Solar regulators

[canals1164]

I have just bought 3 250w solar panels off eBay, I have 4 110ah leisure batteries set up as 24v to power inventor and then a battery to battery charger to a single 12v battery. I am now unsure of the best option for regulators, would a single 30a controller feeding the main 24v bank be best?
I look forward to your thoughts.
Regards
Ian

 

[lysol]

While it would be better to use a single controller for the entire bank, you can use multiple smaller controllers as long as there charge algorithm is the same so they don't work against each other.

 

[Haf-E]

A single solar controller on the 24v battery would be best - the battery to battery charger for the 12v battery should keep it full from the solar.

A 30 amp controller is overkill - the panels probably won't produce that much power but its nice to have the heavier duty unit for reliability.

You don't mention the voltage or number of cells in the panels - many are made for batteryless systems and so are not designed to charge a 24v battery directly - in that case you would need to use a controller which can allow connection of multiple panels in series for a higher voltage which is then stepped down by the controller. This allows getting the most production from the solar panels and can help if there is partial sun on the solar modules due to shading etc.

The challenge is finding a controller which works well with three solar modules in series - that will be a fairly high voltage (~150vdc?) ideally you would have two or four modules - allowing two in series and then the pairs connected in parallel. This would make the maximum voltage about 100 vdc.

Post back with the specs of the solar modules and I can help with the choice of controllers.

 

[canals1164]

Here goes
3x talesun 660 units
Watts 250
V at max power 30.1
Current at max power
Open circuit voltage 37.3
Short circuit current 8.78a
I had presumed that they would be wired in parallel, I also thought the amp rate of controller would be watts of total units / by 24v?
This is why I thought I would need a 30a unit would be needed. Apart from the gadget factor what will having a display on the unit do?
So many questions, sorry
Cheers
Ian

 

[wirenut]

You're correct. You do need a 30 amp controller. I'm not sure why someone would say that is overkill; math says otherwise. Your best option, for maximum power output from the array is to use an MPPT charge controller. Blue Sky, Morningstar, Outback, and others are good choices. Using an MPPT controller the possible maximum output is indeed 750w/24v=31.25 Amps. In cool conditions with very bright sunlight you might even see slightly higher output. However, most of the time, the output will certainly be less than 30 amps.
A display will let you see how much power you are generating and read your battery voltage. Voltage can be a decent indicator of how charged your batteries are. If you can adjust the orientation of your panels you can watch the display and adjust for maximum output.

 

[Joe917]

You're correct. You do need a 30 amp controller. I'm not sure why someone would say that is overkill; math says otherwise. Your best option, for maximum power output from the array is to use an MPPT charge controller. Blue Sky, Morningstar, Outback, and others are good choices. Using an MPPT controller the possible maximum output is indeed 750w/24v=31.25 Amps. In cool conditions with very bright sunlight you might even see slightly higher output. However, most of the time, the output will certainly be less than 30 amps.
A display will let you see how much power you are generating and read your battery voltage. Voltage can be a decent indicator of how charged your batteries are. If you can adjust the orientation of your panels you can watch the display and adjust for maximum output.

750W/30.1v = 29.1 Amps (panel voltage not battery voltage?)
Most charge controllers recommend you give yourself some leeway so go with a 45 amp controller.
Wire in parallel so that a shade on one panel does not kill all your power.

check out http://handybobsolar.wordpress.com/the-rv-battery-charging-puzzle-2/

 

[wirenut]

You would divide by the panel voltage if using a PWM controller. If using an MPPT controller, which I would recommend, you divide by the battery voltage. That's one of the main advantages of the MPPT units. They allow for using the full output of the panel. You can never quite do that with a PWM controller.