diy solar

diy solar

Solid state relay for PV disconnect

" MPPT Voltage Range: 60-115Vdc, "
I’m not sure about that spec. I think it’s because to stay under 145 voc your maximum power point would have to be 115 or less.
Edit for clarity- a panel with a Vmp of 36v should always be operating at 36v for max output.
Actually maximum power point is a moving target depending upon the amount of sunlight. The max power voltage marked on the panel refers to the voltage where the maximum amperage is reached in testing. If max power voltage was a steady maximum power point then we would not have MPPT controllers. My panels produce almost nothing at 90 volts until I am in direct sun and the I will produce my best wattage at those voltages
 
The Powmr 3500 watt hybrid inverter likely does not have isolation between PWM AC sinewave H bridge and PV inputs. This means the PV inputs are riding on top of +/- 250 vdc chopping from inverter's internal HV DC supply. You need dual pole DC breakers so you can break both positive and negative PV lines to fully de-energize panels.

Most solid state DC relays are not bi-directional switches. Just single MOSFET with parallel body diode in MOSFET.

I would highly recommend you not try this. It will likely be a dangerous setup.
 
The Powmr 3500 watt hybrid inverter likely does not have isolation between PWM AC sinewave H bridge and PV inputs. This means the PV inputs are riding on top of +/- 250 vdc chopping from inverter's internal HV DC supply. You need dual pole DC breakers so you can break both positive and negative PV lines to fully de-energize panels.

Most solid state DC relays are not bi-directional switches. Just single MOSFET with parallel body diode in MOSFET.

I would highly recommend you not try this. It will likely be a dangerous setup.
I’m missing something here my array has a max voc of 111.6. When the controller is stuck the voltage max is 65. I do not use the fets as a switch to turn off the array for servicing as I have a double pole breaker for that. I have no abnormal voltages anywhere on the PV when I disconnect one side. Before I figured out how to fit a breaker in my setup (without sacrificing ventilation) I would disconnect a mc4 connector to reset the charge controller. At that time there were no measurable voltages across any of the PV wires that I disconnected. The only way to get a measurable voltage was to reconnect the PV and measure where the solar inputs at the AIO or to disconnect the other mc4 connector and measure open circuit voltage across the +and- of the solar array wires. When PV is disconnected from the AIO the controller turns off instantly and there is no continuity between the PV inputs or voltage from there to any point I can reach from the AIO.
 
When sun is first coming up, the panel illumination current is low. It does not take much illumination for panel to reach Voc dependent only on panel shunt leakage current. Because of low illumination current, the panel voltage will immediately collapse if a small amount of external load is attempted to be placed on panel. Detecting the open circuit panel voltage, the MPPT charge controller starts up but there is not yet enough illumination current to sustain the controller.

It attempts to determine an MPPT point but voltage just quickly collapses because there is not enough current to run the DC-DC converter reliably.

All-in-one HF inverters normally charges to the internal HV DC node, which for a 120 vac HF AIO inverter is typically about 250vdc.

The SCC controller in HF AIO inverters are normally just boost converters. This is why the PV input voltage is never allowed to exceed the internal HV DC supply node voltage.

It might go into a mode that sucks what it can from charged up PV input electrolytic caps, depletes the caps charge down to minimum voltage the boost converter can run on, then repeats the processor over and over again until the illumination current gets great enough to sustain the DC-DC boost converter.

If a poorly desiged AIO SCC boost does this process of sucking what it can from the PV input caps and does not stay off long enough for PV current to recharge the input capacitors to a high enough voltage, it might get locked up in the condition you describe.

You have to be real careful about the AIO PV inputs not being isolated from inverter AC outputs with grounded neutral on AC output.

As I mentioned, most solid state DC relays are not bi-directional switch and will pass reverse current through the single MOSFET body diode. The reverse current I am concerned about is the non-isolated PV input voltage from AC output H-bridge. The PV lines ride on top of this non-isolated H-bridge switching voltage when inverter AC output is active. This is why double pole breakers, breaking both PV pos and neg lines is required.

