Author Topic: DC-only equipment with solar augmentation  (Read 268 times)

GlueGuy2

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DC-only equipment with solar augmentation
« on: March 15, 2021, 06:12:48 PM »
We have some equipment that runs on straight 48VDC. It's currently powered by a DC-UPS system with a medium-sized battery bank. The UPS is on AC power now, and has separate connections for the load and the batteries (similar to a solar charge controller). In the event of a grid outage, the batteries are sized to carry the load for a bit over 24 hours.

The DC-only equipment has a continuous load of about 200 watts, which adds up considering it's running 24x7.  What we'd like to do is add a couple of solar panels in the range of 300-500 watts total to augment the AC power and reduce the continuous power draw from the grid. There is no inverter, because the load is 100% DC. If we connect up a solar charge controller, would we just connect the load side of the solar controller, or both the load and battery, or (maybe) just the battery?

Tnx,
bp

ClassicCrazy

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Re: DC-only equipment with solar augmentation
« Reply #1 on: March 16, 2021, 03:21:27 AM »
I would hook the output of the charge controller to the batteries.
You would want to make charge settings so that when there is solar it would provide the power and the AC power supply wouldn't do  much.
So maybe the solar charger would be set Absorb  and float voltage a bit higher than your AC power supply ?  I would have to think about that but others might have some advice.
Are they sealed lead acid batteries ?
Use the string calculator on Midnite webpage with the solar panels you are thinking about to see how the configuration would work. Since it is 48v you probably need two PV in series to get high enough voltage to charge 48v. 
Are you thinking of using a Kid or Classic ?

Larry
« Last Edit: March 16, 2021, 03:24:23 AM by ClassicCrazy »
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

GlueGuy2

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Re: DC-only equipment with solar augmentation
« Reply #2 on: March 16, 2021, 01:35:19 PM »
We haven't decided on which controller to use; we're just trying to figure out the best way to wire this to provide two basic functions:

  • Take the load off the AC when the sun is shining (we get ~~ 5 hours solar here during winter solstice)
  • Extend the 24 hour battery backup time a little if the AC grid is down for more than 24 hours

Yes, the batteries are AGM. The way it is configured now, we have ~~ 12 KWH of battery (50% utilization)

GlueGuy2

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Re: DC-only equipment with solar augmentation
« Reply #3 on: March 19, 2021, 03:38:13 PM »
Presently, I think I can tie the battery output of both the AC-UPS and the solar charge controller directly to the batteries without isolation. I suppose I could bias the solar controller to be ~~ 1/10 volt higher than the AC-UPS to be sure that the solar controller will win when the sun is up.

Likewise, I could put s silicon power diode between the AC-UPS and the actual load, such that it would have to be supplying ~~ 0.7 volts more than the solar charge controller. That way, when the sun is shining, I know the solar controller will be supplying the power.

I have a couple of 260 watt panels I can run in series, so a KID would be more than adequate to do this.

ClassicCrazy

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Re: DC-only equipment with solar augmentation
« Reply #4 on: March 19, 2021, 09:40:43 PM »
When you get it set up it will be easy to test if it is working - just shut off the ac powered charger and see how many amps the solar is putting in . Then turn the ac back on after awhile and if solar goes down you know you need to up the solar controller voltage some more.
One reason you might consider the Classic is if you want to expand your PV someday more than the Kid can do.
Or if you want some great monitoring and control , then the Classic wins big time on that with lots of remote monitoring options via opensource software . And the AUX contacts give you a lot of control logic to use if you need it for anything.

Larry
« Last Edit: March 19, 2021, 09:42:45 PM by ClassicCrazy »
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

GlueGuy2

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Re: DC-only equipment with solar augmentation
« Reply #5 on: March 25, 2021, 06:04:42 PM »
Maybe this will help. A basic block diagram.

ClassicCrazy

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Re: DC-only equipment with solar augmentation
« Reply #6 on: March 26, 2021, 12:59:37 PM »
Maybe this will help. A basic block diagram.

