That is absolutely correct. Jump start with jump leads = risk. Jump start with a Lithium jump pack = safe.
Stupid battery/jump start question...
- Thread starter ptruman
- Start date
That is absolutely correct. Jump start with jump leads = risk. Jump start with a Lithium jump pack = safe.
Let me try and explain in a different way.
When you start a car with a flat battery either from another vehicle or from another car battery there will always be a voltage spike upon disconnection. The magnitude of the spike will depend on a number of factors.
The spikes happen because you are disconnecting a running alternator from a load. If you have two running cars you are separating two charging sources from a combined load of two batteries. Each alternator will seem some kind of step change in load. A step change in a circuit with an inductive element will cause a spike. The differing state of charge of the two batteries will affect the magnitude of the spike. Bear in mind a flat 100Ah battery will take 10 hours to charge at 10A so you’d have to leave the two cars connected for a very long time to get both batteries fully charged.
Even jump starting a car from a car battery (or another car that isn’t running) poses some risk. One battery is flat the other may only be 50% charged. It will still start the car but upon disconnection there is a step change in load for the alternator in the started car.
If you don’t disconnect the leads cleanly, i.e. instantly with no sparking, then you can create multiple voltage spikes.
For this reason there are international standards for automotive suppliers, SAE J1113/11 and ISO 7637-2. If all the modules in a car comply with this standard and the voltage spike you generate also complies with the standard(!) then everything will be fine. If someone hasn’t designed an ECU very well or you are unlucky enough to generate an excessive spike then an ECU is likely to go pop.
There is a timeline on this issue, in the 1990’s and early 2000’s it wasn’t really a problem. Cars mostly had chunky electrics and electronics; not sensitive microelectronics. I’d say from around 2005 to maybe 2015 cars were quite vulnerable. Multiple ECUs were added to cars and some weren’t tough enough. Then standards evolved, and were updated, and ECU manufacturers improved their designs. Newer cars should be OK but from time to time a module just isn’t designed well or you are unlucky enough to create an enormous spike.
Note that Lithium jump start packs should be completely safe – why because they can’t be charged through the output leads therefore present zero load.
When you start a car with a flat battery either from another vehicle or from another car battery there will always be a voltage spike upon disconnection. The magnitude of the spike will depend on a number of factors.
The spikes happen because you are disconnecting a running alternator from a load. If you have two running cars you are separating two charging sources from a combined load of two batteries. Each alternator will seem some kind of step change in load. A step change in a circuit with an inductive element will cause a spike. The differing state of charge of the two batteries will affect the magnitude of the spike. Bear in mind a flat 100Ah battery will take 10 hours to charge at 10A so you’d have to leave the two cars connected for a very long time to get both batteries fully charged.
Even jump starting a car from a car battery (or another car that isn’t running) poses some risk. One battery is flat the other may only be 50% charged. It will still start the car but upon disconnection there is a step change in load for the alternator in the started car.
If you don’t disconnect the leads cleanly, i.e. instantly with no sparking, then you can create multiple voltage spikes.
For this reason there are international standards for automotive suppliers, SAE J1113/11 and ISO 7637-2. If all the modules in a car comply with this standard and the voltage spike you generate also complies with the standard(!) then everything will be fine. If someone hasn’t designed an ECU very well or you are unlucky enough to generate an excessive spike then an ECU is likely to go pop.
There is a timeline on this issue, in the 1990’s and early 2000’s it wasn’t really a problem. Cars mostly had chunky electrics and electronics; not sensitive microelectronics. I’d say from around 2005 to maybe 2015 cars were quite vulnerable. Multiple ECUs were added to cars and some weren’t tough enough. Then standards evolved, and were updated, and ECU manufacturers improved their designs. Newer cars should be OK but from time to time a module just isn’t designed well or you are unlucky enough to create an enormous spike.
Note that Lithium jump start packs should be completely safe – why because they can’t be charged through the output leads therefore present zero load.
ptruman
Active Member
I'll add that my MB indie changed both main and aux batteries yesterday, and the car starts nice and quick now.
When it was low, apart form slugging/no starting - I lost the lane departure warning system (that happened twice).
Either way, I've got a portable jump start pack and a shiny new battery, and some elementary lessons on electrical load dumping.
(and some popcorn, apparently).
When it was low, apart form slugging/no starting - I lost the lane departure warning system (that happened twice).
Either way, I've got a portable jump start pack and a shiny new battery, and some elementary lessons on electrical load dumping.
(and some popcorn, apparently).
W1ghty
MB Enthusiast
Good to go for another 10 years then buddy .