If the PV SCC in your AIO is suffering the startup condition issue I described, and it does not eventually fix itself when illumination current gets great enough, the only way to break the startup oscillation issue would be break the panel connection until the sun generates enough panel illumination current to supply the SCC startup current demand without the input capacitors voltage collapsing to minimum run voltage of SCC boost converter. You might even need to provide more capacitor storage across panels to provide the initial SCC startup current. Are you going to do this every time a heavy cloud or a shading condition drops out the SCC?

Before going through an attempt at a bandaid fix you should at least try to get a replacement SCC board and see if that fixes issue.

HF inverter block diagram.png
 
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When sun is first coming up, the panel illumination current is low. It does not take much illumination for panel to reach Voc dependent only on panel shunt leakage current. Because of low illumination current, the panel voltage will immediately collapse if a small amount of external load is attempted to be placed on panel. Detecting the open circuit panel voltage, the MPPT charge controller starts up but there is not yet enough illumination current to sustain the controller.

It attempts to determine an MPPT point but voltage just quickly collapses because there is not enough current to run the DC-DC converter reliably.

All-in-one HF inverters normally charges to the internal HV DC node, which for a 120 vac HF AIO inverter is typically about 250vdc.

The SCC controller in HF AIO inverters are normally just boost converters. This is why the PV input voltage is never allowed to exceed the internal HV DC supply node voltage.

It might go into a mode that sucks what it can from charged up PV input electrolytic caps, depletes the caps charge down to minimum voltage the boost converter can run on, then repeats the processor over and over again until the illumination current gets great enough to sustain the DC-DC boost converter.

If a poorly desiged AIO SCC boost does this process of sucking what it can from the PV input caps and does not stay off long enough for PV current to recharge the input capacitors to a high enough voltage, it might get locked up in the condition you describe.

You have to real careful about the AIO PV inputs not being isolated from inverter AC outputs with grounded neutral on AC output.

As I mentioned, most solid state DC relays are not bi-directional switch and will pass reverse current through the single MOSFET body diode. The reverse current I am concerned about is the non-isolated PV input voltage from AC output H-bridge. The PV lines ride on top of this non-isolated H-bridge switching voltage when inverter AC output is active. This is why double pole breakers, breaking both PV pos and neg lines is required.

If the PV SCC in your AIO is suffering the startup condition issue I described, and it does not eventually fix itself when illumination current gets great enough, the only way to break the startup oscillation issue would be break the panel connection until the sun generates enough panel illumination current to supply the SCC startup current demand without the input capacitors voltage collapsing to minimum run voltage of SCC boost converter. You might even need to provide more capacitor storage across panels to provide the initial SCC startup current. Are you going to do this every time a heavy cloud or a shading condition drops out the SCC?

Before going through an attempt at a bandaid fix you should at least try to get a replacement SCC board and see if that fixes issue.

View attachment 97787
This is really interesting to me I have limited experience with circuits especially once I get past resisters and diodes so I really appreciate you laying out your concerns. I’m not sure that what you are describing is happening in my situation. I don’t usually bother to switch the panels on and off if I am taking in less than 200 watts of power because if I do the controller will simply go back down to the low 60s as the maximum PowerPoint and get stuck there. If there is just enough sun for the controller to find a maximum PowerPoint in the 70s its output will actually be 30 to 50% less than the output I was receiving in the low 60s. So I have found that I have nothing to gain by switching the solar on and off if I’m producing 200 W or less. It seems to me that 200 W should be an adequate amount of power for the controller to work properly.

