I’ve picked up threee Voltaic Systems V15 battery packs to build stationary relay node power systems with in recent weeks. The Always On feature is wonderfully handy for keeping things alive overnight when the sun goes down, leaving the node’s solar panels in the dark.
The V15 hooked up to the goTenna Mesh indicates that it charges for a period of time, then quits for a considerable period before charging again as the GTM draws down its internal battery.
I also have a number of other Chinese-made battery packs I’ve also experimented with. One that I recently purchased featured a “unplug the charge button” button. Just guessing here, but it does lead to what appears to be Always On mode. Left a GTM powered by it on it and it ran for 3.5 days. Not bad, consudering it cost $15. It’s labeled as 20000 mAh, but was sold as 8000 mAh, which makes more sense as that is close to the actual time it ran compared to similar use by the V15.
While plugged into the GTM, the LED indicating GTM charging would come on and go off frequently compared to the way that the Voltaic V15 handled things.
What I’m wondering is does this difference in the charging protocol make any difference in battery life for the goTenna Mesh?
Rahul,
It’s not the size of the battery pack, but the way it handles charging. The V15 obviously is a more patient creature, [I assume] letting the voltage of the goTenna drop a ways before kicking in and charging continuously for some time before going back to it idle state of monitoring the charge of the battery in order to eventually start the next cycle. I haven’t made notes, but it seems the charge level goes to the low 90%s before the charging starts.
My [perhaps somewhat mislabeled/mistranslated] generic battery pack is way more OCD. Every time I turn around, it’s got the red charge light lit, but it then quickly shuts down again. Seems to want to keep the charge level as close to 100% as possible. It does work as Always On, but I worry about the thing’s fickle charging behavior.
I fly drones, where there’s always debate about how to best care for your batteries [perhaps too much debate and not enough data on the subject IMO], but was wondering is there is a preferred charge rate/protocol for the goTenna Mesh battery? Even more importantly, is there a charge rate/protocol that would tend to damage or prematurely age the battery?
@bbwr10coqsm goTenna Mesh’s charging circuitry controls when the device starts/stops charging. The charging circuitry, stops charging the device when the onboard battery reaches 100%. It kicks back in when the charge % drops down to ~98%.
That being said, the battery pack must be capable of providing the current goTenna Mesh would require to trickle charge. I feel your generic battery pack is probably capable of providing the low currents needed to trickle charge the onboard battery.
This difference in battery packs should not affect the life of the onboard battery. goTenna Mesh uses a Lithium ion battery - so it does not suffer from any memory effects either.
Rahul,
Thanks, that’s reassuring that the GTM is engineered to be happy either way. There was such a dramatic difference in charging behavior I needed to ask. I’m waiting on an adapter now to hook up a solar panel to the same battery pack to verify the behavior of its own charging cycle.
Am I the only one here that has considered replacing the Gotennas battery with a much larger one? It seems like it might be more efficient then an external battery. My main concern is how the charging circuitry would handle it. We don’t want to start a fire.
I could see that, but for me the tiny package size and ~24 hour runtime as currently is sufficient for general portable user needs. The Voltaic V15 is a nice compact outboard power supply in a size that’s around that of a pack of cards or ciggies if I need to supplement portable power in a pocket-size package.
Where I’m running into battery issues is with the winter sun or lack of here in the often cloudy Midwest. I’m certain the V15 would be fine during the summer, but I suspect that the relative lack of solar input and the cold tend to suggest the need for greater capacity in stand-alone node design around here.
Bigger solar panels and/or bigger battery packs come at a cost that adds up quickly if you’re doing multiple nodes. I’m not sure bigger battery packs are entirely the answer here (the much-anticipated firmware update that allows recovery after power loss to the previous state will be the real game changer), but a modest increase in capacity powered by the same solar panel (I’ve concluded the Voltaic 2 watt panel is too small, so have moved on to their 3.5 watt) would be helpful if I can get the cost to be less of a factor.
There is an interesting design that was tested emulating the position of plants leaves that might work well. It consists of many small panels each angled differently so one always caught maximum sunlight. In a small setup actually tracking the sun isn’t always feasible so it may be a good alternative.
For rooftop use in a fixed position, I’m thinking that a formula might be something like this. Figure what a generally ballpark demand would be, buy x2 for that, then angle one somewhat towards the east and the second similarly biased towards the west.
The more experience I get with solar, the more I think you just need to anticipate buying more capacity than needed on paper, because conditions in the field are almost never close to what is needed to produce the rated output. That extra capacity cushion goes a long way towards ensuring reliability.
adafruit has a few different LiPo charging systems. including a solar powered board. That bypasses the external battery when external power applied. I have been testing the solar board. It has been working for a couple weeks, even through the cloudy & stormy (4) days. Electronic goldmine has surplus solar panels that I am using plus a Linear regulator [5 v]