help regarding current draw

[BABASON]

Everytime i suspect i have a battery drain I connect up a multimeter, in series to the battery and try eliminate drain by pulling fuses and various components untill the current reading drops to manufacturer spec.

But this always seems to blow the fuse on my meters. I understand that this is due to the surge of current going through the meter being more than the fuse amperage in the meter. I was using a 20amp max meter. and changed to a 30amp max meter, still same problem.

The question is How can I measure amps draw without the risk of blowing meters and get an accurate figure.

I have tried using my pico scope and can not make head or tail of the readings. Although thats my fault because Iam still coming to grips on how to use a scope properly.
can anyone tell me the correct amp clamp to use for the this procedure using the picoscope and exactly how to connect it up and interprete the data.

alternatively the CORRECT way to use a meter and not blow the fuses, or is there another too I can use ????

thanking you all in advance.

 

[sixpack]

current draw

Hi Babason,
connecting a meter in series with the battery can upset some electronic bits so the reading you get may not be accurate anyway. If you have a digital meter you could try measuring the voltage drop over a section of the battery + lead. That way nothing is disconnected. The reading would only be in the region of a few millivolts but most digital meters should read this, Ive used my Fluke 75 like this in the past. I dont know if the Pico reads low DC, but it would be a bit fiddly to use on a car anyway. I dont think a clamp type ammeter would read low enough to see the current you are expecting, Ive never used one so cant say. Final thought, using your original idea of multimeter in series with main feed, put a diode across the meter so it wont see any more than the forward drop, about .6 volt.
Hope this helps
Peter

 

[Ian Parkin]

You cant use a clamp meter for dc
a way round the problem of high current draw whilst reconnecting the battery is to connect it and let the car settle down then attach meter leads (one to battery post one to lead ) and carefully disconect the battery so the meter will then read the small cuurent draw which hopefully with the car at rest nothing switched on should be less than an amp.
ian

 

[BABASON]

Thanks guys I have read both replies and they make good sense but, Iam now in the middle of a job and can not digest and reply inteligently at moment but will post another reply later this evening (yes I know its sunday, and Iam mad)

thanks for taking time to reply.

 

[Ellsy Tanners]

The way i conduct the test is to clamp a pair of mull grips to the battery post, then hang the vehicle lead onto this, which gives good continunity for when you lock the car and allows the car to settle.

Then with the multi meter already connected as per before, you can just lift the lead of the mull grip and there is no break in continunity and begin the test, then the same for ending the test.

Make a note witch fuse goes where and don't replace the fuse,s until you have done the whole fuse board. As you replace the fuse,s it wakes every thing back up a give higher readings until it settles down again and so on!!

Its hard to explain but i hope that helps

 

[turnipsock]

Why not get a bulb and then connect it accross the fuse contacts (with the fuse removed)?

The bulb will glow brighter on the circuits that are drawing the most current.

Then you can put your ampmeter in place of the bulb without the risk of blowing the fuse in the meter. Don't put the meter anywhere the bulb is glowing brightly.

30 amps is a lot of current.