voltage with mppt controller too high?

wxh3 · August 2008

I recently installed a Morninstar mppt charge controller. I have measured voltage at charge controller and have seen between 18-19V for a panel that has a spec 17.7 Vmpp at STC. I tried briefly a different panel (that I don't know the specs) and also saw similar high voltage. I have not measured current. The air temp was well over 90F during these readings.

There should not be much of a voltage drop between the panels and the controller as the cable runs are quite short. I think my voltmeter is fairly accurate.

Any idea as to why this might be the case? I was expecting to see 15-16V due to the heat. I am hoping that my controller isn't incorrectly placing too high a voltage to the panels and reducing the power output. It looks like current really drops off quickly when you pass the Vmpp point.

wxh3 · August 2008

Re: voltage with mppt controller too high?

One thing just occurred to me...if it does not need the maximum available power at the time for the load and battery charging does it maybe put the panels at a voltage where it gets less out of them? I think my battery charging was in the absorption phase during my readings and I had a very small load.

boB · August 2008

Re: voltage with mppt controller too high?

wxh3 wrote: »

One thing just occurred to me...if it does not need the maximum available power at the time for the load and battery charging does it maybe put the panels at a voltage where it gets less out of them? I think my battery charging was in the absorption phase during my readings and I had a very small load.

Being in the Absorb stage would definitely make that PV input voltage higher, and right around the V you said (higher than 17 but lower than 21, for example)

boB

mike95490 · August 2008

Re: voltage with mppt controller too high?

Why is the battery full at this time of day ? Burn some juice, then test it.

I'll warn you though, I doubt the charge controller, even a Morningstar, can "overvoltage" the PV's.

wxh3 · August 2008

Re: voltage with mppt controller too high?

mike90045 wrote: »

Why is the battery full at this time of day ? Burn some juice, then test it.

I am probably not using enough energy now so I'm wasting a good deal of solar energy from my panels....especially in the the current sunny summer conditions. During cloudy winter periods though it will likely be a different story.

So I guess I was incorrectly thinking that an MPPT controller would always try to operate at Vmpp and the excess power would just not be used by controller. A traditional controller I guess just sends the extra current not needed by battery charging or load into a different parallel circuit path?

BB. · August 2008

Re: voltage with mppt controller too high?

No, the MPPT and Traditional PWM controllers behave roughly the same when they are no longer pumping out 100% possible current. They both simply use less energy from the solar panels for final charging/floating of the batteries.

There is no parallel circuit path to divert the "extra" energy--simply because it is not required. Solar Panels can operate very nicely between 100% load (or even a dead short) and 0% load.

Wind Turbines, on the other hand, need a "diversion" load/circuit to keep the turbine loaded--otherwise, without a load (or bake or some other alternative over speed prevention mechanics), the turbine will probably overs speed and self destruct in high winds.

And yes, you are wasting/losing potential energy from your solar panels on sunny days to make up for poor weather/sun angles in other seasons.

People have experimented with optional loads (such as water pumping, resistance heating, etc.) that can be turned on once the batteries are nearly fully charged. But, usually, these end up being compromises as you may need more water, or not properly charging the batteries (diversion controllers seem to not control the battery charge state as well as series connected controllers used for solar panels).

-Bill

wxh3 · August 2008

Re: voltage with mppt controller too high?

BB. wrote: »

No, the MPPT and Traditional PWM controllers behave roughly the same when they are no longer pumping out 100% possible current. They both simply use less energy from the solar panels for final charging/floating of the batteries.

....

And yes, you are wasting/losing potential energy from your solar panels on sunny days to make up for poor weather/sun angles in other seasons.

-Bill

I guess I could then look at it as simply the effective "resistance" of the battery changes and thus results in a different amount of current from the solar panels while held at the same voltage. (I=V/R.)

The one good thing about my current "wasting" of solar energy is that my batteries at least should last a longer time. I calculate I am now using roughly 15% of my battery capacity every day for my load. Maybe 2/3 of that is at night so I think I am getting around 10% discharge most days. That 10% amount is pretty close to the STC power rating of my panels for one hour.

crewzer · August 2008

Re: voltage with mppt controller too high?

Stand by for more information on the new "AUX Diversion Solid State Relay" feature in the OutBack FM80 and FM60 charge controllers.

This PWM-type feature allows the controller to simultaneously manage an "opportunity" load such as a water heater connected to the battery bank in Absorb and Float modes by varying the duty cycle of the load and without significantly affecting the target battery voltages.

The benefit of this unique new feature is that it allows the charge controller to harvest more of the available solar power while operating in the output current limited Absorb and Float modes, rather than leaving the power behind "on the table".

