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Forum Index : Microcontroller and PC projects : How do you power Micromites?
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lew247 Guru  Joined: 23/12/2015 Location: United KingdomPosts: 1702 |
Some of you have remote mounted or externally mounted Micromites How do you power them? I am looking for ways to power my weather station when I mount the outdoor unit but I can't find any way to do it reliably I've been using 18650 3.7V 3A (3000mAh) batteries and with 4 of them in parallell (12 amps) this will power it for around a month I was hoping to use solar charging to recharge the batteries, and while during the summer months it did charge the batteries a bit, now in the winter months it's not getting any charge I'm using a 25W 12V solar charger with a solar charging circuit that converts the 12V to 4.2 to charge the batteries Any other suggestions on how to power external Micromites in conditions where the sun isn't strong enough to charge batteries? |
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Azure Guru Joined: 09/11/2017 Location: AustraliaPosts: 446 |
First thing I would do is try and work out the average daily power requirement of your weather station. If you can't do don't want to run power to the outdoor unit then power required will be needed to try and work out what can be done. |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2442 |
12000mAh divided by (30 days * 24 hours) = 17mA (approximately). i'd be really surprised if your solar panel, even on a dim day, couldn't provide enough energy to keep your batteries topped up. are you 100% sure your charger circuit is working correctly? you only really need a single 18650 cell, which will rarely see more than about 10% discharge overnight given the above 17mA current consumption. you might like to set up your solar panel at ground level, connected via the charger circuit to just a single 18650 cell. as a simulated load, use a 180 ohm resistor across the cell (4.2 volts / 180 ohm = 23mA). monitor the cell voltage and the charging current. a couple of good-old-fashioned analog multimeters are ideal for this job. i'd expect the cell voltage to ramp down from 4.2 volts slightly overnight, and then rapidly come back up to 4.2v during the first hour of sunlight in the morning. due to the very low discharge level (10%) i'd expect a good quality LiIon cell to have a service life of quite a few years. btw, your charging circuit is also current-limited, isn't it? LiIon requires CC as well as CV when charging. cheers, rob :-) |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1667 |
Hi Lew, There's quite a lot of little Li-Ion charge modules about. I use one with a pair of 18650's to run the FARS on my Weather Station. Some use a TP4056, specifically a charge controller, & many also have a BMS chip (Battery management system), to prevent over discharge. Have a look at some of these. I've also junked a few cheap Phone Juice Banks as well for their modules & batteries. Modules are always fine, but the batteries are generally pretty low grade. Cheers Phil. |
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twofingers Guru Joined: 02/06/2014 Location: GermanyPosts: 1593 |
Which brand of Li-Ion batteries? Maybe you should check the capacity. causality ≠correlation ≠coincidence |
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| kg4pid Regular Member  Joined: 08/03/2015 Location: United StatesPosts: 50 |
I wanted to use some Li-Ion cells but then I saw this.... http://batteryuniversity.com/learn/article/charging_at_high_and_low_temperatures "Many battery users are unaware that consumer-grade lithium-ion batteries cannot be charged below 0°C (32°F). Although the pack appears to be charging normally, plating of metallic lithium can occur on the anode during a sub-freezing charge. This is permanent and cannot be removed with cycling. Batteries with lithium plating are more vulnerable to failure if exposed to vibration or other stressful conditions. Advanced chargers (Cadex) prevent charging Li-ion below freezing." It got down to 6F / -14C a few days ago and we were below freezing for about 5 days. I have not found a suitable battery for cold weather other than the old lead acid. Max |
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redrok Senior Member  Joined: 15/09/2014 Location: United StatesPosts: 209 |
Hi kg4pid;I agree. Good old reliable lead acid starting batteries are the most reliable I have found for low power remote applications. 1. Use smaller size, possibly lawn tractor types. 2. Use "Wet Cell" types. Ya, the ones that have caps, that way they can be watered if needed. 3. Trickle charge continuously at 1% or 2% of the "Amp Hour Capacity", no regulation required. I like 1% for new batteries and 2% for a bit older. Again, you should check if water is needed periodically. 4. I use 12V types but 6V is also a good choice. 5. Starting wet cell batteries are generally much cheaper and lighter than deep cycle types. I have 1 "New" battery that is 20 years old and another "Well Used" battery with 10 years. These have been very reliable. The loads are quite low and would easily run for a couple of months before the charge would get to 90%. They have never been fully discharges. redrok |
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| lew247 Guru Joined: 23/12/2015 Location: United KingdomPosts: 1702 |
They are genuine 3500mAh Panasonic batteries, and maybe "30" days was a little optimistic The unit draws around 35mA when not transmitting data and around 65mA when it is. I started off with the Solar cells going into a 5v regulator feeding a TP4056 module to charge the battery, this was working in the summer but now it gets no charge whatsoever as it's winter. I then bought one of THESE solar chargers but unfortunately it's still giving no charge to the batteries, the sun doesn't seem to be strong enough in the UK during winter This unit is only giving 1.55V to the battery to charge it which obviously isn't anywhere near enough. The input from the Solar cells is 14.9V so plenty of voltage, I'm guessing nowhere near enough current though from the sun in this part of the world |
