Buck Gizmo -Volts vs Amps ? UPDATED
Update 5 Nov. (It didn't work out as hoped) I got my little gizmo, see close-up photos here http://www.ebay.com/itm/DC-DC-15A-Converter-Buck-Adjustable-4-32V-12V-to-1-2-32V-3-3V-5V-24V-Step-Down...
Forum Discussion
I hate watts.
Anyway I am using this gizmo to try and understand what my MPPT controller does, since watching it at various times is just too confusing.
Eg, once in Float (and so in PWM with no MPPT) it still bucks. When the solar panel can still do lots of watts, but the battery doesn't accept that many, the watts showing on its controller mounted display (always reflects battery voltage x amps to the battery) will be low. Turn on an "extra" load, and now the display shows more watts with the battery voltage the same but amps now up.
So the "input" available watts for the buck converter is out there in the panel ok, but is only seen at the output of the controller according to demand. Does the little buck gizmo only take input on demand so the DC power supply providing the gizmo's input does variable output? what if it has a steady output at full gizmo input rating, but the gizmo output demand isn't that much?
The solar controller is just a buck converter with an MPPT so the input watts will be the optimum the panel can do at the time. If the panel is sitting out there with lots of "extra" watts doing nothing, MPPT won't get you any more amps since there is no demand for them.
I presume this is why the controller goes over to being just PWM with no MPPT as soon as bulk charging is finished and some "extra" wattage becomes available during Absorption and Float.
The gizmo I have is too small in watts rating (voltage input limit, amps output limit) for my solar panel, but the solar controller is also limited the same way except it has higher limits. It is still just a buck converter with lipstick (MPPT) added.
My plan is/was to prove that you could run a 230w panel just fine with a buck converter without any MPPT and you would get just as many amps. (unless the demand is max panel watts) The MPPT does not increase the buck converter's input or output ratings, it just tunes the solar panel for best watts input to the buck converter.
If my little gizmo can run my derated 230w panel as well as my MPPT controller can in PWM mode, then for the same money, you could replace the
-$102, 20a Eco-Worthy MPPT ( rated limit 250w panel and 42-45 volts input) with this
-$105 buck converter with fancy readouts attached, which has way higher voltage input limit of 60v (so it can run two 12v panels in series, which the Eco-W at 42v cannot)
http://www.ebay.com/itm/DC-DC-60V-20A-1200W-Constant-Voltage-Current-Regulated-Power-Supply-Module-Digit/180970836951?_trksid=p2047675.c100011.m1850&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D25410%26meid%3D83c21e0e82aa453ba14571fddaad9a0d%26pid%3D100011%26prg%3D10672%26rk%3D1%26rkt%3D10%26mehot%3Dpp%26sd%3D221225616719
Up to now we are saying you cannot run a 24v panel with PWM, you need MPPT. In fact IMO you can run the 24v panel in PWM as long as you have the right "size" buck converter in the solar controller, which the Eco-W has and it does when not in Bulk. For some reason, they only sell the big buck controllers with MPPT and that has confused the whole thing.
Anyway I am using this gizmo to try and understand what my MPPT controller does, since watching it at various times is just too confusing.
Eg, once in Float (and so in PWM with no MPPT) it still bucks. When the solar panel can still do lots of watts, but the battery doesn't accept that many, the watts showing on its controller mounted display (always reflects battery voltage x amps to the battery) will be low. Turn on an "extra" load, and now the display shows more watts with the battery voltage the same but amps now up.
So the "input" available watts for the buck converter is out there in the panel ok, but is only seen at the output of the controller according to demand. Does the little buck gizmo only take input on demand so the DC power supply providing the gizmo's input does variable output? what if it has a steady output at full gizmo input rating, but the gizmo output demand isn't that much?
The solar controller is just a buck converter with an MPPT so the input watts will be the optimum the panel can do at the time. If the panel is sitting out there with lots of "extra" watts doing nothing, MPPT won't get you any more amps since there is no demand for them.
I presume this is why the controller goes over to being just PWM with no MPPT as soon as bulk charging is finished and some "extra" wattage becomes available during Absorption and Float.
The gizmo I have is too small in watts rating (voltage input limit, amps output limit) for my solar panel, but the solar controller is also limited the same way except it has higher limits. It is still just a buck converter with lipstick (MPPT) added.
My plan is/was to prove that you could run a 230w panel just fine with a buck converter without any MPPT and you would get just as many amps. (unless the demand is max panel watts) The MPPT does not increase the buck converter's input or output ratings, it just tunes the solar panel for best watts input to the buck converter.
If my little gizmo can run my derated 230w panel as well as my MPPT controller can in PWM mode, then for the same money, you could replace the
-$102, 20a Eco-Worthy MPPT ( rated limit 250w panel and 42-45 volts input) with this
-$105 buck converter with fancy readouts attached, which has way higher voltage input limit of 60v (so it can run two 12v panels in series, which the Eco-W at 42v cannot)
http://www.ebay.com/itm/DC-DC-60V-20A-1200W-Constant-Voltage-Current-Regulated-Power-Supply-Module-Digit/180970836951?_trksid=p2047675.c100011.m1850&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D25410%26meid%3D83c21e0e82aa453ba14571fddaad9a0d%26pid%3D100011%26prg%3D10672%26rk%3D1%26rkt%3D10%26mehot%3Dpp%26sd%3D221225616719
Up to now we are saying you cannot run a 24v panel with PWM, you need MPPT. In fact IMO you can run the 24v panel in PWM as long as you have the right "size" buck converter in the solar controller, which the Eco-W has and it does when not in Bulk. For some reason, they only sell the big buck controllers with MPPT and that has confused the whole thing.
