[Will M]

This makes sense. The interface between the 12 volt and 144 volt system is one-way. The 144 volt system works like an alternator to charge the 12 volt system. When the 12 volt system has higher voltage, the link between the two is switched off. If the 12 volt system voltage goes low (like when you turn your lights on), then there is a demand on the 144-volt system to charge it.

Since the transformer that steps the 144 volt power down to the charging voltage for the 12 volt system has one fixed step-down ratio, that means that the control system would want the 144 volt system topped off in order to provide that power to the 12 volt system.

I would expect it to have a minor negative effect on gas mileage, but still quite small. It just depends if the 144-volt generator's drag on the engine affects the threshold for lean-burn mode, and that also involves how fast you are driving and whether you have a head-wind or tail-wind, if it's raining, etc.

 

[Will M]

Re: not quite

Sorry, Will, but I think you are a little off. The DC-DC converter that provides 12V power is not a transformer at all. And it does not have a fixed conversion ratio. (This wouldn't work, since the NiMH battery's voltage varies between 120V and 180V during driving!)

It's always good to learn. Thanks for the info, though it still seems a bit vague yet. (I've returned to edit this down quite a bit, since much of the discussion was more appropriately moved to personal messages...)

The DC-DC really provides very well regulated constant 13.9V output. Also, the charge current that I measured and talked about in my earlier email is the current going into the 144V battery. This should not be affected by current drains in the 12V system, since those are usually supplied by the IMA motor/generator while the engine is running.

You doubt the accuracy of the Encyclopedia on this list in reference to the details of how the system charges the 12 volt system. Until we can resolve who has the more accurate model, that ends most of the discussion.

Also, the effect is opposite what it would be, if it was just the current supplying the load. (it would be a discharge on the battery, or reduced charge current).

We are miscommunicating... All variables are managed by the control system and if it's priority is on maintaining a 13.9 volt charging current, then it will manage all the other variables in order to acquire that value.

No the only way to explain the symptom is that there must be a software feature that says "when there is x load on the 12V system, increase charging the 144V system." For whatever reason.

I'm only suggesting that the reason is to maintain the charging voltage at 13.9. If you have a better reason, let's hear it.