Honda Civic Hybrid electrical system

No, not here to discuss the merits of EVs or other competing products. I was just wondering about this specific platform's implementation of its electrical system. Discussion of EV's should be saved for the other thread that already exists for that purpose

I had a chance to peek under the hood of a Civic Hybrid yesterday, the one that's built on the 8th-gen Civic platform (and 2nd-gen hybrid technology according to them). One of the things I noticed is that it STILL has that antiquated 12V SLA starter battery under the hood. The first thought that struck me was "Why do they need THAT??! Doesn't the NiMH pack supply enough cranking amps?"

Which leads me to ask, at low speeds - isn't the takeoff powered by the IMA motor, which should not need a 12V battery? Well.. not when you have 144 NiMH cells powering it..

Then as the vehicle comes up to speed, the ICE should already be rotating and all it needs is a dose of fuel and air with a spark to start the combustion cycle. Of course, this is based on my understanding that the IMA is integrated as part of the main engine and spins up the main engine as well. Do correct me if I'm wrong.

So to begin with, if my interpretation is correct, the Hybrid doesn't even 'crank' the way a normal vehicle does?

And the other question - what is the purpose of the 12V SLA on this platform? I was hoping to get rid of that miserable piece of problems that fails every 12-18 months in my weather. Having a vehicle powered entirely off NiMH is a step in the right direction, IMO. Unless the 12V SLA is meant for powering the rest of the electrical systems (lighting, audio, electronics).

The conventional starter and battery provide a failsafe backup in case the IMA system fails, or has too little charge.

Hondas also operate IMA-only under much more limited conditions than Toyotas, because at 20hp it can only deliver less than one-third of the power output vs. the Prius.

The nimh system isn't 12v is it? You still need something to power the rest of electronics which use 12v.

Honestly I think it was the easiest thing / least expensive thing to do. Rather then get a more expensive high voltage to 12vdc converter to power the 12v electrical loads they just went with a traditional 12v battery. As mentioned it does offer redundancy and if you left your lights on you don't risk running the high voltage pack dead and potentially damaging them. The impression I have got from the Honda setup is that it was a "regular" car with extra parts, where the Prius was built different from the ground up. Most of the US big three also just take a "stock" car and add things to it leaving it intact as a gasser..

My experience is with the generation I and II Priuses. I can answer your questions according to the Toyota platform, which I suspect is similar to the Honda.

I had a chance to peek under the hood of a Civic Hybrid yesterday, ...... it STILL has that antiquated 12V SLA starter battery under the hood... "Why do they need THAT??! Doesn't the NiMH pack supply enough cranking amps?"

In the Prius the function of the 12 volt is to supply power to the stereo, lights, and computers that manage the car. It is quite small, no bigger than a motorcycle battery. This is because it never cranks the engine. What it does do is power up the computers that manage the NiMH traction battery, and they tell the big beefy traction battery to crank the gas engine when they need it.

Which leads me to ask, at low speeds - isn't the takeoff powered by the IMA motor, which should not need a 12V battery? Well.. not when you have 144 NiMH cells powering it..

I don't understand this question well enough to answer it. What are the takeoff and IMA?

Then as the vehicle comes up to speed, the ICE should already be rotating and all it needs is a dose of fuel and air with a spark to start the combustion cycle. Of course, this is based on my understanding that the IMA is integrated as part of the main engine and spins up the main engine as well. Do correct me if I'm wrong.

In the Prius all the different parts come together in something called a planetary gear system. Any component can put in or take out power, or sit idle if needs be. The ICE sits still when it is not called for.

So to begin with, if my interpretation is correct, the Hybrid doesn't even 'crank' the way a normal vehicle does?

Correct. The Prius doesn't even have a starter motor.

And the other question - what is the purpose of the 12V SLA on this platform?

It powers up the computers that run the car, handles the owners 12-volt needs, and stays out of the way while the big boys do the work.

I was hoping to get rid of that miserable piece of problems that fails every 12-18 months in my weather. Having a vehicle powered entirely off NiMH is a step in the right direction, IMO.

You could go with a preventative schedule, change your battery once a year whether it needs it or not. You could get the largest battery that will physically fit in the space. You could get two batteries and mount them in parallel. You could add an amp meter and a volt meter to the dash, take a look at them now and then. You could look at high end batteries, or some of the other chemistries that are available. They all cost more, but you get more. You could get one or two of theose solar trickle chargers and see if they help.

