OT Car Battery Replacement

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On 3/2/2016 8:31 PM, snipped-for-privacy@snyder.on.ca wrote:
<snip> > The same principal can be used to make the 9 volt battery safe too -

A 1N914 or 1N4001 diode is probably cheaper than a 1/2 watt resistor, but both wholesale for only a couple of cents so those commercial products could use either.
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On 3/3/2016 5:44 PM, sms wrote:

Shorting an output with a diode in series will take out the diode ("Hey, this memory saver I bought is a piece of crap!")
OTOH, a resistor will just get warm(er).
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On Thu, 03 Mar 2016 18:40:28 -0700, Don Y

And a light bulb will get bright (ish)
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On 3/3/2016 7:27 PM, snipped-for-privacy@snyder.on.ca wrote:

Safe -- as long as you use a ~12V lamp!
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On 3/3/2016 6:27 PM, snipped-for-privacy@snyder.on.ca wrote:

Remember, the internal resistance of a 9V alkaline battery is 1.5-2 ohms. The short-circuit current is about 3-3.25A because the voltage falls to about 5V when short-circuited. So you'd need a high-wattage resistor to protect against a short circuit, but only about a 5A diode.
But those cigarette lighter plug battery-keepers are not going to short out. Even a "dead" car battery is not a short to ground. The diode is only to stop the car battery from sending current into the 9V battery.
I suspect that they just use a diode. A 20 watt resistor would be expensive (and large), but even if they wanted to protect against a short circuit a 5A diode is just a few cents. If they really want to get fancy they could use a resettable polyfuse but that costs about 10x the cost of a diode.
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On 3/4/2016 2:11 AM, sms wrote:

And how much POWER will be dissipated in that diode?
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On Friday, March 4, 2016 at 4:11:10 AM UTC-5, sms wrote:

You don't need a high wattage resistor. You've completely neglected that the resistance of the resistor gets added to the circuit. The backup battery only has to supply a small current to the car when it's turned off, ~30 ma max for my car. You could put in a 100 ohm resistor.
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On 3/2/2016 8:32 PM, Don Y wrote:

I was going to check current drain on the battery for our car to get a feel for how long a 9V "transistor" battery would last. (The car battery is equipped with a shunt which I figured would be a convenient way to get at this measurement!)
But, simply turning the ignition to "accessory" (to provide power to the "cigarette" outlet) made it clear that a 9V battery wouldn't last long enough for me to raise the hood!
[First, I'd have to check the workshop manual to determine HOW power is gated to the cigarette lighter outlet; i.e., if there is a semiconductor switch between the lighter and the battery, then the car might not take kindly to trying to *inject* power through that connector!]
For our vehicle, ACC mode illuminates three graphic displays (LCD's), the instrument panel plus lots of little lights (probably all LED's) scattered around the dash and console. This would be in addition to the keyless entry electronics (that are powered regardless of ignition state) as well as any "memory keeping" circuitry throughout the vehicle (auto-power window memories, seats/mirrors, etc.), "HomeLink" remotes (for the garage door opener), cell phone (BlueTooth) interface, etc.
No idea if the concierge-service radio link (and/or "emergency 911") circuits are powered ("standby").
Of course, you'd have to plug the device into the lighter, exit the vehicle (which turns on the courtesy light) and close the door BEFORE disconnecting the battery cables and keep things in that state until AFTER you'd replaced the battery.
Note that "battery" is available at the OBD-II connector. But, no idea whether this is directly connected to "Battery" (which means supplying any power through this connector would power EVERYTHING that hangs off the battery) *or* if it was designed specifically to support just the ECU functions (and, as such, could be used as a "backup battery" source)
Note to self: when it comes time to change battery, drag out a lab supply to power the *entire* vehicle during that transition (don't rely on some little battery!)
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On Friday, March 4, 2016 at 5:47:56 PM UTC-5, Don Y wrote:

Are any of the small battery memory holders intended to be used with the car switched on to accessory? I can't imagine they are. In accessory position a lot of stuff is going to be powered up. I would think you could either connect them to a cig outlet that is always hot or hook them up directly to a jumper terminal, the cables, etc.
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On Wed, 02 Mar 2016 18:07:26 -0500, snipped-for-privacy@snyder.on.ca wrote:

And when the new 12V car battery is connected, that 9v battery better be removed really fast, or there's a good chance it will explode.
Sure, the voltage is only 3v more, but you're dumping hundreds of amps into that tiny battery.
When 9v batteries are used as backup power in devices such as your home clock radio, they are NOT wired directly into the power supply. They supply power to the clock chip and are isolated from the power suppply with special circuitry. If you post this to one of the electronics newsgroups, I imagine someone could give you an actual schematic.
But be my guest, and blow it up. It's only a one dollar battery and I'm sure no one will die when it blows, but you wont catch me doing it. Having hot battery acid all over the interior of my car is not something I want to clean up. And there is a slight chance it could get hot enoigh to start a fire, if it's touching flammables.
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On Wed, 02 Mar 2016 21:47:15 -0600, snipped-for-privacy@unlisted.moo wrote:

Nope. Iy has a diode in it. Lets power out, but not in

Nope. Nothing goes back into the battery

It's a simple diode "or gate" Either one or the other supplies power - whichever has the highest voltage. Any diode will do the job, but a schotky has a lot lower forward voltage drop.

