[ASK] Measuring car's current consumption during ignition. - Page 1
Forum section: electronics / projects

author: BravoV
author_rank: Super Contributor
timestamp: April 07, 2016, 11:52:27 am
content: When it comes to car's electronic, as an enthusiast I'm abit scared, to be honest had few board toasted when I was a noob back then, was thinking the 12 volt rail was clean since it was sourced from battery , well, hard lesson learned and learned really fast about TVS too.Now, I have a friend asking whether I can help with my handheld Tek scope, coupled with Hall effect sensor, put battery to power the sensor, totally separated from the car's system. Feeling abit nervous to be honest, especially my scope.Question, is this sensor good enough for the job ? Please, don't suggest me to buy a high bandwidth current sensor for scope, thats beyond our's pocket depth.The sensor I'm talking is Tamura model L03S600D15 which is rated current at 600 Amps ->PDF datasheetor the product's page ->L03S Family, Linear Open Loop current sensorsAny comments or suggestions are welcomed, tia.

author: Miyuki
author_rank: Frequent Contributor
timestamp: April 07, 2016, 12:04:43 pm
content: What do you wan to measure ?

author: nctnico
author_rank: Super Contributor
timestamp: April 07, 2016, 12:07:39 pm
content: If you are using a battery powered handheld scope I'd use a good old current shunt. They are very resillient against short high current peaks and have an excellent frequency response.

author: BravoV
author_rank: Super Contributor
timestamp: April 07, 2016, 03:35:04 pm
content: Quote from: nctnico on April 07, 2016, 12:07:39 pmYou mean like these below that have been gathering dust for years in my junk box ?

author: max_torque
author_rank: Super Contributor
timestamp: April 07, 2016, 07:58:03 pm
content: What "Current" do you want to measure?ie, the starting current will be 600Amps of so, for several seconds, but the current to say an individual ignition coil will be around 5 to 8amps for 4ms, and the current to say the engine coolant temp sensor around 1mA.Until you know what you want to measure, then it's hard to suggest a suitable sensor!Also, what is the bandwidth of your hand held scope, and what is it's input impedance and probe scaling capability etc?

author: BravoV
author_rank: Super Contributor
timestamp: April 08, 2016, 02:14:38 am
content: Quote from: max_torque on April 07, 2016, 07:58:03 pmThe overall bulk current from the battery supplied to the car, until the car's engine is fully on.Quote from: max_torque on April 07, 2016, 07:58:03 pm60 Mhz with probe scaling 10X.

author: floobydust
author_rank: Super Contributor
timestamp: April 08, 2016, 04:58:06 am
content: Is this for temporary measurements? You want to measure current in two or three places - alternator output, battery output and vehicle current drain.I use hall effect clamp-on probes to measure vehicle/alternator/battery current. LikeFluke i310sThey drift a lot with temperature so you constantly have to zero it. Good to 20kHz.Here's a DIY one using hall-effect sensor from RC Groups forumhttp://www.rcgroups.com/forums/showthread.php?t=1145870Hard part is splitting up and grinding the ferrite core.

author: tautech
author_rank: Super Contributor
timestamp: April 08, 2016, 05:29:14 am
content: Quote from: BravoV on April 08, 2016, 02:14:38 amFor what good reason?I don't get what you are trying to prove.For any one particular vehicle starting current measurements could be affected by all or any of the following:Battery CCA capacityBattery state of chargeMotor warm or coldTime of year (ambient temp)Age of motorCondition of starter

author: Miyuki
author_rank: Frequent Contributor
timestamp: April 08, 2016, 06:27:27 am
content: Older cars used to have this measure at dashboardbut without starter, it have its rated power so why measure it ?

author: notsob
author_rank: Frequent Contributor
timestamp: April 08, 2016, 06:34:06 am
content: If you just want indicative measurement, they used these in a workshop when I was many years younger, just hold the semi circular rear of the meter against the starter leadhttp://www.stuttgartperformanceengineering.com/inductiveammater.html

author: cat87
author_rank: Regular Contributor
timestamp: April 12, 2016, 01:38:00 pm
content: If the setup is as you say, then it should be quite safe. Everything is isolated and floating, so no chance of getting return currents. Also, the voltages involved aren't that high, so again, you're safe....no reason to feel nervous.That Tamura seems like it'll get the job done, if what you just want to measure the peak current value. I see it takes a lot of current before saturating, so for a small car it should be OK. The thing I don't understand is that you mentioned hooking up the scope to a Hall effect (current ?) sensor and the Tamura, from what I understand, is just a magnetic type, which means you'll only get a spike on your scope corresponding to the initial current pulse (maybe when starting the car)....that again, maybe I'm missing something....

author: Brutte
author_rank: Frequent Contributor
timestamp: April 13, 2016, 10:29:00 am
content: Quote from: BravoV on April 07, 2016, 11:52:27 amEverything depends on the bandwidth and accuracy of the measurement and the depth of your pocket.From what I understand you do not need a 0,001% accuracy. Typically batteries are tied to starters with a stranded copper wire of decent thickness (with beefy clamps at the ends so your sensor won't fit). How about measuring Cu cross section? That way you can find out the linear resistance. Copper does change specific resistance with temperature slightly but that should be easy to compensate if you accepted 2-3% errors. The advantage is that you do not need any serious hardware or tweaks, just two thin wires. And no bandwidth limitations.

author: zlymex
author_rank: Frequent Contributor
timestamp: April 13, 2016, 11:53:34 am
content: I have a Fluke 319 clamp meter, there is a key(and function) specifically for inrush current.They didn't say much about it except 'Integration time 100 ms'http://media.fluke.com/documents/317-319_umeng0000.pdf