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lew247
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Posted: 06 January 2018 at 11:07pm | IP Logged Quote lew247

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
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Posted: 06 January 2018 at 11:51pm | IP Logged Quote Azure

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
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Posted: 07 January 2018 at 1:06am | IP Logged Quote robert.rozee

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
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Posted: 07 January 2018 at 6:42am | IP Logged Quote Phil23

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
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Posted: 07 January 2018 at 7:05am | IP Logged Quote twofingers

lew247 wrote:
I've been using 18650 3.7V 3A (3000mAh) batteries ...

Which brand of Li-Ion batteries? Maybe you should check the capacity.
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kg4pid
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Posted: 07 January 2018 at 10:44am | IP Logged Quote kg4pid

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 0C (32F). 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
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Posted: 07 January 2018 at 12:06pm | IP Logged Quote redrok

Hi kg4pid;
kg4pid wrote:
I have not found a suitable battery for cold weather other than the old lead acid.
Max
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
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Posted: 07 January 2018 at 9:10pm | IP Logged Quote lew247

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
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Posted: 08 January 2018 at 3:53am | IP Logged Quote kg4pid

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
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Posted: 08 January 2018 at 4:13am | IP Logged Quote lew247

kg4pid wrote:
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


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
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Posted: 08 January 2018 at 5:35am | IP Logged Quote JohnS

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
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Posted: 08 January 2018 at 5:41am | IP Logged Quote palcal

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.


Edited by palcal on 08 January 2018 at 5:47am


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