Backup inverter thoughts

[2una]

Hi Guys, been doing a crash course reading up what i can for which way would be a reasonable way to step into a load shedding backup system.

This is for a unit in an apartment building so no PV future likely. I do have a gennie stashed but it would never pass coc being in a building like this where it cannot be fixed install & it is also v-o-v but i do have it should long outages hit.

Most of my draw is from running a fishtank where i'm responsible to keep the critters i keep alive,  2 hours on /off isn't much of a problem but i don't see this Eskom issue going away anytime soon so think it is time to sort something out, not just for that but for ourselves as well.

Using this 3kva gennie i have it will run what i need (constant 2.8kva output on paper)

For inverter i'm thinking a 3000 that will do a constant 2400 might be a bit border line so was thinking more a 5000 unit. Most seem to rate the Victron units in high regard so was looking at them versus the like's of going Axpect  BUT i also see with the like's of Cape Town where they haven't managed to hit the approved list so that's another angle in the back of my decision making should that virus spread which it is bound to (I'm KZN).

Multiplus   48/5000/70-100 = R27500 exc 

QUATTRO   48/5000/70 = 28122 exc 

MultiPlus II 48/3000/35-32  = 12794  exc

With neither the Multiplus or the Quattro on the approved list would it be wiser to maybe go with 1 x multiplus II that is approved with the intention to add another & still be under the cost of the Multiplus or Quattro.

You think that would be the smarter move to make? Is that just a simple cable attachment to parallel 2 or is there hidden complications i don't know about whilst considering that ?

Would anyone advise a differant brand inverter to take a look into?

[___]

9 hours ago, 2una said:

no PV future likely

It seems to me that you don't have to worry about SSEG regulations then, seeing as you are in KZN and won't be putting up PV modules.

Given the kind of money you'd have to spend on batteries to do 2.8KW for 2 hours (between 35k and 50k), I'm kinda thinking see if you can reduce the consumption by a bit, then get the 3KVA. It will save you money twice over, plus the 14k you save on the inverter can buy better batteries.

[The Bulldog]

The Victrons are probably the best small scale battery based inverters money can buy but they are at a bit of a premium. They are quite bullet proof though and can certainly take a punch and produce more power than they are rated at provided you keep them cool.

I agree with Plonkster, since you will be relying on stored energy in batteries - this is where your attention needs to go. The best inverter does not help you if the batteries are rubbish or you cannot store the amount of power you need.

Batteries are the weak link. Perhaps one day they will really be up to the job. Right now we are fudging it.

Since you will not be creating an SSEG in the defined PV sense you have no issue with SSEG regulations. You are simply using a UPS. No more and no less and the Victrons can be used just like that with greatest of ease. As UPS it is compliant with SANS, even the old Mutliplus which I suspect some will be able to pickup at bargain prices as many will have to throw them out to replace them with the types on COCT's list.

 

[2una]

Thanks, If that's correct that would open a lot more doors not having to worry about that side,  I don't know the details but thought as soon as one went near the DB with a cable that we fell into that SSEG.

Would you have any opinion on the Conext inverters? Was fishing around last night and saw these specs here that would suit me better than what the blue box's do.

Yet to get some price idea or availability on it but being able to have a continuous 3400 with ability to go to 4000 for 30 mins would be me covered i think

  

[___]

11 minutes ago, The Bulldog said:

you will not be creating an SSEG in the defined PV sense

Yup. This is something I also only realised recently. The embedded generator is NOT the inverter. The inverter is the coupling interface, the energy converter. The PV modules are the generators. No PV... no EG.

[The Bulldog]

Correct. 

Any Victron installation is perfectly legal in Cape Town (including the Multiplus) as long as you do not connect PV to the batteries.

So if you have a Multiplus - you can add a grid tie inverter (that is on the list) - preferably a Fronius since that plays nicely with ESS. The PV panels generate the electricity. The Fronius is your approved grid tie inverter. This is where SSEG stops. 

The Multiplus and its battery don't even need a mention. That is your UPS.

