81–90 of 192 posts
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If the car has no signal, how is it unlocked?
They could give your phone a signed token indicating your rental times, and then let your phone directly connect to the car to hand it off. Presumably it is easier for a human with a phone to move to a location with service than moving a locked car, usually just out of the cave you're in.
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Looks like it. They got a tow to somewhere with reception but the car wouldn't start. That implies they did get into it, but were still stuck due to the dead battery. So presumably the door unlock system has it's own backup battery?
No, the power required to unlock the door (a small motor) is usually a lot less than the power required to ignite the fuel. You'll probably find that the radio and internal lights still worked too (though likely not for long).
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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.
> 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 t…
I got banned from using Zipcar last year. I lived in a condo building with an under ground parking lot in SF. A few times I rented a Zipcar and left it parked in the parking lot at my condo building. About 50% of the time, the car would not unlock. In all cases, I successfully contacted Zipcar who informed me the only thing they could do is tow the car (usually 24+ hours later). The parking lot had no cell service. O…
The bit about the cell phone discharge seems pretty unlikely. A charged car battery has at least 2MJ of stored energy. GSM in its highest-power mobile station state draws 800mW. Add maybe another 150mW for the GPS, call it 1W total. The battery should power such a phone for weeks. You should be able to smell-test this fact by considering that your mobile weighs nothing and runs all day whereas a car battery weighs 20…
A low current is usually allowed (200mW is the top end in my experience), but anything over will, over time, sulfinate the plates in the battery and cause it too loose charge and capacity rapidly.
Generally if you want to run a low current device on a lead acid battery, you should use a deep cycle battery with plates designed for it. Starter battery have large, flat plates to carry a lot of current for only a few seconds tops, then be charged up again.
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I also seem to recall that standard car batteries respond poorly and inefficiently to trickle-discharge, being designed mainly for providing a lot of amps over a short period. Providing long term off-grid power is what deep cycle marine batteries are for, and they are a separate product.
As far as I know standard car batteries are fine with this kind of trickle discharge. Where they fall short compared to deep cycle batteries is providing a more substantial current (think tens of amps) over a prolonged period of time.
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Your smell test is a bit misleading in that most car batteries have a drastically lower energy density than Lithium Ion cells. There’s still a lot more energy in the car battery, of course, but not by nearly as much as a naive comparison of the weights would suggest. If it had the energy density of your cell phone, the lead acid battery in your car would only weigh 5 or so kgs. Your cellphone will also last a lot les…
OK, here's another test. A common way to end up with a dead battery is to leave the lights on overnight. The lights on a car draw over 100W (standard halogen headlights and incandescent tail and marker lights). But you can leave your lights on for hours and still start the car. Therefore it stands to reason that the same battery could power a GSM radio for hundreds of hours.
Even lithium cells already don't; high currents causes them to warm up, reducing capacity. So a device that draws 1 Watt will last longer than one that draws 10 Watts from a small lithium cell.
Lead Acid responds even worse, especially starter batteries, less so on deep cycle, and it's capacity rapidly changes, without temperature influence. A 1 Watt device might only last a day while it's fine starting up an engine with 10 times the total power consumption
I guess mission failed then...
It is so easy to call something mission-critical. I am always tempted to ignore it when I hear it, because most of the time it is a red herring. Instead I use it as a launching off point for a conversation with clients about priorities for a given solution.
The reception underground is nil, so it took me quite a while fiddling with phone position, with my arm through the entrance gate, to be able to get out...
> Still, cars without reception become vulnerable in a few scenarios: when members lose or do not have their physical Zipcard with them, when they exceed their reservation time or want to extend their Zipcar reservation, or when the vehicle battery dies. That last scenario was the one my family and I found ourselves in, though we did not know it at the time. Can someone change the title to reflect that cell phone rec…
> But the problem with using services dependent on a network is that you are then dependent on the network.
This – for me – is the main problem with IoT devices, e.g., many privacy issues would go away if devices were designed to operate without needing to regularly “phone home” (excepting explicit, intentional data-mining by the manufacturer).