PWM diversion control and a MPPT regulator in parallel?

[Olberg]

I am about to add a small wind turbine to my off grid PV-setup. So I’ve bought a Morningstar TS-60 to use as a diversion control. I will connect it directly to the battery in parallel to my MPPT Victron Blue Solar 150/70 charger (and Victron inverter).

I want to keep my MPPT to get the most out of my panels.

My plan is to set the MPPT controller to disconnect the solar array at one volt above what the diversion control is set to turn on. I do not want the solar charge controller disconnecting the array as I want to use the excess power to operate my water heater (=dumpload =diversion). Also if the dump load were to fail, the MPPT controller will be set to disconnect at one volt higher than usual to protect my batteries from over voltage.

Will this work or do you wise people here see any problems?

(I have a 24V system 1520Watts of PV-panels and a 640Ah battery bank)

[inetdog]

I am having a hard time understanding from your description just what you are proposing to do, so I cannot really comment very well.
By "disconnecting the array", do you mean you have set the Absorb and Float voltages to a value which will keep the solar charger from trying to deliver any power to the array?
That seems inefficient in terms of charging.
And the same question for how you would set the MPPT CC to "disconnect" at one volt higher than usual if and only if the dump controller fails.
A wind turbine with a failed dump controller will be very difficult to control and perhaps unsafe, so a backup dump load on the turbine is a critical element.

[Olberg]

Sorry perhaps I should have I written that I wish to use all PV-power there is and not having the MPPT go into float and loose the potential PV-power as when the batteries are fully charged. And at the same time have a dump load for my soon to be wind turbine.
Perhaps I can clarify.

Say my batteries need max 27V (here, I am of course simplifying the whole charging program).
I set my MPPT at max 28V
I set the Diversion controller to max 27V
Now the MPPT will still be maxing power (as it would not do if I set it to max 27V it would go into float, remember) and the diversion controller can PWM power into my water heaters.

The question is really about how the MPPT regulator will react when reading battery voltage if there is PWN regulator parallel in the system with a slightly different charge cycle?

[inetdog]

Sorry perhaps I should have I written that I wish to use all PV-power there is and not having the MPPT go into float and loose the potential PV-power as when the batteries are fully charged. And at the same time have a dump load for my soon to be wind turbine.
Perhaps I can clarify.

Say my batteries need max 27V (here, I am of course simplifying the whole charging program).
I set my MPPT at max 28V
I set the Diversion controller to max 27V
Now the MPPT will still be maxing power (as it would not do if I set it to max 27V it would go into float, remember) and the diversion controller can PWM power into my water heaters.

The question is really about how the MPPT regulator will react when reading battery voltage if there is PWN regulator parallel in the system with a slightly different charge cycle?

OK, you are simplifying the charge controller side by looking only at the Float voltage.
If the diversion controller diverts the input power from the turbine to your dump load instead of to the batteries I would expect the solar CC to overcharge the batteries. If the diversion controller is actually only a shunt controller that takes current directly from the batteries, and there is a separate wind controller that goes between the turbine and the batteries to provide MPPT functionality there (the turbine voltage will vary with wind speed unless there is a regulator built into the turbine), then you may have interaction problems. The shunt controller will cause a rapidly cycling battery voltage over time and the MPPT controller could well be confused by that.

If you want to be able to send power from the PV array to your dump load too, I would look for that functionality in the solar CC (with external relays?) and not try to run everything through the batteries. To get the best match between your panel output and a fixed resistance load for best power transfer you really need to include MPPT. Your way of trying to do that by connecting the dump load to the battery side may not work well.

I would like to see some contributions from other members with practical experience in this area. I am out of my comfort zone.

[Olberg]

I can´t believe that nobody in this off grid section has experience of having both wind and solar power connected to the same battery bank.
And that some of you also has mppt regulators for your pv-panels in that setup.

Here is a wiring circuit I’ve found (http://scoraigwind.co.uk/) but unfortunate it does not include a mppt.



Wind turbine Pv panel circuit.jpgWind turbine Pv panel circuit.jpg



How would you/ have you connected wind and solar together?
Anyone?

[Mike90250]

I can´t believe that nobody in this off grid section has experience of having both wind and solar power connected to the same battery bank.
........
How would you/ have you connected wind and solar together? Anyone?

First, there are few sites that wind makes much sense at.

Second, it's complicated. Really complicated if you value your battery investment, as Inetdog mentioned. It can't be done with cheap PWM & simple shunt controllers, unless you are using scrap batteries and don't have a lot of $ invested in them.

