RE: The pocket jump starter
Monday 28th April 2014
It's rare we see a sure-fire petrolhead gift idea that's not silly money but this is one.
Up to 300 amps possible with a 6Ah capacityThe device comes from a seemingly well-established Californian smartphone charger specialist called Juno Power so, who knows, it might actually work. The battery pack is lithium polymer instead of lead-acid in standard chargers, hence the high power-to-weight ratio (it tips the scales at 200g, versus 8kg for Halfords' Power Pack 200).
And it can charge your phone!Juno has posted a video on YouTube showing its device recording a voltage of 12.54. There's also another video from the company claiming to demo it juicing up a dead Honda via its own dedicated jump leads. We're very much hoping it's a valid test, particularly as we like that you can also charge up a phone from another socket on the device.
The pocket jump-starter
Smartphone-sized battery pack costing £40 claims to be able to jump start your car
Jumpr is potentially one of the most useful motoring gizmos invented – it's a portable charger not much bigger than a smartphone that's claimed to pack enough power to jump-start a dead car. No more lugging that boat-anchor of a Halfords charger from the garage, only to discover it's out of charge too.
Up to 300 amps possible with a 6Ah capacity
The maker claims it'll deliver up to 300 amps to a 12-volt battery, with a storage capacity of 6Ah (amp hours). Looking at the specs of the Halfords device, that's well down on Halfords claimed 17Ah, but Juno reckon it'll be good to power up four and six-cylinder engines with no size limit, while Halfords says its model is good for up to an engine size of 2.0 only.
And it can charge your phone!
The price is pretty good, with the company currently offering it an introductory $69.99 (£41.50). That's almost half what Halfords charges for its Power Pack, albeit without the extra gadgets like the invertor and tyre compressor.
The big question remains: does it work? We've put in a request to test one, so we'll get back to you on that. If the answer's yes, the AA should offer these half-price to members. Imagine the call-outs they'd save.
Discussion
I can't see why this wouldn't work in theory.
For example you can already buy a LiPo battery for an RC car which has a 5.3Ah capacity and a discharge rate (burst) of 689A.
They are quite expensive though, compared to this.
But if this can deliver 300Amps for a minute or so as its specs suggest, and the leads are kept nice and short, why not?
Might not start the biggest of cars, not sure what bigger cars require in terms of cranking amps.
For example you can already buy a LiPo battery for an RC car which has a 5.3Ah capacity and a discharge rate (burst) of 689A.
They are quite expensive though, compared to this.
But if this can deliver 300Amps for a minute or so as its specs suggest, and the leads are kept nice and short, why not?
Might not start the biggest of cars, not sure what bigger cars require in terms of cranking amps.
If that can deliever 300Amps AT 12v DC, at the end of the jump lead crocclips, i'll eat my hat!
I'm sure that the spec for the LiPos includes a theoretical 300A SHORT CIRCUIT current for the cells, but that is into a ZERO OHM load, not another battery, and not via a couple of poxy small wires.
Now, if you have a "low" voltage lead acid battery, in otherwise good conditions, you might get lucky, and indeed, that extra battery will provide just enough power to keep the system voltage high enough to enable a warm engine to be started (say >6.5V). But you ain't going to see AA and RAC (wo)men chucking out their massive truck sized jump batteries just yet!
I'm sure that the spec for the LiPos includes a theoretical 300A SHORT CIRCUIT current for the cells, but that is into a ZERO OHM load, not another battery, and not via a couple of poxy small wires.
Now, if you have a "low" voltage lead acid battery, in otherwise good conditions, you might get lucky, and indeed, that extra battery will provide just enough power to keep the system voltage high enough to enable a warm engine to be started (say >6.5V). But you ain't going to see AA and RAC (wo)men chucking out their massive truck sized jump batteries just yet!
McWigglebum4th said:
Could you use one of these instead of a battery in something silly light
it depends on the capacity and recharge capability.if there is something with almost no demand on the electronics such as :
small lcd readout
no radio
no fans (or fans driven off the engine)
then yes
McWigglebum4th said:
Could you use one of these instead of a battery in something silly light
Why not? If it can start it and there's not much else to power... But the thing looks suspiciously small IMO. The light weight LiPO thing has been going on a while, Voltphreaks one possible supplier: http://www.voltphreaks.com/products_street.php . The VPH300 is a good deal heavier than this at 3 pounds, but apperently their stuff works.Not sure I would want to keep something that can deliver 300 amps in my pocket! Would be like a taser...
