Backyard Aquaponics
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My understanding was that MPPT regulators take pretty much any voltage above 14 volts, and then use a DC->DC converter to step that down to what is required to make the battery happy. This is how they are more efficient than conventional regulators -- they don't just connect the panel to the battery, they keep the panel at its peak power producing voltage, and also keep the battery at its correct voltage.

Auto switching means the controller can be 12v or 24v and will just switch to whatever the battery is.

Combining wind and solar on the same input is not a good idea.
The voltage is best keept the same from all sources.
It is even recommended to use the same size panels when connecting more than 1.

A wind turbine controller needs to convert the three phase ac from the turbine and then rectify to dc to then charge a battery.
You can add that input to a mppt controller but you will need a dump load to protect the system from over voltage.
Combining the two technologies is a bit over my head.

This may be a stupid question, but it's 40 years since I did circuit theory...

Can't you run something else in the circuit to cut the power flowing to the battery. Resistance will give a voltage drop across it and if the battery only takes the current it needs...? You could add in a fridge, stereo system, fan to cool you in the still air...

Cool. I wasn't sure if it auto switched to the battery voltage or the source voltage.

The solar panel put's out different voltages over a day. Is that going to be an issue regarding "The voltage is best kept the same from all sources." ?


Does that mean I don't need a dump load with a solar panel?


Thanks for everyone's input on this. I've had my large solar panel for ages and haven't done anything with it, and figure it's about time I did.

A solar panel puts out roughly the same voltage all day, it is the current that changes.
Wind turbines are different. In a wind generator, the voltage output is a calculation of the rpm of the generator so the voltage increases as the wind speed increases. The charge controller waits until the generator reaches a given voltage before it kicks in and supplys power to the battery bank.
I would suggest using a night switch controller and switching to wind at night and back to solar when the sun comes out.

Good idea krozbolt. I must have missed that post.

These are the pins on the back of my solar panel.



Is there some magic way to do something like connect pins 1 & 3, AND pins 2 & 4 to get 23 volts open circuit voltage, and will that be around 18v once it has a battery attached:?:

If so, my MPPT solar charge controller says it can handle 20v max input(or 40 if I ever hear back from the ebay seller). Is that max the open circuit voltage of 23v, or the 18v that it might see if there was a battery attached:?:





In full sun, when I put a multimeter to the pins on the back of my solar panel, I get...

11.6v between pins 1 & 2

11.6v between pins 2 & 3

11.2v between pins 3 & 4 (there's some damage to the panel)

The pins are all connected with what look like diodes...


When I check the voltage between...

pins 1 & 3 I get 23.6v

Pins 2 & 4 I get 23.1v

Total voltage between pins 1 and 4 is 35.2v


According to the specs on the back of my panel...

Open circuit voltage is 37.2

Maximum power voltage is 29.7v.

Dont mess with them- they are the bypass diodes, one for each string of cells, to protect against hot spots if part of the panel is shaded.



If it can handle 40V, then your Voc is at ~37V so that is fine. If it can only handle 20V, then that panel is not suitable, and connecting it might let the magic smoke out... which is a very bad thing!

cheers, Gordon
who has been living off-grid for over 20 years and has spent a lot of time messing aorund with solar and wind power.

It looks like you've got a 24V panel, ie one that is designed to charge a 24v battery.

I previously thought it might be for 36v operation, but that isn't the case.

I think this means that your controller will be fine to charge your battery :-)

Re wind generators- it is possible to connect a WTG and a PV panel in parallel to the same MPPT regulator- I have been doing just that, successfully, for many years. You do need to have them reasonably well matched though.
I use the cheap Chinese WTGs from Jaycar et al, and throw away the controller box that comes with them, they are basically junk! I rectify the 3phase AC from the WTG with a 3phase bridge rectifier and connect that in parallel with the PV to the MPPT regulator (only some MPPT regulators are suitable for this, and parallel PV panel arrangement and specs need to be correct). I don't use a dump load, as I only have a 200W WTG connected ATM, although it does peak at over 500W occasionally (off-grid, 4kW tracked PV, 800AH @26V Lithium battery), and sufficient continuous loads on the system to cover that -so over-charging wont happen.

I must be learning something after all. I think I understood most of that. Thanks

Do you mean as it is, or by spitting the different sections of the panel to get a lower voltage.

I don't understand this business of having a open circuit voltage and then some other voltage.

I spoke too soon about having learnt something

Assuming you got the MPPT controller you linked to a couple of pages back: http://www.ebay.com.au/itm/MPPT-15A-Sol ... 35b92199a9?

If so, it has auto voltage detect and will be good with that panel. No need to mess with the cell strings in the panel. Voc is no load voltage, Vmp is the voltage it delivers maximum power at- what MPPT controllers use.

I notice in the specs:
" Thunder protection"
Now that is something I havent seen before! Does it also protect against other loud noises, say someone sneaking up on it and going BOO!

I have searched for solar option before. There are 2 kinds of panel for low voltage use. The 18+V use to charge 12V battery and 37+ volt for 24V system. There are cheap regulators and some cheap MPPT that can sue to charge 12v or 24V.

To use for 12V system, you have to use 18+ V solar panel and for 24V you have to use 37+V panel. If you have 37+ Panel then you can only charge a 24V battery system with those cheap regulators.

The cheap MPPT have advantage of convert voltage to current so you get more Amp on sunny hours while the normal regulator just dump load to reduce voltage. To make it more clear, these regulators only can reduce volt from 37+V down to 24V or 18+V to 12V, it can't convert 37+ down to 12V.

There are expensive MPPT regulators that some call them the real MPPT. It can accept input up to 100V and can out put 12V or 24V and with that wide range of input voltage, this regulators can be used for both solar & wind system.

For the system that connected to both solar and wind sources, the simplest way is to attach a diod to each source to prevent the current from going back to the off line source.


Cheers,
Long.

I think you are referring to Pulse Width Modulation or PWM type regulators as the "cheap" ones.
They do not shunt the extra voltage to a dump load as part of the normal regulation, but switch the source, in this case a PV panel, on and off very rapidly.
With PWM regulators you can only work at the battery voltage, so much of the potential output of most, but not all, solar panels is wasted.
For example, a 200W panel with Vmp (maximum power voltage, found in the specs) of 37V will deliver 5.4A at 37V to a MPPT input, and this will go into the battery or loads, at say 25V, at 8A = 200W
With a PWM regulator, the output to the battery will be about 135W

The above ignores efficiency losses within the regulator, and also cell temperature, solar radiation intensity etc, so actual power will almost always be less than the above. There are circumstances when it can be more than 200W with a MPPT controller, due to what is known as cloud edge effect, but that's not important right now

Most panels these days will have 60, 72 or 96 cells, to deliver Vmp around 30, 37 and 48V respectively. The old "12V" panels are still around, but very much in the minority these days, mainly used for camping applications.