Reason for Resting "9" on rectified input

[Tom]

Hi,

My classics are connected to my hydro turbine's AC output via a diode bridge. Turbine generator output is 240VAC. Turbine is governed at 60hz. The input to the diode bridge is 60VAC, and DC output to the classics peaks at about 124VAC. My battery is 48v.
The two classics frequently have trouble "picking up" the load from the turbine. The relay contacts for an instant, then releases almost instantly. The Classic waits for 3 seconds, then tries again, almost always unsuccessfully. This happens whether one, the other, or both are connected to the turbine. After reading these forums and doing a little internet snooping, I determined that the "reason for resting" value is 9, which means "Too much negative current while operating." Any ideas on  why this is? It seems to be worse when the turbine is putting out more power.

A second, likely unrelated problem: When the Classics do sometimes successfully connect, and the turbine is putting out maximum power, the Classics reach their maximum input amperage and go into 'resting'! I have the amp limit set to 41 due to constraints on my transformers. Is there any way to tell them to just back off instead of giving up entirely when they hit their input amp limit?

Thanks,

Tom

[boB]

Hi Tom...

Not sure exactly why it is giving up (going to Resting) but the latest software might help
the RFR = 9....   It basically makes the input voltage move around a bit more carefully.

What version or date does your Classics have now ?  Press STATUS a few times and it
should show up.

boB

[Tom]

I have the current firmware from June.

What appears to be happening is this: as you hinted, they are pulling the voltage down too quickly and sucking down a lot of watts immediately. I can watch the amps spike on my analog meter. Somehow this is triggering the RFR=9. I have tested this by changing the "min. volts" value (under Hydro mode). I can set it to a high number, and the Classic will connect to the source. I can then progressively lower the min volts until I reach my approximate MPP. This works, but I would have to do this with both Classics each time they start a charge cycle, so it would get tedious.

Is there any way to convince them to drop the input voltage more gently?

[Halfcrazy]

Are you using Hydro Mode? I have seen the RFR# 9 a few times on rectified single phase with older code but never had any issues with the newer stuff. Not sure why it would track down "To Fast" Hydro should be relativity slow.

With the new Hydro mode I do the similar thing you are talking about I have 120vac rectified and I set the Min voltage to 140 and MPPT voltage to 141 and do not use the current limit. The Controller turns on and slowly sweeps to 141 volts. Of course the 141 volts worked for me but you will need to slowly work down to a voltage that works for you.

Ryan

[Tom]

Halfcrazy:
I am in Hydro mode.
What you're describing is exactly what I had hoped to do: set the MPPT and set the min volts just below it. I'm not positive that it's sweeping down too quickly, but it sure seems that way.  Definitely a big spike in current. I had been thinking that my setting the MPP voltage might have caused this problem, so I was letting it sweep on its own.

Interesting that you rectify 120VAC. I tried it through my diode bridge and ended up with over 300VDC open circuit. Had to put in another transformer.

Question: does the MPP voltage setting in Hydro mode work even if there is a sweep interval set? Or does it only work if you peg it there? I've noticed that (when the classics do sometimes take up the load) they don't always drop all the way down to the MPP voltage that I give them. This leads to low power output.

Is there a manual that contains more detailed information about the settings in hydro mode? The one that came with my Classic is not terribly informative.

[boB]

Tom, what is the power rating of your generator ??

It may be that your generator is just too powerful, which means that its source impedance is very very low and the symptom you might see with this is that the output (battery) current will rise extremely sharply with even a very small drop in input voltage on the Classic.

What is the open circuit voltage (Voc) of your generator and how far below that input voltage does "high" current appear at ?

Also, you might try setting the Mpp Voltage just barely below the Voc of your generator.  But maybe you are already doing this
or the voltages move around too quickly ?

When you are set for manual Mpp V in hydro mode, it shouldn't be sweeping the input voltage.  It will take the input voltage up from the manual set point of course when output current limit, input current limit or battery set point voltage is exceeded.  That is the only way it can really regulate those values.  It may be also that the Classic is somehow trying to bring the input voltage up higher than Voc and that alone might cause the RFR = 9.
But that should only happen (usually) if the generator has extra capacitors or some way of actually loading the classic input down to draw any current from the classic input.  There are current limits in the Classic and they ~can~ be adjusted slightly if necessary.  Not something we really advocate doing but might be needed once in a great while.

boB

[Tom]

My hydro generator can put out up to 6KW. It is more than the capacity of my two classic 200 charge controllers. I would expect voltage to be extremely stable until the turbine is reaching maximum load.
The open circuit voltage is about 90 when the classic is resting. When it hits the capacitor of the Classic, I see closer to 120. It could be that this is causing the connection problems - the classic might start sweeping at 120, when the VOC is more realistically lower. (See my post titled "240VAC diode bridge input" http://midnitesolar.com/smf_forum/index.php?topic=607.0)

Somewhere around 68V seems to give about 2000 watts. I've tried to park the MPP there.

