Enginer PHEV automatic over/under voltage protection

I thought I'd give an update on this thread. I've been using the PHEV kit consistently since about April. I haven't gone through many tanks of gas since then (only 5, yay), but the performance of the kit has been pretty good. Without the kit I normally average about 55 mpg in summer and 45 mpg in winter. The first full tank with the kit I didn't keep track of kWh used, and I was getting used to it and figuring out how to best use it. I got 64 mpg. By the second tank I had gotten the hang of it and kept track of my kWh used. Actual mpg was a very nice 79.0, and mpge was 65.3. That was my best tank for the season as most of the other tanks had more long distance driving where the PHEV kit couldn't be used as much since it has ~40 mile range. Now that it is working well with my custom BMS, I am very happy with the setup. I love EV mode and use it every day going to work and back.

I am pulling the kit out one more time though. I have a few weak batteries due to the abuse from the crappy stock BMS. I'll be returning them for new ones under warranty as my warranty is up at the end of this month. I'm confident that it'll last a long time once I get fresh batteries in it. I'm not deep cycling them at all during the daily commute, and I'm also limiting the max charge to about 80% to increase their life. I currently have no low voltage/low charge cutoff. However, I'll be adding an LED that lights up when the low voltage alarm on the celllogs goes off since I can't hear the alarms while driving. Unfortunately this can't be used to automatically shut down the PHEV kit due to issues with voltage sag variation. I may eventually add some sort of amp hour logging to automate some sort of low side cutoff, but its not really an issue for me 90% of the time since I only commute 15 miles a day. I will also be adding an ammeter on the output of the PHEV kit to show how much power its putting out. The SGII will show the OEM pack's in/out power use, but it doesn't really give an accurate picture of what the PHEV kit is actually doing.

 

Time for an update on the BMS system and PHEV kit. I'll have my parts back tonight and will shortly be testing out rev 2 of the BMS.

Rev 1 had:
- over-charge protection

Rev 2 adds:
- over-discharge protection
- PHEV battery SOC meter
- Prius off PHEV operation


I ended up wanting to beef up the system to add low charge protection for the batteries. This will prolong the life of the batteries and make it more useful for when I take it places other than just work. It'll also allow for idiot proofing for anyone else to use it as well. The more I thought about it the more I didn't like the idea of just using the low voltage alarm on the celllogs since load and temperature drastically effect the voltage sag. So, I did as I mentioned above and have added an ammeter to the circuit and am now using it to count amp hours used. Once it gets down to 30% DOD (changable via the program) it will turn the dc-dc converter off. While I was at it I also added an LED bar graph display to act as a PHEV SOC meter. Last, but certainly not least, I will be adding circuitry (havne't finished this part yet) to leave the PHEV kit on after the car has been turned off so the PHEV kit can charge the batteries up to a pre-determined SOC (might as well go all out, right?) so next time you jump in the car you're ready to go. Previously, I just had to sit in the car waiting for the PHEV to re/charge with the car on because turning the car off turns the kit off. I'm sure other enginer owners know what I'm talking about.