Elbow

Yes (no?), there was no load on the battery. And according to the batteries data and my BMV the battery was not drawing any power.

Here's what happened when I turned off the mains side and put load on the battery: It happened almost immediately: I'm not sure that this means, but I guess I must try the 53.2V again.

Hi @plonkster, My evidence is different. (Though I haven't got that much data yet). I've been running with a float voltage of 52v since 11th Feb. In that time the battery wasn't discharged. The battery has been reporting a current flow of 0A (charger says about 0.4A is flowing. BMV says 0.00A Over that time the cell balance has got worse - when I was cycling the battery lightly - say 5% DOD - then the battery was between 0 and 0.1% out of balance. It's now 0.8% out of balance, so its got worse over that time, not better. It's one cell in each battery that is low. So it looks like 52v is not enough to allow the battery to balance cells. I'm actually going to put my load over to battery now and I think as the battery discharges the cells will come into balance. (I still don't know if my alarm is related to the balance of the batteries. Since the last alarm the battery balance is no better and I didn't get another alarm).

I connected up the RS485 monitoring. Here's what the two batteries are saying right now: Master battery (address 2): Send { "time":1551332544, "VoltageUpperLimit":53.25, "VoltageLowerLimit":47.0, "MaxChargeAmps":10.0, "MaxDischargeAmps":-25.0, "BatteryCycles":3, "BatteryVoltage":51.987, "BatteryAmps":0.0, "BatteryWatts":0.0, "BatterySOC":100.0, "RemainingAh":50.0, "RemainingWh":2497, "MinutesToRun":9999, "CellMaxVoltage":3.7, "CellLowVoltage":3.05, "CellUnderVoltage":2.9, "cellVoltage0":3.461, "cellVoltage1":3.463, "cellVoltage2":3.457, "cellVoltage3":3.456, "cellVoltage4":3.461, "cellVoltage5":3.448, "cellVoltage6":3.461, "cellVoltage7":3.463, "cellVoltage8":3.474, "cellVoltage9":3.473, "cellVoltage10":3.474, "cellVoltage11":3.474, "cellVoltage12":3.475, "cellVoltage13":3.474, "cellVoltage14":3.473, "highestCellVoltage":3.475, "lowestCellVoltage":3.448, "cellImbalancePct":0.7, "temp0":27.0, "temp1":25.0, "temp2":25.0, "temp3":25.0, "temp4":25.0, "highestTemp":27.0, "lowestTemp":25.0 } Slave Battery (address 3): Send { "time":1551332476, "VoltageUpperLimit":53.25, "VoltageLowerLimit":47.0, "MaxChargeAmps":10.0, "MaxDischargeAmps":-25.0, "BatteryCycles":3, "BatteryVoltage":52.012, "BatteryAmps":0.0, "BatteryWatts":0.0, "BatterySOC":100.0, "RemainingAh":50.0, "RemainingWh":2497, "MinutesToRun":9999, "CellMaxVoltage":3.7, "CellLowVoltage":3.05, "CellUnderVoltage":2.9, "cellVoltage0":3.468, "cellVoltage1":3.468, "cellVoltage2":3.468, "cellVoltage3":3.444, "cellVoltage4":3.469, "cellVoltage5":3.47, "cellVoltage6":3.47, "cellVoltage7":3.47, "cellVoltage8":3.468, "cellVoltage9":3.468, "cellVoltage10":3.469, "cellVoltage11":3.471, "cellVoltage12":3.469, "cellVoltage13":3.469, "cellVoltage14":3.471, "highestCellVoltage":3.471, "lowestCellVoltage":3.444, "cellImbalancePct":0.7, "temp0":27.0, "temp1":25.0, "temp2":25.0, "temp3":25.0, "temp4":25.0, "highestTemp":27.0, "lowestTemp":25.0 } That's after floating them a long time at 52V. The figures look healthy to me. Cell voltages are well in range. Balance is <1% out. Temps are fine. I will look in the docs to see if I can find anything else I can query over the RS485 (Modbus?) interface. I suppose the inverter may have misread the battery voltage and switched out of constant voltage. I'll leave the monitoring on and see if I can capture another event.

I do not. I’ll sit down tomorrow evening and see if I can retrieve some sort of log.

I think the BMS does limit operation outside the parameters of the cells. I don't have a problem with that especially where you have an inverter that can take the data feed from the BMS and respect what it asks for. In principle that means that you can't kill your batteries. Dumb batteries of course will let you do what you want and if it kills your batteries so be it. In my opinion I didn't do anything to my batteries that should have triggered a fault, so I am interested to see what it is unhappy about since nuisance alarms where the battery goes offline aren't welcome. My monitoring will need to make an alarm since otherwise it is quite possible I won't notice.

Yes, it does. The second battery was blinking its light and I think would have worked, but last time they both had an alarm.

Yep - all fine again when I turned it off and on. i think there is some sort of log you can read on the console - I’ll go digging.

Hi, For the second time I found my one US2000B battery with the alarm light on. The other one was happy. Did anyone else see this? I float the charge at 52v so there is no way the battery could have been over-voltage.

So now I’m paying attention. My inverter max voltage is 500v. I was going to use 10 of the Canadian Solar 350W panels which makes a max VOX of 462v. Cape Town. Do I need to go to the 330w panels, or use 9 not 10? Thanks

Yeah - you yank on the big handle. it pivots at the bottom and pulls the fuses out of their connections. Any arc safely contained inside.

