MINI JUMP STARTER

Discussion in 'Automotive Electronics' started by xchcui, Oct 3, 2015.

  1. xchcui

    Thread Starter Member

    May 12, 2014
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    Hi.

    I saw in the net,that there are a mini car jump starters(very small gadget-relative to the old fashion ones)that can start the car several times with battery capacity of 8000mAh,14000mAh etc..
    My question is related to the 12V lithium ion polymer battery that this jump starter has.
    If i will buy the 8000mAh jump starter(this model is enough to cars less that 2000CC engines) and i will charge it only to 40% capacity,will it be enough to start the car with totally dead battery(at least one time)?
    If not,what is the minimum capacity that the jump starter battery should have in order to be able to start the car at the wrost case(as i mentioned-totally dead battery)?
    I know that 40% capacity at 3.7V LI-ION battery is about 3.75V-3.8V(open circuit voltage),What is the OCV value of the a polymer li-ion battery of that jump starter when it has 40% capacity?
    My question is based on the fact that while keeping the li-ion batteries in storage the best capacity value for it,is 40%,while more than that into the area of the 100% capacity will speed the degradation of the battery,therefore the day that i will need to use it,the battery might be degraded in such way that it will not be able to start the car(failed battery).

    Thanks in advance.
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
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    I have used several different types of battery powered jump starters, although all were SLA, and my experience is that nothing short of jumping with another vehicle (i.e. good battery) or using a charger with an adequate boost option will start a vehicle with a dead battery. They just can't provide enough amps...
     
  3. xchcui

    Thread Starter Member

    May 12, 2014
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    I didn't understand your answer.
    What do you mean?
     
  4. dl324

    Distinguished Member

    Mar 30, 2015
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    Those battery powered jump starters are not intended to start a vehicle with a dead battery.
     
  5. tcmtech

    Well-Known Member

    Nov 4, 2013
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    If you are intending to jump start a vehicle with a totally dead battery you will need to be able to provide at least 14 - 15 volts at a Ah level of at least 10% of the main battery capacity.

    Given that if you have a small vehicle that has a smaller 40 - 50 Ah capacity battery you would need a booster unit capable of supplying at least 4 - 5 Ah of current while staying above 14 volts which to do that with a LiPo type battery at ~40% charge itself it would need to have a cell rating of at least 15 Ah and 14 volts or higher at load.

    Going by that requirement and the general voltage drop to current draw ratings of the average lithium based battery that would require a 5 cell system that would have a 15 - 16+volt no load voltage to be able to supply 14+ volts at a several tens of amps or higher current draw at the battery being charged.

    That's my thoughts on the concept based on real life working conditions relating to jump starting dead vehicles with external power sources.

    Realistically that would mean building your booster/charger out of a 18.5 volt 15+ Ah set of lipo batteries and having roughly 8 - 10 feet of 10 ga copper wire for the leads to give you a ~ 14 - 15 volt charge at the dead battery at a several tens of amps charging rate from a lipo battery bank that is at ~40% charge itself.
     
    Last edited: Oct 4, 2015
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  6. xchcui

    Thread Starter Member

    May 12, 2014
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    Thanks for the answers.

    I see that 8000mAh jump starter is out of the question.
    And i need,at least 15000mAh jump starter,if i would like to start dead battery with 40% jump starter capacity.
    I got the idea,but i still try to figure out what is the OCV of the 12V jump starter when it will be at 40% capacity.
    Just to compare it to the case that i have only 1 lipo cell(3.82V when it is 40% capacity of the battery).
    If the mini jump starter has 5 cells as you mentioned,is it mean that the OVC when full charged is 4.2V*5 cells=21V? and when it is 40% capacity,it is 3.82V*5 cells=19.1V?
     
  7. dl324

    Distinguished Member

    Mar 30, 2015
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    I have an electric battery charger with a 55 amp boost mode. I've tried using it to start my car with a dead battery and it wouldn't crank. My engine is 2.8L but my battery is huge (over 1100CCA) for unknown reasons.

    I've also tried to boost start a vehicle with a 3.6L engine with a dead battery, but a more typical sized battery without success.

    Maybe a better solution would be to address what is causing your dead battery scenario...
     
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  8. tcmtech

    Well-Known Member

    Nov 4, 2013
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    That would be about right. Most of the 5 cell batteries I see are rated as being 18.5 volts but yes that value is not exactly right just as a 12 volt vehicles typical running voltages are around 14 - 15 volts.

    As I said factoring in the voltage drops associated with loading the batteries down plus lead wire losses and connector losses the actual applied voltage at the vehicle battery will be right in the same range as what would be expected from most any line powered booster unit that has a high boost starting mode which can be over 16 volts at the battery when its charging in high boost mode with a 20+ open circuit voltage when its not.