The feature is already included in the new FLEXmax controllers, and I'm currently running some application tests. See: http://www.outbackpower.com/forum/viewtopic.php?f=29&t=2865

Stay tuned! :cool:

Regards,

Jim Goodnight
"crewzer"
Eastern Regional Sales Manager
OutBack Power Syatems

Solar Guppy · August 2008

Re: voltage with mppt controller too high?

The MorningStar SunSaver Mppt already has a second "opportunity" output, its a load controller output and can be user programmed to add an additional load at user specified or default settings. best of all its here NOW and built in to every MorningStar SunSaver Mppt unit shipped at no extra cost

crewzer · August 2008

Re: voltage with mppt controller too high?

Interesting!

I'm sittin' here looking at a SunSaver MPPT (SS-MPPT-15L, s/n 08210363), and I don't see a "second" set of outputs.

I did see a reference to wind- or hydro diversion control in the controller's data sheet, but I found no mention of it in the user manual.

Just to clarify, the AUX Diversion SSR feature I mentioned above has been standard on the FM60 and FM80 controllers since they were introduced.

Jim / crewzer

mike95490 · August 2008

Re: voltage with mppt controller too high?

Solar Guppy wrote: »

The MorningStar SunSaver Mppt already has a second "opportunity" output, its a load controller output and can be user programmed to add an additional load at user specified or default settings. best of all its here NOW and built in to every MorningStar SunSaver Mppt unit shipped at no extra cost

Does the XW series have this, or planned for a follow up, like an XW+ ?

crewzer · August 2008

Re: voltage with mppt controller too high?

Does the XW series have this...

Not at the present. Here's what's currently available from the XW controller's AUX output (per the online user manual):

Auxiliary Output Functions

The XW SCC has a configurable auxiliary output (producing 5 to 13 volts and up to 200 milliamps) to drive a relay for load control or to turn on devices such as vent fans or indicator alarms. The auxiliary output can be configured to perform only one function at a time.

See “Configuring the Auxiliary Output” on page 3–12 for information about auxiliary output trigger sources and how to enable and configure the auxiliary output for your application.

Load Control
The XW SCC auxiliary output can be configured to drive a relay to disconnect or reconnect loads depending on battery voltage. This load control function enables the XW SCC to help prevent damage to the battery from over-discharge during periods of poor charging (due to ambient temperature, for example) or excessive loads.

Vent Fan
The XW SCC auxiliary output can be configured to power a small DC fan to clear a battery compartment of harmful gases. The XW SCC auxiliary output must be configured to activate when the batteries reach their gassing voltage.

Alarms
The auxiliary output can be configured to trigger an alarm or indicator light when a pre-set condition occurs, such as low or high battery voltage, high PV array voltage, or a XW SCC fault.

HTH,
Jim / crewzer

Solar Guppy · August 2008

Re: voltage with mppt controller too high?

Not quite true crewzer, the XW-60 can be pwm, it has a setting for the trigger duration in seconds ... for most diversion/aux loads this will function well for handling conditions where a user would like to use harvest to a second load. The conditional settings are very robust on an XW

On the MorningStar Sunsaver Mppt, it has a load output

crewzer · August 2008

Re: voltage with mppt controller too high?

It's my view that the XW CC AUX features do not include a feature comparable to the FM60 and FM80 AUX Diversion SSR. The FM's feature is activated by parameters plus the charge controller state (i.e., absorb mode), and thus include temperature compensation for the target voltage. As best I can tell, the XW CC will can turn the AUX on and OFF w/r/t battery voltage (and other value triggers), but that's not the same thing.

But, I'm always open to fresh and objective perspectives.

I see the Load output (for load control - low voltage disconnect/reconnect) on the SunSaver MPPT, but not the "second opportunity output", and, if there, it would be handy to have some instructions on its diversion / opportunity application.

Thanks,
Jim / crewzer

Solar Guppy · August 2008

Re: voltage with mppt controller too high?

The XW can be voltage and or state and or intervals ... Also with the adjustable voltage, you can connect it to a much wider array of loads ... very handy for the one-off setups.

I have on hand just about every controller made and have learn a great deal looking at the construction, testing the functionality and features of each manufacture.

BTW, I'm not in anyway suggesting the new FLexMax units don't have some nice new features. I'll probably get one to check out at some point so I'm up to date on whats out there.

crewzer · August 2008

Re: voltage with mppt controller too high?

Henry,

I agree the XW’s variable AUX voltage feature is a nice touch, and there are a few others as well.

However, returning to the original AUX Diversion SSR issue, I just haven’t seen that particular capability in XW controller. I’ve gone through the documentation (again, including the 7/14/08 update to the user manual), especially Section 3-12, “Configuring the Auxiliary Output”, and, while there are several useful value triggers, I found no reference to a state trigger (i.e., Absorb or Float).

I also agree that “hands on” experience with all of this equipment is invaluable. For example, we have an XW at our plant in WA, and I have an SunSaver MPPT controller in my “lab” here in VA.

Regards,
Jim / crewzer

System2 · August 2008

Re: voltage with mppt controller too high?

Using "every last electron" and using the wasted energy otherwise "left on the table" by CC's during absorb and float modes seems to be gaining interest.

The Sunsaver is too small to be relevant, IMHO, unless your objective is to heat water for afternoon tea.

boB's disclosure that the Classic will have this feature, if ever brought to market, is further evidence that it's a valuable and differentiating feature. We'll continue to wait and see.

The Schneider/Xantrex XW makes no clear mention of this capability. They seem to allocate little resources to their online forum and appear to place little value in customer feedback. I would expect that they will only modify their product with this feature after successful implementation by competitors and proof of market value.

Only OB has devoted resources toward testing and implementing this concept. I look forward to Jim's (Crewzer) complete report on sample implementations of this new concept of solar diversion mode.

(stepping down from soapbox)

boB · August 2008

Re: voltage with mppt controller too high?

Geee, it's only only "SMOP", or a Simple Matter Of Programming...

Also, the idea just comes from looking at how things work in a slightly different way, or from another angle so to speak.

boB

crewzer · August 2008

Re: voltage with mppt controller too high?

Update on the OutBack Forum: http://www.outbackpower.com/forum/viewtopic.php?f=29&t=2865&p=17545#p17545

HTH,
Jim / crewzer

FreeBrrd · August 2008

Re: voltage with mppt controller too high?

(just wanted to subscribe to this thread and couldn't find means without replying, so please ignore, thanks )

mike95490 · August 2008

Re: voltage with mppt controller too high?

crewzer wrote: »

Stand by for more information on the new "AUX Diversion Solid State Relay" feature in the OutBack FM80 and FM60 charge controllers.

This PWM-type feature allows the controller to simultaneously manage an "opportunity" load such as a water heater connected to the battery bank in Absorb and Float modes by varying the duty cycle of the load and without significantly affecting the target battery voltages.

So, is this a "dry contact" to power another relay, or can I attach my water pump to it directly, and pump water, when there is surplus power?
(this will be for my "cloudy day" when the genset won't start, the batteries are low, and the water tank up the hill is full, and I open the valve for the micro water turbine)

crewzer · August 2008

Re: voltage with mppt controller too high?

The AUX output is a solid state switch spec'd at 12 V x 200 mA. Don't forget an anti-kickback diode if the AUX connection is used to energize a conventional relay coil.

HTH,
Jim / crewzer

boB · August 2008

Re: voltage with mppt controller too high?

crewzer wrote: »

Don't forget an anti-kickback diode if the AUX connection is used to energize a conventional relay coil.
HTH,
Jim / crewzer

Isn't there a diode built into the MF80/MF60 already ?? There should already be one built in across the aux connector.

The proper diode is probably harder for the customer to choose, procure and hook up than just the relay itself.... Not to mention the user has to get the polarity correct when connecting this all up. The customer would most likely need to solder the diode into the circuit, too... If they have a soldering iron and solder.

boB

crewzer · August 2008

Re: voltage with mppt controller too high?

I don't know if there's a diode across the AUX output terminals...

I'll check!

I've had pretty good luck installing 'em across the terminals of the relay socket...

Regards,
Jim / crewzer

wxh3 · August 2008

Re: voltage with mppt controller too high?

Hello,

I know this thread has gone down a tangent since my original questions.

Anyway, I now have a different question regarding the same Sunsaver MPPT controller. In absorption phase of charging I am seeing a battery voltage of 27.6V both via voltmeter and the controller's serial data logging output. This is almost as low as the float voltage. According to manual, absorb voltage should be 28.6V. I have not programmed any custom setpoints.

Do you think this indicates a faulty controller or could there be another explanation? I have two almost new 110AH AGM batteries in series.

Thanks

BB. · August 2008

Re: voltage with mppt controller too high?

What is the temperature of your battery bank?

And, what is the Vmp rating of your solar panels, and what is the solar panels' voltage when charging (or near floating).

-Bill

If the solar panel voltage is near your panels' Vmp--then the controller would seem to be working OK on that side.

If the Vmp of your panels is near your battery charging voltage--then the panels need to be rewired to up the voltage such that their Vmp is, at least, a couple volts higher than your battery bank voltage (say ~30+ VDC battery + 2 Volts = Vmp of solar panels >= ~32 volts).

