what voltage for the 'house'?

BFL13 wrote:
The 14.8v at 60 amps would be output while input voltage is at Vmp. Over-panelling the input would refer to the 60 amp output limit. Getting lost here somehow.

Yup, my controller input is about 8A at 90V+.

MS has a 25 amper that says nominal operating limit is 350w so that is at 14v, while the 15L says 200w and that is 13.3v.

Not clear if the MS limit is for input like the Tracer's limit so their 13v may not be comparable.

The 14.8v at 60 amps would be output while input voltage is at Vmp. Over-panelling the input would refer to the 60 amp output limit. Getting lost here somehow.

Anyway, yes, I like over-panelling too for greater AH haul over the whole day even if you don't get full amps for a short time at high noon.

Blue Sky doesn't want over paneling, in fact they want a 25% 'cushion'. So 30 amps / 1.25 = 24 amps. There reason is "cloud effect lensing".

Even though I have room for another pair of panels--I'd have to replace the charge controller. My panels are holding up well and still do 17 amps. (Mad dogs and Englishmen)

That said, my system does appear to "punch above its weight" in cloudy conditions.

The MS MPPT 60 lists the Nominal Voltage of 12V at 600W. So that is 13.3V right? Not really as it's a guide. The hard limit is 60A even at 1000W or more for the 12V battery setting. That's one reason why I have 750W panels. Over paneling is not a problem for this controller. So at 14.8V battery voltage and 60A that's 888W not counting controller to battery voltage loss.

Solar panels rarely if ever have adequate light to reach their stated capacity especially for RV's for various reasons. That's why overpaneling was a consideration for me.

CA Traveler wrote:

MrWizard wrote:
Bob , don't you mean 60a*14v 840 watts
You know you can't charge 12v battery with 12v,bit requires a voltage, above battery nominal full charge which is 12.6v,
A fully charged fla battery should read 13+v when charging is turn off

Of course but the post was intended to emphasis the difference between 12V and 48V in terms of the controller output and the nominal solar panel wattage. But perhaps I should have qualified these are the generic voltages and I have now updated the post.

In that context what voltage would you suggest? 14.0, 14.4, 14.8, 56.0, 57.6, 59.2 or some other voltage which is dependent on the various mfg specs, not to mention that the voltage is also temperature dependent.

Or the commonly used terms of 12 or 48 volt battery systems. There is no one size fits all.

Tracer MPPT controllers at 12 or 24 volt specify max input power for their controllers. Eg. the "20 amp" size has :

260w for "12v" and 520W for "24v", but 260/20 =13v and 520/20 = 26v, so that's how they do it. (And other brands ISTR)

Does the fact that he’s trying to sell a 48V, 135AH (540AH at 12V) battery for $4500 have anything to do with pushing 48V. How much is a 48dc/ to 12Vcapable of his 800A cost? Four 135AH batteries plus BMS is no bargain as I just finished a DIY 12V, 600AH Lithium battery bank for $1200 including BMS.

BobsYourUncle wrote:


Not a cheap venture at 4500 bucks for a battery! I'm sure the price will come down as more things like this become widespread in use.

Good stuff. :)

Hi Bob,

Thanks.

As you probably know I'm in the SiO2 camp due to cold weather. I'll have more than 7 kwh based on 80% depth of discharge.

If you have a couple of years wait time, you may want to consider Aluminum Ion batteries. They charge 60 times faster than Li and are 3 times the energy density.

Keeping the amps as low as possible was my goal. Wire handles voltage much better than amperage.

MrWizard wrote:
Bob , don't you mean 60a*14v 840 watts
You know you can't charge 12v battery with 12v,bit requires a voltage, above battery nominal full charge which is 12.6v,
A fully charged fla battery should read 13+v when charging is turn off

Of course but the post was intended to emphasis the difference between 12V and 48V in terms of the controller output and the nominal solar panel wattage. But perhaps I should have qualified these are the generic voltages and I have now updated the post.

In that context what voltage would you suggest? 14.0, 14.4, 14.8, 56.0, 57.6, 59.2 or some other voltage which is dependent on the various mfg specs, not to mention that the voltage is also temperature dependent.

Or the commonly used terms of 12 or 48 volt battery systems. There is no one size fits all.

Great article Don, thanks for posting.

I like the SXS comparison in easy to understand language.

I have been following solar and optimum configurations for a while, wanting to learn more, as we want to build an off grid support system for our Tango.

This article helps a lot.

Not a cheap venture at 4500 bucks for a battery! I'm sure the price will come down as more things like this become widespread in use.

Good stuff. :)