Downside: Batteries have to be charged via the Multiplus charger which is not the most efficient so you loose a bit here.

The Fronius can be connected to the output side of the Multiplus so it continues operating during loss of grid power.

Revised SANS 2018 appears, on the face of it, to be OK with this.

It's one of my current go-to options but I don't like it due to loss of efficiency.

 

[___]

14 minutes ago, The Bulldog said:

The Fronius can be connected to the output side of the Multiplus so it continues operating during loss of grid power.

This is a rather interesting setup. So practically, as long as the backfeed relay in the Multi is closed, that Fronius is just connected directly to the grid. But the Multi can ALSO feed in from the battery (and does when running ESS). Even if you have the Fronius connected to the input side: The Multi can still see the current the Fronius pushes into the grid, and use that to charge the batteries... or feed power from the batteries into the grid. But... and this appears to be the clincher: The Multi is NOT the interface between the PV modules (aka the embedded generator) and the grid... and hence you could probably declare that a UPS and move on...

It has been suggested before that a cheap way to get legal would be to buy the cheapest PV inverter you can get (a Solis by the looks of it). Costs less than the changeover witch @ebrsa is contemplating. Now if only you could tie it to the output of an Axpert everyone would be sorted (but sadly you cannot).

[The Bulldog]

Yes. 

I am sure COCT will find something wrong with this (but perhaps I am just a pessimist).

The ESS also regulates the Fronius power so you can simply switch the Fronius Zero Feed-in option in the ESS setup on if you do not want any back feed into the grid.

ESS works pretty much as before. In my case I set a minimum SOC of 80% so if the batteries reach this I keep the 80% in reserve for a grid failure and use 100% power from grid or PV with PV having preference. Any excess PV recharges the battery. The 20% of battery gets me though the night. Since I only cycle 20% I should get a lot of cycles out of the battery bank.

I'd hate to loose ESS due to bureaucracy. It works so well.

 

[___]

47 minutes ago, The Bulldog said:

I'd hate to loose ESS due to bureaucracy. It works so well.

I am so glad to hear that

[2una]

Took a ride out to Current Automation & that Schneider Conext is same pricing as the blue box's & is a import to get here & a export to fix so that's off the list.

 They can pull in a Multiplus II 48/5000 so thinking to go that way.

With a clamp meter on 2 breakers it looks like average load i can sit about 8A but to run luxuries for a few minutes i can push 14A (230x14 = 3220) so a 3000 is like i thought a bit on the under side.

 At the moment for batts i need to find out some more but wondering if i have the insanity to maybe try going with one of those revov 10kwh 2nd life units , that or ditch that idea & go pylon but lighter kwh. Being a noob i'm wondering if that 2nd life route is such a hot idea.

Any sponsorship for guinea pigs around here?

 

[ebrsa]

@plonkster perhaps you would take a look at Marius Fourie's video on YouTube again. He effectively seems to be using the Axpert as a UPS with a Solis handling the solar. What is unclear to me is what happens to the Solis output during a grid blackout. Will it still feed to the Axpert's input so as to prevent loss of Solar energy. Perhaps you would be so kind as to post a wiring diagram if you figure it out. As you said it will be cheaper than the transfer switch and more elegant. If I could go that route,  I would install the additional Solis gadget to prevent feed in to the grid. To find Marius' video,  search for Greenpro on YouTube. 

[___]

38 minutes ago, ebrsa said:

He effectively seems to be using the Axpert as a UPS with a Solis handling the solar

I think I've seen it.

38 minutes ago, ebrsa said:

What is unclear to me is what happens to the Solis output during a grid blackout

It shuts down and you lose your PV power. If you live in a country with few and short power outages, that is a perfectly good way to do it. UPS for the blackout, PV-inverter for saving money.

With load shedding where you can be down 5 hours a day sometimes... and where you need the PV because your batteries are not that big... it's kind of a deal breaker.

[Guest]

2 hours ago, plonkster said:

It shuts down and you lose your PV power.

