Any reason not to hook up a battery tender to the 12 volt battery ?

[scottm]

One kind of HV battery loss you can't stop, is if the BMS detects that it's cold outside and does a battery warming cycle...
That will chew up percentages loss... overnight.

... and is why I leave my chargeport cable plugged in while parked at home in the winter.

 

[jerry33]

One mile per day loss if far less than I am experiencing with the same settings. I have seen 2 to 15 mile loss in one day.

That is my experience too. However, I've never been gone from the car for more than one day, so I don't have any experience with 15-20 days of power off. It's known that the car sleeps deeper the longer it's left alone, so perhaps they have changed the drain over multiple days. Power off unplugged may be different than power off plugged in as well.

 

[brkaus]

I think it would be interesting to plot the power put in by a battery tender over a week long idle period.

From that, one would know the base vampire load and could possibly calculate the additional loss from the DC-DC conversion (which wouldn't happen while connected to a 12v source with adequate output).

 

[scottm]

The c-tek seems to settle on 20 watts consumption from the wall while trickle charging the 12v in a steady state mode after a long while (overnight) of just sitting there... it's been a while since I looked at the kill-o-watt meter that I've got the c-tek plugged into

The c-tek itself gets warm.. so it's not 100% efficient... so the actual vampire is somewhat less than 20W on my car

 

[GJ79]

I think it means battery tender likes snake oil.

Personally I have the CTEK 3300 US (a 3.3a unit) but If I didn't have that I'd go for the 4.3 amp version Amazon.com: CTEK (56-864) MUS 4.3 12 Volt Fully Automatic 8 Step Battery Charger: Automotive

Is this CTEK Capable of Jump Starting a Tesla with a dead 12 Volt Battery ?

 

[scottm]

Is this CTEK Capable of Jump Starting a Tesla with a dead 12 Volt Battery ?

I would hazard a guess "yes"... since there's no actual cranking going on.. or anything like that.

CTEK has difference models... you need about 2 Amps just for keep alive, and you'd need more than that to operate all 12v systems... A 20A unit could supply 250Watts or so if that was what is needed for the to operate various things inside the car HVAC fans, screens, radios, etc...

The question is, but what then? If you need to actually drive and unplug the CTEK... you're not going anywhere quick.

Maybe the real question is... can I use "any old car battery in good condition" stuffed in my frunk with jumpers to the Tesla battery to keep the car rolling... to get somewhere in an emergency, or get to a shop where the battery can be replaced.

I would hazard a guess, yes... that would work.

 

[Snerruc]

There is a previous thread about chargers and floating a Tesla in storage. I believe ingineer said the charger needs to be capable of 4+ amps charging to run the electronics. He reccommended the CTEC. One owner floated his Tesla for several months main not plugged in with no loss of main charge. This keeps the 12v from cycling.

 

[CuriousG]

Is this CTEK Capable of Jump Starting a Tesla with a dead 12 Volt Battery ?

No. CTEK requires minimum 2V input before it outputs any power. I found it in their FAQ somewhere. Found this out when my other car was at 1.6V and I thought the CTEK was dead.

 

[brkaus]

No. CTEK requires minimum 2V input before it outputs any power. I found it in their FAQ somewhere. Found this out when my other car was at 1.6V and I thought the CTEK was dead.

Some of the CTEK models have a "supply" mode that bypasses the safety feature. The minimum voltage requirement is so that the polarity can be verified.

 

[apacheguy]

If connecting a battery tender for long term storage... Charge to 50% then pull the touchscreen fuse. With the gateway down there will be no thermal management and load will be very minimal.

 

[CuriousG]

Some of the CTEK models have a "supply" mode that bypasses the safety feature. The minimum voltage requirement is so that the polarity can be verified.

Then I can only speak for my CTEK 4.3 which did not charge. There is also a status light that lets you know when you're able to start your car. Don't know if that would apply to the Tesla.

 

[dhanson865]

Is this CTEK Capable of Jump Starting a Tesla with a dead 12 Volt Battery ?

For some values of dead. (math joke, mixed with a real answer). As in if the battery isn't damaged too much but the voltage is presently too low to start the car then yes plugging in a charger will start the car because you can just plug it in long enough (seconds or minutes) to get a surface charge and start the car while AC power from your wall source is still feeding the 12v system more than 13 volts.

also fwiw I now recommend using the Noco Genius 7.2 amp instead Amazon.com: NOCO Genius G7200 12V/24V 7.2A UltraSafe Smart Battery Charger: NOCO: Automotive because it plays nice with lithium ion batteries and I expect at some point down the road you may find that aftermarket 12v batteries switch over and maybe Tesla does also. If so might as well get one that can charge lithium ion 12v safely and save having to buy a new one later.

You could wimp out and grab the Amazon.com: NOCO Genius G3500 6V/12V 3.5A UltraSafe Smart Battery Charger: NOCO: Automotive 3.x amp version but I'd watch for the 7.2 amp to be on sale and grab it instead.

 

[dhanson865]

No. CTEK requires minimum 2V input before it outputs any power. I found it in their FAQ somewhere. Found this out when my other car was at 1.6V and I thought the CTEK was dead.

If there isn't a short or dead cell and it's just very low on charge you can unplug it from the car for a few mintues and the voltage will rise naturally with no load. The charging process would start then even on a charger that is looking for more than 2V.

Heck the deadest I've ever seen my 12v on the Prius was 9.x volt so you'd have to be awful hard on your battery and likely need to buy a new one if you couldn't get it above 2v.

