feedback on dual battery system design?

[snare]

It will run without a battery, of course it will run without the battery ground lug, which obviously doesn't do anything without a battery present. You really should do some thinking about how an engine works before spouting off.

agreed

 

[Rando]

for all the other comments... i don't know about every other rig out there - but i do know for sure that my JK will not start from a lithium jump pack alone - at least the one i test and a different brand that a friend tested. i'm almost certain it won't run if you start it then pull the battery - Jeeps are pretty notorious for lighting up the dash or acting very strange in general with even a somewhat low battery.

EDIT - i stand corrected on that second point - i just started it and pulled the negative off the battery afterwards to put this to bed. it did stay running. some LED lights flicker, but no crazy warning lights and the idle stayed smooth.

Thanks for trying that. It is a good thing to know going forward that if you did have a battery fail as a short, all you need is a jump to get home.

 

[dwh]

Those red manual marine battery switches come in either "make before break" or "break before make".

Normally, you'd want the make before break.

 

[scottL]

Anyway, I think OP plan will work fine, but daft. Unless starting batt is regularly killed (what shortens its lifespan greatly...) & needs frequent self jumping, Its carrying around an extra battery what does nothing... ever.
If determined to use this ”just in case” battery scenario, might as well save money, forget ACR & and use a dumb relay for its charging. Using jumpercable or override switch when self jump is needed.

 

[Umbrarian]

It will run without a battery, of course it will run without the battery ground lug, which obviously doesn't do anything without a battery present. You really should do some thinking about how an engine works before spouting off.

So, just to confirm, you have never actually tried to run "without the battery at all"? You just had a "ground lug broke off my battery cables" on a car WITH a good battery, still connected to everything else? And as a result of this incident, you are generalizing that ALL cars "would likely" run "without the battery at all"?

So who is the one spouting off?

eta

And for the record, I am not claiming all cars will not run with a failed battery. Of course some can. Many cars can run with a failed battery, they often need a jump to get going for instance. Many will die as soon as RPM drop. But to suggest a stock car is likely to run "without the battery at all" would be very rare. I was unable to do it with my CJ-7 this am, and it has very little current draw, and a high AMP Alternator and computerized regulator. Could not even push start it.

 

[Rando]

So, just to confirm, you have never actually tried to run "without the battery at all"? You just had a "ground lug broke off my battery cables" on a car WITH a good battery, still connected to everything else? And as a result of this incident, you are generalizing that ALL cars "would likely" run "without the battery at all"?

So who is the one spouting off?

eta

And for the record, I am not claiming all cars will not run with a failed battery. Of course some can. Many cars can run with a failed battery, they often need a jump to get going for instance. Many will die as soon as RPM drop. But to suggest a stock car is likely to run "without the battery at all" would be very rare. I was unable to do it with my CJ-7 this am, and it has very little current draw, and a high AMP Alternator and computerized regulator. Could not even push start it.

Yes I ran my car (4runner) without a battery. As a I said the negative terminal on the battery connector broke, so the battery was not connected - ie no battery. The OP tried it with his jeep and it ran just fine, another poster talked about doing it on his Toyota's and Fords without issue. So clearly this works on many vehicles. Would it work on all vehicles, I can't say, but from a engineering standpoint it should. A well regulated alternator should keep the alternator voltage relatively constant regardless of load. The loads to operate the vehicle have to be less than the alternator output as otherwise your battery would go flat while driving.

To rudely claim is impossible when clearly it is possible is spouting off without knowing what you are talking about.

 

[Umbrarian]

Yes I ran my car (4runner) without a battery. As a I said the negative terminal on the battery connector broke, so the battery was not connected - ie no battery.

The negative ground broke does not disconnect the battery from the rest of the system. That just affects things that are grounded through the frame. The battery is still working and putting out charge to everything else connected to it. How much works or does not work is dependent on how it is wired. Anyone who has offroaded much has seen this work.

You keep claiming "It will run without a battery, of course it will run without the battery ground lug, which obviously doesn't do anything without a battery present", but every example you cite has a battery installed.

Y The OP tried it with his jeep and it ran just fine, another poster talked about doing it on his Toyota's and Fords without issue..

No they both had batteries present. OP was at 10v, the Ford was a disconnected lead.

To rudely claim is impossible when clearly it is possible is spouting off without knowing what you are talking about.

