Precharging isn't as simple as it first appears. Here are a few things off the top of my head:
Precharge circuits *must* used DC-rated parts with an appropriate voltage rating. An AC-rated switch, relay, or fuse will fail *on*! If the switch or relay fails "on", the precharge resistor can overheat, or simply run down the pack. Your precharge circuit should include some way to sense the pack voltage, and abort if it fails to precharge in a reasonable time. Some load on the pack (like a DC/DC converter) can prevent it from precharging. A simple precharge resistor works, but will get extremely hot and fail (or even start a fire) if some fault condition leaves it on for too long. If you use a resistor, it should be a flameproof type that is guaranteed to fail "open" in case of a fault. It's hard to specify the wattage for a precharge resistor. It depends heavily on how much current and how long it will be connected. Resistors have peak current specifications that can be hard to find. The usual approach is to use a much higher wattage wire-wound resistor than you might expect, just in case something goes wrong. You can use a tungsten light bulb as your precharge resistor. Their "cold" resistance is very low (about 1/10th) of their "hot" resistance), so you get a high peak precharge current. Then the bulb lights, and you get a much lower "holding" current that can stay on without damaging it. Obviously, use enough light bulbs in series to handle your pack voltage (one for 120v or less, two for 240v, etc.) There are also special PTC (positive temperature coefficient) resistors, whose cold resistance is low, but go to a much higher resistance when hot. If I recall correctly, the Manzanita chargers have little or no output capacitance. They depend on the battery as their output "capacitor". You must be sure the battery is connected to the output before AC power is applied. Otherwise, the output will go overvoltage and fail (bang)! Check with Rich Rudman at Manzanita Micro for details and advice on this. Lee Hart -- Excellence does not require perfection. -- Henry James But it *does* require attention to detail! -- Lee Hart -- Lee A. Hart https://www.sunrise-ev.com _______________________________________________ Address messages to [email protected] No other addresses in TO and CC fields HELP: http://www.evdl.org/help/
