Maximizing brake regen with a PHEV

[GeneralAnarchy]

Hi. I am new on this forum, and have had a Prius for 3 years. I have the Enginer on order, but not received it yet. I'm looking forward to learning to get the most from it.

An idea I have is to add a brake light relay that shuts off the converter. Maybe with pull-up capacitor on the relay input so the converter stays off until say 1 minute after last brake pedal use. That way if you tap the brake to decelerate or de-cruise going into congested/low speed limit area, the converter stops to make the most of kinetic energy without Enginer plus regen brakes competing to fill the NiMH battery.

It would seem if the converter is on and battery almost full, the Prius would be more reluctant to dump even more into the battery, so kinetic energy could go to waste that a normal Prius would have captured. Plus it seems like a real cheap & simple mod. I would like to hear if there are negatives or if it's even worth the trouble to try it.

[Daox]

Welcome to the site GeneralAnarchy.

Your idea is an interesting one, however I don't think it'll work out very well. I too have the Enginer kit. And, while I haven't used it a ton, I think you'll understand why this won't work out well.

First off, the Enginer kit doesn't pump out enough juice to go real fast in EV mode. Therefore, you want it charging the OEM pack as much as possible, especially when stopped to keep the OEM pack topped off. Second, you would need to turn off the converter well before you come to a stop so you can take some time to use that power to lower your SOC. This is going to have to happen well before you hit the brakes. Third, you can still use regen. You just have to be lighter on the brake pedal as you will (hopefully) have a higher than normal SOC. However, this is usually not the case due to the first reason state.

[GeneralAnarchy]

Thanks for your ideas. That makes sense especially for stop and go driving. My commute is mostly 55 mph rural highway, just a lot of hills and small town school zones - absolutely no stops though. I don't expect much EV mode, but just assist the ICE. To save the most gas, its best to switch off about 1 minute before approaching a town or downhill run? In my regular Prius sometimes I'm at full bars at the bottom of a hill. If I'm below 42mph the ICE often starts and stops to burn off juice. If I forget to switch off Enginer a mile before, I guess that problem could be more frequent. It would be cool to have a circuit, maybe with accelerometer, that could automate the converter shutoff spots. If it could be done, I wonder is it only a miniscule amount of improvement for the effort?

[Daox]

That will help, but I think the benefit will still be minimal. If you are already getting 8 bars, theres not much you can do to avoid that unfortunately. You can't tell the Prius to use more EV propulsion at highway speeds (other than charging the OEM pack as the Enginer kit does). Its really too bad too, a MIMA type mod would be awesome for the Prius.

I guess I would try to bleed off speed (coasting using EV glide mode/ice @ ~900 rpm) coming up to the hill to try to get rid of a bit of power. That way you won't have as much speed to regen going down, and also you might lower the SOC enough that you can capture it all. It is hard to lower SOC on the highway though. The Prius really likes to stay at 6 bars at higher speeds.

If this only happens in one place on your commute its really nothing to worry about. If it happens more than a couple places, then it would be something I'd look into more.