    Or at least that's the as seen voltages I have seen many times with the higher powered booster units and they don't do any damage to a vehicles electrical system.
     
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  9. tcmtech

    Well-Known Member

    Nov 4, 2013
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    The old rule of thumb I have went by was a minimum of one amp per cubic inch of engine displacement for warm starting and double that for cold weather starting.

    Going by that your 2.8 L engine would need at least ~170 amps and your 3.6 would need ~220 amps if the engines were warm. Cooled off and sitting for a while I would expect at least 50% more to get them moving.
     
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  10. WBahn

    Moderator

    Mar 31, 2012
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    FWIW, I have a truck with a 460 cu in (7.5 liter) and had a problem with a fuel pump that wasn't always turning off and was draining the battery dead enough such that no dome light came on when left overnight in that condition. I had taken it in to have some work done on it and, sure enough, the battery was dead when I went to pick it up. One of the guys there had a "microstart" unit (the thing was about a foot long and maybe three inches wide and an inch deep) and that thing fired the truck right up. I was pretty impressed. The only thing that has kept me from getting one of them (aside from the couple hundred dollar cost) is that they don't like being left in the cold for an extended period of time and it will really only do me any good if I can leave it in the vehicle -- if I have to remember to take it in and out then one of two things is guaranteed to happen: either I will leave it in the car and ruin it or I will leave it in the house and not have it when I need it.

    I've toyed with the idea of making a highly insulated enclosure and then putting a thermostatically controlled heating element in there to keep it above a reasonable floor temp. If the energy to do that isn't too much, then I could draw it from the main battery and, if I draw too much, I could use the microstart to get going.
     
  11. tcmtech

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    Nov 4, 2013
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    I've kicked the idea around about building a good high powered jump starter as well many times but for the life of me I have yet to ever justify its existence being I have a set of home made 20 foot 2/0 jumper cables I made about 20 years ago and any time anything has had a battery that was too dead to stat it it was either within reach of an extension cord and one of my high powered battery charges or it was far enough away that I would have to drive something there and the big cable would be coming with.

    Now that I picked up a 94 Ford F250 service truck and I have that outfitted with its own 5400 watt generator I have even less reasons for building a booster pack.
     
  12. WBahn

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    Mar 31, 2012
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    It's the times that it's "far enough away" that I WANT that jump starter available. Just a month or so ago the battery in my Toyota started failing. It was an odd fail mode and I was pretty sure that I actually had a problem elsewhere in the electrical system -- but after taking it to three mechanics no one could say what the problem was as the battery checked good and so did the starter and charging systems. But that was because each time I had just drive the car there and the battery was holding it's own when it was freshly charged. But after sitting for many hours it would often not want to start the car -- yet if I kept kicking it in then, often after the tenth or even twentieth try, it would turn over and start. So I was thinking that I had a starter or solenoid problem. Yet something was causing the battery to drain, too. So I had no idea what was going on. So I made sure that I had a jump starter (the SLA type) in the vehicle. The fact that it was actually the battery failing made itself known when I drove home but stopped at the mailhouse to check the mail and the car wouldn't start. This was well after midnight and there is no traffic on the road at that time of night and the mail house is three miles of mountain road away from our house. Plus there is no cell reception anywhere near there. So without the jump starter I would have been looking at a three mile hike with the kitties and cubs (mountain lions and bears). But the jump starter fired it right up and then the next day I had to use it every time I stopped anywhere, but it let me get it down into town to where I could buy a battery. No problems since then.

    I definitely like having a jump starter (with an air pump built in) in the car that my wife drives. I've trained her how to use both and if that will let her get home without having to flag someone down, that gives me significant peace of mind. I imagine that will be true in spades in another eight years when my daughter starts driving. She will know how to change her own tires, check and fill all her fluids, and other basic roadside tasks (though that list is getting shorter and shorter with today's cars) before she ever even attempts to get her license.
     
  13. tcmtech

    Well-Known Member

    Nov 4, 2013
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    I can relate to that to a point. About two or three years ago I went though a run of my wife constantly leaving the headlights on in her car when she went to work and then calling me to come and jump start her. (once or twice a year is forgivable but not 3 - 4 times a week every week.) :rolleyes:

    After about the 8 - 10th time in less than three weeks of getting called to come get her going I just put a set of 2 ga jumper cables and a good used tractor battery in the trunk and told her to either figure it out herself of get a coworker to help her.

    I figured that having to either do it herself or ask her coworkers to jump start her car and then have to tell them that her husband has a big battery and cables in the trunk already would be enough inconvenience and or embarrassment to snap her memory into shutting off the lights when she got to work.

