Let's design our own UPS

[Paul_S]

Mmmm...

Am I missing something or can that actually work?

Yes, you're missing two things:
1. 140Wh != 1400Wh. It's 11Ah - not 107Ah
2. The BlueNova LiFePO4 batteries are a drop in replacement in terms of form factor but not charge characteristics. One still needs a LiFePO4 charger - a UPS charger designed for SLA batteries will not work (properly).

 

[Thor]

Yes, you're missing two things:
1. 140Wh != 1400Wh. It's 11Ah - not 107Ah
2. The BlueNova LiFePO4 batteries are a drop in replacement in terms of form factor but not charge characteristics. One still needs a LiFePO4 charger - a UPS charger designed for SLA batteries will not work (properly).

Got it, yea they made a mistake.

Back to the original plan. DIY UPS and leave these LiFePO4 stuff for another time.

18650 all the way

 

[wingnut771]

Got it, yea they made a mistake.

Back to the original plan. DIY UPS and leave these LiFePO4 stuff for another time.

18650 all the way

View attachment 997376

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They come in different sizes.

 

[Pineapple Smurf]

I doubt Blue Nova are selling drop in lead acid replacement batteries that need a lithium charger
I reckon the battery management system inside the battery will take care of charging the lithium correctly.

Otherwise whats the point? Why call it a drop in lead acid battery?

 

[Pineapple Smurf]

Are your 18650 batteries going to be balanced @Thor ? This would be ideal as each 18650 would be charged 'individually' and not just your entire bank. This is what will make the batteries last longer

 

[wingnut771]

I doubt Blue Nova are selling drop in lead acid replacement batteries that need a lithium charger
I reckon the battery management system inside the battery will take care of charging the lithium correctly.

Otherwise whats the point? Why call it a drop in lead acid battery?

13.8V vs 14.4V.

 

[newby_investor]

13.8V vs 14.4V.

Yeah. That won't hurt the lithium cells, in fact it will probably be better for their longevity if they're charged slightly below the typical max.

But you won't get as much usable capacity, this is really the only thing that I can see being a problem.

The reason I haven't done this with my RCT UPS is mostly that the UPS is pretty noisy. Fan goes and beeping sound when the power is out.

 

[eddief1]

Got it, yea they made a mistake.

Back to the original plan. DIY UPS and leave these LiFePO4 stuff for another time.

18650 all the way

View attachment 997376

18650's can be tricky, might not be ideal for a UPS scenario, basically u will save weight and space, not that NB

 

[wingnut771]

Yeah. That won't hurt the lithium cells, in fact it will probably be better for their longevity if they're charged slightly below the typical max.

But you won't get as much usable capacity, this is really the only thing that I can see being a problem.

The reason I haven't done this with my RCT UPS is mostly that the UPS is pretty noisy. Fan goes and beeping sound when the power is out.

That's why i said 80% capacity, but I agree, it's actually better for the life of the battery not having it fully charged, but also it's not good to go below 20% either.

 

[newby_investor]

That's why i said 80% capacity, but I agree, it's actually better for the life of the battery not having it fully charged, but also it's not good to go below 20% either.

The guys behind Accubattery seem to think that this isn't really the case, but I still would try and avoid it. I would imagine that Blue Nova's BMS has an appropriate cutoff either way.

 

[wingnut771]

The guys behind Accubattery seem to think that this isn't really the case, but I still would try and avoid it. I would imagine that Blue Nova's BMS has an appropriate cutoff either way.

I'm not saying you can't use 100% DOD, just saying it has a negative effect on cycle life, same as keeping it at 100%. If you keep between 20-80%, cycles life improves exponentially.

 

[Pineapple Smurf]

13.8V vs 14.4V.

who says the battery management system inside the battery cannot up the voltage whilst reducing the amps?
DC-DC Converters have been around since @Gordon_R left school in 1954

 

[wingnut771]

who says the battery management system inside the battery cannot up the voltage whilst reducing the amps?
DC-DC Converters have been around since @Gordon_R left school in 1954

Wouldn't the lead acid charger in ups overrule bms? When it thinks battery is full (13.8V) it floats? I asked https://lithiumbatteriessa.co.za/ this question and they said it would work but you'll only have 80% capacity indicating the voltage is the limiting factor to me.

 

[Pineapple Smurf]

Wouldn't the lead acid charger in ups overrule bms? When it thinks battery is full (13.8V) it floats? I asked https://lithiumbatteriessa.co.za/ this question and they said it would work but you'll only have 80% capacity indicating the voltage is the limiting factor to me.

I dont know.
Good Question
But it might be a case of how the battery 'talks' back to the charger

It could be faking it, like that one time when @cavedog was doing me and then he pulled out and spat on my back.

We will never know what happens

 

[ReeceDBN031]

If someone could make smallish 12v UPS in like custom color 3D printed enclosures it could be a neat little side business.. if you can i am interested

saw a vid on youtube.. peeked my interest

 

[Thor]

Are your 18650 batteries going to be balanced @Thor ? This would be ideal as each 18650 would be charged 'individually' and not just your entire bank. This is what will make the batteries last longer

We definitely need to add a BMS to this, luckily they are dirt cheap.

 

[Pineapple Smurf]

If someone could make smallish 12v UPS in like custom color 3D printed enclosures it could be a neat little side business.. if you can i am interested

saw a vid on youtube.. peeked my interest

@AlphaJohn can make porno laser cut metal devices

 

[Thor]

If someone could make smallish 12v UPS in like custom color 3D printed enclosures it could be a neat little side business.. if you can i am interested

saw a vid on youtube.. peeked my interest

Depending on the output, you basically want a glorified powerbank then, the normal powerbanks are all 18650 cells

 

[Pineapple Smurf]

We definitely need to add a BMS to this, luckily they are dirt cheap.

Yes they are, balancing each cell is very important with lithium.
We're not talking about a bunch of lead acids in series here

 

[ReeceDBN031]

Depending on the output, you basically want a glorified powerbank then, the normal powerbanks are all 18650 cells

I guess that's correct, but obviously without the USB port.. or with but would need to have router plug output