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Monitoring the Tristar TS-xx with a PI.

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Simen:
I just bought a Tristar TS-60, because i've added 200W of solar panels to my bank, and blew my old Picaxe dumpload controller due to too much load. ;)

Since the Tristar comes with a rs232-port, i just had to try to communicate with it, and i wanted to use a Raspberry Pi to do it.
Now, i'm no programming genius, but with a good deal of searching the net, studying documentations, and some 'borrowing' of code, i actually managed to get data out of the Tristar; make sense of it, and put it on a 'live' webpage... ;)

http://mwlmf.net/monitor/monitor.py
(Refreshes every 15 sec.)

The Tristar uses the Modbus protocol to communicate, and i found a free library for Python called pymodbus which installed on the Pi without problems. I'm using a 'Prolific pl2303' based usb to rs232 cable between the Pi and the Tristar, which the Pi accepted without any fuss.
The Pi uses around 3.5W, which i find acceptable for a full computer. ;) It runs directly from my bank via a 12V to 5V usb plug.

The Python script on the Pi gets data from the Tristar every 5 sec., and stores the data in a textfile directly on my webserver, where another Python script picks it up and creates a webpage every 15 sec.

I can publish the scripts here, if there are any interest. :)

Here's a pic of the Tristar and the Pi, and some other of my mess...


Since my basement (where my 4x Rolls S-530 batteries are) keeps a cool temperature all year (10C-16C), i really should get the external temp sensor for the Tristar, but for now, i've set the Absorption stage to 14.8V to compensate for the cool temp.

But i do wonder about the behavior of the Tristar; it doesn't seem to get out of Absorption and over to Float at all?! It tapers down to approx. 5A charge, and stays there for the rest of the day. Now, i do have around 2A continuous load on the battery during daytime, but should that be enough for the Tristar not getting over to float? Or do i need a proper equalize? ;)

bob golding:
thanks for that will have a play when i get time. as regards  the tristar never getting out of float, i have similar batteries to you the 460 amp hour ones. i have 8 of them wired for 24 volts. i have noticed they very rarely get out of absorption also. i normally have 750 watts of solar and 500 watts of wind turbine on the system. no wind at the moment as the turbine  needs a bit of work. i have a backup  genny to equalise the batteries every now and again. i haven't noticed any major problems over the last 4/5 years? cant remember when i brought them. but they are around that age. the genny is also broken at the moment as well so totally reliant on solar at the moment. lets hope the sun keeps shining :)

Simen:
To quote from the Rolls Battery Manual; ( http://support.rollsbattery.com/helpdesk/attachments/1073177 )


--- Quote ---Absorption Charge
Arguably, the most important part of the charge cycle is the absorption charge. Since the bulk charge only recharges the battery bank to an 80% level, the absorption charge completes the charging cycle. Most chargers on the market have a timer that allows the user to adjust the duration for the required time to return the battery to full charge. In order to set the correct time, a simple calculation is required. With the help of the 20 AH capacity, you can figure out the remaining charge required for the battery bank.

As stated previously, the bulk charge brings the bank to an 80% charging level. The remaining 20% of the capacity is a function of time and current. The charger will maintain current level until the bulk set point has been reached, then the charger switches to the absorption timer. The current levels start decreasing as the internal resistance in the battery increases. Assume over the time of the absorption charge that 50% of your maximum charge current will be available (this is factored into the equation). 0.42 = (20%/50%) + 5%. 5% is added due to losses.

Absorption Charge time
Where : T = 0.42 x C /I
T = ABSORPTION CHARGE TIME
C = 20 hr RATED CAPACITY (of the Bank)
I = Charging Current ( 10% of C20 max)
0.42 = ( 20%/50%) + 5% (5% is added due to losses)

Example
2 Banks of 6 V S-530 models
20 hr rate = 400 x (2 strings) = 800 ah
I = 10% of 800ah = 80 amps. If charger is 60 amps max, 60 is used
T = 0.42 x 800/80 = 4.2 hrs OR T = 0.42 x 800/60 = 5.6 hrs

--- End quote ---

This would mean that these batteries require a considerable time to absorb properly.
The S-4000 series are a strange breed i think. For example, after a charge, they fall down to 12.5V-12.4V very fast under load, but they stays there for a long time...

bob golding:
to add to the somewhat unusual charging characteristics they also seem to have a lower SG than most batteries as well. i just  make sure they are topped up with water and  test the SG occasionally never seems to get to fully charged state on a normal hydrometer. as long as they are all around the same SG they seem to be happy. well mine are anyway. i give them a  good charge from the genny every month or so. just to be safe.

sorry forgot to ask can you post some more details of your PI project. haven't played with one yet but have friends who have.

Simen:

--- Quote from: bob golding on April 06, 2013, 10:38:28 AM ---sorry forgot to ask can you post some more details of your PI project. haven't played with one yet but have friends who have.

--- End quote ---

What do you want to know? About the Pi itself, or the communication part?

Spec etc. about the Pi can be found on the raspberrypi.org site. All one needs to get it going are the Pi itself and a usb-cable for powering the device, and a 2GB SD-card (or larger). If one want to use it as a standard Linux machine, the os offered at the Pi site works well, and have good support for programming in Python. There are also specific MediaPlayer os available, for example XBMC, which makes the Pi able to play full hd films etc.

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