I think you should have the load going directly to the batteries.
Larry
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

GlueGuy2

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Re: DC-only equipment with solar augmentation
« Reply #7 on: March 27, 2021, 03:33:54 PM »
Maybe this will help. A basic block diagram.

I think you should have the load going directly to the batteries.
Larry

That would defeat the multi-stage charging. Both the UPS and the solar controller have LVD plus isolation between the batteries and the load. We do not want to lose that. Where I'm leaning now is to remove one of the load lines (either the solar controller or the UPS).

ClassicCrazy

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Re: DC-only equipment with solar augmentation
« Reply #8 on: March 27, 2021, 06:26:20 PM »
Not sure how you think it would defeat multistage charging ?
 I didn't think that you were going to use the Load control on a Kid. If you were using a Classic you would need to use the Aux relays to go to a relay to control loads.
You would need to make sure the load control on Kid can handle the load .
A Classic Aux with a relay could control any size load and even be put in series or parallel with the other load control if needed.
Larry
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

GlueGuy2

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Re: DC-only equipment with solar augmentation
« Reply #9 on: March 31, 2021, 01:47:53 PM »
Larry,

You seem to be trying to sell me on the advantages of a Classic. I acknowledge that a Classic is far more capable than a Kid. However, our loads are only in the neighborhood of 4 amps or so. Further, with a pair of solar panels, the highest voltage we anticipate is probably only in the 80-90 volt range, which is well within the capability of the Kid.

Also, if you don't separate the load from the batteries, how does the controller distinguish between battery charge draw, and load draw? Those two dynamics have to be separated in order to do true multi-stage charging, unless something fundamental has changed.

ClassicCrazy

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Re: DC-only equipment with solar augmentation
« Reply #10 on: March 31, 2021, 03:27:01 PM »
Larry,

You seem to be trying to sell me on the advantages of a Classic. I acknowledge that a Classic is far more capable than a Kid. However, our loads are only in the neighborhood of 4 amps or so. Further, with a pair of solar panels, the highest voltage we anticipate is probably only in the 80-90 volt range, which is well within the capability of the Kid.

Also, if you don't separate the load from the batteries, how does the controller distinguish between battery charge draw, and load draw? Those two dynamics have to be separated in order to do true multi-stage charging, unless something fundamental has changed.

I only mentioned the Classic capabilities in case those were some that you were looking for.
Below is how I believe  it would work based on not using load control from Kid. 
The controller is going to charge based on what it is set up for - Absorb Voltage, Absorb Time, Float ( and ending amps if you were to use that feature but Whizbang is needed )
If the solar controller is satisfied on charging( or has extra not needed for charging )  it will pass whatever power is available to the load. Of course if you have two power supplies you would need to set the voltages so that one would cut out before the other . Or you could use load control to run a relay to shut off the power output of the other controller.
So you would set the Solar higher voltage than the AC supply so that it would provide power when the sun is out. When sun goes away and the voltage drops on solar then the AC charger will supply the power.
The Solar controller is going to go through it's three stage charging (Bulk, Absorb, Float ) just once a day ( though you can set it differently ) . If the batteries are already floating from the AC charger the Absorb cycle will probably complete pretty quickly. Then the Solar goes to float and as said above - it will provide the power over the AC one if the voltages settings are set up correctly. 
The other option I mentioned was putting a relay in the AC charger output line so that it switches that off when it gets a signal via the load control on Kid  - but that doesn't seem like the best way to do it.

Larry
 
« Last Edit: March 31, 2021, 03:28:47 PM by ClassicCrazy »
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

GlueGuy2

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Re: DC-only equipment with solar augmentation
« Reply #11 on: April 05, 2021, 02:50:08 PM »
Thanks for your input. After cogitating on this a bit, it sounds like the direction we will go. It may not happen for a bit, although we do have a half dozen 260 watt panels we pulled from another site. I think we also have a few spare solar charge controllers laying around in spares.