Automotive current draw measurement and data logging

Ask any questions relating to the PicoScope hardware or kit contents here.
If you have any questions prior to purchasing the kit post them here.

Automotive current draw measurement and data logging

Postby chriso » Sat Jan 05, 2008 12:04 pm

Hello
I am intrested in how your data logger / oscilloscopes can help me measure , log and display current draw from a vehicle to assist fault finding flat battery concern. Measuring bus sleep time and wake up.
How is this measured eg a current clamp. I have never used a scope /datalogger for this function. I presently use a multimeter that has pc interface and a velleman hand held scope. :)
chriso
Newbie
 
Posts: 2
Joined: Sat Jan 05, 2008 11:42 am
Location: Australia

Postby picojohn » Wed Jan 09, 2008 2:06 pm

Hello Chriso,

Do you wish to monitor current in a moving or stationary vehicle and how frequently do you wish to measure and over what period of time?

Also, what maximum and minimum current will you measure and what resolution do you require?

Could you also please explain the significance of 'Measuring bus sleep time and wake up' in your application?

Regards
John
picojohn
Site Admin
Site Admin
 
Posts: 4
Joined: Mon Jun 11, 2007 1:10 pm

Postby Carl Grotti » Wed Jan 09, 2008 10:10 pm

Hi John,

It appears as though Crisco is investigating an elusive parasitc load. Personally, I've never seen a need to log something like this for long periods of time. All the modules on board should typically power down in 45 minutes or less. Maybe he has a node waking up and unable to catch it with normal procedures.

Of course, this is all speculation on my part until more information is given. However, if something like a 12 hour recording is wanted, maybe PicoLog would suit his needs since a high sampling rate would not be needed for something like this. Also, I can't imagine needing a voltage reading anything higher than 200mV since he is probably using a current probe that would reflect 100mV/Amp. The "bus" that was mentioned could be a CAN bus system I guess. Speculation once again.

Crisco,

A little more information and John can certainly point you towards an easy solution.

Regards,
Carl
User avatar
Carl Grotti
User
User
 
Posts: 32
Joined: Thu Nov 21, 2002 5:17 am
Location: Missouri, USA

Automotive current draw measurement and data logging

Postby chriso » Thu Jan 10, 2008 12:25 pm

Thank you for the replys.
I am certainly chasing the elusive parasitc load. The need to log this is to try to determine what is responcible for repeat flat battery concern. Senario: Holden commodore 08 model year. Same car as the new pontiac G8 in the USA :) or VXR8 in the UK. Vehicle has High and low speed can bus and a regulated voltage controlled charging system. This condition occurs when the vehicle is off and parked key out and locked for between 5 hours to 48 hours. Can-bus shut down time on this vehicle is 15min. A data logging multimeter in series between battery and negative lead reveales a current draw at start of teat of aprox 1.5A and 15min later this has reached a 10 -20 mA as it should. but if the meter is left on vehicle for 5 hours plus on a min/max setting there is a high of 300ma(only on one occcasion) on the meter that has occured at some time through the test but when i return to view it is back down to 10mA. the vehicle has 10-12 low speed moduels and 6 high speed and count less other things that could have caused this. I am inquiring as to the correct product could capture this so i can determine how long the current stayes above the 10-20 mA spec. I am in the market for a PC scope ( for sensor testing and genera diagnosis) but am unsure if a data logger is what i need to do the above test or which scope i need. Can the PP264 clamp be used to avoid open circuiting the battery. We see aprox 2-3 high level cars a week with this concern( by that i mean DVD, Tyre pr monitoring, ect) repete tests with meter connected befor the battery is disconnected has found no high current draw that could cause battery discharge this quick. I am unsure what resolution i would require in a scope / data logger. Can one unit do both. Thank you. form Chriso.
chriso
Newbie
 
Posts: 2
Joined: Sat Jan 05, 2008 11:42 am
Location: Australia

Parasitic Draw.

Postby Autonerdz » Thu Jan 10, 2008 6:05 pm

Chriso,

A low current probe like the PP264 would allow you to monitor this without circuit intrusion. Two issues with the PP264. One is that the jaws are too small to go over a battery cable. The second is battery life. Put in a fresh battery for a long test. You may have some zero drift over a long period.

For detail, a 3000 series automotive scope would be good for this. You would have to make sure the PC didn't go into hibernation or power down the USB. You could set up a trigger to capture the current rise and when this triggered, you would capture the event. You could set this up for a very long time base to be sure to catch the entire event. If it were to occur more than once, you would capture each of them up to 32 events.

Tom Roberts
(The Picotologist)
http://www.autonerdz.com
skype: autonerdz
THE PicoScope Automotive Authority
In North America
Tom Roberts
(The Picotologist)
Autonerdz
User avatar
Autonerdz
Zen Master
Zen Master
 
Posts: 265
Joined: Wed Nov 20, 2002 4:19 pm
Location: Washington State USA

Postby Guest » Sat Jan 12, 2008 4:26 am

Battery draws… I’ll jump in if you don’t mind, I’ve been down this road. I hope this helps you out and sheds some light on the subject. What follows is my experience working on battery draws for BMW, so I cannot help you with your car, but maybe this will help to answer your questions in general and show you how Pico can help.

The question begs asking as to why one should look at some sort of graph, and of course, how.

