12V battery misconception

[GeordieAl]

Hi MG community.
Another question, I have an MG4 Trophy LR 73 plate, UK. The salesman told me charging my phone, and heating the steering wheel and seat were all powered through the 12V battery. I haven't seen any written evidence of this, so can anyone shine a light on this for me? I am skeptical myself, but curious enough to ask.

 

[Rolfe]

As far as I know, everything except the car's heater is powered through the 12V. In some ways it's a legacy from ICE cars, where that's inevitably the case, and EVs use the same technology to keep costs down.

 

[tommasov]

Yes that's right, all those appliances run on 12V except the HVAC, but the 12V battery is recharged by the HV one so it doesn't make much difference except on the efficiency side.

 

[GeordieAl]

Ok thanks guys, that's interesting. So would heating the seat and the steering wheel instead of using the HVAC be more efficient for range?

 

[Rolfe]

Yes, it's said that that is the case. Although personally (not having the heated seat or steering wheel anyway) I just run the car to be comfortable and charge when I have to. It's not like it's expensive.

 

[GeordieAl]

Thanks, again, just getting a handle on everything with the new car. I've a few long distance drives coming up so just planning ahead.

 

[Ian Key]

Thanks, again, just getting a handle on everything with the new car. I've a few long distance drives coming up so just planning ahead.

Unless you need maximum range don't worry about the heating. Using it for the full journey will only decrease the overall range by less than 10 miles.

 

[GeordieAl]

OK, that's interesting, when I put it on the range drops considerably, but I assume that's just a guesstimate, never actually put it to the test on a full drive, plus not cold enough yet I guess to experiment.

 

[Ekips]

Ok, that's interesting, when I put it on the range drops considerably, but I assume that's just a guestimate, never actually put it to the test on a full drive, plus not cold enough yet I guess, to experiment.

If you do lots of short journeys in the winter then heating will use a lot of power as its trying to reach the set temperature from cold and may not even get there depending on how short, so effectively the HVAC is on 100%
But on a long journey the HVAC will switch off once it reaches the set temperature and then come back on sporadicly to top it up. So over the journey its impact will be much less.

What the GOM is seeing is the HVAC on at 100% and guessing based on that, it will adjust its guess as it gets more info

 

[Rolfe]

OK, that's interesting, when I put it on the range drops considerably, but I assume that's just a guesstimate, never actually put it to the test on a full drive, plus not cold enough yet I guess to experiment.

It's just a nominal reduction of about 5% of the current range, irrespective of the temperature set or even if the heater is on at all. You can toggle the HVAC on and off at any set temperature and see it happen. It's probably a reasonable rule of thumb, but if you only have cooling on then the reduction won't be so great. It's just a rough guide.

As an aside, it's funny to see these anti-EV videos, and someone turns the HVAC on, and then screams "I've lost ten miles of range already!" It's just the car's guess that if you keep it on for the whole journey you'll lose that amount.

I honestly don't think it's worth worrying about. The difference isn't huge and it's not worth freezing or frying for that. (Putting on the A/C reduces the range of an ICE car too, but you don't see people hair-shirting about that.) If you're playing chicken with your charge level then a much more effective way to get some range back is to slow down.

 

[GeordieAl]

Thanks everyone, very sensible comments and all very much appreciated

 

[kenneth104]

A/C and seat heating are both high voltage, There is no steering wheel heating in China, so I don't know
I need seat ventilation.
XD

 

[Coulomb]

A/C and seat heating are both high voltage,

A/C is high voltage, yes; cabin heating also. But seat heating? I very much doubt it. It's a pain to turn on and especially off high voltage DC; you can't use a standard cheap thermostat. Plus you really don't want high voltage cables running around inside the cabin if you can help it.

 

[kenneth104]

A/C is high voltage, yes; cabin heating also. But seat heating? I very much doubt it. It's a pain to turn on and especially off high voltage DC; you can't use a standard cheap thermostat. Plus you really don't want high voltage cables running around inside the cabin if you can help it.

The F2 it's 5 amps

The fuse says "high voltage electric heater", but the PTC vehicle heating fuse has not been found yet. 5 amps is not enough for PTC vehicle heating.

 

[ReintjeWA]

This may be silly, but if you can run heated seats and steering wheel before the car says "ready" wouldn't that suggest it doesn't need the high voltage battery to operate?

 

[mg4mc]

The F2 it's 5 amps

The fuse says "high voltage electric heater", but the PTC vehicle heating fuse has not been found yet. 5 amps is not enough for PTC vehicle heating.



View attachment 31687

The PTC is high voltage so it will not have a fuse in the 12V fuse boxes. The one highlighted will be the PTC control system not the heater itself.

The seat heaters are 12V, you don't want 400V running through heater elements under your "seat"!

 

[kenneth104]

Yes, me too , I also don't want high-voltage electricity to run under the seat

As mentioned above As mentioned above, the car will not be powered on with high voltage before preparation, which is incorrect because once you get into the car, it will turn on DC/DC convert Indicating that the high-voltage power has been connected

I will run the test that fuse tomorrow

 

[Coulomb]

you can run heated seats and steering wheel before the car says "ready" wouldn't that suggest it doesn't need the high voltage battery to operate?

Ready mode is the most common, but not the only, time that the contactors are on, making high voltage available. For example, when charging or V2L discharging, contactors are on but the car is not ready. Mainly Ready mode is an enable to the motor controller. Without the ready signal, the motor controller must not allow traction.

The state that an MG4 is in after opening a door, seeing a weight on the driver's seat, but before the brake pedal is pressed seems to be another case where the contactors can be on, so as to run the HVAC system if it's turned on.

So unfortunately no, this doesn't prove that the deat and steering wheel heaters are 12V.

 

[T1 Terry]

Don't forget, the huge power draw on the 12V battery is the steering, the bit a steering wheel heater and seat heater would use I doubt would amount to much more than a rounding figure.
We would use the seat heaters in the Gen 2 Prius so we can drive on electric only (when we had the extened range battery in it) .... if the climate control is turned on, the ICE will run until it gets up to temperature, we had generally arrived at the local destination before that happened ....

T1 Terry

 

[siteguru]

I guarantee that the seat and steering wheel heating elements are 12V sourced ... 100% guarantee. There's absolutely no way in hell that 400Vdc wiring will be routed within the cabin space, especially not at touch points.

The PTC heater is a different matter as that is located behind the firewall, and a heating element of up to 7kW wouldn't be possible from a 12Vdc source as you'd need wiring to cope with 583A.