Connecting a Generator to a Classic

[BobWhite]

Some responses to the responses!

Iotas are adjustable & have smarts , what is your model , I have 12,24,V in 45a&90&120A in 24V
>> I have a DLS-45.  In dual voltage mode - it puts out 14.2V and 13.6V.
>> In Smart mode: Bulk:14.8V, Absorb:14.1V and Float 13.6V
>>At  cool temps, these voltages are too low.  The Bulk needs to have the ability to be about a half volt higher than it is.


This is obviously is something that you really want to do.
>> Yes!
On this Forum,  MidNtie Engineering said that this is not recommended  --  a polite way of saying DO NOT DO THIS.
>>I can understand the liabilities that some have explained.  I also understand that MidNite may not want to spend time explaining how to do this.
>>I'm willing to accept the responsibility it I destroy my Classic.  I was hoping that someone on the forum had experience.
There may not be enough time in a day to discuss this in detail,  at least there is not enough time in my days.
>> Understood.  On the other hand, if others have done this - then the answer could be fast and simple.
I have no horse in this race.  You seem to have the answers,  so who am I to try to dissuade you from your task.
>>If I had the answers, I wouldn't be asking for help or suggestions!

My thought about building the ideal generator rectifier like you are talking about is that by the time you engineer to  put in all the parts and design to consider all the details  you will have something like what you see in an inverter charger or the better Iota chargers mentioned above. 
>> I think that people are over analyzing this problem.  The answer should be as simple and a few diodes, a capacitor and maybe a resistor.  If the Classic had a mode that does not sweep, we would be all done.
I am not an electrical engineer so couldn't begin to design such a device like you want. I watch tear downs of devices on EEV blog on  youtube and he explains in detail all the engineering and design details of devices - there is so much to consider.  Check out that youtube channel - he can spend 45 minutes just scratching the surface on what thoughts went into some electronic device.
>> I do have a background in electronics.  Really, really, it's not all that complicated....
And as mentioned above by vic - no matter how big your generator capacity is , for lead acid batteries once they reach the Absorb setpoint the current is going to taper back. If you want a battery pack you can quickly dump a lot of power into then you should consider getting lithium batteries
>>Correct.  But if the Bulk and Absorb voltages are too low, then one is not putting as much current into the batteries as one could.  This means that the generator ends up running longer than it should.  Even a completely unloaded generator eventually runs out of gas.  Where I have my cabin, it is very difficult to get fuel - not to mention the  philosophic issue of wasting something that you don't have to.


So the "Real" issue is the stiffness of the generator, The Classic (like other MPPT controllers) is used to working with things it can through around in voltage. So if it tries to sweep all the way down to battery caboom goes the FETs.
That said I have a set up just like this, 120vac generator rectified and filtered slightly with capacitance fed through a resistor and then fed to a classic. I use Hydro mode with a low voltage limit of like 145 and current limit set to 40 amps. The Resistor acts as a shock absorber. I use 2 ohms and it seems ok.
>> Thanks for the data.  I'm not sure where you got the 145V from?    The rectified, filtered, unloaded voltage should be around 170V.  But as you put a load on the output, you're going to come back down to the 120 RMS voltage.  I guess if you are lightly loading your generator, you could be at 145V?
Of course tech support will tell you this is "Unsupported" and will "Void your warranty"
>>I accept the consequences.

I can agree with them on both parts as it can be a large consumption of time to walk some one through making it work and then they have the liability if the Classic blows up. So long story short, yes it can be done, Yes it is slightly tricky and YES it can blow up the classic if not done right.
>>Having said that - I would think that Midnite Solar could get some marketing mileage out of being able to use their CC in such a mode.  Heck, they could even build the interface box and add a mode that does not sweep the input.  They might sell even more CC's.

Wow    ! That's heavy and not sure how to absorb it all, I'm not very smart here but will try to follow along! We have a lot of knowledge here and I'm grateful for that!

Hi .....rob,

There have been a number of Threads on this subject here,  and elsewhere.

MidNite  Engineering has said that this is NOT RECOMMENDED.

As Tom noted,  adding some reasonable resistance in series with the Vin to the Classic  will help 'soften"  the input,  but would waste a lot of power.

It was also mentioned here,  that having the battery voltage close in voltage to the external Power Supply would help protect the Classic  --  this was in the context of an external PS,  and your situation seems far from this recommendation.

