Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Everything Else Anything related to audio / video / electronics etc) BUT remember- we have many new forums where your thread may now fit! .... Parts, Equipment & Tools, Construction Tips, Software Tools......

Deeply discharged car battery - basic questions (no charger around).
Deeply discharged car battery - basic questions (no charger around).
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 13th November 2018, 06:01 AM   #1
Vortex is offline Vortex  Hungary
diyAudio Member
 
Vortex's Avatar
 
Join Date: Jan 2004
Location: Budapest, Hungary, Europe
Send a message via ICQ to Vortex Deeply discharged car battery - basic questions (no charger around).
Question Deeply discharged car battery - basic questions (no charger around).

Hi all,

I simply cannot find a correct answer from physics side for my questions so I thought I might ask this here. Maybe some good electricians can answer me these questions or think about it a bit.

Situation1: for whatever reason, the car's battery is deeply discharged. Let's assume the car's charging system is in good shape.

Q1: can I jump start the car from another car, batteries connected directly ?
Meant here: direct connection. Lot of people say we shall directly connect battery positive leads but on the charged car the negative shall go onto the body instead of the negative battery lead. Why ?

Q2: shall the charging car's engine run meanwhile or not ? To compensate for quick discharge of the charging car's battery itself.
Meant here: won't there be a quick current rush onto the bad battery at the moment I connect the cables ? Which can then destroy the diode bridge on the providing car's charging system.

Q3: some people suggest a 50W bulb in series with the positive lead (a non-bulb load, big resistor is even better) so this way at the beginning when the discharged battery cannot pick up much current (due to high internal resistance) the current gets dissipated on the bulb but there's still some little current flowing towards the battery. When it starts to fill up slowly, its internal resistance gets lower which again contributes to even more charging current (because the giving side is a voltage generator and constant charging voltage makes current flow depending of resistance).. so there's sooner or later a point where the charging car's charging system might be overloaded.

Q4: OR not ? If not, why ? Are there any kind of charging circuit protections employed in modern cars ? ( = cars of the last ca. 20 years).

Q5: does a direct battery-battery connection quickly discharge the giving battery while charging the dead battery too fast ? -> Cable overload, too much current. If that's the case, why does it happen, when we talk about discharged battery's big internal resistance ? Can it be that at the beginning nothing strange happens but then as after couple of minutes the internal resistance of the dead battery lowers, currents begin to rush and be too much for a cheapo normal cable ? (Is there an internal resistance / charging curve for normal car batteries ? I haven't seen some yet). I know too much current within a given time can make the receiving side battery "boil" so there's definitely an upper limit of charging speed for the receiver part. (And also a discharging speed of the giving side if that's another battery).

Q5: can a car with a discharged battery be push-started ? What will happen in the charging circuit side ? So when a voltage generator meets a big internal resistance and only a minimimum of current flows. I assume after couple of minutes as "R" lowers, it starts to charge more, more, more - is there a maximum of it and does some kind of protection kick in to apply less charging and be gentle with the battery AND with the charging circuit itself, diode bridge, etc. ?


Besides explanation of basic physics and the happenings (with respect to Ohm's law) this might also clarify how to quick-start cars and how don't do it.

Winter is coming. (At least here on the northern hemisphere).
Attached Images
File Type: png winter.png (295.9 KB, 376 views)
__________________
IT guy with a broad taste of music: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16
  Reply With Quote
Old 13th November 2018, 07:33 AM   #2
simon7000 is offline simon7000  United States
diyAudio Member
 
Join Date: Nov 2008
Location: Oakmont PA
Proper technique is to start the good battery car. Attach the red positive lead between the batteries first. The attach the black lead to the good battery terminal. Second attach the black lead to the dead car on the frame away from the battery. That way any spark will not ignite any possible hydrogen gas from the battery. If you just jump the two batteries there is a good chance you will have two dead cars.

The dead battery must charge for a bit before you can start the car as the jumper cables have high enough resistance to prevent a good start.

That resistance is also why you can just jump the batteries.

Yes you can roll start a car with a manual transmission. Best is to roll it downhill and then once moving nicely pop it into second gear.

If you have a good charging system and the battery has died without a cause such as leaving a light on or let it run dry, you will need a new battery.

Last edited by simon7000; 13th November 2018 at 07:37 AM.
  Reply With Quote
Old 13th November 2018, 07:43 AM   #3
gj00023 is offline gj00023  United States
diyAudio Member
 
Join Date: Aug 2015
Location: Western Siskiyou County, CA
Q1: can I jump start the car from another car, batteries connected directly ?
Meant here: direct connection. Lot of people say we shall directly connect battery positive leads but on the charged car the negative shall go onto the body instead of the negative battery lead. Why ?
A1: I always connect direct. It's easier than finding a good ground connection. I think the idea is that since flooded lead acid cells can discharge hydrogen, and since there is usually a spark when you connect the batteries in parallel, there could be an explosion.

