When Does the 12-Volt Battery Charge?

that is not what was implied ... if you put the car in Parked (with the P button) and keep it in READY mode you are OK (engine will come on when driving/main battery's charge is low). Note this is not necessarily safe (and legal .. you can get a ticket for idling).

But as JimboPalmer says DO NOT EVER leave anything like a cooler (5 AMP) on in AUX mode !! you will kill the 12 V battery in very short time....

ALSO you mentioned you directly wired your cooler to the 12 V battery THAT is not wise at all. It will be on ! Unless you switch it off. This just asking for a disaster ... (like you stop turn off the car distracted and cooler left on and in a short time probably witihin an hour you kill (permanently damage) the 12 V battery)

 

Reasons for heating your plug is thermoelectric design of the cooler....that make a lot of resistance ...
Not the draw of current....only way to make this type of cooler work without heating plug is to hard wire for good solid connection

 

".... is thermoelectric design of the cooler" what ?? this is nonesense (forgive me) IT IS ONLY by the current and the plug design. the issue is not the cooler ... (pls stay away from things you do not have a clue)

 

I think you really don't have clue how thermoelectric cooler work and i will not start off topic....j
So i will stay out....

 

Not sure how much you remember of the basic theories of electricity Ohm's and Joule's law covers this issue (hope this is still taught in high-school)


I do know how termoelectric cooler works ... but the plug DOESN'T and neither it does care. As I said " IT IS ONLY by the current and the plug design." So yes it is better to use a permanent connection rather than the "cigarette" plug. Although in the 5 AMP range it should be fine

The plug (any connection and or wire) heats up because a current flowing thru it and it has some resistance. (P=I*I*R the power generated) In the plug those connecting surfaces are imperfect and thus have higher resistance so those points will heat up. If it cannot dissipate the power generated by the current, the things' temperature will rise until it reaches a balance (or melt down) ...

It doesn't matter what the load is !!! Therefore it has NOTHING to do with the 'thermoelectic cooler' either. Yes those things are very in-efficent and you would need to cool the "hot" surface somehow. But for the plug only the current matters ...

 

If using a permanent connection to the battery, I would install a fuse and a "solenoid" (as often done for head/fog lights to protect switch contacts) that would activate when in "Ready" so as to prevent accidental draining of the little 12v battery.

JeffD

 

I assume you meant a relay. Relays control switches. Solenoids, generally control other mechanical devices.

 

Or find a connection point which is ONLY on when car is in READY mode (good example the lighter socket ). It is done regularly for dash-cams forexample .... I would suggest to check the fuse on that line of course.

I already commented that directly connecting to the battery (even with a fuse) is not a sound idea.

 

If you anticipate maybe adding other things later that you would also want powered only in READY, it can be handy to make an aux-power distribution thingy, once, and be able to connect more stuff later just by adding appropriately-rated fuses. I based mine on a VCM-06 module, which is handy because you don't need to tap any particular circuit, it detects the voltage rise when the car is in READY, and you can also set a time delay (from instant up to an hour or two) before it turns off when you turn the car off. That allows you to leave, for example, the TE cooler running while refueling, grabbing a quick bite to eat (not a five-course meal), but limiting how far it can drain the aux battery while the car is off.

The module will also shut off immediately, regardless of the time delay, if it sees the battery voltage drop past a lower limit. And it has a 15 amp output capacity with overload and short protection, so in some simple cases you might not need a discrete relay or fuse in your design.

-Chap

 

Can you provide a reference for this comment? I believe the 12 volt battery only charges with ICE running with alternator

 

There is no alternator on Prius...


Posted via the PriusChat mobile app.

 

Why is a 12 volt battery needed in a Toyota Hybrid?
Once the high voltage battery system is turned on a high voltage to 12 volt converter turns on that produces about 14 volts. At this voltage the sealed 12 volt battery charges and will not over charge but it is a slower charge rate than you might be used to.

Now provide a reference that the Prius has an alternator

 

in the lift back, it only charges when in ready. you should be able to measure the voltage difference at the battery or jump point, with the car off vs ready. with the engine on vs off.

i cannot provide a reference, but it has been mentioned many times here on priuschat. i suppose that doesn't prove anything though.

 

The little 12v battery charges in "ready" mode as Bisco indicated.

JeffD

 

Not only is there no alternator, the 12V system jumps to 13.5-14.2V volts immediately upon 'Ready', even when the ICE has not yet fired up. And when the ICE is locked off by EV mode. And when the ICE has gone into auto-shutoff. To verify this, add a voltmeter or engine monitor (e.g. ScanGauge or many others).

The Prius propulsion system has the same number of motors / generators as a traditional non-hybrid. Think of MG1 and MG2 replacing the traditional electric starter and alternator. But MG1-2 do so much more too.