 

[brkaus]

Then I can only speak for my CTEK 4.3 which did not charge. There is also a status light that lets you know when you're able to start your car. Don't know if that would apply to the Tesla.

This is the model I have - CTEK Multi US 7002

Not sure why they have so many similar models!

 

[CuriousG]

Heck the deadest I've ever seen my 12v on the Prius was 9.x volt so you'd have to be awful hard on your battery and likely need to buy a new one if you couldn't get it above 2v.

The car isn't driven and alarm wasn't even on. There must be some huge idle draw I'm not aware of. It didn't even recognize my keyfob and I didn't feel like reprogramming it.

 

[GJ79]

For some values of dead. (math joke, mixed with a real answer). As in if the battery isn't damaged too much but the voltage is presently too low to start the car then yes plugging in a charger will start the car because you can just plug it in long enough (seconds or minutes) to get a surface charge and start the car while AC power from your wall source is still feeding the 12v system more than 13 volts.

also fwiw I now recommend using the Noco Genius 7.2 amp instead Amazon.com: NOCO Genius G7200 12V/24V 7.2A UltraSafe Smart Battery Charger: NOCO: Automotive because it plays nice with lithium ion batteries and I expect at some point down the road you may find that aftermarket 12v batteries switch over and maybe Tesla does also. If so might as well get one that can charge lithium ion 12v safely and save having to buy a new one later.

You could wimp out and grab the Amazon.com: NOCO Genius G3500 6V/12V 3.5A UltraSafe Smart Battery Charger: NOCO: Automotive 3.x amp version but I'd watch for the 7.2 amp to be on sale and grab it instead.

Do these chargers keep the Battery "on Float" like the Ctech ? In the description they talk about a maintenance charge which keeps the battery fully charged which I believe is not what we want here.

 

[tga]

I have a 36A 12V bench supply - that would keep the vampire away!

 

[scottm]

Tesla car is consuming power all the time so these float chargers are not just keeping the battery floated ... they are supplying the power being drawn by the car. On older cars like mine, that draw is about 2Amp continuously. A float charger of anything less than that is not even keeping up with the car... the battery would still be declining and the occasionally still kick in the HV pack for a top up. Although, less frequently.

From the charger's perspective, it must appear to be a really large capacity 12v battery that has been connected to it, trying to juice up ...constantly "absorbing" a pretty stiff output and never being "happy". Or maybe it appears like the battery has really poor retention - like an internal short or high resistance cell.. In any case, the smart charger is constantly reading the battery and adjusting its charging behavior. So I'm trusting it doesn't bake the battery.

I haven't experimented with different types of 'smart chargers' or even a dumb charger... C-tek happens to be working well with out-of-the-box settings just plug and play. Non-smart chargers (where you set the Amperage and it's held constant) could be worrying - they have ample current to supply the car but might be roasting the 12v battery at the same time by putting out much more than what is actually needed in excess of car demand plus "some" to keep that battery floated.

 

[ig_epower]

Do these chargers keep the Battery "on Float" like the Ctech ? In the description they talk about a maintenance charge which keeps the battery fully charged which I believe is not what we want here.

I have a very similar unit and I will try to put that on my battery as well - good suggestion to try. Here is what I understood about these fancy new smart chargers - they can run special currents to condition the plates, check for the condition of the chemistry, even shock it into better health if needed. Then of course it also charges and when it is topped off, it regulates the output to a Float charge mode where it can keep the battery topped up indefinitely without harming the battery. I have studied this topic for my sports car that I keep in the garage in the winter. I have tried using older trickle chargers but they aren't very smart. Eventually, I ended up killing the battery because it Over-charged it and dried out the chemistry.

In a normal car, there is some current demands to keep the computer, clock, security etc running, but it is nowhere near what Tesla drains.

I will plug in my 6A smart charger to not only bypass the vampire drain by shunting away from the 12V battery but I want to know if my charger will have the capacity to run the maintenance cycles to condition my battery as well. The unit has status LEDs where I can see what modes it will be running so time will tell when I actually hook it up.

 

[scottm]

I will plug in my 6A smart charger to not only bypass the vampire drain by shunting away from the 12V battery but I want to know if my charger will have the capacity to run the maintenance cycles to condition my battery as well. The unit has status LEDs where I can see what modes it will be running so time will tell when I actually hook it up.

I think all these economically priced smart chargers have a goal of getting the battery to the top, and safely keeping it there. Its idea of "maintenance" is to properly manage the float at the top of battery capacity.

I'm not aware of a charger that periodically deep cycles a load to draw the battery down, just so it could be maintained again with another charge-up cycle. But it wouldn't surprise me if there's just that sort of thing out there for longer term storage of cells that are not seeing any load.

Just driving the Tesla will start causing natural deeper cycling all day long. As long as you're actually using the car, it will see its 12v use its whole range from top to bottom and back again. If you're not driving your Tesla, you could just unplug the trickle charger and the 12v will start deeper cycling on its own again, to exercise the chemistry or metal plates, or whatever.. But I don't even know if that is needed or appreciated by the battery they've installed for 12v.

I use the trickle charger to reduce frequency of contactor wear, reduce the number of charge cycles on the 12v to make it last longer, and to keep my main pack juiced to where I want it and set it while parked at home, at night. Or over the weekend when I'm not driving for a day or two. Yes, the c-tek draws constant current while doing this.. 'smoothing' load out over time, whereas without c-tek the same amount of juice would come through HPWC in a much shorter period of time as a sharper hit of the couple percent needed per day.