Why are people afraid of High Voltage Batteries?

[jpwhit]

I find it interesting that people are scared of HV batteries. High voltage DC isn't as dangerous as high voltage AC. Most everyone has HV PV inputs already in their system as well. If you're so scared of HV DC, then you should wire all your PV panels in parallel and have 30-50V coming into your MPPT inputs at really high amperage. But wait, everyone would say that's stupid and inefficient. Yet they turn around and do exactly the same thing with their batteries........

I know the answer above is you don't find inverters setup for MPPT inputs with that low of a voltage. But they did make inverters like that back in the early days. But nobody does now simply because it's inefficient. The same is true with battery inputs and it's only a matter of time before all inverters move to HV batteries for the increased efficiency.

12, 24, and 48V battery inverters exist because of the heritage of lead acid batteries in those voltages. Along with the desire to support battery / inverter setups where you didn't have to start with more than a few batteries because they tended to be large individually. Now that lead acid batteries are being replaced by newer battery technologies that naturally come in smaller cells, there is really no reason to continue with these limited voltages.

I've heard the argument that with DIYers it's safer to stay with low voltage because they can make more costly / dangerous mistakes with higher voltages, but I don't really buy that argument because almost nobody makes any of this equipment with DIYer's in mind. And if that argument were really true, you'd still have some inverter makers providing inverters with low voltage MPPT PV inputs.

I also hear the argument that HV BMS'es are hard to find. And there's a little truth to that, but that's also just a lack of experience with HV battery design as well. For example, I've studies or been involved of the design of EV battery systems from Tesla, GM, Ford, and others as part of my career being involved in the industrial / automotive / defense industry. None of the EV makers HV battery systems have a single monolithic BMS for the entire HV battery system. All of them consist of modules somewhere between 24 - 100V. They all follow the pattern of having a BMS system at each module level. And they typically do balancing of the cells in the scope of a module. And of course, they have a master BMS controller to understand the bigger picture. And that's probably the missing link for the DIY community.

That's because as long as the number of cells in each module is a high enough number of cells to statistically represent the typical behavior of the battery cells in aggregate, which is the case with 24v modules and Li-Ion or LFP cells, there isn't much of an improvement in the reliability of the system to balance cells beyond the module level. Said in another way, if the frequency where one module made of multiple cells gets out of balance with another module of the same design is really tiny. Then it's not worth spending any money to handle that case. If that happens statistically 1 in 100,000 battery systems. It just makes more sense to have the 1 in 100,000 battery system shut itself down as "failed". Cases where a module gets out of balance with another modules because one of the cells is simply failing doesn't really matter. Because typically balancing can't really save a battery system in that case anyway.

It's not a safety issue as long as the BMS in each module has the ability to signal system shutdown if an error occurs in the sub-system. And that signaling almost always happens via the CANBUS communications.

 

[Mattb4]

High DC voltages can sustain arc for longer separation distances. PV voltages being high have led to arc fires but are constrained by the typically lower amperage involved versus a battery. Protective equipment for high DC voltages is rarer and more expensive compared to the older voltage standards from LA days.

You are correct though that it is slowly changing in the PV world to have higher voltage battery setups. On an individual level it comes down to power needs. Some folks get by with small amounts while others have multiple 200a main services to feed their McMansions with heated backyard pools, spas and pleasure domes.

 

[DIYrich]

While "It's the volts that jolts but it's the amps that kills", 500v at 20a max from a string is different to me than 500v at 100+ amps a HV battery can put out. Maybe I'm being naive, but 48v at 1000a is less scary to me.

Plus devices to handle 48v dc are easier to find than 600v dc. Hard enough to find a 60v actual on/off switch.

 

[IGBT]

10kV at 100mA will kill you three times over, while a 12V battery at 100 amps won't even give you a tingle. 48V is there in the middle ground I guess.

 

[jpwhit]

While "It's the volts that jolts but it's the amps that kills", 500v at 20a max from a string is different to me than 500v at 100+ amps a HV battery can put out. Maybe I'm being naive, but 48v at 1000a is less scary to me.

Plus devices to handle 48v dc are easier to find than 600v dc. Hard enough to find a 60v actual on/off switch.

That's right, but the amps a system can put out has little to do with the amps that'll flow when I person makes contact with a conductor. That's determined by the impedance of the person's body. And people have a lower impedance for AC vs DC. Also the path through the body has a huge factor on the amount of danger. Power flowing from hand to hand for example is really deadly. But power flowing from hand to foot is much less dangerous. Which is the source of the old saying in the electrician world of don't use both hands if you can help it....

The lower the impedance, the higher the current flow.

