Guru
Joined: 08/02/2015
Location: New ZealandPosts: 1162
| Posted: 10:06am 22 May 2020 |
Well the few more items remaining has expanded some what; after tromping all over my roof armed with a tape measure last week to work out where to put the new PV panels that have now arrived; I'm limited to various series combinations that will fit.
The existing solar thermal hot water panels residing in the center of the roof means the best combinations of PV that will fit are groups of 5 panels in series, so the mppt voltage will be 156v with an upper unloaded value of 192v. Means I need 250v capacitors of which I have none, after re-doing the calculations for the buck converter components I need an input of around 2000 to 3000uf 250v with approx 30 amp ripple rating. The output caps require approx 1500uf with 26 amp ripple.
The previous design needed a few modifications to the pcb to fit the extra components, I have implemented a relay for the PV isolation should that feature be required, or shorted out if not. Added modular plugin pcb's for the double pole analog filters and edge mounted cpu card. The mosfet driver card solders to the pcb pins.
RS sell these 30mm dia 560uf 250v items each with a 5.43 amp ripple rating, so 6 are required for the input.
The output capacitance is better achieved with many smaller items in parallel, These 100uf ones each have a 2amp ripple rating, so 15 in parallel will give me an easy 30 amp and 1500uf. I could have used the bigger 560's but then I would have too much capacitance and the voltage feedback response would be way too slow for stability.
Here is the first cut of the new layout.
Cheers
Mike