Grid Hopping

[Scruff]

This is going to be a bittova work in progress thread if yee don't mind...I'm a mite fussy how my electrons are behaving and have a tendency to rearrange things.

Prompted to start my own thread from questions I have in this one http://www.navitron.org.uk/forum/index.php/topic,24605.60.html.

...Just to get things up to speed before I start interrogating Jonesy again.  

I've recently come by a set of 14kWh of AGM tippy top batteries willing to work for food and lodging. They came from a theatre emergency lighting system and are just 4 years old iirc. They've been on float since commissioning and get tested every few months to a reasonable discharge. The whole system was retired after an insurance claim due to a control board letting the smoke out.  
It only took me 3 years of gentle persuasion to be the first called scrap merchant.  


I've 9 of these I left 4 behind for a turnip pilot to make use of.

That's the runt of the litter that had a holding voltage of 12.67V when I found it. Seen here floating on a fixed algorithm Victron charger but I've thrown it into the main pack for the time being because that charger does a weekly "refresh" charge to prevent stratification except all that is doing is gassing because AGMs don't suffer from that ailment.

12.79V is the next lowest of the set. I haven't discharge tested them but I'm fairly confident they're only broken in.

Currently the whole bank is wired 12V because all my kit and caboodle is 12V.



The loading is balanced, every battery has 5 links; a main +12V and 0V and three interconnects, one fat and short, one long and one short.
It's based on SmileyPete's config Gibbo posted. http://www.smartgauge.co.uk/batt_con.html
'cept 4 more batteries.



And here they are sporting the 48V look how they'll be again, once I get PV on the roof/garden/somewhere.



The cables are all under-rated and the wrong colours, we're still prototyping and it's adequate for the no-load float service current they're seeing for now. The main conductors are 65A and the interconnecting wires are 35A. The battery bars are a few hundred more than I need.



Temperature compensated 4/5ths decent mains charger. That's a cheapo recon'd unit that has an ammeter 1.3A low of calibration fault (looked to me like some service tech. soldered the current shunt bodgineering a burnt PCB trace). Performs well enough for a mains charger but populated with rubbishy CapXon electrolytics.  

This is the system I'm planning at the moment.
Comments/feedback appreciated.



Simple idea really; use photons instead of fossils where possible, Economy 7 when it's not and keep the batteries happy.





 

[Scruff]

I should not drink coffee before posting.

Ha I'm the opposite.

I've remedied a few misnomers on the plan.

Replace 20A RCBO with 100ma RCD & 6A type B MCD. 30mA RCBO's for others, to give discrimination, else a socket fault will kill the lights too.  The Isc of the inverter will likely not clear more than a 6A mcb, or even 3A, so that's most diversity lost, but little you can do about that without fitting lesser ones downstream.

Updated Inverter DB:



Looking at this Swiss inverter it's 2.3VA, 1.3 times rating for 15 mins. Where did you get this 6A figure from and how do you find an inverter Isc the easy way?

The inverter is floating until it's bonded.  You have to tie one side of it to mains earth, otherwise you've got yourself at IT system.  Earth monitoring for IT systems are eye watering in cost (RCD not adequate) and have onerous maintenance requirements. Same with a genny.  N on them is normally connected to chassis, and we always bond the genny frame to an earth spike as the instructions tell us.
You should never create smoke by connecting the inverter N to earth (effectively TN-C-S), but you create a dangerous situation by not connecting, as you rely on RCD (not permitted) and you'll never clear a fuse on single fault to earth, because there is no path for fault current.
Your double pole switch ensures you don't mix the grid earthing with the inverters.
Depending on the inverter, you may find there is no isolation between mains N and battery 0V. In that case, you've tied the panels to earth.
It's not unsanctioned TN-C-S as you are never connected to the grid. Only the earth is common between systems. The only tricky bit is which colour to use.  Blue link to earth or G/Y to N? Or both to a marked terminal.
Sketch it out and work it through, remembering the inverter is floating, and everything has to have a earth fault path

Deadly thanks for the explanation, yurp makes sense.
Ok...so hypothetically if my inverter has a live-earth or neutral-earth fault and the inverter RCD(s) sticks closed, and the fault goes to the grid neutralising point backfeeding the Grid RCD, no smoke?

