Parasitic Draw Test on Battery
Mike RoenDescription
In this video, Mike covers a parasitic draw test for checking for, or measuring a draw on the battery of your Harley Davidson.
Always be sure that you are using a quality, known good battery in your motorcycle. Sometimes an owner may be looking for a parasitic draw, but is really only dealing with a weak battery. The only way to definitively determine a battery’s health is to have it professionally load tested at a local garage. Fully charge a battery before performing a load test.
When testing for a parasitic draw, it is important to use a multimeter that has a DC AMP setting. This setting is used for measuring amps or milliamps.
Disconnect the ground cable from the battery. Connect the multimeter with alligator clips. One lead needs to be connected to the battery’s negative post and the other lead, to the negative battery cable. Now, read the meter’s result and compare it to the spec in your electrical manual. Different years and models will vary greatly. A touring Milwaukee Eight or Twin Cam that has a radio, and alarm system will have more draw on a battery than a Softail or Sportster.
When trying to determine the source of a parasitic draw, start by looking at any accessories that may have been added to the motorcycle. Those are a common source of voltage draw. Especially when that electrical component may not have been specifically engineered for the motorcycle. Otherwise, unplug one electrical component at a time until the meter indicates that the draw has diminished.
You have to watch all the videos in this multi-hour project series:
Okay, got another little bonus tech tip for you here and you're not gonna find this in your manual anywhere. But what we've, what we're gonna do is just kind of measure the amount of draw on the system as it's just sitting, not running. Now, there's a lot of people putting a lot of accessories on their motorcycles these days, a lot of stereo equipment, a lot of lighting, a lot of whatever, And you know, so they, they kind of start chasing their tail. You know, they, they put a regulator rectifier in it, you know, their battery's gone dead is what's happening. So they, they buy a new battery and then a week goes by and their battery's dead. So they buy a starter, a stater, a regulator rectifier and continually it's going dead. Well, they've got a draw in the system. So I'm gonna show you a way to measure that. Get your volt-ohm-meter and you take the positive here and put it over this slot, turn it to DC amps. Now you can see I've got the negative cable disconnected from the battery and what I'm gonna do is just measure this. Go ahead and connect this there and what's gonna happen when I connect these, is it's going to energize the ECU and it's gonna kind of spike on the number. You hear that? The ECU is getting energized. Now you gotta wait probably 10, 15 seconds. Watch that value go down. And that's gonna be the value for your motorcycle. If you've got a bagger, it's probably gonna be a lot higher number. In fact, if I can, it's down to zero almost. That's because this came off. Let's go like this. Okay, energize ECU, let it drop back down. Typically, it's gonna sit around there somewhere. Now, what I'm gonna do is I'm gonna trip the trip meter button here just to show you what the draw is. You can see it kind of illuminate the dashboard there and spike back up. So once you get the value for your motorcycle, and if it, you have a problem with the discharging, you can do this test to see where it's at. Now, what I've seen in the past, for whatever reason we had an ECU that was draining the guy's battery and it ended up needing an ECU, which unfortunately, even an independent shop like me. can't replace because I can buy the ECU, but I can't download the base map for that particular model. So if it was something like that, you'd have to take it to Harley and have digital tech married to the bike. But, that's just a, you know, a nice little tech tip to show you, you know, how to verify if you do have a draw in the system somewhere.
found mike;s description of what he was doing and why he was hooking up the meter very poor.