Question: What happens if a 12V Battery Protection Package (aka. CTEK Battery Tender) stays plugged in the cigarette lighter outlet without being plugged in to a 120V outlet over a prolonged period? Will it drain the battery at a faster rate than without it?

Otherwords, what is the parasitic loss to the car's battery with the Battery Tender plugged into the car but not to a 120V outlet?

Is it smart enough to open its internal circuit in this case?

 

You have to figure that the car itself never disconnects from the battery - its doing things all the time. There is a parasitic draw from the car because of that. And, the car intermittently or periodically wakes up certain functions and draw a little more when that happens. This process is described in the service manual. I measured the parasitic draw and after the electronics settle down it is about 10ma.
https://www.corvetteforum.com/forums...e-battery.html

The point is, I doubt that the battery maintainer will draw anywhere near that while it is unplugged but still connected to the car. I have looked for info in the past on that but did not find it.

In post 16 below, I reported some measured results. It is very possible for a battery maintainer to draw current that approaches that of the parasitic draw of the car and thus contribute to rate of battery discharge. The Corvette branded maintainer did not draw measurable current when unplugged (less than 1 mA) but the Deltran maintainer did 5 mA (compared to 10 mA parasitic draw).

Having said that, I do not think it is a good idea to have it connected but unplugged regardless.

 

A circuit for a typical battery charger
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I looked at a couple battery charger circuits they are much the same layout, give or take extra features.
The attached circuit is an example of basic schematic example of a "linear" as opposed to "switch-mode." This means the circuits takes
AC through a transformer to step it down to something like 28 VAC before moving to the rectify & regulate section.
In this application, It does not matter which circuit type is used.
________________________________________ ________________________________________ ________________________

In the top-right corner note the circle at the end of a "wire." This is the ~~ +12 VDC output terminal. The -12 VDC connection is chassis ground.
At first look, +12 VDC terminal is connected to components that will isolate it when no AC is turned on.

However, just to the left of +12 VDC is a connection to Resistor R5, then to VR1 (variable resistor for voltage adjustment) and finally to R6.
This is a part of the circuit that will drain a small level of amperage to ground: draining the battery very slowly.
Of course, our on-board computer circuits will only operate above a certain minimum voltage (around 10 VDC) and is wise to use a battery charger when the car is stored

My conclusion: disconnect the DC leads and AC power when the charger is not in use.

 

Mine is connected all the time to the 12V always hot outlet in the frunk with no known ill effects.
I will add, I do drive the car often, as the weather improves.

 

I'm doing the same with my C8.

 

Thanks for the link, very good info.

Thanks, this is what I was looking for, R5 + VR1 + R6. between 12+ and the ground. I knew about the car's own parasitic loss and periodic wake ups.

As I suspected the parasitic loss is there, however it is low. Not enough to matter on a frequently driven car.

 

Well, one needs to know the resistor values of R5, VR1, and R6 to actually make the calculation. If that diagram is accurate and if we can ignore the backflow through the diodes, then
draw = (12/(R5+VR1+R6).

 

I thought current flow was unidirectional through functioning diodes? Isn't that their purpose?

 

Thats why I said assuming we can ignore backflow through the diodes. Even when the polarity is reversed on a diode, as it would appear to be if the charger is unplugged, there will be a very, very small current in the reverse direction. Small enough to ignore and treat it as "unidirectional" like you said.

 

I guess when you start throwing up schematics and other diagrams/flow charts, I (and others?) may occasionally misunderstand your point, or intent, based on the way you phrase the intricacies of the various parameters on display. I'm a "dumb it down for me, please" kind of forum member.
Sorry for questioning you on something that may be obvious or second nature to everyone else on here.
I'll try to avoid asking in future.

 

Yes, indeed. Was wondering if the 120V is not active the secondary side is completely disconnected or not. It appears that is not, so there is some current flowing through the 3 resistors.

 

When my 2023 C8 is Parked in My garage it is connected to a Deltran Battery Tender !! I started doing this back i 1987 with my first C4 and have had Batteries last 10 years !!

 

What? I meant no disrespect! I appreciate questions. I thought I was answering your question. Diodes can be thought of as unidirectional, like you said. I threw in my original comment about backflow not to confuse anyone but (honestly) in anticipation of someone that might point out that there is little bit of current flow in that direction through diodes. Since the context of the OP question was about current that might backflow through a battery charger that is unplugged, it may involve very small current flows, so that backflow is potentially relevant, but I don't know if it is. The schematic posted by the other person seems to show that there is a path to ground that does not involve a diode, so that is probably the path that allows the most drain. That chart just illustrates that when reversed, a very small current does flow through the diode, until the voltage exceeds the diode design limit, then the diode will fail and pass lots of current.