I am still a bit confused about what the danger is from the 250 V that is being produced inside the AIO. From a wiring standpoint the PV wiring is completely isolated from anything none of the wiring attached to the solar panels or the AIO is exposed and the MOSFETs are rated for 250 V. The timer is set to turn the solar panels off for one minute and back on for 23 hours and 59 minutes. I’m not sure if it makes any difference or not but I am switching the negative side of the PV with The Mosfets. Regardless of whether I switch the PV off and on with the MOSFETs or if I switch it on and off with the circuit breaker the appearance of the unit is identical. The screen goes dead instantly and turns back on as soon as either type of switching is turned back on. If I happen to have the inverter turned on when the PV is reset The screen will not go dead because it is powered by the inverter but the PV voltage read out immediately drops to zero.
 
Would it ever make sense in these type of situations to temporarily add a high voltage output dc power supply that functions like a pseudo solar panel or solar panel string ? Wake up the MPPT.
 
Would it ever make sense in these type of situations to temporarily add a high voltage output dc power supply that functions like a pseudo solar panel or solar panel string ? Wake up the MPPT.
Likely not practical.

But related to your comment, I just watched a video of a cheapo AIO inverter repair that appears to not have PV input filter caps. It has an additional power supply fed from AC inverter output to power the SCC converter so it can startup. The additional power supply 47 uF filter capacitor went bad so the SCC would not startup.

So on this inverter, if you are off grid, and your battery gets depleted so it cannot run the inverter, it cannot generate the power to startup SCC to recharge the battery. Great design!

 
When sun is first coming up, the panel illumination current is low. It does not take much illumination for panel to reach Voc dependent only on panel shunt leakage current. Because of low illumination current, the panel voltage will immediately collapse if a small amount of external load is attempted to be placed on panel. Detecting the open circuit panel voltage, the MPPT charge controller starts up but there is not yet enough illumination current to sustain the controller.
I had a chance to observe the charge controller as it came to life this morning. Here are my observations. It is around 7:20 on the morning we are having light steady rain and it is heavy overcast but the clouds are high in the sky. My inverter is off so I have no screen unless the solar is providing enough power to turn it on. At around 7 this morning the screen was turning on and of so I took advantage of the situation to see how the unit was handling barely sun. At first the controller would read low 70s for voltage and gradually reduce the voltage not showing any amperage until the voltage read 57 and the screen went dead. Thi happened multiple times but once the ( I am assuming) open circuit voltage reached the upper 70s the screen voltage read out did not go below 59 and the voltage would climb to 80 ish and work itself down to 60 with no amperage showing on the screen. Eventually the controller started to find amperage at 63 volts and settled hunting between 60and 63 volts and outputting about 1.5 amps and reading between 70 and 90 watts. It is now 7:51 and the amps are reading about 2.1 and the wattage is at 110 voltage has settled at 62. I am going to turn off the array and observe. I turned off the array and waited for the screen to go dead that took about 20 seconds or so. When I turned on the array the screen was reading 95 v open circuit. The read out icon showed an active solar panel but no attempt at charging after another 10 seconds or so the screen indicated connection between the array and the controller and the charging light began to flash. The voltage slowly dropped slowing it’s decent in the 70s and eventually landing at 64v 2.1 amps. The rain picked up and by 8:00 it was reading 1.5 amps at 62volts. I had to leave and returned to the camper to check things on my through the area at about 11:30 it wasn’t quite as overcast but still drizzling. the charger was charging at about 230watts 65 volts so I reset the array and it settled at 380 watts at 88 volts.
 
Likely not practical.

But related to your comment, I just watched a video of a cheapo AIO inverter repair that appears to not have PV input filter caps. It has an additional power supply fed from AC inverter output to power the SCC converter so it can startup. The additional power supply 47 uF filter capacitor went bad so the SCC would not startup.

So on this inverter, if you are off grid, and your battery gets depleted so it cannot run the inverter, it cannot generate the power to startup SCC to recharge the battery. Great design!

Does https://www.frontiersin.org/articles/10.3389/fenrg.2020.00014/full explain a concept at bit like what I described? Possibly supply electricity from the battery to power that PWM circuit?
 
