CDT quiescent drain measurement with clamp meter
 

In another thread a member mentioned the use of a clamp meter for measuring the quiescent current with a clamp meter.

Well, here it is being done earlier today just as a check.

Note the use of a brick to simulate closed bonnet.

https://the75andztclub.co.uk/forum/a...1&d=1632607692

Measurement at time 0 - a few seconds after car being locked with everything switched off

https://the75andztclub.co.uk/forum/a...1&d=1632607830


Measurement at 2 minutes (the drain reaches this value in a number of steps as systems shut down)

https://the75andztclub.co.uk/forum/a...1&d=1632607830


Measurement at 12 minutes

https://the75andztclub.co.uk/forum/a...1&d=1632608005


Measurement at 20 minutes

https://the75andztclub.co.uk/forum/a...1&d=1632608031


The final value is about 25mA.


I would accept up to 50mA but would definitely investigate if the final value was over 75mA


A clamp meter certainly makes taking these measurements rather straightforward. However, the cheap clamp meters are of no use as they only measure AC current. An AC/DC current clamp meter is required and the one being used here is the cheapest decent one of which I am aware. It is available for just over £40 to £50 from various suppliers. It is a UNI-T UT210E.


Some cars have more complex, multi-lead, connections to battery posts e.g. our Vauxhall Twintop. In that case I just use a jump lead to bring out a single lead for the clamp.

Have you read/heard about the Parkside one? If I recall, was about £15, only bought as a 'just in case' option in the tool bag. No idea how good or bad it is, but it seemingly does DC also. Can also be used as a normal meter too.

https://www.youtube.com/watch?v=wkMS...TechGuruAndrew

As far as I can see the Parkside does not measure DC current - only DC voltage.

This is the case with all the cheaper clamp meters - they either measure no DC at all or are stated to be AC/DC but only measure DC voltage..

The one I have comes with probes to plug into sockets at the bottom. So it can be used as a normal DVM but I prefer a standalone unit for general measurements.

I would never buy a measuring instrument from a supplier in China in order to save a few £.

If it is DOA or has any other issues, the buyer will at least have long wait, most likely have to return the faulty unit to China at his/her expense and possibly wasted the full amount for the sake of a few £.

My recommendation would always be to purchase from a reputable UK supplier such as Rapid, RS or CPC/Farnell as returns are easy and free.

Remember that UK buyer safeguards do not apply when buying from far-away places. Also, there is no contribution to the UK economy/tax revenue.

But, it's individual choice at the end of the day.

What do you mean when you say measuring quiescent current?, is it the same as finding parasitic drain?

For all practical purposes they are the same.

For an engineering pedantic like myself, the term I used is technically more correct. :}

don't you mean pedant? :getmecoat:

I think there is a distinct difference - quiescent current is the expected drain on the battery once all the ECUs have gone up the wooden hill to Bedfordshire, and parasitic drain is any extra current drain due to one or more faults.

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, or indeed demonstrate a level of pedantry, 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 but for our purposes they are an inherent part of the quiescent consumption.

Everyone happy? :}