Todays vehicles use more and more electronics. And it’s only going to get worse. Electric vehicles, hydrogen vehicles, hybrids of all sorts. Control units that control other control units. The BMW 7 series has over 50 modules alone. Each one is programmed and coded. There is a central ‘Power Module’ that controls virtually all power to the vehicle. On the newer vehicles there is a microprocessor on the negative battery cable that monitors every electron. It sends the data it collects to the DME and other modules for processing. There is now an ‘Energy Diagnosis’ test plan built into the factory test equipment we can use to help determine the cause of a flat battery. The amount of data processed and presented can be overwhelming sometimes. There has been concern in the shop lately as to when too much information gets in the way.

The power module has the ability to shut off different circuits if it is determined that there is over 80ma of current leakage.

It can take up to 70 minutes for the vehicle to go to sleep. Different vehicle systems and creature comforts require this. The telephone control module for example: if a handset is plugged into the system, it can charge the handset battery for up to one hour. Furthermore, some TCU’s can cause 500ma spikes every 15min, lasting for 14hrs. This is normal behavior. The instrument cluster: you will see tiny spikes of about 200ma lasting about 2 seconds. The cluster is interrogating the outside temp sensor. But in order to calculate a correct outside temperature, you must also take into consideration the waste heat from the engine. In order to read the coolant temp sensor, you must wake the DME, which means waking up the PT-CAN bus, that’s 8amps for just under 5 minutes. It’ll do this at pre-determined time intervals. There is a basic draw of 200ma for the first 30-40 minutes while the system keeps the body relay active.

That brings us to the 8 minute rule. The power module is set to ignore draws that last under 8 minutes as they may be just normal activity. After 70 minutes, the circuits that are capable of being monitored begin being monitored. If the draw lasts only a few minutes, and then goes away, the circuit is never cut. This intermittent action can kill the battery even though the circuit is monitored. You need the graph. Because looking at the graph allows you to determine right away normal vs. not normal. You can tell even before the vehicle goes to sleep. What if the draw is on a monitored circuit, and you let the vehicle go to sleep, when you check for a draw… there is none.

You must also keep in mind that the software that runs all these modules is constantly being updated and improved, so what might be normal now, no longer is after a module change or vehicle squirt.

Sooo… Looking at the graph, you will be able to see what’s normal and what’s not. You will see if the PM cut the power, and you will see exactly how much leakage you have. 200ma – dome light, relay coil, etc. 8 amps – which control module is waking your bus?

My personal experience is that you need to see the graph. To do so, I use my old 212/3. It supports using Picolog. As far as I know, my 3423 is still incompatible w/Picolog (haven’t tested it in quite a while). I suggest using the logger because it’s tailor made for the job. There’s a software setting that you can use to scale your clamp properly. As far as readings and duration, set it up to take a reading once every second and set the total duration in seconds to whatever you want. This is more than enough detail and Picolog allows zooming etc.

I use the Prova 15 amp clamp to get the signal into the scope. It’s jaws are big enough to get around the negative cable and it scales from 0 - 400ma, 0 - 4 amps, and 0 - 30 amps. I can use it intermittently during the day and it’ll run overnight 3 to 4 nights before I have to replace the batteries. It also serves as my current ramper. For those quick checks, I hook it up to my Fluke 77. I created a reference chart that correlates the readings on the meter to the chosen amp clamp scale.

The Prova 15, like most other amp clamps is prone to saturation. The higher the current and the longer it lasts, the faster it will saturate. In all cases you will easily recognize it on the graph. Not to worry.

I’ve seen quite a few draws in my day. No two seem to be alike. They are all challenging, especially the intermittent ones. The trick in finding a draw isn’t in diagnosing where it’s leaking from, but getting it to leak. It leaves no stains.

The usual disclaimers apply and of course ymmv.

Jim / jperras

It would appear that I can no longer login as I've forgotten my password and the email I used to register is no longer valid :roll:
Guest
 

Postby Carl Grotti » Sat Jan 12, 2008 11:42 am

Thank you, Jim.

There are a few things I'd like to add to your post.

The PP264 current probe conductor clearance is quite capable of handling most battery terminations for parasitic load monitoring. An excess of 10mm is not that common. That current probe should work well with the vehicle Crisco has.

Like you mentioned, PicoLog does work with the 212/3 but not with the 3423. I can't tell you why that is.

Do we need to log all of this anyway? Just set to trigger on the wake-ups with the scope. That seemes simple enough.

Regards,
Carl
User avatar
Carl Grotti
User
User
 
Posts: 32
Joined: Thu Nov 21, 2002 5:17 am
Location: Missouri, USA

Ve Commodore flat battery

Postby Guest » Mon Oct 05, 2009 8:16 am

Hi in realtion to the battery going flat and trying to test the draw in the system, I dont know who or where you work but VE commodores have several things to try, firstly you have to check the possitive battery terminal under the bulk head and ensure it is not cross threaded on the nut and not loose, this can give the illusion of a fat battery more so when jumping from the posts under the bonnet, Yes most of the can-bus issues staying awake and were rectified to 15 mins but not the solution to all cases,Next there is now a revised piece of software comming out in the near future poss Nov from holden which reprograms the IPC ( Instrument Pannel Cluster ) as this is causing lots of issues with the battery going flat, they are pretty positive this is the answer to all of our prayers. This is something that should fix the problem on all VE commodores, It is in the worshop foreman handouts, so your local dealer should be able to confirm this for you if they look into it.
Guest
 


Return to Automotive kit hardware

Who is online

Users browsing this forum: No registered users and 1 guest