Hacker News Reader

Comment by baroffoos | Hacker News Reader

If the battery is flat on the car then you are still pretty much out of luck even if you can get in. The only advantage to being able to open it is to use it as shelter in a emergency situation

View on HN

That depends on the vehicle. If it's an ICE with a manual transmission, and you can get it moving fast enough, you can pop the clutch to start it. Back in the day, with a ~dead battery, I'd park on a hill. Even without a hill, 2-3 people can generally just push.

And what percentage are manual transmission vehicles these days? Probably less than 1

90% of southern Europe?

Why just southern Europe? Here in West Europe there is still a vast majority of manual transmission.

True. But some of us still like them.

I'm not hard core enough to have a pre-computer vehicle, though.

Some models it’s much higher, but overall definitely single digits in the U.S.

Europe has a much higher take rate on manuals.

>>90% in Germany

> That depends on the vehicle. If it's an ICE with a manual transmission, and you can get it moving fast enough, you can pop the clutch to start it.

This depends on just how dead it is on newer cars.

If it's able to run the electronics but just unable to crank enough to start, this can work. If it's dead enough that you can't unlock the doors it's probably also dead enough that the fuel pump, ECU, etc. aren't going to be able to do their thing.

Carbureted vehicles can be bump started from flat dead for the most part, but EFI and especially direct injected vehicles need some electricity to operate.

Good point. I should have noted that I've only done that with a 60s VW Bug. Just to see, I have turned off and restarted my ~10 year old Civic, going down a hill. But not with the battery disconnected. Maybe I'll try it. Not now, though.

Edit: And upon reflection, maybe not. Because I'd have to pay someone to reset the computer.

Edit: But wait a minute. If the vehicle is moving downhill, and you engage the clutch in first gear, the engine will be turning. And even if it's not firing, the alternator will also be turning. So you should have enough power for the computer, ignition and fuel pump. Or am I missing something?

Don’t do it with battery disconnected, it can cause the voltage to go too high and you may fry things. Back in the day only bulbs, nowadays who knows.

Thanks. I'm not going to try it.

It wouldn’t surprise me if newer cars require a higher battery charge to start, which means you would need to roll the car for longer, or (worse) don’t effectively charge the battery at all at lower speed because the partially booted system takes too much power, so that you need a higher speed to start charging the battery enough to power the ignition system.

Also, are there cars where you need the electronics to disengage the brakes?

Careful! Shutting off the ignition will lock the steering wheel on older cars.

That’s called powered steering.

It depends on the vehicle. Power steering can either be electric (EPS) or mechanical, with a compressor that's belt-driven off the engine. My Civic has rack-and-pinion steering with EPS. When the engine is off, it's still steerable, but there's no power assist. But you don't want to turn the ignition lock all the way off, because that does lock the steering wheel.

The alternator needs to get some decent RPM to generate enough power. You'd have to go downhill quite fast.

In first gear, so not that fast.

I don't remember ever having any problem starting my 92 Civic that way. It definitely had EFI and an ECU. I know I started it when the alternator was bad, as well as when the battery was dead. (not at the same time)

My Civic is mid 00s, but I'm pretty optimistic that I could manage it. Hopefully won't need to, though.

Interestingly enough, early automatic transmissions also allowed this, since they had a rear pump that could build up enough hydraulic pressure to power the rest of the transmission without the engine running first:

http://oldcarmanualproject.com/manuals/Buick/1953/Owners/ima...

This feature disappeared in the early 60s for cost reasons.

> If the battery is flat on the car then you are still pretty much out of luck even if you can get in.

With an EV yes, but not with an ICE. Just keep a jump box in your trunk.

These "jump boxes" are amazing! I used to keep big jumper cables and have AAA in case of a dead battery. Last time AAA came (after I waited hours...), they just pulled out a little "jump box" and instantly started my car. I found and bought a random one on Amazon (there are dozens -- https://www.amazon.com/s?k=car+jumpstart). It's very small, can also be used to charge a cell phone, as a flashlight, etc., and really works. Every ICE should have one of these in the trunk.

Note that the battery in a "jump box" is probably capable of discharging a dangerous amounts of energy at very high current. BigClive measured[1] over >500A when he tried to discharge one of these batteries, which didn't actually work. The internal Li plates probably separated, breaking the circuit before fully discharging. After starting to disassemble the battery and realizing the that the plates had separated he attached a voltmeter and measured a full 3.6V across the supposedly-discharged, partially disassembled battery (squeezing the battery with his hands, "This still is fully charged, but it's just puffed up... that's a bit scary." Later, after the Li plates start changing color (!) - probably metallic Li starting to rapidly oxidize - they spontaneously ignited (pyrophoric).

The benefits of having a spare "jump box" in the trunk are obvious, but it's important to remember that this means carrying a dangerous amount of energy in form that is a very serious fire risk if anything damaged the battery.

[1] https://www.youtube.com/watch?v=0tGK1nqXr28

And having shelter from the rain while you wait for someone to arrive can be a great advantage.

I'm sure there are many other fantastic reasons to want access to your vehicle when the battery is flat.

Yep, that's potentially a huge difference.

If you can't open the car, you probably can't pop the hood latch to get a jump-start, which makes the difference between a tow and a simple drive to a store. And "stuck alone at the trailhead with a dead battery" is nothing new to hikers, but being able to spend the night in the car if you have to makes it a lot more pleasant.

Last year, we push-started my dads car where battery was so bad it could not be charged or jump started from another car. Push start worked the first time (car from 2009).

Reply on news.ycombinator.com