4 ms·

I have to admit that I really dislike using ~12V batteries for high power applications like this. I say this having built a ~400A ~14V system. It’s miserable.

by amluto 3y ago

I have to admit that I really dislike using ~12V batteries for high power applications like this. I say this having built a ~400A ~14V system. It’s miserable. 1 kW at 100V or 250V or similar uses a nice, small, flexible wire. It can be quite safe because it can be fused or otherwise protected at low currents, which mitigates the risk of welding things, starting fires, or arcing. Ground fault protection, arc fault protection, and general loss-of-isolation protection are available. It’s easy to rework (lever nuts! screw terminals!). 400A (or even 80A or so like in this article) is a whole different ball game. Sure, you have to work hard to electrocute yourself. But you can easily set things on fire or weld things together without coming close to blowing a fuse. And you need to protect both ends of wires in a parallel arrangement. And the wires are enormous, expensive, and hard to terminate. I would much prefer one of three alternative designs to become popular: 1A: a series arrangement of batteries at a civilized 48V or so. You can do this with an aftermarket BMS, but they tend to be janky. 1B: same but actually high voltage (a few hundred V, like an EV) 2: batteries with microinverters and a civilized way to share current. A manufacturer could make a single package with a 1kWh battery, a BMS, a low voltage, low current DC auxiliary output, and a ground-fault and overcurrent-protected 110-250V AC input/output. And an RS485 or 10BASE-T1S or CAN connection so that they can coordinate their I-V characteristics to appropriate distribute charge or discharge current. Now you can connect as many microinverter-batteries as you like in parallel, using #14 wire, to one ordinary circuit breaker per battery plus (depending on the overall arrangement) one big breaker to protect the common bus. edit: Also, with this design, no one, not even the manufacturer, needs to touch a heavy-gauge wire. Everything in the battery would use cheap, painless busbars or small wires, depending on the internal voltage, and the manufacturer could set the voltage however they like. Although 12V internally might be entirely reasonable if the end user also wants to consume 12V at very low currents through the aux output.

