Parasitic Draw

F

finfont

Member
Re: 1972 P6 3500

A couple of questions about this car:
1. I’m getting a reading of 1.20 ma on a parasitic draw test. (Should only be the clock requiring electricity). Is this a normal amount of draw?

2. I’ve added an aftermarket radio/cd player wired such that the unit will function independently of the ignition. The display is not powered when the unit is off. Should be memory only drawing electricity. When installed but not operating the draw jumps to 178.00 ma. Is this draw enough to kill the battery over a short ( 2 wk ) period of inactivity?
Thank you in advance.
 
Why have you wired radio to operate independent of ign? Most HU have permanent 12v to keep station selections alive, and a separate switched 12v input to turn them on, and raise an aerial if so fitted.
The clock is an intermittent draw, not steady (winds the spring periodically). ability to read down to fractions of MA is unusuall? Does it disappear when clock disconnected (fuse pulled)?
Maybe when battery is near new 178ma wont kill it in 2 weeks, but later on...Try pulling fuses until it disappears, then chase down whats on that fuse.
BTW, how and where were you measuring drain?
 
jp928 said:
Why have you wired radio to operate independent of ign? Most HU have permanent 12v to keep station selections alive, and a separate switched 12v input to turn them on, and raise an aerial if so fitted.
The clock is an intermittent draw, not steady (winds the spring periodically). ability to read down to fractions of MA is unusuall? Does it disappear when clock disconnected (fuse pulled)?
Maybe when battery is near new 178ma wont kill it in 2 weeks, but later on...Try pulling fuses until it disappears, then chase down whats on that fuse.
BTW, how and where were you measuring drain?
Click to expand...
jp928 said:
Why have you wired radio to operate independent of ign? Most HU have permanent 12v to keep station selections alive, and a separate switched 12v input to turn them on, and raise an aerial if so fitted.
The clock is an intermittent draw, not steady (winds the spring periodically). ability to read down to fractions of MA is unusuall? Does it disappear when clock disconnected (fuse pulled)?
Maybe when battery is near new 178ma wont kill it in 2 weeks, but later on...Try pulling fuses until it disappears, then chase down whats on that fuse.
BTW, how and where were you measuring drain?
Click to expand...
JP- Thanks for your response. The previous radio was wired independently of the ignition. Here’s the weird thing; the amperage draw does not decrease when fuses are pulled. I could not isolate the draw by pulling any individual fuse, so I pulled all 4 of them simultaneously. The draw did not decrease at all. Is it possible that I have a primary ground (earth) problem somewhere? To measure the drain, I removed the negative battery terminal and hooked up the multimeter in series with the battery and terminal. Thanks.
 
If you are storing a car unused for a period an isolator switch is a good idea anyway. In fact as the hooks are a pain a switch is helpful for any work.
 
For isolation, here is what I did. Note that any changed earth strap needs to be covered with shrink wrap.
6rOQ5jS.jpg

My reading of S1 electrics gives no mention of radio connection. Is this your case - only 4 fuses, and S1 in 1971? Nor does the S2 circuit diagram mention radio pickup point???? Does the draw drop if radio is disconnected? Does the radio have its own inline fuse - common in my experience. If there is no inline fuse you may have to chase its supply to find where it picks up power.
Correction - one of my S2 diagrams shows point 73 as radio pickup point, connected to fuse at 76(23-24), for heater motor. The way its show is that the radio is unfused, possibly relying on most radios having their own inline fuse.
 