Also,  a simple bridge/filter capacitor  would seem to present a poor Power Factor to the Genset.

One way that many MPPT CCs protect themselves is that they reduce the load on the input power source,  which causes the input voltage to rise.  In Solar Mode,  the Classic "knows"  that the input source IS from PV,  and this operating point WILL reduce the input power to the CC.  With your direct output from the filter to the CC,  this is not really the case.

It was also noted in that same Thread,  that running the Classic in Legacy P&O  would probably be the preferred Mode for these relatively risky approaches.

Your comment,  "I do have an Iota 12v charger - but the output voltage is not high enough.  It starts charging with a reasonable current, but this soon levels off and I waste a lot of gas without much charging going on",  probably indicates that the Bulk charging has finished,  and the Absorption voltage has been reached,  so the battery charge current will continue to taper.

This apparent battery charge current taper,  could also be that with FIVE STRINGS (!!!) of batteries,  that there could be poor current charge current sharing between all of those batteries,  and the one or two batteries that are hogging much of the current have gotten to Absorb ...  just  guessing.

Your thoughts are common ones,  at least about using an external PS that feeds an MPPT CC input.  Direct rectification for this input is also risky,  as there is NO isolation between the genset AC output,  and DC side of the system ...   this is often risky in its own right,  for Safety reasons.

To determine the approximate value of the "softening" resistor,  you could look at the Vmp verses Voc curves of the PVs that you are using,  and figure out about what is the output impedance is of the String of PVs that you are using,  this could possibly guide you.   BUT,  this will become a bit of a heater.

And so on,   GOOD LUCK !   Vic

.....rob,

This is obviously is something that you really want to do.

On this Forum,  MidNtie Engineering said that this is not recommended  --  a polite way of saying DO NOT DO THIS.

There may not be enough time in a day to discuss this in detail,  at least there is not enough time in my days.

I have no horse in this race.  You seem to have the answers,  so who am I to try to dissuade you from your task.

Vic

My thought about building the ideal generator rectifier like you are talking about is that by the time you engineer to  put in all the parts and design to consider all the details  you will have something like what you see in an inverter charger or the better Iota chargers mentioned above. 

I am not an electrical engineer so couldn't begin to design such a device like you want. I watch tear downs of devices on EEV blog on  youtube and he explains in detail all the engineering and design details of devices - there is so much to consider.  Check out that youtube channel - he can spend 45 minutes just scratching the surface on what thoughts went into some electronic device.

And as mentioned above by vic - no matter how big your generator capacity is , for lead acid batteries once they reach the Absorb setpoint the current is going to taper back. If you want a battery pack you can quickly dump a lot of power into then you should consider getting lithium batteries .

Larry

It is a wonderful thing we all have opinions, and all are different, if all were the same---not everyone would be needed

[cabinrob]

Having thought and read about this some more... 
It seems that the "don't do it" comments are mostly directed towards rectifying mains/line and trying to feed that into a Classic.  I would agree that this is a bit more dangerous.

I think that people are extending this to include generators.

Remember, the Classic has a Wind Mode and a Hydro mode.  I really don't see a lot of difference between wind/hydro and a gas generator.
(Ok, maybe some variances based on the characteristics of the output - whether it is "raw" or coming through an inverter.)
I haven't seen anyone saying I can't hook a hydro generator to the Classic.
I wish the Hydro mode was a bit better explained in the manual.  I did watch the video, but it sure would be good to have a bit more detail than that.

For anyone else watching this thread, I quote boB in one of his posts:  http://kb1uas.com/mnsforum/index.php?topic=917.msg6112#msg6112

So, maybe our discussion should really focus on how a gas generator is different from a hydro generator.  Let's assume a constant flow rate for now.
If we can't come up with any real differences.....  then the conclusion should be obvious....

[cabinrob]

Let's say that I want to connect my hydro generator to my Classic.
My hydro generator puts out AC RMS 120V.
I can full wave rectify this and end up with a lot of ripple.
I can filter this and end up with "less" ripple.

Does anyone know how the Classic responds to this ripple?
Does the rectified waveform need to be smoothed out?  If so, how much?
Is there a spec for acceptable ripple at the input of the Classic?

