Enginer PHEV automatic over/under voltage protection

Sure Eric. I used a 12V power inverter and some lightbulbs. I hooked the inverter up to a set of 4 cells in series to make a 12V battery. I then powered up the inverter which had 3 75W light bulbs connected to it to give me a 225W draw. Combined with the inverter's ineffiency, I estimate that I'm pulling around .5C and that the battery should theoretically last about 2hrs.

 

Out of the 32 batteries, I got ~20 to take a charge. Obviously, the capacity is a bit low on these cells, but I'm going to play around with them until I get the new ones, and make sure my BMS works. So, thats what I've been doing... Unfortunately it hasn't been done very successfully. I've been having issues getting the celllog's alarm port to work properly. One just isn't working and one is working, but not the way I would expect it to. When hooked up over one lithium cell, I get a 3.2V differential which is expected. When the transistor closes, the voltage only drops to 1.6V. Both of these voltages are high enough to keep the optical isolators closed and thus I'm not getting the correct signal to the arduino to kill the power to the dc to dc converter and charger. I tried putting a ~3k resistor across the leads on the alarm port wires, this dropped the voltage to 1.2V. Perhaps a lower ohm resistor will drop it enough.

 

Well, I decided to throw the kit back in the car while waiting for new celllogs to arrive. At least one of mine has a toasted alarm port, so I can't do a ton as is. So this means manual charging for now (watching for alarms and checking it at certain intervals).

I did use it on the way to work this morning with great success. My commute is 7 miles now and has a top speed of 45 mph. I turned the kit on and was able to use EV mode until I was out of town and the speed limit increased to 45 mph. After I got into the next town, I was able to keep it in electric only until I got to work. The commute itself was a pretty good one. I only hit one red light and I was in town and in EV mode. However, halfway to work I noticed a warm plastic smell so I turned the kit off. Once I got to work I double checked my connections and sure enough one of the bolts was loose. My mistake there and I'm glad I caught it. The lock washer was keeping tension on the joint, but not a ton. I was able to turn the screw with my fingers to tighten it up. All in all though, it was a great commute. I got 108 mpg on the way in and I'm incredibly happy to see that I'll be able to hit ~100 mpg on my daily commute. The only downside is that on the trip home I always get 10-20% worse mileage. I'm also not sure when I'll hit the low voltage alarms on the kit. I have them set pretty conservatively to short cycle the batteries to extend their life. I'm not sure how much capacity this is causing me to loose. I estimate with only half the batteries, the batteries being somewhat dead, plus setting alarms conservatively my capacity is quite limited compared to what it will be.

 

I got to use the kit one more time last Friday. I was on my way to work and was a few hundred feet from the parking lot going down a 25 mph road and I started to smell something. I shut the kit off and haven't been able to take a look at anything yet, but I know its the dc to dc converter. The light on the switch panel doesn't light up anymore. I'll be removing it soon to see what happened.

 

I popped the cover off the converter tonight and found what I think is the bad component. It looks like it over heated. The fuses all look fine.

 

Hmm, I haven't altered any settings on the converter since getting it. Honestly and unfortunately, for the 1.5 years I've had the kit now, it has been used very little.

 

I just picked up my converter and box of batteries from the Fedex store last night. Over the next week I'll start the process of balancing the entire 4kwh pack at the low end.

 

The other day I got the BMS working for the kit. This is the main thing that is lacking in the kit, or at least my version of it (mottcells).

I have changed a thing or two on the schematic since it was last updated. I'll post up a new one once I get a chance to change it.

I have gone through one tank with the PHEV so far using it a fair amount of the time. The result was 63.6 mpg. Not too bad, but I'm definitely looking for more. My daily commute averages in the 80s I'd say. The long high speed trips are what really kills the mileage. Charging was a pain since I didn't have the BMS hooked up yet. I am charging for the first time tonight with the BMS and am loving that I don't have to check it every 15 minutes.

 

Last night right before heading to bed I checked the phev kit and the carger. I noticed it had kicked itself off. I had drained it down quite a bit and was surprised that it was done already. So, I plugged it back in, watched it a few minutes and saw it turn off not nearly at a voltage where it should have. It wasn't even up to 3.5V yet. I also turned the car on and PHEV to top off the OEM pack for tomorrow morning's commute. I noticed as soon as the PHEV kit was turned on the charger turned off. These two instances lead me to believe that there is some electrical noise back there. At the first sign of an alarm, the PHEV disconnect kills power. So, I think I'm getting a voltage spike here and there that is triggering the disconnect. I'm thinking a very easy fix will just be to add a timer to the programming. This timer will ensure that the alarm has been going for 3 seconds before killing the power. That will take care of any voltage spikes.

 

I just got in from checking the charging of the pack again. I found a/the issue. For some reason my charger is suddenly cutting out at a lower voltage than before. It used to way overcharge the batteries if left alone. Now, its cutting out before any of the cells even hit 3.45V. I haven't changed anything with the charger. Has anyone had issues with the charger's cutoff voltage changing? I have the instructions on how to fix the issue, but I'm just wondering why its happening.

 

Yeah, that could be done. It would be pretty far down on the list of things to do though.