If you get the hybrid you might skip all this. When the 12-volt doesn't have to crank anything you don't need that much power out of it. If I have a dead 12-volt I can jump it with eight flashlight batteries.

The Tesla roadster:

http://www.teslamotors.com/display_data/TeslaRoadsterBatterySystem.pdf

the Tesla roadster uses 18650 lithium ion cells- a much better system than the nimh batteries used in the civic hybrid.

Firstly, thanks for the answers it provides a lot of insight into how this car works.

Ken_McE said:

It powers up the computers that run the car, handles the owners 12-volt needs, and stays out of the way while the big boys do the work.

You could go with a preventative schedule, change your battery once a year whether it needs it or not. You could get the largest battery that will physically fit in the space. You could get two batteries and mount them in parallel. You could add an amp meter and a volt meter to the dash, take a look at them now and then. You could look at high end batteries, or some of the other chemistries that are available. They all cost more, but you get more. You could get one or two of theose solar trickle chargers and see if they help.

If you get the hybrid you might skip all this. When the 12-volt doesn't have to crank anything you don't need that much power out of it. If I have a dead 12-volt I can jump it with eight flashlight batteries.

Click to expand...

Excellent - yours has really cleared up a lot of the confusion. So the 12V system is really to power the control electronics and other 12V gear. That explains why the Hybrid's 12V is much smaller than the normal ones we have, indeed it looks more like a motorcycle battery.

I am considering THIS particular hybrid somewhere down the road (and my choice is not open to debate, really, hence no interest in competing solutions).

Brock said:

The impression I have got from the Honda setup is that it was a "regular" car with extra parts, where the Prius was built different from the ground up. Most of the US big three also just take a "stock" car and add things to it leaving it intact as a gasser..

Click to expand...

That's exactly why I like it - because it is like the garden variety Civic with a little bit more but I suppose yes, we then live with the design tradeoffs which that approach entails.

I am hoping that their 3rd-generation uses A123 cells though.... I am beginning to really like the A123s (got four in a HID spotlight, with many more to come!)

The Prius has a 12 volt auxiliary battery too. People expect to be able to run 12 volt stuff off their cigarette lighter. Car stereos need 12 volts as does every other kind of vehicle electronics. So do the lights, the horn, the windshield wipers…

The aux battery on the Prius in NOT in the engine compartment, it is in the rear of the car, on the right side (which is nice for hooking up radio gear, no need to find a way through the firewall).

KevinL said:

I am considering THIS particular hybrid somewhere down the road (and my choice is not open to debate, really, hence no interest in competing solutions).

Click to expand...

*BUT *BUT* *Sputter* that might almost suggest that they're just cars, not a religion. You might wind up driving something different than I do. I might have to admit that the diesel hummer a few threads over even looks kind of cool. I, well, I guess maybe that'd be alright then...

It's OK Ken. It's OK.

After he gets a taste for hybrids, he'll find that considering only one model is like buying a Surefire without looking at all the other fine lights out there.

Besides, by the time he buys one there may be even better models out there!


Daniel

BTW, this was meant to be humorous.

KevinL said:

Which leads me to ask, at low speeds - isn't the takeoff powered by the IMA motor, which should not need a 12V battery? Well.. not when you have 144 NiMH cells powering it..

Then as the vehicle comes up to speed, the ICE should already be rotating and all it needs is a dose of fuel and air with a spark to start the combustion cycle. Of course, this is based on my understanding that the IMA is integrated as part of the main engine and spins up the main engine as well. Do correct me if I'm wrong.

So to begin with, if my interpretation is correct, the Hybrid doesn't even 'crank' the way a normal vehicle does?

Click to expand...

My wife and I have a 2003 Honda Civic Hybrid. The car starts with the 12v system and runs at low speeds with it's ~80hp gasoline engine (just like a regular car). The IMA Motor only kicks in when you need additional power to accelerate or climb a hill (hence the meaning Integrated Motor Assist). Linky to article I found on the net

I believe the Prius behaves more like you describe (uses only electricity at low speeds).

Ken_McE said:

*BUT *BUT* *Sputter* that might almost suggest that they're just cars, not a religion. You might wind up driving something different than I do. I might have to admit that the diesel hummer a few threads over even looks kind of cool. I, well, I guess maybe that'd be alright then...

