plwsm2000 Posted April 30, 2019 Share Posted April 30, 2019 Does anyone have any information on (or given any thought to) how the battery charge efficiency relates to the health of the battery? The battery charge efficiency is just the ratio between the number of Ahrs you draw from the battery vs. the amount of Ahrs needed to fully charge it again. My thinking is that as the battery ages, it will require more charge to return it to its fully charge state from a given depth of discharge. If measured regularly, it should give some warning of the battery failing so allowing you to do something about it before leaving you stranded somewhere with a dead battery! I have designed my own battery monitor that sits between my EBL223 and the DT220 display unit that monitors the various voltages and currents on the battery. My 2 year old gel battery is currently giving about 86% efficiency which seems about right. This project actually started life as a LPG, water and "spirit level" but I was inspired by Allan's knowledge of battery care and maintenance to add some battery conditioning monitoring features such as the number of D.O.D cycles and battery charge efficiency. (BTW this is just a hobby project and I have no intention to turn this into a salable product!). The unit connects via Bluetooth to my Android app. and I have included some typical screenshots below to give you an idea of what it does. The fact that it uses Bluetooth also comes in quite handy when I am filling the van with water as you can see how full the tank is while you are operating the outside tap. Any comments or thoughts would be appreciated. Link to comment Share on other sites More sharing options...
spirou Posted April 30, 2019 Share Posted April 30, 2019 How do you measure charge efficiency? Ah back in to what state? Link to comment Share on other sites More sharing options...
plwsm2000 Posted April 30, 2019 Author Share Posted April 30, 2019 spirou - 2019-04-30 7:30 PM How do you measure charge efficiency? Ah back in to what state? Mathmatically, the charge efficiency is just - (discharge Ah from fully charged / charge Ah to full charge ) * 100% The discharge Ah is relatively straightforward to calculate as I am measuring the actual current several times a second and just add then up over a time period to give the Ahr figure. Each current sample is converted into the equivalent Peukert corrected value before being summed. The charge rate is just the accumulated current readings when the current is positive (i.e going into the battery). The "full charge" state is detected when the charge current drops below a certain threshold AND when the battery voltage is above 13.5V (this only happens on the charger). It also has to be in this condition for several minutes. I realise that this may not be exactly 100% full, but it is going to be close to it. Also my theory is that if the same criteria is used even time, the calculated charge efficient should at least be consistent and I am only looking for a relative change in the efficiency. I also use this fully charge to update the %DOD counters for that particular discharge level. Link to comment Share on other sites More sharing options...
spirou Posted May 1, 2019 Share Posted May 1, 2019 I'm just asking because a victron battery monitor looks at Ah going in (peukert and preset efficiency included) and will reach 100% much quicker than the EBL goes to float regime and you might consider it as 100% charged. It will reach 100% on solar or alternator as well and those will never charge as long as full cycle on hook up. Absorption phase on victron solar reg is quite a bit shorter than via schaudt EBL. Hence my question of what do you consider as 100% to be able to calculate long term dropping efficiency? Link to comment Share on other sites More sharing options...
plwsm2000 Posted May 2, 2019 Author Share Posted May 2, 2019 spirou - 2019-05-01 4:24 AM I'm just asking because a victron battery monitor looks at Ah going in (peukert and preset efficiency included) and will reach 100% much quicker than the EBL goes to float regime and you might consider it as 100% charged. It will reach 100% on solar or alternator as well and those will never charge as long as full cycle on hook up. Absorption phase on victron solar reg is quite a bit shorter than via schaudt EBL. Hence my question of what do you consider as 100% to be able to calculate long term dropping efficiency? spirou, Thanks for the Victron info. After further reading, it seems that the charge efficiency depends on the actual DOD rather than a fixed %. I read that the charge efficiency is higher when the battery is at a lower charge state and the efficiency reduces (becomes less efficient) when the battery approaches its fully charged state (almost a reverse of the peukert effect). It would be good to know if the Victron uses a fixed preset efficiency or something more complex. I suspect it probably uses a fixed value which may explain why it reads 100% sooner than the EBL goes into float mode. Showing 100% may give people a false impression. I think I prefer the idea of checking the current drops below a certain threshold to determine if the battery is full or not. Link to comment Share on other sites More sharing options...
aandncaravan Posted May 2, 2019 Share Posted May 2, 2019 Plwsm2000, That is an amazing project, I love the idea of being outside filling the water tank while watching it fill up on my phone. The issue with monitoring battery capacity via charging efficiency is there are so many variables. A Banner Energy Bull is very prone to fast losing efficiency through internal corrosion with the battery giving back far less amps than you put in as it ages. That is one of the reasons they make poor Solar Power batteries, where Solar charge current is generally low so wasting up to 25% of each charge phase has a bigger impact. A Varta LFD90 doesn't suffer corrosion and claims to be up to 70% more electrically efficient as it ages. But even these will be drawing less current as the Plate Active material 'expires'. As many know a batteries natural degradation causes it to lose a little bit of the Battery Plates 'Active material' which fails to convert back each time the battery is cycled, causing the battery to slowly lose capacity. This happens in all Lead Acid batteries and is just a feature of the chemistry. When a battery can no longer deliver 80% of the rated label capacity the industry regard it as exhausted and due for replacement. A battery that has dropped to 70% capacity (even though it's efficiency might still be close to 95%) contains 'expired' Plate Paste that will no longer take part in the battery chemistry so won't draw any charge or give up any amps. That might mean a 100Ah battery may be drawing 30+amps less current than it needed to fully charge when new. In the case of the Banner Energy Bull the higher current it might have consumed through internal corrosion may be balanced by the reduced 30% charge it will no longer draw through expired active material. This behaviour was ably demonstrated by the first stupid "Smart" charger we came across in around 2013/2014. The owner used it to demonstrate that the MH original mains Leisure charger was faulty because his car 'Smart' charger proved it was. The charger, just think of a well known make, lights showed the battery was fully charged from flat in just 2 hours. When we discharge tested the battery at 5 amps it dropped below 12v in under 40 minutes. The charger was showing that the remaining 10% paste material still active in the battery was totally recharged, not the 100% of the label capacity. The lights were rather misleading. Because the battery had not suffered any structural failures, like Paste shedding, Plate shorting, antimony poisoning, no serious corrosion, etc it held it's charge and performed like a new battery. Just a very, very small battery. Some of the expensive capacity monitors out there don't even take account of battery technology with their varying qualities and different voltage ranges, let alone inefficiencies between the different executions of those technologies which some do well and others very poorly. Some of the ones we have seen even assume a conventional wet battery range of 12.6 down to 11.8v for all technology batteries. So the software algorithm needs to take account of this and be quite complex. However, even just a guide would be far more than we have now so I love your work and ideas. Link to comment Share on other sites More sharing options...
spirou Posted May 4, 2019 Share Posted May 4, 2019 Victron has a fixed efficiency factor that you can change as the battery ages or are just trying to find a set of parameters that reflect reality better. I forget what ours is set at, probably 80%. Link to comment Share on other sites More sharing options...
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