 

[Lt.Dan]

HV PV is much more common, but is way easier to handle because you don't have any open Conductors (usually). If someone were to DIY a HV battery, could you imagine the potential of touching the wrong terminal, or some idiot dropping a wrench across 400v?

HV PV was also more pushed because of distance. Going 250-500' was unreasonable until 500v VOC MPPT came around. Batteries on the other hand are typically less than 15', and more often than not, less than 3 feet away from the inverter.

4/0 cable (which is still mostly affordable) can support hundreds of amps, which will cover 99% of people's needs at 51v.

The reason we haven't pushed to as much HV batteries is because we don't need to IMO.

 

[v_green57]

More BMS's = more complexity = more points of failure.

Also the user base of low voltage stuff is much, much larger. That experience and knowledge base is priceless.

 

[Delmar]

Soon a natural resource will be degraded EV batteries in the 350-400 volt range, however there is no easy method to utilize. Producing HV inverters will be an expensive proposition.

Would it be easier [and safer] to make a charge controller with 350-400V input and 48V output? Will power a smaller 48V battery bank with plenty of inverters to choose from.

You can do this now by using the 12V accessory battery with boost controller for 48V, but you are limited with amps.

 

[green mountain boys]

You might find this interesting. I have seen several of his videos. He posted some videos under another user name, GaryR i think.

 

[DIYrich]

100ah battery at 400v is 40kWh, or 134 cells. Expensive increments. Also, does the bms have to be designed to be put in series to make 400+ volts?

 

[efficientPV]

I run HV from my panels right into an old inverter. I have it set so the 12V boost section only turns on should a small cloud passes overhead. If I only need 30W to make up what the cloud deducts, that is all the 12V inverter will add. I ran for years with no battery till last year which was exceptionally cloudy and the smoke from Canada.

 

[Bluedog225]

You might find this interesting. I have seen several of his videos. He posted some videos under another user name, GaryR i think.

I don’t understand he panel layout. Looks like the rows shade each other. I only see 3 vids. Don’t see one on the array.

 

[billvon]

Soon a natural resource will be degraded EV batteries in the 350-400 volt range, however there is no easy method to utilize. Producing HV inverters will be an expensive proposition.

There are already over a dozen. New inverter/battery systems for residential use are around 50/50 48V and high voltage. It's actually easier to design for; it's easier to convert similar voltages (320VDC for 240VAC, 200-600V PV and 300-400V batteries) than dissimilar voltages (like 12/24/48V to all the above.)

 

[billvon]

I find it interesting that people are scared of HV batteries.

Well, they're scared because they are more dangerous to work on live.

However, every HV battery I have seen has a BMS and/or a manual disconnect that shuts down power. This is something that lead acid batteries (and even some of the cheaper LFP's) do NOT have - which is a safety issue. Sure, 48V isn't going to electrocute you, but dropping a tool on a 48V lead acid battery has a high probability of starting a fire. Much safer to be able to turn off the battery when you're working on it.

So, to me, a 400V battery with an on/off switch (say, an LG RESU H) is a lot safer than a 48V lead acid bank.

That's because as long as the number of cells in each module is a high enough number of cells to statistically represent the typical behavior of the battery cells in aggregate, which is the case with 24v modules and Li-Ion or LFP cells, there isn't much of an improvement in the reliability of the system to balance cells beyond the module level.

Gotta disagree with that. You could use exactly the same argument for massively paralleled modules - "as long as the number of cells in each paralleled group is a high enough number of cells to statistically represent the typical behavior of the battery cells in aggregate, there isn't much of an improvement in the reliability of the system to balance each of the groups." Which of course isn't the case in Tesla batteries, for example.

You could certainly argue that the failure rate is low ENOUGH that replacing batteries is cheaper (on average) than the additional hardware to move balance power within the pack, of course.

 

[jpwhit]

There are already over a dozen. New inverter/battery systems for residential use are around 50/50 48V and high voltage. It's actually easier to design for; it's easier to convert similar voltages (320VDC for 240VAC, 200-600V PV and 300-400V batteries) than dissimilar voltages (like 12/24/48V to all the above.)

That's absolutely the case. Building an inverter to cover HV DC to HV AC is much easier than having to boost low voltage DC up to HV and then convert it to an alternating waveform.

It's also much easier, and therefore cheaper, to build a more efficient inverter with HV DC rather than LV DC.

 

[jpwhit]

HV PV is much more common, but is way easier to handle because you don't have any open Conductors (usually). If someone were to DIY a HV battery, could you imagine the potential of touching the wrong terminal, or some idiot dropping a wrench across 400v?