Nothing, rude, and never said impossible. I see you have moved from "your car will run just fine without a battery at all" to "it is possible". On that we agree.

 

[Umbrarian]

LOL !!
My Toyotas will all run without a battery. (Of course starting is a different matter...)

If manual, you might be able to clutch start it. I have seen it a couple of times with older cars (a CJ-5 and a Datsun 240) that have few electrical requirements. As the overwhelming majority of cars are automatics, this option is not usually possible.

Newer vehicles also have a ECU that will not allow a start/run if the voltage is too low. My DuraMax is like this. Too low voltage the and the fuel rails cannot pressurize, even though there is plenty of juice to crank the starter or keep going.

So yeah, it is possible to start a vehicle without a battery, but the it is rare as lots of circumstances have to be just right.

 

[DaveInDenver]

Only if its magneto ignition or oldschool diesel. Without electricity, spark wont create.

Kind of a chicken-and-egg issue. Lots of vehicles will continue to run if you disconnect the battery but getting them started is a problem. I suppose that leads back to the jump pack, though.

 

[Rando]

The negative ground broke does not disconnect the battery from the rest of the system. That just affects things that are grounded through the frame. The battery is still working and putting out charge to everything else connected to it. How much works or does not work is dependent on how it is wired. Anyone who has offroaded much has seen this work.

Yeah without the negative terminal connected to the battery, the battery is very much disconnected from the system.

You keep claiming "It will run without a battery, of course it will run without the battery ground lug, which obviously doesn't do anything without a battery present", but every example you cite has a battery installed.



No they both had batteries present. OP was at 10v, the Ford was a disconnected lead.



Nothing, rude, and never said impossible. I see you have moved from "your car will run just fine without a battery at all" to "it is possible". On that we agree.

You may want to check your reading comprehension - he clearly stated " i just started it and pulled the negative off the battery afterwards to put this to bed." He disconnected the negative terminal from the battery and it continued to run with out any issues. Same experience I had and same experience Verskstad has had.

The discussion here is not about whether you can start it without a battery, it is whether it will continue to run without a battery and so far in most cases this is true. The point being if your battery failed as a short, you could disconnect your battery, start the car with a jump pack and drive home.

 

[Umbrarian]

Yeah without the negative terminal connected to the battery, the battery is very much disconnected from the system.

Uh, no, and again you are generalizing. Lots of stuff is grounded directly, and not through the frame. For example, my Jeep ECU will work, it will pressurize the fuel pump, send fuel to the rail, but not turn the starter as that is frame grounded. Radio and many other accessories work just fine.

You may want to check your reading comprehension - he clearly stated " i just started it and pulled the negative off the battery afterwards to put this to bed." He disconnected the negative terminal from the battery and it continued to run with out any issues. Same experience I had and same experience Verskstad has had.

OK let's check:

"i just started it and pulled the negative off the battery afterwards to put this to bed." No mention of removing both cables or even removing the battery from the car. Like I wrote, every example you cite has a battery installed.

The discussion here is not about whether you can start it without a battery, it is whether it will continue to run without a battery and so far in most cases this is true.

Your anecdotal stories are nice. But they in no way can be generalized to apply to most cars.

 

[Rando]

This is getting whacky- without the negative terminal of the battery connected, the battery is disconnected, you need a return path for current to flow. It makes no difference where things are grounded - without a return path to the battery, the battery is disconnected from the circuit.

 

[Umbrarian]

This is getting whacky- without the negative terminal of the battery connected, the battery is disconnected, you need a return path for current to flow. It makes no difference where things are grounded - without a return path to the battery, the battery is disconnected from the circuit.

Try this, disconnect negative cable from battery like you say. Then put a 12V test light on terminals of battery. Does it light up? So yeah, it DOES matter how things are grounded.

 

[Rando]

Which would show the battery produces 12V and tell you nothing about it being connected to the car. Take it one step further disconnect both leads from the battery remove it from the car, put it your garage and then put a test light on the terminals - and the test light will light up, telling you precisely nothing about its connection to the car. Instead, leave the battery in the car, disconnect the negative cable form the battery, and then use your test light from anything in the car (ground, alternator, really anything) to the positive terminal of the battery and it won't light up, coz the battery is not connected.

 

[Rando]

This has gotten truly asinine, my apologies to the OP for talking this so far off track.