progress bar + eta

Discussion of ideas for your ultimate dream charger/analyzer
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2114L3
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Joined: Sat Jun 28, 2014 7:44 am

progress bar + eta

Post by 2114L3 » Sat Jun 28, 2014 8:53 am

while an ETA time is very hard or impossible - short of the operator keying in battery rated capacity. it would be nice to have simple progress bar that shows progress based on the starting/lowest voltage and what a common peak voltage is.

visual aid is great when your glancing the charger so you dont have to stop and mentally working it out by looking at voltage, time etc

an eta could be added as the inflection point approaches as the curve can be estimated to the point that the slope meets cutoff.

Mark
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Re: progress bar + eta

Post by Mark » Sun Jun 29, 2014 2:54 am

I think that calculating an ETA is just going to be too hard to do with NiMH cells.

I could add in an indicator to give a rough idea of how full each battery is based on the voltage - It would only ever be a very rough estimate, and I'd need to analyze the data that I've collected to work out the appropriate voltage levels to use.

individual

Re: progress bar + eta

Post by individual » Tue Aug 19, 2014 7:17 am

The correct monitoring charge/discharge would be using a Coulomb Meter / Batery Gas Gauge, which may be software based or maybe based on a hardware IC (although there are not many for NiMh technology; most of them are for Lythium batteries).

Mark
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Re: progress bar + eta

Post by Mark » Tue Aug 19, 2014 8:34 am

Can you provide some more details on how that would work?

As far as I'm aware, there is simply no way to accurately calculate the capacity of a NiMH from just reading the voltage from it - in either software or hardware.

If you know the starting state of charge and the capacity of a NiMH cell, you can work out its current capacity based on how much charge you have added/removed from it, but in most cases you don't accurately know it's starting state of charge or it's total capacity.

Lithium cells are a different beast because their state of charge directly correlates to their resting voltage.

individual

Re: progress bar + eta

Post by individual » Tue Aug 19, 2014 9:09 am

Indeed, ther is this drawback if the batteries are discharged outside the controlled environment. If this is the case, then only the charge could be monitored, or when formating batteries, it can be monitored so that it could be discharged completely first, and then recharged to full capacity by counting the coulombs inserted to the batery.

Maybe a mix between the two could be used. That is, to have a charging program that first discharges the battery to a certain voltage/temperature, then initiate the complete charging, correctly counting coulombs. The advantage would be that batteries will always go through full cycle. That would prolongue their life and capacity.

Mark
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Re: progress bar + eta

Post by Mark » Wed Aug 20, 2014 12:54 am

individual wrote:Indeed, ther is this drawback if the batteries are discharged outside the controlled environment. If this is the case, then only the charge could be monitored, or when formating batteries, it can be monitored so that it could be discharged completely first, and then recharged to full capacity by counting the coulombs inserted to the batery.

Maybe a mix between the two could be used. That is, to have a charging program that first discharges the battery to a certain voltage/temperature, then initiate the complete charging, correctly counting coulombs. The advantage would be that batteries will always go through full cycle. That would prolongue their life and capacity.
You can certainly do a discharge/charge cycle already with the charger as it is. Doing so would allow you to know the initial state of charge before commencing the charge process, but it still wouldn't provide information about the capacity of the cell unless you were to provide that information to the charger each and every time you inserted a cell to be charged. To be honest, I don't think that many people are likely to be bothered to do something like that.

Doing a discharge first before each charge means that the process will take a heap longer - I'd expect that most people would prefer faster charging without an estimate compared to significantly slower charging that does give an estimate - it's quite possible that charging a partially discharged cell would take less time than it would take to discharge it, so you'd end up with a full cell before being able to even get an estimate of time remaining etc if you were discharging first!

I think that there is reasonable evidence to suggest that occasional full cycles are good for NiMH cells, but I don't think that there is any reason to think that doing it every cycle would be good for them - I think that you would end up just putting unnecessary wear and tear on the cells and end up doing more harm than good. The IEC standard for rating cell cycle life time is based on mostly (98% in fact) partial charge/discharge cycles, so I think that is a reasonable indicator that you get more cycles when not doing full charge/discharge cycles. If I recall correctly, Toyota also limits the level of charge and discharge on the NiMH batteries in the Prius so as to increase cell longevity.

I haven't processed the data that I've got yet, but I'm hopeful that it will be possible to give an estimate of current cell capacity during charging that works in 20% increments - maybe even 10% increments might be possible.

individual

Re: progress bar + eta

Post by individual » Wed Aug 20, 2014 4:57 am

You are right, it is not practical. I just thaught that it would be cool to have a formating batteries program. As for complete charge/discharge, I think it depends where you get the informations from. The RC community uses a lot of NiMh technology and you will find such smart chargers a lot there, although mostly for C type batteries. The thing they are afraid most is complete depletion of batteries, otherwise they prefer a full discharge/charge.

But the fact is that is imposible to apreciate what is left in the battery, if it is discharged outside a controlled system. The voltage indication is just a best guess, and is better than nothing. Trickle charging ending the charging program has also it's role, for ending a proper charging.

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