How to identify and locate a parasitic drain

we're going to demonstrate how to perform a parasitic drain test so this is a test that you perform whenever you have a battery that continues to die um we're measuring the amount of of drain or current that's flowing out of the battery when everything should be turned off at night when you shut the key off and shut all of your doors everything in the car should be off but often there are still things that remain on and continue to drain the battery so to test this we come to the battery and the first thing we want to do is measure the amount of current flowing out of the battery but we'll start by making sure that all the doors are closed sometimes it'll be helpful later to get inside of the car so what we can do here is come and open the the driver's door and then trick the car into believing that the door is closed if there's a door jam switch anywhere we can uh trip that switch so that it's it thinks it's closed in this case the switch is actually in the latch and so we can we can trick that door trick the car into thinking the door is closed by flipping that latch over now as far as the car is concerned the door is closed in other cases you might find a a switch right over here or a switch up in this area that you just need to make sure it's pressed but but we've got the car assuming the door is closed we come back to the battery and now we're going to use our multimeter to measure current some people have asked if you can use an amp clamp here and the answer is usually no current probes are not accurate enough for the small amount of current that we're going to be measuring so what we need to do is is open up the circuit disconnect the negative battery cable and connect the multimeter in series so any current that's flowing out of the battery has to flow through the multimeter he's using pliers here because sometimes it's difficult to uh get your alligator clips on your multimeter to fit around battery terminal so just using the pliers as a as a way to connect so connect one one lead to the battery terminal is what we've done here right and the other lead to the battery cable now if there's any current flowing out of the battery into the vehicle it should show up of course when we're measuring current we need to we need to come over here and move the red lead move it over to the amp setting the reason we want to go to the Y and we set it on amps here and on the amp setting you usually have two options we have amps or milliamps I would recommend that you always use the amp setting it's got It's fused at 10 amps on this meter some meters it's 20 amps use that setting because we don't know how much this is but it's less than 10 amps I'm sure if we go here we have a a high probability of blowing the fuse it's only fused at about half of an amp or in this case it says 400 milliamps so so don't use this setting use the amp setting we've got the set of amps it's telling us right now we have 2.5 amps that's a lot the rule of thumb is that it should be 30 mamps or less basically if you want to if you want to know why if you have one amp flowing out of a battery your battery will last about 24 hours before it won't start the car anymore so you can see at this rate now we're at 3 amps 2 and a half at this rate it won't even last two or three hours just a just a fraction of a day so we sit here and we watch this now you can see that going down what's happening is the computers on the car are going to sleep we woke them all up when we opened the door a minute ago or when we reconnected the battery you could use a memory saver here when you disconnect the battery if you want to so you don't use memory lose the memory in the vehicle but you got to make sure that the memory saver is removed from the car before you take this measurement otherwise you could have two sources of current flowing into the car and this measurement is now accurate so now we're down to 250 milliamps that's better but that's still about 10 times more than we'd like it to be we'd like it to be 30 milliamps or less which is 030 amps so you should let this sit for about 30 minutes and allow all the computers to time out it may take less time than that but uh if it does take that long you need to make sure that everything has a chance to go to sleep before you take this measurement you also might look around to see if there are other things you know just just take a glance around the car do you see a glove box that's left open do you see you see a light on in the trunk maybe a a dash light or a dome light that's left on make sure all of those things are turned off and look for a a switch like this this has a a hood switch and so we need to unplug or disable that somehow we don't want the car to think that the hood is open and make sure there are no hood lights underneath the hood so nothing is on and oh it looks like by pushing that hood switch we caused it to wake up again so we'll wait for a little bit and we'll watch this and see where it ends up okay we're back it's been 30 minutes we' still got a pretty significant parasitic drain so this is the first step of the parasitic drain test is to measure how much current is draining from the battery and to see if it's uh more or less than the than the minimum which is or the maximum I'm sorry which is 30 milliamps once we've determined we do have a drain now we need to isolate where that drain is and narrow it down the easiest way to do this is to go to the fuse box there are two fuse boxes on most cars this one has one fuse box here by the battery has another fuse box in underneath of the the dash that's why we open the door before we started and tripped the door switch in the olden days we used to come to the fuse box and start pulling out fuses to see