[Shop-talk] Jump starting a late model car

[Bob Spidell]

I got into a discussion on a Mustang forum when I posted I wanted to 
swap batteries without losing all my radio and other presets (I would 
have connected another battery in parallel). People on the forum brought 
up Fords's 'BMS;' which was new turf to this old dog. There are, 
apparently, some possible issues with this system (the Mustang has them 
too). In the end, I pulled an Elon--'F-it'--and just swapped the 
batteries like I always have and only lost the settings for my custom 
drive mode. I think it possible that some who don't understand the BMS 
may have started this rumor; I suspect you can damage these somehow but 
a simple jump shouldn't do it as you're not passing any current through 
it (unless you connect to a hot lead somewhere). The only modification 
to this time-proven technique--jumping a car--is you're now admonished 
to hook ground to the chassis somewhere instead of the common battery 
terminal, which I've always assumed was to avoid a spark which could 
ignite any lingering H2 gas.

https://www.youtube.com/watch?v=I_KmO-KaR4A

bs

On 12/1/2023 4:22 AM, Donald H Locker wrote:
>
> And if someone can point me to a reputable site with information to 
> the contrary, I'm open to changing my mind.
>
> Thank you all,
> Donald.
>
> On 2023-12-01 07:21, Donald H Locker wrote:
>>
>> I think someone is pulling someone else's leg. There is nothing (that 
>> I know of) in any post-2000 vehicle that can be "fried" by providing 
>> or accepting a jump, provide it's done properly (+ to + and - to -).
>>
>> The "dead" battery does not appear as a short because the cables and 
>> clamps have significant resistance. That is the big reason that the 
>> "dead" battery needs to be connected for a period of time before 
>> cranking. (I usually wait 30 sec (longer in winter); not very long, 
>> but it really doesn't take much to bring a dead battery up to 
>> sufficient charge.)
>>
>> The protections on vehicle electronics and electrical systems are 
>> amazing; I've helped design and test quite a few of them. Protection 
>> is built in to every component against: over-voltage; reverse 
>> connection; shorts to ground; shorts to power. The battery itself is 
>> a very simple electrochemical device that _can_ be damaged, but it's 
>> difficult: freezing (-40F if charged; -20F if significantly 
>> discharged); reverse charging; mechanical damage is the most common 
>> problem.
>>
>> Provided the jumper and jumpee batteries are connect properly (+ to + 
>> and - to -), there is almost no way to damage either of the vehicles' 
>> systems.
>>
>> Donald.
>>
>> On 2023-11-30 17:12, JohnT Blair wrote:
>>> I come to the well of knowledge looking for information.
>>> My sister just emailed me about her having a friend jump start her 
>>> late model Lexis from his F150 pickup.  He got her started and then 
>>> drove his truck to someplace and parked it.  When he tried to start 
>>> it, it wouldn't start.  He had it towed to a dealership and they 
>>> said his battery was fried.
>>> In my sister's email she said that she has found out that you 
>>> shouldn't jump start a car made from 2000 on.
>>> My question is why and how do you start a car with a dead battery?
>>> I realize that the jumping car should be running, so that gives the 
>>> possiblity of too much current being drawn from the jumping car as 
>>> it's got a good battery and an alternator capable of putting out 
>>> well over 100A!  So the jumped car's dead battery looks like a short 
>>> circuit.  Bad - lots of current!
>>> So disconnecting the dead battery and putting it on a battery 
>>> charger to give it a more controlled charge should be OK.
>>> But that's not easy to do in a parking lot.
>>> What about these jump boxes, especially the little ones like
>>>
>>> https://www.walmart.com/ip/NEXPOW-Battery-Jump-Starter-1500A-Peak-12800mAh-Car-Starter-up-7-0L-Gas-5-5L-Diesel-Engine-12V-Portable-Booster-Power-Bank-Box-LED-Light/534414164?adsRedirect=true
>>>
>>> But that is supposedly capable of 1500A!!!
>>>
>>> I did a google search on the subject and found an article talking 
>>> about all the problems that you can have doing this.  But the 
>>> article really didn't say if these problems were to the jumping or 
>>> the jumped car or both.
>>>
>>> So what is the collective knowledge about this?  What am I missing?
>>>
>>> JohnT,
>>>
>>>
>>> John T. Blair  WA4OHZ     email: jblair1948 at cox.net
>>>
>>> Va. Beach, Va Phone:  (757) 495-8229
>>> 65 Morgan 4/4 Series V (B1106)   75 Bricklin SV1 (#0887)   48 
>>> TR1800    48 #4 Midget
>>> 65 & 77 Spitfire   71 Saab Sonett III   65 Rambler Classic   65 
>>> Volvo P1800
>>> Morgan: http://autox.team.net/morgan/
>>> Bricklin: http://www.bricklin.org
>>>
>>> If you can read this             - Thank a teacher!
>>> If you are reading it in English - Thank a Vet!!
>>>
>>> From Dennis Prager - The American Trilogy:
>>>      e pluribus Unum, "from many, one."
>>>      In God We Trust
>>>      Liberty - the  power  of  choosing,  thinking,  and  acting for
>>> oneself; freedom  from  control  or  restriction
>>>
>>>
>
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