HV PV was also more pushed because of distance. Going 250-500' was unreasonable until 500v VOC MPPT came around. Batteries on the other hand are typically less than 15', and more often than not, less than 3 feet away from the inverter.

4/0 cable (which is still mostly affordable) can support hundreds of amps, which will cover 99% of people's needs at 51v.

The reason we haven't pushed to as much HV batteries is because we don't need to IMO.

I would contend that dropping a wrench across open conductors on a LV battery system can be much more catastrophic than doing the same thing on a HV battery system. Let's take a 12kw system as an example. For such a system a 48v battery system would be designed to handle 250 amps. A 500V battery system would be designed to handle 24 amps. If you drop a wrench across somewhere that 250 amps can flow, the wrench will vaporize in a cloud of red-hot metal. Dropping a wrench across the HV system won't have the amperage to vaporize the wrench. You'll get some nice sparks, but more than likely the 10ga wire needed to carry that kind of current will burn open somewhere with little fanfare.

In terms of battery distance from inverter, HV battery systems let you easily put the batteries up to 250 - 500 feet away. That often lets the batteries be placed somewhere that there is inherently greater safety.

I think the reason for HV batteries is simple. Higher efficiency for a lower cost of implementation. And that will become more important as PV based power will need to be time shifted for the power to be available when most useful.

 

[Suijkerbuijk]

High volt dc .
Thare is a reason that over 48volt is high energy and you have to watch out .

Ac you need a low amp to stop your hart beating.
Dc can kill red blood cells.
That is the reason that electric cars can only be done by people that have special license to work on.
400 dc volt you do not feel it , but kill the red cells .
On that moment you need blood transfusie from the hospital.
This is something that is not tell by Danger of a high volt dc .
I have learn this information about it.
I have that certification to work on those cars.

So long the dc volt is low it can not move through your body .
Till the dc is higher and can do it.

 

[dcjohn]

I think we all agree that HV will be better if it was safe. So, just wondering, if anyone knows Class 4 - Fault Managed Power (new NEC standard - Article 726) and if it will be soon the solution for HVDC solar systems. Because if that's the case that changes everything, this will make HVDC much safer ever with all the AC protection that we have till today.

 

[Nobodybusiness]

High DC voltages can sustain arc for longer separation distances. PV voltages being high have led to arc fires but are constrained by the typically lower amperage involved versus a battery. Protective equipment for high DC voltages is rarer and more expensive compared to the older voltage standards from LA days.

You are correct though that it is slowly changing in the PV world to have higher voltage battery setups. On an individual level it comes down to power needs. Some folks get by with small amounts while others have multiple 200a main services to feed their McMansions with heated backyard pools, spas and pleasure domes.

Pleasure domes?
I got to see one of these..

 

[HowlerMonkey]

I’m curious about the certifications for electric cars.

 

[Mattb4]

Pleasure domes?
I got to see one of these..

Here's the one I built a few years ago. A bunch of the locals dropped by for a picnic.

 

[green mountain boys]

I don’t understand he panel layout. Looks like the rows shade each other. I only see 3 vids. Don’t see one on the array.

View attachment 221335

He posted videos under 2 different youtube accounts. Most of his videos were under the name garyr, however he has removed some of the videos. To make things even more difficult, he does not do a good job of explaining and summarizing his content. He has LiFePO4 cells, DIY in a 64S configuration, resulting in a battery with a voltage of just over 200 volts and a high voltage inverter. He has several of these 200 volt batteries in parallel.

 

[1201]

He posted videos under 2 different youtube accounts. Most of his videos were under the name garyr, however he has removed some of the videos. To make things even more difficult, he does not do a good job of explaining and summarizing his content. He has LiFePO4 cells, DIY in a 64S configuration, resulting in a battery with a voltage of just over 200 volts and a high voltage inverter. He has several of these 200 volt batteries in parallel.

Do you know if his inverter operates in closed loop or open loop? Which bms does he use?

 

[Nobodybusiness]

Here's the one I built a few years ago. A bunch of the locals dropped by for a picnic.
View attachment 221605

Looks like a fury convention.

 

[green mountain boys]

Do you know if his inverter operates in closed loop or open loop? Which bms does he use?

I cannot remember. I think he may have taken down the videos where he discussed that information. He said in his last video (2 days ago), if there was interest in the comments and he got some "likes" he would post a new video summarizing his system and all of the components. I hope he does. He has stated several times that he thinks YouTube is hiding his content, so he is not too happy with YouTube. I don't know much about how YouTube works but I did notice none of the 20 or so videos he posted on his 2 different accounts had more than a few hundred views. I just checked his second YouTube account and he had less than 100 subscribers a few days ago and now he has 1,260 so hopefully he will make the video.