Q2: shall the charging car's engine run meanwhile or not ? To compensate for quick discharge of the charging car's battery itself.
Meant here: won't there be a quick current rush onto the bad battery at the moment I connect the cables ? Which can then destroy the diode bridge on the providing car's charging system.
A2: A fully charged lead acid battery is 13.2VDC, but to charge a battery up to that voltage you need to present it with an even higher voltage, which your alternator will do. So the charging car's engine shall be running. I don't know anything about destroying the diode bridge.

Q3: some people suggest a 50W bulb in series with the positive lead (a non-bulb load, big resistor is even better) so this way at the beginning when the discharged battery cannot pick up much current (due to high internal resistance) the current gets dissipated on the bulb but there's still some little current flowing towards the battery. When it starts to fill up slowly, its internal resistance gets lower which again contributes to even more charging current (because the giving side is a voltage generator and constant charging voltage makes current flow depending of resistance).. so there's sooner or later a point where the charging car's charging system might be overloaded.
A3: Never heard that.

Q4: OR not ? If not, why ? Are there any kind of charging circuit protections employed in modern cars ? ( = cars of the last ca. 20 years).

Q5: does a direct battery-battery connection quickly discharge the giving battery while charging the dead battery too fast ? -> Cable overload, too much current. If that's the case, why does it happen, when we talk about discharged battery's big internal resistance ? Can it be that at the beginning nothing strange happens but then as after couple of minutes the internal resistance of the dead battery lowers, currents begin to rush and be too much for a cheapo normal cable ? (Is there an internal resistance / charging curve for normal car batteries ? I haven't seen some yet). I know too much current within a given time can make the receiving side battery "boil" so there's definitely an upper limit of charging speed for the receiver part. (And also a discharging speed of the giving side if that's another battery).
A5: It'll discharge the "donor" battery, but will not do it all that fast and definitely not too fast for the discharged battery.
Q5: can a car with a discharged battery be push-started ? What will happen in the charging circuit side ? So when a voltage generator meets a big internal resistance and only a minimimum of current flows. I assume after couple of minutes as "R" lowers, it starts to charge more, more, more - is there a maximum of it and does some kind of protection kick in to apply less charging and be gentle with the battery AND with the charging circuit itself, diode bridge, etc. ?
A5: I have no idea.

Besides explanation of basic physics and the happenings (with respect to Ohm's law) this might also clarify how to quick-start cars and how don't do it.

Winter is coming. (At least here on the northern hemisphere).


The alternator includes a voltage regulator and that combined with the battery's internal resistance is what regulates charging current.

When I need a jump I find the largest vehicle I can. They usually have larger alternators and can supply enough power for the starter motor on the disabled vehicle. Thus very little actual battery charging by the donor vehicle is needed, it just supplies the starter motor with the power needed to get the engine running again.
Oh, also: buy and carry really thick jumper cables. Lots of power just gets turned into heat with thin cables.

Last edited by gj00023; 13th November 2018 at 08:08 AM. Reason: spelling
  Reply With Quote
Old 13th November 2018, 12:21 PM   #4
kevinahcc20 is offline kevinahcc20  United States
diyAudio Member
 
kevinahcc20's Avatar
 
Join Date: Apr 2009
Location: Farmington Hills, MI USA
Beyond the jumping queries there is the question of why the battery is dead in the first place. A battery in good condition should easily last more than a month in a parked car and still be able to start it. If this is not a "maintenance free" battery the obvious first step is to check the electrolyte level in each cell...it should be filled to the bottom of the fill tube so that a meniscus forms and should at least show all plates covered when checked.

If the battery itself is not shot then the reason for a dead battery is either a charging system malfunction or a parasitic load on the electrical system when parked. Modern vehicles go through a sequenced shutdown of the various controllers in the vehicle that typically takes some minutes after shutdown to reach the full sleep state. Even in full sleep there will be a current draw of a modest number of milliamps so that the vehicle can respond to a keyfob command to unlock.

If you find that the current draw 15 minutes after shutdown is still substantial then something is interfering with the shutdown sequence. You can pull fuses one at a time to isolate which circuit(s) is responsible for the high quiescent current draw and take it from there to identify the controller that is the insomniac.
__________________
Kevin(ahcc20)...I'd rather have a bottle in front of me than a frontal lobotomy!
  Reply With Quote
Old 13th November 2018, 06:01 PM   #5
PRR is offline PRR  United States
diyAudio Member
 
PRR's Avatar
 
Join Date: Jun 2003
Location: Maine USA
Don't fret over-much. Unless you spent a fortune on jumper cables, their resistance will limit peak current to much less than infinity. They typically will not pass starting current (100A) without many volts of drop. Peaks to 300A, once or twice, do no real harm to car batteries.