RetpolineDrama 3y ago
> 1A: a series arrangement of batteries at a civilized 48V And here I am mad that home-storage server rack batteries are all 48V it seems, but for the same reasons (huge 400+ amp cables required to get decent wattages). When each car charger can do ~14.4kw you need a lot of fat cables running to battery banks
- numpad0 3y ago
  That's because 48-50V is threshold for "High Voltage", what THAT sign actually signifies, and licenses are required!
  - stephen_g 3y ago
    Technically not, actually. By the IEC standard, 50V (RMS AC) is about the highest you can go for 'Extra-low voltage'. IEC actually has DC up to 120 V as ELV but often regional standards will have a lower value (like EU seems to be 75V and Australia/New Zealand at 60V) Only above 1000V RMS AC or 1500 V DC is considered 'high voltage'. That's why a correct sticker on domestic equipment will usually use the wording 'Dangerous voltage' or 'Hazardous voltage' or the like, not 'high voltage'. An actual correctly placed 'Danger - High Voltage' sign tends to mean something like 11kV AC
ilyt 3y ago
> I have to admit that I really dislike using ~12V batteries for high power applications like this. I say this having built a ~400A ~14V system. It’s miserable. The schematic looks to be pretty adaptable to higher driving voltage, just need separate 12V for control board. There is even one in datasheet for 24-36V operation >2: batteries with microinverters and a civilized way to share current. A manufacturer could make a single package with a 1kWh battery, a BMS, a low voltage, low current DC auxiliary output, and a ground-fault and overcurrent-protected 110-250V AC input/output. And an RS485 or 10BASE-T1S or CAN connection so that they can coordinate their I-V characteristics to appropriate distribute charge or discharge current. > Now you can connect as many microinverter-batteries as you like in parallel, using #14 wire, to one ordinary circuit breaker per battery plus (depending on the overall arrangement) one big breaker to protect the common bus. You can build it right now. AC coupled batteries exist; here is some random one that scales up: https://www.fortresspower.com/ac-coupled/ https://www.fortresspower.com/ac-coupled/ The problem is that you generally want batteries when you want renewables and in that case just having one big box handling batteries and solar panels is more economical than microinverters everywhere 48V battery pack + BMS is significantly cheaper than same thing with microinverter, and when you scale up one big inverter is cheaper than a bunch of smaller ones. So yeah, it is "best" but also most expensive way. And frankly, the hardest to develop, which is probably why there is little to no open designs for that.
samtho 3y ago
I use 48v for all my high power DC applications and I usually spin PCBs. Part of the reason I use 48vdc is that there are bunch of ICs and reference designs for PoE applications that run at this voltage level. 12v is a miserable voltage to work with in general: too high for most logic circuits and for LDOs to work effectively but it’s too low for any large load with high-power applications become cost prohibitive quickly due to the cost of the conductors. Fun fact: Auto makers have gotten away with under sizing starter conductors, despite it drawing 80-100A, because it is only energized briefly and the length of the run is very short.
- Animats 3y ago
  Much industrial automation runs on 24VDC. High enough that the losses within a cabinet are tolerable, low enough that there's no electrocution hazard.
  - deleted 3y ago
    [deleted]
  - amelius 3y ago
    If you keep your hands dry or if you're a male, then 48VDC can be quite safe too. https://www.allaboutcircuits.com/textbook/direct-current/chpt-3/ohms-law-again/ https://www.allaboutcircuits.com/textbook/direct-current/chp... We're running out of copper. So better keep your voltages on the high end (but still safe of course). https://www.cnbc.com/2023/02/07/there-isnt-enough-copper-in-the-world-shortage-could-last-until-2030.html https://www.cnbc.com/2023/02/07/there-isnt-enough-copper-in-...
    - mbreese 3y ago
      To save someone else looking for the answer to why being male is a factor here… (which I didn’t know about!) > Oh, and in case you’re wondering, I have no idea why women tend to be more susceptible to electric currents than men! The pain thresholds are given in a table that is split by men and women. I believe the assumption is different conductivity between “typical” male/female bodies, but it’s really not spelled out.
londons_explore 3y ago
> And an RS485 or 10BASE-T1S or CAN connection so that they can coordinate their I-V characteristics Note that simply voltage/frequency alone can communicate everything necessary to evenly distribute load. For example: Output frequency = 60 + X Hz Where X varies between -0.1 and 0.1, indicating the percentage of max load the inverter is under(in charge or discharge direction). Such a scheme will self synchronize any number of inverters, even of varying capacities, into a stable grid, and they will all be the same percentage loaded. The grid can even have a few dumb gas generators on too and remain stable. No fancy comms needed.
- amluto 3y ago
  I think this works for discharge, possibly with some extra cleverness needed if the batteries are at different SoCs. But I’m not sure how it could handle being tied to the grid intelligently or how charging could be managed without some additional controls. Also, can a pure frequency-based scheme handle the case where a whole bunch of inverters are in parallel and a load that’s much larger than any one of them can handle individually starts up?