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| kg4pid Regular Member Joined: 08/03/2015 Location: United StatesPosts: 50 |
If you have 14.9V from the solar panel and it's not charging then you have something else wrong. If the 1.55V is the voltage at the battery then your batteries are most likely bad, as that is well below the cutoff for a good battery. Were these protected cells? Were they charged below freezing? Have you checked the charging circuit? Max |
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| lew247 Guru Joined: 23/12/2015 Location: United KingdomPosts: 1702 |
The batteries are fine, they are new and work perfectly I said I have 14.9V from the solar panel INTO the charging circuit and only 1.55 out of the circuit which goes down to zero when the clouds get heavy and at night. |
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| JohnS Guru Joined: 18/11/2011 Location: United KingdomPosts: 4044 |
Well why don't you have a decent charging voltage coming out? Worst case it would be at low current but the voltage should be OK - right? John |
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palcal Guru Joined: 12/10/2011 Location: AustraliaPosts: 1993 |
Hi Lew, AS kg4pid said do you have any protection circuit such as THIS It will charge the cell to about 4.2v and cut off when the cell reaches about 2.4v. Over discharging Li ion cells will cause them to fail. Paul. Edit. When you say you only have 1.55v from the charger is this with the cell connected. If only 1.55v with no cell then the charging circuit is faulty. Even shining a bright electric lamp on the solar cell should cause it to charge. "It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all" |
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| lew247 Guru Joined: 23/12/2015 Location: United KingdomPosts: 1702 |
I have protected LI batteries with the protection built in 4 of these  I have a 12V solar charger going into this  The charger part is based on the LT3652 solar charger IC and charges lithium batteries (Li-Po, Li-ion, LiFePO4) at a rate of 1000mA (can be set to 2A max) Tomorrow when the sun is out I'll measure the current coming from the Solar cells In the summer I was using one of these fev via a 5v regulator to drop the 12V down to 5V  This was working fine during the summer but once autumn came it stopped working, I thought it might be the module so changed it for another and then eventually got the proper solar charging board I'm using now |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
Your charger has a limit of 1 amp at 4.2 volts Allowing for losses in the conversion, lets call that 5 watts required. Your solar panel is 25 watts so even allowing for the London smog, there should be plenty available from your solar panel for a reasonable period of the day. You need to measure the current coming from the solar panel and the current going into the battery with the load disconnected at (roughly) the same time. Also need the battery terminal voltage. Measuring the output with the battery disconnected will confuse the controller. With one amps out of the unit, there should be approximately 300mA coming from the solar panel. If ned be, discharge the batteries a bit so you should be getting the full one amp charge. The 14.9V you are seeing will be the 'Maximum Power Point' of the solar panel which is set by the trimpot on the controller. 14.9 sounds about right. The rating plate on the panel will have the correct figure for your panel. Jim VK7JH MMedit |
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| lew247 Guru Joined: 23/12/2015 Location: United KingdomPosts: 1702 |
I measured the current as well as the voltage from the solar cells today just after midday Voltage 14.9V but the current is only 8.9mAh I guess the sun really isn't strong enough to give any decent amount of current out of this cell pack |
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| redrok Senior Member Joined: 15/09/2014 Location: United StatesPosts: 209 |
Hi lew247;Just to characterize the solar panel: 1. The panel Open Circuit Voltage? I.e not connected to anything. 2. The panel Short Circuit Current? Ya, dead shorted current through the meter. 3. What type of panel? Silicon or thin film? Silicon generally has visible cells. Thin film is generally made with Stripes. This will give us a lot of information. redrok |
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| kg4pid Regular Member Joined: 08/03/2015 Location: United StatesPosts: 50 |
I think your logic is flawed. You're not showing much current because the load (your charger) is not attemping to charge your battery. Either your charger is bad or your batteries are. The supply voltage and load determine current flow. Without a load you have no current. Connect a small 12V light bulb or any small load that would draw about 1 amp directly to the solar panel. You should see the solar panel voltage drop some. How much it drops depends on how much sun your panel is receiving. Now measure current. I suggested a light bulb because you will see instantly that your panel is working or not. Max |
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| lew247 Guru Joined: 23/12/2015 Location: United KingdomPosts: 1702 |
I’ll try that tomorrow once the sun returns 😊 |
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| redrok Senior Member Joined: 15/09/2014 Location: United StatesPosts: 209 |
Hi lew247; Do the measurements I suggested. We will get more information. Measuring current while the load is present can be very misleading. redrok |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
I agree that open circuit voltage and short circuit current readings are needed. You don't need much sun to get better readings than that. A shadow on one of the cells will really shut the whole panel down. Are you sure a squirrel hasn't shat on the panel? Jim VK7JH MMedit |
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