Jump Starting An Xm, Does not seem to work

[xmexclusive]

Hi All

One of the SORN cars has a flat battery, and this evening I found that I could not jump start it even from the battery of a running 2.5TD.
I will take out a fully charged battery and swap it for the flat one tomorrow. On past experience it will start with no difficulty. I always seem to fail to jump start XM's. Anyone got any ideas why having a very flat battery in circuit should cause these difficulties. It just seems to suck in the available current. Before I tried to jump start it the immobiliser was not working. When I left it after trying to start it there was enough power in the battery to work the immobiliser.

Regards

XMexc

[rowanmoor]

You may already know this - but I found with my old BX (only a 1.9 petrol, nothing like the size of a 2.5TD) that putting the negative jump lead onto the flat battery negative gave this sort of problem. Putting it onto a suitable large bit of metal (anything on the engine or somewhere that is definitely earthed) works much better.

I think this is how the AA etc always do it.

I have been told the reason is something to do with the battery taking all the power to try to charge up instead of giving it to the engine to start up - but I don't really understand how a different earthing point makes a difference.

[Peter.N.]

It's not just XMs, any diesel doesn't start well using jump leads because unless they are very expensive ones they are not capable of carrying the current that a diesel starter requires. With the starter engaged you may only have 6 volts at the end of the leads. As Rowan says, you need to get a good connection both ends or you lose more voltage. You will probably find that the leads or connections get hot, thats the current that should be turning the starter! The only solution is to put the good battery on the car, or uses jump leads that have the same current carrying capacity as the starter lead on the car.

If you can get a couple of battery leads from a mini at the scrap yard, they run the length of the car and make good heavy duty jump leads. I made up a pair once, but I lent them to somebody......

Peter.N.

[xmexclusive]

Hi Rowan, Peter and All

Thanks for that. It explains a lot. It also indicates how much resistance a bit of wiring and a few connections can add to the current path. I will see if using a metal earth works the trick. Yes Peter the jump leads were getting a little warm so I will make up a tempoary set using some lengths of copper mains tails that I have somewhere in the heap. You do not see many mini's in scrap yards round here so I guess I will have to come west. I take it that it is old style mini only, are the cables flexible (braided) or stiff (cored) as unless they are flexible I might just as well stick with the mains tails.

Regards

XMexc

[techmanagain]

The idea of connecting the negative lead to a metal prt of the engine is to prevent any possibility of a spark at the battery. That is of course presuming that the final connection from the slave to the car battery is the negative on the car. Watch the way an experienced AA/RAC man does it next time you are unfortunate enough to need his services. I once saw the - rare, luckily - result of a batter explosion so I stick to this rule.

[Peter.N.]

Hi XM exc

Thinking about it, it was probably about 20 years ago I made up those leads! Mains tails should be better than your average jump leads but welder cable is reasonably priced from the right place.

Your starting current is probably 300 - 400 amps so its not difficult to imagine what even 1/4 ohm can do!

Peter.N.

[xmexclusive]

Hi Peter and All

I had a try again tonight. Jump starting with the clamp on a metal earth got the starter trying a bit harder than last night but not enough to start it. So I put the charged battery in the car and it started first turn of the key.

Regards

XMexc

[xmexclusive]

Hi Techmanagain

Thanks for the timely reminder about sparks near gassing batteries. I was something I had overlooked.

Regards

XMexc

[noz]

Hi all,

I thought I'd add my tuppence worth. I've just had the exact same issue starting both the SORNed XM and CX just last weekend. Even with a fully charged battery and good jump leads you can still see the same problem particularly if the battery in the car is flat. What happens is that the car battery is sitting at 0-3v, say, and the jumper battery is sitting at 12v. You connect them together using high quality jump leads in parallel ie positive to positive and negative to negative. Assuming both negaitves are at the same potential for a second (not necesarily true but makes the explanation easier to understand) the positive leads now have a difference of say 10v. Lets assume the jump leads have a resistance of say 0.2ohms. The current which flows from the charged to the flat battery is therefore 10 divided by 0.2 which equals 50A.

So whats happening is that the flat battery is absorbing a lot of the available current from the charged battery leaving little for the starter motor. You'd probably be left with 6v or so at the starter terminals which wouldn't even be enough to pull in the solenoid never mind turning the motor. Charging the flat battery even for a short time before trying to start would help enourmously. However, if the car battery is completely flat it will take several days of charging to bring it back to full strength.

In terms of the risk of explosions the explosive gas in question is hydrogen. This is released from the water in a lead acid battery during the charging process. Production of hydrogen is not instantaneous the second you begin charging. It will take 10 min or so before the bubbles start to appear. Most modern batteries are not lead acid in any case. The lead ones have changed to use a gel instead of water. The hydrogen produced is chemically absorbed into the gel on charging and released by the gel back to the plates upon discharging. Thus the battery is sealed from the atmosphere and never needs topping up. These are called maintenance free or sealed lead acid batteries . Even newer batteries use weird and wonderful chemical combinations ( including calcium) which don't have the hydrogen problem.

