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As devices like home fridges move towards “inverter drive” with switch mode power supplies, I wonder how low of a voltage they could still run off. And if they’

As devices like home fridges move towards “inverter drive” with switch mode power supplies, I wonder how low of a voltage they could still run off. And if they’d happily accept 48VDC and still function. Saw a teardown/repair of a big home flatscreen TV and while the label on the outside said “120VAC”, the power supply inside said 120/240V, so it was the same internals worldwide, but labelled differently to discourage gray-market imports.

kube-system 3y ago
It could have just been that one team labeled the housing according to the requirements, and another team built the internals to meet (or exceed) the requirements.
- Goz3rr 3y ago
  Or the power supply is sourced from multiple vendors, and other units might not have the same range
  - woleium 3y ago
    Or the power units were from a run that ended up as defective at the higher voltage
    - Scoundreller 3y ago
      Going to be no bueno if donor boards end up on the secondary market. But now that I think about it, it’s possible they’re fitted with different replaceable fuses (half the amperage in 240v areas).
mschuster91 3y ago
> As devices like home fridges move towards “inverter drive” with switch mode power supplies, I wonder how low of a voltage they could still run off. And if they’d happily accept 48VDC and still function. The technical side should continue to work until you reach the lower limit of what the bootstrap circuitry can handle. The problem will be the amperages required... say, a fridge. Its motor will run at ~200 watts, which means 1A at 230V. No biggie. But if you're going down to 48V, the high-voltage side will now run 4A, and more the lower you go on voltage - and that's without taking peak inrush currents into account which can easily go to 10A@230V (or 40A@48V) for a few split seconds. If your current source or the wiring can't hold that, you'll likely run into serious issues.
- sokoloff 3y ago
  I thought one major advantage of inverter drives was the well-managed starting currents. This is a noise/vibration advantage but also an electrical win.
  - hinkley 3y ago
    But a wire pulling 2 amps at 3.3 volts experiences very different physics than a wire pulling .6 amps at 12 volts.
- quickthrowman 3y ago
  Inrush current is much less of an issue with a VFD/inverter driven motor then a motor controlled by a basic DOL motor starter. ABB claims that the inrush current of their VFDs is 100-150% of the motor FLA, which lines up nicely with the NEC rule to size motor conductors at 125% of the FLA of the motor. A typical DOL/across the line starter has an inrush current 6-7x higher than the FLA. https://library.e.abb.com/public/71d5526a71b34360bb3a258c950acb8a/LVD-EOTN151U-EN_VFDs_And_Maximum-Inrush-Current.pdf https://library.e.abb.com/public/71d5526a71b34360bb3a258c950...
hinkley 3y ago
I recall someone stating rather authoritatively that they were confident that the WRT54G could comfortably run directly off of automotive "12 volt" DC power, which in practice can go up to 16 volts due to the alternator. This person has a thesis that it can go up to 20 volts (which is 80% of the rating of one of the capacitors)
- Scoundreller 3y ago
  Which could be user upgradeable with a snip and a soldering iron. It’s just a smoothening capacitor, so higher voltage rating is the critical part and can probably get away with non-exact muF capacity. Possibly removable if you have a lead acid or lithium-ion battery capable of providing lots of current when needed and cleanly.
- userbinator 3y ago
  Automotive power has lots of very high spikes (>100V), it's definitely not recommended to connect electronics to it without a large amount of filtering and protection.
stephen_g 3y ago
Just looking at a random AC/DC converter (Meanwell EPP-100) the likes of which from it and other brands that I’ve used many of, it specifies 90-264V AC at 47-63 Hz. Interestingly it does also specify 127-370VDC, but nothing on the data sheet specifies that it should be expected to operate with DC input (and that corresponds as a peak value to the RMS AC voltage which is probably what it means). Potentially it could work with a DC input though (since DC will pass a regular bridge rectifier), but it could screw with things like the power factor correction… I’d try it if it was a unit I didn’t mind potentially destroying.
- exmadscientist 3y ago
  370VDC input capability is common on industrial rated power supplies. It isn't ubiquitous but it isn't a surprise either.
- nomel 3y ago
  > like the power factor correction If they only assumed AC, and if they used AC coupling for the sine/peak/phase detection, then DC would probably look closer to 0V, and just shut the switching off, right? I can't think of an "easy" way to do it that wouldn't require extra smarts, to handle DC, and everyone knows smarts costs money!
blagie 3y ago
I'm not so sure. There are two different problems: 1) What conditions equipment works under 2) What conditions equipment went through testing under, as per regulatory regimes Equipment I worked on needed to be tested for a variety of failure modes (e.g. a power supply doesn't cause a house fire), EMI/EMC, and so on. I would guess that also varies internationally, as well as by use (UL-listing is not legally required, but it is required if you sell to customers who want to have fire insurance, for example). Some of this is wonky administrative overhead, but some of it is not. For example: - A DC-DC converter will have a different switching frequency if running from a different input voltage. This might work fine, but it will have a very different profile for EMI/EMC. Testing that might be $40k. If I know I have a 12V wall wart powering it, there's no reason to spend $40k to be able to label the box "5V-40V." - If a PCB has creepage / clearance for 120V, even if the power supply works fine for 240V, I can't sell it as 120V equipment. The reverse holds true the other way for wire gauge. These things wouldn't cause problems very often (indeed, it'd be exceptionally rare), but if we have a house fire 0.001% of the time people bought a TV set, we'd have hundreds of thousands of preventable house fires. That's why there's testing before products are sold.

kube-system 3y ago

It could have just been that one team labeled the housing according to the requirements, and another team built the internals to meet (or exceed) the requirements.

