Switching between mains and solar charging

[PaulRainbow]

I have 120w of solar panels and a 30a Sterling Pro Charge Ultra mains charger, charging 220ah domestic bank and a 110ah engine start battery.

During the Summer the panels almost keep up with my usage. I always check the battery voltages in the evening and if they look a bit low i put the mains charger on for a while.

The solar panels are connected to a Victron MPPT controller that has configurable load terminals. One configuration is for the load terminals to become "live" at Sunset until midnight. I'm thinking of connecting this to a 12v/240v relay and connecting the 240v side of the relay to the output of the switch that is used to switch the charger on/off. The switch is supplied by it's own MCB in the consumer unit and i can use the switch to manually power the mains charger, should i need to.

Pretty sure running the charger until midnight would ensure the batteries would be fully charged (i'd still keep a manual eye on them). The only thing that's on during the night is the fridge.

The reason behind my thinking is that if i leave the mains charger on all of the time, it keeps the batteries fully charged and the solar controller shuts the panel output down, so i'm wasting the solar power.

Any thoughts ? Any reason not to ? A better solution ? Suggestions for a suitable relay ?

 

[William_H]

Yes quite a reasonable approach if indeed you do need more charge during the night than the solar can provide during the day. Relay type should be fairly easy. I have a relay fitted in my power box at home to switch on an irrigation pump 240v 1000w from 24v dc which might be OK on 12v or a 12v version may be available. However your battery charger should not represent a huge challenge to an ordinary relay. (not too tiny) olewill

 

[Lon nan Gruagach]

I have 120w of solar panels and a 30a Sterling Pro Charge Ultra mains charger, charging 220ah domestic bank and a 110ah engine start battery.

During the Summer the panels almost keep up with my usage. I always check the battery voltages in the evening and if they look a bit low i put the mains charger on for a while.

The solar panels are connected to a Victron MPPT controller that has configurable load terminals. One configuration is for the load terminals to become "live" at Sunset until midnight. I'm thinking of connecting this to a 12v/240v relay and connecting the 240v side of the relay to the output of the switch that is used to switch the charger on/off. The switch is supplied by it's own MCB in the consumer unit and i can use the switch to manually power the mains charger, should i need to.

Pretty sure running the charger until midnight would ensure the batteries would be fully charged (i'd still keep a manual eye on them). The only thing that's on during the night is the fridge.

The reason behind my thinking is that if i leave the mains charger on all of the time, it keeps the batteries fully charged and the solar controller shuts the panel output down, so i'm wasting the solar power.

Any thoughts ? Any reason not to ? A better solution ? Suggestions for a suitable relay ?

A very elegant solution.
This: http://cpc.farnell.com/omron-electronic-components/g2r-2-12dc/relay-pcb-dpco-12vdc/dp/SW03308 will do the job.

One word of warning though. Best to label all equipment after the relay, indicating that the circuit may automatically become live and that the circuit before the relay should be isolated before maintenance is carried out. Not for your sake on a good or average day, you wouldnt need to be reminded, but for those times when its all going pear shaped or someone else is fiddling with your boat (the cheek of it!)

 

[BabaYaga]

Depending on the latitude and season, the time between sundown and midnight might be a bit short for the mains charger to fully charge the batteries. So my only suggestion would be to occasionally (every fortnight or so) let the charger run through the night to give them a healthy top up.

 

[rogerthebodger]

I have 120w of solar panels and a 30a Sterling Pro Charge Ultra mains charger, charging 220ah domestic bank and a 110ah engine start battery.

During the Summer the panels almost keep up with my usage. I always check the battery voltages in the evening and if they look a bit low i put the mains charger on for a while.

The solar panels are connected to a Victron MPPT controller that has configurable load terminals. One configuration is for the load terminals to become "live" at Sunset until midnight. I'm thinking of connecting this to a 12v/240v relay and connecting the 240v side of the relay to the output of the switch that is used to switch the charger on/off. The switch is supplied by it's own MCB in the consumer unit and i can use the switch to manually power the mains charger, should i need to.

