Car battery jump-starting gizmo?

(Sorry, bit OT for uk.d-i-y...)
Normally I fight shy of these sorts of offerings, but SWMBO pointed out the following item today in one of those 'gadget' cataglogues which fall out of the Sunday papers.
Basically, a glove-compartment-sized ciggy-lighter attachment which serves as an emergency battery charger: http://www.easylifegroup.com/products/2815.asp
Personally I'm perfectly happy with making damned sure I remember to turn off the headlights etc, and if all else fails, jump leads or a push start will suffice; and I can't actually recall the last time I got causght out. But realistically I can see it's a different proposition when SWMBO, or worse, my teenaged daughter, are driving the car alone (esp at night).
So, are these any good? Are there better/cheaper versions available? Any thoughts welcome.
Thanks David
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Do you really see a little glove-compartment sized battery turning over the starter motor on a car?
Starer motors draw around 80A.
That's why jump leads are thick heavy wires.
Is that little flex and a cigarette lighter socket going to pass 80A?
Still - it can probably deliver enough juice so you can listen to the radio until someone arrives with jump leads.
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40 would get you a toolkit that works. Just teach them how to push start it, and to engage gear when there isnt enough power to turn the engine over.
NT
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NT wrote:

I thought starter motors draw a couple of hundred amps.
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wrote:

They tend to.
The idea of plugging a small battery into a a cigar lighter socket is to put a sufficient charge into the car battery so it can then turn over the engine. If the car battery is completely naff, then this whole idea fails.
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yes
jump leads are somewhat slow at givig enough charge to a flat battery to get it to start, imagine how long it would take using a bit of speaker wire!
NT
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wrote:

You can't push start many new cars. If you don't have enough volts in the battery the electronic engine management doesn't work properly and you risk doing something bad like blowing the cat to bits.
As for the subject.. it claims to be an emergency charger not a jump starter. You are supposed to plug it in for a few minutes while it charges the main battery and then start the car. This could well work if its battery has enough capacity.

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wrote:

When an enging is push started the alternator produces power. I've push started completely flat cars too many times. Yes, it does take a bit more speed than with a full battery, but its perfectly doable.
I cant iamgine how any electrical failure could do that to the cat convertor.

With speaker wire it'd take more like 30-60 minutes. For 40 as well!
NT
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wrote in message

Its not a failure, it is operating outside its design parameters. Things like the fuel injectors working but not the spark. That would fill the cat with unburnt fuel and probably destroy it.

It isn't speaker wire (well it probably is as my speaker cable was ex-exchange power wire at one time).
Such a device could probably supply 10A, which would fully recharge a typical battery in about 6 hours.
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Every EFI system I know requires a signal from the ignition before the injectors will work. For that reason.
--
*Women like silent men; they think they're listening.

Dave Plowman snipped-for-privacy@davesound.co.uk London SW 12
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On Sat, 5 Sep 2009 21:28:59 +0100, dennis@home wrote:

Hum, so a less than 10AHr SLA can fully charge a 60AHr car battery in 6hrs, interesting... I think dennis has just solved the world energy crisis.
--
Cheers
Dave.




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wrote:

You are TMH ICMFP as you can plainly see that I said nothing of the kind.

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dennis@home wrote:

"Such a device could probably supply 10A, which would fully recharge a typical battery in about 6 hours" - sounds pretty much like teflon Dennis is at it again...
Explain the difference between your statement at that of Mr Liquorice halfwit.
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wrote:

On the face of it the difference is in the units. He said 10A, not 10Ah. With no other information he could have meant that the device could produce 10A for 6 hours.
But this suggests that he unaware of the difference between amps and amp/hours. Surely that isn't the case. Or is he unaware that the total number of Ah available is limited by the Ah capacity of the device's battery, and that these devices have quite small batteries. But he must know these things.
So it's a mystery.
Bill
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wrote:

No mystery at all, you know the difference and therefore know that I never claimed the device could charge the battery.
Even in English the bit that says "which would" refers to the last "object" talked about, "10A", so says exactly what I intended, that 10A would charge a typical battery in about 6 hours. It had already been stated that the unit would only run for a few minutes. It is typical of TMH to misread everything I post just so he can be an arse.
Even his question "Explain the difference between your statement at that of Mr Liquorice halfwit." is insulting Mr Liquorice by calling him halfwit. He really doesn't understand English and his lack of punctuation is worse than mine. At least I would have put the comma after Liquorice. I gave up trying to explain anything to TMH as he is incapable of understanding even basic stuff.
I don't want to read what he posts anymore, please don't quote him.
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Nowadays, the alternator is often controlled by the engine management (which is essential for some batteries) and it won't produce any output at all unless the EMU is already working. Indeed, some (maybe even all) EMUs won't let EMU controlled alternators start generating output until they are sure the engine is started, to reduce the load on the engine whilst it starts and the starter is pulling the battery volts down, which would otherwise cause a heavy alternator load.

With a flat battery, it takes less than 5 minutes with a 4A charger to get enough into it to start the engine, providing the engine normally starts first time. One problem you might have is that many EMU's lose their learned memory of the optimum engine settings when they lose power, and that can mean that an engine that normally starts first time might not in this case as the EMU falls back to initial factory settings until it relearns the engine characteristics.
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Andrew Gabriel
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wrote in message

An alternator doesn't spin fast enough to generate meaningful volts whilst an engine is being cranked. However depending on the type of alternator, it does make sense not to provide field current until the engine is running, so at least the drain on the battery is minimised before and during cranking.
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I did it enough times with 2 vehicles I owned, so it does at least on some. They weren't modern designs though.
NT
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In message

That's not the point, the idea of many of the booster packs and 'normal' retail jump leads is to charge the battery to the point where it can start the car.

And the rest.

Ever dissected a set? Most are just lots of thick insulation.

--
Clint Sharp

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writes

Depends on the car.. I tried to jump start a Merc diesel a couple of months ago. I put on my jump leads which are 10 mm2 copper (from System X exchange power distribution) and got sod all. I had to fit a second set before I could start it.
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