Having used the panels during a failure, for me this is not negotiable as panels = Stuff Eskom woes.  

 

On 2019/03/05 at 9:35 AM, plonkster said:

It seems to me that you don't have to worry about SSEG regulations ...

Regs are coming to a city near you: https://www.businessinsider.co.za/draft-rules-require-solar-pv-backup-generators-to-be-registered-2018-5

[seant]

If the pannels are the generator and then interfaced to the inverter which charges the batteries and the inverter has an Eskom feed then you have to register ,but then what if you had a seperate charge controller handling the battery interface wouldn't that make your inverter a " UPS " setup too?

[The Bulldog]

44 minutes ago, seant said:

If the pannels are the generator and then interfaced to the inverter which charges the batteries and the inverter has an Eskom feed then you have to register ,but then what if you had a seperate charge controller handling the battery interface wouldn't that make your inverter a " UPS " setup too?

A UPS is very narrowly defined in SANS 10142.

If your solar array charges a battery via a charge controller and you have the separate inverter to create A/C the whole thing is a SSEG. The very moment you remove the charge controller from the battery or charge from Grid only then you do not have a SSEG and there is no registration needed. The battery/charger/inverter can now be a UPS provided it fits in what SANS thinks a UPS should look like.

If you have a solar array and you are using it to generate power it has to be registered. No way around that. Does not matter how you use the power.

 

[2una]

I have a question i've overlooked if someone might set me straight to the answer please

Whether it be Victron or Axpect type inverter on a battery only system(UPS), are we allowed to have this hooked up to make use of the "20ms changeover" or must it always be a manual deal with manual changeover switch?

[2una]

 

Zoom zoom up & running

A 3kva for now till some 5kva stock gets in next month & do the trunking then

Changeover switch & plug for gennie also there so that takes care of any longer term outage that the batteries can't get thru.

[2una]

Could someone tell me where the inverter is going to tell me to go take a fly

Is a 3000VA where they say 2400W continuous & peak power 5500W

this is avrge sort of load here

 

Go make a coffee & i can make it go here (lets say 1-2mins)

 

Pylontech 3000b batt specs say

 

So with 64A the batteries are still ok but getting up there.

Have tried briefly with a kettle & seen 4100W but that was just a on & off me being curious..

I'm guessing batteries might complain anything over 74A & best not to be there anyway but where will the inverter pull the plug ?

 

Spec sheet there for inverter

 

 

[___]

42 minutes ago, 2una said:

Is a 3000VA where they say 2400W continuous & peak power 5500W

The more the overload, the faster it switches off. It also depends on ambient temperature (ie cooling efficiency). You can run it at 2400W continuously and it won't switch off. You can run it at 3000W for an hour or so before it might switch off with a temperature alarm. If the temperature is below freezing, you might be able to run it at 3000W continuously. As you go over 3000W, the time it takes to switch off could be minutes (if you are only 10% over) to one second (at max peak). The inverter can handle 5500W for one second before it switches off. So this is meant for starting inductive motors, not for boiling a kettle!

Now we get to the battery. Maximum discharge is 1C (74A), ie full to empty in one hour. That is pretty typical for LFPs. Again, you can go over that, up to 100A for a few seconds, but do it for too long and the BMS will disconnect the battery. Similarly, if you run it at the full 74A for too long, the battery temperature will rise, and if it exceeds 40°C it will ask the inverter (via canbus) to reduce the discharge rate, and if you don't (cause you can't when the grid is down) it might also eventually disconnect you.

I have not been able to make a Pylontech disconnect on discharge rate. Even with a dead short for half a second (scope probe... don't ask) it did not alarm. It seems to be pretty tough. The only thing that makes it disconnect immediately is if you exceed 54V. So I'd say you're inverter should almost always shut down before the battery complains.

