General > General Technical Chat
12V DC UPS
beanflying:
And the termination of charge here is what exactly?
Your BMS NON solution will see the Pack going from open to closed circuit at the top of charge EVERY CYCLE which is anything but desirable for a UPS. Your Schottky diode option is a dud as the forward Voltage drop across it varies with current so how again are you picking your end point and exactly what is it? Add to this you are already requiring a stable supply as part of your charge circuit. Balance charge solutions exist for a reason and are CHEAP.
Long term 'storage' of LiPos is generally recommended well below 4V for better life but below the 4.2 is 'better' but not a lot. Want to talk about weight not being a factor here and cost being one then clearly there is a good reason most UPS supplies use AGM Lead batteries ::)
NiHaoMike:
--- Quote from: beanflying on July 27, 2022, 02:53:21 am ---And the termination of charge here is what exactly?
Your BMS NON solution will see the Pack going from open to closed circuit at the top of charge EVERY CYCLE which is anything but desirable for a UPS. Your Schottky diode option is a dud as the forward Voltage drop across it varies with current so how again are you picking your end point and exactly what is it? Add to this you are already requiring a stable supply as part of your charge circuit. Balance charge solutions exist for a reason and are CHEAP.
--- End quote ---
The diode is for discharge. The charging stops by means of the supply voltage being limited. I suppose one could use a current limited LDO instead of a resistor if a fancier solution is desired.
--- Quote ---Long term 'storage' of LiPos is generally recommended well below 4V for better life but below the 4.2 is 'better' but not a lot. Want to talk about weight not being a factor here and cost being one then clearly there is a good reason most UPS supplies use AGM Lead batteries ::)
--- End quote ---
Maybe you have been living under a rock but lithium is cheaper than sealed lead acid nowadays, especially in small sizes. And unless you go for an even more expensive premium brand, lead acid nowadays generally doesn't last past 3-5 years even when kept under optimum conditions. Contrast that to (name brand) 18650s which easily last past 10 years when treated well.
beanflying:
--- Quote from: NiHaoMike on July 27, 2022, 03:18:31 am ---
Maybe you have been living under a rock but lithium is cheaper than sealed lead acid nowadays, especially in small sizes. And unless you go for an even more expensive premium brand, lead acid nowadays generally doesn't last past 3-5 years even when kept under optimum conditions. Contrast that to (name brand) 18650s which easily last past 10 years when treated well.
--- End quote ---
Size and non specified brand specific :bullshit: Stop making stuff up to suit YOUR narrative. Lithiums are across the board offer less capacity for more $.
I have AGM's doing well after your apparent time frame. I still have a few NiCads that are well over 20 years old that doesn't make them a good option because of this. Some of my Lithiums are close to or might be over 10 years old in spite of regular high current use and frequent charged state storage. I have also had LiPo's in particular (good branded ones) puff well under max current after a few uses
Don't throw insults you can't back with actual fact!
--- Quote from: NiHaoMike on July 27, 2022, 03:18:31 am ---The diode is for discharge. The charging stops by means of the supply voltage being limited. I suppose one could use a current limited LDO instead of a resistor if a fancier solution is desired.
--- End quote ---
So you are now suggesting a voltage fully regulated power supply and LDO's and ..... instead of the $3 Balancing Charger board (good for 500mA-1A)? Stop trying to weasel this out as a good solution it is NOT. Use a proper charger that exists and works instead of an imagined make believe bad solution.
NiHaoMike:
--- Quote from: beanflying on July 27, 2022, 03:43:17 am ---Size and non specified brand specific :bullshit: Stop making stuff up to suit YOUR narrative. Lithiums are across the board offer less capacity for more $.
I have AGM's doing well after your apparent time frame. I still have a few NiCads that are well over 20 years old that doesn't make them a good option because of this. Some of my Lithiums are close to or might be over 10 years old in spite of regular high current use and frequent charged state storage. I have also had LiPo's in particular (good branded ones) puff well under max current after a few uses
--- End quote ---
Here's a source for pretty cheap name brand lithium batteries:
https://batteryhookup.com/
As an example, here's 15x 2.5Ah cells for $8.50: https://batteryhookup.com/products/genuine-lithium-polymer-4v-2520mah-10-08-wh
In 3S configuration, you get 12.5Ah. I have never seen a 12Ah 12V lead acid battery for that cheap.
Lead acid is really in the "they don't make them like they used to" category, especially for the smaller sizes which are mostly used in low cost applications.
--- Quote ---So you are now suggesting a voltage fully regulated power supply and LDO's and ..... instead of the $3 Balancing Charger board (good for 500mA-1A)? Stop trying to weasel this out as a good solution it is NOT. Use a proper charger that exists and works instead of an imagined make believe bad solution.
--- End quote ---
Find me a low cost 3S charger that can be configured to stop at 4V/cell or 4.1V/cell instead of the usual 4.2V/cell. The only ones I have seen with that capability are R/C chargers which aside from being relatively expensive even for the budget ones, are not at all desirable for this application in that they need to be manually started.
beanflying:
Wow for one specific instance and size of YOUR choosing you 'allegedly' find and option to prove what exactly? Someone selling bulk single cell leftovers sourced from the factory floor in China is cheaper than someone selling a packaged 12V AGM Battery? This is a bogus argument Lithium is across the board more expensive than AGM this is just a simple fact.
As to the second part of your attempted weasel it is not rocket science or hard to design a comparator to switch or reset the trigger of a micro to start and stop a charge process at certain over or under voltages. There you go it even has built in BMS ::) eBay auction: #384879258895
Something like this from Lewis is likely an ok start point https://www.bristolwatch.com/ele2/battery_charger.htm
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