The charger.

Manufacturer: BRUSA Elektronik AG
Cost $4,400
Available from Metric Mind Engineering

As far as I can tell from talking to other EVers and browsing their web sites, the charging is seldom gets adequate attention and often is seen as a secondary system. Perhaps the thinking is that the charger is kind of like the wheels for an airplane - it's important part for taxiing, but is just a supporting system, not directly needed for the plane to *fly* well.

It is obvious that the charger quality among other things directly affects the battery life. Yet, people are often reluctant to invest in a good charger. Simple calculation shows that if $1,500 charger can extend the life of $3,000 battery pack by 50% (very real number); by the time the pack is dead and need replacement, the charger is already paid for itself. So from that point on having good charger it will actually save you money for every next pack making them last longer, not to mention less labor replacing it. Remember, no matter how good or conservative driver you are, your battery is disposable item which will need replacement sooner or later, but the charger is permanent part of the car, like its motor. Do it right in the first place. If your budget is limited, my advise is to get the best charger for the job you can afford, and use the money left for the battery. Not the other way around. In future you lay decide to upgrade your first battery, and the charger will be up to the task. You will thank yourself. So-so charger will ruin the best battery quickly. Years ago with my first lead acid pack I was tempted to use "bad boy" charger (nothing else but a rectifier with step-down transformer) as my first charger, it allowed to get on the road quickly. Constantly overcharged, my pack of 10 Trojan 27 TMH went dead just six month later. I turned bad boy down a bit. Now it was taking longer to charge and still the pack was boiling at the end. A couple times a day I had to run outside on the parking lot and turn down the autotransformer to get the right current. This $2,200 pack of 10 Trojan 5SHPs went dead in less than a year. Well, some progress and some lessons learned. Well, my third pack of 5SHP has been charged with KW-20. Better than bad boy, still a dumb charger really unusable for anything other than cheap and forgiving flooded lead acid batteries.

Charging is like fueling your conventional gasoline vehicle. Fueling procedure was streamlined and perfected over the years; this straightforward process allow no deviations other than picking the grade of gasoline. Infrastructure is there and equipment / procedure for any car in this respect is boring the same - open the hatch, unscrew the cap on the inlet to the fuel tank and stick the pump nozzle into it. Oh, don't forget relevant part of the process: sticking your credit card into the card reader first...  In contrast, charging batteries still is more art than the science. But the process of plugging it in is far easier than pumping gas. Every night I charge my car, palm and cell phone, and  plug them in almost uncontiously. Don't know exactly how much time each device takes, but I don't care as long as all three are ready in the morning full of juice. And they are. What else could you wish for?

No two EV conversions charge identically.  There are many opinions for the charger, type of battery, and also vehicle usage pattern. Overall the charging technique depends on:

- Battery type
- Battery SOC (state of charge) level
- Battery temperature
- Battery age
- Desired life time vs. charge completeness trade-off
- Need for equalizing phase (applies to lead acid batteries)
- Available mains power
- Available charger ratings
- Available charging time

Charging LiIon battery is relatively simple process. The only requirement - some values like voltage per cell and total charging time must be very strictly adhered to, this battery is not forgiving. The price for outstanding energy density is danger of damage if unattended or poorly adjusted charging system tries to put more energy into the pack than it can accept. Major role here plays BMS - Battery Management System, which supervises each individual cell. But the Amp hours put in power and overall pack voltage and current depend on the main charger, so it has to be flexible and programmable to accommodate particular requirements recommended by manufacturer. It has to have enough output voltage to cover max pack voltage, as much charging power as possible for its size and cost, be safe, reliable and quiet. Preferably it should allow to see the charging status on remote display.

The charger of my choice is gorgeous BRUSA NLG513-WA unit which has been working with my pack flawlessly from day one. Its main advantages are:

- Isolated output. Necessity of the isolation is debated and I did use non-isolated charger before. It is quite safe as long as you remember every time working on your car what you can or cannot do. Well, after few years of ownership, and seeing how professionals make these things, using non-isolated charger is out of question, just like not wearing seat belts. We all drove without them before they got mandated, so apparently it is OK. Now, however you don't' even think if you want to use it- you just buckle up. Same here, isolation is not being discussed. I don't have not only non-isolated equipment, I don't even have any exposed terminals with line or battery voltage on them - like those power bars sticking out of cheap motor controllers. I don't want to think that safety in my EV is somehow compromised. You decide for yourself. With the pack isolated from the vehicle there is just no chance I can get line voltage on the vehicle chassis while charging.
- Universal mains input. 240VAC nominal for full 3.6 kW output can be reduced to 120VAC. Charging power is reduced, but the amps keep flowing.
- Programmable 7 - stage charging profile. Why would anyone need 7 stages? It gives you flexibility and bring advantage you won't expect at the first glance. For instance, I program first 1 min dummy cycle charging with 0A current. This allow avoiding sparks and burned terminals on the mains plug since at the moment I plug it in, no power is drawn. A minute  later the charger starts full bore, but the contacts are already made. Sweet.
- A library of free downloadable charging profiles exist - no need to wonder about right settings if you don't want to.
- Water cooling. This option allowed to have smallest physical size and quietest unit - no fans needed. The charger can work at full power in totally enclosed spaces without any air flow. This option makes sense if the drive system is also water cooled and the plumbing is already there - I just plumbed the charger "in series" with existing cooling system for the main drive This takes advantage of the water pump, radiator, etc.
- Temperature compensation. The charger adjusts its output based on programmed compensation curve.
- Temperature sensing. Standard 3 sensors (and up to 48 temp sensors with optional expansion board) can be connected to it.
- Remote control and indication. The charging status can be seen on small LED display I can mount anywhere. Also, if the capacity of the mains is limited (for instance I'm allowed to plug in into 120VAC outlet for opportunity charging, but other loads exist on the same circuit, so I can only draw 5A from the mains to keep the circuit breaker from tripping. Well, I can remotely adjust and limit AC mains input current without looking at the DC output current.)
- Ability to observe running parameters on a PC screen using simple hyper-terminal software.
- Reliability. Time will tell, but my expectations are high in this respect.
- Flash upgradeability. When new software released, I can take advantage of it.
- Last - but not least - it looks oh so cool!     (...and it literally is - it's barely warm to the touch while pumping more  than 3600 watts into the pack).

Any disadvantages you may ask? 

- It is not cheap, but to me worth every penny. Will leave it at that.
- Software interface currently is only available in German. The GUI is intuitive though, and one can start using it with minimal hassle. Once initial parameters are set up, amps are amps and watts are watts, English or German. Doesn't bother me. Besides, technically it is not *charger*s "problem", rather software developers'. English software is beta tested and will be released soon, so it won't be an issue at all.

- Some my question sufficiency of 3.6 kW output power. For one, this is not the limit, for more money one or two booster modules can be connected in parallel doubling or tripling the output. I just see no need for it. As I mentioned, the car is ready every morning, so increasing the charger output will only increase idle period during night after the charging is done. Also, with well over 100 miles city range, I don't use opportunity charging, but even if I would, there is unlikely 240VAC 50A outlets everywhere waiting for me. Most likely I can find 120VAC outside the buildings, restaurants etc, but even with 20A breakers, they can provide only 120V*20A=2.4 kW full bore before the breaker trips. And that is, if no other loads are on this circuit.   So in this situation I can't even take full advantage of the 3.6 kW charger I have because of mains supply limitation - I have to turn it down when plug into 120V outlet. So why bother with more charging power?

NLG5-WA EV charger.
There is nothing fancy about interface connector pins provided with the charger ...
... until you realize they belong to the totally water tight interface connector (on this photo -being assembled).
Done. The wiring is color coded. Keep good notes which wire is which!
Being installed on the fire wall near brake vacuum booster reservoir.

Installation and programming of the charger.

The charger can be installed in any position. It is water proof, AC in, DC out and interface connectors are sealed. Preferably status LEDs should face up or be well visible and the power connections as short as possible, otherwise there is no preference.

I mounted the charger near fire wall next to the power steering booster tank. The cleat tubing water hoses are connected to the outlet of the drive motor and to the inlet of the stock radiator. As I drive, the cooling liquid runs through the charger too, which makes no difference for the drive system. The water pump runs from 12V DC-DC converter output.

When I charge, the water still runs through all the components including motor and power inverter, but as long as it also runs through the radiator and cools off, the charger doesn't care. The water pump runs from the mains, powered by a small 60 Hz 12V output transformer.

Actual charging profile consists of two phases - constant current and constant voltage. Initially the constant current is set to be as high as the charger is capable of, 8.7A into 412V pack (about 4.3V per cell on charge), and then this voltage is kept constant until the current drops to 900 mA or 8 hours elapse, whichever comes first. Just in case, I also have capacity criteria - not to put more than 90Ah into the pack, but I know this criteria will never be satisfied. Just extra safety for peace of mind at no extra cost. Why not?

The rest of fine adjustments and balancing will be taken care by the Battery Management System. For now, until BMS is ready, I will use simple voltage clamping shunts which turn on when the voltage reach 4.3V or whatever voltage I set. Since the current each module is able to bypass (10A) exceeds max total charging current, this guarantees no cell voltage will exceed shunt's set threshold. This works only if complete charging is done, below threshold regulators do not conduct and have no effect. I do charge completely every time I plug in the car, so no problem.

Not terribly sophisticated, but inexpensive, allows me to drive *now*, and works well.

The charger programming software running on the PC (captured while disconnected from the charger)
The monitoring program running on the PC