HI there. I use this. In my case 80A fuses are fitted but you can get higher values. Its a pretty chunky unit and makes you feel pretty safe. I got it from thepowerstore.co.za

Ah- understand what you are saying and the distinction. Swaar-stroom. It’s a learning curve.

So I think its very interesting what @Rautenk wrote in your application. Since this is exactly the area where its not clear what is required and why. Unfortunately I'm sure it will be months before there is any clarity. The fun one is that you can't be compliant to both the NRS and the CoCT in respect of voltage levels? Seems like your application also claims that CoCT is not compliant to their NERSA licence? Or am I reading between the lines wrongly?

I think there is scaremongering in this article - situation is indeed serious but I think we can gradually start to undo he damage if only we can find common cause for the tough road. Just my opinion though I do need to try to be optimistic since it’s my future world in my old age. I think the matter of renewables vs high tech coal plant is worth discussion and on-topic. For me I believe in renewable generation but I think the key is decentralized generation - like we do, or think about doing. Putting generation with consumption means efficient use of power - You all know that the first step to PV success is to assess and reduce your usage. Government should consider incentivizing personal generation - capital assistance. Especially for businesses where consumption peaks are in the day. I’m also now imagining a world with attractive grid-tie incentives and rates, then add neighborhood battery storage - nice economy of scale to get a neighbourhood through evenings. All about flattening the consumption curve. Base-load capacity will always be needed but with a good local generation policy a reduced amount should be adequate. Of course I may be talking out of my hat ... ?

Hi, You said the same to me in person. And it is very good to have hear from someone with practical experience. Are there physical constraints to thermosyphon systems - the panel positioning relative to the geyser itself? Presumably you also need a geyserwise or home made control system to turn on the electric element if required (or, mark-I eyeball and a switch...) My point about heating with PV was simply that if you put in a typical 3Kwp PV system then it is likely to have excess capacity much of the time. So you can opportunistically divert some to hot water as and when load permits. It maximizes the use of the system you already have and understand. So it’s an incremental cost argument - only requiring a lower power element, a temperature probe, and a little bit of control logic.

Heating water with PV is much much less efficient than using a regular solar geyser. But if you have spare power from your panels above your daytime load and battery charging then pushing it to a low power element in the geyser can make sense. In my case 4.5kWh of electricity needed to heat the water. With a 1kw element I could put that into the geyser in 4.5 hours (existing 3.2kw element can do it in 1hr 20 mins or so) A 1kw heatpump is also an option and much more efficient (3x apparently) than a traditional geyser. So with that you could do the job with 1.5kwh from the solar.

Yeah - I've got gas hob, but electric oven. My hot water uses about 4.5kWh/day so its not the biggest user of energy in my house. I have Openenergymonitor so I know lots of detail about what uses what and when. I have Homeassistant/NodeRed and smart power switches so I will use that to manage loads as I go along.

Hi, Yes, I decided that for me I will register my setup as off-grid and implement it that way. I’ve come up with a design that puts most of the high total energy using stuff on the inverter, but leaves the intermittent but power-hungry stuff (appliances etc) on the grid. I’ll put a changeover switch for the appliances so under my control something like the microwave can be used on the inverter in a power cut. the net benefit of this comes out better than paying for the AMI meter and I think will get quite close to what my 3.5kw array can deliver in terms of energy. I’ll find out in practice and I can always tweak.

I see you have multiple changeover switches? Looks like each is fed by a different phase from the grid side. Is this so you have finer control over which loads are on the inverter, or just to avoid a 3 phase changeover switch?

Hi Mark, I wanted to ask you how you setup your loads on the output side of the inverter? Since surely if your grid supply goes off when the inverter is pushing through much more than 3kW then something bad will happen? At best the inverter shuts down, worse - the fuses blow - worst of all the mosfets let their smoke out. I'm trying to figure out how to do the breakers on the output side of the inverter. The inverter manual doesn't say what breaker to use - it says that the nominal output current is 13A, "maximum output fault current" 51A - that's a big range. So I can size the breaker based on the capacity of the inverter when the grid is present - say a 32A breaker so about 6000w - and then we'll ride out the burst of heavy load (hairdryer and kettle and ... ) Or I can size for the 3000W - so a 15A breaker I suppose. But there will be lots of accidental trips. Can't figure out how to square this circle and protect my inverter.

Looks like you cut out the back and fitted it over the top of the recess for your old board?

Hi all, I want to try to finish building my sub-board for my inverter. I have about 300mm of space to the left of my main board - but I will need more than 12 spaces. So I'm looking for a good quality but not over-expensive surface mount DB with 2 rows. Veti (Major-tech) sells this one for R459: So these DBs are definitely on the cheap side - but this would work size wise and the 12 way I used at the inverter looks neat. I found also this Hager one - VS212TF, This is the "Golf" range - not sure how much it costs and where to get it in Cape Town: Are there other options I should look for - I looked at Schneider but the prices seemed to be very high. Thanks!

Well a 1kg mass 1m high has 9.8 joules or potential energy. 9.8 joules is 9.8 watt-seconds. So to scale this up, 1000kg 50m up in the air has about 490 000 joules of energy, or 136 watt hours. So it’s not looking too promising.... I think the idea is better suited to get a sudden burst of energy since you can get all 490 000 joules in a very very short time if you drop it!

Great, thanks @plonkster