Unplugging charger with battery still attached to charger

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Is there any problem with unplugging the charger while leaving the battery attached to the charger?  The reason I ask is that I am considering building a circuit with a photocell that detects when the 50% light on the charger begins to blink.  After the 50% light is blinking for a few minutes, my circuit will cut the power to the charger so that the battery will stop charging after reaching about 30% charge.  I'm concerned that without power, the charger may begin to deplete or damage the battery.  Any comments out there?
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Sam Kaplan

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Posted 3 years ago

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Adrian Ramirez

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I don't stop at 50%, but I do delay charge, which requires the battery to be on the charger while the charger is unplugged. I just use a 7 day timer and set it to turn on Thursday a couple hours before I get home to mow. Then I use the battery and don't put it back on the charger for 2 weeks. I can get about 3 mows out of one full battery, so I started only charging after 2 mows and time it to charge right before I normally mow.


I haven't had any issues yet, but I don't keep it on the unpowered charger for weeks or months, only a few hours, maybe 2 or 3 days max so far without issues.


We have a Keysight DC power analyzer at work, maybe I'll bring the charger there one day and see how much current it consumes while unplugged. The analyzer is pretty awesome, can measure down to nA.
(Edited)
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Blue Angel, Champion

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Ever thought about that approach before... if leaving the batteries on the charger has no negative impact, I could use my WEMO (smart wifi connected plug) to turn the charger on remotely from anywhere if I thought I needed to mow right when I got home!
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Brad Carey

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I love this idea. I'm new to my mower and I often mow the grass on a spur of the moment decision and I don't like the idea of waiting for the 7.5 battery to charge before I can begin. Setting a timer for early Saturday morning would have it ready for the weekend but avoid it sitting fully charged all week long. I see this of a middle ground that works well for me and is better for the battery.
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Eric

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Testing iHome and WeMo myself now.  This is a great idea that I completely did not think about.
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(a)Typical Engineer

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Two things Li-Ion batteries don't like is being over charged, and being left in a depleted state.  I will usually use my tools, and if I run them down to red, I will let them cool for a few hours, and them re-charge them to 50%, and then shut-off the charger.  I would not leave a battery that is red until the next weekend (or longer).
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Blue Angel, Champion

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While we know the cells are safe down to a certain depletion voltage, there is likely a set voltage in the Ego battery system below which the battery will no longer charge. We would be wise to make sure that the battery could not be drawn below that point while sitting in the unplugged charger, no?
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Adrian Ramirez

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Good point. The charger probably has an under-voltage limit somewhere. The normal limit that I've seen in all designs I've looked at is 2V per cell, as thats pretty conservative for safety concerns. But I've also seen accidental limits higher than that because of noise issues in some designs. And since I have no idea where Ego sets their lower limit, i would agree it's probably best to stay away from the lower side.
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Adrian Ramirez

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Oh, and the battery doesn't appear to have any switch that I could find which would prevent it from being charged. It looked to me like all of their charge protection was in the charger.
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Blue Angel, Champion

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Agreed, though the battery does have the ability to communicate with the charger and could simply tell the charger not to proceed if it had monitored activity outside pre-set parameters. I would think at a minimum cell-to-cell voltages would be monitored inside the pack.
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Adrian Ramirez

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Yeah, you're probably right
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David HD, Champion

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Sorry Brad but you missed the HUGE block party Blue & Adrian had over the weekend ... it was a Li-ion battery BBQ Block Party.  Anyone who was anyone was there, sorry we missed you - just kidding!!!!




That said; my post was simply to say that I tried to use the "appropriate" Ah battery for each tool, to get the best performance of the tool and battery.  For example, a backpack blower would work with a 2.0Ah battery, but EGO recommended 5.0Ah or higher for greater performance - that was it.
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Brad Carey

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I didn't realize battery size could have an affect on performance, I thought only run time was affected. It'll be interesting to see the real world difference between the 2.5Ah and 7.5Ah in the 21" SP after my Bermuda goes "carpet mode" as I like to call it.
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David HD, Champion

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Brad, like I said in my post from above, I am not a Li-ion battery guru, but I try to keep up with the knowledge of this "current" technology.  That said; the link below is a good read from Pro Tool Reviews on How It Works: Lithium-ion Batteries Explained.

This article ( April 2013) will gives you a good perspective on the different Ah batteries and how they are made.  The article is about 4 years old, but good enough to help you understand why you should use the "appropriate" Ah battery for each tool - happy reading .... :-)

https://www.protoolreviews.com/news/how-it-works-lithium-ion-batteries-whats-the-big-deal/5331/

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