Jump starting question
Discussion
Probably a basic question.
I've got a 2 litre car and a family member has a 1.4 car.
I have a battery drain problem which means I come out to a flat battery every morning - the car is booked in to the garage for next week but in the meantime I am relying on a jump start to get me going each morning.
Day before yesterday the breakdown man came and used his portable machine which worked straight away. Yesterday I used family members car and it also started straight away.
Today - had it running for a few minutes - and nothing.
From what I can see online a smaller car should be able to jump start a bigger car - you might just need to leave it running for a long time - say 10-15 minutes.
Is this correct?
Another family member has a 1.6 so they are coming round tonight to try so shoudl their car be able to jump start me quicker than the 1.4?
I am not sure why it worked so quickly the first time yesterday but not today.
I've got a 2 litre car and a family member has a 1.4 car.
I have a battery drain problem which means I come out to a flat battery every morning - the car is booked in to the garage for next week but in the meantime I am relying on a jump start to get me going each morning.
Day before yesterday the breakdown man came and used his portable machine which worked straight away. Yesterday I used family members car and it also started straight away.
Today - had it running for a few minutes - and nothing.
From what I can see online a smaller car should be able to jump start a bigger car - you might just need to leave it running for a long time - say 10-15 minutes.
Is this correct?
Another family member has a 1.6 so they are coming round tonight to try so shoudl their car be able to jump start me quicker than the 1.4?
I am not sure why it worked so quickly the first time yesterday but not today.
lightthefuse said:
First - absolutely NAFF ALL to do with engine size! All to do with the battery capacity. The higher Ah the better!
Would a biger car have a higher Ah? (whatever that is!)What should I look for on the battery.
Some reading suggests most normal cars prob have a 12v battery.
After what amount of time should you give up on the basis it ain't working?
Mojooo said:
Would a biger car have a higher Ah? (whatever that is!)
What should I look for on the battery.
Some reading suggests most normal cars prob have a 12v battery.
After what amount of time should you give up on the basis it ain't working?
In the old days, I'd have said yes, but most modern cars, even superminis, should have enough juice to jump start a car.What should I look for on the battery.
Some reading suggests most normal cars prob have a 12v battery.
After what amount of time should you give up on the basis it ain't working?
Essentially a higher Ah than your own car is always a good start, a lower Ah works but you've got little margin for error.
ETA - Ah = Ampere-hours. In layman's terms how long the battery can keep things going before draining.
The engine size doesn't matter; it's to do with the battery.
A battery has a rating for 'cold cranking power' or something - effectively how much power it can push out in one go. Cold cranking is just that, when everything is cold and sluggish it's harder to turn the engine over.
Most cars have a battery with a higher cold crank rating than they actually need. This allows for a couple of tries of the starter, and takes up any slack. Thus the battery is, in effect, over powered for the application.
In terms of engine size, again that's another one that doesn't make a huge amount of difference. The main factors that affect starting are number of cylinders, compression ratio and oil thickness. The first and last things are to do with rotating mass: more cylinders mean more weight for the starter motor to turn and thicker oil is more resistive to a turning action. The middle one is to do with squish on the compression stroke. If there's more squish then it's harder to start the engine.
I guess you're comparing two fairly normal cars with four cylinder engines? If so the compression ratios are likely to be similar (unless one is diesel), swept volume won't really enter the equation. The 1.4 car's battery will likely be capable of turning a two litre over happily. Same if it was the other way round.
Where this fails is on older sports cars and stuff; manufacturers often fitted rubbish batteries to save weight and asked them to start multi-cylinder engines. It's why Reliant Scimitars were hard to start.
A battery has a rating for 'cold cranking power' or something - effectively how much power it can push out in one go. Cold cranking is just that, when everything is cold and sluggish it's harder to turn the engine over.
Most cars have a battery with a higher cold crank rating than they actually need. This allows for a couple of tries of the starter, and takes up any slack. Thus the battery is, in effect, over powered for the application.
In terms of engine size, again that's another one that doesn't make a huge amount of difference. The main factors that affect starting are number of cylinders, compression ratio and oil thickness. The first and last things are to do with rotating mass: more cylinders mean more weight for the starter motor to turn and thicker oil is more resistive to a turning action. The middle one is to do with squish on the compression stroke. If there's more squish then it's harder to start the engine.
I guess you're comparing two fairly normal cars with four cylinder engines? If so the compression ratios are likely to be similar (unless one is diesel), swept volume won't really enter the equation. The 1.4 car's battery will likely be capable of turning a two litre over happily. Same if it was the other way round.
Where this fails is on older sports cars and stuff; manufacturers often fitted rubbish batteries to save weight and asked them to start multi-cylinder engines. It's why Reliant Scimitars were hard to start.
Another point: No matter how good the battery is on the "donor" car, you have to get that power to the car you're trying to start, with minimum voltage drop. That's where you realise that there are jump leads, and jump leads. Cheap ones have thin cables, crap connectors and just can't transfer enough starting current - they might work if you give the dead battery a bit of time to charge, but they won't transfer enough current to turn the starter properly.