[2una]

5 minutes ago, plonkster said:

The more the overload, the faster it switches off. It also depends on ambient temperature (ie cooling efficiency). You can run it at 2400W continuously and it won't switch off. You can run it at 3000W for an hour or so before it might switch off with a temperature alarm. If the temperature is below freezing, you might be able to run it at 3000W continuously. As you go over 3000W, the time it takes to switch off could be minutes (if you are only 10% over) to one second (at max peak). The inverter can handle 5500W for one second before it switches off. So this is meant for starting inductive motors, not for boiling a kettle!

Now we get to the battery. Maximum discharge is 1C (74A), ie full to empty in one hour. That is pretty typical for LFPs. Again, you can go over that, up to 100A for a few seconds, but do it for too long and the BMS will disconnect the battery. Similarly, if you run it at the full 74A for too long, the battery temperature will rise, and if it exceeds 40°C it will ask the inverter (via canbus) to reduce the discharge rate, and if you don't (cause you can't when the grid is down) it might also eventually disconnect you.

I have not been able to make a Pylontech disconnect on discharge rate. Even with a dead short for half a second (scope probe... don't ask) it did not alarm. It seems to be pretty tough. The only thing that makes it disconnect immediately is if you exceed 54V. So I'd say you're inverter should almost always shut down before the battery complains.

Ok thanks, that makes sense

I had it in my head anything over 3000W other than for a few sec's & the inverter would be off but that doesn't seem to be the case.

With 2 heavyweights turned on i got this

 

 

The overload light on the inverter was starting to flash then but that was maybe from the bms complaining about amps anyway huh? Neither batts or inverter shut down before i turned the load off.

Its starting to appear to me this 3000VA model is pretty matched up with what these batteries can do anyway & a 5000VA its just going to have the batteries trip out.

The inverter is giving me what i need,,,,,avrge load its fine & for my coffee addition it holds together also......anything more & one's going to hit the batt's max amp shutdown anyhow

[___]

Just now, 2una said:

The overload light on the inverter was starting to flash then but that was maybe from the bms complaining about amps anyway huh?

Nope. We don't feed alarm conditions from the battery to the Multi. If the Multi flashes an alarm LED... it is because the Multi itself has an alarm condition (Overload). It goes into Warning first (which is what you are seeing), and then it will move into Error state and turn off eventually. When it turns off it will wait 30 seconds and then restart. It will try three times, and if not successful it will remain off waiting for a manual reset.

It also makes an almighty drone while working this hard.

[2una]

Thanks good info

Missus overloads it throwing the kettle on it takes a 30sec kit kat then tries again, that's a nice safety....think i'm just going to stay with this model now, for the short period extra loads i throw on it it seems to hold together & anything more of this type of load is just going to trip out the batteries.

Ran it for 5 hours today & it went down to 23% SOC so it still had some juice left, was 48.68V there & the setting for off from the victron/pylontech sheet was 47V...bms turns off at 44.5v which must be pretty low.

[2una]

Plonkster that 100A cutout on the battery spec sheet does that stay the same figure whether its 1 battery or 3 or 5 or does that figure change with them stacked?

[___]

3 hours ago, 2una said:

Plonkster that 100A cutout on the battery spec sheet does that stay the same figure whether its 1 battery or 3 or 5 or does that figure change with them stacked?

That's per rack, so as you have 3 racks... you don't really have to worry about this

The 30-second feature is indeed meant for that. It gives you some time to turn off the thing you just turned on that caused the overload.

3 hours ago, 2una said:

think i'm just going to stay with this model now, for the short period extra loads i throw on it it seems to hold together

I also find that 3KVA pretty much handles all the loads I throw at it. If I have to use the kettle, vacuum cleaner, or microwave, I can usually pause any appliance that might be on (washing machine, dish washer), and I generally don't use these appliances simultaneously. Since I have only around 7kwh storage, it's not like I can go completely wild anyway

[2una]

Thanks - that's added food for thought for me tho if it means i've not got that 100A limit & its rather 300 that then changes the picture. Nothing much extra i want to run but another thing i see is these batteries now seem to take as long to charge up as what they were run for with this 35A charging on this one. Guess i have a month to make my mind up.

Thanks a lot for your help much appreciated