I fully understand the difference between the Prius and the Honda IMA systems. I agree the Prius is much better for converting because you can run on electric only. In my case however I live in South Dakota and there really is no such thing as city driving or stop and go traffic. Since I don't have to hit the brakes much the IMA battery hardly ever gets charged.
This is what I have observed with my Honda Accord;
If the battery SOC (state of charge) is at half then it almost never provides any assist unless I really tromp on the throttle. Remember most of my driving is 55 to 75mph driving with rare need for braking.
If the SOC is at 60% then I get modest assists on the uphills but only when the engine revs are low.
If the SOC is 70% then I gets more aggressive assists but this drains the battery down to 60% or 50% fairly quickly.
If the SOC is 80 or 90% (I've never had it all the way up to 100%) Then you get very very aggressive assists but again they don't last long because the battery capacity or temperature or both limits the assist.
So you might be thinking to yourself, how does he get up to 90% SOC if he hardly uses his brakes? I ran some tests where I found the IMA won't assist if the the automatic transmission is in 2nd gear. So when I was doing some slower driving one day I kept it in low gear but put it in drive when using the brakes and eventually I got the batteries charge way up.
So what can we learn about this? I conclude that if I can keep the SOC up with an auxiliary bank of batteries that the IMA would assist more often and more aggressively. I planned to use a 48 volt battery pack with a DC to DC Converter
that converted the 48 volts up to the Honda pack voltage. The current would be limited so as to not build up too much heat in the hybrid pack. The 48 volt pack would be charged at home from the grid.
So when I'm cruising down the road at 65 the IMA would kick in more often. Providing modest gains of which probably would never pay for the batteries, DC to DC Converter
, relays, charger and wiring. But it would be fun to try. Besides I've been in a Prius, I like my Hybrid Accord Waaaaayyyyy more. The thing is like a rocket! To bad I only get 30mpg.
My real electric vehicle will be a Toyota RAV4.