As part of the Mesh Helper Device Prototyping process we are exploring various options for running these devices off of a solar power system.
We are considering various options for this, from higher-cost and hopefully low-hassle solutions down to cheap and cheery ebay sourced equivalents.
Here is what we are trying:
For all tests we are using 12v 10AH LiFePO4 battery packs. These are similar in power density to LiPo / LiIon battery packs, but are “intrinsically safe”, in that they are not prone to catastrophic failure if dropped or pierced. We see this as important for disaster/developing/rural-remote use. The trade-off is increased weight and about 20% lower energy density. We will weigh the units when they arrive. The products we have sourced are:
We chose optimum on the basis that they apparently provide battery packs for a lot of electric vehicles, and seem to have made a stable and useful product.
We opted for batteries with separate charge and discharge leads. They come with a battery protection circuit that seems to provide over charge protection as well as discharge protection. They were very helpful answering all our questions. Now we await the arrival of the batteries themselves to see if they are as good as they appear to be.
We chose 4 cell 12v packs largely out of habit. This actually made things a little trickier than they had to be, because it meant that we needed an up/down converter for charging from a 12v source (like a car accessory outlet).
The Dragino can run on 9v, so a 3 cell battery pack would have worked. In that case a down-only DC/DC converter would have sufficed, and been somewhat cheaper and simpler. We will probably do that next time. But as things stand, all that we describe here should work with sealed lead acid and similar more “conventional” batteries than the LiFePO4 packs.
To keep life simple, we ordered a 40W panel from RedArc, from whom we also ordered one of our solar systems. The idea here was that, although not cheapest, we have reasonable expectation of the RedArc components all working together, and that we can complain if it doesn't work. RedArc are a local company, and one of their ex-employees works in our department, and even designed some of the components we have ordered from them.
As mentioned above, we needed an up/down converter. I will put the part number and estimated cost in here soon.
Here we opted for a Maximum Power Point tracking regulator that could easily handle our 40W panel, and would be compatible with the LiFePO4. There is some residual uncertainty about the compatibility, as while Optimum were very helpful, their english documentation is not entirely unambiguous.
We are still researching options here, and will probably try a few combinations.
We will probably try:
They are only AUD$10.49, and claim to be CE mark approved, unlike most of the others we have seen on ebay. Not yet clear if they are Maximum Power Point Tracking or not.
We will probably try this one:
Aside from the strange comments about blood pressure in the description, it seems to be a good solution.
The RedArc solar regulator did not come with any leads, so we needed a pair of standard solar high-voltage PV leads. Cheapest source we could find was to got to Jaycar Electronics and buy a Duratech solar Y-adapter cable for AUD$19.95 to chop up to obtain a male and female connector. You can buy the connectors bare with no lead for AUD$12.95 each at Jaycar, so not only was the combined cable a cheaper source of connectors, it gives us the short length of lead we need for each connector.
Yet to be obtained, but the DC/DC converter comes with no leads, so we will need to supply this as well. These are also available from Jaycar electronics for a few dollars.
We will likely use clear plastic lunch box/storage containers from the supermarket here. More on this when we have settled on one.