Battery Power Options

Yes, you could attach a 4.5v alkaline battery pack to the LIPO battery connection, but since you never know who might come along later and plug a solar panel into the SOLAR jack, it’s good practice to only connect LIPO batteries to that jack. That’s why I designed a separate 2-pin header (unpopulated) on the Mayfly that’s labeled “Ext 5V” so you can solder a little 2-pin header (preferably polarized) on there and connect an external battery pack that way. I like this particular connector/header combo: http://www.allelectronics.com/item/con-242/2-pin-connector-w/header-.10/1.html

I have a related question. Why should I not plug two LIPO batteries to the battery jacks. Is it because I would risk too much charging current? If I refrain from charging, wouldn’t having two batteries plugged in simply extend operating time?

The charging circuitry on the Mayfly isn’t capable of charging 2 parallel battery packs simultaneously, so it’s not advised to connect two packs to the Mayfly if you ever connect a mucroUSB cable or solar panel to it because either of those will start the charging process.

The second LIPO connector on the Mayfly is for providing a direct connection to the battery for high-current accessories like a GPRSbee module. It’s not supposed to be used to provide a secondary battery input for the Mayfly.

However, if you take precautions to make sure you never connect a microUSB or solar panel, then theoretically it’s possible to connect two parallel batteries to power the Mayfly, but you run into the usual issues related to parallel battery operation, like making sure both batteries have identical capacity and are charged to the same initial voltage, along with other precautions. Given the dangers of short-circuiting LIPO batteries and causing a fire, EnviroDIY does not recommend that users connect more than one battery to their Mayfly at a time.

Also, if you connected 2 LIPO batteries at once, you can’t use the onboard LIPO charging circuitry on the Mayfly, so there’s no benefit to using LIPO batteries and you might as well just use a single high-capacity battery pack of a different chemistry (like lead acid or alkaline) if you’re looking for longer lifespan.

Thanks, I’ll avoid plugging in two LIPO batteries.

I’m planning to replace some existing datalogging equipment with the Mayfly and keep some of the existing power equipment.

Today I have several stations each with Campbell Scientific dataloggers & sensors, standalone modems, solar panels, lead-acid batteries and charging circuits. The equipment is all 12v based. My desire is to pull out the dataloggers and modems and replace them with Mayflies + Digi modem modules. I have all the software working which includes interfacing the CS pressure transducers and cellular communications.

The question is: can I use/keep the existing power (12v 8aH battery, 24v solar panel and charging circuit) and how should I connect to the Mayfly? Also – do I need a LiPo battery to supply the modem?

Thanks for any ideas/help. – Cal

Depending on the version of the Mayfly you have, there’s a 12V power input that you can step down and use. If I remember correctly, though, @aufdenkampe once told me he’d had smoother power and less loss using a separate 12V to USB step down and powering the Mayfly via the USB port.

Unfortunately, though, with either option you would still need a LiPo to supply the modem. The Digi cellular modems require more amperage than the Mayfly can provide on its own so the only option is to power them directly off the battery by way of SJ13. If you don’t have a battery plugged into one of the Mayfly’s battery jacks, the modem wouldn’t be powered at all.

Thanks Sara. I think a cheap 12v to 5v phone charger will work well for me then.
As for the LiPo battery – I will use a small one. Our transmissions are short and the LiPo will be recharged from the lead-acid battery.

I have the V0.5b version of the Mayfly – so I could use the 12v input. But I’m a little worried though that the voltage may spike above 14v during sunny days. Do you think that would be a problem?

I have a small disagreement with your last comment: “the modem wouldn’t be powered at all”. I often run my Mayfly + Digi modem WITHOUT a battery! It works (most of the time) so it does get power from my USB source – but I know it’s on the edge. I have the SJ13 soldered.

Cal

Oops, yes, sorry, the modem would have power without the battery, just not enough. The naked u-blox SARA R410 cellular chip uses just barely under half an amp at peak. (Assuming you’re using the LTE model.) Add the Digi processor and it’s too much. I’ve never had any luck getting it to connect without a battery. It browns out and stops responding. Often it needs to be completely powered off (or yanked from the board) before it will be happy again.

I think @acgold might have gotten the Sodaq SARA R410 uBee working with the Mayfly without the solder jumper: https://github.com/EnviroDIY/ModularSensors/issues/228

Hopefully @aufdenkampe will confirm but I think he went the USB route mainly to avoid power losses in the step down. If you go that way you probably need a relatively expensive 12V to USB to make sure you are getting less loss than the built in step down.

Next week I’m deploying several units – Mayfly with XBee using Hologram SIM, logging data from CS451 SDI-12 pressure transducers. They are replacing old 12v systems with Microhard 3G modems and CR300 Dataloggers. The old modems are power hungry and unreliable. The AT&T service is expensive and 3G will go away eventually. The dataloggers have trouble switching power to the modems and their solar charging circuit is unreliable. So I’m getting more reliability at a FAR lower equipment cost and monthly charge while using the existing sensors, enclosures & power (solar/12v batteries). I’m also getting more flexibility since I own the Mayfly sketch and the Internet server code.

