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| JX18B "Car Jump Starter Emergency Charger Booster Power Bank Battery" |
Real Capacity?
It is advertised as 68 Ah (sic!), which can't be true.Why not?
This is what a modern 60 Ah lithium car starter battery, produced by the somewhat famous A123 company, looks like:
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| A123's real 60 Ah |
See also here for a real life test of an similar Lunda model.
Here are the different likely capacities values for our JX18B baby:
7 Ah
Why? Let's compare the sizes of 6.2 Ah Fujitsu notebook battery with this one:
They weigh about the same, while size for size, we arrive at 7 Ah.
10 Ah
Now, the most enlightening discussion happens on YT, where they suggest the same value.From a sellers's description thereof:
"This Emergency Jump starter can be made up to capacity, the real capacity of this jump starter actually is 9900mah. But the label will be marked with 50800mAh.Please know it in advance before your order. Thank you."One YouTube tinkerer concurs:
I tore down one of these and yes, it does use a heatshrunk stack of li-pos to generate voltage close to 12V. The electronics are small and only used to produce stable 5/12/16/19V on USB/DC jack output, simple step-up boost converter like in most powerbanks. The jump-start plug goes directly from the cell and is not under control by any electronics - found out the hard way, when I made myself a power supply for car light bulbs out of that device only to find out that the cell stack went undervoltage down to 6V and lost most of it's capacity. And since we talk about how much energy is stored in that cell: not much. Best case scenario gives you 10.0 Ah at 12V, but the cell is quite poor quality, therefore when you push it hard it gives even less. The 50Ah description is the standard lie of these low-quality ebay/aliexpress products (technically you might be closer to 50Ah at lower voltage when you would hook up these cells in pararell, but that not how they are used there).
The following higher values are thrown around there, too:
12 Ah
[It] would be 12,000mah roughly, so if that is the case that brick is only a 12k unit which would be onpar with the chinese 1500mah common cell usage15 Ah
See the quote above.[Update 1:]
Real life
And what do my test say? |
| Plugging in the bits |
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| Let there be a 20 W light! |
I connected a 12 V, 20 W lamp (the 30 W and above were too "heavy" for JX18B). The current (ampers) went from 1.6 A, quickly to 1.55 A and way down to 1.45 A, when the lamp turned off, and the battery meter showed no juice left. The experiment lasted 103 minutes only. (Yes, less than 2 hours).
Let's assume 1.5 A average current for ease of calculation. We arrive at:
1.5 A * 103 min / 60 min =
2.6 Ah
Or , as 1.5 A * 12 V= 18 W , so:18 W * 103 min / 60 min = 31 Wh
Kinda low, huh?
To test it further, I used a real-life scenario: the above-mentioned HP Pavilion notebook, running Heavy Load to arrive at a steady average 24 W discharge rate, connected to this external battery. Do note that this configuration did not recharge the internal battery at any moment, as the third (signal) wire with the feedback info to the usual AC power adapter was missing in this configuration, so only the notebook itself was drawing down the power.
I used PassMark's Battery Monitor, which logged the (dis)charge rate to a CSV file. (To signal when the power switched back to the internal battery, I changed the control .BAT in the Batt Stat by adding my fav MP3 jingle thereto.)
Here is the graph of what happened:
JX18B Battery was connected at 9:59 and ran out of juice at exactly 11:13, so we get 74 minutes here. Let see how it happened:
Let's do the maths:
24 W * 74 min / 60 min = 29.6 Wh
which is equivalent to:
2.48 Ah !
It ties in with the 2.6 Ah measured above.
Now, let's entertain its geek uses:
Emergency car jump starter
It can even start the car, they say,The trick may hide in the high ambient temperature (30 C degs here) and my waiting some seconds with the ignition switch turned, before cranking her up, so that the coils heat up.
External notebook battery
Now, assuming 2.5 Ah capacity, as per the experiments above, then seemingly one has additional 3 h (three hours only) of notebook juice, assuming a -10W discharge rate, as measured by BatteryBar:
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| HP Pavilion average power use |
(Or is my maths cum physics wrong? See here to check how I calculated it.)
Other cool uses?
Sound amplifier
Powering up the guitar or a music amp for days on end, see my other blog post.
Camera trap?