Hope this helps shed some light.

cheers

noz

[Peter.N.]

What Noz says is good, exept when a battery is completely flat. By this time it has usually started sulphating and has a fairly high internal resitance as is indicated when you connect it to a charger and it shows little or no current. When its reached this state its usually had it, which shows the importance of keeping idle batteries charged....... I know, I forget as well

Peter.N.

[xmexclusive]

Hi All

I think we have this sorted now. Just have to change the battery and accept that it is going to upset the radio etc each time.
Noz's calcs are interesting but a little pessimistic. A dead flat battery should read 10.4volts with a meter if it is servicable and capable of being recharged. This useless piece of information comes from experience with underperforming domestic batteries on a canal boat.
First time I played at jump starting I was of course using a vented battery with liquid and also doing it in the dark so could clearly see the sparks as I connected up. Last night I was a little more cautious. When I have another battery recharged I have to repeat the process to move the Blue 2.0TCT estate that has been stood for nearly a year.

Regards

XMexc

[Ciaran]

I know the feeling. I have stupidly let the batteries in both the XM and Xantia go flat as they sat for the past few months while I awaited the money to put them on the road.
I bought one of the little solar chargers recently, which I hoped would keep the XM topped up after a full charge, but this doesn't work, and I fear it may be too late for that particular battery.

Last night it was payback time, I needed to move the XM from the bottom of the drive in order to make space for a painter who is doing the outside of our house. Got in, ignition lights on, great, turned the key to stage 3 and saw the lights dim and the climate fan slow down as the glow plugs kicked in. They came back to life afterwards, but all I got when I attempted to turn the starter was a pathetic groan or two, then the inevitable reset of the dash electronics and the alarm.
I thought 'right, it obviously has some charge, I'll get the Mondeo round and jump it'. So I parked behind the XM, but unfortunately the distance was too far for the jump leads, so I had to join 2 sets together. The heat at the join was phenomenal by the time I finished, which certainly proves the resistance theory !

To my surprise, it took about 10 minutes of the Mondeo's engine revving at about 2k before the XM would even entertain starting. On previous occasions, merely connecting another battery without the donor engine running was enough to make it start right away...
I did eventually get the XM started, and reversed it onto the street to turn.... where of course it promptly stalled in the middle of the road, and my quick attempts to restart were in vain. I think it's new battery time... trying to push a dead whale up the street at 11pm in the dark isn't funny....

Interestingly, there has been some discussion about dead batteries on XM-L recently, with varying opinions on the recoverability of dead batteries. A few people mentioned trickle charge devices, and even adding a chemical called EDTA to each cell, which could fix sulphadised plates... I may well give that one a try, nothing to loose where these batteries are concerned.
Oddly, the battery in my last XM sat in it, outdoors, flat as a pancake for a year, yet worked fine when charged up again, and yesterday my cousin loaned me a battery for the Xantia, that had lain uncharged on his shed floor for 6 months, and it worked fine on the first turn of the key....

[Peter.N.]

The probem with modern car batteries is that they are not designed to be 'deep cycled', you can only charge and completely discharge them a very small number of times before they cease to function. The are constructed with a large number of very thin plates to give a large surface area and thus a high discharge current and are designed to be more or less fully charged all the time., as the alternator will replace the charge lost in starting in a few minutes. The plates are very fragile and fall to peices easily.

Such is the discharge capability of them that a battery can lose probably 80% of its active material and still start the car, providing it starts quickly. Thats why they appear to fail suddenly, with probably only about 10 - 15 ah capacity, you only have to leave the lights on or let them go flat to lose the remaining capacity.

Leisure batteries are 'deep cycle' and have fewer but thicker plates, so they are mechanically stronger so last longer, but cant deliver as much instantanious current.

Peter.N.

[xmexclusive]

Hi All

Took the charged battery out to the TCT this evening in the dark. Did not play about with jump leads just swapped the batteries topped up the radiator turned the key and away it went so I let in tick over for a few minutes then drove it to the new parking spot. It is fun to drive as the clutch is nackerred.
Peter the canal boat has a bank of 4 batteries so shelling out for the extra cost of lesiure batteries is not worth it because of the initial outlay. As it is a shared boat it gets used about 44 weeks a year with the batteries taken to near flat most nights by the lights and the fridge. Typically we get 2 to 3 years out of a set of batteries, roughly the same life as a car battery despite the heavier cyclic loading. I think it is the 3 stage charge from the special altenator that makes the difference. I have taken to using a similar 3 stage mains battery charger for the car batteries and it seems to rescue some of the batteries that others have declared as dead.

Regards

XMexc

[Ciaran]

Well, I just went out the back with the multimeter and tested the Xantia's battery that has been sitting outside the door for a week.... 5.62V. Guessing that one won't be coming back then

I might try some of that chemical stuff in it if I can get some cheap, just out of morbid curiosity....