  - londons_explore 3y ago
    > extra cleverness needed if the batteries are at different SoCs The scheme as presented keeps the inverters under equal fraction load, but does not guarantee the batteries end up at equal state of charge. The formula can easily be modified to over time achieve this too: X = 60 + (fraction load of inverter)*0.1 + per_battery_factor The per_battery_factor would be set based on the batteries state of charge and/or any user instructions from buttons to charge or discharge a specific battery.
  - londons_explore 3y ago
    > handle the case where a whole bunch of inverters are in parallel and a load that’s much larger than any one of them can handle individually Yes, but with caveats... The grid will startup, smoothly (ie. gradually), but during startup every inverter will be at its maximum configured load (with the maximum load config ramped during startup). When the maximum load is hit, the frequency sits at the minimum design frequency (59.9 Hz in this case), and voltage drops instead. So your large device will see a sine wave at 59.9 Hz that starts at zero volts, and increases in amplitude to 230 volts gradually over many seconds, and as soon as it hits 230 volts, the frequency will almost immediately become 60 Hz. For large motors, thats a problem. Large motors typically don't like line frequency at a reduced voltage - they can end up not having enough torque to turn, and will just rapidly heat up. They would do better without the gradual startup ramp - but that startup ramp is necessary to ensure the inverters stay in sync. In reality, this scheme works for AC type motors rated up to about 30% of the capacity of the inverter set, or up to 100% as long as another motor is already running on the same grid.
h2odragon 3y ago
Depending on the load, you can often skimp on the conductors and get away with it. Someone else mentioned undersized starter power cables. There's really only a few loads that are full draw, full duty cycle. Old car stereo trick, to power big amplifiers in the trunk: use a second battery and big power lead to it, small power leads from the main battery to the secondary. That secondary can be backed or replaced by big capacitors, too; with commensurate increases in cost and possible risks when things go wrongs. But you can provide rich chunky amps and use skinnier cable than you'd think on the long run to do it.
- mschuster91 3y ago
  Never forget to put an override relay (normal open, closing when the engine has run for a set amount of time or when manually bypassed) and a fuse in the path though (and that also applies for campers). There are a number of things to consider, and if done badly, also serious risks: - you don't want a permanent connection between the main and aux battery to avoid accidentally sucking both batteries dry on the aux-battery side, and to avoid the starter overloading the cable between the two batteries - you don't want to risk an empty aux battery charging itself on the main battery and engine with more current than the cable supports, hence the fuse - you do want to be able to connect both batteries in a scenario where you accidentally drained the main battery (e.g. a light left on) to "self-start"
  - h2odragon 3y ago
    All very good point, tx. I liked diodes as well as fuses, especially on the inputs of capacitors. Automotive power is never clean.
mjevans 3y ago
There's a push for '12vo' or 12 volt only PSUs for PCs... but with the major power consumers mostly the GPU, CPU, RAM (?), and possibly spinning drives, would a similar to telecom gear 48V make more sense? For GPUs and any USB PD connections ('standard' is up to 20V 5A while 'extended' is 48V 5A) a system power level of ~48v might be very useful. It would also give a chance to replace the recent higher density connectors that aren't designed with a sufficiently robust user experience with improved versions that more clearly lock into solid connection.
- myself248 3y ago
  Yes, I thought 48vo was already on the drawing board.
- crote 3y ago
  Not really. Pretty much the only PC part which wants native 12V would be the fans. All the other parts drop it down to 5V / 3V3 for auxiliary components, or 1-2V for the CPU and GPU cores - which use the vast majority of power. Dropping 12V DC to 1.5V is reasonably doable, but dropping 48V DC to 1.5V is a bit of a pain. In general you do not want to go beyond a 1:10 ratio for efficiency reasons, so 48V doesn't really gain you anything, while at the same time resulting in a massive compatibility break. The push to 12VO is driven by a desire to get rid of technical debt. The 3V3 / 5V wires can't handle the current you need on those rails, so those are converted from 12V anyways. And literally nobody is using the -12V and -5V wires, so keeping those around is pointless.
  - mkj 3y ago
    Why does the ratio affect efficiency? Naively it seems like it should just be able to use differently sized inductors.
  - namibj 3y ago
    Open compute platform switched to 48V years ago, to afford having multiple PSUs feeding multiple servers, with (those days) a fixed 4:1 switched capacitor down converter right next to the existing 12V-to-0.5~1.5V DrMOS VRM power stages. There are iirc GaN devices from epc-co these days that make it feasible to go directly from 48V with the VRMs to the 0.5~1.5V for the core.

