offgrid, modern household. usecase for 204+VDC battery packs

Thread Starter

quitenoob

Joined Mar 27, 2022
262
TL : DR; update
use cases of going high found so far;
* Economics of wiring
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I am looking to offgrid my modern, 3 phase 25 amps mains connected, home with at peak a power draw of 15KW.

All the wiring (https://forum.allaboutcircuits.com/...or-204-vdc-battery-packs.186114/#post-1723323) of the house is already in place and the breaker cabinet is designed to be used in a 3 phase manner.

I am in the process of designing a LifePO4 battery power source.

What use cases can one think of of going for more than a 16S (16 cells in series) solution?

Of course 16S is nothing remarkable to begin with. Perhaps there is something to be said about going for 4S4P, or any other configuration.

I am aiming at having 64 cells at 280Ah. But since there are 4096 ways of configuring those I am not sure how to proceed.

I started thinking that having all of them in series at 204VDC might be a good start but I am not sure anymore.
 
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KeithWalker

Joined Jul 10, 2017
3,137
Be aware of the safety issues here. IEC 62368-1:2014 defines "safe" as 60VDC or 2mA DC, whichever is less.That is why the usual limit for battery supplies is 120VDC, center tapped to ground.
 

Thread Starter

quitenoob

Joined Mar 27, 2022
262
Thank you for pointing safty issues out. Can you think of a use case in where going well above that limit is needed?

I will admit to not having read those guidelines yet but why then are we allowed to drive 300+VDC timebomb electrical vehicals into our garages ;)
 

Ian0

Joined Aug 7, 2020
10,005
Large UPS tend to use 384V battery packs (32 off 12V lead acid battery in series). Three-phase UPS without transformers are often above 500V.

With the present copper price, I can see an advantage for the higher voltages, though availability of suitable inverters may limit your choice.

That’s not a cheap battery pack, about £16,000 by my reckoning. It would be £5,600 in lead-acid.
 
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Thread Starter

quitenoob

Joined Mar 27, 2022
262

Lo_volt

Joined Apr 3, 2014
321
I will admit to not having read those guidelines yet but why then are we allowed to drive 300+VDC timebomb electrical vehicals into our garages ;)
Electric vehicles are assembled and tested to specific safety standards. They're not timebombs.

There are makers of off-grid inverters that can do 3 phase. Outback is one manufacturer that comes to mind. I just checked their website and they say their 3 phase unit can work with lithium batteries. Look around, there may be others out there.
 

Ian0

Joined Aug 7, 2020
10,005
Electric vehicles are assembled and tested to specific safety standards. They're not timebombs.

There are makers of off-grid inverters that can do 3 phase. Outback is one manufacturer that comes to mind. I just checked their website and they say their 3 phase unit can work with lithium batteries. Look around, there may be others out there.
Another is Victron - their single-phase inverters can be linked in threes to do three phase. The highest voltage they do is 48V.
 

Thread Starter

quitenoob

Joined Mar 27, 2022
262
Electric vehicles are assembled and tested to specific safety standards. They're not timebombs.

There are makers of off-grid inverters that can do 3 phase. Outback is one manufacturer that comes to mind. I just checked their website and they say their 3 phase unit can work with lithium batteries. Look around, there may be others out there.
yes of course. I was being a little cynical. No ill intend meant of course.

But it does begs the question, if I understood correctly in the first place, why there are rules in place that 'forbid' high voltage applications while we can all park an EV in our garage without breaking any rules.
It could also be that I should really read up on that link before making assumptions.

So anyway, current status of use cases for going high in voltage with batteries is the economics of wiring yes?

Can one think of other use cases?

It's ok if we can't. I certainly can't anymore so it's ok if we end up with several 48V packs or maybe even more 24V packs. Still many configurations possible. A few 48V and a bit more 24V packs. why not ;)
 

Ian0

Joined Aug 7, 2020
10,005
Power semiconductors are another factor.
The world is well supplied with low Rds(on) MOSFETs at 100V Vds(max), which you would use for a 48V inverter.
The next common voltage would be 72V, which would boost charge at 90V (for Lead Acid), which is rather close for comfort on a 100V transistor.
The next common battery voltage is 108V, which would require 200V transistors, and the choice is not so good.
Higher battery voltages may require IGBTs, or SiC devices.

If the project is in any way experimental in nature, then choosing a battery voltage that you can experiment with, without having to take extreme safety precautions is an advantage.

If you are using a commercial product, someone else has taken all those risks, and you are free to choose any voltage for which there are products available.
 

Thread Starter

quitenoob

Joined Mar 27, 2022
262
If the project is in any way experimental in nature, then choosing a battery voltage that you can experiment with, without having to take extreme safety precautions is an advantage.
it's through experimentation I need to settle on a working design. This is not an experiment just for the sake of it. This is a mission to get my household offgrid

If you are using a commercial product, someone else has taken all those risks, and you are free to choose any voltage for which there are products available.
I prefer DIY over store bought. It will improve on the ability to fix issues when they come about. That is not to say I am against buying from store.

I've updated the OP to reflect the current status
 

Thread Starter

quitenoob

Joined Mar 27, 2022
262
He should already be a big fan of Victron!
hahhaha. sure they have their HQ near us. but then again I am aiming at self reliance.

But why is the third phase red? Shouldn’t it be grey.
Are two-pole MCBs required in NL?
This is because I did not have other color wires available at the time. I am aware though that this is not ideal

Are two-pole MCBs required in NL?
Can you please elaborate?

I am not sure if it helps form an idea but here goes the breaker cabinet
View attachment 264541
The less than ideal wiring, including color coding, is due to that I did not find fast enough the components that I was looking for. So I made due with what I did was able to source at a moments notice.

But here lies proof of the concept that a test, how ever bodged, becomes final if it does not break ;(
 

Lo_volt

Joined Apr 3, 2014
321
...rules in place that 'forbid' high [DC] voltage...
The rules don't forbid high voltage DC. They specify conditions for safe use of high voltage DC and therefore tests against those conditions. There are no "Ten Commandments" of electricity and electronics, i.e. "Thou shall not..." As they are finished products EV's comply with those conditions to reduce the risk to the consumer and the liability of the manufacturer. That's also the reason I suggested an off-the-shelf product vs. DIY.

If you want to use voltages higher than ~48 volts DC, it can be done, but I would strongly suggest you do your research especially as regards to safety. There is a reason my moniker is Lo_volt.
 
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