Charge 12V battery when engine off?

[cowboynils]

Hi Guys,
I am watching this forum from overseas for a while now. And I enjoy my 1st-Gen Insight for more than 5 years.
I have made a few nice little modifications in that time like for instance a simple but effective car-pc with a 10" touch screen (who needs the air outlet in the middle anyway?), cruise control, sound module (www.hiir.com) with car alarm and finally a park heater Webasto Thermo Top E.(Small and subcompact cars)
The only problem here is that the tiny tiny 12V battery in the Insight isn´t able to power the park heater long enough in the winter.
The heater needs 30 minutes to make my baby cozy and ready for a gentle warm engine start. But although I changed the 12V battery a few months ago the heater stops after 15min. I think it shuts off when the voltage drops under 9 or 10V.
And here is my question to all of you that understand more about the Insight´s electronics than me (so it´s nearly to all of you):

Is it possible to make the IMA battery (respectively the DC-DC module) charge the 12V battery even if the ignition is off? That would give me some ampere-hours to get warm and safe?

I already used the "fan relay" of the park heater to give power to the car´s climate control unit. Maybee I can do the same with the DC-DC module? Or do I need more components to charge the 12V battery?

The 12V battery has about 45Ah and I think the IMA battery with it´s ~900Wh could give me another 75Ah@12V. Am I right?

I hope someone can help me because Kiel/Germany is cold and snowy right now.
Many thanks in advance.
Nils

[Eli]

I think the stock Insight 12V battery is more around 35Ah.

Just buy another deep cycle 12V battery and find a place to put it. Using the IMA battery for something like this is a terrible, terrible idea. Even more-so if the system safeties aren't in place.

The IMA battery, in perfect condition, will only give about 550Wh(60% of 6.5Ah @ 144V) with the system safeties in place. The DC-DC draws about 2A from the IMA battery with a 25A system load.

You will just have to replace this energy with fuel, killing your fuel economy.

[cowboynils]

Hi Eli,
I already replaced the stock 12V battery. That´s why I have 45Ah. Sadly that´s still not enough.
Of course I thought about adding another 12V battery but WHERE??? Placing the park heater under the hood was already close to an act of magic, I can tell you.
Maybe I´ll find a place behind the bumper...Ah no, that´s where my pressurized air system is going to go...
I don´t want to put a battery in the passenger cell because then I would have to make a hermetic housing and some ventilation to the outside because of the oxyhydrogen. Or ill take one or several of these gas tight gel batteries...

Anyway, I wanted to check first if there is another solution. But you´re probably right: I wouldn´t want to risk my IMA battery´s health for that.
Thanks a lot for the clarification!
Nils

PS: I will always have to replace the electric energy by fuel no matter in what battery I store it. But the enhanced efficiency of a warm engine also saves something on the first kilometers. I tried to estimate that before I bought the park heater, which consumes about 0.17 Liters (0,045gal) of gas per heating-up. And I think in practice the it nearly levels. I still enhance my exhaust gas emissions, the engine health and my own (by being able to see through the windows )

[aisbell]

I installed a DEFA WarmUp 411241 block heater in my Insight (this is what the Honda dealer in Uppsala, Sweden, is selling). It has an optional interior heater that sits on the passenger floor and is powered by the 230 v. AC power that powers the block heater. So there is no drain on the car's 12 v. battery. Expensive system, but it seems to be well-designed and of very high quality.