by amluto 3y ago

RetpolineDrama 3y ago

> 1A: a series arrangement of batteries at a civilized 48V And here I am mad that home-storage server rack batteries are all 48V it seems, but for the same reasons (huge 400+ amp cables required to get decent wattages). When each car charger can do ~14.4kw you need a lot of fat cables running to battery banks

numpad0 3y ago
That's because 48-50V is threshold for "High Voltage", what THAT sign actually signifies, and licenses are required!
- stephen_g 3y ago
  Technically not, actually. By the IEC standard, 50V (RMS AC) is about the highest you can go for 'Extra-low voltage'. IEC actually has DC up to 120 V as ELV but often regional standards will have a lower value (like EU seems to be 75V and Australia/New Zealand at 60V) Only above 1000V RMS AC or 1500 V DC is considered 'high voltage'. That's why a correct sticker on domestic equipment will usually use the wording 'Dangerous voltage' or 'Hazardous voltage' or the like, not 'high voltage'. An actual correctly placed 'Danger - High Voltage' sign tends to mean something like 11kV AC

ilyt 3y ago

> I have to admit that I really dislike using ~12V batteries for high power applications like this. I say this having built a ~400A ~14V system. It’s miserable. The schematic looks to be pretty adaptable to higher driving voltage, just need separate 12V for control board. There is even one in datasheet for 24-36V operation >2: batteries with microinverters and a civilized way to share current. A manufacturer could make a single package with a 1kWh battery, a BMS, a low voltage, low current DC auxiliary output, and a ground-fault and overcurrent-protected 110-250V AC input/output. And an RS485 or 10BASE-T1S or CAN connection so that they can coordinate their I-V characteristics to appropriate distribute charge or discharge current. > Now you can connect as many microinverter-batteries as you like in parallel, using #14 wire, to one ordinary circuit breaker per battery plus (depending on the overall arrangement) one big breaker to protect the common bus. You can build it right now. AC coupled batteries exist; here is some random one that scales up: https://www.fortresspower.com/ac-coupled/ https://www.fortresspower.com/ac-coupled/ The problem is that you generally want batteries when you want renewables and in that case just having one big box handling batteries and solar panels is more economical than microinverters everywhere 48V battery pack + BMS is significantly cheaper than same thing with microinverter, and when you scale up one big inverter is cheaper than a bunch of smaller ones. So yeah, it is "best" but also most expensive way. And frankly, the hardest to develop, which is probably why there is little to no open designs for that.

samtho 3y ago

I use 48v for all my high power DC applications and I usually spin PCBs. Part of the reason I use 48vdc is that there are bunch of ICs and reference designs for PoE applications that run at this voltage level. 12v is a miserable voltage to work with in general: too high for most logic circuits and for LDOs to work effectively but it’s too low for any large load with high-power applications become cost prohibitive quickly due to the cost of the conductors. Fun fact: Auto makers have gotten away with under sizing starter conductors, despite it drawing 80-100A, because it is only energized briefly and the length of the run is very short.

Animats 3y ago
Much industrial automation runs on 24VDC. High enough that the losses within a cabinet are tolerable, low enough that there's no electrocution hazard.
- deleted 3y ago
  [deleted]
- amelius 3y ago
  If you keep your hands dry or if you're a male, then 48VDC can be quite safe too. https://www.allaboutcircuits.com/textbook/direct-current/chpt-3/ohms-law-again/ https://www.allaboutcircuits.com/textbook/direct-current/chp... We're running out of copper. So better keep your voltages on the high end (but still safe of course). https://www.cnbc.com/2023/02/07/there-isnt-enough-copper-in-the-world-shortage-could-last-until-2030.html https://www.cnbc.com/2023/02/07/there-isnt-enough-copper-in-...
  - mbreese 3y ago
    To save someone else looking for the answer to why being male is a factor here… (which I didn’t know about!) > Oh, and in case you’re wondering, I have no idea why women tend to be more susceptible to electric currents than men! The pain thresholds are given in a table that is split by men and women. I believe the assumption is different conductivity between “typical” male/female bodies, but it’s really not spelled out.

londons_explore 3y ago

> And an RS485 or 10BASE-T1S or CAN connection so that they can coordinate their I-V characteristics Note that simply voltage/frequency alone can communicate everything necessary to evenly distribute load. For example: Output frequency = 60 + X Hz Where X varies between -0.1 and 0.1, indicating the percentage of max load the inverter is under(in charge or discharge direction). Such a scheme will self synchronize any number of inverters, even of varying capacities, into a stable grid, and they will all be the same percentage loaded. The grid can even have a few dumb gas generators on too and remain stable. No fancy comms needed.

