How to make a mobile jump-box?

I am a master auto technician, and I am seeking the opinion/advice of other master technicians who work in the field.
We've all come to know (and love, in my opinion) battery jump-boxes in
the last 10 years or so. The days of jumper-cables are pretty much over.
What would it take to make a jump-box part of an automobile?
Let me explain... a jump box can easily be connected to a battery, and even left there if desired. A basic parallel circuit. It would then take a charge from the alternator right along with the regular car battery. Trouble is, if something were left on such as an interior light, the jump-box would be drained right along with the car's battery. Not the result I am looking for.
What device might be created that would allow a jump-box to be wired into a vehicle were it would be charged during vehicle operation, but not drained when the vehicle was turned off?
Example: vehicle drives from point A to point B. The battery and the jump-box are charged along the way. Owner shuts the car off but accidentally leaves the dome-light on, thus killing the battery.
How might it be possible for the jump-box to receive the alternator's charge but not be drained by the forgotten dome-light?
Some sort of magnetic switch (a solenoid, perhaps) comes to my mind, but how that configuration might be alludes me.
It has occured to me that constant charging of a battery (jump-box) might not be a good thing, but I have also observed that a vehicle can charge a battery for dozens of hours without said battery exploding. I have also seen jump-boxes be left on a plug-in charger for weeks (even a month) with no apparent negative effect.
The final product I seek: An jump-box stored in perhaps the trunk or elsewhere that is kept charged by the alternator during vehicle operation, but would not be drained if a device were accidentally left on after the engine was shut off. Should the vehicle have a dead battery, just take that jump-box out of the trunk and get going.
Is it possible? It must be. It has to just be a matter of power here, switch there, relay here, jump-box there...
Calling on the best of the business, I know you're out there!
Matt
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Matt wrote:

I believe that you can buy a box that will cut off your battery before it drains, thus leaving enough juice for one attempt at starting before it goes dead flat. I think you pop the hood and press a button to reset it before starting or something like that.
The other option would be an extra full sized battery with one of those electronic isolators like RV's use, with a switch to cut over the auxiliary battery when the primary goes dead. Space and weight are the downsides of that setup.
nate
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"Electronic isolator" is what I am searching for. I can take care of space, weight, long wires, etc... anyone out there who might be able to elaborate? I think it should be possible to connect a jumper-box *that could be used on any vehicle*.
Think how the towing business could profit!
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Matt wrote:

They already make mobile jump-starters... and they do work on pretty much any vehicle; you can indeed start a 6V vehicle from a 12V battery if you a) know what you're doing and pay attention to polarity (the vast majority of 6V vehicles were positive ground) and b) make sure that *ALL* accessories are turned off until the 12V battery is removed.
nate
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Huh. I'd guess that increasing the redundancy of vehicles' starting power, and the self-reliance of drivers, would mean *less* business for them. Of course, in big cities that might be a good thing, weeding out the silly little "one minute's worth of problem at the end of half an hour's trip" calls and letting them work on the backlog of accident and serious failures.
One might envision a slightly evolved version of the now familiar and pretty cheap jump-start box that can trickle-charge off the car's circuit (suitably isolated) and sit in a well in the engine compartment -- sounds like what you're talking about. However, that's space and weight that a lot of people begrudge in the already tight engine compartment; and the environmental factors in there are not kind.
Several years ago there was a brand of car battery that had a small auxiliary built in. After a few minutes of coulda-shoulda-woulda regarding the headlight switch, you opened the hood, flipped a lever or something, and (unless the car was really balky or the system wasn't working properly) started off this reserve of power. I haven't seen those in a long time, though, and seem to recall them as having a premium price, which might have been the reason.

I see them in use quite often, and have them in every vehicle. The days of people willing to pull over and help a stranger may not be what they used to in some places, of course. For sure, jumper cables don't do you much good in situations where no one is likely to come by for some time (a suitably stored -- and reasonably charged! -- jump box might be your only friend there!) And people can be goosey about doing it wrong and frying some electronics. But a great many people, at least where I live, haven't gotten word that their days pretty much over...
Cheers, --Joe
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wrote:

Didn't the first wave of these have the Champion brand name? I haven't seen them in years either.

Really small jump boxes are becoming popular now. I bought one back when they were a bit newer and no reviews existed for such a product. Luckily it has been absolutely great. I see no reason to carry around the larger portable type units (almost the size of a car battery), let alone a roll around monstrosity, when these mini jump units work so well. I wouldn't bring it to start a diesel though...
Toyota MDT in MO
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I haven't taken one apart, but wouldn't be surprised to discover a row of lithium-ion laptop-computer batteries or at least the cells used therein. A lot of those batteries happen to have output of 14-ish V, and the economies of scale must be sizable.
--Joe
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wrote:

I'll be taking mine apart when it fails -- hopefully not for 10 years though.
Toyota MDT in MO
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19g2000hsx.googlegroups.com:

A diode?
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"A diode?"
Thank you, Tegger.
Yes, I agree that a one-way gate is the trick here...
But how to make it happen in a real-life situation?
Where exactly might that diode be positioned? That where I am asking for some help.
Matt
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Diode?
On the positive connection to the 'on board jump box' (OBJB). Then have a separate circuit for 'jump starting' the main battery with a relay jumping the "DIODE" controlled from inside the car whose power supply would run off the OBJB, providing a direct connection between the car battery and the OBJB. How many ASEs do you have?
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it is very simple, limos have been doing it for years. you use a solenoid to isolate the 2nd batt. and it charges and everything normally when key is on but is isolated when the key is off. also providing a built in boost when cranking. KB
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in

Thanks, that makes perfect sense. I haven't seen one because I rarely service limos. Great response, thanks again for helping me to solve this little puzzle.
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It is besides the point, but I have 9.
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A diode block that goes between the alternator and the two batteries. You can buy such a thing at an RV store... lots of RVs and vans are set up with dual-battery systems so the RV appliances run off a deep cycle battery that is charged by the alternator, but which cannot discharge the starting battery for the vehicle. Same thing. --scott
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Matt wrote:

Wow!!!!
They have had dual battery setups for 4x4's and RV's for many many Many years with various types of isolators available.
Tow trucks are also set up with front 'plug in' booster cables and have also been this way for years!
How can someone 'claim' to be a 'master auto tech' and not know this?
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's - Gone to the rust pile... Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id !15147590 (More Off Road album links at bottom of the view page)
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One battery, in your vehicle, and jumper cables.What more could you want? cuhulin
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Sorta the same thought I had...
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On Aug 14, 3:06 pm, snipped-for-privacy@webtv.net wrote:

Sometimes there is not another vehicle to jump off of. Another poster gave me a response that helped me think of the solution, so thanks.
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I used to drive a Deuce and a half truck (ammo truck) in Vietnam.It had two 12 volt batteries.I own a 1960's Mercedes Benz four cylinder diesel engine.It requires two 12 volt batteries. cuhulin
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