48V charging via ST generator and solar charge controller (no ST mod)

[mbryner]

Someone with a greater electronics background will be able to give a better answer than I can, but if I'm putting the generator charging circuit in parallel with the PV panel, how would it sense overvoltage?   (The PV panel max is <100 VDC, while the generator will output slightly higher rectified VDC.)   How it affects the MMPT circuit in the charge controller is beyond me.   Current should be limited by electronics in the MX80.   And I'm planning on running the generator when the sun isn't shining enough (rain, too little sun in winter, etc.).

[BruceM]

Here's a bridge rectifier module:  digikey # CC1656-ND  

It's rated double your max current, but that's not bad in my book.  

You can save some money with post type diodes as Geno did, but then you must find the mica isolators, and a suitable heat sink.  The brick type module would save you a bunch of time.

Now you just need a big heat sink to mount it on, and use some thermal grease.  

Do an ebay search for big heat sink.  There's one guy selling new heavy aluminum finned heatsinks, in various sizes and widths.  I've used his stuff- it's nice quality.

Llyod- the AC charger voltage is limited, and the two voltages aren't additive.  

[Lloyd]

Hi Bruce,

I must be missing something.

I thought Marcus was, rectifying the ac from the gen to dc to feed the charge controller to then charge the bat.

Now it would seem that if the PV is feeding it's max voltage at the same time as the gen is feeding the same charge controller it's rectified dc voltage, then the controller is going to exceed it's rated voltage.

What am I missing? I better go back and re-read this topic.

Lloyd

[mike90045]

What if the PV is at full ouput at the same time as the gen, wouldn't the charge controller see over-voltage and exceed the amp?

Charge controller is about 130 - 140VDC max, but don't let your AC ripple trigger the 150V warrenty void flag.

The controller will limit it's output current to a safe range, the Outbacks usually thermal limit before you reach the amps limit.

i'm not sure what the PV's will do with "lumpy" DC comeing, if the peaks will try to back drive them or what, maybe a blocking diode on the feed from the PV so the DC does not screw with them, or use 2 seperate charge controllers, or genset at night, early AM, and PV only when daylight.

[mbryner]

Yes, you have the config correct, but think parallel not series input to charge controller.

Thank you very much Bruce, you're awesome!

mike90045, see few posts back same thread about blocking diodes in PV panels, something I had forgot about.   Two separate charge controllers would be too easy, and too expensive.

[BruceM]

Marcus- here's a used bridge module for a good price on ebay
180468944390

Marcus is going to inductively filter his DC, so volts are going to be 80VDC with little ripple. The inductive filter also gives him a good PF.

Llyod- imagine a 24 and 12 volt supply,  with a common ground.  Put a diode on the 12V so it can't back feed. Now if you hook the positives together, after the diode, what would an applied load see?  Still just 24V. 

[mbryner]

Arrgh.   Just thought of something else.  The toroid transformers limit will be 2400 watts.   The charge controller is set up to take the full 3400 watts from the PV panels in full sunlight.   Will I have to throttle back the gen input to the charge controller somehow?

Thanks, Marcus

[BruceM]

If there is no current draw limiter on the solar charge controller, we'll have to limit the current draw externally.  Let me go look at the MX60 spec.

[mike90045]

  Will I have to throttle back the gen input to the charge controller somehow?

Nope, throw all the amps at the charge controller, nearly all MPPT designs limit the output to within the safe margins (amps or thermal)

[mbryner]

Mike, it's not the MX80 charge controller I'm worry about.   It's the risk of overdrawing the toroid transformers btwn the ST head and MX80, which are only going to give me 2400 watts.   If I had a 4th transformer, the problem would be solved, because the charge controller could do the current limiting.   But, alas, I have only 3 transformers.

[BruceM]

Yep, Marcus, that's a problem. I forgot that you were planning such a big PV array.  The toroids will typically do 20% over rated on 60Hz without getting too hot.  But that's still not up to the capability of your PV array.

I checked the MX80 manual-  there are no tricks available there- just a fixed programmable max current out.  Manually reprogramming the max current out would have to be done every time you wanted to run the AC charger.

So if you can't live with an output that limits your input to the capability of the charger, then we either have to add current limiting to your charger's output or you'll have to get one of the $200 charge controllers just for the charger.  I'll have to think about the current limiting;  it may be more than $200 worth of work.  

PS-
What is the maximum AC load your Listeroid can sustain continuously?

[Geno]

Marcus, I don't know how familiar you are with the Flexmax control panel but it only takes a few seconds to change the charge amps. Just put a little chart on the wall with what you need from each source....and don't forget. I have a whole regime for starting and stopping the "system". Valves, pumps, breakers, etc.

Thanks, Geno

[mike90045]

The toroid transformers limit will be 2400 watts.

Throttle back the genset ?  Different pulley ratio ?

[mbryner]

with the Flexmax control panel but it only takes a few seconds to change the charge amps. Just put a little chart on the wall with what you need from each source....

That would work fine for me, but how would my wife remember to do all that.   As it is, she can't start the Listeroid alone consistently, which is why I'm building an electric start.   It's going to be hard enough for her to remember to oil it!     Don't you guys have problems like this, too?!  

P.S. Bruce, I've never loaded my 6/1 more than about 3500-4000 watts.   A 2nd charge controller wouldn't break the bank, if that's what it takes.  Just don't tell me to get another MX80!   I mean, a little cheaper would be nice...

[mike90045]

Morningstar TriStar 45 Amp MPPT $412 http://store.solar-electric.com/motr45ampmps.html

Morningstar TriStar 60 Amp MPPT $520 http://store.solar-electric.com/motr60ampmps.html

Xantrex XW MPPT 60 Amp  $530 http://store.solar-electric.com/xaxwmp60amps.html

Outback Power FM60 MPPT 60 $598  http://store.solar-electric.com/ouchco.html


This is where I got my TriStar 60 Amp MPPT, should be hooked up by the end of this week, if the rain allows the trenches to be dug.