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Old 26th September 2021, 19:59   #11
bigblue75
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thanks for the thread, an affordable clamp meter able to read DC current would be a handy addition to the toolbox.

Last edited by bigblue75; 26th September 2021 at 20:01..
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Old 27th September 2021, 07:43   #12
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I agree, but didn't really want to start differentiating between the two as otherwise some may have thought I was being a pedant. Oh, I see that someone already has!

The reason I said that the two are the same for practical purposes is that most of the internet seems to use the term parasitic drain to describe the total of the two quantities (incorrectly I think you will agree, Mike)

If we do want to be pedantic, what I was doing was verifying that my car's post switch-off transient and long-term steady-state quiescent power consumption fell within expected bounds and was not excessively increased by the presence of parasitic power drains (consumptions). (Of course some of the quiescent drain will include drain due to parasitic effects within the electronic components)

Everyone happy?
Thank you for the explanation, the reason for asking was to find out if the instrument you are using can be used for tracing parasitic drain, I suppose it can be, since a reading of greater than 50mA, will need investigating to find the cause.
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Old 27th September 2021, 08:08   #13
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Thank you for the explanation, the reason for asking was to find out if the instrument you are using can be used for tracing parasitic drain, I suppose it can be, since a reading of greater than 50mA, will need investigating to find the cause.

Yes - it can - since anything above about 25mA will be indicating an amount of parasitic drain.

All you are really doing with the instrument is what you would do with a normal ammeter, which is to measure current flow from the battery to the car's electronics.
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Old 27th September 2021, 08:18   #14
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Yes - it can - since anything above about 25mA will be indicating an amount of parasitic drain.

All you are really doing with the instrument is what you would do with a normal ammeter, which is to measure current flow from the battery to the car's electronics.
Thanks MSS, good enough for me.
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Old 27th September 2021, 09:40   #15
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Yes - it can - since anything above about 25mA will be indicating an amount of parasitic drain.

All you are really doing with the instrument is what you would do with a normal ammeter, which is to measure current flow from the battery to the car's electronics.

Once you have found a parasitic drain the next important thing, but not as simple, is to find the circuit causing it, not as easy as simply finding the overall drain.


There are several ways of finding the circuit with the drain.


1) Pull each fuse in turn and measure the current, if any, across the fuse holder terminals, problem with this way it is time consuming and with many components these days that go into a progressive shut down, some up to 30 mins, it could take quite a while.


2) Measure the volt drop across each fuse whilst in situ, the fuse is a resistance in the circuit and acts like a shunt, on a circuit using no current there will be no volt drop, on a circuit using current, however small, there will be a volt drop, however small.


Using this volt drop reading and comparing it with a " Blade fuse voltage drop chart. " ( there are many to view and download on the internet ) it will give you the Amp draw across the fuse, bearing in mind it is important to read the column for the type of fuse, mini, standard, maxi.



This is a good 8 page PDF which covers all fuses that may be found on a car, go to here https://www.powerprobetek.com/knowle...e-drop-charts/ and just click on the chart it will download a PDF to store on your computer and you can then print them all off, or just the page you need.


The link is safe.



3) This way is a doddle, I have an Amp Hound, other than switching it on and selecting the type of fuse and applying the probes, all the calcs are done and the amps comes up on the screen, not cheap for a one off test, but worth it for the time it saves if used fairly frequently.


Hope this helps.
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Old 27th September 2021, 10:37   #16
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I have seen the Amp Hound in use and it is a handy tool for small workshops. For one off use, I think £80 could be better used on other more universal tools. But it does do what it is intended to do.

Personally, I would not recommend people to start messing about taking measurements in the fuse box unless they have fine probes intended for the purpose.

With the basic method, there is no need to spend excessive time waiting for systems to go back to sleep. A system powers down when a fuse is pulled. All one does is not put the fuse back in after it is pulled and fails to show an excessive current drain. The fuses can be pushed into a piece of cardboard as they are pulled out and then reinserted after the tests are complete. Also, there is no need to measure the current in each fuse holder. All you are looking for is a significant drop in the total current flow from/to the battery - a drop of 20mA or more when any one fuse is extracted will be highlighting a problem circuit as the total consumption for all circuits should only be around 25mA. I have not come across a case where shutting down one system wakes up another, but will happily accept others alternative view if anyone has found such an occurrence.

I did once experiment with hall effect sensors to see whether a reliable method could be devised by just placing the senor on top of the fuse. I didn't work well so was a no goer.

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Old 27th September 2021, 13:22   #17
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Taking a quick photo of the fusebox before you start removing fuses helps to prevent them going back in the wrong empty space.
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Old 27th September 2021, 14:18   #18
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Taking a quick photo of the fusebox before you start removing fuses helps to prevent them going back in the wrong empty space.

I'm afraid that's a bit too high-tech for us Rover drivers - I still use marked-up wooden clothes pegs to identify leads and pipes under the bonnet!
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Old 27th September 2021, 19:14   #19
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I'm afraid that's a bit too high-tech for us Rover drivers - I still use marked-up wooden clothes pegs to identify leads and pipes under the bonnet!


I used to do that too until the missus gave me hell for getting her washing oily.---
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Old 27th September 2021, 19:20   #20
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Quote:
Originally Posted by MSS View Post
I have seen the Amp Hound in use and it is a handy tool for small workshops. For one off use, I think £80 could be better used on other more universal tools. But it does do what it is intended to do.
I have one of these and indeed it is a good piece of kit (if I can ever get it back from my younger brother who uses it regularly on customers cars)
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