Warren

Coulomb will know. I think that's the voltage as measured by the charge controller (the mppt) as opposed to the voltage measured by the inverter side.
 
Edit: After some crafty googling, I believe the answer is Solar Charge Controller.
 
:-)

A tin star for the Plonkster
Yes, the SCC and the DSP (Digital Signal Processor) both measure the battery voltage independently, and send their readings to each other. If the SCC finds that the readings differ by more than a certain amount, initially 0.2 V I believe, then the SCC will adjust its readings to agree better with the DSP.
 
Most of these values are stored as decimal numbers, with an implied decimal point between the last and second last digits. For example, your 00502 value represents 50.2 V, presumably the battery voltage as read by the SCC/MPPT/solar charger.
The SCC charge current I believe is no exception. Yet the current is always displayed as a whole number, i.e. they divide the number transmitted by 10 before displaying it on the LCD, thus throwing away one decimal place. Changing this is on my list of things to consider in future firmware upgrades. (Of course, the number may prove to be too noisy or inaccurate, but I say show it anyway.)

To be honest and blunt I dont really care if it is a bit inaccurate as long as it works and I dont drain my batteries to fast and I have lights when loadshedding starts and I also have a ROI.

Download the Trial version that Jaco created. Awesome software and a 1000 times better than watchpower! Download here: http://aicc.org.za

Of course there's a bit of an inventor in me thinking that if you charge them separately and combine them in some manner at night, you'd get a lot of extra life out of an old bank. You won't replace it... You'll continue using it along with the new bank until it's well and truly dead :-)

Banks in parallel is more of an issue when charging, than it is during discharging. During discharge, each string naturally contributes according to its own capacity. You can even parallel up different capacities (not different chemical setups or technologies though) and it will distribute the work according to their relative capacities.
 
The trouble comes when you recharge. One string will reach 100% SoC before the other does. This leaves you with two options: Stop charging, in which case the lesser string will develop sulphation in the long term, or continue charging, in which case the better string is overcharged. If the strings are similar in capacity and vented lead-acid types, this bit of overcharging is usually not a deal breaker. You pay a small price in terms of charge efficiency and overall life of the batteries, but not too terrible.
 
See this paper: http://neuralfibre.com/paul/wp-content/uploads/2007/05/can-we-now-sin.pdf

Done properly there should be no negative effects (apart from different aged strings).
 
 
 
Connect your two strings via a bussbar. Ensure that the cabling for the one string is the same length as the cabling for the other string. This is for all cabling from one busbar to the other so if your 1st string has 1 long cable, 1 medium cable and 1 short cable  then you have to replicate this for the 2nd string. I just have a standard length and all my cables are the same length. The cables connecting either end of the string to the busbar must be the same length in both strings. The reason for this is that you want each string to have the same total resistance and therefore charge at the same rate. Uneven charging/discharging is the major cause of battericide (a wonderful term).
 
 
If you have 4 batteries you need 3 BBs  you can then link 1st string and 2nd string and still use 3BBs for the additional string. 
 
https://www.victronenergy.com/upload/documents/Datasheet-Battery-Balancer-EN.pdf
 
The Victron BB to my mind is pricey at just over R1k a unit so it is almost like buying a 3rd string. Victron makes very good kit and if money was no object my house would be blue (like Plonky's).
 
There is a Chinese manufactured battery balancer that I have installed on my 4 x 260Ah batteries and after 4 months it appears my batteries no longer go out of balance. I have been tossing some ideas around but unfortunately spent my Xmas break doing crisis management with stock drink water supplies failing and 40+ oC temperatures.
 
Jaco has asked for me to put up a review which I will tackle tomorrow.
 
Chris

SBU = Solar->Battery->Utility
 
Explains the ordering exactly

After looking at my pharmacies growing electicity bill and cost of diesel for our standby generator I knew I had to do something. A good friend of mine had recently opened a game lodge and gone full solar and assured me that solar had come of age and was cost effective in the medium term.
 
