Where does the headlight power come from?

wayne325 said:

You are right, in the case of the REX version cars the 12V battery will be driving the (small) starter motor - yet another reason the 12V battery is required - and it's not "doing nothing". The converter will not be able to source all the current needed by that motor. And the battery is needed also to reduce the voltage spikes when that motor is engaged and disengaged.

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Hi Wayne.

I'm led to beleive that the REx generator is also the starter motor, so it is to be expected that the REx actualy starts from the main battery. This is also more or less obviuous because BMW's tech info states that an i3/REx will maintain a relative 0.4% of the main battery as absolute minimum so as to be able to start the REx. Please do correct me if I'm wrong...

Regards, Steven

Stevei3 said:

wayne325 said:

You are right, in the case of the REX version cars the 12V battery will be driving the (small) starter motor - yet another reason the 12V battery is required - and it's not "doing nothing". The converter will not be able to source all the current needed by that motor. And the battery is needed also to reduce the voltage spikes when that motor is engaged and disengaged.

Click to expand...

Hi Wayne.

I'm led to beleive that the REx generator is also the starter motor, so it is to be expected that the REx actualy starts from the main battery. This is also more or less obviuous because BMW's tech info states that an i3/REx will maintain a relative 0.4% of the main battery as absolute minimum so as to be able to start the REx. Please do correct me if I'm wrong...

Regards, Steven

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While not 100% sure, but I think most hybrids work that way. Toyota and Lexus anyway I know have very small 12 volt batteries and also have 12 volt battery problems too.

The DC-DC converter serves the same function as an alternator in a normal car. I.e., it is feeding the 12 v. circuit only when the 12 v. battery's voltage is a bit low or the 12 v. load is high. Running the DC-DC converter continuously when the car is in the Ready state isn't the most efficient way to operate.


The i3 doesn`t work this way. The DC-DC is working continuously, delivering all the 12V power simulaneously as needed and leaving very little for the 12V battery.

I frequently drive a road with a very long, very even downhill grade. There I can go into neutral mode and simply let the car roll, it will maintain a speed of some 45 miles per hour for about 5 miles - more than 6 minutes with the motor switched off. What happens? I really expected some on an off operation in the display for momentary power. But it doesn´t behave like that at all. There is a permenent power flow of some 0.6 kWh/100km with some flicker between 0.5 to 0.9 kWh/100km, but mostly around 0.6.
This is clearly the power flow from the 360V to the DC-DC, which transforms down to 12V.
If the system were working as you suspected - DC-DC operating on-off and handing over to the 12V battery in between - this would appear during such a long downhill drive in neutral mode. Nothing of the kind, permanent and rather even power flow. I was really surprised about that when I first tried it out because just like you I expected on-off behaviour with the 12V only recharged when the voltage has dropped.

There is some very odd behaviour in this.
I wrote that there is a power flow of 0.6 kWh/100km ( which amounts to some 430W ) when driving without light, heating or anything else. But: if I have previously been in regen mode this will go down from 0.6 to only 0.1 kWh/100km, again with some flicker between 0.0 to 0.2 kWh/100km.
If I have been on the accelerator last thing bevor switching into neutral power flow will remain at 0.6 all the 6 minutes downhill. If last thing the car was in regen it will stay at 0.1 all the way down. You can switch between the 2 modes any time, going into regen or accelerating for a second is enough.
Any explanations for this? The car in neutral with the motor switched off seems to need much more power in one mode compared to the other.

If going downhill with 0.1 kWh/100km I Switch on both seat heatings the power flow goes up to 0.4 kWh/100km.

Frank

Stevei3 said:

Hi Wayne.

I'm led to beleive that the REx generator is also the starter motor, so it is to be expected that the REx actualy starts from the main battery. This is also more or less obviuous because BMW's tech info states that an i3/REx will maintain a relative 0.4% of the main battery as absolute minimum so as to be able to start the REx. Please do correct me if I'm wrong...

Regards, Steven

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Steven,

Seems very unlikely the starter is on the HV system. It means more HV wiring to kill unsuspecting amateurs (and professional mechanics who've never before in their careers dealt with such dangerous electrical systems) poking around in there, and a custom built motor. Holding back energy in the HV battery does not imply the Rex starter is on that supply directly - the 12V system gets its energy from the HV system, so holding back energy in the HV battery indirectly reserves power for the starter even if it's on the 12V system. But I'm not sure.

Cheers,

W/

fdl1409 said:

The i3 doesn`t work this way. The DC-DC is working continuously, delivering all the 12V power simulaneously as needed and leaving very little for the 12V battery.

