Solar Storage System : System testing

Yesterday I finished all the wiring on the control board, the high power DC wiring, AC distribution wiring and sensor and fan control.

The only thing left to do is add the Raspberry PI and it's I/O boards and finish writing the software. I'll start on that next week, I've ordered a case for the R-Pi, ribbon cable and a few plugs and sockets to connect all the boards - annoyingly only two of the I/O boards have a hole to add a mounting post, the largest I/O board (PiFace) doesn't, and the smallest (2 in, 2 out analogue channels) is too small to have one, so I'll have to mount them in their own case and figure out some way of keeping them stable.

So in the meantime I wanted to test the assembled hardware. 9 SSR relays plus associated heatsinks, temp sensors and cooling fans, the three inverters, DC fuseboard, AC fuseboard, AC distribution block, and all the wiring and crimped connections.

I dug out nine nice old chunky switches to control the relays, fitted them to a bit of wood lying around, connected all the wiring up, used my DC PSU to provide the 12V for the relays and fans and, after a final check for short circuits, connected the battery and charger and turned the input mains power on.

I'm happy to say that everything works fine. At least to start with!

All three inverters running consumed about 45A, which is about half of what they should be drawing.

A quick check revealed that the main battery disconnect SSR was dropping about 1V, the 1KW inverter DC SSR was dropping about 0.7V, and the 500W SSRs dropping about 0.5V.

So the 1KW inverter voltage was 1.7V down, and both 500W inverters were 1.5V down. Not ideal, as the inverters are producing about 1KW between them. Without any voltage drop they produce approx 1.5KW. It'll do for now, my typical evening usage is 900W so it will cover that nicely.

The main battery disconnect relay did get nice and toasty, which tested the temp sensor and cooling fan which worked perfectly. Cut in at about 70 degrees C and turned back off at about 60 degrees C.

After running the system for 20 minutes the two smaller inverters turned their cooling fans on at an internal temp of about 45 deg C, and I know that the 1kw inverter cooling fan works when I tested it in isolation.

So, happy that everything was working properly I turned off both inverters, checked the battery charger and it's relays (both good), and was just turning everything off to finish for the evening.

The battery charger was on and charging at it's minimum of 6.6A. I turned the main battery SSR off, and the charger current sat at 6.6A. Uh? What's it charging? The battery is disconnected. Oh no it's not! The SSR has fried itself and short circuited. I was monitoring it's temperature and it only got upto about 80 degrees C, and I have checked the specs of reputable brand SSRs and they are good for 125 degrees C. Just goes to show that if you buy cheap SSRs, you need to derate their maximum current and their maximum temperature by a lot!

Not a big problem, as it was dropping 1V across it I think I will change it for a good old fashioned 300A physical relay. I didn't want any moving parts anywhere (yes, I know, the fans are moving parts!), but to get the system working at maximum output power it's looking like I'll need to change all the DC SSRs for normal relays.

If any readers know of any eBay sellers selling decent 300A relays (and 100A relays too) please do let me know.

Well, it is a prototype system so finding out parts aren't suitable is part of the game! :)

Piccy of the controller board (excuse the mess at the bottom of the board - this is all the controller wiring connected to the switches, this will all be tidied up when the R-Pi and I/O boards are installed)

Components from left to right, top to bottom:-
Top row
* DC current shunt (partially hiding behind the black box)
* DC fuse box (the black box just under the DC current shunt), 250A main fuse, 75A for 1KW inverter, 60A for each of the 500W inverters, 100A for the charger)
* Main battery SSR (fried)
* Charger DC relay
* DC ground distribution block (hey, it's huge I know, it's what I found on EBay and I couldn't be bothered to chop it down :) )
2nd row down
* DC relays for 1KW inverter
* DC relay for 500w inverter #1
* DC relay for 500w inverter #2
3rd row down
* 1kw inverter
* 500w inverter #1
* 500w inverter #2
4th row down (just below the 500w inverters)
* AC relay for 500w inverter #1

* AC relay for 500w inverter #2
* 4 x main fuses for the AC connection for the three inverters and the charger
* Main AC distribution block
5th row down
* Main 240V AC grid connection (almost off picture to bottom left)
* Charger 240V AC connection (almost off picture to bottom left)
* AC relay for 1kw inverter
* AC relay for 2.5kw charger
* Temporary manual switches used to test the other components

Solar Storage Unit starting to come together

I've got all the bits I need at last, and the external case is being built and should be here in a couple of weeks.

All components are being mounted on a spare cupboard door I had lying around which happened to be the ideal size.

Four rubber feet on the bottom of it with the signal and sense wiring to the controller on the underside, and the DC and AC high power connections on top.

All the DC solid state relays are mounted on small heatsinks with their own fan, controlled by a 70 degree C switch mounted on the heatsink.

The past couple of days I've been mounting the heatsinks, fitting the fans and done the positive DC wiring:-

The heatsinks came with one milled flat space for one SSR, but the top right one required two SSRs fitting, so I had to finish fitting a new DC motor to my CNC mill so I could use that to mill the whole of that heatsink flat so it would accept two SSRs. All things that take time!

You can see fitted to each heatsink the little temperature controlled switches, they just look like transistors. Better than the old style thermostat type switches. The fans require 12V 0.25A which these will handle with ease. I will also add a second feed to all the fans, via diodes, so that the controller can turn them all on when the overall temp in the unit case gets too high. The inverters are also getting one of these temp switches each which will feed into the controller to let it know that inverter is too hot. I also have different style temp switches that I'll (try to) fit in between the battery cells. I want to be able to monitor all parts of the system and either not use parts that have failed (or are just too hot) or shut the whole thing down.

Tomorrow I'll finish the negative DC high power wiring and then the controller wiring, and then mount the inverters and finally the AC wiring side.

This board will sit next to the battery in the case, with the charger unit suspended above this board on its own little shelf. I've also got two temperature speed controlled fans which will get mounted in the case, left and right.

I know this project has kind of grown from a few parts that were going to just be assembled on a desk, to something that monitors itself in loads of ways and will shut off if needed, so it can be put in a garage and completely forgotten about by anyone.

I just hope that at the end of it, my solar panels produce enough extra power to charge the battery in a typical day!

Richard