What's the size/function of the diode - commissioning protection against incorrect battery polarity?  Needs to be absolutely enormous to clear the fuse.
IIRC the tristar 0V is a link, so connect the panel 0V to the star point? Not sure, as this may introduce unwanted current flow & noise towards the star.

Transient suppressor as recommended in the manual for protection against inductive loads.

Ah yes.  Essential for large contactors too.
It would be a good idea to put some smaller, say 1A diodes across your relay coils too, as you can kill the power supplies with the back EMF. Noisy too.

In previous incarnations of my feeding TriStars with SMPS and Pulsed DC i found resistor capacitor snubbers much more effective than diodes. I tried the diodes first and they didn't work. They'd chatter on disconnect. The coils had parallel resistors indicated but I stuck a few RCs in the schematic for good measure.

There are a few manufacturers of AC breakers who will rate them at much lower DC volts/amps.  If you PM clockmanFR he can tell you. You can also use 3 phase breakers and put all 3 in series to get a higher DC voltage breaking as a single pole device. Depends how the budget is holding out on DC breakers/isolators

I picked the midnights because they claim to be rated to break full load current (can be used as a switch). I can get the 80V ones cheap enough when I buy enough of them. I was wondering what Mr. CM was doing with the 3 phase breaker.
Yeah we'll see about the budget when it comes to it.

[biff]

Oh,Scruff,!
        Looking at those pics and reading that prose, I got all wobbly at the knees.
 You my friend, are obviously in a land of much happiness and contentment, Your smile widens and your step gets jaunty every time the sun shines and the wind blows.
  Long may it be so.!
                       Biff

[roys]

Think I am going to like this thread.

[Nickel2]

Please take that black battery out of the electronics-box! They have bad breath and will eventually spoil the party atmosphere in the box.
Put a fuse in every thin wire that is connected to the big battery as near to the battery as possible. (sense-wires?) Those wires will vapourise in the event of an accidental short, giving an orange glow to the horizon as your installation goes up in flames.
Use the thickest cable physically possible to all battery connections. If you pass 60A continuously through any of the cables in the pics, they will get hot to the touch, plastic will soften, and at the places where the wires cross/touch will get thinner and flow. BZZZT!  Bus-bars look good though.

Can I get some of those batteries pleeeze!

N

[jonesy]

Looking at this Swiss inverter it's 2.3VA, 1.3 times rating for 15 mins. Where did you get this 6A figure from and how do you find an inverter Isc the easy way?

The 6a figure came from the SMA SI3.0M manual, which is a 2.3kW unit, for which they recommend B6.  Basically it's limited by the output impedance, which rises a tad as the inverter warms up.  Is it in the manual?
You'll have a loop impedance tester. Had odd results trying that on a large diesel genny, and IIRC the PWM output of an inverter ain't going to help.  Or try a 10A mcb and a 6kw load.  If it doesnt trip, drop the breaker. It's a really tricky subject, particularly on large island generation, as fault levels change depending on source.  Protection engineers earn their money.
Hopefully another member will have a good answer.

Ok...so hypothetically if my inverter has a live-earth or neutral-earth fault and the inverter RCD(s) sticks closed, and the fault goes to the grid neutralising point backfeeding the Grid RCD, no smoke?

