Electrical system explanation?
 

I'm in the waiting process for my new FEH, meantime I'm planning my upgraded audio system....I know it's not a popular topic around here but I've been addicted to having great audio in my cars for 15 years, not going to stop now :) Plus I turned my addition/hobby into a business years ago so my daily driver has to sound great to use as a demo...anyway I'm obviously accustomed to dealing with alternators and amperage capacity...they hybrid layout is new to me. The system will be very mild compared to what I'm used to, but none the less there will be at least and amp or two so can I get some cliff notes on how the electrical system is laid out? I've caught bits and pieces from reading posts over the last month or so...I know the truck starts off the hv battery, the radio, interior lights etc will run off the 12v battery after that, but what charges that 12v battery? Is there a small alternator on the ICE or is there a DC/DC converter off the HV system to charge the battery like I believe the civic has? Anyone know the output of the alternator or dc converter? Any other tips on adding 12v electronics to the truck? I know it can lower mpg so no need to let me know that :)


P.S. I'm happy to search and read old posts about it if there are any...my searches didn't show much though, if there are old posts how about a tip on what to search for :)

Re: Electrical system explanation?
 

I believe that the 12v battery is charged via the HV battery with a DC-DC step down convertor. I don't even think there is an alternator as the electric motor (one of them anyway) acts as a generator to charge the HV battery.

Re: Electrical system explanation?
 

Have no fear... you can pull more than 100 amps off the 12v side of things, as long as you have the car "running" and able to recharge with the gasoline engine turning the "alternator". Actually, technically, this car has TWO alternators... one in the 94 kW range, and one in the 40kW range... but for some STRANGE reason, everyone calls them "generators". But they are AC with rectifiers to charge the big battery, and then the big battery can charge the little 12v battery any time the key is in run.

The 12v battery only powers your radio ( directly ) when the key is off or to ACC. In "run" the big battery powers everything.

Re: Electrical system explanation?
 

On this site--look for the thread Eclipse 5150? as this is a aftermarket radio/navigational/DVD player. John Morton has one in his Escape and has links to more photos of this. You can check Escape-Central.com as there are numerous threads on this subject and installation of Eclipse and Kenwood KNX7100 headunits.

I had a Kenwood KNX7100 headunit installed in my vehicle. I also replaced the stock door speakers and two tweeters in the sail panels. You have to remove the inner door panels to access the speakers. Since I had access to the inner door area, I decided to install dynamat extreme around the speaker locations and dynaliner around the rest of the door areas. I also dynalined the cargo door and cargo area. I also had a backup camera installed. It can be done. Report back on your results.

Re: Electrical system explanation?
 

This last sentence is misleading, maybe terribly so. All 12 volt devices will be powered by the 12 volt buss, itself primarily powered by the 12 volt battery with the DC-to-DC down converter serving only as backup when the battery is sub-standardly charged.

All things considered I doubt of the down converter supply capability will be much more than the expected FULL twelve volt load current plus a little to provide for a reasonable battery recharge rate.

If I wanted a terrific sound system outside of being parked inside my garage with the engine off and the winddows rolled up I would probably start with a good deal of sound insulation, undercoating within the wheel wells, nice and quiet and comfortably riding summer only tires and maybe an "anti-noise", noise canceling system under the driver's seat.

As an alternative a bit of digital signal processing might help. Pre-process all of the sound content so everything is above the average noise level of the interior of most vehicles traveling down the highway at cruising speed. That would generelly be above 70Db.

Re: Electrical system explanation?
 

Willard, I'm 100% sure about this, and I would like you to perhaps edit your post to delete the part that may confuse novice readers. Then I'll delete this to tidy up.

With 100% certainty, once the 12v battery closes the contacts on the HV battery, the HV battery, via DC/DC stepdown converter powers everything. I'm 100% sure about this, it has been tested and proven correct time and time again.

The proof is in the pudding, and electrons, like water, only flow downhill.
A 12v battery at rest under the hood has 12.5 to 13 volts.

AS SOON AS the HV battery contacts close, the DC/DC converter applies 14.4 volts to the "buss" as you put it.
Since this voltage potential is higher than the 12v battery potential, amperage may only flow into the battery, not out of it. And funny thing.... if you park with your headlamps on ( key in run ), the HV battery loses state of charge, and the 12v battery does not. The 12v battery can act like a capacitor to take out spikes in power demand, the inrush of current that happens like the instant you switch a load, like the fan on. Is the Prius substantially different in this regard?

Thanks.

Re: Electrical system explanation?
 

That would agree with both what I've seen and what I think it should do. I'm an electrical engineer so I have some experience. I've never worked with automotive systems but essentially all the mobile systems I have worked with use the battery simply as a capacitor when they are plugged in. They pull current from the other source. The handheld instrument I've designed for my company does the same. The converter powers the handheld.... the only time current would be pulled from the battery is if the converter voltage dropped below that of the battery. You use various mechanisms to prevent too much charge on the battery but I'm not sure thats much of a problem for a lead acid chemistry.

When the system is on you get about 14.4 V. With no load on the battery its probably higher than 12V, but less than 14.4V I'd have to check my scanguage but have no doubt of John's observation.

Re: Electrical system explanation?
 

As John says, I also believe the down converter provides the current to run the 12Vdc components. When the load exceeds the down converter capacity, the extra current is supplied from the 12V battery. This all works if the average load does not exceed the down converter capacity. If it does, the battery will eventually be discharged.

So, make sure your audio system does not present an average load greater than the down converter capacity (Amps).

....you could custom build a FET or tube amp to connect to the HV battery. That could really make some noise! (Only for you design engineers with too much time on your hands).

Re: Electrical system explanation?
 

Assuming the 12 volt battery is lead-acid, there MUST be a regulator controlling the output of the DC-DC down-convertor. There are systems that control the charging rate of the battery via sensing the battery's thermal level but I think not here. But even those must have a method of tapering the charging voltage down when/if the battery's thermal level begins to rise above a safe level.

If you were to apply a SOLID 14.4 volt source to a lead-acid battery with only a 10% charge you would soon have boiling electrolyte and shortly thereafter a very high probability of an explosion.

In short, the lead-acid battery's charge level will ALWAYS dictate the 12 volt buss' actual voltage level.

Re: Electrical system explanation?
 

I expect it is regulated, just like an alternator!