Car jump start
Car jump start
(OP)
I`ve been always told that when you jump start a car with low battery by using another car (I belive it is called JUMP START) you must do it while the good car engine is ON and at mid range rpm
Is this really true? why?
Is this really true? why?





RE: Car jump start
RE: Car jump start
Not totally true; cell phone power packs are just that, one battery charging another. A more accurate statement would be that one battery cannot FULLY charge another; any battery that is at a higher voltage will charge one at a lower voltage, TO SOME DEGREE. Effectiveness of charge is what requires the higher voltage.
TTFN
I can do absolutely anything. I'm an expert!
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers
RE: Car jump start
RE: Car jump start
( Long ago, my wife managed to blow up two batteries by jumping 'red to red' and 'black to black', using a borrowed car that had a red ground cable and a black hot cable. She was just barely uninjured, and doesn't jump cars anymore. )
Probably for related reasons, the owners manual for my 2013 Navigator expressly forbids use of jumper cables and another vehicle. The only recommended tool is a battery in a box, whatever you care to call it.
Mike Halloran
Pembroke Pines, FL, USA
RE: Car jump start
TTFN
I can do absolutely anything. I'm an expert!
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers
RE: Car jump start
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Car jump start
On a vehicle that is idling, the alternator is not putting out enough energy to charge a battery.
http://www.cartalk.com/sites/default/files/feature...
(Technical review provided by Society of Automotive Engineers (SAE). Copyright 2012
Dewey, Cheetham & Howe)
RE: Car jump start
TTFN
I can do absolutely anything. I'm an expert!
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers
RE: Car jump start
That is not generally true. That is what voltage regulators are for, to control the alternative output voltage as engine speed varies. Sure, there is a minimum speed where the alternative will not function, but on all the cars I have owned you can see the head lights brighten after the car has started, and the brightness does not vary from idle. Brightness is a direct indication of alternative voltage.
RE: Car jump start
Definition:
Rescue Vehicle (RV)- has the able battery
Distressed Vehicle (DV) - unstartable
Investigate:
Try a start as-is in your presence. Is there anything? Or is the battery flat?
If there is some life in the battery risk is low, a quick-start is likely.
If it's flat, risk of explosion is high and any start will require co-charging for some significant time.
1) To jump place the two vehicles as far apart as to not clothes-line the jumper cables but to 'use them fully'.
2) Assure the vehicles are not touching to prevent and inadvertent conductive path.
3) The first jumper clamp goes to the DV positive battery terminal. You want as low a resistance path to the DV battery as possible hence direct terminal clamping.
4) The other side of that jumper goes to the positive side of the RV.
5) One side of the negative jumper goes to the negative terminal on the DV battery.
6) Get everyone away ~10 feet from the battery of the DV.
7) You do not want to complete the jump circuit near the RV's actively charged battery which will have hydrogen gas in the top of its cells. Survey the RV engine compartment for a spot on the engine that is bare metal, will likely receive and retain the clamp well, and is approachable from not near the RV's battery. Common spots are manifold bosses, thermostat housing bosses/bolts, and A/C brackets.
8) With face away from the DV battery, aggressively clamp the remaining negative clamp on the chosen point. The resulting arc will, to some degree, demonstrate the rate of charge in effect.
If a large arc was noted or the DV battery was known to be flat then with the RV running wait the same 10 feet from the DV battery for 5 minutes before attempting a start. If the battery was known to be not flat or the DV almost starts go for an immediate start of the DV.
Once the DV is started remove the negative clamp from the RV.
Turn on the headlights of the DV and see if the engine continues running. If it does then speed up the engine from idle to a very high idle and check for the headlights getting slightly brighter. If they do likely the DV will carry on with no issues.
If a fast idle shows no headlight brightening then likely a failed charging system stands before you and the DV is running total loss. Re-connect the negative ground to the RV and proceed with 15 minutes of charging. Headlights definitely off on the DV. While waiting the parties involved need to consider whether it's day or night(headlights needed) how far the DV destination is and whether it can be reached with limited electrical energy available. With electric radiator fans and other loads being considered, because a random stall somewhere could be disastrous to people or the budget.
Once the 'jump' is completed remove the cables in the reverse order (only to reinforce the order) decline any payment (increasing good karma) revert to staid living.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Car jump start
RE: Car jump start
In easy cases you don't even need to start the RV (the RV(car) should NOT be running if jumping a motorcycle); usually it's necessary to start it and hold at a fast idle to get full power from the alternator. If that doesn't work after about a minute, in tough cases I have shut everything down and then hooked the batteries direct and repeated, although that's risky as the problem may NOT be the battery and if it isn't discharged it could more likely have H2 present. Giving a longer charge time seems prudent, but I'm usually eager to let the random Good Samaritan be on their own way.
