[Shop-talk] Jump starting a late model car

Fri Dec 1 11:17:35 MST 2023

The BMS was my first thought.  In connecting to the battery posts to 
start the car, you would be bypassing the BMS, so it wouldn't "know" 
about the charge and would think the battery was still dead.  But this 
would have affected the Lexus (which had the dead battery), not the F150.

Other than that, I agree.  I can't think of any reason it would cause 
damage.  Just don't put the two batteries in series.

- GeneG

On 12/1/23 06:32, Bob Spidell wrote:
> 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
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>>>>
>>>> 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
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>>>>
>>>>
>>
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