Would this DIY surge protector work to protect MPPT charger?

[fmeili1]

Series diode has to be present in boost converter MPPT. Unless it's a design that steps solar down to 48V battery voltage first.

Ok, so I will design the PCB with just one schottky diode on the PV- side.

 

[AntronX]

Ok I thought it was split phase inverter that runs on up to 500V DC bus. It looks like PV- will have -250V square wave with potential peaks into -400V from ringing. Would really have to measure it with a scope to be sure. You may be able to use lower voltage MOVs for better protection.

 

[fmeili1]

Ok I thought it was split phase inverter that runs on up to 500V DC bus. It looks like PV- will have -250V square wave with potential peaks into -400V from ringing. Would really have to measure it with a scope to be sure. You may be able to use lower voltage MOVs for better protection.

Ok, thanks for clarification. I'll try to check with a scope. I'll take a while to get a scope. Will keep you updated.

 

[fmeili1]

I like PCB idea. Just make sure diodes point in correct direction and place them on a heatsink. I am not sure if diodes will offer protection the way I imagine. I need to think about it more.

Just double checked the forward voltage of high current schottky diodes vs standard diodes. I'm a bit confused, but it looks like that at higher current (at about 15A), a schottky diode has a higher forward voltage (between 2-3V) compared to standard diodes (about 1.2-1.5V)?! Only at low current, the forward voltage of schottky diodes seems to be lower.

So for the design, a standard diode seems to be the better choice to reduce losses. For further reading I will post updates on the other thread which will cover surge protection, arc fault detection and ground fault protection for PV.

 

[efficientPV]

Why would you want to use a Schottky diode.

 

[fmeili1]

Why would you want to use a Schottky diode.

I thought I remembered that Schottky diodes has less forward voltages (beside higher speed) compared to standard diodes (e.g. 0.2V-03V instead of 0.7V). To reduce power loss and implement easier cooling, this was my first idea. But I've found, that the lower forward voltages of Schottky diodes are only true for low current in the mA range. At higher current like 10-20A, it's vice versa and the standard diode has lower forward voltage (2-3V compared to 1.2-1.5V).

 

[efficientPV]

Schottky diodes typically have low forward voltages up to about 40V rated inverse voltage. Forward voltage is also lower when they run a bit toasty.

 

[fmeili1]

Schottky diodes typically have low forward voltages up to about 40V rated inverse voltage. Forward voltage is also lower when they run a bit toasty.

I only found view Schottky diodes with a high DC blocking voltage Vdc between 500V-600V. And these high voltage types have a lot higher forward voltage compared to low voltage Schottky diodes (at about the same current between 10A-20A). It looks like for PV switching the Schottky diodes are not ideal because of the high string voltage requirement. So I think, in this case classic diodes makes more sense and they are cheaper.

 

[fmeili1]

I like PCB idea.

Just want to let you know that I've done some further design of the PCB idea... see the corresponding thread.