Dead Battery

[Deleted User]

It is plausible that you will get a voltage transient from the alternator if you suddenly dump load by disconnecting the leads whilst the engine is running. A step change in the load contains high frequency components outside the bandwidth of the regulator feedback loop, so the voltage will rise momentarily until the regulator recovers.

The source resistance of the battery is of the order of 0.01 ohm though, so even with a 100A alternator that would only be a 1V spike. It's hard to imagine this is likely to be much of a risk in practice, the transient when the starter motor switches off will be bigger than that anyway.

We used to have radios in service with the LTE (London Transport Executive), some of which were installed in the heavy recovery trucks they were using. These particular ones were failing regularly, and it turned out that there were 140V transients being generated by the solenoids on the preselector gearboxes, but that was exceptional, we never had any particular problems with 'normal' sized vehicles.

When we got to the stage of designing computerised radios with microprocessors in, they didn't prove any more susceptible to dirty power supplies that their more primitive predecessors.

Richard53

colino wrote: »

Well done for Sealey in selling a product to a customer and allegedly then telling them its not safe to use.

Not quite. When asked specifically about using the power pack on a modern ECU they recommended the method I stated above instead of the traditional way. They did not say it was unsafe to use.

To put that in context, the company bought the Sealey to jump start a couple of classic coaches we were running, and the company's fleet of ancient Transits and such. Then we started getting requests from customers to start their cars (we are a holiday destination and cars are left for several days in our long-stay car park) and we thought it would be wise from a liability point of view to get the manufacturer's advice. Faced with helping to start Mr Angry's brand-new Merc, you tend to go by the book.

Anyway, as you say, we've been over this before. I drive cars old enough or basic enough for it not to be an issue as far as I am concerned.

Nodding_Donkey

TrickyWicky wrote: »

You need to check your alternator. Get a multimeter and with the engine running, check the voltage of the battery. If it's 13-14v then your alternator is fine and your battery is defective. If it's below that then the alternator is not functioning correctly and you've probably knackered your battery relying on it so much with no recharges.

This is the answer you are looking for OP. I'm betting the battery isn't getting charged with the engine running. The fact that it stops shortly after removing the jump leads is a big clue.

As for the rest of the thread I've never read so much mis-information about using something as stunningly simple as a set of jump leads or a booster pack!

[Deleted User]

TrickyWicky wrote: »

I jump started a young lady

Is that a euphemism?

[Deleted User]

Richard53 wrote: »

I have been told by Sealey that the big power pack we use in work is not safe to be used on a car with modern electronics.

Provided it isn't too small, the capacity of a Jump Starter Pack is irrelevant.

The starter motor draws only as much current as it requires.

Richard53

Bedsit_Bob wrote: »

Provided it isn't too small, the capacity of a Jump Starter Pack is irrelevant.

The starter motor draws only as much current as it requires.

I think you are commenting on something I didn't say.

TrickyWicky

Richard53 wrote: »

To be fair, you did say that was many moons ago.

Yes, five years approximately. Thats still a significant number yet both cars at the time were reasonably modern. The car I was using was french, full of delicate electronics and still survived.

Richard53 wrote: »

I have been told by Sealey that the big power pack we use in work is not safe to be used on a car with modern electronics.

Who at Sealey told you that? Was it a qualified tech or someone in their call centre with half a brain cell?

12V is 12V regardless of where it comes from. Most flat car batteries are 9v or below (lowest I've seen was about 5). You hook up 12V to it and suddenly there is 12V applied to everything. What do you think happens when you turn on the ignition key? - 12V is suddenly applied. What do you think happens when you take out the old battery and put in a nice new one? 12V is applied.

Richard53 wrote: »

The risk is a voltage spike frying some sensitive component in the ECU or somewhere and costing hundreds to rectify.

In one of my previous jobs a few years back I was jump starting cars every week. Everything from £60k mercs to £70k top end range rovers. The site was one where people with plenty of money but little common sense, park their cars, leave their headlights on and then go abroad for several weeks. Needless to say I was jump starting peoples cars every other day and not once did we have reports of anything frying. You should have seen the power pack we used too, I kid you not it was huge.

Richard53 wrote: »

The method they recommend on a modern car is: connect the two batteries, start the second car, let it run for 5-10 minutes, stop the engine, *disconnect the jump leads*

So what you're effectively saying is that Sealey recommend you risk running the donor car flat? I find that hard to believe. Besides, what do you think is going to happen when you connect the two batteries? - Thats exactly the point you are saying that sealey say is dangerous - connecting two batteries via jump leads. Then you continue to say that not only do they say to connect them but try to start the flat car using them? :rotfl: I have news.. thats how you jump start a car - from any power source - car battery or battery pack.

Richard53 wrote: »

and then try to start the first car. In effect, the second car is being used as a massive quick charger to put some charge in the slave battery before a normal attempt at starting.

Which is basically the same as a normal jump start. Most folks however recognise that its common practice to start the donor car so that the alternator can supply enough power to let the second car start. The difference you face is that you have no igition / engine / alternator so all you can do with your power pack is hook it up to the flat battery.

Richard53 wrote: »

With an older car with points ignition or even a simple CDI unit, these risks are negligible or non-existent.

You still had fuses right? - They can burn if too much current is conducted. The point is even in a modern car, the alternator will still chuck out around 14- 14.5 volts so when you jump start a car from a donor car it's only doing the same thing as the flat cars own alternator.

Richard53 wrote: »

Personally, I would use a power pack or second car to jump start mine, and accept the small risk of damage. But I wouldn't do it to anyone else's car.

I've done it loads of times and even had people sign disclaimers for their courtesy jump start t(he disclaimer being worth nothing legally) and even the customers with the big expensive cars really were not bothered - most in fact did not like the delay and just wanted us to get on with it so they could be on their way.

One other comment on jump started.. I mentioned using my wheels to jump start someone once. I've also used it in other jobs to jump start other customers where no power pack was available or the site was too far away (eg a remote car park) to get a power pack or recovery truck into. My motor has been fine. I've also had to jump start my motor many times (eg after leaving it sat for a month or two unused while using another car) and it has been fine.

Like I said, far too much paranoia about jump starting.

TrickyWicky

Richard53 wrote: »

Not quite. When asked specifically about using the power pack on a modern ECU they recommended the method I stated above instead of the traditional way. They did not say it was unsafe to use..

Yes, yes they did you told us so yourself:

Richard53 wrote: »

I have been told by Sealey that the big power pack we use in work is not safe to be used on a car with modern electronics.

You HAVE told us that Sealey said it was not safe to use on a modern car. Then you claim they haven't. :T

EdGasket

TrickyWicky - suggest you put the following in your pipe and smoke it:

http://www.dailyrecord.co.uk/authors/the-judge/driver-vents-fury-after-simple-1558512

Nodding_Donkey

At a guess they put the leads the wrong way round.

I don't really see how a woman getting mugged off by the garage that damaged her car really proves anything.