Sharing an array

tallgirl · May 2011

I have a small array I use for software development that I'm trying to share between multiple charge controllers. It seems that there is current flowing from the battery of one system, out the charge controller to the shared PV connection, then in through the other charge controller and causing periodic high current issues since the batteries are infinite current sources, as far as the charge controllers are concerned.

My guess is that a really phat blocking diode on both PV inputs is in order here? Anyone every do this? Anyone care to admit to doing this?

And no, "Don't do that!" isn't an option.

Cariboocoot · May 2011

Re: Sharing an array

Shall I state the obvious and say that a charge controller should not allow battery Voltage to leak back to panels, even without a blocking diode?

I don't know why you'd want to do this anyway, as the PV's power will be unequally divided among however many charge controllers you attach to it. Possibly what is happening is one controller "shuts off" causing a sudden rise in the PV current available to the other(s) resulting in a momentary spike?

arkieoscar · May 2011

Re: Sharing an array

I had a pair of C-40's that I had lying around hooked to same array and to two battery banks. One battery was a 12v gel 245A and the other was 4 L-16's. Had no problems while it was charging this way. I charged the small battery and then hooked up the second controller to the L-16's. They stayed that way until I installed the L-16's at their permanent home.

Cariboocoot · May 2011

Re: Sharing an array

arkieoscar wrote: »

I had a pair of C-40's that I had lying around hooked to same array and to two battery banks. One battery was a 12v gel 245A and the other was 4 L-16's. Had no problems while it was charging this way. I charged the small battery and then hooked up the second controller to the L-16's. They stayed that way until I installed the L-16's at their permanent home.

Switching an array between one system and another isn't a problem. Trying to run multiple systems simultaneously off one array is.

boB · May 2011

Re: Sharing an array

Julie, MPPT charge controllers are sometimes Bi-Directional... At least the more hardware efficient ones are. This is just an artifact of the design, and so that has to be taken into account in the design itself. You will need to add a switch or a diode on those inputs, but at least need to be able to switch off the controller that isn't wanted for a particular test. Diodes of course will lose a small amount of power.

The XW60 MPPT and the Blue Sky controllers are two that I know of
that aren't built this way.

boB

tallgirl · May 2011

Re: Sharing an array

Cariboocoot wrote: »

Shall I state the obvious and say that a charge controller should not allow battery Voltage to leak back to panels, even without a blocking diode?

I don't know why you'd want to do this anyway, as the PV's power will be unequally divided among however many charge controllers you attach to it. Possibly what is happening is one controller "shuts off" causing a sudden rise in the PV current available to the other(s) resulting in a momentary spike?

C.C.,

Hey, the more weird it behaves the more interesting. Besides, I don't use the power for anything other than periodically recharging my lawn mower.

tallgirl · May 2011

Re: Sharing an array

boB wrote: »

Julie, MPPT charge controllers are sometimes Bi-Directional... At least the more hardware efficient ones are. This is just an artifact of the design, and so that has to be taken into account in the design itself. You will need to add a switch or a diode on those inputs, but at least need to be able to switch off the controller that isn't wanted for a particular test. Diodes of course will lose a small amount of power.

The XW60 MPPT and the Blue Sky controllers are two that I know of
that aren't built this way.

boB

boB,

One is MPPT and the other is PWM -- it's a Morningstar SunSaver MPPT and a SunSaver Duo. And totally understand about the forward voltage drop. I want to put the TriStar I have back in the mix and that's why I care about it now -- if I'm having these problems with two charge controllers, it will only get worse when it's all three of those.

What happens is the SS-Duo tries to turn on and conducts through the SS-MPPT. It then experiences an "Over Current" error and shuts down. The device driver detects the error, waits 30 seconds, then clears the fault. Lather, rinse, repeat.

Prolly should stop clearing the error after the first few times ...

Slappy · May 2011

Re: Sharing an array

would this help...............

http://www.morningstarcorp.com/en/support/item.cfm?ItemId=181

...................

techntrek · May 2011

Re: Sharing an array

Slappy gets the cheese.

tallgirl · May 2011

Re: Sharing an array

techntrek wrote: »

Slappy gets the cheese.

Heh.

That's what I thought needed to be done -- wasn't sure my diagnosis of the problem was correct.

Slappy · May 2011

Re: Sharing an array

"Slappy gets the cheese." hopefully that is sharp chedder and not swiss.

techntrek · May 2011

Re: Sharing an array

I'll take a nice Roquefort. Expensive, but really good.

tallgirl · May 2011

Re: Sharing an array

Well ... Slappy needs to return the cheese. I'm still having problems.

XRinger · May 2011

Re: Sharing an array

Pretty simple. All you need is a couple of good diodes.

Since my main battery bank was designed to provide emergency power
during a power failure, it's almost always in "Float"..

So, I could just built a duplicate bank & charger, and have a nice source
of power that I could use whenever, and not worry about it's SOC or the weather forecast. 8)

techntrek · May 2011

Re: Sharing an array

Diodes are what Slappy's diagram specified.

So Julie, you are still getting reverse current through your charge controller even with diodes in place???

notsobright · May 2011

Re: Sharing an array

I have now tested four brand new sunsaver duo controllers and all of them go into over voltage. I have seen as high as 16.78 volts from them. the company is not admitting the problems but I have found others on the web that has experienced this. ms denies it is an issue.

my 210ah lifeline AGM has popped the valve because of the ssd overvoltage.

Ive been testing this unit extensively and it seems to only occur with custom settings (AGM specs) and on battery one only so far but oddly it will not go into over voltage while connected to pc with ms adapter while monitoring.

I am able to recreate this overvoltage condition now that I have learned more and can direct others on how to also.

their RM-1 meter is also not acurate and rarely shows the overvoltage but has on occasion.

I have been recording voltages from two of them at the same time on the same batteries, one connected to pv and the other not. they do not agree with each other on voltages, not even close.

I want ms to do the right thing but its doubtful at this point since they deny the ssd has any issues. Im gathering info from other ssd owners that have noticed the problem right now.

when I am satisfied I have enough I will aproach the ms execs about refund and damage reimbursment.

Im hopeful they will deal with this honerably.

XRinger · May 2011

Re: Sharing an array

tallgirl wrote: »

Well ... Slappy needs to return the cheese. I'm still having problems.

Still? Doing the same thing as before? I can't see how those two systems
would not be isolated by the diodes.. Are you using a common grounding method?

I'll bet it's nice in Austin these days.. (Says a Texan living in MA)..

Cheers,
Rich

tallgirl · May 2011

Re: Sharing an array

XRinger wrote: »

Still? Doing the same thing as before? I can't see how those two systems
would not be isolated by the diodes.. Are you using a common grounding method?

Yup, still having the same problem. Not sure what the heck is causing it, but I'm starting to wonder if the charge controller is bad.

I need to put a Fluke on the thing and figure out which way the current is really going. All I know right now is I see an over-current error and the SSD shuts down. I've been busy adding Shark 100 (three-phase watt-hour meter) support and haven't had a chance to pound on the Morningstar kit ...

XRinger · May 2011

Re: Sharing an array

If the charge controllers are interchangeable, maybe you could just swap them around?
If the over-current problem moved, that might tell you it's the charger..

Or, one of your diodes shorted after it was installed..
It's very hard to see how current could back-flow with those diodes inline..

notsobright · August 2011

Re: Sharing an array

TallGirl, just curious if you solved this issue, and if so what it was?

thanks

Sharing an array

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