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That is surprising. You provide good evidence to support your theory. Conclusive proof would be provided by monitoring the voltage of the 12 v. circuit at the auxiliary power outlet/cigarette lighter. Not high on my priority list, though

alohart said:

fdl1409 said:

The i3 doesn`t work this way. The DC-DC is working continuously, delivering all the 12V power simulaneously as needed and leaving very little for the 12V battery.

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That is surprising. You provide good evidence to support your theory. Conclusive proof would be provided by monitoring the voltage of the 12 v. circuit at the auxiliary power outlet/cigarette lighter. Not high on my priority list, though

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I seriously doubt that the 12 volt is used to start the rex.The battery is so similar to my Prius plug-in and my hybrid Lexus 450H and they both use the traction battery. Both cars suffer from the small size of the 12 volt and have problems from the 12 volt loosing charge from parasitic draws just like the BMW i3.

wayne325 said:

Seems very unlikely the starter is on the HV system.

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Hi Wayne,
in principle, you'd be right, but in this case (as perhaps in most hybrid cases) the generator *is* the starter motor. If you apply power to a generator, it becomes an electric motor and vice versa (consider how regen works when braking). The HV leads to/from the generator/starter and HV control systems are already in place anyway.
Regards, Steven

PS: edit: pardon my English, but with 'generator' I mean the bit that is hooked up to the engine that produces the actual electric power (called a 'dynamo' over here)...

If you don't hear a typical 12 v. starter motor when the REx motor starts, then it's likely that the generator is starting the engine in motor mode. As has been stated, this is the way all gasoline-electric hybrid engines are started, at least above a certain temperature. My hybrid also has a 12 v. starter motor that is used when temperatures drop below a certain level. So I wonder whether the REx motor also has a 12 v. starter that would be used under certain conditions.

To finalize the last few posts about the REx engine "starter", Steve is correct. The REx engine is started by the Range Extender Electrical Machine, which is also what generates power while the REx is running. This is a high voltage component. The beauty of electromagnets...

alohart said:

If you don't hear a typical 12 v. starter motor when the REx motor starts, then it's likely that the generator is starting the engine in motor mode. As has been stated, this is the way all gasoline-electric hybrid engines are started, at least above a certain temperature. My hybrid also has a 12 v. starter motor that is used when temperatures drop below a certain level. So I wonder whether the REx motor also has a 12 v. starter that would be used under certain conditions.

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I seriously doubt that there is a 12 volt starter for colder temperatures as the 12 volts battery is way to small for that duty.

To answer the questions about how the REx motor is started, quoting the i3 technicians manual:
"At a low state of charge of the high-voltage battery the W20 engine is started using the range extender electrical machine. In this case the range extender electrical machine works in engine mode. The electrical energy for starting the W20 engine comes from the high-voltage battery. As soon as the W20 has been started, the range extender electrical machine changes from engine to alternator mode and generates electrical energy which is used for the electric motor of the vehicle via the (main) electrical machine."

One very big function of a 12v battery in most any car, including the i3, is that it acts like a big filter for noise. As already noted, it also can provide a surge of power, should the 12v needs exceed the output of the DC-DC converter. IN this manner, the converter is working more like an alternator on a conventional car.

how many amps does the 12 volt dc-dc converter provide?

there are poeple using the leaf and or prius with the ice running to provide backup power on a power outage!
did anyone do this with the i3 ?

Look at the sizing of the fuses, it should give you a rough idea. I can tell you from my memory that each power outlet in the cabin is fed by a 20Amp fuse.
Converting 360DC to 12DC and than to 120AC will be inefficient, but you might be able to run a fridge off it.

gt1 said:

Look at the sizing of the fuses, it should give you a rough idea. I can tell you from my memory that each power outlet in the cabin is fed by a 20Amp fuse.
Converting 360DC to 12DC and than to 120AC will be inefficient, but you might be able to run a fridge off it.

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thats 240 watt 12 x 20 amps

not a lot! i need to know when i connect a converter to the 12 volt battery if the i3 can sustain its 12 volt charge.

in the chevy volt the dc-dc is like +175 ampps. that can run somethings
2100+ watts

i hope the I3 also got somthing around that but when i see the smaller 12 volt batter compared to that one in tthe volt i guessing not.

The battery in the Volt needs to be able to crank a fairly large ICE over...in comparison to the 2-cylinder, small displacement motor in the REx, the Volt needs a much bigger 12vdc battery to do that.

It is coming - higher voltage systems for cars. Every ounce that can be deleted has some advantages, and at some point, they'll get to that. With the higher voltage systems, the wires can be smaller. That did not happen with the i3. BMW (and others) have moved most of their electronics to being computer controlled, so your switches do not actually 'switch' power to much of anything...the switch triggers a microcircuit to send a message to the computer, and the computer then applies power, saving a lot of extra wiring. So, the weight saving in wiring to go to higher voltage components isn't as great as it would be if those switches still actually were switches of power, verses signals.

