Jump starting modern vehicles!

[PeteB]

I had to jump the GreenMech tow tug today after it has been idle for two weeks. Couldn't tell you why the battery was flat but the man from the AA suggested that I remove all of the charging plugs for phones etc next time I leave it.

 

I put my battery charger on the terminals and over an hour later it was still too dead. He tells me that it was only accepting 10-15 amps when it should be 40+! He then gave us a top tip. Never go to the terminals with the Negative cable - always go the neg earth strap or another point. Apparently, modern systems have a sensor attached that thinks that the input from another source is the level in the battery and doesn't allow the charge. We got it going easy enough and sure enough, without another source, the Alternator was charging at over 40amps. He even thought that modern vehicles have to have a certain battery condition to accept a rolling bump - without this then it hasn't got the beans to energise all systems....

[cornish wood burner]

Battery charger on the battery terminals should be fine. Negative jump lead on starter/ engine may be an advantage. If you had a dead flat battery then you only put in 10 ah so probably only 10% charged assuming 100ah capacity. Charging current would depend on your charger and battery being heathy. Alternators put in more than most chargers. He was right about the bump though, eng management etc.

[Shane]

Some of the modern transits (bless dear old Ford) cannot be bump started.

Apparently the diesel injector pump can get damaged - leading to an expensive repair.

 

Happened to a colleague of mine who is a member on here. No doubt lots of other engines are tha same.

[slim reaper]

He even thought that modern vehicles have to have a certain battery condition to accept a rolling bump - without this then it hasn't got the beans to energise all systems....

Even not so modern vehicles if they had an alternator wont start with a bump if the battery is 100% dead , an alternator needs a bit of juice to excite the field to get it charging

[aspenarb]

Some of the modern transits (bless dear old Ford) cannot be bump started.

Apparently the diesel injector pump can get damaged - leading to an expensive repair.

 

Happened to a colleague of mine who is a member on here. No doubt lots of other engines are tha same.

 

 

Transits can be jump started but not from the battery, there is a post under the bonnet to do this from, its under a red plastic cap. You are right about pump damage if you do it from the battery, this has happened to us but I dont have a clue why. We have a set of surge arresters we use when welding up plant , I would imagine they would protect the electronics of a modern motor if you were junp starting .

 

Sealey Auto Electronics Protection Device 12V : Tooled-Up.com

 

Bob

[openspaceman]

Battery charger on the battery terminals should be fine. Negative jump lead on starter/ engine may be an advantage. If you had a dead flat battery then you only put in 10 ah so probably only 10% charged assuming 100ah capacity. Charging current would depend on your charger and battery being heathy. Alternators put in more than most chargers. He was right about the bump though, eng management etc.

 

The point about not connecting the negative directly to the pole but rather further away at a good earth point was to avoid a spark near a battery that had recently had a heavy charge. Battery in poor health cannot take the charge and the electrolyte is split by the high current, giving off hydrogen. Hydrogen can be sparked off as the leads are removed once the engine is running so you remove the remote earth lead first.

 

It was a very long time ago but the first tractor I was allowed to play with was a 50s 4 cylinder MF35 which was a pig to start at the best of times. I jumped it from the 55A DC supply from a welder for a number of minutes, it started so I unclipped the charger and whoomph the battery plates were blown out of the pitch sealant holding them in.

 

That was 1970 after I had repaired the frost spalled block with araldite, it was still running 4 years later when sold at the farm auction and exported to Pakistan.

 

Re batteries going flat during a fortnight's holiday, a typical diesel battery (644) is 95Ah I guess it will start a cold engine from half charge so parked up after a run you have 47.5 Ah left, 14 days at .5W or 44 milliamps, some of that can be self discharge about 10mA can be the immobiliser and a tracker will do the rest.

[cornish wood burner]

Others might disagree but I always charge as near to the battery as possible to minimize any poor connection problems, stray current paths and voltage spikes. I always turn the charger off at the mains (as we all should) before disconnecting. A good habit to get into as no choice if you are charging on the bench.

Jump starting I use a different point for the reason openspaceman has explained. Spark when disconnecting and a better connection are two reasons for the negative jump lead on the block or similar. High current can still be flowing when both engines are running.

I suspect even with the welder supply off a current path exists through the windings. I too had a welder/charger and it certainly would make the batteries bubble. Effective though especially with those 4 cylinders. Across the water is the best place for them.

[kimtree]

Some of the modern transits (bless dear old Ford) cannot be bump started.

Apparently the diesel injector pump can get damaged - leading to an expensive repair.

 

Happened to a colleague of mine who is a member on here. No doubt lots of other engines are tha same.

 

i have an old HJ47 Landcruiser not only can you pull start it but also the engine can run backwards if someone mucks up the gear selection

No harm was done as i switched it off when a great guff of black smoke came out of the air filter.this happened 15 year ago and it still runs great