Well, GM does a lot of stupiider things - like producing an engine with the same fatal flaw for something like 12 years - and not just one, either (ignition switch, egr problem in plastic i ntake manifold (3.8 v6) and timing cover problem (3.1) - just for a few....... You can have your GMs. I've had my last one.
I like the sound of a well tuned engine talming through dual 3 inch pipes myself - - -
Salvage one out of just about any piece of electronic scrap you can find - or just use a resistor or a light bulb - - - as described earlier.
I've never had one take more than 3 days. And that was without having the drive cycle spec. We are allowed one monitor not set - and that is generally the evap code because the tank needs to be between 1/4 and 3/4 full, and the temperature needs to be right.
I say Honda, you come back with Chrysler. How come?
By the way, it's not a stupid feature, it was user error.
You can hear birds singing while you're driving?
In most cases I listen to talk radio, Tune In Radio or Pandora One. No commercials on Pondora and with Tune In I can pause the stream and then fast forward through the commercials.
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).
And a light bulb will get bright (ish)
Safe -- as long as you use a ~12V lamp!
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.
And how much POWER will be dissipated in that diode?
I think I jumped using portable pack once before removing battery for some reason. Just make sure dome lights off and disconnect hood light if It has one.
Greg
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.
Radio Shack isn't gone. They only closed some stores. How can one person be wrong about so many things?
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
seems like it would be able to retain memory (although not as convenient as something plugged into the cigarette lighter receptacle).
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.
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
The opposite problem exists, there. Most (inexpensive) things designed to charge (big!) batteries do so by simply ensuring they can develop a high enough open circuit voltage to "push" current into the targeted battery (i.e., more voltage than the nominal CHARGED voltage of the battery).
They typically have no "smarts" to tailor the charge current to the actual sensed state of the battery (i.e., limit the amount of current when the battery is low and taper/cut off the charge current when the battery reaches "full charge" (over charging a battery shortens the life of a battery).
Instead, they are usually simple "trickle chargers" -- a voltage source behind a current limiting resistor (sets maximum charge current). Often, that "limiting resistor" may be the windings of the transformer!
As big batteries have lots of "electrical inertia" (bogus term), this arrangement works out OK -- the battery dictates how the charger operates because it is so much more "massive" than the charger's capabilities. The charger just gets a little warm as it's struggling to coerce the battery to raise its float voltage.
Because the battery has so much say in the matter (very low impedance), the charger doesn't need to be filtered *or* regulated -- one or more diodes to insure the output of the charger is always "positive" (instead of "AC"). Instead of "pure" DC, you end up with half (or full)
-wave rectified AC:
/\ /\ HALF __/ \____/ \____
\ /\ /\ /\ /\ FULL \/ \/ \/ \/ \
(the lowest point in each waveform is "0" volts) Ideally:
__________________ DC
But, the peaks in each of the above waveforms are typically higher than the nominal 12V desired (14.4 charged?).
When you attach the charger to a battery, the battery smooths out those peaks -- makes them *pure* DC (because the battery has such a low impedance, it controls the circuit's behavior). Only over time will the "DC" seen at the battery slowly start to creep up -- as it accepts charge from the charger.
Eventually, the charger will try to push current into a FULLY CHARGED battery and the battery will resist (a function of the chemistry of the battery) -- dissipating that extra power as heat *in* the battery (gas formation in some chemistries).
Without the battery in place, there is nothing to hold the output of the charger at this nice "pure DC" level (dictated by the battery). And, if the load represented by the rest of the car is tiny (because you've deliberately turned everything off -- except for the "quiescent currents" of the memory circuits and any other circuits that remain powered when the car is "off" -- keyless entry, burglar alarm, etc.) COMPARED TO THE CAPABILITY OF THE CHARGER, then these peaks appear everywhere the "battery" signal is delivered throughout the car.
So, you now have to imagine what measures each of the little bits of electronics took to protect themselves from "high voltage" appearing on their inputs.
And, what measures the charger manufacturer SKIPPED to ensure its output always was "reasonable" -- given that it EXPECTS to be connected to a battery!
I can, for example, design a charger that puts out *30V* with "no load" but that has a high enough output impedance that attaching it to damn near ANY 12V battery immediately causes that voltage to appear as 12V (or, whatever the battery dictates). The charger will keep hoping to drive the battery up to its 30V (which is when the current would fall to *0*). But, I could rely on characteristics of the particular battery(ies) being charged to never let that happen!
Unless, of course, there is NO battery present -- in which case, you'll happily see 30V on the output of the charger!
I'd *guess* the charger you cited would work -- cuz the automotive electronics designers assume the folks servicing these things aren't rocket scientists and want to ensure there aren't nuisance problems (because someone disconnected a battery cable before disconnecting a *shop* charger).
OTOH, the folks making the charger (People's Cheap Battery Charger Factory #884A) only marginally care that their product appears to work IN THE APPLICATION FOR WHICH IT WAS DESIGNED. What recourse do you have if something goes poof in the night?
[I.e., try using it as a 12V "battery eliminator/substitute" and I'm sure you will be disappointed] [[By contrast, a 9V "transistor battery" is 9V -- no "peaks" to worry about]]
Might work, but some battery chargers will not continue to charge without being able to sense voltage from the battery - even after you get them "kickstarted" and voltage regulation on many cheap chargers into a basically open circuit is next to non-exixtant - so who knows how high the voltage might go.
There are battery minder/chargers that plug into the cig lighter that would likely do the job - with the 2 aforementioned caveats to keep in mind.
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!)
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.
Voltage could be all over the place..
Greg
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