John P
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| posted on 5/11/13 at 08:22 AM |
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Battery Jump Starter (How can this work?)
I had a break down the other evening when my battery suddenly failed with absoluteley no warning. (Went into a shop and when I came out
wouldn't even try to turn the car over).
When the recovery arrived he checked the battery and said he could jump start it so I could get home.
I expected he's use normal jump leads or a battery pack but he actually got one of these out of a small wallet and the car started straight
away.
http://www.tvc-mall.com/details/Multifunction-Car-Jump-Starter-Battery-Charger-Power-Bank-HHC-2825/?c=35&gclid=CMmoys2ZzboCFfMbtAodZg4AIw
Such a small piece of kit I was wondering what sort of battery technology it uses to give enough power to start an engine.
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bi22le
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| posted on 5/11/13 at 08:28 AM |
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Did he leave it on for a while?
Maybe it discharged with speed to get enough power in the battery but did not crank from the jump pack.
Almost like a large capacitor.
Track days ARE the best thing since sliced bread, until I get a supercharger that is!
Please read my ring story:
http://www.locostbuilders.co.uk/forum/13/viewthread.php?tid=139152&page=1
Me doing a sub 56sec lap around Brands Indy. I need a geo set up! http://www.youtube.com/watch?v=EHksfvIGB3I
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MikeRJ
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| posted on 5/11/13 at 09:17 AM |
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You can pull a lot of current from Lithium Ion or Lithium Polymer cells for a short length of time, which is what this pack probably uses. It
doesn't do the cells much good though, and if the engine didn't fire up quickly it would be useless.
You can actually buy car/bike batteries that use Lithium Iron Phosphate cells that can deliver an incredible current for their size, but their energy
density is quite a bit lower than Lithium Ion/Polymer so they don't tend to get used in this kind of application/
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wilkingj
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| posted on 5/11/13 at 10:40 AM |
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quote:
Originally posted by MikeRJ
You can pull a lot of current from Lithium Ion or Lithium Polymer cells for a short length of time, which is what this pack probably uses. It
doesn't do the cells much good though, and if the engine didn't fire up quickly it would be useless.
You can actually buy car/bike batteries that use Lithium Iron Phosphate cells that can deliver an incredible current for their size, but their energy
density is quite a bit lower than Lithium Ion/Polymer so they don't tend to get used in this kind of application/
Yep thats about it. My 5Ah Lipo battery will let you have 50Amps drawn as a burst. However, the battery capacity is reduced at x10 rate.
You cant get a Quart out of a Pint Pot. Usual rules apply. ie 5 Amps for 1Hour, or 50Amps for about 6 Mins. You wont get 50A for 1 hour, as its only a
5Ah battery.
Be aware that Lipo batteries, whilst are very good, they need careful handling and proper care / charging.
I keep mine in a fireproof bag (£5 off Ebay)
You need the correct type of charger that monitors the voltage between the individual cells. A std battery charger could well give you a nasty
chemical fire. Equally overdischarging them can have the same effects.
A couple of examples.... Probably staged, but it gives you a preview of what can happen if it all goes wrong 
Linky 1
This one looks like its deliberately being overcharged, but it shows just how bad it can be if you dont do it correctly!
Linky 2
1. The point of a journey is not to arrive.
2. Never take life seriously. Nobody gets out alive anyway.
Best Regards
Geoff
http://www.v8viento.co.uk
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bi22le
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| posted on 5/11/13 at 12:53 PM |
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quote:
Originally posted by MikeRJ
You can pull a lot of current from Lithium Ion or Lithium Polymer cells for a short length of time, which is what this pack probably uses. It
doesn't do the cells much good though, and if the engine didn't fire up quickly it would be useless.
You can actually buy car/bike batteries that use Lithium Iron Phosphate cells that can deliver an incredible current for their size, but their energy
density is quite a bit lower than Lithium Ion/Polymer so they don't tend to get used in this kind of application/
Although this is possible the lead and clamp type probably wont be able to provide the sort of current required to turn over a sizeable engine without
getting hot and resisting the current too much.
Hence Why I think these bits of kit pack a punch into the current battery then cut out when they feel high current getting pulled while cranking.
Track days ARE the best thing since sliced bread, until I get a supercharger that is!
Please read my ring story:
http://www.locostbuilders.co.uk/forum/13/viewthread.php?tid=139152&page=1
Me doing a sub 56sec lap around Brands Indy. I need a geo set up! http://www.youtube.com/watch?v=EHksfvIGB3I
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britishtrident
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| posted on 5/11/13 at 04:18 PM |
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A lot of times if the battery is failing with a dead cell just a few moments connected to another battery will be enough to kick the dead battery
back into life.
The jumps leads that work by connecting between two cigar lighter sockets don't transfer any great flow of current but are often all that is
required and they work.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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