Ups style build plan (guidance welcome)

So I think I'm past the planning stage and ready to start building.
I have 100 or so cells on their way tested and ready to start building with (thanks jon)
A 24v ups to use for the inverter and low voltage computer shut off.

My plan so far is to make a 14p7s, chances are it will only have about 20ah of capacity to start with.
Im thinking of using thisBMSwith a heat sink and maybe fan. This is over kill for my size system but nothing to what most people want/need.
Im hoping to feed this through a solar setup using cheapy eBay panels as i can afford them, or maybe even build some custom stuff for the hell of it.

Now for more questions
With the solar does it just go straight to the charging of the BMS? or do i need to make sure that the voltage from the panels is above 24v? (cant find much info on li-ion solar regulators)
On the same note for topping up the system from mains if required could i simply plug the UPS in and use its internal charger through the BMS?

Bit confused about the BMS stuff
Does this all make sense?

I guess you plan for 7s14p? Ie 7 packs in series with 14 cell in each? (Not 14 packs with 7 cells in series)

Seem to be fair BMS in terms of decent voltage protection. Note that this bms will work fine in beginning but very limited balancing. Should not have more than 1kWh of storage for it though.

You need to have a controller between the solar panels and the battery. The BMS does not handle charging. The only active thing it have is the balancing. The other parts are only last resort protection.

You can probably not plug in the mains and charge from it no. Its running lead acid charging curve. If so you need to be able to change that. Its better off getting a proper charger if so.

BMS = Battery management system. the cheaper ones, like the one you look at is cheap because it does not do that much that well. It do balancing and should do the protection. Everything related to charging as such you need to sort yourself.

To get the best out of the solar panels you need an MPPT charge controller. There are several out there that charge lithiums.
You "could" use the UPS charger, but you'd need to have a charge controller in-between to handle the actual charging properly. You would have to test your UPS in charge mode to find out what it outputs to charge with and get a charge controller that could use that as input. However, it'd be better to get a BMS that can do both the balancing and charging as it needs to be truly between the batteries and the UPS to handle "all" power transfers to make sure there is no mishaps.
So you're looking at a much more involved process of using the UPS to charge. It'd be far better to have an external charger that kicks on to charge from the grid if need be. And turn off the charging capabilities of the UPS if possible. Depending on the brand, you can lower the float voltage really low and that would essentially keep it turned off.

daromer said:

I guess you plan for 7s14p? Ie 7 packs in series with 14 cell in each? (Not 14 packs with 7 cells in series)

Seem to be fair BMS in terms of decent voltage protection. Note that this bms will work fine in beginning but very limited balancing. Should not have more than 1kWh of storage for it though.

You need to have a controller between the solar panels and the battery. The BMS does not handle charging. The only active thing it have is the balancing. The other parts are only last resort protection.

You can probably not plug in the mains and charge from it no. Its running lead acid charging curve. If so you need to be able to change that. Its better off getting a proper charger if so.

BMS = Battery management system. the cheaper ones, like the one you look at is cheap because it does not do that much that well. It do balancing and should do the protection. Everything related to charging as such you need to sort yourself.

Click to expand...

Yes sorry 7S14P.
I doubt ill get that high on this set up, maximum this will get to is maybe 100AH so 1/10th of the BMS limits.
Dam thought it did due to the charging ports.

Korishan said:

To get the best out of the solar panels you need an MPPT charge controller. There are several out there that charge lithiums.
You "could" use the UPS charger, but you'd need to have a charge controller in-between to handle the actual charging properly. You would have to test your UPS in charge mode to find out what it outputs to charge with and get a charge controller that could use that as input. However, it'd be better to get a BMS that can do both the balancing and charging as it needs to be truly between the batteries and the UPS to handle "all" power transfers to make sure there is no mishaps.
So you're looking at a much more involved process of using the UPS to charge. It'd be far better to have an external charger that kicks on to charge from the grid if need be. And turn off the charging capabilities of the UPS if possible. Depending on the brand, you can lower the float voltage really low and that would essentially keep it turned off.

Click to expand...

Any recommendations on a MPPT controller for lithium, preferably just a cheap eBay options. Just getting into so would prefer to destroy sub hundred dollar equipment than a batrium unit for such a small system.

Also what sort of external charger are you talking about? Again could you recommend something?

Check out the ones that daromer has worked on on his channel. Julian Ilett has also reviewed some. I personally haven't used them so I'm not sure which ones are better over others.

Potentially charging from AC grid is easy in the most cheap terms you can do with a PSU that you can set specific voltage to. Then you add a Cheap BMS from china with decent cut off voltages.
The important part is that the voltage does not exceed the top voltage of the pack and that the bms do protect and shut off charging if it goes above.
With those rather simple devices you can charge it and this is how many of the devices out there in the world are built.

I think i have the Charging from the mains sorted. Using a power supply with buck boost converter which i have lying around from another project.

Now to figure the solar stuff out. I even thought about a cheap normal solar controller -> AGM battery -> inverter ->240v charger but very messy and means i need two separate charging systems.