I’d like to confirm a few things I think I know before connecting the power of Mayfly v0.5b:
1. the Ext 12v input will NOT charge a connected Lipo battery.
2. the voltage on the solar JST must be <= 6v, not the 20v-1a that’s listed on the LIPO CHARGER section of the hardware diagram
3. best option is to use a 12-5v USB charger (that Shannon has suggested in other posts) to power the Mayfly and charge the Lipo.

Thanks, Cal

I have a really similar issue (12V powered sensor + SPI-12) that I would appreciate some advice on. We want to monitor solar radiation (shortwave) under forest canopy, for which common silicon diode pyranometers (e.g. Apogee SP212) are not suitable – a thermopile pyranometer is needed. We have two options for thermopile pyranometers. 1) Apogee SP510. Self powered, output range 0-144mV. 2) Campbell Sci CS320. 6-24V excitation, SPI-12 output. We will not be using the optional 12V heater on either of these. Both sensors are actually manufactured by Apogee. I saw in another comment that the millivolt SP510 signal will be noisy with the Mayfly (an amplified version of SP510 is not available). We are working in a low light environment, so noise will be an issue. Thus, I was leaning toward the CS320 due to the SPI-12 output (hence zero logger/cable noise). But the CS320 has the same power issue as the CS451 pressure sensor mentioned above. Which would you suggest for the mayfly? Is it better to tackle the noise/signal amplification issue or the power issue?

Also, just want to say thanks for all the awesome work going on here – super exciting initiative for ecological monitoring!

Thanks, Shannon, for your response, clarifications and tremendous work with the Mayfly. Addressing your questions:

I’m powering the CS451 with the same 12v battery that powers the Mayfly from the 12-5v USB converter. The ground (-) of the Mayfly & battery are common. I could not find anywhere in the Campbell Sci specs the voltage level for the signal. But I did find in the SDI-12 Serial-Digital Interface Standard (SDI-12 Support Group, Utah) that the standard for the signal is essentially 0-5v. So, I plugged the signal line in Digital Pin #7 and it’s been working fine. If I had an oscilloscope I could confirm the voltages.

Cal

My stations as described above have been working fine for 3 years in the field.  I’ve had a few components fail (12-5v buck converter, XBee daughter card, resistor divider) but otherwise very stable.

However, one Mayfly (0.5b) seems to be performing fine with 2 exceptions:

• the red LED3 is either solid ON or dim
• the ADC that records the 12v battery voltage across a resistor divider is a bit flaky

Is this a problem?  I can’t understand from the logic diagrams what would turn on/off red LED3.

For anyone reading this in 2022, the posts above in this thread are from 2016 to 2019, and the operating voltage and other electrical specification have changed with the Mayfly boards released in the past year.  The older Mayfly v0.5 boards had completely different input voltage limits compared to the new Mayfly v1.0 and v1.1 boards.  So the advice above about connecting 12v batteries directly to the Mayfly is not applicable to the new boards.

For v0.5b, LED3 should only be on if the mosfet transistor on the Mayfly is turned on, which should only happen if you set pin D22 to high in order to turn on the switched sensor output power circuit.  If yours is on all the time, or partway, then either that mosfet is electrically damaged, or there’s something wrong with another part of the board.  Since you’re saying the onboard ADC is not always right, then my guess is that you’ve got a tiny bit of corrosion somewhere on the board (probably around the main processor chip in the center) that’s causing noisy input to the analog ADC input pin, and also causing D22 to appear high, triggering the mosfet.  Has your board been subjected to high humidity and/or condensation?  Or ants?  We had a station start malfunctioning after a few tiny ants made their home in the logger box and laid some eggs on the circuit board, resulting in corrosion and failure of the Mayfly after just a few days.

And if you’re still using a Digi LTE module with EnviroDIY LTEBee adapter, that could be contributing to the odd behavior as we saw lots of random failures of those due to a still-unresolved issue with the Digi boards, which is why we stopped using those cell modules and designed our own.  Have you tried removing all sensors, the solar panel, any external power sources, and the cell board and just operate the station with nothing attached but a lipo battery and/or a USB cable to see if it operates normally and records data to a card?

Shannon – thanks for your thoughtful reply.  I’m sure I’ll be able to find the problem now.  Answering your questions:

1. I’m not switching D22 on.
2. Humidity is a possibility. I’ll look for corrosion and add desiccant .
3. I’ve had ants at another location but not this one…yet.
4. I’ll make some tests as you suggest to isolate the problem.  It might be easiest to just replace the Mayfly/modem as this station is far from my home.  Then I can test the original equipment at home.

I do have a Digi modem and adapter card at all my locations.  I plan to, but won’t be able to convert to new Mayfly and LTE BEE for another year as it will require substantial desk work – a winter job.