Better wire for solar panels -> charge controller?
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rossvtaylor
Adventurer
Hi all... I hesitated to post this, because I didn't want to sound like I was being contrary to some of the excellent points being argued. But... <said sheepishly> nobody has pointed out that voltage rise may be a factor in some of the measurements here. Now, I'm not a solar expert by any means... my background, and current full-time career, is in wind energy and mechanical generators operate differently than PV arrays, I know. But I regularly see issues with voltage rise in lines, where the cabling is undersized. Voltage drop occurs where there is a load at the end of a line, which has resistance (as they all do, unless super cooled like was pointed out). SO, your 1800W heater load will cause a drop in voltage at the load/heater end of the line, as compared to the voltage measured at the line/source end.
But, in a generator configuration the opposite happens. People who haven't seen this happen have a hard time picturing it, so I use a water pump example. If the hose it too small, as the pump runs it can raise the pressure on the pump end of the system. The same happens with inverter or generator sources, as they push energy through a line... there will always be some voltage rise, due to line resistance. The goal is to make it manageable, so inverter and wind generator manufacturers have tolerance limits. It's even built into the UL 1741 and IEEE specs, so that systems don't shut down inappropriately. I know of one popular system where the tolerance is 2% but some are 5%. And, I've personally had to diagnose and resolve issues with systems (installed with wire too small) where the inverters shut down because they were "pumping" energy into a wire which was too small for the length of run... voltage would rise above the threshold limits and the system would shut down.
People don't talk much about voltage rise, because we're used to working with loads (that cause a drop, because we're measuring at the load end). But it happens in the opposite direction with generation systems... at least the ones I'm familiar with. Having said that, I have NO idea if PV output can work this way. But if you're working with charge controllers (on the DC side) or inverters (on the AC side), then this is a very real and measurable phenomenon.
But, in a generator configuration the opposite happens. People who haven't seen this happen have a hard time picturing it, so I use a water pump example. If the hose it too small, as the pump runs it can raise the pressure on the pump end of the system. The same happens with inverter or generator sources, as they push energy through a line... there will always be some voltage rise, due to line resistance. The goal is to make it manageable, so inverter and wind generator manufacturers have tolerance limits. It's even built into the UL 1741 and IEEE specs, so that systems don't shut down inappropriately. I know of one popular system where the tolerance is 2% but some are 5%. And, I've personally had to diagnose and resolve issues with systems (installed with wire too small) where the inverters shut down because they were "pumping" energy into a wire which was too small for the length of run... voltage would rise above the threshold limits and the system would shut down.
People don't talk much about voltage rise, because we're used to working with loads (that cause a drop, because we're measuring at the load end). But it happens in the opposite direction with generation systems... at least the ones I'm familiar with. Having said that, I have NO idea if PV output can work this way. But if you're working with charge controllers (on the DC side) or inverters (on the AC side), then this is a very real and measurable phenomenon.
verdesardog
Explorer
Even if there is no controller there will still be less voltage at the battery than at the solar panel. (No one is talking about what is happening inside the controller PWM or MPPT, we are talking voltage drop across the wires going to the controller)
In this case current will be limited buy the difference in voltage of Pv and Bv and resistance of the circuit. Bv will be lower than Pv.
In this case current will be limited buy the difference in voltage of Pv and Bv and resistance of the circuit. Bv will be lower than Pv.
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verdesardog
Explorer
So here's another way of looking at it:
As long as there is current flowing through a resistor there will be a voltage developed across that resistor which will subtract from the source voltage. There is no way of getting around the laws of physics. If the controller is an MPPT it can output more current than the pv is supplying but the power is the same as what the pv is outputting minus power lost due to resistance of the wires. P=IE. There will ALWAYS be a loss of power due to resistance of the wires.
As long as there is current flowing through a resistor there will be a voltage developed across that resistor which will subtract from the source voltage. There is no way of getting around the laws of physics. If the controller is an MPPT it can output more current than the pv is supplying but the power is the same as what the pv is outputting minus power lost due to resistance of the wires. P=IE. There will ALWAYS be a loss of power due to resistance of the wires.