which one would make the go the drain go away but we have so many computers on board now that all that does is cause additional problems it'll cause computers to wake up it'll cause things to shut down and it'll uh it'll leave us confused so rather than pulling any fuses we should be stealthy about this we don't want the Cardon over here but here's the secret if there is current flowing out of this battery and flowing through one of these fuses we'll have slight voltage drop across the back of the fuse we've got two little terminals on the back of each fuse and so what we're going to do is we're going to get uh we have another meter here you could use the same meter if you wanted to pull it out of your your circuit but we have another meter we've got it set on volts and actually let's turn it to Mill volts we're going to be looking for even a fraction of a mill volt being dropped across each fuse so now we'll come over and one one fuse at a time you hold it on there just long enough to see if it goes to zero and it should go to 0.0000 hold those leads steady when they go to zero that means there is no current flowing and those fuses are not part of the problem again just to reiterate while he's performing this test there are two two steps to this the first step is to measure current flowing out of the battery the second step is if there is a parasitic drain to go and measure individual fuses and we're measuring the voltage rather than the current here we're measuring the voltage dropped across each fuse okay so now we're we're measuring one of these fuses and what we see is he's measuring across the back of that fuse is there is a little bit of voltage drop fact it says here that we have I can get that it says here that we have about two to three Mill volts it's varying a little bit whatever that that drain is it's changing and that's from from one side of the fuse to the other side of the fuse right here again that should be zero but if you're measuring something it's because there is current flowing through that fuse so the next step is to figure out what fuse that is go to the wiring diagram and find out for example if that's a u a fuse that leads to the radio we'd want to get the diagram for that and find out how to to narrow that down we want to continue to check fuses too we may find that there are other other fuses that have drains as well but anything besides zero .0 when you're measuring this voltage drop is something that we should be concerned about anyway that's how you narrow this down that's how you that's how you measure voltage drop and that's how you determine which circuit has I'm sorry that's how you measure a parasitic drain and that's how you determine which circuit has the drain in it is by performing those steps now one last thing when it comes to connecting connecting your multimeter again there's nothing complicated here we've connected connected the multimeter so that it's in series we just disconnected the battery the multimeter in series with the the battery terminal so all the current flowing out of the battery has to go through the multimeter and we read it over here it's it's changing again we we've just uh opened the door it's changing but there is a tool that makes this easier got this parasitic drain tool and all it is is a battery shut off switch you open and close the switch by turning that knob let's go ahead and hook it up and show it how how it this connects here so this parasitic drain tool just goes onto the battery post like this all it is is a battery shut off switch that somebody has adapted into a a tool to make this easier and then we connect the battery cable so this is an option this isn't required but this this tool is made for to make measuring parasitic drain easier all it is is a battery shut off switch that someone has adapted for this purpose they put a a battery terminal a battery post on one end and so it connects onto the battery cable and then it fits over onto the battery terminal on this end and it has two small pins that are used so that you can connect your alligator clips of your multimeter one on this side that's connected to the battery terminal and then one on the on the back side down there there's a pin right down there it connects onto it and once we have our our leads on there now we now we have the current flowing directly through this well this closes the current flows through the tool when this is closed and when I open it when I open that switch like this current now has to flow through the multimeter and we'd read it on the multimeter screen so it's just another way of doing it it makes it a little bit easier so the first thing we need to do is disconnect the negative battery cable it's been loosened remove it with that disconnected now we need to hook the meter up in series with that so we basically reconnecting the battery to the cable with our multimeter so we hook hook now at clip onto the cable and hook the other lead onto the terminal however it's pretty difficult to get that to clip on there um so here's an idea if you if you can't get your clip to fit onto the battery terminal we have a pair of pliers locking pliers like these here clamp that down onto the terminal and that gives us something else that we can clamp onto that will make this easier by clipping onto that it makes it makes it so that we've got a good connection and now we can take our measurement

Channel: Justin Miller

Views: 1,190,468

Keywords: parasitic, drain, key off, key-off, parasitic drain, draw, parasitic draw, key-off draw, how to, locate, find, ammeter, multimeter, voltmeter, fuses, voltage, drop, voltage drop, circuit, draining, battery, dead, dead battery, cause, causing

Id: YhC8xj5vHUg

Length: 12min 35sec (755 seconds)

Published: Wed Apr 29 2015