Finding Parasitic Drains

13-Jun-2013

Parasitic drains SUCK… customer complaints like, "car won't start after being lift for a few days" can be troublesome.

Here are some steps to take to make diagnosing parasitic drains a little less painless

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As always the first step is to confirm the fault with a

  • fully charged battery
  • load tested battery
  • and vehicle "asleep" (has been sitting for about 30 - 40 minutes or up to 2 hours on newer vehicles) determine how much current draw exists in the system.

The total amount of current flow can vary across manufactures and year, however as a general rule of thumb, I consider up to 100mA normal on older vehicles and up to 200mA on a current model vehicle.

Check the basics firsts.

  • Any lights staying on, interior lights, parkers.
  • "hot all times" aftermarket accessories fitted.
  • Moisture build up on the battery (causing current to leak between terminals)

Locating a battery drain

Using a current clamp on the negative battery terminal or your multimeter (set to mA) in series on the negative terminal.

  • 1 : With your current clamp or meter already installed, at the battery, remove fuses from the fuse pannel taking note in the drop in current flow as each circuit is disabled. keeping an eye our for the circuits that #1 cause a drop in current flow #2 the amount of current flow that is reduced by removing that fuse.
  • 2 : Using your multimeter, measure the voltage drop across the fuse, at the fuse pannel, (you you may need to set non auto raging meters to milivolts). A fuse (circuit) that has voltage drop across the fuse has to have current flow (no voltage drop no current flow). Then remove the fuse and measure each circuits current draw with your meter.

Measure the current draw and see if it is above or below the limits suitable for the vehicle.

  • Do the total amounts of current draw equal what you measured at the battery ?
  • If not head back to the battery and isolate leads fitted directly to the battery terminals.
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