A N/E fault doesnt always trip an RCD (in PME), and the fault current will be minimal and won't exceed the touch voltage. The live fault would go inverter L, (RCD) MCB, RCBO, load, load case/E, earth point, inverter E = inverter N, so the MCD should trip in 0.4s. On a socket circuit.
If the breaker didnt go, then the inverter would probably shut down on over current. So other than sharing the earth point, there is no connection to the grid. If you're still in doubt, drop an earth rod and use that for the inverter.  Your protection will be worse due to rod impedance/touch voltage. Hmm. Wouldnt recommend that as you'd then have different earth potentials in one room, and that will be outside the regs.
For info, note that you have the potential for 380V at your inverter only sockets WRT grid, as the two aren't synchronised.  Many years ago there was a 'rule' that you couldn't have socket outlets on different phases in the same room, but I can't remember reading that anywhere that mattered.
Just noticed you're using DP MCB.  You could go single pole safely, as inverter N & E are linked.

With a 12 year life on those batteries, if you limit the continuous current to c/10 = 125/10 = 12.5A, twice for each string, = 25A x 48V = 1.2kva, they will probably go on longer.
I got a similar set up to you (10 year Yuasa 100Ah), in similar circumstances. All 8 lasted ok for 12 years, 2 died at 13 years, but I didnt notice as they were in series on a 24V setup. Now at year 15, they are not in great shape and have around 25Ah capacity.  Time to scrap them.

Calculations for cables assume an operating temperature of at least 60C, and a lot higher depending on insulation.  I have to admit not liking feeling incomers at that temperature in factories, etc. Good tip on the sense cables. I have used bolt on fuses in the past, covered in heatshrink.

No more pictures of your solar po*n.  We'll need to call a nurse for Biff.

[Scruff]

Your smile widens and your step gets jaunty every time the sun shines and the wind blows.

I love the smell of electrons in the morning.  
Not long ago I used to see my ammeter before I opened the curtains...those were exciting times...

Please take that black battery out of the electronics-box! They have bad breath and will eventually spoil the party atmosphere in the box.

But but but N2 smelly batteries are my favourites...bit like cheese I suppose...
That particular battery is filled with magic pixie dust of mystery, it's held 12.9V for a year without charge since I rescued it from Mrs Scruff's scrapped motor.
It's actually my patented XT5002 Current Limited Variable Bench Lab Power Supply Extreme Mk II^TM.  

Put a fuse in every thin wire that is connected to the big battery as near to the battery as possible. (sense-wires?) Those wires will vapourise in the event of an accidental short.

The sense wires aren't currently installed, they were on the Eltek - TriStar setup.
The fuse was out of shot. It's my own brand of holder F500mA in I think they're called female bullet crimps.
They fit perfect...thing is though they sometimes break when you try to separate them..



The main conductors are protected with a midi fuse.



The charger wiring is protected by a 40A fuse and it's own internal fuses.

The interconnects are protected by a combination of solid terminations, torqued fasteners, insulation and prayer

Use the thickest cable physically possible to all battery connections.

There's 10m of 16mm² just out of shot of that photo ...no way I'm chopping it up for a prototype though. I'll invest in some 35mm² once I start making things permafied and wall mounted.

Can I get some of those batteries pleeeze!

You can come visit and stroke them if you'd like?

The 6a figure came from the SMA SI3.0M manual, which is a 2.3kW unit, for which they recommend B6.  Basically it's limited by the output impedance, which rises a tad as the inverter warms up.  

I wonder if it has anything to do with MCBs taking 4-5 times the rated current for an instantaneous trip.
Could be up to 20 secs for 2X rated on the bi-metal trip.

SwitzSwoo Manual sez max: 3.5 x nominal for 5 seconds, so 35A, which will trigger the magnetic trip on a 6A MCB but not a 10A. Hrmmm...

If you're still in doubt, drop an earth rod and use that for the inverter.  Your protection will be worse due to rod impedance/touch voltage. Hmm. Wouldnt recommend that as you'd then have different earth potentials in one room, and that will be outside the regs.

Also not great in lightning storms or for interfacing earth referenced lekytronics.

