Okay I am embarking on a mission and want to share my work + Code in case someone else might benefit. also any suggestions or thoughts along the way are appreciated. (not sure if this is the correct place for me to post but it is my best guess)
This is a more matured thought from an earlier post I made here: https://diysolarforum.com/threads/d...tery-cheap-simple-mostly-off-the-shelf.70339/
Goal: - Fully automatic, continuously adjustable, high power AC battery charger which captures excess solar energy.
- Does not require any house/ mains voltage wiring what might require electrical certification.
- 12v, 24v, 48v compatible
- 2000W to 4000W capability
My reason: Home in the UK, 2.8KW grid tied setup on the roof. this was installed with a subsidy so I cant interfere with it. I want to expand the solar and add a battery. I can not connect any more inverters to the mains as that will take me over the 3.9KW limit and require planning permission. My DNO would only let me do that through an approved installer which would cost three times as much. This makes islanding the house and recapturing the grid tied power with a diverter, awfully tempting. However there are no AC 48V battery chargers out there that have this intelligence. AC coupled inverters do, but that brings me back to the planning permission, also I am an electrical engineer and although my day job is working on micro-grids I do not have electrical certification so technically cant so much as tickle a breaker
proposed solution:
(1) PV inverter CT clamp type £17
(2) House CT clamp type £17
(3) Arduino or other MCU. Running the PID control library ~£10
(4) Adjustable SwitchModePowersupply (SMPS) MZMW S-4000 AliExpress, £300
(5) Solid State Relay 4-32VDC - <280VAC RS Stock No: 903-2977 £24
(6) Battery CT clamp type (make sure no current flows back) £17
(7) Keenso SSR-100DD 3-32VDC £16
(8) Voltage sensitive relay DVRD-48, saftey measure to stop overvoltage £30
(9) Battery, 280Ah prismatic cells 16s DIY with Gobel or JK BMS-14-15KWh £1600
(10) 2.9KW PV with Fronius IG inverter (already exists, DC coupled solar will be added)
(11) Connect to circuit with >4000W breaker. might limit power to~2KW so normal wall socket would suffice
(12) Standard UK house grid connection, 60A
Rough costimate: £450
(ignoring battery)
Signals
(1) 0-5V control signal generated using PID library in arduino CT1 - CT2 = 0 setpoint
(2) enable signal to only turn on SMPS when there is worthwhile power being wasted to grid, say ~50W
(3) enable signal for DC battery output. can disable connection to battery if current begins to flow backwards or goes bellow a threshold when SMPS enters CV mode. this is unecessary if this charger is the only charger connected to battery but in future there will be some DC coupled solar and I am concerned if the absorbtion voltage setpoint is highter than the max voltage setpoint of SMPS, it could force current backwards. there are current blocking circuits, RCPs, that can be bought out of the box but they are expensive ~£200, alternative is mosfet and comparitor DIY circuit as described in https://www.ti.com/lit/an/snoa971/snoa971.pdf but I would rarther avoid the faff and want to keep this as out the box as possible.
There are details I have missed such as signal conditioning to turn Arduino outputs 0-3.3V PWM into true 0-5V analog but the psudo detail is all there
Any thoughts?
At this point i think my main concern is the potential interaction with other chargers such as a MPPT. I may yet implament a current blocking circuit and accept the lost Watts.
This is a more matured thought from an earlier post I made here: https://diysolarforum.com/threads/d...tery-cheap-simple-mostly-off-the-shelf.70339/
Goal: - Fully automatic, continuously adjustable, high power AC battery charger which captures excess solar energy.
- Does not require any house/ mains voltage wiring what might require electrical certification.
- 12v, 24v, 48v compatible
- 2000W to 4000W capability
My reason: Home in the UK, 2.8KW grid tied setup on the roof. this was installed with a subsidy so I cant interfere with it. I want to expand the solar and add a battery. I can not connect any more inverters to the mains as that will take me over the 3.9KW limit and require planning permission. My DNO would only let me do that through an approved installer which would cost three times as much. This makes islanding the house and recapturing the grid tied power with a diverter, awfully tempting. However there are no AC 48V battery chargers out there that have this intelligence. AC coupled inverters do, but that brings me back to the planning permission, also I am an electrical engineer and although my day job is working on micro-grids I do not have electrical certification so technically cant so much as tickle a breaker
proposed solution:
(1) PV inverter CT clamp type £17
(2) House CT clamp type £17
(3) Arduino or other MCU. Running the PID control library ~£10
(4) Adjustable SwitchModePowersupply (SMPS) MZMW S-4000 AliExpress, £300
(5) Solid State Relay 4-32VDC - <280VAC RS Stock No: 903-2977 £24
(6) Battery CT clamp type (make sure no current flows back) £17
(7) Keenso SSR-100DD 3-32VDC £16
(8) Voltage sensitive relay DVRD-48, saftey measure to stop overvoltage £30
(9) Battery, 280Ah prismatic cells 16s DIY with Gobel or JK BMS-14-15KWh £1600
(10) 2.9KW PV with Fronius IG inverter (already exists, DC coupled solar will be added)
(11) Connect to circuit with >4000W breaker. might limit power to~2KW so normal wall socket would suffice
(12) Standard UK house grid connection, 60A
Rough costimate: £450
(ignoring battery)
Signals
(1) 0-5V control signal generated using PID library in arduino CT1 - CT2 = 0 setpoint
(2) enable signal to only turn on SMPS when there is worthwhile power being wasted to grid, say ~50W
(3) enable signal for DC battery output. can disable connection to battery if current begins to flow backwards or goes bellow a threshold when SMPS enters CV mode. this is unecessary if this charger is the only charger connected to battery but in future there will be some DC coupled solar and I am concerned if the absorbtion voltage setpoint is highter than the max voltage setpoint of SMPS, it could force current backwards. there are current blocking circuits, RCPs, that can be bought out of the box but they are expensive ~£200, alternative is mosfet and comparitor DIY circuit as described in https://www.ti.com/lit/an/snoa971/snoa971.pdf but I would rarther avoid the faff and want to keep this as out the box as possible.
There are details I have missed such as signal conditioning to turn Arduino outputs 0-3.3V PWM into true 0-5V analog but the psudo detail is all there
Any thoughts?
At this point i think my main concern is the potential interaction with other chargers such as a MPPT. I may yet implament a current blocking circuit and accept the lost Watts.