I originally wrote this as a private response to a thread I started here.
But I figured it might be benificial for alll of us. So here it goes:
Here are some basics on how DC-DC converters function: The explanation on insightcentral.net is simlified to a degree of being misleading (no offense). You don't need a linear transformer to convert voltages. There are other ways to do that. The DC-DC employed in the Insight is most likely a conventional Switched Mode Power Supply (SMPS).
SMPS's are commonly found in lots of electronic equipment these days, for example, your computer is powered by one. An SMPS basically takes the input AC and rectifies it first. Of course, in the Insight we can skip this step (it's already DC!). Then, a high-frequency oscillator and drives a power switch that chops this DC and feeds the primary of a small transformer. On the secondary side, a synchronus rectification system recovers DC, passes it through a filter and on to the load. Voltage regulation is achieved by driving the primary swich (adjusting its opening v. closing times) based on the secondary output voltage. That way a very well regulated output can be maintained regardless of input voltage or load current. This system is usually very efficient 80%-95%, compared to linear transformers and regulators usually below 50%.
In the Insight, the DC-DC is always active, except (as you expected) when 12V load current is very small and it would be inefficient to operate the DC-DC. While the engine is running, the ignition system alone consumes more current than this limit, so DC-DC is always on and the 12V system is always at exactly 13.9V
Now to how the current flows:
There is only one system to charge the 12V battery: the DC-DC converter. It draws it's input from the 144V bus. There are three things connected to this bus: the IMA motor, the 144V battery and the DC-DC converter.
Power is managed such that at any time the engine is running, the IMA motor is made to recuperate exactly the amount of current required to feed the DC-DC converter. That way, the 144V battery is not supplying or receiving any current. Althogh it is still connected to the 144V bus, it's not contributing at all.
Of course, this is only the case if the battery management has determined that no charging is needed and the power management has found that no assist is requested. This is neat, since it allows battery and power management to be independent of the needs of the 12V system.
But then, as I mentioned, there are exceptions to this that, I think, may be of benefit to people with low SoC and/or recal problems. For some reasons, the 144V battery gets charged more aggressively when there is sufficient 12V load present. (I found it with the lights, but it might also work with other 12V loads). So driving with your lights on may help improve the charge on the 144V battery. That was the whole point of my original post.
But I figured it might be benificial for alll of us. So here it goes:
Here are some basics on how DC-DC converters function: The explanation on insightcentral.net is simlified to a degree of being misleading (no offense). You don't need a linear transformer to convert voltages. There are other ways to do that. The DC-DC employed in the Insight is most likely a conventional Switched Mode Power Supply (SMPS).
SMPS's are commonly found in lots of electronic equipment these days, for example, your computer is powered by one. An SMPS basically takes the input AC and rectifies it first. Of course, in the Insight we can skip this step (it's already DC!). Then, a high-frequency oscillator and drives a power switch that chops this DC and feeds the primary of a small transformer. On the secondary side, a synchronus rectification system recovers DC, passes it through a filter and on to the load. Voltage regulation is achieved by driving the primary swich (adjusting its opening v. closing times) based on the secondary output voltage. That way a very well regulated output can be maintained regardless of input voltage or load current. This system is usually very efficient 80%-95%, compared to linear transformers and regulators usually below 50%.
In the Insight, the DC-DC is always active, except (as you expected) when 12V load current is very small and it would be inefficient to operate the DC-DC. While the engine is running, the ignition system alone consumes more current than this limit, so DC-DC is always on and the 12V system is always at exactly 13.9V
Now to how the current flows:
There is only one system to charge the 12V battery: the DC-DC converter. It draws it's input from the 144V bus. There are three things connected to this bus: the IMA motor, the 144V battery and the DC-DC converter.
Power is managed such that at any time the engine is running, the IMA motor is made to recuperate exactly the amount of current required to feed the DC-DC converter. That way, the 144V battery is not supplying or receiving any current. Althogh it is still connected to the 144V bus, it's not contributing at all.
Of course, this is only the case if the battery management has determined that no charging is needed and the power management has found that no assist is requested. This is neat, since it allows battery and power management to be independent of the needs of the 12V system.
But then, as I mentioned, there are exceptions to this that, I think, may be of benefit to people with low SoC and/or recal problems. For some reasons, the 144V battery gets charged more aggressively when there is sufficient 12V load present. (I found it with the lights, but it might also work with other 12V loads). So driving with your lights on may help improve the charge on the 144V battery. That was the whole point of my original post.
