2nd Gen Prius PHEV Conversion (Enginer plug-in lithium ion battery kit)

[starcraper]

From my experience, driving at very slow speeds, and mostly stopped in heavy traffic in Manhattan, the Prius' battery state showed only one bar of purple (unfortunately I don't have a ScanGague yet, as I imagine it would show the SOC?) utilizing the battery for every start, and only turning the engine on when I was ready to go a bit faster. I was getting a little bit worried, but figured the Prius knew what it was doing...

[Daox]

I am now home and the car is already off the charger. The killawatt shows that it only took .22 kWh to recharge the pack. Sounds like I'm not using the pack very much!

At the suggestion of another Enginer user, I checked the voltage coming out of the dc to dc converter. I powered the car and phev kit on. The voltage started out around 220V and slowly rose to just above 230V. Once it got much higher than that, the voltage started jumping randomly around between 233V and 240V. It wasn't steady in the minute or so that I watched it. I don't think this jumpy voltage is normal, but I am inquiring over on priuschat.

[Daox]

Oh yes, I should also mention I still have the charger cutoff voltage turned down. The peak voltage I saw tonight before the charger cut out was 56.3V. At this voltage I'm getting no alarms and can pretty much charge without worry. I will probably continue this until I have some form of automatic over voltage protection.

Also, I am not planning on deep cycling the cells for the first couple of weeks (probably a month even). Some digging around on the net shows that some manufacturers recommend not going below 33% for the first 20 cycles. (Lithium iron phosphate battery - Wikipedia, the free encyclopedia) I figure it can't hurt.

[Daox]

I've started talking to a robotics guy I know from the local EV club about how we can use the balancer's warning to trigger some sort of pack disconnect. IMO this is pretty simple thing to do and can be done without cutting anything, and very minimal rewiring. I'm just not an electronics guru, so I need help to put it all together.

My current thought is to use a simple VOX circuit (microphone activated switch) that is triggered by the buzzer on the balancers. The VOX circuit will feed a signal to a programmable micro controller (the arduino is what I'm familiar with and its cheap). The micro controller will then control a relay to disconnect the pack from both the charger and dc to dc converter. This allows protection from both over and under voltage.

Once the pack is disconnected, we need to reconnet it somehow. But, with the arduino, we can do pretty much anything with it. We could wait an hour then reconnect the pack, hoping that the balancers have pulled the high cell back down and continue to top off the pack. As soon as the buzzers go off again, it would disconnect for another hour. Another alternative is that we could wait for a manual signal from the user to connect the pack again. This signal could be from another switch added up in the dash area, or even from turning the phev system of and back on (this would require tapping into the phev switch). At that point, the pack would be reconnected and ready to go.

The setup would cost less than $50.

The drawbacks of course are you are stuck with the balancer's set voltage points. Personally, I'd like to adjust them a little bit. However, this is a quick fix and I'm hoping Enginer eventually comes up with something on their own.

Thoughts?

[NiHaoMike]

It might have been better to build your own power management system, including battery charge balancing, charging, and output control. (Hey, some members here have built EV controllers, inverters, and chargers...)

[Daox]

It definitely would be better to build my own power management system. However, I'd like to keep the warranty and as I said, I'm hoping Enginer comes up with their own fix in the future. I know that they are currently working on an improved balancer atm. In the mean time, I need something that will get me by so I can charge the pack unattended.

[Daox]

Well, I used the pack more yesterday, more like 40 miles total (to and from work). Mileage was hard to tell since roads were snowy and people were driving slow.

When I got home I tweaked the charger voltage up just a hair and started charging. At that point, the difference in cell voltage was .02V on one balancer and .015V on the other, not too bad. The pack voltage got up to 55.4V last I checked and had pulled 1.4 kWh from the wall. About 15 minutes later I went to check on it and an alarm was going off so I went to unplug it and the killawatt pulled out of the wall instead of the extension cord, blah. My wife drives alone on Fridays (we carpool every other day of the week), so I'll let the cells balance all day and plug it in again when she gets home tonight. I don't think the pack voltage even got up to 56V last night before the alarm went off, and unfortunately I didn't check it before I unplugged the charger.

So, it seems like the kit definitely is working, but just not putting out as much power as it should? According to some quick head calculations, the pack will last at least 80 miles setup as it is now.

[Daox]

I ordered the VOX circuit this morning. The current plan is to just deal with charging. This seems to be the area where we are having most of the problems due to charging unattended and not being able to hear the balancer buzzers going off.

I am thinking that I will make an additional box that goes between the charger and the wall. Inside the box is the VOX circuit, arduino, a wall wart (for 12V power), and a solid state relay. There will be leads going to the inside of the phev box to the microphone. Since we aren't charging on the go, sound won't be an issue. When the balancers go off, it cuts power to the charger. Pretty simple. Once the charger is unplugged, the arduino powers down and it operates as normal.

I'll keep this thread updated as I build it.

[hugho]

Good luck buying Chinese junque. I hate to throw cold water on someone willing and brave enough to be out there in front of the Pack. What happens if it catches fire? Will your insurance cover it? Probably not. I would keep my mouth shut. Unless cost and reliability show some positive direction, the Lithium battery future will be a dead end. It is so far. But good luck and good on you for trying to push the envelope.

[Daox]

The kit comes with a fire extinguisher that is temperature activated. Plus, these aren't the hot running lithium ion batteries used in laptops. This is Lithium iron phosphate, it is much more stable. You'd REALLY have to abuse these batteries to get a violent reaction. In addition to this, there are safety mechanisms in place like fuses and breakers.

If it did happen, I'm sure insurance wouldn't cover that. I know the risks and I'm willing to take em.

Lithium is already the lowest cost per amount of total use you get out of the batteries. Their high cycle life makes them superior to others. If you think that other battery chemistries have a cost advantage in the long run you are mistaken.