I am also totally unsure it would work. The battery has a 6Ah capacity. A small engine takes 300 amps to start it. At that current the battery would last less than a minute.
Add in a cold engine, one that is tricky to start, a less than full battery then it won't contain enough power.
Furthermore, I don't believe that a small lithium battery could deliver the needed current. Just look how think jump and battery cables are!
I am also totally unsure it would work. The battery has a 6Ah capacity. A small engine takes 300 amps to start it. At that current the battery would last less than a minute.
Add in a cold engine, one that is tricky to start, a less than full battery then it won't contain enough power.
Furthermore, I don't believe that a small lithium battery could deliver the needed current. Just look how think jump and battery cables are!
Edited by gck303 on Monday 28th April 13:17
Article said:
Looking at the specs of the Halfords device, that's well down on Halfords claimed 17Ah, but Juno reckon it'll be good to power up four and six-cylinder engines with no size limit, while Halfords says its model is good for up to an engine size of 2.0 only.
I'm not sure why people still quote engine capacity limits on chargers/boosters/jump leads.Try and turn over a 4.0L 6 pot with 8.5:1 CR and then go turn over a 1.9TDI....
Wikipedia claims continuous discharge rate for LiPo batteries is up to 70x the capacity of the battery, which means that if the battery is 6Ah it may well be able to produce >300A, maybe even 2x that in a short burst.
Regarding energy density Amicell seem to make 250Wh/kg batteries: 12.6Ah at 3.7V and <200g, for example.
So this does seem believable, actually. The key is the discharge rate - I didn't know you could empty the charge out of a LiPo battery that rapidly.
To the previous poster who said "it will last less than a minute" - how on earth long do you normally crank your engine over for? ;-)
This all begs the question, why don't mobile phone manufacturers realise I'd buy something 4mm thicker and 100g heavier in a heartbeat, if the battery normally lasted five days?
Regarding energy density Amicell seem to make 250Wh/kg batteries: 12.6Ah at 3.7V and <200g, for example.
So this does seem believable, actually. The key is the discharge rate - I didn't know you could empty the charge out of a LiPo battery that rapidly.
To the previous poster who said "it will last less than a minute" - how on earth long do you normally crank your engine over for? ;-)
This all begs the question, why don't mobile phone manufacturers realise I'd buy something 4mm thicker and 100g heavier in a heartbeat, if the battery normally lasted five days?
As i mentioned above, the "peak non repetitive discharge" specification will be into a ZERO OHM load, ie a dead short. This is because the short term peak discharge current is limited by the internal resistance of the battery cells themselves. IE to push 300A at 12v, the total system resistance is (from V=IR) 0.04 Ohm (40mOhm).
This value also depends upon the effective capacitance of the battery cells, because the chemical reactions that generate the electrons are NOT instantaneous, and so for a "small" area cell, where there is limited space along the electrodes where the chemical reaction can generate the electricity, you will see the peak discharge current fall incredibly rapidly with time (unlike for a massive Lead Acid battery, which has a HUGE "plate" or electrode area, and hence can develop and sustain massive discharge currents, which is why we use them for starting cars!) Without the actual discharge curve being shown for this system any of the numbers are completely meaningless!
This value also depends upon the effective capacitance of the battery cells, because the chemical reactions that generate the electrons are NOT instantaneous, and so for a "small" area cell, where there is limited space along the electrodes where the chemical reaction can generate the electricity, you will see the peak discharge current fall incredibly rapidly with time (unlike for a massive Lead Acid battery, which has a HUGE "plate" or electrode area, and hence can develop and sustain massive discharge currents, which is why we use them for starting cars!) Without the actual discharge curve being shown for this system any of the numbers are completely meaningless!
This could absolutely work but I would be very careful about how I used/looked after it and where I kept it. Lithium polymer batteries can deliver remarkable currents for their mass but they have to be carefully managed as the consequences of completely shorting them, overcharging them or puncturing them can be spectacular.
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