Of course with all the electronics on today's cars, voltage chaos resulting from cross-connecting could cause other component damage, and may be a factor in more owner's manuals recommending against giving or receiving jump starts at all.
RE: Car jump start
That is not generally true. That is what voltage regulators are for, to control the alternative output voltage as engine speed varies. Sure, there is a minimum speed where the alternative will not function, but on all the cars I have owned you can see the head lights brighten after the car has started, and the brightness does not vary from idle. Brightness is a direct indication of alternative voltage.
Numerous automotive battery experts disagree with your opinion:
See the comment from Interstate Battery:
"Generally, running the engine at idle or short stop-and-go trips, during bad weather at night, will not recharge the battery effectively."
http://www.batteries-faq.com/activekb/questions.ph...
Or from AGCO:
"The average alternator is capable of producing around 100 amps at 2,000 RPM. This supplies energy consumed by the vehicle and some to recharge the battery. The problem is the alternator has to rotate around 2,000 RPM to achieve its potential. At idle a 100 amp alternator may only produce 50 amps. With a load of 75 amps, there is a shortage of 25 amps. This is a draw on the system, and the battery discharges to make up the difference. This causes chemical changes in the battery."
"Problems develop when vehicles are not driven enough. This is because the alternator on an engine at idle may actually discharge. Driving short distances and idling long periods in traffic will not allow the battery to charge. Each time the vehicle is driven, the battery gets weaker, due to sulfating of the plates."
http://www.agcoauto.com/content/news/p2_articleid/...
Or from NAPA:
"Most alternators on late model vehicles are capable of producing up to 70 amps or more at idle, and up to 160 to 180 or more amps at 2,000 to 2,500 RPM."
http://jcwnapa.com/wp-content/uploads/2014/06/TE_0...
Or from DENSO:
"A low idle can cause the charge lamp to illuminate dimly."
http://densoautoparts.com/charging-system-diagnosi...
Or from Alternator 101
"At idle, a vehicle's electrical loads may exceed the low-speed current (amperage) output of the alternator and when this happens the shortfall comes from the battery. This will result in a drop in the electrical system voltage as the battery delivers the additional electrical current to meet the demand."
https://www.google.com/url?sa=t&rct=j&q=&a...
RE: Car jump start
RE: Car jump start
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Car jump start
RE: Car jump start
Pressures to improve mpg include declutching or otherwise turning off the alternator under some conditions, which could make a difference if the margin of overall charging capacity vs overall charging needs is scraped thin enough.
Norm
RE: Car jump start
RE: Car jump start
An alternator that is purposely cycled off must have a quite good ability to charge the battery when it is called to operate because it has to re-charge the battery that has been discharged while it wasn't working.
RE: Car jump start
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Car jump start
Of course for 'gel cells' call it 40% with a further 10% per hour.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Car jump start
One would hope so. But what will the battery tolerate, long term, in higher than 'traditional' recharging rates? I have a 2A/12A charger that also has a 50A start-assist mode. I don't think the 50A mode is intended for recharging purposes, but what I don't know is whether the limitation is on the battery or the charger/starter.
Norm
RE: Car jump start
Do you have any data or link to info on the damage rate of 'gel cells' Keith?
RE: Car jump start
I have looked high and low for something quantitative in that regard but never found anything. I sure the makers know about this and have no interest what-so-ever in it getting published and no one else is interesting in destroying expensive batteries to gather useful data or if they have, they have their own reasons for not wanting to publish it.
I'm stating that on my experience of using or working with probably ~300 gelcells in my career. Early on gelcells were fairly robust. Some like Exide state their gelcells are more robust than AGM batteries and they could be. Gelcells can be made very robust by having extra electrolyte and less antimony for plate strength owing to supporting gel etc.
However, about 10 years ago the cells I work with; Panasonic, BB Battery, Power-Sonic, GNB, and Yuasa all got extremely touchy about the same time. A battery that we'd get new, install in a test and run down overnight would be found to have lost significant capacity in the exercise. This got progressively worse until we actually got some that lost essentially all capacity when severely drained overnight and then attempted to be charged the next day. These were batteries purchased from reputable places like Digikey, received, fully charged by us, and used and completely useless 48 hours later.
Perhaps in a specsmanship war the makers all upped their Ahr ratings in the standard footprints by more plates and insufficient electrolyte or some other cost cutting measure. Now I treat gelcells with extreme care and attention. Any I have around I recharge every 30 days if they have been out of circuit or leave floating.
Keith Cress
kcress - http://www.flaminsystems.com