are 96V LiFePO4 a good idea?

[JAndle]

Seeing 96V charger inverters out of China and thinking this is an emerging trend... Allows higher MPPT efficiency for long strings, so reduced copper needs and reduced copper losses. EG 3s and up 144 half cell systems with 120V+ Vmpp would readily charge 96V banks and 96V would be more efficient for the inverter than would 48V.

The obvious concern is the electrical room. UL says under 72V (60V after allowing +20%) is 'safe extra low voltage' in most of their standards, so would a 96V system need a special enclosure? Are there other concerns besides lack of time on the market?

 

[John Frum]

96 volts is 3.2 volts * 32 cells or 102.4 volts.
That voltage is dangerous.
I imagine it will be difficult but not impossible(to rhyme with expensive) to get
all the balance of system bits.

 

[JAndle]

Well, 240Vac is dangerous too. I work with up to 40KV so I don't tend to think that way, but I should...
It would require all the battery connections be in a NEMA enclosure, so there is cost and effort involved.

I can find MPPT chargers up to 384Vdc/80A etc. and 96V charger/inverters that almost look well designed... Since my project is 1-2 years out I wonder if the tech will head there. I guess over 48V is really industrial and not residential then?

 

[Kodack]

Seeing 96V charger inverters out of China and thinking this is an emerging trend... Allows higher MPPT efficiency for long strings, so reduced copper needs and reduced copper losses. EG 3s and up 144 half cell systems with 120V+ Vmpp would readily charge 96V banks and 96V would be more efficient for the inverter than would 48V.

The obvious concern is the electrical room. UL says under 72V (60V after allowing +20%) is 'safe extra low voltage' in most of their standards, so would a 96V system need a special enclosure? Are there other concerns besides lack of time on the market?

Have you ever seen a hotdog cooked instantly, from cold to flaming hot in under a second? That is what high voltage DC can do to a limb. If you were equipped and trained to handle 96v you wouldn't be asking if it were a good idea or not. My 2cents.

 

[jasonhc73]

96 volts is 3.2 volts * 32 cells or 102.4 volts.
That voltage is dangerous.
I imagine it will be difficult but not impossible(to rhyme with expensive) to get
all the balance of system bits.

I have 250V DC from my Solar panels, why is it more dangerous?

It isn't any more dangerous. It is more efficient to have fewer amps for the same given watts. The only way to have more watts is to have more volts.

Telephones worked at 90V's DC since they were invented, they are perfectly safe.

China right now has a 1,000,000 Volt DC line from the far west desert areas all being fed by DC Solar Panels. This Million Volt DC line travel 2,000 kilometers. It is no more dangerous than any 600kV AC transmission line.

 

[Kodack]

I have 250V DC from my Solar panels, why is it more dangerous?

It isn't any more dangerous. It is more efficient to have fewer amps for the same given watts. The only way to have more watts is to have more volts.

Telephones worked at 90V's DC since they were invented, they are perfectly safe.

China right now has a 1,000,000 Volt DC line from the far west desert areas all being fed by DC Solar Panels. This Million Volt DC line travel 2,000 kilometers. It is no more dangerous than any 600kV AC transmission line.

Are your PV's capable of putting out hundreds of amps at that voltage? The voltage being high is a problem because it starts becoming enough to overcome skin resistance and start forming a path through your limbs. The huge danger with batteries at that voltage though is the amount of amps they are capable of outputting instantaneously. A 12v battery for instance has amps, but it's difficult for it to do much to your body because of skin resistance, but as the voltage climbs, this acts like less of a barrier. At high enough voltage even air stops acting like a insulator.

DC burns can be hideous, branching out through a limb or the body like roots of a tree, damaging muscle, cardiovascular tissue, nerves, not to mention the actual burns.

The main advantage to going with higher voltage in a power system is that the interconnects and transmission lines can be smaller because Amps X Volts = Watts, so in a given wattage, the higher the voltage, the less amps are needed, which means the thinner the wiring can be. But the added complexity, danger, and other factors should make higher voltage DC less desirable than 24 or 48v systems. An exception would be if it's for a special use case, like driving large motors such as in an electric car, boat, etc where the load is high enough that lower voltage, thicker cabling would be prohibitive.

 

[Hedges]

Be like me and buy quality surplus 48VDC and high voltage string inverters.
I don't need to be on the bleeding edge. After a decade + of proven reliability, I know what to expect.