Real jump leads have thicker (preferably copper) cables, properly connected to decent croc clips. I bought a heavy duty set years ago and they've come to the rescue of 1 or 2 neighbours whose jump leads couldn't hack it.
Maybe that's not your problem, but a lot of people don't think about this.
Real jump leads have thicker (preferably copper) cables, properly connected to decent croc clips. I bought a heavy duty set years ago and they've come to the rescue of 1 or 2 neighbours whose jump leads couldn't hack it.
Maybe that's not your problem, but a lot of people don't think about this.
The reason these things are referred to in terms of the engine size (e.g. if you buy a battery charger in Halfords it will be rated by engine size) is because your average Joe knows nothing about amp hours, cold cranking capacity and suchlike. It's simpler to average out what size batteries are typically used to start what engine size - the bigger the engine, typically the bigger the battery.
It's not accurate, or scientific, but in general it works ok for the average punter.
Which reminds me, I must retrieve my Clarke Jump Start 4000 from my mate! That can start **anything**.
It's not accurate, or scientific, but in general it works ok for the average punter.
Which reminds me, I must retrieve my Clarke Jump Start 4000 from my mate! That can start **anything**.
Gruber said:
Mojooo said:
Some reading suggests most normal cars prob have a 12v battery.
Really?!Have you tried Sellotaping 8 AA batteries together in a row and attaching a jump lead to each end? That should do the trick.
k off. Some people don't have a huge amount of knowledge about cars and you just go and take the piss.Mr Classic said:
Gruber said:
Mojooo said:
Some reading suggests most normal cars prob have a 12v battery.
Really?!Have you tried Sellotaping 8 AA batteries together in a row and attaching a jump lead to each end? That should do the trick.
k off. Some people don't have a huge amount of knowledge about cars and you just go and take the piss.
Gruber said:
Mojooo said:
Some reading suggests most normal cars prob have a 12v battery.
Really?!Have you tried Sellotaping 8 AA batteries together in a row and attaching a jump lead to each end? That should do the trick.
Or maybe not.
Skyedriver said:
Gruber said:
Mojooo said:
Some reading suggests most normal cars prob have a 12v battery.
Really?!Have you tried Sellotaping 8 AA batteries together in a row and attaching a jump lead to each end? That should do the trick.
Or maybe not.
Yeah. Something like that.
It has a lot more to do with the output of the alternator on your car than the battery size, assuming you have the engine running when you jump start the other car.
Batteries do get tired from repeated charging and discharging, so it's likely that cycling this battery every day, especially if it's not a fresh battery, is going to kill it fairly soon.
http://batteryuniversity.com/learn/article/can_the...
Options are to leave the car at the top of a hill and bump start it, or disconnect the battery at the end of each trip.
Batteries do get tired from repeated charging and discharging, so it's likely that cycling this battery every day, especially if it's not a fresh battery, is going to kill it fairly soon.
http://batteryuniversity.com/learn/article/can_the...
Options are to leave the car at the top of a hill and bump start it, or disconnect the battery at the end of each trip.
OK so if I disconnect the black wire after every journey/overnight then I will prevet the battery fro mworkign and losing its charge.
I recall that when I had the battery repalced last time certain lights came on in my dash which had to be reset by the garage - I think the seatbelt or airbag.
Is a flat battery different from a battery with positive only connected or totally taken out in that sense?I would have thought the battery that is flat is the same as a battery that is not there. But on the occasions it has been jumped I haven't had problems with lights on dash - only think is the clock needed resetting.
I recall that when I had the battery repalced last time certain lights came on in my dash which had to be reset by the garage - I think the seatbelt or airbag.
Is a flat battery different from a battery with positive only connected or totally taken out in that sense?I would have thought the battery that is flat is the same as a battery that is not there. But on the occasions it has been jumped I haven't had problems with lights on dash - only think is the clock needed resetting.
I know exactly where you're coming from on the engine size thing, its usually a good indicator of how to match the car to the jump without looking at or studying the battery.
I found this out when I had to go and help a mate out, he called me to tell me he needed a jump on a 1.4 diesel metro, but in the time I took to get there, some kind soul in a 1.1 clio had offered to jump him and this had just killed his own car.
I don't think for a min that a fresh battery for a 1.1 petrol couldn't start a 1.4 diesel, but one thats already turned an engine then driven only a short distance, maybe had the lights/wipers radio on just took it down enough to stop it having enough to start it.
So I suppose the odd jump is ok, but too many between long runs and you'll kill the battery, and other such waffle
I found this out when I had to go and help a mate out, he called me to tell me he needed a jump on a 1.4 diesel metro, but in the time I took to get there, some kind soul in a 1.1 clio had offered to jump him and this had just killed his own car.
I don't think for a min that a fresh battery for a 1.1 petrol couldn't start a 1.4 diesel, but one thats already turned an engine then driven only a short distance, maybe had the lights/wipers radio on just took it down enough to stop it having enough to start it.
So I suppose the odd jump is ok, but too many between long runs and you'll kill the battery, and other such waffle
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