I first changed 120 x 4ft fluorescent tubes to 16w led tubes as well as changing 20 x 50w down lights to 6w led. I put a time clock on my external signs as well as a light switch and ran them from 6pm to 10pm only.
 
As my business only operates from 8am to 5pm a battery free grid-tie system was the obvious choice. I decided to install a larger inverter than needed initially so that I have capacity for expansion.
 
Phase one installation was as follows:-
1 x Socomec Sunsys B20 three phase 21kva grid-tie inverter
45 x 250 watt panel array

If you send the command  QPIGS<right-alt-7><right-alt-shift-0><enter>
 
then the inverter returns
 
QPIGS

Hi Warren, 
 
Do not pay any attention to the % charged on Watchpower. It does a woefully wrong calculation based on voltages.
 
It also has much to do with your final battery voltage - if set to 42V (dangerous) the % is more or less right, but if set to 48V (right) it goes totally wonky.
 
Best way to determine state of charge is with something like a battery monitor or by simply making sure your batteries charge at full bulk voltage each day, falls back to float and then stay there for ate least an hour. That is the main indicators - not a % based calc.
 
Just make sure your charge voltages are 100% correct as Chris said. And listen to the batteries like you listen to your wife. If something is wrong they will not last as long as they are supposed to on a daily basis (undercharge and sooner and sooner voltage drop) or they will boil (you can hear it with the naked ear...)

Hi Warren
 
If these one-way valves open it is because gas build up. At a voltage of 2.35 V per cell about half of the energy put into the battery causes the electrolyte to separate into H2 and O2. In a vented battery this escapes to the atmosphere and you top up your electrolyte periodically. In a sealed battery this gas is retained and during discharge the gas re-combines to form water. If however if the gas level become so high that there is a danger of the battery case rupturing this gas is vented off through the one way valves and you have now lost electrolyte you cannot replace.
 
As Edmund mentioned the Axpert readings are dicky. Watch your voltages. Early in the morning (assuming you charging by PV) you are in your first phase of charging and the charge current will be maximum (if there is enough sunlight) set in the Axpert's menu. Mine is set to 20A to remain below C10 (a charging rate based on the Ah of your batteries - read up about charging rates or there is a thread on this forum a while back that explored this). At this charging rate your battery voltage will slowly rise and this is known as the bulk phase. Once your bulk voltage is reached the voltage is maintained and as the battery charges its ability to take charge drops and the current flow drops. The battery's internal resistance does increase slightly but this does not account for the tailing off of the current, this is due to the chemistry. Once the battery is 98-99% full and the battery is accepting very little current the charger will drop the voltage to float which is basically a maintenance charge which is below gassing voltage but above the rested 100% full voltage (12.9 V).

I can set it to 48 V in Watchpower. Strange. I know you cannot change settings outside default limit interrogating the inverter directly but you should be able to set it to 48V.

Having re-visited the manual program 29 (cut-off V) can only be changed from the default 42V if program 5 (battery type) is set to user defined. 

https://github.com/scottwday/AxpertTest

Hi Warren
 
The Axpert battery cut-off at 42V is madness. Rested and under no load that would be the state of a fully discharged battery - hopeless. The maximum setting is 48V which is roughly a DOD of 50%, also not good enough in my opinion. Battery voltage varies with load, state of charge (SOC) and temperature so it is an impossible task to determine SOC from voltage as load and temperature also have an influence. A 105Ah battery with a current draw of 1 A will take a theoretical 105 h  to drain @ 12V. 4 batteries in series will still take 105 hours to drain with a current draw of 1A. How can this be? What must be remembered is that the voltage is now 48V rather than the previous 12V so 4X more energy is being  supplied still at 1A. Batteries in series result in an increase of voltage but not in Ah. Batteries in parallel the voltage does not change but the Ah is cumulative. The inverter's wattage seems fairly accurate . I don't own a Efergy but I presume it will track the VA reading (apparent power). The only way I know of tracking SOC is an ammeter (using a shunt) with a current logging capability. Then software needs to take into account battery and charging inefficiencies.   

