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Thank you for the great forum, Safe Driving over the weekend. Sincerely Jason
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Crit my idea ... pull it to pieces, I can take it.

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1 hour ago, Elbow said:

How do you mean a "weak" neutral?  Too much resistance?

Let's just work from the basic reality that a copper cable has an inherent resistance, and when it is working hard there will be a voltage drop across it. In a proper installation there is no current on the earth wire, and the earth and neutral is at the same potential where they are bonded.

If you then measure between earth and neutral further away from the NPE bond, they will not be at the same potential. There will be a difference in voltage equivalent to the drop across the neutral cable, and thus directly proportional to the current draw. If the voltage difference appears to be proportional to the load, then it might reflect a voltage drop on the cable. If not, then it potentially indicates a poor NPE bond.

This resistance in the neutral cable might be as simple as a loose screw terminal somewhere.

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5 hours ago, plonkster said:

Let's just work from the basic reality that a copper cable has an inherent resistance, and when it is working hard there will be a voltage drop across it. In a proper installation there is no current on the earth wire, and the earth and neutral is at the same potential where they are bonded.

If you then measure between earth and neutral further away from the NPE bond, they will not be at the same potential. There will be a difference in voltage equivalent to the drop across the neutral cable, and thus directly proportional to the current draw. If the voltage difference appears to be proportional to the load, then it might reflect a voltage drop on the cable. If not, then it potentially indicates a poor NPE bond.

This resistance in the neutral cable might be as simple as a loose screw terminal somewhere.

Ok, with you.  I will check the N voltage at more points since it might just be a certain socket-outlet, or circuit that has the problem.

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Right, to continue where I left off, since I got approval to legally grid tie.

That piece of paper that says we are NRS and SANS legal:

image.thumb.png.ad6d1c54bbd56b7dc3c38b7dec701470.png

 

Since then I have had a blind luck to:
- Doubling my battery capacity from 225ah to 450ah thanks to a nice price for a near perfect 5 year old T105v bank.
- AND a opportunity to up the array from 2.1kw to 3.5kw - replacing the EV tubes with 4 more panels.

Why the array of 3.5kw?
- 3.5kw being the max I can do on 24v using a 150/100.
- 2S so I am well within the MPPT's volt max.
- 3kva inverter with 2.4kw continued output, with loads scheduled, leaves a 3.5kw array with lots of spare for the batts to recharge.
And because of the array, in CPT winter, I can now take away another +-500w from Eskom between 12 - 9am every day. (Programmed the Venus to do that - see at the end)

image.png.19f1c2a22507152728535fcf6d8ef151.png

And I see moments of that 100A in winter. 🙂 

image.png.f3a1941b863bd8e1b988c548330b4e39.png

 

However, the above changes necessitates a new CoC + application + engineers report.
Application is free, CoC with the upgrades and the engineer check is also quite quick. So nothing bad there.
Titbit: And it is possible that 3.5kw will also be seen as a "hardware limit" on a 63amp breaker.

 

The new Combiner Box - overkill with a plan. By using 350W panels, 2S/5P (3.5kw), and 6mm2 wires:
- I can switch each string off to check production per string.
- NoArk 16amp breakers only with Surge Protection. No need for fuses.
- And I have the option to go 3S / 5P (5.25kw) or 4S / 5P (7kw) with no changes to breakers or wires, just need a 48v 250/100 and a new inverter - ONLY IF Eskom brings it on.
Expensive yes, worth it, O YES!

image.thumb.png.847d7587d533c52c42382333170d0a7b.png

image.thumb.png.295dc89b91b99978759632c9f3966ff3.png

 

The 10 panels: 350w connected 2S/5P, slightly West of North, so the long Cape Town summer afternoons a awesome time to schedule a lot of loads.
Connected like so to the roof sheets:

387157764_Panels-2.thumb.jpeg.7ceaec5ebe1ff2137d391396d3b6287e.jpeg

Angle, no idea. Does not really worry me either because too costly to perfect and 3.5kw on a 24v system ... I've got spare believe, me.