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4x4junkie
Explorer
Well I guess I do have to give you credit for your persistence in not making sense...
Too bad you're completely wrong on this one (which I find very odd too, because most of your other posts always seem to be dead on the money
).rossvtaylor's post is also dead-on accurate, and PV systems certainly are subject to voltage rise too (which was exactly the example I gave about a panel's operating voltage potentially rising above it's Vmp). It all comes from too much resistance in the wiring (too-small gauge conductors) and of course this will always diminish performance.
While a PWM controller is in the bulk charging phase, you should see nearly the same voltage on the input (PV) side of the controller as the output (battery) side. This is because a PWM controller simply passes the PV current straight through the controller to the battery during Bulk charging. Once the controller go into the Absorb phase, then you may start to see the voltage on the PV side rise as it begins to pulse the circuit on & off. My post is specifically about while it is in the Bulk phase (same as if the PV panel is connected directly to the battery).
verdesardog
Explorer
Well I guess I do have to give you credit for your persistence in not making sense...
Too bad you're completely wrong on this one (which I find very odd too, because most of your other posts always seem to be dead on the money
rossvtaylor's post is also dead-on accurate, and PV systems certainly are subject to voltage rise too (which was exactly the example I gave about a panel's operating voltage potentially rising above it's Vmp). It all comes from too much resistance in the wiring (too-small gauge conductors) and of course this will always diminish performance.
While a PWM controller is in the bulk charging phase, you should see nearly the same voltage on the input (PV) side of the controller as the output (battery) side. This is because a PWM controller simply passes the PV current straight through the controller to the battery during Bulk charging. Once the controller go into the Absorb phase, then you may start to see the voltage on the PV side rise as it begins to pulse the circuit on & off. My post is specifically about while it is in the Bulk phase (same as if the PV panel is connected directly to the battery).
So let me get this straight ... you are saying there is something magic in a pv system that makes no voltage developed across a resistor (the wire) when there is current flowing through it? YOU ARE WRONG.
4x4junkie
Explorer
Did you quote the wrong post?
Or maybe you misunderstood me... I was referring to the voltage being the same at the input terminals of a PWM controller as at the output terminals of the controller.
I already agreed with you and said if you measure at the panel itself, the voltage will always be higher than at the battery (or the battery will be lower than that of the panel, whichever way you want to put it).
dwh
Tail-End Charlie
Good god...
I've said this before many times in many other posts. But I'll say it again and anyone who fails to understand it is not worth trying to educate.
A CIRCUIT IS A LOOP.
Anyone who thinks voltage drops from one end of a loop to the other end of the loop just doesn't understand that A CIRCLE HAS NO ENDS.
I've said this before many times in many other posts. But I'll say it again and anyone who fails to understand it is not worth trying to educate.
A CIRCUIT IS A LOOP.
Anyone who thinks voltage drops from one end of a loop to the other end of the loop just doesn't understand that A CIRCLE HAS NO ENDS.
verdesardog
Explorer
Don't be so dense. You guys are all wrong! If there is no difference in potential (voltage) there will be NO current flow. How difficult is that to understand?
AS far as crimping or soldering, it all depends on the terminals that you are using.
AS far as crimping or soldering, it all depends on the terminals that you are using.
verdesardog
Explorer
In America the convention is current flows - to +, Europe the conventional thinking is + to -. How does it get from solar - to solar + ? through the battery otherwise there will be no current flow through the battery to charge it. What makes it flow? Difference of potential, voltage. Consider two sources in parallel, if they have the same voltage there will be no current flow.
Maybe you need to go measure the voltage of your system at the output of the solar panel and the input to the controllerwhen it is running 10 amps and see for yourself. Of course since we are talking voltage drop in the wires it will be a very small voltage. Any decent volt meter should be able to show millivolts which is what you should expect to see. This whole thread started out discussing voltage drop across the wires which has nothing to do with output of the controller or how different controllers work.