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Mini DC UPS packs
#11
Close to what I'm looking for. I'm sure I've seen a design where the circuitry for 4 or 5 cells was all on one board, and powered by a single supply connection.

Wolf - What do you use yours for... is it just to pre-charge cells to increase the throughput of your testers? I've been doing just that with my singular D4. With only 2 testers, its a slooow process. Darn COVID has meant shipping from China is taking over 6 weeks.
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As at Mid May 2020 -Total cells 1,135/Shucked 1,045/To be shucked 90/Processed 194/To be processed 608/Zero volt 183/Bad/rusted 19/Sanyos 1/21700s 24
All tool batteries comprising of Milwaukee, Makita, AEG, Hilti, with Samsung, LG, Sony and Sanyo cells from 1.3AH to 3.0AH (OEM)
Chargers... 1 x Nitecore D4/1 x LiitoKala 500/1 x iMAax B6AC
On order... 5 x LiitoKala 500/1 x LiitoKala 500/1 x iCharger 4010 Duo
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#12
You could make packs & run the gear from them via suitable buck step downs & keep the pack charged by running it from a larger CCCV charger/supply set to eg 4.0V/cell per suggestions?
Eg mains > charger/PSU > cells > buck > device.

This way, when the mains goes down, the devices don't even notice & continue on, when mains comes back, PSU recharges cell & powers device again....?
Running off solar, DIY & electronics fan :-)
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#13
(06-23-2020, 04:48 AM)Redpacket Wrote: You could make packs & run the gear from them via suitable buck step downs & keep the pack charged by running it from a larger CCCV charger/supply set to eg 4.0V/cell per suggestions?
Eg mains > charger/PSU > cells > buck > device.

This way, when the mains goes down, the devices don't even notice & continue on, when mains comes back, PSU recharges cell & powers device again....?

That was my original plan and I apparently asked the question poorly. How bad is it for the cells to be held at the top end? I'd be happy to overbuild the capacity and then knock down the top charge to even something lower like 3.9. This time of year we have frequent power outages due to heavy monsoon storms. Otherwise our power supply is fairly stable for the other 8 or so months of the year. The cells would likely spend around 98-99% of the time on mains power.
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#14
Beware that many off-the-shelf consumer-level DC UPS suffer from various problems.

Some are bogus U = Uninterruptible because the switch time is too long for many devices.

Most also provide no control over the standby charge level and simply maintain the battery at 100% SOC (or close).  While this yields the max runtime on battery it also yields the worst battery life because Li-ion battery life is seriously degraded by the amount of time they spend at extreme SOCs and temps (e.g. NASA's deep space missions use very shallow cycles around 50% SOC, which may increase cycle/calendar life by more than an order of magnitude - possibly lasting a couple decades).  The difference can be quite extreme - e.g. only 6 months battery life when always fully charged on standby vs. more than 10 years when intelligently maintained.

Generally the rule of thumb is that to maximize Li-ion cell life we should strive to minimize the time that the cell spends at extreme voltages and temperatures (which accelerate internal parasitic reactions and other degradation processes). Because these degradation processes are typically nonlinear (even exponential) even a small change away from the extremes can reap large rewards in battery lifetime.  See these slides for a very nice summary of the primary degradation / aging mechanisms in Li-ion batteries (and see the further discussion in surrounding posts there).

For some real-world numbers regarding such see the graphs I posted here, which highlight how Li-ion chemistry behaves so differently in this regard vs. other common chemistries (e.g. lead acid, whose cumulative lifetime energy delivered does not exhibit such strong dependence on said discharge depth and its balancing around 50% SOC).  This deserves to be much better known since it can yield tremendous improvements in battery lifetime when competently exploited.

A common mistake is that many folks try to transfer their intuition from other chemistries to Li-ion, which fails miserably in this case (and in others too, e.g. vaper pants-on-fire incidents caused due to lack of knowledge that - unlike other common cells (e.g. alkaline AA) - for cyclindrical Li-ion cells the entire 18650 can is negative  so even a small metallic object like a key can short the cell),
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#15
[quote pid='64461' dateline='1593703006']


A common mistake is that many folks try to transfer their intuition from other chemistries to Li-ion, which fails miserably in this case (and in others too, e.g. vaper pants-on-fire incidents caused due to lack of knowledge that - unlike other common cells (e.g. alkaline AA) - for cyclindrical Li-ion cells the entire 18650 can is negative  so even a small metallic object like a key can short the cell),
[/quote]


Jokingly   -  Nooobody here knows what the magic smokes is , we like ozone,bright lights and burnt nose hair. the other guy did it. Big Grin
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#16
(06-22-2020, 10:40 PM)Wayne\s World Wrote: Wolf - What do you use yours for... is it just to pre-charge cells to increase the throughput of your testers? I've been doing just that with my singular D4. With only 2 testers, its a slooow process. Darn COVID has meant shipping from China is taking over 6 weeks.

I just sits in my shed now not being used. Too bad you are on the other side of the world otherwise I'd ship it to you as I only used it in the beginning of my harvesting adventure. This was before I found out about IR, and was testing every cell that came across my grubby little fingers.
Now the ones that don't pass the "IR" test don't need to be pre charged.
I pretty much know what I'm getting now and straight to the tester they go.
Wolf

Waynes World and OP
Just realized this is kinda hijacking the OP's original post. Sorry
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#17
Apologies from me 2 Tongue
-----------------------------------------------------------------------------------------------------------------------------------------------------------
As at Mid May 2020 -Total cells 1,135/Shucked 1,045/To be shucked 90/Processed 194/To be processed 608/Zero volt 183/Bad/rusted 19/Sanyos 1/21700s 24
All tool batteries comprising of Milwaukee, Makita, AEG, Hilti, with Samsung, LG, Sony and Sanyo cells from 1.3AH to 3.0AH (OEM)
Chargers... 1 x Nitecore D4/1 x LiitoKala 500/1 x iMAax B6AC
On order... 5 x LiitoKala 500/1 x LiitoKala 500/1 x iCharger 4010 Duo
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