1865419111_Panels-6.thumb.jpeg.6fb5fae1410b42d91a03cdf8784faf9f.jpeg

 

I'm now done - till I get a bee in my bonnet to go 48v. 🙂 

 

Running ESS - with a small alteration in a Cron Job on the VenusGX:
Comments: 
Being winter I'm seeing what loads are best powered when ito the 2.4kw limit of the inverter and how best to balance it all - summer and winter obviously differs.
In the end I may have a Cron job that runs over a 12 month period - will see how that goes or if it is worth it.

Option 1:

  • 9am - Maximum Inverter power
  • 2pm - 6pm - Keep Batteries Charged - to store power for use 12am-9am so use all the power to recharge the batts and whatever loads are running at the time
  • 6pm - Batteries set back to Optimized.
  • 6pm - 12am - Inverter power set to Zero to save batteries with batteries being on Optimized
  • 12am - 9am - Limit Inverter to 500w

00 07 * * * root /usr/bin/dbus -y com.victronenergy.settings /Settings/CGwacs/MaxDischargePower SetValue -- -1
00 12 * * * root /usr/bin/dbus -y com.victronenergy.settings /Settings/CGwacs/BatteryLife/State 9 - not working yet, still figuring out why.
00 16 * * * root /usr/bin/dbus -y com.victronenergy.settings /Settings/CGwacs/BatteryLife/State 1 - not working yet, still figuring out why.
00 16 * * * root /usr/bin/dbus -y com.victronenergy.settings /Settings/CGwacs/MaxDischargePower SetValue 0
00 22 * * * root /usr/bin/dbus -y com.victronenergy.settings /Settings/CGwacs/MaxDischargePower SetValue 500

 

Option 2: More simplistic version.

  • 9am - Maximum Inverter power
  • 6pm - 12am - Inverter power set to Zero to save batteries with batteries being on Optimized
  • 12am - 9am - Limit Inverter power to 500w

00 07 * * * root /usr/bin/dbus -y com.victronenergy.settings /Settings/CGwacs/MaxDischargePower SetValue -- -1
00 16 * * * root /usr/bin/dbus -y com.victronenergy.settings /Settings/CGwacs/MaxDischargePower SetValue 0
00 22 * * * root /usr/bin/dbus -y com.victronenergy.settings /Settings/CGwacs/MaxDischargePower SetValue 500

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Right, continuing on the idea to criticise my install, since I went from 2.1kw to 3.5kw array, I have had some "issues" with the "small" battery bank.

Yes, I can "Keep batteries Charged" and let the batts die from old age because Eskom is "ok".

Or I can expand the bank and be bold, breaking all the rules YET not everyone of them.

So here is my next project / test / exploration / "I can now say I did-it".

Step 1:
You have 4 x 6v 225ah T105RE batteries connected for 24v, age about 4.5 - 5 years in perfect condition still - hydrometer and load tester.
Now you add 4 x 6v 225ah T105  batteries connected for 24v, age about 4.5 - 5 years in perfect condition still - hydrometer and load tester.
Total AH: 12v 450ah bank.

Why did I mix them? 
1) After 5 years, what is the RE part going to matter if I can get 2-4 years out of the combined bank USING it to 20% DOD / 80% SOC?
2) And who will complain when you can double your bank for R2k (basically the lead price) and +-R650 courier?
3) Now I can run 500w from 12am - +-8am without breaking a sweat at 20% DOD / 80% SOC each and every day.

Nicely in the new "box":
image.png.2292209cfd6c917521e15280d54a5935.png

 

Step 2:
So now you get 4 x 12v AGM Sonic NPS-250-12 SS batteries.
Age about 3-4 years still in prefect condition having only used 500 cycles at 30% DOD out of the effective 2000 at that DOD.
Like these:
image.png.326f7199808caaaba44d9435068284d7.png

 

 

So why not connect them all into one big 24v bank? 500ah + 450ah = 950ah 24v bank = 22 800 / 2 =  11.4kWh bank?
Now I can either run 1kw from 12am to +- 8am OR I can run 500w from 8pm-8am every day.
By:
1) Setting the Victron kit to use the full 100amps of the MPPT - see, this is where the 3.5kw array comes in nicely see.
2) Set the charge settings to the AGM's settings - ja, so what if the Trojans are a wee bit under charged, I get that BUT ...
4) Always a BUT ... one can equalise the Trojans every 2-4 weeks by easily disconnecting the AGM bank using this switch - bought it already:
image.png.3f43c1518b5e2c5053a40f0b88a7688c.png

 

 

... O come on, you know you want too!!! 🤣

 

Or, if it really freaks people out:
Step 2b: Because charging is the issue, not discharging:
Set switch to 1: Alter Victron charge settings to the Trojan settings and be done with it.
Set switch to 2: Alter Victron charge settings to the AGM's and be done with it.
And then when there IS load shedding, one switches to 1+2 and use the full bank's capacity, recharge them separately over 2 days.

