Wolfnexus - Random Stuff
Solar powering a Raspberry Pi for Bitcoin mining - Part 5
Like this page? Donate with the QR code below!
Introduction:
So it has been a few months since I brought the solar powered Bitcoin mining setup online on a more permanent basis. In this time I've learnt quite a bit, and my key findings are below.
Finding 1 - Panels:
Adding the second 90w panel has made a huge difference to how well the system performs. Since coming into Spring, daylight hours have gotten longer (and hotter) and I've found the charge controller reporting anywhere between 50-60Ah of charge handled in a day, which roughly equates to the usage of a Jalapeno during the day plus replenishing the previous night's drain on the batteries. With a single Jalapeno in the circuit, this is sustainable, so long as the sun keeps shining brightly. Efficiency can definitely be improved if the panels are mounted at the correct angle to the sun and wiring to the charge controller is kept to the right gauge to minimise loss.
Finding 2 - Charge Controller:
The controller I am using has served remarkably well at maintaining the batteries and handling the output from the panels. I am at about 2/3rds of its capacity, so adding another panel will probably mean an expensive upgrade (or a lower wattage panel). Impressively, the controller still barely gets warm, even when handling over 100W!
Finding 3 - Batteries:
This has probably been the area I've learnt the most so far. In a nutshell, it really seems that no matter how many panels you have, you can never have too many batteries. A single cloudy day and even my beefy 100Ah battery would usually discharge to the point where the charge controller would disconnect the load to protect the battery from excessive discharge. More panels could probably fix this, or at least mitigate the poor output on a cloudy day, however that gets expensive very quickly in panels and charge controllers to handle the bright days.
After a few months, it became abundantly clear that even with a best estimate of 152Ah, I would need more batteries, but where to get them? Brand new, a 12V 100Ah battery can go for as much as $3-400, which was well outside any budget I could dedicate to the project (I simply didn't get enough donations!). My only option was to seek out a source of cheap batteries, as I did with the ex-marine 100Ah battery.
Second-hand VRLA AGM (Sealed) batteries can be sourced on many auction sites, such as ebay, craigslist and the like. The danger of course is that you can end up with a mostly dead or dying battery, however the cost savings are substantial! After a bit of hunting, I managed to find a seller who had a large collection of 12V 80Ah batteries from a large UPS setup. These had been removed well before their use-by date due to heat damage from a failed air conditioning system which had caused the electrolyte to be boiled away, however using the same technique as I used previously to resurrect my 26Ah batteries, the seller had managed to recover many of the batteries at close to their design capacity. They were also a much more reasonable price of $80 each, Jackpot!
Lead-Acid batteries are very heavy things, so try to avoid getting them shipped anywhere. Many postal services won't ship them due to being hazardous, and they also stand a good chance of being mistreated during transit (dropped, hit and beaten around, which will damage the plates.) It is easier to transport them yourself from a local seller, and you also get the benefit of being able to inspect and, if lucky, choose which batteries you would like out of a larger selection. All the ones I chose had the cell seals cracked open so I could refill them when necessary with distilled water.
When you get your batteries home, test them and ensure they are fully charged before adding them to your circuit, this way you avoid any unpleasantness from sparks due to voltage differences, or excessive outgassing from large current flows from your charged batteries. Remember, sparks around potentially gassy lead-acid batteries can cause very serious explosions!
I ended up purchasing three more batteries, which has brought the capacity of my system up to a theoretical 392Ah, more than double the previous capacity. This should ensure no more crashes from a single cloudy day.
Finding 4 - The Jalapeno, Raspberry Pi and Wireless Bridge:
The Raspberry Pi is an incredibly solid platform. So far it has never needed to be rebooted due to failures or crashes, and has only ever been rebooted due to power loss. This hasn't even caused data corruptions (I consider myself lucky here). Overall, the Pi has performed well above my expectations, and I'm seriously considering getting some more to mess around with should money be available for me to do so.
The Jalapenos have also been rock solid. Since reflashing them both, they have continued to operate between 7.5 and 8 gigahashes each, so I've simply left them alone rather than trying to upgrade the firmware further. As these are mark 2 Jalapenos with the first version of BFL ASIC in them, I doubt I would get any benefit from the latest versions of firmware that can run engine zero of the second version of the BFL ASICs (the first version had a defect that made engine zero unusable). So far no issues with heat damage or with the fans, although these little beasties do get quite warm after running for a while. There is a reason they sound like small hairdryers! I've also opted to keep them cased up as while airflow is somewhat restricted it does ensure the board and VREGs are kept cooler too.
The wireless bridge has had a few issues since I installed it, for some reason it gets the idea that it should pretend to be a DHCP server, which promptly causes all hell to break loose on my wireless network. Fortunately the occasional reboot usually fixes it. Sadly, the same can't be said for my neighbour, who has set up at least four separate wireless networks, all running on different channels. This makes it virtually impossible to not end up colliding with at least one of their networks and has made coverage a little spotty at times. If you are wondering, the wireless network setup is purely because they don't seem to know how to configure their Apple Airport, two smart TVs and broadband router to all play nicely together on the same SSID. Before you ask, there is zero chance I'll be offering to fix it for them either.
Finding 5 - Weather:
I don't know whether it is pure coincidence or not, but somehow every time I manage to put the Jalapeno back on 100% solar power, the very next day is cloudy or rainy, which pretty much ruins any chance of long term mining. The extra batteries should hopefully fix this, but the troll weather is pretty annoying nonetheless.
Conclusion (for now):
My setup, as it stands now looks very similar to the following...
Having just added the extra batteries, I'm now going to monitor the system and see how well everything performs. A week worth of metrics on generated power and battery voltage should let me know if any further changes will be necessary too. As for ASICs, I'm well aware of the huge rise in difficulty levels. While I have broken even on the Jalapenos, it is starting to feel like time to buy a little more mining equipment. At the moment I'm considering some Bitfury offerings that would play well with the solar setup, even if the hashrate isn't huge.
Keep those donations coming! Every little bit helps!
For Bitcoin donations: 1KPgXmNEmXmC1AtowjzmWgWfTS2QALp96Z
Or for Litecoin donations: LgXkAUTQLBKcU3VGLuEmroxNEFmXiw5TmV