Charge controllers in series?

[yzahmad]

A long-time stroller, signed up today for my first post

Inspired by the forum members, made my first step towards solar electrification of my house today The installers had put the panels up earlier in the week, but came with the epSolar MPPT charge controllers today and finished the wiring. This is what they look like:

DSC_0129.JPG

My concern with the above is, is it OK for the wires coming in from the panels to go straight into one, and then to the second charge controller from there? Although they are identical charge controllers, will they get equal voltage in?

Presently setup 800w of panels, we have two inverters (one for each floor) with seperate batteries hence the installer suggested to get seperate charge controllers. If this thing works, the idea is to increase the panels (hopefully double the present).

I hope this setup will work?

[inetdog]

A long-time stroller, signed up today for my first post

Inspired by the forum members, made my first step towards solar electrification of my house today The installers had put the panels up earlier in the week, but came with the epSolar MPPT charge controllers today and finished the wiring. This is what they look like:

[ATTACH=CONFIG]2317[/ATTACH]

My concern with the above is, is it OK for the wires coming in from the panels to go straight into one, and then to the second charge controller from there? Although they are identical charge controllers, will they get equal voltage in?

Presently setup 800w of panels, we have two inverters (one for each floor) with seperate batteries hence the installer suggested to get seperate charge controllers. If this thing works, the idea is to increase the panels (hopefully double the present).

I hope this setup will work?

They will get very close to the same voltage in. That is not a problem, but....

If the two MPPT controllers are not communicating with each other, then running two CCs off one set of panels could be a problem regardless of how you run the wires. They will both be trying to maximize the power that they get as individuals, potentially at the expense of the other, and will not together find the actual MPPT of the panels.
If they had been PWM controllers, then it would not be as much of a concern.

Having two CCs run off separate panel arrays charging a common battery bank, on the other hand, is frequently done.

[inetdog]

EPSolar has a specific model, EPIDB-COM, which is designed to run two battery banks off one set of panels.

That strongly suggests that they do not think that two of their regular controllers together can do this.
Has your installer ever done this before???

[SolarWatt]

By the way - I think they are connected in parallel not in series.

[inetdog]

MPPT Charge Controllers in parallel off one panel array.

By the way - I think they are connected in parallel not in series.

But isn't one after the other a series connection?

I noticed that.

[SolarWatt]

[yzahmad]

It's the first time he has tried this with mppt controllers, which is why I was concerned. So I guess I should has him to split the arrays going into separate controllers?

[inetdog]

It's the first time he has tried this with mppt controllers, which is why I was concerned. So I guess I should has him to split the arrays going into separate controllers?

That would definitely be my advice, yes. You can try it first to see how it works. Look at the voltage and power indications on both CCs together, then turn off one of them and see what the voltage and power indications are. This will only be a useful test if you have loads connected or the batteries are so discharged that the CC selects the Bulk charging stage though. Otherwise the power input to the CC will be limited by what is being accepted by the batteries.

Anyway, what I would worry about would be a situation where the two CCs are repeatedly changing power settings, with one or the other first taking more power then less power, or a situation where the sum of the power taken by the two CCs is less than the power taken by one CC with the other turned off.

It is too bad that it is set up this way, since you will not be able to use the combined array power to charge just one battery bank if it gets more use than the other bank.

[Sunking]

Sounds to me like an incompetent installer.

[yzahmad]

OK the installer came today to finish up some wiring, I told him this setup doesnt make sense why would you not split the arrays and wire into separate charge controllers.

So he said under the present setup the entire array is connected to both battery banks, so you will not face a situation where one bank is fully charged and the other may require more power but doesnt have the unutilized panels attached to it. I hope he is right about this!

At the time, one battery bank was fully charged while the other was nearing complete charge (90%+). He asked me to add load on the the bank that was fully charged, so I powered four ceiling fans and a bunch of lights. When I came back, the panels were giving 10 volts/amps (I'm not sure ) to the first CC, and the same amount was going to the second CC; the second CC was sending 13/14 v/a to the battery bank (again, not sure what the numbers meant just that the MPPT CC was sending out more than it was receiving). The first battery bank (with higher load) had consumption of 25amps and getting charged in 22/23amps, and its voltage was now at 24v instead of the previous 29v at full charge. The second battery bank (with negligible load) was only drawing 0.5amps, and was showing voltage of 24v. (I'm sure I've messed up alot of the units here but I'm sure you guys get it )

So I guess while not an ideal setup, it seems to be working. Now I will get that device he had (something that clips around a wire and shows the voltage/amperage going through) and observe if the condition inetdog mentioned occurs or not.

Thanks for all the help!

[Sunking]

Do I understand you correctly that you have two Charge Controllers in parallel connected to a common solar panel array? If that is correct is insane and will not work worth a darn.

[yzahmad]

Yes sir that is correct, could you help me understand why it is incorrect so I may convince the installer to fix it.

My present setup is two inverter/ups each powering one floor, both having their own two batteries (24v aystem). The solar panel ray is coming in and is connected to both controllers as shown in the first post. Each controller is connected to the batteries of one inverter.

The installer claims it is setup this way so that the entire array is feeding both the battery banks, so if one bank is near full charge the other bank will pull the maximum power the controller can channel from the panels.

[inetdog]

Do I understand you correctly that you have two Charge Controllers in parallel connected to a common solar panel array? If that is correct is insane and will not work worth a darn.

Not just two CC, which might work, but two MPPT CC, which surely will not.

[Sunking]

Yes sir that is correct, could you help me understand why it is incorrect so I may convince the installer to fix it.

Are you certain?

It is fine to have 2 MPPT controllers feeding a common battery bank, where say one controller has 1000 watts of solar panel connected to its input, and the other has another 1000 watts of panels connected to its input. Then the the output of the two controllers paralleled connected to a common battery.

You cannot parallel inputs on a MPPT controller as it would drive the MPPT tracker insane.

[yzahmad]

I'm sorry but I'm zero technically, but the picture on the first post shows how my system is wired: one wire coming down from the panels, into the first CC and then another wire connecting it to the second CC.

Sorry for being a dimwit but I don't understand how it would drive the MPPT insane: wouldn't the total voltage get divided and each CC take 50% (assuming both banks need charge) until the smaller bank is charged, then one CC reduce its demand automatically?