[Vic]

Read,  carefully,  the following;

   ...   That said I have a set up just like this, 120vac generator rectified and filtered slightly with capacitance fed through a resistor and then fed to a classic. I use Hydro mode with a low voltage limit of like 145 and current limit set to 40 amps. The Resistor acts as a shock absorber. I use 2 ohms and it seems ok.

Of course tech support will tell you this is "Unsupported" and will "Void your warranty"

I can agree with them on both parts as it can be a large consumption of time to walk some one through making it work and then they have the liability if the Classic blows up. So long story short, yes it can be done, Yes it is slightly tricky and YES it can blow up the classic if not done right

[TomW]

Since HalfCrazy (Ryan) is Sales Manager  at Midnite Solar you can take his advice with complete confidence.

He has been "stress testing" Classics for years now. 

Just saying...

Tom

[cabinrob]

Yes, I read the post.
It validates the whole process.
But in the post from HalfCrazy:
     That said I have a set up just like this, 120vac generator rectified and filtered slightly with capacitance

The term: "filtered slightly" is not very specific.
Interpretations of this could lead to a ripple well over a hundred volts, or maybe only a few volts.
If probably matters....

[TomW]

The term: "filtered slightly" is not very specific.
Interpretations of this could lead to a ripple well over a hundred volts, or maybe only a few volts.
If probably matters....

I think his point is that is NOT necessary to have a pure DC voltage on the input.


I will tag him on this see if he is online to get you a more precise  answer.

Tom

[Halfcrazy]

Let's say that I want to connect my hydro generator to my Classic.
My hydro generator puts out AC RMS 120V.
I can full wave rectify this and end up with a lot of ripple.
I can filter this and end up with "less" ripple.

Does anyone know how the Classic responds to this ripple?
Does the rectified waveform need to be smoothed out?  If so, how much?
Is there a spec for acceptable ripple at the input of the Classic?

The Classic really wont care much about the ripple. If it is real bad you may get a RFR of #9 witch is reverse current is greater than 9 amps and if so you need to add a little filter capacitance

[Halfcrazy]

Since HalfCrazy (Ryan) is Sales Manager  at Midnite Solar you can take his advice with complete confidence.

He has been "stress testing" Classics for years now. 

Just saying...

Tom

Remind me tomorrow to post my first attempt at charging with a classic from my 120vac generator there was smoke and fire yes!

[Halfcrazy]

Yes, I read the post.
It validates the whole process.
But in the post from HalfCrazy:
     That said I have a set up just like this, 120vac generator rectified and filtered slightly with capacitance

The term: "filtered slightly" is not very specific.
Interpretations of this could lead to a ripple well over a hundred volts, or maybe only a few volts.
If probably matters....

Honestly the filter caps really dont seem to effect the classic so to speak. Again I think like you do so when I had the reason to do this I did it. Of course it helps I get free classics 

[cabinrob]

I cant' wait to hear about  your smoke/fire experience.

Life is to short to make all of the mistakes yourself....   :-)

I would have thought that a lot of ripple would have driven the Classic a bit nuts.  Your comment about reverse current on the input side sort of substantiates this.
I'm guessing that there is a "reasonable" (ha ha, there is another one of those precise engineering terms) amount of filtering/capacitance in the front stage of the CC.
Is there a register where one can observe the reverse current?
This would be a good way to tune how much capacitance to add to the generator....   I mean to the hydro generator....  ;-)
I'm thinking that I may put a temporary shunt on the input side and hook that up to a storage scope.  That should take a bit of the mystery out of the setup.

[mike90045]

Generators and hydro plants react differently to loads, and the controller will get into a battle - the weaker device will fry.

120VAC ends up being close to 180V P-P, close to the limits, but not likely to exceed - As long as you have some loading, if you let it go open circuit, you may hit 200V as the caps charge up.  Maybe you can use a variac or a 2:1 step down transformer to
get the voltage down lower, the higher the voltage is, the higher losses in the controller.  Lower DC = cheaper filter caps too.

What size resistor ?  Well you want it to pass a lot of power, but still have enough effect to allow the charge controller to be able to regulate.  Maybe a water heater element (in a tank of water) will be a decent ballast resistor, 120V 1Kw 

You are going to have to play "Limbo" with it and see how low can you go.  The resistor will not be small or cheap, it will have to have a good size heat sink.