I've done it. I know how. It is 100% safe if done properly

There is no "acid" in a 9 volt battery - that's why it is called an "alkaline dry cell"

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On Wed, 02 Mar 2016 23:15:41 -0500, snipped-for-privacy@snyder.on.ca wrote:

Like i said, be my guest and blow the 9v battery up. I'm sure you'll get a thrill out of it. You're right, there is no ACID in it. My bad choice of words, but there are chemicals that will make a big mess. Sure, you can add a diode and will likely prevent blowing up the 9v battery, but that diode will also lower the voltage, which may or may not keep the clock running.
Then again, this whole thread is stupid. How many minutes (or hours) will be spent wiring up the 9v battery with a diode and doing all of this, when it only takes a minute to reset the clock after the car battery is changed. The whole topic is pointless! Change the battery and reset the frikkin clock. DONE!
And on Sunday March 13, 2016 @ 2am, that clock will need to be reset anyhow, when we switch to daylight savings time. Change the battery on Sat March 12, or Sun March 13, and set the clock one hour ahead at that time.
If the OP dont know how to set his car clock, that info is easily avialable online. There's probably even a youtube video about it...
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On Thu, 03 Mar 2016 17:56:20 -0600, snipped-for-privacy@unlisted.moo wrote:

It's not the clock. It's the security code on the radio, and possibly the keyless entry too. It's not hard to rig up a memory saver that is perfectly safe. With something as simple as a light bulb to limit the current it is 100% safe. and 9 volts is almost double what is required to hold the memory..
That said, I just changed the battery on my truck and car last week with no memory saver - but the car, the newest of the 2, is 14 years old.
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On Thu, 03 Mar 2016 20:18:02 -0500, snipped-for-privacy@snyder.on.ca wrote in

Just curious about something. Would connecting a small 12V battery charger onto the vehicle battery _cables_ before they are disconnected from the battery work? Something like this
(Amazon.com product link shortened)57098480&sr=1-6&keywordsv+battery+charger
seems like it would be able to retain memory (although not as convenient as something plugged into the cigarette lighter receptacle).
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On Friday, March 4, 2016 at 8:41:39 AM UTC-5, CRNG wrote:

Probably would work. Only issue is how clean that power is. It's meant to be used with a car battery, so it might just be unfiltered full-wave output, IDK what is typically done.
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On Friday, March 4, 2016 at 12:16:28 PM UTC-5, trader_4 wrote:

By the time we figure this out he could have reset every code, driver setting, radio pre-set and ECU monitor 3 -4 times. :-0
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On 03/04/2016 11:32 AM, DerbyDad03 wrote:
[snip]

How about the "security" codes for the radio, ECU, etc... that you DON'T HAVE and they don't work without?
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On 3/5/2016 9:50 AM, Sam E wrote:

I don't think folks truly understand just how much data is "stored" in modern vehicles (granted, OP was referencing a 2010 unit).
Our vehicle has some 200 "customizations" -- PER DRIVER. And, this does NOT include: - AM/FM/SXM presets - "Favorites" (audio/GPS/phone) - Address Book (Name/Address/Phone/GPS coordinates/icon) - "paired" bluetooth devices (phones, etc) - speed dial - speech recognition "tweaks" - seat/mirror positions - GPS "avoid areas"
Many of these settings are time-consuming to make (do you even KNOW what your radio presets *were*? your GPS destinations?). And, virtually impossible to "remember" -- even if the name of the setting conjures up some *vague* recollection as to its intent!
Typing much text on a touchscreen is an exercise in frustration! And, I have no idea how you'd reload a radio preset for a station that can't be *tuned* locally! (i.e., do you then have to drive to that market just to tune in those station(s)?)
One thing sorely missing (at least in our vehicle) is the ability to download current settings to a thumb drive (ideally, in XML format so you can edit them off-line) -- as well as the ability to UPLOAD settings from said drive!
I made a set of cheat sheets (two, double-sided 8.5x11 laminated sheets that I keep in a seat back pocket) enumerating all of these settings -- along with their defaults and our "preferences". So, *some* of these can be restored with just a lot of patience...
[Early on, I learned that the smart way to address GPS destinations is to create *those* offline and upload them to the car. Anything created ON the car is stuck there! So, not to be used unless necessary!]
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On Saturday, March 5, 2016 at 12:21:14 PM UTC-5, Don Y wrote:

But how many of those get lost when power is interrupted, then restored?
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On Saturday, March 5, 2016 at 12:40:53 PM UTC-5, trader_4 wrote:

THAT *is* "a" _very_ GOOD (question) --- "I" am GLAD *you* _asked_ IT!
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