 

So the question I want to ask all, keeping in mind that:
Both banks are halfway.
Losing a year or so on their marketing material guestimated lifetimes, does NOT matter.
Because any cell can go any day and if the batts have not been used, then you lose.


Will it be enough to equalise the Trojan's every 2-4 weeks?
Or would it be better to keep them split, be a chicken, and alter the charge settings as needed?

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1 hour ago, seant said:

Change it to 48v............

Ok, answer me why?

Convince me I need to sell the 24v Multigrid, when:
When 3kva (2.4kw) on 24v is 100% ok. 
The system is grid tied, so batteries are not "that" important - a must to connect it all - due to no Eskom drama. So the less the bank costs the better.
You can even get away with 2 x 100ah "deep cycle" leisure batts at a push.
When the 24v lithium banks are coming onto the market / are on the market at the same or bigger kWh as the 48v banks.

The 8 x Trojans = 48v bank - and being second-hand ones, at 50% of the price.
The 4 x Sonic's = 48v bank too.

Why is 48v better?

EDIT: I Also keep in mind:
8 x T105's is 10 800 Wh on 48v and 24v.
4 x Sonic's are 12 000 Wh on 48v and 24v.
The ONLY benefit ever is IF one has to replace the T105's or the Sonic's, i.e. you stick to lead acid, then on 24v the bank can be 50% cheaper.

 

Edited by Guest

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Indeed, there is nothing inherently "better" to 48 V than 24 V.  48 V has the advantage of thinner battery/MPPT cables and lower rated switchgear, but higher voltages mean more cells in series in the VRLA string, thus higher probability of eventual cell imbalances.  If your system is already designed for 24 V you're not going to save on cable cost by switching to 48 V, so why bother?

Mmm, is there any advantage in terms of inverter efficiency in having a higher DC voltage? 

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29 minutes ago, Tacet said:

Mmm, is there any advantage in terms of inverter efficiency in having a higher DC voltage? 

Marginally. In an ideal transformer the conversion ratio has no effect on efficiency, but in reality there are heaps of things that affect that efficiency. Higher conversion ratios on transformers mean higher current, which means more heat losses in the windings and easier saturation of the core (at which energy transfer stops and you're just making heat). If course the transformer will be designed to handle it, but I would expect that the lower current levels will always win out even if just by a small amount.

41 minutes ago, The Terrible Triplett said:

Convince me I need to sell the 24v Multigrid, when:

That's the long and the short of it. Do I need to spend more money? Well... no. Not yet anyway 🙂

Edited by plonkster

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12 hours ago, Tacet said:

Mmm, is there any advantage in terms of inverter efficiency in having a higher DC voltage? 

True, but not when the cable between:
MPPT and inverter is 25mm2 and <30cm - yes, that is correct, MPPT connects directly to the inverters battery cable points.
Batteries to inverter is 50mm2 and < 3m
With 300amp fuses per battery bank already in place.
Monies have been spent so no savings at all going 48v and the DC volt drop, negligible if any on said cables.

12 hours ago, Tacet said:

Indeed, there is nothing inherently "better" to 48 V than 24 V. 

And thank you for that. 🙂

 

12 hours ago, plonkster said:

I would expect that the lower current levels will always win out even if just by a small amount.

12v to 48v if you have say a 5kva inverter, THAT is a HUGE issue.
But on 3kva between 24v and 48v, like you expect, but a small amount.

12 hours ago, plonkster said:

Not yet anyway 🙂

Amen. You go 5kva or bigger, then 48v is better by FAR!!!

 

22 hours ago, The Terrible Triplett said:

Will it be enough to equalise the Trojan's every 2-4 weeks?
Or would it be better to keep them split, be a chicken, and alter the charge settings as needed?

Does ANYONE have a thought to share? 
Or shall I just go ahead and we see where this goes? 🤣

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In my mind, there should be very little issues seeing that one can equalise with Victron equipment.