You have two years to quietly gather everything you need.

 

[John Frum]

Well, 240Vac is dangerous too. I work with up to 40KV so I don't tend to think that way, but I should...
It would require all the battery connections be in a NEMA enclosure, so there is cost and effort involved.

I can find MPPT chargers up to 384Vdc/80A etc. and 96V charger/inverters that almost look well designed... Since my project is 1-2 years out I wonder if the tech will head there. I guess over 48V is really industrial and not residential then?

Yes 240VAC is dangerous and special care must be taken.

 

[John Frum]

32s may become a thing someday but it isn't much of a thing yet.
The only inverter that I know of at 96 volts is a signineer unit and I believe it optimized for one the "explody" EV chemistries.
I think its safe to say that our application is moving away from the explody chemistries.

 

[Hedges]

Yes 240VAC is dangerous and special care must be taken.

We let our British friends worry about that.
Over here, we just use 120VAC. Twice. (or maybe three times for industrial applications.)

 

[JAndle]

Have you ever seen a hotdog cooked instantly, from cold to flaming hot in under a second? That is what high voltage DC can do to a limb. If you were equipped and trained to handle 96v you wouldn't be asking if it were a good idea or not. My 2cents.

I have a place where you can store your condescension. Unfortunately it is already full with your incorrect assumptions.

 

[JAndle]

32s may become a thing someday but it isn't much of a thing yet.
The only inverter that I know of at 96 volts is a signineer unit and I believe it optimized for one the "explody" EV chemistries.
I think its safe to say that our application is moving away from the explody chemistries.

There are a number of vendors in China for 96V and higher LPF packs. None I trust yet, but in the decade plus of dealing with China Southern and State grid it has been unsettling that it is them innovating and pushing efficiency and us doubling down on fear over science.

 

[JAndle]

We let our British friends worry about that.
Over here, we just use 120VAC. Twice. (or maybe three times for industrial applications.)

or 240V for dryers, pool pumps, central HVAC, ovens...

 

[Hedges]

or 240V for dryers, pool pumps, central HVAC, ovens...

Do you use 240V for anything?
I use +120V, and if I want more power I use -120V at the same time.
That is, touch any one wire of "240V" or "208V" in the US, and you're only touching 120Vrms.

I have wired "480V" delta, part of a remodel.
I don't deal with 40kV utility power, so if that's what you do I respect that work.
I've been taught what 12kV can do.
I have dealt with extremely low current 15kV. Non-hazardous, the electrical safety department had determined, but considering the angry continuous spark it made when I pulled a Lemo plug I'm glad I didn't get bit.
Other guys dealt with capacitors for flashtubes, I didn't have to.
400 MJ total, but I think only 20kJ per capacitor.

If you want to do higher voltage batteries for PV systems, you could skip over 96V and go to 400V. There are products out now, and that only has to do buck to generate 120/240V split phase.

 

[JAndle]

Do you use 240V for anything?
I use +120V, and if I want more power I use -120V at the same time.
That is, touch any one wire of "240V" or "208V" in the US, and you're only touching 120Vrms.

I have wired "480V" delta, part of a remodel.
I don't deal with 40kV utility power, so if that's what you do I respect that work.
I've been taught what 12kV can do.
I have dealt with extremely low current 15kV. Non-hazardous, the electrical safety department had determined, but considering the angry continuous spark it made when I pulled a Lemo plug I'm glad I didn't get bit.
Other guys dealt with capacitors for flashtubes, I didn't have to.
400 MJ total, but I think only 20kJ per capacitor.

If you want to do higher voltage batteries for PV systems, you could skip over 96V and go to 400V. There are products out now, and that only has to do buck to generate 120/240V split phase.

If you only touch one phase on split 240 yes your body capacitance is only shunting one phase to ground, at the equivalent of 170V peak. We fear what we don't work with, but hopefully we respect what we do work with. I originally started with the 96V batteries would need to be in a NEMA cabinet - or at least all the buswork would. Meanwhile I can just picture exposed 48V bus in a wiring closet because "it's safe"...

Back in the late 70's in a high school TV repair class I hit the CRT high voltage on a color TV. After I bounced off the cement wall I started being careful. That and a stint teaching power lab gave me a deep seated love for RF and sensors and embedded systems instead of power... Until 2008 when those sensors started going in power systems in China, then Taiwan, then pretty much everywhere. The photo is 24KV gear on a Petrobras oil rig. It is of course off and earthed while working on it. Normally. Luckily there was no bleedthough on the 11kV gear that wasn't earthed before it was opened at POSCO...

But, the takeaway is *I* could be OK doing it, I could get it permitted in Belize (and with the right cabinets, in the US), etc, but it could be an issue in the future if I wanted to sell the house and the buyer's inspector got the willies over it...

 

[Kodack]

I have a place where you can store your condescension. Unfortunately it is already full with your incorrect assumptions.

It was not my intent to be condescending. We're all friends here. I just want folks to be safe, don't we all?

 

[Hedges]

There have been a number of house fires.
Coming US electrical code will require battery systems to be UL listed (unless they're lead-acid), but will have an exception for repurposed EV batteries situated 5' or more from the house.

One could always center-ground a 96V pack and say they had two 48V batteries. Fuse both ends in that case.

Tesla Powerwall is high voltage (as alternative energy batteries go.)
So is LG Resu-10H

LG Chem RESU10H High-Voltage ESS Energy Storage Battery System

Low wholesale pricing in the USA on the latest LG Chem high-voltage 400V RESU10H energy storage battery systems. Authorized LG Chem supplier.

www.solarelectricsupply.com

Now recalled after several fires. Made with an explody lithium chemistry.

But you might consider doing 400V battery. There are inverters available, need to have a BMS that communicates with it.

I barely got book education on tubes in the '70's. But now I work with things like ion "optics", electron "optics".
I started with digital ASIC design, moved into analog, RF, sensors. Driving a Pirani, for instance.

 

[John Frum]

There are a number of vendors in China for 96V and higher LPF packs. None I trust yet, but in the decade plus of dealing with China Southern and State grid it has been unsettling that it is them innovating and pushing efficiency and us doubling down on fear over science.

I'm quite interested.
Have you been able to source a bms and an inverter/charger?
I guess a class t fuse will work
Maybe a magnetic breaker for disconnect?

Rough math says a a 32s pack of the big blue cells is <400 pounds for >100kwh.
This is very cool!

 

[JAndle]

I'm quite interested.
Have you been able to source a bms and an inverter/charger?
I guess a class t fuse will work
Maybe a magnetic breaker for disconnect?

Rough math says a a 32s pack of the big blue cells is <400 pounds for >100kwh.
This is very cool!

Rosen (I think) had a 96V/100Ah integrated BMS unit. I may be recalling a different unit. Sigineer has a 96V solar inverter but I am backing off 96V unless it becomes more widely used. There is a difference between state of the art and sole source I think Merit and a few others have 96V banks as well. I am not so DIY that I will make my own, otherwise I'd be chatting up my old classmates at Renesas Intersil and designing the BMS while I am at it! Planned on an array of independtly breaker fed 10kW scale battery banks so if one went bad, the breaker would isolate it. Targeting 40-50KWh. Currently looking at 3x parallel Sigineer '5kW' 3500W solar capable 100A inverters and sourcing the high power panels from Rosen. But, unless I decide to ground mount it is a shed for site power during construction and then relocate it rooftop after construction, new components will likely be available before then.

 

[JAndle]

There have been a number of house fires.
Coming US electrical code will require battery systems to be UL listed (unless they're lead-acid), but will have an exception for repurposed EV batteries situated 5' or more from the house.

Now recalled after several fires. Made with an explody lithium chemistry.

LFP for sure. Not LiPo! I have seen Li titanate lately??
Also Belize, so the rules are ill defined. UL will help and be faster (or at least a CE.IEC equivalent). My credentials and a good engineering job should suffice. Looking for good batteries with fewer middlemen marking them up. I can put boots on the ground in China (second hand) if I must.

But you might consider doing 400V battery. There are inverters available, need to have a BMS that communicates with it.

I might have the skills to series cascade two or more 48V BMS with bank by bank balance, but I already have too much work.

The 96V LFP I am seeing are mostly EV, but that should be suitable. EVs deep cycle and just have much more aggressive discharge specs, right?

I barely got book education on tubes in the '70's. But now I work with things like ion "optics", electron "optics".
I started with digital ASIC design, moved into analog, RF, sensors. Driving a Pirani, for instance.

surface acoustic wave resonator sensors, passive & wireless, for monitoring temperature in switchgear up to 40kW... www.intellisaw.com