    She never did tell me how many time she used it but I know the end of the cables were noticeably arc worn and that battery took a pretty hard charge for several hours to bring it back up when I did take it out of her car a month or so later and that car never took more than 2 - 3 seconds of cranking even with the cable on it to get it to start. :eek:

    BTW I'm still and A hole 'or doing that to her' instead of coming to her rescue several dozen times because of her bad memory. Oh yea I also ended up having 5 spare keys made for it as well due to her constantly locking the keys in it when she got to work. One for me, two for her office desk, one for under the car, and one for her boss to hold onto plus the original. I'm still a jerk for that one too. :p
     
  14. WBahn

    Moderator

    Mar 31, 2012
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    Once again I'm made aware of how incredibly fortunate I am. My wife has her blind spots (though not as many as her husband does) but she seldom gets bit by the same mistake more than a few times. It's infrequent enough in both of our cases that if one calls the other and needs help the other is willing to go do it, even though it is nearly an hour drive from our house to just about anyplace.

    I will be even more tolerant when it comes time to put up with our daughter's misadventures -- in no small measure because there is every indication that this child is going to grow into an exceptionally beautiful young lady and I am going to be absolutely paranoid about what might happen in any situation in which she finds herself stranded.
     
  15. xchcui

    Thread Starter Member

    May 12, 2014
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    The subject is more clear now.
    But refer to the quote above,why does the jump starter need to stay at minimum 14V when it is starting the car?
    When the battery of the car is starting the car,it can drops to 10.5V and even 9.6V while starting.
    So why does the jump starter must staying on such high voltage when starting the car?

    At this case,you can install headlight alarm buzzer,as can be seen in my attached photo. headlight alarm buzzer.JPG
     
    Last edited: Oct 5, 2015
  16. tcmtech

    Well-Known Member

    Nov 4, 2013
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    I didn't say the voltage has to stay above 14 volts when cranking but it helps to have a booster that can hold the voltage up higher when cranking.

    The reason for keeping the battery above 14 volts is to put some charge into it so it can assist on cranking the engine that and the more voltage you can supply the quicker and easier the engine starts.
     
  17. xchcui

    Thread Starter Member

    May 12, 2014
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    OK. i thought it somehow related to the fact that the jump starter is connected to a totally dead battery rather than to some discharged good battery.
    But i understand that it doen't have to stay above 14 volts.
    So,the issue is solved.
    Thanks for your help:)
     
  18. BR-549

    Well-Known Member

    Sep 22, 2013
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    I have spent many hours jumping cold engines. A thin plate of teflon under battery in cradle will help in cold regions. Make sure cradle clamp is insolated at battery surface too.

    I have made many jumpers out of welding cable and strong clamps.

    But if the battery is drained, it’s a bad solution. Look at the load that is on the auto charging system of the jumper car.

    As soon as you connect the jumpers, the dead battery is going to draw a lot of current. This is assuming the battery is good, other than discharged.

    This causes the jumper battery voltage to drop and that system starts charging. You will hear the idle go down.

    This is the worse time to try to start the engine. You need to wait. The reason you need to wait is because of the clamp contact area. This is where the resistance is in the jump circuit. Look at all the loads on the charging system. It’s charging its own battery, it’s charging the dead battery thru the clamp resistance, and if you try to start, it’s supplying current to the starter motor, thru the clamp resistance. Turn on your AM radio while doing this and listen to your alternator scream. And a possible fan belt shriek.

    If you replace the dead battery with the jumper battery, you eliminate both the resistance and the extra loads.

    I have also found that if you clean the dead batteries terminals, it will help....sometimes a jump is not needed.

    I never fooled around with the new cap/bat tech. It looks good. They will get better materials.

    No one likes to fool with a car battery because of the weight, cradle and clamps. Imagine a 6 lb. car battery that plugs into the firewall.

    Until then, the jumpers are in the trunk. But I won’t let the jumpie overtax my charging system.
     
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  19. tcmtech

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    Nov 4, 2013
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    That's pretty much inline with my concept of making the portable unit work as a basic short duration high current charger that gets the main battery charged up high enough for it to start the engine.

    Putting 50+ amps charge rate into a heavily discharged battery for even 1 - 2 minutes is usually enough to get it back up to the point of being able to start the engine on a smaller vehicle. I've done it more times than I can count so I know how it works.

    However with a literally stone dead battery getting it to regenerate enough to even take a charge can take tens of minutes to hours to get anywhere if it even goes at all so even if the jump start get the engine running the vehicle charging systems and electronics are basicly being ran without a battery in place which is not good. :eek:
     
  20. pilko

    Senior Member

    Dec 8, 2008
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