ElectroClassic EV
Classic Cars Reborn into the Electric Future

High Wire Act, Part II

After deliberating, I’ve decided to hard-wire the Zivan NG1 DC/DC converter input directly to the battery pack, resulting in the DC/DC being always on. Some EV builders do this because their BMS needs 12 volts to monitor pack charging while the ignition switch is off. This means the DC/DC converter will run even when the car is parked, although it only consumes a small idle current of a few milliamps which doesn’t generate any heat or drain the traction pack in the short term. Shown above is an Andersen connector tying the NG1 input to the full pack voltage.

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Moreover, the NG1 was primarily designed by Zivan as a 12 volt battery charger that effectively doubles as a DC/DC converter. So another advantage of hard-wiring is that the NG1 will keep the auxiliary battery charged with the key off, drawing power from the Elcon charger while the main pack is charging. Otherwise, the NG1 would only charge the auxiliary battery while the ignition is on and the car is running, putting an extra drain on the traction pack. Shown above is the output of the DC/DC tied directly to the orange auxiliary battery pack, just peeking over the mounting plate. The second fat red wire provides primary 12 volt power to the main fuse panel.

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Like the DC/DC converter input, the Elcon PFC2500 charger is also hard-wired to the battery pack, only on its output side. Both converter and charger can be simultaneously connected directly to the traction pack without harm to either. In fact, the same 10 gauge primary wire pair ties both of them to the battery pack through the tunnel. Most of the current flowing from the batteries on those primary wires will happen when the accessories are on, and the charger is off. Conversely, the current to the batteries happens when the charger is on, and the ignition switch and accessories are off. Like roommates that work opposite job shifts, they will never crowd each other. The shot above shows the charger output and the DC/DC input both directly tied to the battery primaries through a “Y” made of Anderson connectors.

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The pump and fans of the cooling system do not need to be running when the accessories are powered, but should definitely kick in when the main contactor is engaged and the motor/controller is awake. That happens only when the ignition key switch is fully ON. Coincidentally, the engine harness breaks out directly under the former relay board spot, right where the cooling system now lives. The black ignition wire will supply the juice, since it is active only when the key switch is turned on.

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Wiring the heater/fan unit into the EV electrical system is a two-sided process. First the high voltage ceramic heater core needs full pack power of 115 volts DC, and secondly the fan speed control switch needs normal 12 volt DC accessory power. The switch provides three speed settings for the fan motor, but also activates an Albright 60B contactor that controls the high voltage to the heater core. Shown above is the Anderson connector that directs full pack voltage to the ceramic core, regulated by the contactor mounted in the control box.

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When the heater is turned off, the de-energizing contactor coil spits unwanted induced current back into the 12 volt side of the circuit. Another way of saying it is that a strong momentary reversal of potential takes place. For that reason, coil suppression diodes must be included on the low voltage side of the contactor. Current may freely pass through the diodes in one direction to run the fan, but they prevent induced current spikes from traveling in the opposite direction to stress out the 12 volt fan motor and speed switch. Diodes used for this purpose are usually called flyback or snubber diodes. I think I could have gotten away with just one diode on the contactor, and one on the switch side, but after reading about snubber diodes I decided it was voodoo and just followed the heater schematic.

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2 Responses to “High Wire Act, Part II”

  1. This is the most comprehensive, well written, PERFECT source of information I have ever seen on this subject. THANK YOU for all the effort you have put into making it available for others. I have a 914 with steel flares and I want to convert it to electric. I am in ANAHEIM. Perhaps one day I can see your car at a local car show. Please let me know how I might be able to take a quick look at your masterpiece!

    Bill Taormina
    CEO and Founder
    Clean City, Inc.
    714-765-0360 Office
    bill@mycleancity.net


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