amluto 3y ago
I think this works for discharge, possibly with some extra cleverness needed if the batteries are at different SoCs. But I’m not sure how it could handle being tied to the grid intelligently or how charging could be managed without some additional controls. Also, can a pure frequency-based scheme handle the case where a whole bunch of inverters are in parallel and a load that’s much larger than any one of them can handle individually starts up?
- londons_explore 3y ago
  > extra cleverness needed if the batteries are at different SoCs The scheme as presented keeps the inverters under equal fraction load, but does not guarantee the batteries end up at equal state of charge. The formula can easily be modified to over time achieve this too: X = 60 + (fraction load of inverter)*0.1 + per_battery_factor The per_battery_factor would be set based on the batteries state of charge and/or any user instructions from buttons to charge or discharge a specific battery.
- londons_explore 3y ago
  > handle the case where a whole bunch of inverters are in parallel and a load that’s much larger than any one of them can handle individually Yes, but with caveats... The grid will startup, smoothly (ie. gradually), but during startup every inverter will be at its maximum configured load (with the maximum load config ramped during startup). When the maximum load is hit, the frequency sits at the minimum design frequency (59.9 Hz in this case), and voltage drops instead. So your large device will see a sine wave at 59.9 Hz that starts at zero volts, and increases in amplitude to 230 volts gradually over many seconds, and as soon as it hits 230 volts, the frequency will almost immediately become 60 Hz. For large motors, thats a problem. Large motors typically don't like line frequency at a reduced voltage - they can end up not having enough torque to turn, and will just rapidly heat up. They would do better without the gradual startup ramp - but that startup ramp is necessary to ensure the inverters stay in sync. In reality, this scheme works for AC type motors rated up to about 30% of the capacity of the inverter set, or up to 100% as long as another motor is already running on the same grid.

h2odragon 3y ago

Depending on the load, you can often skimp on the conductors and get away with it. Someone else mentioned undersized starter power cables. There's really only a few loads that are full draw, full duty cycle. Old car stereo trick, to power big amplifiers in the trunk: use a second battery and big power lead to it, small power leads from the main battery to the secondary. That secondary can be backed or replaced by big capacitors, too; with commensurate increases in cost and possible risks when things go wrongs. But you can provide rich chunky amps and use skinnier cable than you'd think on the long run to do it.

mschuster91 3y ago
Never forget to put an override relay (normal open, closing when the engine has run for a set amount of time or when manually bypassed) and a fuse in the path though (and that also applies for campers). There are a number of things to consider, and if done badly, also serious risks: - you don't want a permanent connection between the main and aux battery to avoid accidentally sucking both batteries dry on the aux-battery side, and to avoid the starter overloading the cable between the two batteries - you don't want to risk an empty aux battery charging itself on the main battery and engine with more current than the cable supports, hence the fuse - you do want to be able to connect both batteries in a scenario where you accidentally drained the main battery (e.g. a light left on) to "self-start"
- h2odragon 3y ago
  All very good point, tx. I liked diodes as well as fuses, especially on the inputs of capacitors. Automotive power is never clean.

mjevans 3y ago

There's a push for '12vo' or 12 volt only PSUs for PCs... but with the major power consumers mostly the GPU, CPU, RAM (?), and possibly spinning drives, would a similar to telecom gear 48V make more sense? For GPUs and any USB PD connections ('standard' is up to 20V 5A while 'extended' is 48V 5A) a system power level of ~48v might be very useful. It would also give a chance to replace the recent higher density connectors that aren't designed with a sufficiently robust user experience with improved versions that more clearly lock into solid connection.

myself248 3y ago
Yes, I thought 48vo was already on the drawing board.
crote 3y ago
Not really. Pretty much the only PC part which wants native 12V would be the fans. All the other parts drop it down to 5V / 3V3 for auxiliary components, or 1-2V for the CPU and GPU cores - which use the vast majority of power. Dropping 12V DC to 1.5V is reasonably doable, but dropping 48V DC to 1.5V is a bit of a pain. In general you do not want to go beyond a 1:10 ratio for efficiency reasons, so 48V doesn't really gain you anything, while at the same time resulting in a massive compatibility break. The push to 12VO is driven by a desire to get rid of technical debt. The 3V3 / 5V wires can't handle the current you need on those rails, so those are converted from 12V anyways. And literally nobody is using the -12V and -5V wires, so keeping those around is pointless.
- mkj 3y ago
  Why does the ratio affect efficiency? Naively it seems like it should just be able to use differently sized inductors.
- namibj 3y ago
  Open compute platform switched to 48V years ago, to afford having multiple PSUs feeding multiple servers, with (those days) a fixed 4:1 switched capacitor down converter right next to the existing 12V-to-0.5~1.5V DrMOS VRM power stages. There are iirc GaN devices from epc-co these days that make it feasible to go directly from 48V with the VRMs to the 0.5~1.5V for the core.