On top of which when banks get +-5 years old, the chances are there that a cell can go at anytime. 

So when one has large banks of 2nd hand batteries, what are the chances that:
1) They will keep the course and give the 4000 or 2000 cycles or +-10 years
2) Or you go bananas and mix and match - because in THIS case one can equalise - so the AGM's are safe and the Trojan's are "safe" - read "they can take it". 
What does one stand to lose? One year on the +-10 years hoped for lifespan?

Will I or anyone else do this with new batteries? Obviously NEVER!!!

What I hope to achieve, once I found a place to install them, is to show that there are "alternatives" when you have a serious "issue" spending monies on batteries, yet you know you have to spend some monies on batts.

 

Which brings me to another point I am pondering.
Pylontech's and Victron are designed for ESS and grid tied right?
So if / when there are hours / days of repeated power failures, are lead-acid batteries not better, being more like "off-grid" than "grid-tied"?

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48v setup will lead to doing you bit to stimulate the economy by spending a heap of your hard earned cash , 😉 But honestly I cant think of a good reason. Maybe 2 strings of batteries instead of 3 . I'd just go for it and see how it works.

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39 minutes ago, The Terrible Triplett said:

So if / when there are hours / days of repeated power failures, are lead-acid batteries not better, being more like "off-grid" than "grid-tied"?

This "not suitable for off-grid" stuff is such a load of bovine excrement...

The reason for this requirement (with some batteries) is because when there is no grid to fall back on, there is no way to control the discharge rate of the battery. The loads control the discharge rate of the battery. If you use a large load, the batteries are going to work hard (and there is no grid to help out).

But if you size the bank appropriately and don't discharge at high rates... it is simply not going to matter. The LFP will beat the pants off lead acid in almost all cases except the very harshest conditions (repeated 2C discharges to 90% DoD for example).

But if you work it very hard without the grid to back you up, the warranty might be void.

Edited by plonkster

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1 minute ago, plonkster said:

This "not suitable for off-grid" stuff is such a load of bovine excrement...

Excellent. That sorts that ponder.

 

2 minutes ago, plonkster said:

But if you size the bank appropriately and don't discharge at high rates...

But from what I pick up, stompies, is that most go for 1 x 2.4kWh bank first, adding later as needed.

So 1 x 2.4kWh Pylontech is quite "light" on a 3kva system, I mean, that is a 50ah bank (2400 / 48). 

Ask me, I know, having had a 4 x T105RE's bank for years. 😜

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1 hour ago, The Terrible Triplett said:

So 1 x 2.4kWh Pylontech is quite "light" on a 3kva system, I mean, that is a 50ah bank (2400 / 48). 

Yeah. That kind of thing is not really advised. You want to keep your loads below 25*50 ~= 1.2kw. For the average load-shedding rig that is only supposed to carry moderate loads (lights, television) that is perfectly fine, but it is definitely adviseable to have at least two modules.

Also remember: The charge current limit from the BMS is still applied even when you are off-grid.

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2 hours ago, seant said:

48v setup will lead to doing you bit to stimulate the economy by spending a heap of your hard earned cash , 😉 But honestly I cant think of a good reason. Maybe 2 strings of batteries instead of 3 . I'd just go for it and see how it works.

If a man wants to tinker, let him tinker. 😉

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24 minutes ago, plonkster said:

... definitely advisable to have at least two modules.

Two modules 4.8kWh touches easily on R30k right?

6v Rolls 428ah bank costs about wot, R42k = 20.5kWh / 2 = 10.27kWh bank.
12v Rolls 200ah bank costs about wot R23k = 9.6kWh / 2 = 4.8kWh bank.

All boils down to how long would the banks last, how much bang (no, don't) you get from the Rolls vs Pylontech.
And then off course the watering and the acid and the hydrogen ... but R23k vs R30k ... touching my heart a wee bit. 🙂 

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1 hour ago, The Terrible Triplett said:

R23k vs R30k

So let's talk about what you get for that extra 7k (roughly a third).

A very good lead acid battery will give you 2500 cycles to 50%. At that point it will have 50% of its original capacity left. A Pylontech battery can do 6000 cyles (more than twice) and have 60% of its original capacity left. No watering, no acid, no hydrogen sulphide, and it weighs about a third of the lead battery.