The line will always end with a CR character. There will never be a CR in the CRC, so as soon as you get a 0x0d you know you've got the entire response.
static void DataReceivedHandler(object sender, SerialDataReceivedEventArgs e) { var sp = sender as SerialPort; if ((sp != null) && (!_gotResponse)) { //Read chars until we hit a CR character while (sp.BytesToRead > 0) { byte b = (byte)sp.ReadByte(); _rxBuffer.WriteByte(; if (b == 0x0d) { _gotResponse = true; break; } } } }

Right,
 
So I have been playing around with my own solar water heating system now for a couple of years and this is what I have learnt to date:
 
1. Vacuum Tubes is WAY better than Flat Plate collectors.
2. VT orientation is not that important compared to FP.
3. Tilt angle IS important. The more square you can get the sun in cold months, the better. It will also prevent overheating in summer.
4. Thermo siphon works when you follow all recommendations.
5. Problem with thermo siphon is the location of the geyser and the frame to mount it on. Also the circulation effect only starts working at a high temperature.
6. With the geyser located outside, heat loss is a problem.
7. With the geyser mounted outside, hot water piping runs can be very long, resulting in long wait times for hot water.
8. Work on 300L hot water storage for 2 persons.
9. 24 Vacuum tubes is ok for 200L geyser.
10. 2,5m2 Flat Plate collector is not really enough for 200L geyser.
 

Hi Chris,
We first used an Efergy meter and started with a daily consumption of 60kwh (unbelievable yes).  We then switched off the outer buildings (not used unless we have friends over).  Then we converted one geyser to heat pump and another geyser to Plasma.  We also replaced all our lights with LED lights.  We also "learned" to use electricity wisely (don't walk out of a room with aircon running, etc).
Now we are using between 24 and 35 kwh per day and we run everything off solar.

I with Edmund on that one - add readings from BMV and you have a winner.

O for the love of Pete! I will pay you all to do this! I know at least one other non forumite that will pay for a decent app perhaps integrating victron bmv readings.
Must do aggregate calcs as well and graphing.
Like seriously man.

Your efergy meter may not be entirely accurate. It cannot accurately measure any inductive load. Warren, you, scottday and jdp are all trying to improve on WatchPower (which is pretty crap) you should do so co-operatively. I have done a little programming all through my teen years and early adulthood but I am not about to tackle something like that (my time  and the dinosaur's time has come and gone!). 

Hi Warren 
 
Man that is a good feeling and it just does not wear off. I have bought diesel for the generator today for the first time in 6 months.
 
You can ignore the Axpert SOC it is wildly inaccurate. Look at your charging current. If it drops to 2-3A and the sun is shining brightly, your batteries are charged. My 260 Ah the charging rate drops down to 1.2 - 1.3 A and the batteries accept 70 W or so. At that level my batteries are fully charged. Even my Victron battery monitor reckons the batteries are fully charged a bit early but I am making the necessary adjustments slowly. 

The inverter will only reply once it receives a CR (0x0d) character.
 
The last argument to SerialPort.Write is the number of bytes to write. you're always going to need to write more than 2 bytes. In fact it's always going to be 3 more bytes than the command you want to send:
 
The format is <command><CRC_MSB><CRC_LSB><CR>
public byte[] GetBytes(string Command, ushort Crc){ byte[] result = new byte[Command.Length + 3]; Encoding.ASCII.GetBytes(Command, 0, Command.Length, result, 0); result[result.Length - 3] = (byte)((Crc >> 8) & 0xFF); result[result.Length - 2] = (byte)((Crc >> 0) & 0xFF); result[result.Length - 1] = 0x0d; return result;} This code packs the bytes to send. First it's the bytes from a string, then 2 bytes of the 16 bit CRC, then a CR character.
 
If you look at the CRC code it makes sure that it never uses 0x0d or 0x0a because they are characters that denote the end of the command.