Pretty sure running the charger until midnight would ensure the batteries would be fully charged (i'd still keep a manual eye on them). The only thing that's on during the night is the fridge.

The reason behind my thinking is that if i leave the mains charger on all of the time, it keeps the batteries fully charged and the solar controller shuts the panel output down, so i'm wasting the solar power.

Any thoughts ? Any reason not to ? A better solution ? Suggestions for a suitable relay ?

I have a similar issue but not as bad as the UK.

When we have several days of overcast weather the battery voltage goes down to maybe 12.3 volts so a voltage controlled relay that will switch the battery charger on when the voltage drops below your minimum and switches the battery charger off when the battery voltage reaches what ever voltage you wish.

You could also use the current output of the solar panels to do something similar.

You could also include a timer to switch the battery charger off after being on charge for a set period of time.

We have at home some lights that switch on at dusk and off a set number of hours later which is more like some one being home that day night light sensors.

 

[PaulRainbow]

Depending on the latitude and season, the time between sundown and midnight might be a bit short for the mains charger to fully charge the batteries. So my only suggestion would be to occasionally (every fortnight or so) let the charger run through the night to give them a healthy top up.

I'll keep an eye on this. I was thinking it might be OK as the shorter nights would indeed mean the charger was on for a shorter time, but those same days would also feature longer periods of Sun, unless of course it's overcast. I also have the option of setting the "load" output to switch from Sunset to Sunrise, if it turns out that Sunset to midnight isn't enough.

 

[PaulRainbow]

I have a similar issue but not as bad as the UK.

When we have several days of overcast weather the battery voltage goes down to maybe 12.3 volts so a voltage controlled relay that will switch the battery charger on when the voltage drops below your minimum and switches the battery charger off when the battery voltage reaches what ever voltage you wish.

You could also use the current output of the solar panels to do something similar.

You could also include a timer to switch the battery charger off after being on charge for a set period of time.

We have at home some lights that switch on at dusk and off a set number of hours later which is more like some one being home that day night light sensors.

The solar controller has a set of "load" terminals Roger. Basically they just react when the panels stop putting a charge out. I can configure this to various options, such as passing a current at Sunset and stopping the current at midnight or at sunrise. The charger is a sophisticated smart charger, so once the batteries are charged it will just sit at float and run the fridge during the night.

 

[PaulRainbow]

Yes quite a reasonable approach if indeed you do need more charge during the night than the solar can provide during the day. Relay type should be fairly easy. I have a relay fitted in my power box at home to switch on an irrigation pump 240v 1000w from 24v dc which might be OK on 12v or a 12v version may be available. However your battery charger should not represent a huge challenge to an ordinary relay. (not too tiny) olewill

Thanks Will, it's only fused at 7a, so won't need anything too industrial.

 

[PaulRainbow]

A very elegant solution.
This: http://cpc.farnell.com/omron-electronic-components/g2r-2-12dc/relay-pcb-dpco-12vdc/dp/SW03308 will do the job.

One word of warning though. Best to label all equipment after the relay, indicating that the circuit may automatically become live and that the circuit before the relay should be isolated before maintenance is carried out. Not for your sake on a good or average day, you wouldnt need to be reminded, but for those times when its all going pear shaped or someone else is fiddling with your boat (the cheek of it!)

Thanks Dougal. That's made me rethink a little. I have space in the consumer panel, so i can fit a DIN rail relay in there.

240v will be to MCB > relay > charger (all contained within the consumer unit.

12v will use the existing switch (currently switching the 240v supply). From solar controller load output > switch output > relay with a fused 12v supply to the switch input for manual override.

 

[ex-Gladys]

Nothing to do with the technology Paul, but one of the issues I find when visiting Shotley is you lose out on a lot of evening solar charge because of the shading from the South due to the hill...

 

[PaulRainbow]

Nothing to do with the technology Paul, but one of the issues I find when visiting Shotley is you lose out on a lot of evening solar charge because of the shading from the South due to the hill...

Yes, along with the TV and radio signals.