Does https://www.frontiersin.org/articles/10.3389/fenrg.2020.00014/full explain a concept at bit like what I described? Possibly supply electricity from the battery to power that PWM circuit?
This is good article. It covers a lot more than just startup up problems.

I prefer self startup without the aid of supplemental power by other sources, just because if supplemental power source is exhausted you have a Catch 22 situation to establish recharging of battery.

Many of the all-in-one units rely on inverter main controller processor to run SCC and HF AIO's require everything be running to get SCC output converted back to batteries for charging. If all that requires 70 watts of power then PV has to supply at least that amount of power just to startup SCC without battery supporting the idle draw. Present LF AIO SCC's delivers their output directly to battery terminals on inverter, but I believe they still rely on main inverter processor to run SCC.

Each method has its advantages and disadvantages. For HF AIO, PV SCC going to HV DC node makes power going from PV directly to AC output more efficient but PV to battery charging is less efficient. For LF AIO inverters with SCC going directly to battery there is extra power loss going from battery node back up to AC output on PV sourced AC power output.
 
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Does https://www.frontiersin.org/articles/10.3389/fenrg.2020.00014/full explain a concept at bit like what I described? Possibly supply electricity from the battery to power that PWM circuit?
This article is a bit out of my league as far as terminology is concerned so I’m not certain that I completely understand it. But as far as I can tell it doesn’t address my Issue directly. Except for the issue of getting stuck at 60 ish volts ( usually 62 but never more than 65 and it shuts off if below 60 for more than a few minutes) the performance of my controller is excellent. There is almost always a gap of no significant amperage above 65 volts for 5 volts or so with this array. My controller doesn’t range that far unless amperage is increasing or at least fluctuating. The article didn’t seem to address this gap perhaps it is unusual.
 
I thought you might like to see the external look of the fet switch setup. I was able to integrate a PV breaker and 2 fuel gauges into the same tower. I will probably add a switch for the water pump and a switch for the fuel gauges into the same tower soon. I had a 4” gap between the cabinet my AIO is mounted in and the strike board for a sliding door
Just enough space for a tower of 4” electrical boxes. It’s one of the few places that I have space left in the camper. I’m thinking of painting the tower to kind of blend into the corner once I get it finished. ( add the switches and neaten up the breaker cover)
It still isn't good enough, several are needed in parallel to reduce heating. Gate always needs to be tied to source with a resistor to turn off, in this caseabout 100K. Source goes to NEG panel, drain to controller NEG. Remember there is an internal diode. From POS panel, use 100K to 220K to + band of 12V zener, NEG to source. This will provide your +12V drive voltage. Relay contacts from +12V to gate. Each gate could have 100 ohm in series with gate. Not necessary, but helps in diagnosis if one FET shorts. Gates usually short.
Update I have been using this setup since the end of May and it works flawlessly. I upgraded my solar array to 3200 watts and the fets don’t get hot. This fet based timer switch is wired in such a way that it can be bypassed in a few minutes. There’s no detectable loss of wattage between using it or not.
 
Sorry to ressurect on old thread but I have devised a circuit that turns on a solid state relay (SSR) when PV voltage exceeds 100v. The SSR turns off when PV voltage is ~85v..

The SSR is rated for 200vdc @ 25A

A pic microchip continuously samples the PV array voltage via a simple resistor divider. (100k + 3k3 resistors in series)
 
I would suggest starting a new thread explaining what you built and perhaps linking to this thread as an explanation of the problem you were trying to solve.

I would definitely like to read about what you built.

I did one time buy a little adjustable voltage switch that would adjust up to 100vdc for like $4 and change on amazon (still have it), but im not sure what the actual voltage limit on its sensing circuit is.. My solar arrays go up to ~360voc, but my Growatt AIOs dont seem to suffer from this same issue so i don't need to build anything to address it... Like i said, would love to read about your issue/solution.
 
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