Also, modern gensets are pretty scant on their cooling, I've got a 3.3Kw peak, rated for 3Kw cont, but  can only pull 2.5kw at 100% duty and still have to give it a 5 min cool down before shutdown.   Charging batteries is a pretty stout load for a genset, and it won't like it.

[Halfcrazy]

I cant' wait to hear about  your smoke/fire experience.

Life is to short to make all of the mistakes yourself....   :-)

I would have thought that a lot of ripple would have driven the Classic a bit nuts.  Your comment about reverse current on the input side sort of substantiates this.
I'm guessing that there is a "reasonable" (ha ha, there is another one of those precise engineering terms) amount of filtering/capacitance in the front stage of the CC.
Is there a register where one can observe the reverse current?
This would be a good way to tune how much capacitance to add to the generator....   I mean to the hydro generator....  ;-)
I'm thinking that I may put a temporary shunt on the input side and hook that up to a storage scope.  That should take a bit of the mystery out of the setup.

No reverse current can not be monitored on the Classic by the user, The reverse current makes sense if you think about ripple. As the peak hits the classics caps go high. When the spike goes low the power goes back out of the caps. I would start with NO filter caps and see if its an issue. I would also put resistance in series and set the current limit to a very low setting on the start

[cabinrob]

Generators and hydro plants react differently to loads, and the controller will get into a battle - the weaker device will fry.
>>Agreed that a generator is a bit different - in that as load increases, so does engine power. 

120VAC ends up being close to 180V P-P, close to the limits, but not likely to exceed - As long as you have some loading, if you let it go open circuit, you may hit 200V as the caps charge up.  Maybe you can use a variac or a 2:1 step down transformer to
get the voltage down lower, the higher the voltage is, the higher losses in the controller.  Lower DC = cheaper filter caps too.
>> Not sure I see this.  120VAC RMS is (120 x 1.414) 170V P-P    Unless the generator voltage is very unregulated, I don't see how I can get to 200v   Lower DC may mean cheaper caps, but variacs are even more expensive.
>>Even if there were a few cycles that did get to a high voltage, putting a resistor across the caps would solve this.  I would do this anyway as a safety thing - to bleed away any charge so that there aren't surprises after things are shut down.

What size resistor ?  Well you want it to pass a lot of power, but still have enough effect to allow the charge controller to be able to regulate.  Maybe a water heater element (in a tank of water) will be a decent ballast resistor, 120V 1Kw 

You are going to have to play "Limbo" with it and see how low can you go.  The resistor will not be small or cheap, it will have to have a good size heat sink.

Also, modern gensets are pretty scant on their cooling, I've got a 3.3Kw peak, rated for 3Kw cont, but  can only pull 2.5kw at 100% duty and still have to give it a 5 min cool down before shutdown.   Charging batteries is a pretty stout load for a genset, and it won't like it.

>> I guess I'm still not getting this. 
>> Let's work backwards.
>> My Classic 200 is rated for an output of 79A at 14.4V, or 1140W
>> Let's assume 100% efficiencies for now.  So, the maximum load on my generator would be 1140W, or about 9.5A at 120 VRMS.  I should be able to run my 2500W generator all day at this load.
>> If we go with using the Hydro Manual MPP mode and set the Minimum Voltage to say, 110V, why do I need any resistor at all?
>> My interpretation is that in Manual mode, the Classic will not sweep the input.  It won't draw any power if the input voltage is below 110V.
>> I start my generator.  My filter caps start charging.  When they get to 110V, the Classic wakes up and starts drawing power.
>>The Classic by it's own design will current limit it's output to 79A.  The generator will never have to push more than 10A.  (Let's ignore inrush currents for now.)
>> What am I missing

[mike90045]

......>> What am I missing

Let's just hope you are real lucky.

If you don't know how RMS and a bridge rectifier works, and think that setting the controller to 110V min will solve things, you are going to have an expensive surprise.  Just a few little spikes from the generator and you are over 200VDC quickly.

The controller is expecting to be able to vary the loading on the Input (PV or Hydro) and have the input respond in a predicted way.   A generator with 2 or 3x the output capability of the controller will not respond as expected, and you are likely to cook something.

>Even if there were a few cycles that did get to a high voltage, putting a resistor across the caps would solve this
  That is a lesson I learned in high school, on the classroom budget.  V x A = Watts. 

So, anyway, fire it up and tell all us naysayers how it worked.