Goz3rr 3y ago
Or the power supply is sourced from multiple vendors, and other units might not have the same range
- woleium 3y ago
  Or the power units were from a run that ended up as defective at the higher voltage
  - Scoundreller 3y ago
    Going to be no bueno if donor boards end up on the secondary market. But now that I think about it, it’s possible they’re fitted with different replaceable fuses (half the amperage in 240v areas).

mschuster91 3y ago

> As devices like home fridges move towards “inverter drive” with switch mode power supplies, I wonder how low of a voltage they could still run off. And if they’d happily accept 48VDC and still function. The technical side should continue to work until you reach the lower limit of what the bootstrap circuitry can handle. The problem will be the amperages required... say, a fridge. Its motor will run at ~200 watts, which means 1A at 230V. No biggie. But if you're going down to 48V, the high-voltage side will now run 4A, and more the lower you go on voltage - and that's without taking peak inrush currents into account which can easily go to 10A@230V (or 40A@48V) for a few split seconds. If your current source or the wiring can't hold that, you'll likely run into serious issues.

sokoloff 3y ago
I thought one major advantage of inverter drives was the well-managed starting currents. This is a noise/vibration advantage but also an electrical win.
- hinkley 3y ago
  But a wire pulling 2 amps at 3.3 volts experiences very different physics than a wire pulling .6 amps at 12 volts.
quickthrowman 3y ago
Inrush current is much less of an issue with a VFD/inverter driven motor then a motor controlled by a basic DOL motor starter. ABB claims that the inrush current of their VFDs is 100-150% of the motor FLA, which lines up nicely with the NEC rule to size motor conductors at 125% of the FLA of the motor. A typical DOL/across the line starter has an inrush current 6-7x higher than the FLA. https://library.e.abb.com/public/71d5526a71b34360bb3a258c950acb8a/LVD-EOTN151U-EN_VFDs_And_Maximum-Inrush-Current.pdf https://library.e.abb.com/public/71d5526a71b34360bb3a258c950...

hinkley 3y ago

I recall someone stating rather authoritatively that they were confident that the WRT54G could comfortably run directly off of automotive "12 volt" DC power, which in practice can go up to 16 volts due to the alternator. This person has a thesis that it can go up to 20 volts (which is 80% of the rating of one of the capacitors)

Scoundreller 3y ago
Which could be user upgradeable with a snip and a soldering iron. It’s just a smoothening capacitor, so higher voltage rating is the critical part and can probably get away with non-exact muF capacity. Possibly removable if you have a lead acid or lithium-ion battery capable of providing lots of current when needed and cleanly.
userbinator 3y ago
Automotive power has lots of very high spikes (>100V), it's definitely not recommended to connect electronics to it without a large amount of filtering and protection.

stephen_g 3y ago

Just looking at a random AC/DC converter (Meanwell EPP-100) the likes of which from it and other brands that I’ve used many of, it specifies 90-264V AC at 47-63 Hz. Interestingly it does also specify 127-370VDC, but nothing on the data sheet specifies that it should be expected to operate with DC input (and that corresponds as a peak value to the RMS AC voltage which is probably what it means). Potentially it could work with a DC input though (since DC will pass a regular bridge rectifier), but it could screw with things like the power factor correction… I’d try it if it was a unit I didn’t mind potentially destroying.

exmadscientist 3y ago
370VDC input capability is common on industrial rated power supplies. It isn't ubiquitous but it isn't a surprise either.
nomel 3y ago
> like the power factor correction If they only assumed AC, and if they used AC coupling for the sine/peak/phase detection, then DC would probably look closer to 0V, and just shut the switching off, right? I can't think of an "easy" way to do it that wouldn't require extra smarts, to handle DC, and everyone knows smarts costs money!

blagie 3y ago

I'm not so sure. There are two different problems: 1) What conditions equipment works under 2) What conditions equipment went through testing under, as per regulatory regimes Equipment I worked on needed to be tested for a variety of failure modes (e.g. a power supply doesn't cause a house fire), EMI/EMC, and so on. I would guess that also varies internationally, as well as by use (UL-listing is not legally required, but it is required if you sell to customers who want to have fire insurance, for example). Some of this is wonky administrative overhead, but some of it is not. For example: - A DC-DC converter will have a different switching frequency if running from a different input voltage. This might work fine, but it will have a very different profile for EMI/EMC. Testing that might be $40k. If I know I have a 12V wall wart powering it, there's no reason to spend $40k to be able to label the box "5V-40V." - If a PCB has creepage / clearance for 120V, even if the power supply works fine for 240V, I can't sell it as 120V equipment. The reverse holds true the other way for wire gauge. These things wouldn't cause problems very often (indeed, it'd be exceptionally rare), but if we have a house fire 0.001% of the time people bought a TV set, we'd have hundreds of thousands of preventable house fires. That's why there's testing before products are sold.