The downside to LFP is that there is no recycling plans for it yet.

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7 hours ago, plonkster said:

The downside to LFP is that there is no recycling plans for it yet.

And that none of the current R15k batts have been around for 6000 cycles in SA - me, thinking of the temps in SA and where the batts are kept like in garages that can get quite cold and hot. Same issue with lead acids.

But I am NOT arguing against LFP, just pointing out that sometimes the R7k difference can be quite a deal breaker. 

 

7 hours ago, plonkster said:

So let's talk about what you get for ...

And lets talk about getting 2nd hand lead acids for lead prices ... with all the surrounding drama, If you are used to it, man, LFP's can go and jump ito ROI and all that. 😜

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2nd Life LFP's market will grow in the mean time with "warranties" of some sort. Then the ROI might also look a bit different. I am also a bargain hunter,  not much will beat what you have sourced now. 

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By the way,

I am looking for the biggest OPsV or OPzV  48V single string bank for purchase early 2020. (R100k budget in KZN)

If anybody hears anything or has connections before then, I am keen to hear them.

 

Edited by phil.g00

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2 hours ago, plonkster said:

Yeah. That kind of thing is not really advised. You want to keep your loads below 25*50 ~= 1.2kw. For the average load-shedding rig that is only supposed to carry moderate loads (lights, television) that is perfectly fine, but it is definitely adviseable to have at least two modules.

Also remember: The charge current limit from the BMS is still applied even when you are off-grid.

I totally agree . Running offgrid with a 5kw inverter on 3 x US 3000 Pylontech batteries is about the lowest I can go . Although If I use 1500 watt of power early morning with the batteries at 70% SOC the inverter low battery alarm goes off at the recommended setting of 47.5 volt . The size of the Lithuim battery bank when running offgrid must match your needs .

 

 

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1 hour ago, plonkster said:

Yeah. In the end it matters little how cheap it is. If you don't have R2... then even R2 is expensive 🙂

Sitting thinking. When we had only lead acid banks, everyone took time to explain why one needs such a large bank. The panels must match the bank and the loads, you cannot have a big array with a small bank and all that.

The 5/4/3 joke (5kw inverter / 4kw array / 300ah bank) = 300 x 48 = 14.4kWh / 2 = 7.2kWh bank.
Me with my 4 x T105RE had 5.4kWh / 2 = 2.7kWh and boy, I struggled with the larger arrays.
Geez, my 2.7kWh (at 50%) 4 x T105RE's are bigger than the 50ah 48v Pylons and even they can go to wot max 90% DOD?
Ok, I only have 1600 cycles at 50% DOD ... at 20% DOD I had 4000.

Even a 3.5kWh bank at wot R22k x 2 = R44k for 7kWh ... and then you need to deduct for the 90% max usage too.

I quote Segen: 4500 cycles with 90% DoD or 6000 cycles with 80% DOD (please note most devices will set the DOD at 80%)

Lithium banks came hard and fast and we did not think past the convenience, stuck on 80/90% DOD vs what we knew of 50%, having to limit the charge amps thereby the systems efficiency ... AND lower discharge amps compared to lead acids.

I think we have lost the plot here guys. IF load shedding hits, many people may need to spend more monies on more banks. Lucky enough they can do that months / years later, even mix and match US2000 and US3000. So there is that.

Bottom line: Lithiums still costing a pretty penny when you want a 146ah 48v lithium bank = 7kWh bank.

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1 hour ago, The Terrible Triplett said:

load shedding hits, many people may need to spend more monies on more banks

I thin we actually discussed that at least once. One upside to a large lead bank that is only shallowly cycled is when you DO get that one event where you need more capacity, you can cycle it more deeply that one or two times with little effect on the overall life of the bank. So indeed, in a comparison between a large FLA/SLA bank cycled shallowly vs a small LFP bank cycled deeply, the lead bank does have that advantage.

Also, something that I have said before: Just because you can get away with a smaller bank and a large PV array (because you can charge at C/2 instead of max C/5) doesn't mean that you shouldn't still apply some common sense. Your battery bank should still ideally be sized in proportion to the PV array and the inverter size.

I absolutely detest setups with very small batteries and large PV arrays. That kind of thing just doesn't work well if the PV is DC-tied.

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