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I drilled a hole in the battery cover for the disconnect switch so that the toggle can be operated from the outside. This protects the cables behind the cover. I'll send you a picture when I get back from my holiday in the UK.
 
jp928 said:
For isolation, here is what I did. Note that any changed earth strap needs to be covered with shrink wrap.
6rOQ5jS.jpg

My reading of S1 electrics gives no mention of radio connection. Is this your case - only 4 fuses, and S1 in 1971? Nor does the S2 circuit diagram mention radio pickup point???? Does the draw drop if radio is disconnected? Does the radio have its own inline fuse - common in my experience. If there is no inline fuse you may have to chase its supply to find where it picks up power.
Correction - one of my S2 diagrams shows point 73 as radio pickup point, connected to fuse at 76(23-24), for heater motor. The way its show is that the radio is unfused, possibly relying on most radios having their own inline fuse.
Click to expand...
The car is a crossover, having some S1 and some S2 characteristics. The radio was installed by an audio specialist. The radio itself has an internal fuse. I will have to check to see if there is an in line fuse. With the radio disconnected the draw is 1.2 ma, which seems excessive in itself. With the radio connected the draw jumps to 178 ma. I plan on disconnecting the alternator to see if it is drawing current. Thank you.
 
Bernd said:
I drilled a hole in the battery cover for the disconnect switch so that the toggle can be operated from the outside. This protects the cables behind the cover. I'll send you a picture when I get back from my holiday in the UK.
Click to expand...
Thank you
 
PeterZRH said:
If you are storing a car unused for a period an isolator switch is a good idea anyway. In fact as the hooks are a pain a switch is helpful for any work.
Click to expand...
Peter-I replaced the externally regulated alternator on this car with an internally regular one over a year ago. Could this have something to do with the excessive draw?
 
finfont said:
Peter-I replaced the externally regulated alternator on this car with an internally regular one over a year ago. Could this have something to do with the excessive draw?
Click to expand...

Not impossible - pull the alternator connector and find out.
 
If you dont put an isolator switch in , to be opened when its parked for a period, I suggest you supply the radio outside the ignition. Look up the model and see if it has separate unswitched and switched inputs, and implement such connections - that should see the ignition off drain right down.
1.2Ma means it will take 800 hours (> 1 month) to pull 1 AH, which shouldnt cause any problems. See if you can catch the clock winding drain.

My reading of the fusing in S1 cars is the headlights are NOT fused - true???
 
I have the same switch type due to be installed. What I actually did is bought two new ground cables which are insulated. The are super cheap. I think £20. I'll mount the switch on the structural member in the corner of the boot and the cable ground to the same point as before, the cable exiting the battery cover in the same place the positive cable comes out.

Probably the neatest method would be to cut out a hole in the top of the battery box.

I think anyone with a car that's not used for extended period or who frequently works on their vehicle should fit one of these. And that would include probably all of the audience here!
 
PeterZRH said:
Or you can't be bothered with the faff of removing the cover each time:) In which case you might as well pull the cable anyway.
Click to expand...

Oh, yes of course. it depends on whether you just want to turn a switch or twirl a spanner. :hmm:

Colin
 
jp928 said:
If you dont put an isolator switch in , to be opened when its parked for a period, I suggest you supply the radio outside the ignition. Look up the model and see if it has separate unswitched and switched inputs, and implement such connections - that should see the ignition off drain right down.
1.2Ma means it will take 800 hours (> 1 month) to pull 1 AH, which shouldnt cause any problems. See if you can catch the clock winding drain.

My reading of the fusing in S1 cars is the headlights are NOT fused - true???
Click to expand...
I am going to install a switch . The radio draws about 175 ma. Disconnecting the alternator does not affect draw which remains at 1.20 ma. with all fuses removed. Thank you for your time. Drew
 
jp928 said:
If you dont put an isolator switch in , to be opened when its parked for a period, I suggest you supply the radio outside the ignition. Look up the model and see if it has separate unswitched and switched inputs, and implement such connections - that should see the ignition off drain right down.
1.2Ma means it will take 800 hours (> 1 month) to pull 1 AH, which shouldnt cause any problems. See if you can catch the clock winding drain.

My reading of the fusing in S1 cars is the headlights are NOT fused - true???
Click to expand...
I think you are correct re the headlights, but, will check.
 
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