Good MPPT controllers are required, and to protect the turbines, a shutdown system needs to be designed. The one you referenced at http://scoraigwind.co.uk requires a person to manually throw the turbine shutdown switch. I'm not sure if even the fancy Classic Clipper has auto braking. (it does, when used with a Classic MPPT)
http://www.midnitesolar.com/productP...tOrder=2&act=p 1500w and 4Kw AC & DC versions.

[Olberg]

Thank you for answering Mike!

First, there are few sites that wind makes much sense at.

I know this, but having just the one hour (in total) of sun in November and needing only a few backup watts in my empty cabin for internet monitoring made me think of other means than relying on gas generator support. It’s quite windy here in the autumn.

Your and Inetdogs answer makes me confused when Morningstars answer to the same question is:

Hello,

Your proposed application is quite common and should work well.

Best Regards
Steve V.
MS Technical Support

And also here is an offgridder (with five complex systems behind him) who states that this works:

http://solarhomestead.com/dump-loads-for-solar-wind-and-microhydro/

(read under “If you are using a dump load you do not need a charge controller on the solar array. “)


I am of course grateful for any other input on the matter!

[J.P.M.]

Thank you for answering Mike!



I know this, but having just the one hour (in total) of sun in November and needing only a few backup watts in my empty cabin for internet monitoring made me think of other means than relying on gas generator support. It’s quite windy here in the autumn.

Your and Inetdogs answer makes me confused when Morningstars answer to the same question is:

Hello,

Your proposed application is quite common and should work well.

Best Regards
Steve V.
MS Technical Support

And also here is an offgridder (with five complex systems behind him) who states that this works:

http://solarhomestead.com/dump-loads-for-solar-wind-and-microhydro/

(read under “If you are using a dump load you do not need a charge controller on the solar array. “)


I am of course grateful for any other input on the matter!

I'm sure your vendor is completely honest and ethical. But, I'd consider following the money. Knowledgeable posters and moderators around here don't have a lot of, or any, money on the table by suggestions and comments. Given what they're paid ~~$0.00). And so, at the risk of seeming to damn with faint praise, I'd suspect their reputation and self respect are more important.

[Mike90250]

Don't get me wrong, Morningstar makes good gear. I just bought a 2nd MPPT 60A controller for another outbuilding,

But I don't know if their PWM controllers provide 3 stage charge as a shunt controller for a dump load.

Making a dead simple 13.75V shunt controller for a dump load is easy. Making the same thing as a 3 stage controller is more difficult. Making a reliable dump load is tricky too. Any missteps lead to boiled batteries or blown turbine.

The control and dump load have to be able to take full system power on a sunny windy day. the 600W from PV, and the 800W from the turbine, is close to 1,500 watts that has to have power routed to, and then dissipated without setting fire to anything. At 12V, that's 125Amps continuous duty, every connection HAS to be PERFECT or you have a disaster. It can be done, but it has to be done right, or (wait for it) ... disaster.

[Olberg]

I have 2x800watt @24V worth of water heaters on its way from Hong Kong. It and wiring will be able to handle the full 60amp 24V even though I'm almost certain it will never come to this.

And yes, the Morningstar TS-60 gives you full control of the multistage charging.
So does my Victron mppt blue Solar.
I am also temp compensating both at the same pace and reading voltage with separate sensor inputs.

The question is what voltages to set for the different stages? to avoid (wait for it...) disaster.

When it comes to having multiple chargers and regulators I surfed the http://www.cruisersforum.com all evening yesterday. And those guys do this all the time.
But without my dump load heating setup of course.

Here was a beautiful analogy I found:

<sub>Imagine a 55 gal barrel that is filled with water and submerged in the water. But the barrel also has a small hole in it. Your job is to lift the barrel out of the water and hold it at a designated height.

The work involved with lifting the barrel and holding it at a particular height is much like charging a battery.

The faster you lift the barrel, the harder it is. But after you lift it to a certain level, it gets easier and easier to hold it there as the water leaks out the hole. If you lift the barrel slowly, it's not so hard because the water leaks down as you lift, but it takes longer. The faster you want to lift the barrel, the harder you have to lift.

Charging a battery is very similar. The bulk stage is like lifting the barrel out of the water. If you are limited in your lifting ability, you will only be able to raise the barrel at a certain rate, having to wait for water to drain out enough to lift further.

If you have two people lifting, you can get the barrel lifted up faster. It's not so important whether one person is lifting harder than the other, just what the combined lifting force is. Both people will lift as hard as they can until the barrel is at the designated height. Three or four people lifting is even better.

The Bulk charge stage is much the same. One charger will charge the battery as fast as it can, and multiple chargers will charge it faster. It's their combined charge capacity that matters, not how much each contributes individually. And each will work as hard as it can until the battery reaches its bulk voltage.

Things get a little more interesting as the barrel arrives at the desired height and the job changes from lifting to holding. Each of the people lifting has a slightly different perspective on what the "correct" height is, so each starts backing off at slightly different times. Again, it's not a problem since the height is close enough to what we want. As the water drains out the barrel becomes lighter and lighter, and less effort is required by everyone to hold the barrel. Eventually, the barrel becomes light enough that one person is carrying all the remaining weight. Whichever person thinks the barrel should be the highest will be the one left holding everything.

The same thing happens as the chargers hold your battery at its Bulk/absorb voltage throughout the Absorb stage. Note that for simplicity, I'm going to assume that Bulk and Absorb voltages are the same. Each charger measures the voltage a little differently, and each contributes differently to maintaining Absorb voltage. As the battery becomes more charged, the chargers will back off typically leaving one charger doing most if not all the work.

Then things get the most interesting trying to conclude when the job is done. The people holding the barrel will let go when they either a) feel they are making no meaningful contribution to holding the barrel up, or b) conclude they have been holding it long enough and are going to just let it drop back in the sea. As long as one person keeps holding on, the barrel stays up, and after the last guy gives up, it drops back in the sea, eventually floods, and the whole process starts again.

Finishing up your battery charge is similar. It becomes easier and easier for the chargers to maintain the Absorb voltage, and eventually each drops out either because it's no longer producing more than some threshold of charge current, or because it's been in Absorb for longer than some time limit. Ultimately one charger is the last one operating, and it's the charger trying to achieve the highest Absorb voltage for the longest amount of time. Just because others dropped out earlier doesn't mean another charger will run longer. Each has a job to do and will stop when it's done. If anything, they finish up earlier because there were more of them helping throughout the whole process.

The real loophole in the system is if someone is leaning on the barrel while everyone is lifting. Those who are waiting for the load to lighten to a certain level will just keep on holding, unaware that they are holding up a leaning crew member, not the barrel. If waiting for a light load is the ONLY criteria for stopping, the poor guys holding up the barrel can be left there indefinitely. Note that it makes no difference how many people are holding the barrel up. As long as one of them won't stop until the load lightens, he just keeps on going.

Finishing up the Absorb charge has the same loophole, but it has to do with how your chargers operate, NOT how many of them there are. Good chargers will stop when the load gets light AND they will stop after some period of time. This is to protect against remaining in Absorb forever because your fridge is running and the charger is carrying that load PLUS your battery's final charge load.</sub>

[inetdog]

The control and dump load have to be able to take full system power on a sunny windy day. the 600W from PV, and the 800W from the turbine, is close to 1,500 watts that has to have power routed to, and then dissipated without setting fire to anything. At 12V, that's 125Amps continuous duty, every connection HAS to be PERFECT or you have a disaster. It can be done, but it has to be done right, or (wait for it) ... disaster.

With proper design and a smart MPPT CC on the solar side, you could get away with sizing the dump load for only the turbine high wind power, since PV panels are not damaged by being open circuited. Still a substantial power load and resulting current.
And you would have to be 100% sure that the solar CC would shut down completely at the point where the shunt controller was maxing out.

[erikfriend]

I'm doing this. It works great.

I signed up here just to answer this question.

I'm using an EPSolar 4215BN solar MPPT and a Xantrex C60 diversion controller in precisely the configuration you described. It works great. The MPPT never reaches it's bulk voltage and therefore never enters float mode. The diversion controller maintains complete 3-stage charge control over the batteries.

Here are some tips I've learned along the way:

1) Set the MPPT bulk voltage set-point as high as possible unless your MPPT controller has a remote battery voltage sense feature. The voltage drop between the controller and battery under high current will give the controller a slightly high voltage reading which can fool the controller into entering float mode. Give yourself a several volt margin.

2A) Make sure your dump loads can handle max turbine output + max solar. An undersized dump load won't be able to divert enough power to maintain battery charge regulation.

2B) Redundancy: Get a second diversion controller just in case. If one fails, you won't toast your batteries. PWM diversion controllers are cheap. Batteries aren't.

3) Bask in the satisfaction you'll experience knowing that no precious solar power is being wasted. Your dump controller's buzz becomes an audible measurement of power production. Embrace the buzzz...

Erik Friend