Let me lay out the problems I'm having:
Scenario 1: I set the MPP voltage to 68, and the min volts to 66, and switch the mode to "on". The classic tries to connect a dozen times or so, retrying every 3 seconds, with RFR9. When it connects, it sweeps the voltage down to around 73 volts, putting out about 400 watts, and stops there, rather than continuing to my MPP voltage setting.

Scenario 2: I set the MPP voltage to 69, and the min volts to 66, and switch the mode to "on". Ditto, but instead of parking at 73, the classic sweeps to my MPP voltage, puts out about 2000 watts for 4 seconds, then sweeps up to 74 volts/400 watts for four seconds, and then sweeps back to 68. After a few cycles of this is goes to resting with RFR 9. Repeat.

I have tried tweaking the MPP and min volts. I can find a stable point closer to the VOC, but I can't get more than about 700 watts and keep a stable voltage.

On the other hand, if I throttle down my turbine low enough so that one classic can take all of the load, the classic can find a stable voltage on its own in Hydro mode without my having to park the MPP.

I upped the input current limit and I've stopped having trouble with reaching amp limit and resting.

Since these classics are on the same source, I think that I should set them up in a master/slave configuration. Right now if I turn both on they seem to sort of fight each other for voltage. I'm going to work on setting that up today. The only instructions that I've found are on this forum, but it looks straightforward.

Sorry - this is a lot of information at once.

[boB]

I have a feeling that what ~may~ be happening is that there is just too much AC ripple on the input...  120 or 60 Hz
ripple that is and then the Classic might be driving it back into its input.  Question is, where is that current going ?
I ask that because you have a rectifier on the input, right ?  So, what's probably happening is that the Classic,
on the battery side of the Classic, is running current backwards, towards its input and charging up its input
capacitors causing this error.

We might be able to actually adjust the limit for the reverse current using a modbus register.
I don't suppose you have an oscilloscope to look at the input voltage of the Classic while the
generator is running ??

boB

[Tom]

I do have a diode bridge rectifier on the input. (http://midnitesolar.com/smf_forum/index.php?topic=607.msg3845#msg3845)

Unfortunately I left my oscilloscope in the pocket of my other pants this morning. Is there anything that we can do without one?

Another piece of evidence regarding the failure to connect to the source: If I turn off the DC input breaker to the Classic, it will begin charging (with low to no watts because there's no current source) but I can then flip the breaker on and the classic will not disconnect and will charge as normal. (with the problems as stated above.) Otherwise I can sometimes wait for quite a while before it finally makes the connection and begins charging on its own.

[boB]

Ryan thinks it has to do with needing more capacitance.  This would be in line with my thoughts that it
has to do with 120Hz or 60 Hz ripple current/voltage.

I'll let Ryan explain more as he gets the chance.

boB

[Halfcrazy]

I did experience the same issue with my rectified 120 vac source. I feed it into a Classic 200 to charge my batteries and I ended up adding a capacitor to the output of the rectifier. This may or may not be the proper size cap but I used a 5900MFD 450 Volt DC capacitor.

I can tell you without it the Ripple was bad I had the scope hooked up and played with it. I added more capacitance but it did not seem to help.

Ryan

[Tom]

Any suggestions on where to get such a large capacitor?

Before I give up and wait for the capacitor: You imply that I can adjust the capacitance on the Classic. How does one do that?

[Halfcrazy]

The only way to adjust the Capacitance is by adding external capacitors. It is a touchy job as a MPPT controller uses its Input capacitors and inductors in a proper balance to do there job. So to much capacitance can be hard on things.

boB can correct me here If I am wrong but my thoughts are as little capacitance as needed to do the job is what is needed no more. What I did was hook my scope up and watch the ripple and added capacitance I found 5900MFD to be plenty I may have been able to use less but did not have a smaller one.

boB???

Ryan

[boB]

The only way to adjust the Capacitance is by adding external capacitors. It is a touchy job as a MPPT controller uses its Input capacitors and inductors in a proper balance to do there job. So to much capacitance can be hard on things.

boB can correct me here If I am wrong but my thoughts are as little capacitance as needed to do the job is what is needed no more. What I did was hook my scope up and watch the ripple and added capacitance I found 5900MFD to be plenty I may have been able to use less but did not have a smaller one.

boB???

Ryan

Yes, that's about right.   Find just what will do the job and then ~maybe~  just a wee bit more to make sure it is always enough...  Just enough sorta.

That takes a bit of tweaking.   So, what you most likely really need is a decent battery charger that runs off of AC input and power factor corrected too, hopefully.  I guess there just aren't many of those around though.

boB

[Tom]

Thanks for being so helpful and so quick to reply guys!

It sounds like I either need an oscilloscope and a pile of various capacitors, or I need to give up on the Classics and just get some AC input charge controllers.

The reasoning behind getting the classics in the first place was to allow for times when there is low water flow and the turbine is turned down. With AC battery chargers I won't be able to do any charging unless the turbine output is greater than the rated wattage of the smallest charger.