EEVblog 1648 - Input vs Output Referred Battery Capacity EXPLAINED

[EEVblog]

Battery bank charger capacity explained. When you are comparing battery banks you want to use a measured Output Referred capacity figure, not an Input Referred figure the manufacturers marketing department gives you.

[RoGeorge]

From the battery packs I've opened so far, most usual the spec numbers on the assembled battery pack is about the model of the battery cells inside.  Energy or capacity usually correspond to what is written on the cells inside the device, and not to how much the final battery pack ensemble can deliver.

This is usually not a problem, because most of the battery packs (for example laptop batteries), have no DC-DC converter inside.  USB power banks are an exception, though they inherit the habit of telling the cells capacity.

Wh conversion is done considering the mAh capacity at an average of 3.7V/cell, for Li chemistry recheargeables, so mAh=Wh/3.7*1000, unless other than 3.7V average value is specified on the Wh label.

The exact charging/discharging procedure, level voltages, load type and test temperature varies with each cell model.  For example, when testing at a lower current, the total energy delivered will be higher than when testing the same cell at a higher current load (typical load is 0.2C, but some datasheets might specify other value).

To get the capacity imprinted on the cells (not on the final device) the testing conditions and procedure must be followed exactly as specified in the (individual cell's) datasheet.

[EEVblog]

Wh conversion is done considering the mAh capacity at an average of 3.7V/cell, for Li chemistry recheargeables, so mAh=Wh/3.7*1000, unless other than 3.7V average value is specified on the Wh label.

Wh conversion is done by the marketing department to give the great level desired 

Only true way to measure battery capacity is to measure it.

[RoGeorge]

One of the ugliest fine-print marketing bullshit style I've seen was in the datasheet of some of the power MOSFET transistors.  The datasheet says continuous Id absolute max 202A, while the transistor package can withstand only 75A. 

https://www.eevblog.com/forum/projects/transistors-die-pictures/msg5454917/#msg5454917

[nctnico]

One of the ugliest fine-print marketing bullshit style I've seen was in the datasheet of some of the power MOSFET transistors.  The datasheet says continuous Id absolute max 202A, while the transistor package can withstand only 75A. 

https://www.eevblog.com/forum/projects/transistors-die-pictures/msg5454917/#msg5454917

Not quite. You can also buy the transistor as a die to integrate & bond yourself. The package is a seperate thing.

[RoGeorge]

Those numbers are written in the datasheet of a complete hexfet, already mounted in its TO-220 package
https://www.infineon.com/dgdl/irf1404pbf.pdf?fileId=5546d462533600a4015355dae92618b0

[VK3DRB]

Just like Ah capacities on eBay batteries, power battery banks specifications are usually lies and deception.

But check out the car battery chargers:
https://www.ebay.com.au/itm/356018489927

5000A is amazing Chinese technology. Only the Chinese can invent wires so tiny so as to provide 5000A for a few seconds, with an output voltage of 12V, no melting and no explosion, and presumably no voltage drop. They must use superconductivity. No wonder Trump wants to slap tariffs on them when they are decades ahead of everyone else.

(Notes the advertisement is full of lies, including one photo of the size of the clamps.)