Click to expand...

I sold my soul to the Cult of VTEC a long time ago and occasionally they pop up and demand their dues


Besides, it's a different situation where I am.. product availability, product pricing, taxes and how the market works, so this is the only one I really like.

gadget_lover said:

It's OK Ken. It's OK.

After he gets a taste for hybrids, he'll find that considering only one model is like buying a Surefire without looking at all the other fine lights out there.

Besides, by the time he buys one there may be even better models out there!


Daniel

BTW, this was meant to be humorous.

Click to expand...

I could live with ONLY a U2, even if they SAY there are better lights out there

It's quite true the U2 is no longer the most efficient or the sexiest light, because it's based on the 'legacy' LuxV, but I like mine all the same.. I'm not too concerned about having what is technically 'best'. But I am VERY concerned indeed about having what I LIKE

(.... I have some Crees anyway. )

I had a chance to peek under the hood of a Civic Hybrid yesterday, the one that's built on the 8th-gen Civic platform (and 2nd-gen hybrid technology according to them). One of the things I noticed is that it STILL has that antiquated 12V SLA starter battery under the hood. The first thought that struck me was "Why do they need THAT??! Doesn't the NiMH pack supply enough cranking amps?"

Click to expand...

Under normal conditions, the IMA does start the engine in the HCH (Honda Civic Hybrid), that's necessary to restart the engine quickly as it shuts off at stops rather than idling.

A backup 12V starter is also included in the HCH, for situations where for some reason (such as extreme cold, or extreme overheating) the NiMH cells are unable to provide full power. However, as long as the 144v pack is healthy, the 12v starter is never used. The car can't run forever without the 144v system though as the 12v system is charged by 144v pack via a buck converter, not a separate alternator.

This is also one of the few benefits of the HCH system over the Prius design, it's always possible to jumpstart and operate the car as a normal (albeit weak) gas-only car even in the event of a total failure of the 144V system. In the Toyota scheme, the battery/motors are integral to the operation of the transmission, which does make the Toyota design more elegant and efficient, but in the event of a failure in the electric drivetrain, the car is pretty much stuck.

2xTrinity said:

Under normal conditions, the IMA does start the engine in the HCH (Honda Civic Hybrid), that's necessary to restart the engine quickly as it shuts off at stops rather than idling.

A backup 12V starter is also included in the HCH, for situations where for some reason (such as extreme cold, or extreme overheating) the NiMH cells are unable to provide full power. However, as long as the 144v pack is healthy, the 12v starter is never used. The car can't run forever without the 144v system though as the 12v system is charged by 144v pack via a buck converter, not a separate alternator.

This is also one of the few benefits of the HCH system over the Prius design, it's always possible to jumpstart and operate the car as a normal (albeit weak) gas-only car even in the event of a total failure of the 144V system. In the Toyota scheme, the battery/motors are integral to the operation of the transmission, which does make the Toyota design more elegant and efficient, but in the event of a failure in the electric drivetrain, the car is pretty much stuck.

Click to expand...

Very interesting insights into what makes the beast tick.. it certainly does explain a lot of what I'm seeing. Looks like they took care of redundancy and fault tolerance as well.

I'm also figuring that this arrangement would contribute to less wear on the 12V battery and as a result you'd get more years of life out of it? (or months as the case may be)

Depends on your climate the battery can get cooked just sitting there.

2xTrinity said:

This is also one of the few benefits of the HCH system over the Prius design, it's always possible to jumpstart and operate the car as a normal (albeit weak) gas-only car even in the event of a total failure of the 144V system. In the Toyota scheme, the battery/motors are integral to the operation of the transmission, which does make the Toyota design more elegant and efficient, but in the event of a failure in the electric drivetrain, the car is pretty much stuck.

Click to expand...

That's a very good point.

On the other hand....

One of the many benefits of the Prius is that, in the event of a total ICE failure you can still drive to the nearest service center to get it fixed.


As I've said before... The Prius is the only car I know with the warning message " You have run out of gas. Please proceed to the nearest gas station."



Daniel

I'm really amazed by people who actually run out of gas now days (not counting in the middle of nowhere). I mean how could anyone manage it, when your car is flashing and beeping at you for the last hour and there's a gas station every other block.

Well, Seinfeld's Kramer character wanted to return a borrowed car with as little gas as possible in the tank. Life imitates art.