When 12V battery dead, why can't start from IMA?
 

This is more of a design question, I think.

Last night I drained the 12V on my 2007 HCHII by leaving the headlights on for a couple hours. Had to get a jump.

Why is the HCHII designed so that you can get an emergency start from the IMA? Since there's already a 12V converter from the IMA, surely there could be an emergency switch that could be activated to allow an "internal" jump start. The switch could keep the IMA isolated from inadvertent draining, then be pressed to allow for a jump.

What am I missing?

Re: When 12V battery dead, why can't start from IMA?
 

The IMA battery is over 130v and all the regular electronics are 12v. The relay to start the IMA to 12v is engaged by the 12v battery when the key is in II - no battery - no 12v - no start car.

For safety reasons, all parts of the high voltage is safety shielded, (Look for the orange coverings under the hood) - they would have to do that to the wiring and fuse box to put in a 150v relay. Could it have been done, yes. But it would have made things harder to work on and more dangerous and more expensive.

Maybe Jumper Cables should have been a standard item.

Re: When 12V battery dead, why can't start from IMA?
 

Larry,

Thanks for your response. I appreciate the perspective.

On the safety issue, I'm really not following, though. Since the car has no alternator, as I understand it, there's already a converter that provides 12V from the IMA to the battery and the 12V accessories. To protect the IMA it only operates when the car is running.

What I'd be asking for is just an emergency "push button" switch which would allow that existing circuit to operate for jump start.

I wondering if Honda doesn't provide such a switch, because people might tend to defeat it or abuse it.

Re: When 12V battery dead, why can't start from IMA?
 

The "switch" would need to be connected to the IMA at its voltage. It would add some cost and and risk that someone would tamper with it. The penalty for mistakes at high voltage is much greater than the low.

Next the car would need dual systems. 1) A 12V based converter controller. 2) Another IMA high voltage controlled system. Then comes the software to detect the Jump Mode and not fry anything.

It can be done. Won't be easy or cheap.

Re: When 12V battery dead, why can't start from IMA?
 

Cars in general, and hybrids with their puny 12 volts in particular, are a very vulnerable to their battery being killed by an inadvertant headlight (or even map light!) left on.

Would it be possible, and viable, for auto makers to have some system in place that would prevent excess 12 volt battery drain when the key is out, or in position I? I know some current is always needed to maintain various memories. But could something be set up to detect high levels of drain?

Or is it too expensive/impractical? It's seems to me it would be readily marketable.

Re: When 12V battery dead, why can't start from IMA?
 

Just like the headlights cut off automatically after 45 seconds - it is not much harder to put a similar cutoff for all power after 5 minutes or cut the power when the battery is down to 12.4v ( enough for 2 crankings ) until the key is returned to 0 and then back to II. Might add about $20 to the cost.

Re: When 12V battery dead, why can't start from IMA?
 

My understanding is that this car has no alternator - the 12v battery is DC/DC conversion charged from the hybrid pack. However, that can happen slowly over time. There's a big difference between that and supplying the cold cranking amps you need to start your engine.

Also, if the 12v battery is dead then it's a 0v load on the line - it won't let the voltage rise. It's shorting out the cranking path, so to speak.

Kip

Re: When 12V battery dead, why can't start from IMA?
 

Kip,

In addition to not having an alternator, the HCH doesn't have a starter motor . . . so you don't need "cold cranking amps" from the 12V battery. The IMA powered electric motor starts the car.

As you point out, Honda has designed the system so that you do need low amperage 12V power, to open the circuit that allows the IMA electric motor to start the car. Previous posts in the thread, speculate that this is a safety feature.

Re: When 12V battery dead, why can't start from IMA?
 

nope, the hch has a starter motor that gobbles up all the amp the tiny 12V battery can muster. this is the spare starter that gets used in cold weather or when the IMA system got a problem. the car must start with a good 12V cause it is what the ima needs to close the relays. its a safety thing. no 12V, no zoom-zoom.

ks

Re: When 12V battery dead, why can't start from IMA?
 

Nope on your nope.

First paragraph here:
http://en.wikipedia.org/wiki/Integrated_Motor_Assist

or

Fifth paragraph here:
http://www.autocarindia.com/firstdri...a-civic-hybrid