Pl-20

[campingnut]

Gosh guys let him have it -its in a number of places on the web

http://www.rpc.com.au/pdf/plasmatronics_PL_relay.pdf

theres another there for the dingo

[T1 Terry]

Gosh guys let him have it -its in a number of places on the web

http://www.rpc.com.au/pdf/plasmatronics_PL_relay.pdf

theres another there for the dingo

Using this method you can switch either the negative or positive from the solar, you just need to get the polarity correct on the load side. if you wanted to switch the positive simply rewrite the diagram to read from solar neg to read battery positive and battery neg to read solar positive.
don't be tempted to use the cheap $20 evilbay solid state relay, they produce enough heat to cook toast and then the mosfet punches through and no longer turns off. Jaycar have a good quality SSR and heatsink to suit.
No idea who calculated out that resistor, the 5w part is correct but the value is too high and would result in the relay not turning on if the battery voltage was low.

T1 Terry

[campingnut]

Thanks for that Terry -Does this setup Mirror what the PL20 does? Can the SSR switch things fast enough (I asssume it is fast at times)
Would I still be advised to buy a dingo or pl20 rather than a larger mppt? The pl20s look fairly flexible with this relay arrangement.

[dapope]

The pl series, although pwm are pretty bomb proof. If you are running your panels in paralell, then there is little if any efficiency gain to be had with mppt

[T1 Terry]

Thanks for that Terry -Does this setup Mirror what the PL20 does? Can the SSR switch things fast enough (I asssume it is fast at times)
Would I still be advised to buy a dingo or pl20 rather than a larger mppt? The pl20s look fairly flexible with this relay arrangement.

Personally I'd buy the Dingo 20/20, the menu scrolling is easier to work with and the add-ons work with Win7 onwards, the PL20 stopped at XP. The SSR mirrors the PL20/Dingo switching as they drive the load transistor with the same control as the drive the internal charge control transistor. With up to 20 amps capacity on the load output you could drive a lot on solid state relays, so the top end capacity of these little controllers is limitless really, one of the 100amp SSR's could be used to switch more SSRs and so on. The other major advantage is cable runs, they can now go straight from the charging source to the battery compartment, fit the SSR there and run light weight cable up to the Dingo/PL20 to drive the relay. Now the Dingo/PL20 can be mounted where it suits you best, not where it's best for the cable run.
Unless you plan to spend the $$ on an Outback MX80 or a Midnite Solar controller, the $$ are wasted buying any common garden variety MPPT controller, better spent on more solar, and where do you fid the room in an RV to mount one of these top of the line MPPT controllers? The next question you have to ask yourself, if these controllers need to be this big to do the job intended, how could one of these little controllers possibly do the same job?
The cable saving yarn spun by the MPPT lovers is also nonsense, sure the cable diam can be reduced if the panels are all in series, but the series string size is limited by the max voltage capabilities of the MPPT controller, so the total amps in any one string is limited to the biggest panel you can mount on the roof, even 300w is only 8 amps from a 36v panel, 2 panels in series adds up to over 90v open circuit so that rules out a lot of the MPPT controllers, so that limits the set up to all parallel anyway. Yes, you can buy large grid connect designed panels cheap.... but how many can you fit on the RV roof?

End of rant
T1 Terry

[campingnut]

I will be putting in the solar before I buy the batteries. Are 24 volt panels good to work with the dingo if Im going to run 12 volt LIFEPO4 or would I be better with the lower voltage panels. i want to run 500 watts of panels with 200 a/hr of Lifepo4. Which ones favour the PWM process?

[T1 Terry]

I will be putting in the solar before I buy the batteries. Are 24 volt panels good to work with the dingo if Im going to run 12 volt LIFEPO4 or would I be better with the lower voltage panels. i want to run 500 watts of panels with 200 a/hr of Lifepo4. Which ones favour the PWM process?

If you are looking for solar panels to charge 12v lithium batteries look for panels with a Vmp of around 17v. This will drop to a Vmp of around 15.5v to 16v at realistic winter operating temps and 14.5v to 15v at summer operating temps. Lithium batteries only need 13.8v to fully charge but the panel voltage needs to be higher to get the current to flow from the panels to the battery, a bit like the slope need for drainage, the better the slope the better the run off but this must be weighed up with the efficiency losses between the max voltage the max current is generated at the solar panels compared to the battery charging voltage. A VMP of 16v at actual operating temp but a battery voltage of 13.8v is an efficiency factor of 13.8/16 = 0.8625 or 86.25%. As 100% efficiency is an impossibility or unobtainium and MPPT claims at best are 80% efficiency between panel and battery (not within the unit itself which is the B/S figure quoted by manufacturers) you would have a peak efficiency system for winter operation. In summer the efficiency would be 18.8/14.5 = 0.9517 or 95.17% but the instant output is reduced due to the heat, the up side is the sun is out shining on the panels longer so although the instant output is reduced the total daily output is much higher.
Instant output is the tool of the spin doctors, total daily output is what matters in the real world and the above combination will give you the best full days output when charging lithium batteries. Lead acid batteries are a different story, they require between 14.4v and 14.8v charging voltage at the battery and 14.5v available from a hot panel won't charge them at all.

T1 Terry

[cvtripper]

Or go with a good MPPT like the Outback MX80 and 24v panels.
I have seen 94A out of 1200W, but most typically 65A. With low light levels at early morning, they start charging earlier before they get to full voltage even as the voltage is above the 14v or so needed by the batteries.

[campingnut]

thanks Terry -I will stick with the 12 volt ones.