Battery jump starter: 11k mAh total capacity but only 3600 mAh for jumping?

[JEDI]

400amp peak current/200amp starting current

5v = charging cell phones
20v = charging/powering laptops
12v = car battery (im assuming?)

so only 3600 mAh for jumping?
and how does it get 11k mAh total capacity?

 

[NutBucket]

Math is your friend. Mah is capacity. Mutilply capacity by volts to get milliwatt-hours. I'm too lazy to do it but basically it will be the same for 5V, 12V and 20V.

I do agree it is a bit odd they list capacity as 11k mah when it can't even deliver it at 5V. I would guess 11k mah is the nominal capacity of the 3.7V cells.

 

[Yuriman]

Probably has a capacitor bank in it. If you try to draw the entire capacity of an 18650 instantaneously it would likely burst into flames.

 

[mindless1]

Math is your friend. Mah is capacity. Mutilply capacity by volts to get milliwatt-hours. I'm too lazy to do it but basically it will be the same for 5V, 12V and 20V.

I do agree it is a bit odd they list capacity as 11k mah when it can't even deliver it at 5V. I would guess 11k mah is the nominal capacity of the 3.7V cells.

This. Before the Chinese junk electronics invaded Amazon, eBay, etc, a power supply was rated for its capacity @ output voltage. Then the generics, even if trying to be honest (although still misleading) stated spec'ing what the capacity would have been if the cells were in parallel inside, never mind that they're not in parallel, not the output at the intended use as a power supply.

It can't deliver that at 5V because of buck switching losses to drop the series cells' voltage down to 5V.

Capacitor inside, unlikely more than a minimal value in the voltage buck/boost circuits. Otherwise that would be drained almost instantaneously in a jump start scenario, offering nothing useful. It's just an overrated example that "might" jump start a small engine if nothing else is wrong with it besides the battery being drained, not too far.

In that case the moment you hook it up it is putting some charge into the primary battery so both are working in parallel with the primary supplying more of the current. Cell internal resistance will keep it from bursting into flame for the brief seconds it can provide current before dropping too low in voltage, and there's probably a thermal cutout in the protection circuit. Then again maybe not - Chinese. It might just melt some trace on the circuit board or connector and that's the hoped fail safe.

 

[Midwayman]

Math is your friend. Mah is capacity. Mutilply capacity by volts to get milliwatt-hours. I'm too lazy to do it but basically it will be the same for 5V, 12V and 20V.

I do agree it is a bit odd they list capacity as 11k mah when it can't even deliver it at 5V. I would guess 11k mah is the nominal capacity of the 3.7V cells.

Native voltage is what 3.3v? Everyone seems to rate their cells by a tenth or two different depending on how much they want to lie. They'd be 11k @ 3.3v

 

[JEDI]

Native voltage is what 3.3v? Everyone seems to rate their cells by a tenth or two different depending on how much they want to lie.
They'd be 11k @ 3.3v

how did you get that??
math please

 

[NutBucket]

Agreed, nominal voltage of a Li-ion cell is 3.7....always has been!

 

[Midwayman]

how did you get that??
math please

Well the nominal voltage is 3.7 (went and looked it up.) 4.2 at peak charge.

4.2*11000=46200mWh
5*9500=47500mWh
12*3600=43200mWh
20*1600=32000mWh

So there are losses stepping up the voltage. 4.2v isn't a very honest way of rating a battery and they're probably really rating it at 4.3 or more.

 

[thecoolnessrune]

Agreed, nominal voltage of a Li-ion cell is 3.7....always has been!

3.8V (4.3V Peak) cells have been in production for a long time. I remember Anandtech thinking the Droid Bionic was using an over-charged Battery until Motorola reached out and noted they were using a High Voltage chemistry. Since that time, almost every flagship or mid-range phone now uses 3.8V cells. Phones like the LG G5 even use a 3.85 (4.35V Peak) battery.

If the pack is loaded with 18650 batteries or something similar, then a lot of those are still 3.7V chemistry, but if it's using some sort of Li-ion pack, then there's a very good chance it's 3.8V chemistry.