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Discussion Starter #1
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.
 

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Armin,

I do not see the DC to DC converter as being on any time the engine is running. I have a voltage gage on the 12v side and only see the 13.9 to 14.1 volt values only about 30-40% of the time. I have a number of 12 volt items running as my stereo, cd changer, equalizer, and amplifier are on if I am in the car. I also have a 1600 watt inverter for AC power but it is not loaded that often. (I am guessing at the 30-40% time but I am certain it is not on anytime the engine is running). I suspect that the DC to DC converter provides power (to recharge 12 volt battery) when the 12volt system drops below 11.x volts. The voltage meter will go from 13.9 to 12.5 almost imediately and then slowly drop until it gets in the high 11.x range. Once the low voltage is trigered it goes back to 13.9.
I am sure my 12v battery is getting enough of a charge since it works fine (2000 model insight) and is approaching 3 yrs. I guess I could be an exception as I do experience battery recalibrations and perhaps these are related as was recently posted. I did not have the ECM recall performed. I figured why mess with perfection, I like the mileage I get and have no gripes about performance. I may try driving with the lights on when the recalibrations increase with temperature. Have fun, RIck
 

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Discussion Starter #3
Rick Reece said:
I do not see the DC to DC converter as being on any time the engine is running. I have a voltage gage on the 12v side and only see the 13.9 to 14.1 volt values only about 30-40% of the time.
Hm. It doesn't seem logical that there would be a difference from car to car. I have seen the behavior you describe when I'm in idle-stop. The DC-DC runs with 13.9V out until the current drops to some small value (approx. 0.5A on the 144V side). Then the 12V battery voltage drops until the DC-DC comes on again. Repeat.

Maybe, there is something in my car using more 12V power? I have no idea how much variation there is in ignition systems, fuel pumps, etc...
 

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Still trying...

As some of you will know, I have been on a quest to get the Japanese TV & Sat Nav working on my Insight. I have all but given up on the Sat Nav but I have just found a UK website that sells the Tuner & PAL to NTSC convertor that I need to get the TV working. Example product:

http://www.threedoubleyou.com/car-tuner.htm

I have spoken to them and the package will cost me £210 ($330) but I think it is worthwhile to have TV in the dashboard. No, I won't be watching while I am driving!! :D

The company salesperson advised that the tuner and convertor run off 12V DC and 15V DC. However he is recommending also buying an inverter to change up the voltage to 240V AC because the inverter has a surge protector. I understand from this forum that the accessories voltage is normally 13.9V DC but are voltage surges ever experienced? I feel that a inverter would be unnecessary. Grateful for advice.
 

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On its own a battery can not create voltage surges as the output voltage is deternined by battery chemistry and the state of charge. The switching power supply that charges the battery from 144 volts DC has a tightly regulated output by design. The voltage should only vary between the limiting voltages designed into the system. A good 12 volt battery would itself act as an effective surge protector even if this wasn't the case. Furthermore well designed equipment can withstand signifigant over voltage situations by design. (I designed switch mode supplies for communication systems for 7 years.) Nevertheless, if you decide to protect the unit I suggest you do it at the DC level. A series fuse and a beefy zener diode or some other parallel regulator circuit across the power input of you apparatus would suffice and would not waste any power.
 
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