Battery voltage / DOD duty - Page 1
Forum section: electronics / general

author: paulca
author_rank: Super Contributor
timestamp: January 25, 2018, 01:00:51 pm
content: What is the consensus on battery charge level in a solar system?I mean, should you aim to keep the batteries fully charged and draw only the load you expect will be replaced within the next day or is it better to run the battery around it's mid point?At the moment with my mini 50W setup and our rubbish winter daylight hours and weather I am typically pulling anything that has been put into the battery that day into downstream Lithium packs.Yesterday for example the battery gained from 11.8V up to 12.3V, so I charged a decent sized LiPo off it until the battery dropped to 12V. This LiPo will run my bench power supply for a few days.My thought on this is that a lower battery voltage allows the charge controller to engage in PWM mode at a much lower solar panel voltage, if the battery is only at 12V as soon as the panel is producing 13V the charge controller starts pulsing current into the battery (confirmed this morning before dawn the battery showed charging). This seems to allow 100mW or so charging even before dawn or with heavy cloud cover. When the sun comes out properly the charge controller will switch to MPPT, seen by the panel voltage spiking up on graphs.I think it might also be kinder to the battery to use it around it's nominal voltage. However I am also aware I will need to boost charge all the way up to 100% once in a while. I'm just not sure how often I need to do that.

author: fourtytwo42
author_rank: Super Contributor
timestamp: January 25, 2018, 02:22:04 pm
content: I think this charge controller is incapable of boosting from a low panel voltage as it seems many are, this means to make the best use of low light the battery voltage needs to be low to start with. It is I think unlikely to have any energy storage within the charge controller so the operating point of the panel is entirely controlled by the battery voltage rather than being at the maximium power point of the panel.I have seen all sorts of lurid claims by charge controllers, could you post a link to your particular one ?

author: paulca
author_rank: Super Contributor
timestamp: January 25, 2018, 02:36:18 pm
content: http://www.epsolarpv.com/en/index.php/Product/pro_content/id/654/am_id/136I have seen tests by Adam Welch on YouTube which showed it as doing both PWM and MPPT depending on the panel output. It seems to do PWM at low power levels and switch to MPPT at higher levels. I don't know enough to validate that claim, except that it will hold my panel at around 13V when at low light levels and trickle power into the battery. I'm not sure other than the panel voltage jumping up occasionally if I have witnessed it doing MPPT.Apparently the EPEver Tracer A series is a budget version of their more expensive EPSolar Tracer series of controllers.

author: fourtytwo42
author_rank: Super Contributor
timestamp: January 25, 2018, 06:54:54 pm
content: Well the one thing missing from all there specifications is panel ripple current and that is crucial to panel efficiency. If you had a scope you could easily measure it by the voltage across a small series resistance e.g. 0R01. There "conversion efficiency" graphs are pseodo science as they do not indicate efficiency with respect to what, I suspect they are talking about there internal losses.There could be a whole site devoted to dodgy solar electronics sold for to much money but hey most people are happy to buy and use this stuff and there's no law about exhorbitant claims otherwise the entire beauty business would be shutdown!As I don't own batteries and even if I did I would make my own controller I have no direct experience of these products, just a heap of scepticism having seen some circuits for things claiming to do just that on the web and reading experiences like yours.Why can it only manage mpp voltages 2V greater than the battery (according to the spec) that to me points to an ultra simplistic design not capable of extracting the maximium from the panels.

author: paulca
author_rank: Super Contributor
timestamp: January 25, 2018, 09:20:02 pm
content: Okay... but anyway, it seems to take advantage of low light running the battery at a lower voltage seems to be the better plan. That said if the battery+2V you spotted is correct, I will lose efficiency in high direct sunlight as the panel's MPP is 17V.Mostly the question is about lead acid maintenance than solar charge controller efficiency.I understand your scepticism though. I am the same about most home automation stuff. If I see a Wifi light bulb I will automatically assume it will come with and only work with the particular companies hub or controller app and avoid it.This is why I'm doing it my way, as Frank would sign, home heating, solar charge monitor, whatever next. When I come to light bulbs and radiator controls I'll research for open protocol ones or build the thing myself... or hack someone else's to do it my way.I don't see the need to feed everything up into the cloud either. "Here, have all my data, log all my personal behaviours and routines. Sure shut it down and brick all my devices or force me into paying monthly for the privelige of you deprecating all my stuff." </rant>

author: fourtytwo42
author_rank: Super Contributor
timestamp: January 26, 2018, 09:43:48 am
content: Quote from: paulca on January 25, 2018, 09:20:02 pmIt actually says minimium 2V but can be greater, so that means the minimium MPP it can deal with is 2V above the battery voltage. BTW MPP is not the same voltage throughout the insolation range check your panels curves assuming there are anyQuote from: paulca on January 25, 2018, 09:20:02 pmAre you including in that the panels conversion efficiency as this is effected by the charge controller ?Quote from: paulca on January 25, 2018, 09:20:02 pmSpot on there couldnt agree moreP.S. You didnt say if you had a scope so you could check out what this thing was doing ?

author: paulca
author_rank: Super Contributor
timestamp: January 26, 2018, 10:03:14 am
content: Quote from: fourtytwo42 on January 26, 2018, 09:43:48 amNot really sure. I'm not going to be that fussy to be honest. If it works and charges my battery as long as it's not pissing away loads of power I don't think I care.When sourcing it I found a lot of charge controllers which were £100-300 range. I also found claimed MPPT controllers for £5 from China. When I watched reviews of course it was learned that these £5 jobs were PWM and usually absolutely rubbish. One for example had a PWM frequency of about 400mHz. I'd have done better with an Arduino. The TracerA seemed to land right in the middle and I only paid £50 for it. It had a decent feature set and reviews and tests I watched on YT seemed to suggest it performed more than adequately for it's price point. It also had RS485 monitoring which was a plus point.Quote from: paulca on January 25, 2018, 09:20:02 pmSpot on there couldnt agree moreIt was with gritted teeth that I finally subscribed to Spotify. Realistically it was the cheapest/easiest option.I could be tempted to use a cloud service but not as the main interface to a project. I will keep things within my LAN until a cloud based web ui or data intelligence tool presents itself that I can import data too and it is worth the downsides.All this "Thingspeak", "BlinkX", "Alexa" and "Cayenne" stuff, no thanks.

author: fourtytwo42
author_rank: Super Contributor
timestamp: January 26, 2018, 07:15:44 pm
content: Quote from: paulca on January 26, 2018, 10:03:14 amAhh sorry I thought you wanted every drop of efficiencyI have watt mania, anywhere I can save one I do unless the cost is exhorbitant. Getting ready to move completely off-grid on my tropical island

author: paulca
author_rank: Super Contributor
timestamp: January 26, 2018, 07:48:13 pm
content: Quote from: fourtytwo42 on January 26, 2018, 07:15:44 pmSmoke me a mojito.