CJH wrote:I must admit I hadn't thought about whether the solar panel meter would disconnect the panel itself if the meter itself isn't powered. Is that likely do you think? I'm hoping there's a built-in shunt that would pass current even if the electronics to measure the current aren't powered.
Thinking about it, you are likely correct there and it will be fine
My cheap Chinese ammeters arrived in the post yesterday, so I did a quick and dirty connection of the little voltmeter/ammeter into the solar circuit. First and most important, the current from the panel still flows even if the meter isn't powered, so that means I can go ahead with my push button power setup. As for accuracy, the voltmeter seems accurate (against my Draper Expert meter) to 0.1V, and the ammeter seems good to about 10mA, although it's difficult to tell for sure as there's no sun this morning and the panel's only making 10-20mV at the moment! So maybe the ammeter's only good to 50% of the true value
The big 'net flow' ammeter is more difficult to test quickly, as it needs the shunt in the earth lead, so that'll have to wait for now.
"I'm a man of means, by no means....King of the Road!"
CJH wrote: there's no sun this morning and the panel's only making 10-20mV at the moment
I would be interested to see what your panel makes on a dull / medium day (NO clear sun )
I have read that many folk get a useful (amp or 2 ?) from theirs, even on dull days. I am seriously thinking of flogging my 60W rigid panel and getting one of the ones that do an Amp or more on a dull day.
CJH wrote: there's no sun this morning and the panel's only making 10-20mV at the moment
I would be interested to see what your panel makes on a dull / medium day (NO clear sun )
I have read that many folk get a useful (amp or 2 ?) from theirs, even on dull days. I am seriously thinking of flogging my 60W rigid panel and getting one of the ones that do an Amp or more on a dull day.
I'm looking forward to being able to monitor this more easily, so I'll certainly let you know.
Did I say mV? Of course I meant mA, but if we're talking volts, it's working at just over 20V. So clearly what is important is the current flowing at charging voltage, which ought to be about 35%-40% more than it is at 20V, assuming a controller that doesn't just burn off the excess voltage through a resistor. Again, I should be able to monitor this better once both meters are in.
"I'm a man of means, by no means....King of the Road!"
The voltage is pretty much irrelevant if measuring it without the panel being connected to the battery. Open circuit it will rise, as you say, to ~20V but this is irrelevant. Even the very smallest panel will do that. The best way to check how much current is being produced, be it bright or dull outside, is to disconnect the panel and measure it's "short circuit" Amperage. No harm will result, they do this test in the factory QC dept. As long as your multimeter is OK up to 10 Amps you will be fine and on a dull day a 5 Amp capable meter will be fine too. If measuring using your new panel meter, the state (read voltage) of your leisure battery will have a great bearing on how much current flows and so "tests" of output current v brightness done that way can / will be misleading.
The long and short of it is:- If it works then good (and it will), but I am one of those with an insatiable curiosity
ghost123uk wrote:The voltage is pretty much irrelevant if measuring it without the panel being connected to the battery. Open circuit it will rise, as you say, to ~20V but this is irrelevant. Even the very smallest panel will do that.
My meter will be directly in the circuit between the panel and the MPPT controller, which is ultimately attached to my leisure battery. I'm particularly interested in seeing how the MPPT controller finds the maximum power point (which I believe it does by changing the resistive load to vary the panel's voltage - is that right?), so I am expecting to see a variation in the voltage displayed on my meter.
As for the current, the amount going into the battery will certainly depend on the state of charge of the battery (hence my interest in measuring the 'net' flow in the charger system with the other meter), but on the input side I'm not so sure how it works. I've read that an MPPT controller is able to move the production point away from the maximum, so there's less energy to dissipate if it's not needed for charging, but that implies it can't stop the production completely, so there will be current flowing even when the battery doesn't need it. Does the production really depend on the amount being drawn by the load (i.e. the charger)?
"I'm a man of means, by no means....King of the Road!"
ghost123uk wrote:The voltage is pretty much irrelevant if measuring it without the panel being connected to the battery. Open circuit it will rise, as you say, to ~20V but this is irrelevant. Even the very smallest panel will do that. The best way to check how much current is being produced, be it bright or dull outside, is to disconnect the panel and measure it's "short circuit" Amperage. No harm will result, they do this test in the factory QC dept. As long as your multimeter is OK up to 10 Amps you will be fine and on a dull day a 5 Amp capable meter will be fine too. If measuring using your new panel meter, the state (read voltage) of your leisure battery will have a great bearing on how much current flows and so "tests" of output current v brightness done that way can / will be misleading.
The long and short of it is:- If it works then good (and it will), but I am one of those with an insatiable curiosity
Ghost, this post is starting to make more sense to me now, having played with the meter a bit. As you suggested, measuring it in circuit doesn't give a good reading - that's why my measurement of 10mA the other day was so low. So as you suggest, measuring the short circuit current is the way to go. I can actually do that in situ without disconnecting the panel, since putting the meter between the positive and negative leads shorts it out any way. But of course, I can't then measure voltage at the same time, since the two leads will be shorted! So I've come up with a scheme where the meter shows volts normally (and is powered by the panel itself - when there's no volts to power the meter I won't need to see the meter display zero), and when I press my push switch it'll connect the ammeter across to read amps (and zero volts) and it'll connect in a power feed from the battery.
Getting there slowly.
"I'm a man of means, by no means....King of the Road!"
OK, so when shorting the panel to measure it's production of Amps, but not disconnecting it, I take it that the charge controller's input (ie where the panel connects to it) is not going to have the battery voltage present. ie, the way you plan on doing it is not going to short the battery as well as the panel as in, their will / must / might be some electronics in between that make doing what you plan safe. I have not (yet) checked this on my controller.
ghost123uk wrote:OK, so when shorting the panel to measure it's production of Amps, but not disconnecting it, I take it that the charge controller's input (ie where the panel connects to it) is not going to have the battery voltage present. ie, the way you plan on doing it is not going to short the battery as well as the panel (as in, their will / must / might be some electronics in between that make doing what you plan safe. I have not (yet) checked this on my controller.
Correct. Putting a multimeter across the terminals shown, without the panel connected, shows zero volts. With the panel connected it reads just the solar panel short circuit current (and the panel voltage too). This is the same whether the charger is using the output from the panel or not (indicated by LEDs between those two terminals)
"I'm a man of means, by no means....King of the Road!"
)