 

I have an inexpensive maintainer that I use for my generator. If unplugged the green LED remains lit and it draws a small amount of current. It will eventually drain the battery.

 

There is that too.

 

So, in response to the question about whether a battery charger that is connected to the car but unplugged from the wall will increase the draw and contribute to battery discharge, the answer is maybe, it depends on the charger. My advice is do not intentionally leave an unplugged charger connected to the car, regardless. I'm not sure why anyone would, other than a power failure.

To measure this I used an DC clampmeter with a mA range made to measure parasitic draws. It is sensitive to noise at those low current levels and the values fluctuate some. To work around that I used the "relative" mode of the clampmeter to zero out the baseline parasitic draw of the battery and affect of noise. When done that way, it still fluctuates around 1 mA or so with no current. I repeated my measurement sequence and got the same results so I have some confidence in the results.

I first measured the Corvette branded charger, and then a Deltran charger.

1. I put the clamp on the negative battery lead. I verified, subject to noise, that I can measure the basic parasitic draw of on the battery with no charger, and the car undisturbed over night. It is reading around the values I measured in the past - approximately 10 mA. I put the meter in relative mode so it reads around 0.

2. I connected the Corvette charger, plugged in. Initially it drives a higher current (a photo shows 668 mA but it may have briefly bounced higher) but it tapers down to a smaller value as it learns the current state of charge of the battery. It seemed to drop all the way back to near 0 ma (I read 153, 34, 24, and then 1 (which is in the noise) but that would not always be the case as it would depend on the state of charge of the battery. This all happens in a few seconds (5-10 or so). Then I unplugged it. Almost no change in the value. Disconnecting and connecting the charger to the car while it is unplugged from the wall showed essentially no change in the reading - near 0 with small noise fluctuations on the order of +/- 1 mA. Conclusion - this maintainer draws negligible current relative to the 10 mA parasitic draw of the car. I repeated this a few times.

3. But that is not the case for all chargers! I connected the Deltran 4.5 Amp battery tender next. But for this one, I measured the current in the positive lead of the charger rather than in the battery negative cable. I was able to split the charger cord into is positive and negative leads, so I could measure the current directly in/out of the tender. See photo of that. Like the other charger, it initially puts out a high current - this time I measured as high as 1150 mA. Like the other one, it tapered off. But did not get to 0. I measured 24 mA. I did not wait for it to taper further - it might drop further but that was not the purpose of this test. So, then unplugged it but left it connected to the car. This time I measured some discharge current - note the negative number in the image - of -5 mA. Ok, that number is NOT negligible compared to the 10 mA parasitic draw. The cigarette lighter style plug I used for this charger has an LED light it in that shows when it is connected to the car battery. Measuring the current in the charger cord between the frunk plug and the charger as I first did with this one would not include any current drawn by that LED. So, I rechecked the draw on this one with the clampmeter located on the negative battery cable - and got the same result - about -5 mA. So, the LED light draw must be pretty small.


Conclusion - this maintainer draws current that is on the order of the normal parasitic draw - and it would contribute to the drawdown of the battery charge.

Summary
Corvette brand charger - negligible draw when unplugged - less than 1 mA.
Deltran brand chareger - not negligible draw when unplugged - on the order of 5 mA.

Photo shows clampmeter on negative battery cable - 0'd out to read "relative current". There is a parasitic battery draw of about 10 mA that is zeroed out for the relative reading.



Photo show spike in charging current into the battery when the Corvette charger is first connected. 668 mA. May have gone higher.



Charging current tapers off to near 0 with the Corvette charger:



Now the charger is unplugged but left connected to the car:



And, it drops back to 0. So, apparently the draw is very very small - in the noise - compared with the 10 mA parasitic draw of the car. We're still reading relative, so the 10mA draw is zeroed out.



Now try the 4.5 amp Deltran charger.



The clampmeter for the Deltran draw is connected directly around the positive charger cord lead as shown:




The Deltran charger shows large initial current 1150 or higher - that drops quickly as it learns the state of charge of the battery. It drops quickly, to 24 mA.
It might drop further, but I did not wait for that. Now, unplug the Deltran charger leaving it connected to the car. - not shown - I can't get those two images showing the 1150 and 24 mA to upload.


This is now showing a draw. It showing -5 mA - which is current out of the battery - a draw.