I'm a construction guy by profession, this is my first solar project. I have land on water a little ways from my house that I take my kids to fish and hang out at the dock I built them a couple years ago. I'm trying to build a dual 10" diffuser setup that is direct drive since there is not electric on the property. I'm fine with the pump only running on sunny days and not at night.
The components I have: I have 2-100 watt 12 volt Mono panels wired in parallel . They feed to the input side of a buck converter. The voltage output coming from the buck converter is adjustable. Ideally I'm shooting for a 14V output range. The positive wire on the output side goes to the input side of a low voltage disconnect. The negative wire from the buck converter attaches inside a wire nut, where the negative wire from the inverter also comes into, then splits off to the input side of the low voltage disconnect. On the output side of the low voltage disconnect the positive wire runs to the inverter. I have a Matala 120L 210V 130W 4.4 CFM pump plugged into the inverter. I want to stick with the AC pump because I have heard DC pumps have issues in temps below 0 degrees F. I live in central Iowa. We get extremes in both directions. All of these components are housed in a weather tight metal cabinet with a small fan that also connects to the inverter.
A picture of my set-up is attached.
The issues I'm having:
When in full sun I'm getting 20 volts of power out of the panels. I've got 14 volts coming out of the buck converter and the inverter powers up. When I hook anything up to the inverter the voltage drops and trips the low voltage disconnect. The computer fan won't even run. My low voltage disconnect is set up to disconnect at 12 volts with a difference value of 2. It's set to reconnect after 10 mins if the voltage is above 12V.
I'm sure at least one of my components is undersized.... which one is it?
I'd be curious if there is a load issue with the pump requiring more power than is available at startup. Once it's going you may be fine but that initial spike on demand is what I would look at.
Complete rookie...never connected a system like that.
1.5acre LMB, YP, BG, RES, GSH, Seasonal Tilapia I subscribe to Pond Boss Magazine
At startup the compressor is putting a 276 Watt load on the invertor. Depending on the efficiency of the invertor the invertor is putting some figure more than that on the power lead going into it. Less than 500 W. But first figure what you need to deliver 500 W to the invertor. Since this is coming in at 12V the delivery in Amps could be as high as ~ 42 amps (500 W). You may only need around 325 Watts of delivery to the invertor if it 85% efficient. (Less if more efficient). So 325 Watts requires 27 AMPS and, were it me, I would want to be sure the disconnect can handle 30 amps (preferably 40).
You have two 100 Watt Panels, this is enough for when the motor has already been started but it is insufficient to start the motor. So consider adding a 12 volt battery. It should be connected between the leads of the buck converter (on the output side of the converter). What this will do is provide storage for power which will supply the excess needed for startup. Once the compressor is started, the panel will charge the battery to the extent it delivers power in excess of the load of the inverter/compressor.
I am not sure if you omitted the battery over concerns of theft or if you were hoping to lessen the cost/maintenance of the system (being content with only daytime operation). But the battery, given only two solar panels, is essential for the system to work. The startup load is the reason you need it. A bonus is storage of excess power and operation when the sun is not shining (even during the day when clouds obscure the sun). I consider nighttime operation a bonus but if you prefer it not to operate at all at night you could incorporate a timer. Without, a battery, it would require 4 panels, a larger or additional converter, and full sun to start the compressor.
It isn't what we don't know that gives us trouble, it's what we know that ain't so - Will Rogers
I should also mention, 10 gauge copper wire is near the amperage limit on the 12 V side of your circuit. 8 or even 6 gauge would be better to carry the amps on the low voltage side.
It isn't what we don't know that gives us trouble, it's what we know that ain't so - Will Rogers
Maintenance is in my mind more than the theft portion. But if I need a battery I will integrate one into the system. If I buy a 12V lithium 100ah battery I would assume it would store enough power to run the system for a portion of the night before my disconnect shuts it down at whatever voltage reading I set it at, Would that be right? What voltage is safe to disconnect it at and keep the longevity of the battery? And would I need to buy a solar controller or will the components I have work with a battery as well.
I haven't done a ton of research on a battery system.
The converter is essentially a regulator designed to ensure that batteries are not overcharged. Output should be around 14 volts to charge typical lead acid battery without damaging it. For a battery, I would probably choose a lead acid battery and just leave the current settings alone. Not advice and I recommend following recs by others on battery choice and settings.
Yes, the night-time operation would work like you thought.
It isn't what we don't know that gives us trouble, it's what we know that ain't so - Will Rogers
Even lead acid are low maintenance on a small system, I top up my batteries once a winter. Not sure if you have snow but solar requires keeping the snow off them and a lithium battery is not good below zero.
35" of snow is our average a winter. I'm looking at the Renogy 100ah AGM now. I'm planning on having the low volage disconnect charge at a rate of 14-14.4V and have the disconnect setting at 12.4V. If I'm reading correctly, that is where AGM batteries like to live.
What voltage should I stop the battery charge? 13.4V?? Since I'm going to add a battery is the best route to wire the panels in series or parallel?