If the solar panel voltage is >> Vmp of the solar panels, then the controller thinks the battery does not need full current for charging anymore (not bulk, but absorb or float charging).

What is the current going into your battery bank at 27.6 volts? Pretty much, when the controller is dumping current into the batteries, it is the batteries themselves setting the voltage (bulk mode, controller outputting as much current as it can). Once the controller starts cutting back on the current--then the controller itself is setting the battery voltage (typically when the batteries are over 85-90% charged).

wxh3 · August 2008

Re: voltage with mppt controller too high?

BB. wrote: »

What is the temperature of your battery bank?

And, what is the Vmp rating of your solar panels, and what is the solar panels' voltage when charging (or near floating).

What is the current going into your battery bank at 27.6 volts?

Battery bank and charge controller are both inside in an 80F room and in a ventilated area.

I notice that MSVIEW (logging program) shows all temperatures (battery, ambient, and heatsink) as 104F though. I am not using a remote temperature sensor. I don't know if I can trust those values or not...using beta version of MSVIEW that supports the MPPT.

The Vmp is something like 35.4V at STC.

Right now it is a full sunny day and in the upper 80's. This is what I am seeing right now: The array voltage and charge current are jumping around lot when I have a very low load of around 15W (anywhere from 34-37V and 1-4 amps.) Just putting a modest additional load of ~50W seems to stabliize the current (4.5amp) and array voltage (34.6V) so it does not jump around wildly anymore.

In absorption phase of charging shouldn't I see a nearly constant 28.6V at the battery?

BB. · August 2008

Re: voltage with mppt controller too high?

The chargers generally have in internal temperature sensor inside them... And a problem is that the controllers heat up because of the electronics/current inside of them--generally over estimating the "battery" temperature.

Using this rough graph... The difference between 26.42 ~77F (standard temperature) and ~104F would only be ~0.2 volts or so. Less than what you are seeing. [add--see WXH3's post below--Controller's temperature compensation will be around -0.900 volt depression in voltage]

If the controller is in float (or absorb), the solar panel voltage and current will probably jump around a bit.

Is the battery voltage measured on the battery itself the same (within 0.100 volts or less) as you measure on the Charge Controller? (small gauge and/or long wire runs between the controller and battery can case voltage errors too--but since your meter and charge controller read about the same voltage--that should not be a problem).

If you set float your float voltage higher, does the battery voltage/charge current go up?--is the Charge Controller skipping Absorb--or just think the battery is ready for float?

If you reset everything back to defaults in the controller--perhaps some parameter got set wrong in the controller?

Sorry, I have not worked with these controllers to know their details.

-Bill

wxh3 · August 2008

Re: voltage with mppt controller too high?

Yes, the voltage measured at the controller and the battery is the same. I have very short cable runs with sufficient gauge.

The controller is reporting that it is absorption state based on flashing LED and and MSVIEW logging. (It has a different flashing for float.) That is also the state I expect it to be in too...it was in bulk for a while today and then went into the "aborb" state that seems to not have the proper voltage.

It does seem that it is maybe skipping absorb and going to float. The voltage is a little higher than float...maybe due the temperature compensation.

I haven't changed any of the customizable set points . When I read them it looks like they are still at their defaults. I am leary of changing anything (like increasing float or absorb voltage) until I talk to Morningstar tech support.

EDIT: Now it has gone into float state. It is reading betwen 26.5 and 26.6V This is also nearly 1 volt less than what I expect.

wxh3 · August 2008

I believe I see what is happening...

This is what the MPPT is using based on manual:
Temp. Compensation Coefficient -5 mV / °C / cell
(25°C reference)

Thus, when it measures temp as 40C, it adjusts the voltage for 24V battery bank (12 cells) by (40C-25C)(-5mV)(12 cells) = -900mV = -0.9V. That agrees almost exactly with what I am seeing.

The problem in my case is that I believe my batteries are not really the same temp as what charge controller is...they are probably closer to ~27C. I figured that I didn't need a temperature sensor since the batteres and controller were both inside and right next to each other. Looks like I should probably use a remote temperature sensor....

I wonder though if the controller could be doing a better job in figuring out what the air temp is? I don't know where the temp sensor(s) are located and if they try to compensate for the heat generated by the controller itself. The readings coming out from the unit showed the same value for the heatsink temp and the ambient temp.

BB. · August 2008

Re: voltage with mppt controller too high?

Yep, a temperature sensor will help... And ensure that you are fully charging your batteries (that 0.9 volt undercharging difference can be the difference between a 100% capacity battery and a 50% state of charge battery).

-Bill

voltage with mppt controller too high?

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