For info, note that you have the potential for 380V at your inverter only sockets WRT grid, as the two aren't synchronised.  Many years ago there was a 'rule' that you couldn't have socket outlets on different phases in the same room, but I can't remember reading that anywhere that mattered.

We have that same "rule" in stage lighting except it's every 2m not room.  

Just noticed you're using DP MCB.  You could go single pole safely, as inverter N & E are linked.

Indeed. The thick plottens.

With a 12 year life on those batteries, if you limit the continuous current to c/10 = 125/10 = 12.5A, twice for each string, = 25A x 48V = 1.2kva, they will probably go on longer.

I believe the 12 year figure is for standby operation not cyclic use. I'm planning on ~C20 discharge (130Ah) C15 recharge, my base load is between 50W - 200W. Not quite so sure what set points to go with. I've set to 2.35V p/c for the time being no point in gassing an idle battery. I'm more of a FLA head tbh...I tried topping them up with fiberglass matt but they seem pretty full.  

I got a similar set up to you (10 year Yuasa 100Ah), in similar circumstances. All 8 lasted ok for 12 years, 2 died at 13 years, but I didnt notice as they were in series on a 24V setup. Now at year 15, they are not in great shape and have around 25Ah capacity.  Time to scrap them.

Each?! Yup I'd hate to think what their Peukert exponent is.
24V is pretty enticing alright, much easier find gubbins.

Calculations for cables assume an operating temperature of at least 60C, and a lot higher depending on insulation.  I have to admit not liking feeling incomers at that temperature in factories, etc. Good tip on the sense cables. I have used bolt on fuses in the past, covered in heatshrink.

Yurp. Automotive ratings I've found are about 20% higher than installation. Despite the frequency of running in engine bays. I've some 12mm² which came with a 115A alternator in my scrap bin. Alternators aren't fused either high temp silicon sheath though. I wonder if it's because they're "single conductor" instead of multi-core.
I'd not be happy with 60°C either...the cheap stuff is only rated to 80°C.

[biff]

 
                    Biff

[jonesy]

Looks like it's all got a bit too much for Biff.  BIFF. 

I've worked with some cables that are rated to 150C.  Just got good insulation.  Volt drop still spanners you.
24V was easy.  12V was too low.  I also had 48V for a while. And 96V.  I like 96V best, as you could wire up with 4mm and go 3kW in a beat. I also had about 200V DC to run standard CFLs, so I didn't need to run an inverter at night.
Nice fuse holder with the bullet connectors.
My batteries were standby type. The life is lengthened hugely if you keep the continuous discharge rate down.  I did read recently that partial discharge/charges don't count toward a whole cycle, which helps.  IIRC Biff is an advocate of low discharge.
I think it was a 2m 'rule' as you say, not room.
And don't try kidding us the 12V battery and clips are for 'testing'   

[Scruff]

108V would be interesting for running site tools with universal motors. I think I'll stay in ELV-land for now.


Got the batteries holding their own now. The Silver Alloy charger I had floating them was running at 40W with 4W coming out the other side 13.7v @ 300mA float cycle. The thing is not so bad (compared to some I've seen). 84% efficient measured at full load, 90.4% listed. Not a patch on a TriStar though; switching over the TriStar is all like "Ya call that charged?!...stand aside lemme at it!", it's not a unique phenomenon. I've seen the TS outperform every other mains charger I've stood it beside. So much so I don't have a mains charger in my avatar anymore just a switched PSU into the TS. It'll also float with a much closer to zero current reading.
It's not a matter of overcharging either, hydrometers don't lie, most other chargers I've seen call it a day at 90% SOC and the better ones (that I've tried) and only on a good day can do 95%. Hence my love of MorningStar.  

This is the module Jonathan kindly donated me taking the reigns. I haven't ruled out running a 12V mini-ring for the prototyping and lekytrix development laboratory as well as the control circuits for the switchgear of the proposed 48V system. The runt would be happy to oblige if I promise not to short-cycle it all the time, it'd be more efficient than switching regulators and the isolated supply can be a benefit. I'll need another solar controller though...



