB.

Re: Charging two banks with one controller

You probably need to measure the starting load of the boiler too...

Is this a natural gas/propane fired boiler with a "glow bar"... Or something else (oil?).

What are you asking about 220 AC for?... Is this a 240 VAC 60Hz, or a 230 VAC 50 Hz? Or do you need 120/240 VAC 60Hz split phase (like typical North American House wiring)?

If you don't have the neutral grounding correct--the flame sensor may not work...

Inverter-wise, in the end, you might have to see if you can "borrow" one from a local supplier--or possibly even buy a "smaller" one that you can use elsewhere if it does not work on the boiler...

And that is not great--TSW inverters are not cheap. And a line conditioner will not "fix" a MSW waveform in any meaningful way.

You can take a look at the off-grid inverters that NAWS has... There are some TSW inverters with various options (like a DC on/off control circuit--nice to reduce standby loads--or look at the standby "search" current draws and such.

If you need 120/240 VAC 60Hz split phase--and you are close to needing to replace your MSW inverter set--the new Xantrex XW family or the Outback with an autowound transformer may fill those requirements.

Not sure where you really want to go...

-Bill

Jbar

Re: Charging two banks with one controller

Good news I didn't have to start the generator to light boiler for ten days. I can only atrribute this to sunny cold days (batteries were at a high charge the whole time) I had to start the gen twice in the last three days because its been cloudy and snowing.
Assumption

Boiler will light on it's own with a good charge

Nothing like stating the obvious

J-BAR

halfcrazy

Re: Charging two banks with one controller

It may just be me but i seemed to think i noticed the sw inverters got "Noisy" as the battery voltage got lower. I have no data to back this just seet of the pants from experience with them. Maybe that is why the boiler will light at higher battery voltages?