BMW could have configured the i3 to provide residential backup power, but they did not, and I do not think that it would be easy to achieve and maintain your warranty (and safety).

jadnashuanh said:

The battery in the Volt needs to be able to crank a fairly large ICE over...in comparison to the 2-cylinder, small displacement motor in the REx, the Volt needs a much bigger 12vdc battery to do that.

It is coming - higher voltage systems for cars. Every ounce that can be deleted has some advantages, and at some point, they'll get to that. With the higher voltage systems, the wires can be smaller. That did not happen with the i3. BMW (and others) have moved most of their electronics to being computer controlled, so your switches do not actually 'switch' power to much of anything...the switch triggers a microcircuit to send a message to the computer, and the computer then applies power, saving a lot of extra wiring. So, the weight saving in wiring to go to higher voltage components isn't as great as it would be if those switches still actually were switches of power, verses signals.

BMW could have configured the i3 to provide residential backup power, but they did not, and I do not think that it would be easy to achieve and maintain your warranty (and safety).

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uh? the 12volt is not used to crank the volt or i3 rex ice motor.

GI3L said:

thats 240 watt 12 x 20 amps

not a lot! i need to know when i connect a converter to the 12 volt battery if the i3 can sustain its 12 volt charge.

in the chevy volt the dc-dc is like +175 ampps. that can run somethings
2100+ watts

i hope the I3 also got somthing around that but when i see the smaller 12 volt batter compared to that one in tthe volt i guessing not.

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You can find pictures of the fuse box here: http://www.mybmwi3.com/forum/viewtopic.php?t=1271
There is one 50A fuse and several 30 and 40A. You can probably draw 100A from the car if you can mange to wire it up safely.

Ignition, and probably other things are run by the 12vdc systems, along with all of the computers and lighting circuits, HVAC, power steering, entertainment, etc. The generator (regen) acts as a motor to turn the engine, but there's lots of other things that need 12vdc in the car. You can't even immediately start charging the main batteries unless the 12vdc one is charged (there's an 'emergency' path to recharge that until the computers can run before the rest of the system can then start charging the main batteries). Given that the VOlt was not a ground-up design, I would be surprised if it did not require more 12vdc capability than the i3, and thus, a larger 12vdc battery (and maybe DC-DC converter).

FWIW, in Japan, at some time (not sure of when it starts (started), all electric cars must be able to act as a power source for the home (grid). It's not a bad idea, it's just that BMW has not incorporated it into any of their USA releases (yet). Not sure if the average person would be willing to support the increased base price and the home's electrical service must also be changed to make it safe, something BMW can't control, and thus, in the USA's litigious society, could come back to attack them.

BMW has made plans to utilize i3 battery packs as both grid buffers, and to offer them to homeowners (the former is happening, the later has been announced as a future product). For the homeowner, it would be similar to Tesla's Power Wall in function.

jadnashuanh said:

Ignition, and probably other things are run by the 12vdc systems, along with all of the computers and lighting circuits, HVAC, power steering, entertainment, etc. The generator (regen) acts as a motor to turn the engine, but there's lots of other things that need 12vdc in the car. You can't even immediately start charging the main batteries unless the 12vdc one is charged (there's an 'emergency' path to recharge that until the computers can run before the rest of the system can then start charging the main batteries). Given that the VOlt was not a ground-up design, I would be surprised if it did not require more 12vdc capability than the i3, and thus, a larger 12vdc battery (and maybe DC-DC converter).

FWIW, in Japan, at some time (not sure of when it starts (started), all electric cars must be able to act as a power source for the home (grid). It's not a bad idea, it's just that BMW has not incorporated it into any of their USA releases (yet). Not sure if the average person would be willing to support the increased base price and the home's electrical service must also be changed to make it safe, something BMW can't control, and thus, in the USA's litigious society, could come back to attack them.

BMW has made plans to utilize i3 battery packs as both grid buffers, and to offer them to homeowners (the former is happening, the later has been announced as a future product). For the homeowner, it would be similar to Tesla's Power Wall in function.

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the volt was build from the ground up as a range extended vehicle.

the 12 volt do not crank the generator just provide the power for the communication to have the generator started from the high voltage.

i geuss the i3 will have a little less dc-dc power and ofcourse the smaller gastank will mean you have to refill maybe in the middle of night if you want to run it as a backup when the power fails.
not the best situation

the leaf was also not designed to be a backup power
but just what they also can do with the i3 just ( when you have the fast dc charge pack ) take the dc and convert it outside the car to ac for you home.