This blog documents the restoration, and conversion, of a 1965 Humber (Singer) Vogue to a fully electric vehicle. The Vogue will be powered by an 11kW(modified), 3 phase industrial AC motor, controlled by an industry standard Variable Speed Drive (VSD) or Inverter. To be able to produce the 400 volts phase to phase the VSD will need about 600 VDC of batteries. A big thanks to the contributors on the AEVA forum:

Thursday, September 2, 2010

Battery Charger Isolation and Fuses

To charge my 12 battery packs I have 12 x 3 Amp chargers. There are two reasons why I can't simply connect the chargers straight to the battery packs and leave them that way.
1. The chargers draw 6mA of current from the packs when connected and the chargers are not switched on.
2. The chargers have a fuse in the positive lead but not the negative lead.

Why 6mA of current is unacceptable is that this current will gradually drain the batteries when the Vogue isn't in use - not much but enough. Six milliamps per hour adds up to 0.144 Amp hours (Ah) per day. Over 1 week that's 1Ah and that's 5% of my pack capacity. So I choose to isolate the chargers from the packs using 2 of 3 Amp diodes per charger.

Why do I care if the chargers are not fused in both leads? This has to do with the voltage at each end of my 600 Volt pack. If we assume for the moment that the pack centre will be connected to the car chassis (ground, and it may not be) then each end of the pack will be at +300V and -300V respectively. Since the packs can deliver well over 1000Amps momentarily, if the little silicon insulation washer in the charger breaks down then the wires to the charger would vaporise. I don't want a fire, so I'll fuse the negative lead as well.

This is the bundle of bits to build one of my 210mm long fuse and diode charger connections. I have chosen a type of connector used in the RC fraternity called a "DEANS" connector. They are gold plated with a spring steel backing on the pin to ensure great contact. They are rated at 30 Amps - you can see it on the far right of the picture. I make the connection finger and splash proof with a rectangle of fairly heat-proof plastic wrapped around it  with heat shrink covering it. There are LOTS of pieces of heat shrink involved.

The final products. The 6mm lugs go to the battery pack and the other end plugs into the wire emerging from the charger.

Eight finished, 4 to complete. The copper heat sinks are from an old copper fire screen that became available when we fitted a chimney damper in the house. I polish them and file the rough edges off before using them. Every wire is heat shrunk to provide double insulation. I will double insulate the diodes where they can be touched by humans (only a few packs will be "touchable").

For the technically minded the heat sinks settle to 40 degrees above ambient when delivering 3 Amps for an extended period. The heat shrink appears to dissipate enough heat due to the close contact with the copper heat sink.

No comments: