Car battery jump-starting gizmo?

[Lobster]

(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:

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

[RubberBiker]

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.

[NT]

=A340 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

[Bod]

I thought starter motors draw a couple of hundred amps.

[Fredxx]

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.

[Peter Parry]

Not really. It is basically a NiCd or similar battery. The car lighter socket is rated at 10A, the starter on a cold day can draw

200A. If the battery is just a teeny bit flat (it never is) plugging it in and leaving it for an hour might transfer just enough power to give you one brief go at starting but I wouldn't bet on it.

The technology is immaterial though. The first rule of such devices is that when needed they are always found to be discharged. All secondary batteries self discharge and of course you _were_ going to charge it just that night. This is useful for transfer of guilt. It is no longer the problem of SWMBO leaving the lights on all day but you for forgetting to charge the magic box.

jump leads.

[Derek Geldard]

We've had a few of these or similar devices and they've all been based on the cheapest of cheap sealed Chinese lead acid batteries and have never been of up to the job of starting a car even once.

Devices with similar batteries such as the "One Million Candle Power torch" have always let us down without fail by going flat in storage which destroyed the sealed lead acid battery by deep discharge.

One compressor / tyre inflator was different, that jumped about until it literally shook itself to bits the first time it was used. Another was a compressor which worked on the (presumed good) car battery. That just burnt out before it had finished inflating it's first tyre.

Derek

[Dave Plowman]

I'd be very surprised if something that size used a lead acid battery.

Decent lead acid self discharge extremely slowly. But like any battery has a limited life - even when little used.

I bought a jump start pack with built in compressor about 5 years ago from Lidl for 20 quid. It will no longer start a car, but still works the compressor ok. I'd guess it managed some 20 odd jump starts - and paid for itself in bottles of wine from neighbours. ;-)

[dennis]

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.

[Clint Sharp]

In message , RubberBiker writes

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.

[Harry Bloomfield]

Lobster formulated on Saturday :

Better and much cheaper would be a pair of proper jump leads. A gadget that small could not possibly have the capacity to to charge a flat battery up to a capacity where it would start a car - even if it could, the ciggy lighter socket is only able to handle 10amps max. so it would take several hours before it could be started.

I have also never found the much bigger 'power station' thingummies to be capable of starting my car, though I suppose they might work with a really small car like a Ford Ka.

[Dave Liquorice]

As others have said not worth it. And I do like the suggestion of "transfer of blame", that *is* what would happen in reality.

Get set of decent jump leads and teach 'em how to use them or if they don't want to learn, a family membership of the AA/RAC/Green Flag...

Sadly these days the latter may well be the safer option rather than asking a lone woman to request help from strangers.

[Al]

And you should continue to do so :)

enough charge into your battery to start the car.

OK, I lied - I used to carry a little sealed lead-acid battery pack that we used to install as backup batteries for BFO industrial gear. And once I did manage to get enough charge into my Mini battery to get it started :)

Al.

[Andy Burns]

If the gizmo's battery holds enough charge, then 10 amps for 10 minutes could charge the car's battery enough to give 200 amps for 30 seconds, ok in practice perhaps half of that allowing for efficiency losses, but if the car won't start in 15 seconds of turning over you've got more problems that a flat battery ...

[dennis]

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.

[Derek Geldard]

?? Too big, too small, or what ?

It had a couple of nondescript anonymous batteries this sort of size / shape. Except these are proper ones not Chinese rubbish.

These weren't decent.

Derek

[NT]

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

[NT]

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 =A340 as well!

NT

[NT]

The trouble is you'll never get 10A. When charging, battery terminals go up in voltage. When discharging, they drop very slightly - in both cases the exact opposite of what you want to get decent current flow. Hnece to get anywhere you need extremely thick cable.

NT

[dennis]

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.