You are over complicating things. Please check what I wrote.Here's my drawing...View attachment 163255
What I need to know is what to fit inside the mini UPS case and in what order (apart from the batteries - 3 x li-ion 18650 connected in series).
I think I will need a step down voltage converter before the BMS and a step up voltage converter after the batteries.
I also believe there is a need for a relay to direct the current past outside the batteries charging circuit and directly to the output when batteries are fully charged and AC is on and through the batteries when AC is off.
You are over complicating things. Please check what I wrote.
Hi,
If you want to, you seem to understand a few things..., try looking for Li-ion charger ICs from TI/Analog Devices/Maxim/Microchip/In Semiconductor/ST Micro/etc... and use their parametric search tables to see if anything comes up.
Some of these ICs carry out some or maybe even all the tasks you are looking for.
--- Updated ---
...On Semiconductor...
I supply here a UPS system for you as attached.
The specification of the battery bank says output 2A and 1A, but the input is 1.5A max. If you can find an enclousure to supply what you need, it might work.
You requested 18650 batteries. Otherwise I would suggest a car battery charger, connected to a car battery and from the car battery, you can draw all you want with an LM2577 module(DC-DC step up) or an LM2576 module which is a DC-DC step down. Normally I power motors this way. The car charger will supply 4A for example, this is a small car charger. This method has downfalls! The first problem is, if the battery is charged more than the maximum, will it start leaking acid, gases or explode. Some chargers say they are automatic, but they are not. The second problem is, can the charger charge the battery, while its used(like in a car). It also becomes a bit expensive. The charger has to be automatic, start charging at 12.2V and stop charging at 12.6-14.4V.
3 x 18650 = low capacity.
A laptop battery is 4000mAh approximately, it has versions form 10V to 20V, but it can only be charged inside of a laptop.
Hi,
Post a drawing.
Especially how the AC is involved.
Klaus
I want to build a mini ups to ensure uninterrupted power for my router and fiber ONT during grid power outages.
what are these devices plugged into now?
you might consider buying a UPS instead of building your own
there is an amount of surety that it will work reliably
there is also a potential issue with local electrical regulations and fire codes
that a store bought UPS may meet, that a home-made will not.
a place to start:
APC, a flagship brand of Schneider Electric
APC, a flagship brand of Schneider Electric, provides clean battery back-up power, surge protection, and IT physical infrastructure inside and outside the traditional IT environment to deliver ‘Certainty in a Connected World’www.apc.com
The problem here is that you never have a "true" charging mode, because the load alwasy draws current.Setup:
Charger(1.5A-2A) -> Battert bank(3 or 8 batteries in parallel) -> LM2577 -> Router.
A different approach:Don't create a PCB is my advice, prototyping almost never works from the first time and causes a lot of problems and wastes of a lot of money.
Hi
The problem here is that you never have a "true" charging mode, because the load alwasy draws current.
If your charger current is 2A into paralleled batteries, then the power is limited to 2A x 3.7V = 7.4W.
This 7.4W are used to power the load and to chargevthe batteries. If your load is more than 7.x W (as it seems to be) then the batteries never get charged.
...
Klaus
the batteries are not in series and they are not in parallel
in series: + to -
in parallel, all + connected to each other and all - connected to each other
the battery connection looks like anti-series
you have + tied to +, and - tied to -, and - tied to +
you might want to add a battery holder, such as this one, which connects the batteries in series:
Battery Holders, Clips, Contacts | Electronic Components Distributor DigiKey
Battery Holders, Clips, Contacts are in stock at DigiKey. Order Now! Battery Products ship same daywww.digikey.com
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