I'm no roofer and I didn't fancy tiling shenanigans so cheapest mounting solution I could think of was HD brackets on expanding bolts. Makes a not too bad canopy too. Angled 15° SSW for trickle output and self cleaning. The cable is some 10m x 4mm² tinned copper scrap I had, in polyamide conduit, cable clips to be added asap  , 8Ω module to controller so ~3.5% voltage drop.

Measured the high side of 1.5V at 1.69A load.



There was some oddball connectors on this module I wanted to swap them for MC4 but I didn't have any .
3mm banana jacks are a mite hard to source, in the end I just ran a continuous line without a junction bar a 25A toggle sw.....ahem..module isolator.

Here's a poor man's 3mm banana plugs. You can fold the blade rather than cut it.



So that's 1kWh p/d off the base load.  
And for that I only needed 25Wh p/d  

Has anyone forged their own TriStar remote temperature sensor? Can I just thermally pot a thermistor in a battery lug and tail out of it? I have one elsewhere I could borrow to reverse engineer.

[todthedog]

    

[biff]

Im Ere,!
      Just having a little lie down Jonsey, ,
    Interesting set up Scruff,
                                Simple and efficient. I have had different systems, 12v, 24v, 48v,and our present household of 120vdc,which in my mind is the best of all. I am off the opinion that the batts gets a better deal, can deliver quicker and charge quicker and more evenly. We have 60 forklift cells,36flouride 600ah and 24 ordinary Powersafe,850ah, (Ithink) L.A,s. They get on quite well apart from the 36 flourides drinking a little more booze than the other half. And yes,! I believe in the minimum discharge,very very seldom dropping under 124volt under load.
  Our immersions are dump loads 138vdc and work very well. We run most things an ordinary house runs,,washing machine, vacuum cleaner, Microwave and Iron. no problem, I also power the shed now with the house supply, angle grinders,drills etc. The stove installation tools were all powers by renewable energy,drills,grinders and mixer,The system hardly felt it.
                                                                                        Biff

[Scruff]

Biff you put toothpaste in your batteries? 

Yerp fancy myself a set of forklifts eventually.

[biff]

Hi Scruff,
        Never thought of putting toothpaste in our cells,, H,mmmm. I know that it fizzes and burbles but ....in the cells,?
  I did have a 1000ah 24 pack that was lazy and daringly one day decided to add some acid, so I measured out a half cupfull onto each cell. They were off the charge then. Then after a while i put the volt meter on the cells and got the shock of my life, They were all complaining and going mad with the pack voltage going through the floor, at one point the entire pack was registering 9 volts.
  So I packed everything away and went and had a cuppa. I did not go near the pack till late the following day and lo and behold they were sitting up at 26.5volts. I connected up the the pv directly into them and let them frazzle for a few days in good sunlight. I think I was just lucky but the pack has much improved.
                                                                                                                 Biff

[Scruff]

Sorry Biff no funny joke...

Are the fluorides an alkaline type?

I've seen a geezer on youtube convert a lead acid to an alkaline but he didn't instil much faith in me with the endeavour. Hold on...[rummage]....[potter]...here we go..

There's more professional attempts to be found if you look around.
 
Where do you get concentrated H₂SO₄? In a normal LA as long as the SG isn't excessive then you can improve them (<1.300).   If you make the SG too concentrated they'll perform great until they disintegrate their own grids. They say never do it but if you get it right (replace hard sulphates with soluble) then I reckon it works. I suppose just overcharge until the SG stops improving overcharge some more until it's definitely definitely not improving and set that as the baseline SG.

Once upon a time I decided to test the individual cell voltages of a battery I was trying to recover. Popped the caps off, one meter lead on the negative post...couldn't find a 6inch steel nail to dip onto the plates so I tried a 6-inch zinc galvanised screw...