2 systems running at same time

zulupaul

hi ,i have a system in place a 48 volt with outback regulator and xantrex invertor, i have been given a set of 12 2v 1385 exide solar batterie and a victron phoenix multi plu invertor 24 v 3000 70 amp ,i am wondering if i can run the 2 systems to supply my house at the same time ,linking them at a meter i have to read consumption ,is this a possibility at all ,i have 2 sets of solar panels both going into my existing batteries through 2 regulators ,i was also thinking of splitting them so one set charges each set of batteries ,any help gratefully accepted ,paul

BB.

Re: 2 systems running at same time

We have to be really clear here about your intent, and the hardware you want to use...

First what is your present battery bank size (AH, voltage) and your solar array (or solar array per charge controller). You really do not want to drop below 5% rate of charge on a battery bank, and would be much happier with 10% to 13% or so on a deeply cycling batter bank. Lots of batteries and not too much solar panel can give you short battery life (unless you use a lot of generator or grid power to keep the batteries correctly charged).

Next, splitting banks... Personally, I like to suggest one big bank as the first choice (even if batteries are different ages, not same exact size--keep series connected strings with "matched sets" per string). I believe it is easier to keep one battery bank working than to try and keep two separate battery banks functioning while juggling loads/charging current between Bank A and Bank B.

If the batteries are too different (AGM/sealed and Flooded cell), you probably are better off with separate banks.

If I have the correct Victron Inverter, these can be paralleled on their AC outputs (probably have to be identical models to share output--and you probably cannot parallel other brands/models of AC inverters with this Victron model). If so--then you can parallel their AC outputs into a single AC Utility type kWH meter and keep track of your energy usage. I am assuming you are not connecting the output of these inverters to Utility Grid (they cannot "share" utility power on their output--I believe).

One thing to watch with parallel connected AC inverters--Most inverters take a fair amount of power just to be turned on (10-20 watts or more). Check how the Victron units manage parallel inverters. Can you set it up so that one inverter handles 0-3kW and the second inverter turns on for >3kW loads--Or do all parallel inverters run at the same time regardless of loads? The extra 10-20+ watts can be a significant load on your system if 24 hours per day.

You can also use a Battery Monitor (Victron makes a nice one) to monitor the DC side of the system too (and specifically estimate the battery bank State of Charge).

I don't really have any detailed knowledge about these inverters--So you will have to read the manuals closely and some others here can help too.

-Bill

zulupaul

Re: 2 systems running at same time

hi i have a 24 x 2v 985 ah bank at present powered by 9 ldk panels ( see attachment )through a outback mppt controller, i also have 16 panel through a stacca tarom controller ( the more faded picture ) both of these go into the same set of batteries , i have been given a victron phoenix multi plus 24v 3000 70amp invertor and a set of exide solar batteries (12 x 1385 ah 2 v ) and a stecca 24v regulator i think ive enough pv power to do both ,just a little un sure ,im off grid so back up power is via an generator 6.5 kva so i was thinking of running 2 supplys one to each invertor to top up any extra power needed ,paul

Cariboocoot

Re: 2 systems running at same time

No, you can not link the AC outputs of two inverters unless they are specifically designed to be 'stacked'.

You can not run a 24 Volt inverter from one half of a 48 Volt battery bank without causing serious power imbalance in the 48 Volt bank.

You can not (successfully) run two MPPT charge controllers from the same array as they will get 'confused' about how much power they have available.

You could pull power from a 48 Volt battery bank through an MPPT controller to charge a separate 24 Volt bank.

You can separate AC loads so that some run from one inverter and some from another.

That's the short-hand version.

zulupaul

Re: 2 systems running at same time

ok , i do have 2 sets of batteries as i have said a 24 x 2v set and a set of 12 x 2v exide , i only have one mppt controller and a stecca tarom going into the 48v bank from 2 sets of panels the one is static with the stecca and the outback mppt is on a set with a tracker ,i could i dare say isolate say my swimming pool and run the one set on that .paul

Cariboocoot wrote: »

No, you can not link the AC outputs of two inverters unless they are specifically designed to be 'stacked'.

You can not run a 24 Volt inverter from one half of a 48 Volt battery bank without causing serious power imbalance in the 48 Volt bank.

You can not (successfully) run two MPPT charge controllers from the same array as they will get 'confused' about how much power they have available.

You could pull power from a 48 Volt battery bank through an MPPT controller to charge a separate 24 Volt bank.

You can separate AC loads so that some run from one inverter and some from another.

That's the short-hand version.

stephendv

Re: 2 systems running at same time

What you could also do, is use the one system as a "generator" for the other. I.e. use the xantrex system as your main system (let's call it the front system) as it currently is. Then connect the victron system's output into the AC input of the Xantrex as if it was a generator or the grid. Then program the Xantrex to only use the AC input when the batteries fall below a certain state of charge.

Which system you use as the "front" system will depend on how you can program it to use the AC input. If you have the USB cable for the Victron then you can do some detailed programming on it, to tell it when to switch to it's AC input so it might be preferable to use the Victron as the front system, and the Xantrex as the backup.

Photowhit

Re: 2 systems running at same time

Beware of free gifts....

Looks like your system has marginal array for your current battery bank, about 4000 watt array for a 985Ah 48v bank or about an 8% charging rate. While you could split your array and charge the battery banks separately, your charging rate would be inadequate for either. I'd guess you could either generator charge the 'new' set of batteries and keep the inverter as a catastrophic failure spare (in case you lost a battery or the 48v inverter and need to rewire to 24v to run your loads).

I was once give a trailer for free, it had a bad bearing and a couple bald tires cost me nearly $150 by the time I got it home...

zulupaul

Re: 2 systems running at same time

hi, the batteries are all ok ,the guy who gave them to me has kept them charged via a generator so they are ok ,but you think im underpowered for charging via the panels ,what would you advice to increase harvest at minimal putlay , thanks Paul

Photowhit

Re: 2 systems running at same time

Depending on use, normally you look for a 5%-13% charging rate, amps in to amp hour capacity(20 hour rate). For a regularly used home/cabin 10-13%. For a weekend use you might be fine at 5-7%.

Cariboocoot

Re: 2 systems running at same time

I think Photowhit's main point was that the array is enough for the existing bank and asking it to charge the additional capacity of the 'new' lower Voltage bank as well (whatever way it is done) will result in poor charging performance for both. It is a very valid point.

So if you have to add panels anyway ... might as well have two entirely separate and redundant systems.