I used to "push"-start my Willys for weeks on end. The available rebuilt starters were crap, and never in stock. It rolled easy. At home and at work I parked on a slight grade. Traveling though south Delaware (DEAD flat), two friends at the back were able to gain start-speed.

It is "possible" to pop-start a car with another car and a rope. Very Dangerous! When the towed car catches it tends to ram the towing car.

Last edited by PRR; 13th November 2018 at 06:03 PM.
  Reply With Quote
Old 13th November 2018, 06:46 PM   #6
MAAC0 is offline MAAC0  Portugal
diyAudio Member
 
Join Date: May 2010
Plenty information about batteries here.


https://batteryuniversity.com/learn/
  Reply With Quote
Old 13th November 2018, 09:01 PM   #7
phase is offline phase  United States
diyAudio Member
 
Join Date: Oct 2004
If a car battery has suffered a constant, low drain, I will charge it back again slowly, over the course of a day or so, or at least long enough to get it part way back before hitting it with a bunch of amps.
When they are totally dead, you can charge them up in reverse polarity!

There are battery terminals that have a feature that allows one to isolate the battery from the carís electrical system, and help prevent draining when the car is being stored.
  Reply With Quote
Old 13th November 2018, 09:25 PM   #8
martin clark is offline martin clark  Europe
diyAudio Member
 
Join Date: Jul 2003
Location: Bath, UK
Q1


The reason you connect the black lead to target car chassis ground (ideally, the engine block somewhere) is becasue this is the most direct return to the target starter motor ie minimum impedance - does not involve the target car's Negative battery terminal to body, in series with the body-engine ground links (either of which add a further smidge of impedance)

Q5

A manual-transmission car can be push-started but it it has been built in the last 15yrs or so don't do it. It won't start, and it won't help.

Long answer - these days the engine management unit won't even instruct the injectors to run and the ignition circuit to fire until the engine is turning over a certain min rpm (often 120-150rpm) to guarantee a rapid start (min unburnt fuelling). This is to protect the catalytic converter(s) and lambda sensors, and it is not enough to get your engine up to that once at a clutch-dump downhill - needs to be sustained, and battery terminal voltage also above say 11.5v (also checked by the DME as part of the firing cycle...) - and a push won't be enough for the alternator to bring the dead battery system voltage up far enough for all 3 conditions to be sustained. Don't even bother.

Long story short - not likely to be useful. Hook the battery to a known -good car or charger, let the known-good car idle to supply some bulk charge in for 5-10mins, try a start on the target then.

HTH
  Reply With Quote
Old 13th November 2018, 09:28 PM   #9
evanc is online now evanc  United States
diyAudio Member
 
Join Date: Sep 2009
Location: New Jersey. About 1 hour from NYC and 1 min. from the beach
Deeply discharged car battery - basic questions (no charger around).
It is best to get the battery charged with a battery charger or at least give it some time to charge with jumper cables from another car before starting your car. I have seen many alternators ruined when they work full out to charge a totally dead battery.
__________________
http://www.evancotler.com
  Reply With Quote
Old 13th November 2018, 10:22 PM   #10
Vortex is offline Vortex  Hungary
diyAudio Member
 
Vortex's Avatar
 
Join Date: Jan 2004
Location: Budapest, Hungary, Europe
Send a message via ICQ to Vortex Deeply discharged car battery - basic questions (no charger around).
Many-many thanks gentlemen, what a great forum. A lot of useful information here. The topic didn't get easier and there's no black & white answer but I at least got a deeper insight into this all. Thank you again.



(Maybe these posts here will be once useful for somebody else too).
__________________
IT guy with a broad taste of music: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16
  Reply With Quote

Reply


Deeply discharged car battery - basic questions (no charger around).Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Battery Charger Questions JhonDoe Power Supplies 5 15th February 2010 08:08 AM
Battery Charger for 15V Li-ION Battery Pack ??? Jan Dupont Parts 2 11th April 2009 02:18 PM
R/C battery and charger jaudio Power Supplies 3 18th February 2009 07:27 PM
12V Battery Charger for Car Wynand Everything Else 10 15th November 2006 11:25 PM
Battery Charger ThSpeakerDude88 Everything Else 13 6th September 2006 10:40 PM


New To Site? Need Help?

All times are GMT. The time now is 11:32 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki