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Sparrow >> Service >> Modifications >> Defanging

1.  Intro

Many Sparrows with KiloVac controller have the 12 V circuit connected to the high voltage circuit. This is very dangerous, and prone to major damage to the controller. Tghis was done so that the controller could measure the battery pack's voltage, and reduce the drive if that voltage was too low. It was a very bad solution, and now we have to deal with it.

"Defanging" is the process of changing the circuit to disconnect the high voltage from the low voltage.

What worked for me may not be the same for other Sparrows. My #237 is a pizza butt with a first generation Kilovac controller (contactors outside the controller). My DC to DC is mounted on the side of the Kilovac controller in the back right compartment. I had a jumper wire from the 156 volt (pack) ground to the 12 volt ground on the DC to DC. I also have an EVBC black box in the back and an EVCL black box in the front. If you do not have all these pieces parts the modification may be different.

2.  Defanging instructions

2.1  Wiring modification

  • Push down the BRB and pull the main power connector.
  • Remove the tie wire from the input ground to the output ground on the DC to DC. The picture below shows the wire in a green box. On Sparrow #220 the wire itself was black. On #237 it was green.
  • Remove all green wires from the current shunt. The green wires must be connected to the 12vdc output ground terminal of the Vicor, do not isolate as they must be connected to the 12vdc ground to allow proper power distribution. Put the black wires back onto the shunt.
  • A modification needs to be made inside the back EVBC box to disable the low battery-monitoring feature. This monitoring feature had to have the 156V pack ground tied to the 12V ground. By doing this mod you lose the feature of not pulling in the main contactor with a low battery voltage (below 150V?) The replacement EVBC board from Black Sheep Technology does not have battery monitoring, however this mod of moving the green wires to the Vicor Output Gnd is still required.

2.2 EVBC modification:

The EVBC is the black box below the controller, the shunt and the DC-DC converter. See the orange wire on the rear most connector, this is the high voltage wire for the battery monitoring, this orange wire should be clipped flush on connector and trace back to it origin and removed entirely from the harness. You should find a fuse holder and wiring back to the main contactor. Remove all of this high voltage circuit.

R24, R25, and R21 makes a voltage divider that is .0182 of the input voltage, so a 200 volt input will provide 3.64 volt to the processor chip.

  • Remove R24 (222k)
  • Add a 5.6K resistor from the junction of R25-R1-R21 to the +5 volt power on the board. This will provide 3.5 Volts to the processor at all times, so it thinks the pack voltage is 192VDC.

Click to enlarge

EVBC PCB modification
Click to enlarge

2.3  Final

  • Check the modification with an Ohmmeter from the current shunt (pack ground) to the 12 V ground (green wire) and from each ground to the frame. Each should now show an open......."De-Fanged".
  • Plug the main power connector back together and pull up the BRB up and verify that your E-meter still shows the proper pack voltage.

2.4  Better Isolation

When the instructions above are followed, you end up with reasonable isolation between the 12V subsystem and the battery/motor/controller high-voltage subsystem. The two are joined, however, by a tiny isolation chip called the NTE1212 DC/DC converter which powers the Link-10, which shares a ground with the battery pack. You might consider installing a better DC/DC converter, one with better isolation properties, particularly if you're planning on installing a non-isolated charger like the Manzanita Micro PFC series. The following is a quote from Lee Hart, one of the people who's spent the most time trying to educate the electric vehicle building community.

Jake Oshins <> wrote:
Sparrow... Corbin used a tiny 12VDC-to-12VDC converter to provide isolation between the 12V system and the Link-10 in the EVCL box... The part was an NTE1212. It can only handle 1W, but that's plenty. These are very cheap. They can also break (electrically). The more reliable parts that also fits the EVCL PCB is a Cosel DC-DC converter, these are much more reliable.
  Cheap, but not good.

  The Link 10 (aka E-meter) draws about 150ma at 12v in full 
  sunlight (it brightens its display based on the ambient light 
  level). 12v x 0.15a = 1.8 watts, which is a significant 
  overload for a 1 watt DC/DC converter.  The input voltage 
  range for the NTE1212 is 10.8-13.2v. This is inadequate; 
  the accessory battery and its DC/DC converter can easily 
  range from 10.5v to 15v.

  Most importantly, the input/output isolation for this part 
  is wholly inadequate for an EV. The advertising claims 
  1000vdc; but read the data sheet 
  It says:
A question commonly asked is, "What is the continuous
   voltage rating that can be applied across the part in 
   normal operation?"
   ...less than 42.4 vac peak, or 60vdc... The part 
   should never be used as an element of a safety isolation 
   system... The NTE series has toroidal transformers, with 
   no additional insulation between primary and secondary 
   windings of enameled wire.
The DC/DC converter that you use to power a Link-10 / E-
  meter needs *guaranteed* isolation sufficient to withstand 
  your full pack voltage continuously. You aren't going to 
  find this on a cheap DC/DC. The one Cruising Equipment 
  used was a Datel part that cost over $30; but it was rated 
  at 1500vac, UL listed, 9-19vdc input, and 12vdc at 0-250ma 

  Or, you can use an AC/DC universal input, DC-output power 
  supply to power the Link-10 / E-meter directly from your 
  pack. Such supplies almost always have isolation voltage 
  ratings of 1500v or more, and are UL listed (which means 
  they have to GUARANTEE that it is isolated). For example, 
  I am using an Astrodyne MSCC-5003 which has 3000vac 
  isolation, 85-265vac (90-370vdc) input, 15v, 0-0.33a. This 
  is a potted module with screw terminals that sells for $80, 
  they have cheaper versions if you want to package it 
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Page last modified on October 04, 2011, at 11:40 PM