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OA47

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Joined: 11/04/2012
Location: Australia
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Posted: 01:18am 20 Feb 2018

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I have a project that uses a 5 or 10w solar panel to charge a 12 V SLA battery and I am finding that these batteries (manufactured in China and Indonesia) seem to have a short life and I think it is due to the high temperatures they have to suffer during summer, drying out the paste inside. I have 3 regulation circuits being 13.8, 5.0 and 3.3 all of which add temperature to the enclosure during hot/sunny times. I can run the system down to 6V and I am wondering if I should look at another variety of battery such as Li @ 7.2V that may have better resilience.

Any comments very welcome.
OA47

redrok

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Joined: 15/09/2014
Location: United States
Posts: 209

Posted: 02:30am 20 Feb 2018

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Hi OA47;
Are you using a "Temperature Compensated" charger specifically designed for this type of battery?

redrok

Boppa
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Posted: 02:52am 20 Feb 2018

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by 'I can run the system down to 6v' I hope you arent actually running the battery down to 6v?
eta, I have a solar powered electric fence with a 4ah sla, I put a new one (chinese) in it 2 years ago with no issues since, and I havent heard on the grapevine of any real issues with them (I have a friend that uses probably hundreds a month in solar powered yard lights and he's not had any issues that I know ofEdited by Boppa 2018-02-21

OA47

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Posted: 03:20am 20 Feb 2018

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Quote Are you using a "Temperature Compensated" charger specifically designed for this type of battery?

Redrok, the current charging cct uses voltage and current regulation, it does not have any temp compensation.
OA47

OA47

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Posted: 03:22am 20 Feb 2018

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Quote by 'I can run the system down to 6v' I hope you arent actually running the battery down to 6v?

What I meant was that I am not tied to a 12v battery, I can use 6v and above.
OA47

Boppa
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Posted: 03:28am 20 Feb 2018

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No worries, just checking

OA47

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Posted: 10:40am 20 Feb 2018

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One of the questions I have pondered is that if I reduce the battery voltage but keep the solar panels would I be having to dump more heat inside the enclosure to regulate the charging voltage and current?
OA47

flip
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Joined: 18/07/2016
Location: Australia
Posts: 114

Posted: 11:47am 20 Feb 2018

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Hi OA47,
I'm not sure about SLA, but I know general Lead-Acid batteries used for telecomms (24-cell) are continuously floated at 52.8...i.e. would be 13.2V for a 6-cell. Telecomms applications use this to obtain optimum balance between capacity and long-life.

You could use boost (only after any moderate discharge) to 13.8 then drop back to the float level.

If you're worried about heat maybe you could use either a pulsed charger so no resistive losses or else maybe an external pre-shunt regulator with zener and amplifier transistor on a heatsink to drop the panel voltage to say 15V before your internal linear regulator?

Regards Phil

Boppa
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Posted: 12:25pm 20 Feb 2018

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I found a link to a site with the following derating formula for high temps

Quote
The recommended compensation is a 3mV drop per cell for every degree Celsius rise in temperature. If the float voltage is set to 2.30V/cell at 25�C (77�F), the voltage should read 2.27V/cell at 35�C (95�F). Going colder, the voltage should be 2.33V/cell at 15�C (59�F). These 10�C adjustments represent 30mV change.

Depending on your enclosure, the internal temp may be considerably higher (the charge rate is normally written on the side of most sla batterys- usually its rated at 25 deg C)

OA47

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Posted: 04:02am 31 Jul 2018

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Further to the development of this project, I have come to a brick wall and hope another shedder may have managed to succeed where I am failing. As these field units rely on solar charging, I would like to reduce the idle power consumption to a minimum. By running the Micromite at 5 Mhz, putting the SDI-12 probe in sleep mode and minimising current flow in the associated logic circuits I have an idle current draw of 21mA. The documentation for the LoRa RS232 radio modules (Download brief handbook state that the modules can be put in power save mode by setting M1=1 and M0=0.

If I set the recieving units to Mode 1 (WakeUp M1=1 and M0=0) the idle current draw reduces to 6mA which is a lot better than 21mA but even though I set the Tx unit to Mode 1 (M0=0,M1=1) which is supposed to wake the Rx units with additional preamble they do not respond.

If I set the Rx units to Mode 2 (Power Saving M1=0 and M0=1) there is no reduction to current draw but the Rx unit replies OK.

OA47

Azure

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Joined: 09/11/2017
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Posted: 04:32am 31 Jul 2018

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From reading the module specs, Using the Module Aux pin and setting the appropriate mode you would be able to put the MM to sleep and wake it using an interrupt pin tied to the module Aux. This would provide a large reduction in average power consumption.

It looks like you might need to send configuration parameters to initialise the preamble.

Can you post some more info about the intended tx/rx operation and/or post some of the relevant code and you might get some useful feedback/suggestions.

OA47

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Posted: 09:14am 31 Jul 2018

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Azure, thanks for replying. I have the CRO on the AUX pin and It doesn't change level when there is signal although I do see more noise on the trace during signal reception. The reciever is set to the minimum timing for Wake on Radio which is 250mS. I am assuming that the data will be held back to allow for this lag by the transmitting unit when it is set to send the pre-amble first. I am currently happy with the micromite drawing around 5mA so I dont think that there is as much gain putting it into sleep mode when I can possibly reduce the LoRa module by around 15mA.

OA47

OA47

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Posted: 09:46am 31 Jul 2018

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I think I may have found the problem. On page 22 of the manual there is a table in the chapter Operation Mode. The columns of the table start, Mode (0-3) then M1 and M0. If I reverse these column headings (to M0 and M1) all seems to work as it should.

It seems throughout the manual you have to read M1 as M0 and vice versa.

This time I shouldn't have RTBM

OA47

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Posted: 05:04am 03 Aug 2018

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Another head scratcher has emerged and would like to get some help with this one. Having succeeded in getting the LoRa serial unit to behave as I would like running in low power mode I am faced with another issue.

The issue is that the LoRa module only recognises the settings from the Micromite when I use RUN to launch the program. If I power cycle or press the RESET button relying on Option Autorun On the LoRa module does not wake on radio.

Has any body got any clues?
OA47

TassyJim

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Posted: 05:27am 03 Aug 2018

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Try a big pause at the start of your program.

Jim

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OA47

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Posted: 05:37am 03 Aug 2018

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Thanks Jim, a one second pause at the start of the program seems to do the trick. Not sure of the science behind it but it might have something to do with the delayed reset circuit.

Regards
Edited by OA47 2018-08-04

TassyJim

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Posted: 09:47pm 03 Aug 2018

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"Slow and steady wins the race"

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isochronic
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Joined: 21/01/2012
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Posted: 11:10pm 03 Aug 2018

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If you have scales that will do it, it would be worth weighing the batteries new and again after fail, see if there is a serious loss. I have seen some "sealed" cells completely dried out, I think some SLA's were not designed for continuous trickle charge or tropical temperatures.

OA47

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Posted: 03:02am 04 Aug 2018

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Quote I think some SLA's were not designed for continuous trickle charge or tropical temperatures.

Chronic I am sure that you are right. I don't think that SLA batteries especially the oriental ones like being cooped up in an IP65 enclosure at temperatures that hit 60 degrees Celsius in the middle of summer.

I will experiment with other types of batteries now that I have reduced the idle current draw.

OA47

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