Why don't motor vehicle manufacturers include a circuit that prevents a starting battery from being completely discharged?

My pickup is old, and the key can be pulled from the ignition switch in most any position. My wife pulls the key out as soon as the engine stops, which sometimes leaves the switch in the aux position, and discharges the battery to zero overnight. She has done this twice, which considerably shortens the life of the battery.

It seems that it would be easy (for the manufacturer) to include a circuit which prevents the battery from being discharged below a certain voltage (maybe with a manual override.)

Is there a technical reason why they don't do this, or is it a cost issue, or have they not thought of it?

 

Good question. I don't have the answer, but I am working on just that function. It started out as a project to disallow my accessory battery from discharging in my boat. In the meantime, I accidently left a door in my van ajar, and the battery discharged down to 1V. That is an expensive mistake. I'll end up installing one of these in each of my vehicles before it's all said and done.

 

Not to be a smart-ass (which comes very easily to me), the manufacturers DO provide a method to prevent the battery being discharged when the key is removed. It's called the ignition lock. Repair it!

It seems to me that it just has to be cheaper and easier to put a new lock cylinder in than to design a new circuit to replace its function.

Please forgive me if I'm assuming too much, but, "Old pick-up truck" tells me, "Ford". All you have to do is put the proper key in the cylinder of any similar Ford and stick a tiny rod in the hole next to the key. The cylinder comes right out. (Easiest way to hot-wire a pick-up ever invented.)

Designing something to disconnect the battery involves something that will connect the battery. If you include the starter motor, you will be using a relay that can handle over 400 amps. You immediately decide to control only the loads that are NOT the starter. I have drawn a basic circuit that might work if you can find a P-MOS that will handle all the loads except the starter. If not, you're going to end up with a relay or design something to use an N-MOS.

Here's an idea:

 

I've had two company cars, a Peugot Express and a Fiat Scudo. It's basically the same car, coming out of the same factory in two different doors. Both had a very irritating feature: While listening to the radio with the engine off, it shut down after appx 45 minutes. Another irritating feature was the "auto-lock" all doors after speed is faster than 10km/h. It's supposed to be a safety feature, when you stop at a red light,doors are locked, and you can't get mugged.

But hey, I'm in Norway...

 

"auto-lock" all doors after speed is faster than 10km/h. It's supposed to be a safety feature, when you stop at a red light,doors are locked, and you can't get mugged.

Don't worry. The muggers can break the window to rob you

 

Don't worry. The muggers can break the window to rob you

I know. Tell that to Peaugot and Fiat. I almost went crazy! Now I have a Volkswagon Caddy.

 

Not to be a smart-ass (which comes very easily to me), the manufacturers DO provide a method to prevent the battery being discharged when the key is removed. It's called the ignition lock. Repair it!

It seems to me that it just has to be cheaper and easier to put a new lock cylinder in than to design a new circuit to replace its function.

Please forgive me if I'm assuming too much, but, "Old pick-up truck" tells me, "Ford". All you have to do is put the proper key in the cylinder of any similar Ford and stick a tiny rod in the hole next to the key. The cylinder comes right out. (Easiest way to hot-wire a pick-up ever invented.)

Yeah, I tend that way myself, but I am trying to do better. Sometimes I just say the sarcastic comment in my head, but sometimes it echoes around until it comes out my mouth.

I guess I will fix it, but I don't have any trouble with it...just my wife. That is, my wife has trouble...you know what I mean.

No, it's not a Ford; it's a 2000 S-10 4WD that I bought new, and it holds a special place in my little black heart. How hard is it to change the part that needs changing, and will I have to change the door locks to match, or else have two different keys?

 

I'd just have 2 keys. And it doesn't need saying, but, you can't fix a wife.
I have had very good experience (prices) hiring locksmiths to match locks or scramble the information, then hand me 2 or 3 matched locks that are NOT the same key they used last week. See about buying a new ignition lock and having it matched to the old keys.

I don't know what a 2000 S-10 is so I can't tell you how to get the cylinder out.

 

Not to be a smart-ass (which comes very easily to me), the manufacturers DO provide a method to prevent the battery being discharged when the key is removed. It's called the ignition lock. Repair it!

Doensn't help my situation. I suppose you're going to tell me to close the door now My thing is, I have vehicles that see very intermittent use. I only drive my van a couple times a year (It's my day coach) I want to monitor the battery during all the time it's setting. I am actually working on a uC project with LCD readouts of various parameters. It's slow because I'm still getting spun up on PIC programming.

Designing something to disconnect the battery involves something that will connect the battery. If you include the starter motor, you will be using a relay that can handle over 400 amps. You immediately decide to control only the loads that are NOT the starter.

The trick will be breaking the circuit that runs all the BS but leaving the starter circuit intact. Shouldn't be too hard to do. The starter relay usually has a direct connection to the battery apart from the rest of the car's system.

Have I hijacked this thread by talking about my proejct? I am assuming the rules are relaxed in the 'off topic' section, but I may be wrong.

 

@Brownout,
Let me rid you of your anxiety by pushing this further off-topic.

I've had two company cars, a Peugot Express and a Fiat Scudo. It's basically the same car, coming out of the same factory in two different doors. Both had a very irritating feature: While listening to the radio with the engine off, it shut down after appx 45 minutes. Another irritating feature was the "auto-lock" all doors after speed is faster than 10km/h. It's supposed to be a safety feature, when you stop at a red light,doors are locked, and you can't get mugged.

But hey, I'm in Norway...

I always lock the doors the moment my car starts.
In the city, this protects me from anybody curious enough to check the contents of my trunk or back seat. Never saw that happen, but it's a step of precaution that I don't mind taking.
In the highway, this merely gives one more chance to a passenger absent-minded enough to try to open the doors while the vehicle is running. I know that's silly but when I was younger my mind would often drift and end up wondering what would happen if I opened the door when the car was speeding.

 

Not to be a smart-ass (which comes very easily to me), the manufacturers DO provide a method to prevent the battery being discharged when the key is removed. It's called the ignition lock. Repair it!

No, it would be a circuit that monitors the battery voltage and opens a master relay to isolate the battery when it gets too low. Probably isn't done because a failure of that monitor circuit would cause the car to go stone dead while you are driving it....

 

Don't worry. The muggers can break the window to rob you

They don't have to break the window. They just point their gun at you and tell you to open the door. This is AMERICA where every bad guy has a gun.... it's just the citizens who are unarmed.

 

They don't have to break the window. They just point their gun at you and tell you to open the door. This is AMERICA where every bad guy has a gun.... it's just the citizens who are unarmed.

We're going there again?