EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: FearTec on March 28, 2016, 09:00:46 PM
I am a coder by day and play with electronics every few weeks (when off family duties). I have a random blog here http://simon.fearby.com (http://simon.fearby.com) anda development blog here http://www.fearby.com (http://www.fearby.com)
I have Raspberry Pi 2 Setup guide ( http://simon.fearby.com/blog/?p=2202 (http://simon.fearby.com/blog/?p=2202) ) and a Raspberry Pi Batter and Solar journal here ( http://simon.fearby.com/blog/?p=2292]http://simon.fearby.com/blog/?p=2292 (http://) ).
I am a real noob when it comes to batteries and solar panels and am hoping to learn loads and not kill too many batteries to the sulfer build up of death.
I am blogging my battery journey here http://simon.fearby.com/blog/?p=2292 (http://simon.fearby.com/blog/?p=2292)
Q1) Does anyone know what the cells this battery has?
http://www.jaycar.com.au/Power-Products-Electrical/Storage-Batteries/SLA-GEL-Rechargeable/18-0-Amp-Hour-12V-Sealed-Lead-Acid-Battery/p/SB2490 (http://www.jaycar.com.au/Power-Products-Electrical/Storage-Batteries/SLA-GEL-Rechargeable/18-0-Amp-Hour-12V-Sealed-Lead-Acid-Battery/p/SB2490) (and datasheet http://www.jaycar.com.au/medias/SB2490-dataSheetMain.pdf?context=bWFzdGVyfGltYWdlc3wxNDA5MDF8YXBwbGljYXRpb24vcGRmfGltYWdlcy9oYjMvaDgxLzg4Mzg0ODc3MzYzNTAucGRmfDQzODdjMzZjN2E1Y2FlZjk1MTQ0OGZkMDYwYzg1ZWYzNWU0MDM1NzJkOGNjZThhMTMyZmRjOWU0NWJiMWZkZWE (http://www.jaycar.com.au/medias/SB2490-dataSheetMain.pdf?context=bWFzdGVyfGltYWdlc3wxNDA5MDF8YXBwbGljYXRpb24vcGRmfGltYWdlcy9oYjMvaDgxLzg4Mzg0ODc3MzYzNTAucGRmfDQzODdjMzZjN2E1Y2FlZjk1MTQ0OGZkMDYwYzg1ZWYzNWU0MDM1NzJkOGNjZThhMTMyZmRjOWU0NWJiMWZkZWE) )
Q2) What is the safe lowest voltage charge this battery should be take to before being re-charged?
I am assuming I don't let it get below 30%?
Once I move on from these gaps in my knowledge I will move to running the battery in Standby and have it topped up by solar during the day.
Thanks In Advance
P.S This is the live web server that this camera is serving: http://sipi02.fearby.com (http://sipi02.fearby.com)
Nice project. I noticed you are using a WiFi dongle. Maybe try Pi3 which has built in, to lower power need? I'm not sure how they compare. On the software side, thoughts about having the Pi monitor charging levels and solar output, etc... get some real world data and then use the information to make modifications. Also if voltage drops too low will need to prevent Pi from booting until the charge has had time for ramp back up or it will keep bleeding the battery and not boot to a usable state. This all depends on whether your solar installation is big enough to cover the losses from Pi and battery use, as well as taking account weather variability. Keep us posted, I'd like to learn how you do it also.
You urgently need to reconfigure your MoPi. The battery datasheet gves an absolute minimum cutoff voltage of 10.5V. Going down to 9.48V will kill your battery fairly quickly. The maximum voltage will be something like 12.8V under load when fully charged - check this with a DMM and use the actual value. As a rule of thumb, without a smart charger you can only safely use 50% of the nominal battery capacity, as it never gets fully charged if you only charge it to the maximum float voltage of 13.8V and you always want some margin on the low end to reduce the risk of premature failure. 30% is a good cut-off point for practical cyclic applications, but the actual voltage depends on the discharge rate.
You *WILL* need some sort of charge controller to avoid overcharging in the summer.
The Pi 2's idle current with no peripherals connected apart from Ethernet, is probably somewhere around 0.25A. WiFi dongles tend to be power-hungry. Hardwire the Ethernet!
If you are running this 24/7, that's 30WH/day. It wpuld be advisable to log the actual current drawn from and voltage of the battery over a 24H period running your actual applications so you can refine the power budget calculations. Your nominal 2W panel, best case will give you something like 15WH/day and worst case, in the month of June will average around 8WH/day. See http://aussiervproducts.com.au/solar-mapping (http://aussiervproducts.com.au/solar-mapping)
IMHO you'll need something like four or five times your current panel area to keep the battery charged under worst case conditions, as you must allow for losses in the charge controller, the battery itself, and in the MoPI.
Thanks for the replies Ian.M and edy. I have set my Pi to shutdown before 11.1v and updated my blog with new battery monitoring info http://simon.fearby.com/blog/?p=2292 (http://simon.fearby.com/blog/?p=2292)
New Power Limits
Testing the Limits
I have disconnected the MoPI and and am recharging the battery (you can watch the live camera here http://sipi02.fearby.com (http://sipi02.fearby.com) )
Good post on power for the rPi3 with built-in wifi http://raspi.tv/2016/how-much-power-does-raspberry-pi3b-use-how-fast-is-it-compared-to-pi2b (http://raspi.tv/2016/how-much-power-does-raspberry-pi3b-use-how-fast-is-it-compared-to-pi2b)
Installed 12v supply, 5v backbone, master off, RTC and Dual PSU safe shutdown reset triggers. Next analog/digital sensors (smoke/co2, light, lazers, temp, humidity, pressure, moisture, motor and proximity motion sensor and vibration sensor), speaker and 240v relay for external control. Wifi, SMS and push notification code ready.
I killed a MoPi dual power input Pi board (silly me put the wrong colour shrink wrap protective layer over the top) and when I turned on the power with reverse polarity much blue smoke was released.
The main compartment will we air right with silica bags and protected from the elements with loads of styrofoam. I don't think I need active cooling (therms electric peltier element).
Follow here: http://simon.fearby.com/blog/?p=2292 (http://simon.fearby.com/blog/?p=2292)