Electrodacus with 1.8kWh PV and 2.4kWh battery with water heating diversion

sidkdbl07

New Member
Here is the first iteration of my concept for solar and water heating (i.e. component and wiring diagram). I am posting it here to get constructive comments and a bit of help selecting a water heating element.

Note: red lines typically connect positives, and negative lines typically connect negative leads

I am considering the following components:
- Battery Cells: Fortune 3.2v 100Ah LiFePO4 6C
- BMS: Electrodacus SBMS0
- PV Panels: Yingli 315W 60 CELL YL-315D-30B
- PV Charge Controllers: Electrodacus DSSR20 with DEXT16 (diversion model)
- Battery Protect: Victron BP-220
- Inverter: Cotek SP4000-124

Items I need help selecting:
- Water heating resistors (heat)

Any constructive comments are welcome.

electrodacus v1.0.png
 

sidkdbl07

New Member
You probably need more than three heating elements. Check into 3 phase 380V heating elements.
I figure I'll be running something in the neighborhood of 10G tank (this will be an RV setup). The nice things about the Electrodaccus setup is that it is fairly scalable, so I can add PV panels two at a time.
 

sidkdbl07

New Member
This thermometer is 24v and seems to have approximately 19mA / 50mA (456mW / 1.2W) consumption when the relay is open / closed respectively.

I would need one thermometer for each heater (not ideal). I also saw some talk about swapping out the relay with an optoisolator in order to decrease the consumption. This seems a bit over my head, but maybe someone has a link to how to do this.
 
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BiduleOhm

Electronics Sorcerer

efficientPV

Solar Addict
You can interrupt the common lead that powers all the solid state relays to control temp. Those three phase heater elements will fit a US water heater ports. Only thing in question is will the length fit. What voltage are you using?
 

sidkdbl07

New Member
The SBMS0 can't act as a thermostat?
This is quite a point of contention for most. The SBMS0 does not have a low-temperature cut-off (no thermometer). In any case, I would be using the temperature reading in a different way. I need to measure the temperature of the water and set a high-temperature cuttoff.
 

sidkdbl07

New Member
You can interrupt the common lead that powers all the solid state relays to control temp. Those three phase heater elements will fit a US water heater ports. Only thing in question is will the length fit. What voltage are you using?
I intend to have a 24v battery system (8s3p). I will have a 24>12 converter (as shown), so that is an option too. The panels have Vmpp of 33.3v, and Impp of 9.46A as per the documentation. Remember that I have 2 panels in parallel for every DSSR20, so the effective I will be 18.92A. I was thinking of using a 36V 1200W (2 parallel 600W elements). I would need to connect 2 DSSR20 to each element if I went this route (I think) and so I would need to add two solar panels and a DSSR20 to the schema above: that would afford me 2 elements (8 panels and 4 DSSR20).
Heating element: 36v 1200W Healing Element
 

sidkdbl07

New Member
Well I can't seem to find a low power thermostat, so I think I will go the DIY route. I will likely use a raspberry pi (since I'm using this anyway to log the Electrodacus data). This way I can use a one-wire DS18B20 and 4 generic 5v relays. I may include an LCD that I can turn on and off to get a view of the temperature.
 

sidkdbl07

New Member
Here's the latest diagram.
- I added an Automatic Transfer Unit for connecting to shore power.
- I increased the fuse in front of the inverter to 200A
- I added a 4th PV panel
- I added my controls for the water heating setup

electrodacus v1.0.png
 
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Dzl

A Danger to Himself and Others
This is quite a point of contention for most. The SBMS0 does not have a low-temperature cut-off (no thermometer). In any case, I would be using the temperature reading in a different way. I need to measure the temperature of the water and set a high-temperature cuttoff.
As I understand it, the SBMS0 does have low temperature protection, and the manual has a short section on this and recommends a particular external sensor:
5 Battery Temperature
It is possible to add external temperature sensor but in most cases not needed and so is optional.
All Lithium batteries require temperature above freezing (> +5°C) during charging otherwise they will be damaged.
Best way when possible is to have the battery inside the living space were temperature is ideal for battery operation.
The SBMS is designed to accept a thermistor as temperature sensor connected between pin 3 (XT1-) and 4 (XT1+) of the 8 pin connector
The SBMS is calibrated for a particular 10kΩ thermistor made by Murata NCP21XV103J03RA (this same thermistor type is used internally to measure the power board temperature) but a common 10kΩ NTC with B25/50 = 3900 to 3950 will work great.
The low and high temperature limits for this external temperature sensor can be set from the Advanced Parameter Setting submenu parameter 29 and 30.
I believe the issue though, is that charging and discharging cannot be controlled separately, so a low temperature disconnect of 0*C or 5*C would apply to both charging (desired) and discharging (probably undesirable). This is unideal but not a huge deal for most people.
Dacian's perspective is that low temp disconnect is not an optimal solution to a problem. In his eyes, (1) avoiding freezing temperatures (2) insulating the battery box (3) heating the battery compartment, are better solutions (roughly in that order). Setting that aside, it would still be better and more flexible to be able to have separate temperature limits for charging and discharging.

relevant convo here
 
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