The Trainer #28: Testing Battery/Starting/Charging Systems

Not too long ago, I got a call late in the evening from my youngest son's girlfriend. Her Ford Explorer wouldn't start, she said, and could I please come and help? What was I going to do, say no?
I grabbed a meter and some basic tools and drove over to see what the problem was. It didn't take long to discover that the negative battery cable end had been replaced with one of those aftermarket clamp-style ends and it was spinning freely on the battery's ground post, a classic case of voltage drop. The connection was enough to allow the lights to work, but as soon as the high current demand from the starter tried to make its way through, the connection gave up and went open. I removed the clamp and cleaned the connection, then reattached the cable to the battery and tightened it up. She started the truck right up and I told her to stop by the next day so I could make a more permanent repair and check out the rest of the system.
Did she listen? Of course, not...she's a kid.
The next night I got another call from her, with the same complaint. Only this time the fault wasn't a matter of voltage drop but of voltage period. When I arrived the battery only read 8.64 volts, nowhere near enough to start the Ford's 4.0-liter engine. Heck, not enough to start my lawn mower's engine! But why is there a problem with the battery now, just a day later, when the truck started fine last night and all during the day?
When you have a problem with the "no crank" or "slow crank", you need to make sure you test both the battery and starting system to see where the culprit lies. And if the battery is weak, you need to know why. Is there a problem with excessive resistance in the cables, like I had the first night? Is the charging system doing its job to keep the battery healthy? Or did the battery just die of old age or neglect?
#battery_service #battery_testing #howtotestabattery

[@mike-yp1uk]

Great video it's always cool to show some bad scope patterns to identify bad powers and grounds or bad solenoid or brushes. Thanks for the video

[@MotorAgeMagazine]

For those that don't know, a battery may read much higher than the ideal 12.6. Doesn't mean it's bad. This is "surface charge" and can be reduced by using the 3-start DMM method shown in the video or just turning the lights on for a few minutes. Thanks for the comment!

[@stuzman52]

Hey Pete, nice work! Yes, the scope shows a lot more info that just using a DVOM. Thanks for the video.

[@user-nw9kc7dz3l]

I have used in the past a very great tool , from NAPA Auto parts ; this tool , tests : battery , starting system , and charging system , except voltage drop , and this tool even tell when a battery has one bad cell . And I remember , after testing the battery , with a bad cell and tool message suggesting to replace battery , . I recommended battery , customer said , I don't even have starting problems , so he declined replacement . One week later , customer came back to shop , vehicle did not start due to bad battery 🤣🤣 I done all those tests , still learning watching your video .👍👍👏

[@nickayivor8432]

Good Afternoon Pete Meier motor age Take care and have a great day 👍 Great tutorial thank you 👍 From Nick Ayivor from London England UK 🇬🇧

[@spelunkerd]

Nice job, Pete. Next time I have a starter problem I'll put a DSO with an inductive current probe on, to look at the waveform. Lots more info.

[@billsmith2212]

Pete : At 11:05 you mentioned " diodes OK " . I recently purchased a Model 725 Battery and Charging System Tester from Electronic Specialties . On the menu is a check for ripple voltage from the alternator . In old cars that had a red light on the dash that would go on if you were not charging , it would also glow red with the key off if you had a bad diode . The diode no longer blocked current from draining the battery . I am dealing with a friend's 2002 Taurus , 3.0L , 24 OHV , with some " low voltage cranking issues " . The alternator is HORRIBLY buried and makes that test almost impossible . On newer cars , excessive ripple voltage ( bad diode or diodes - there are several ) would give you a UNFUSED , PARASIDIC DRAIN - with the key off . My point is for the few EXTRA SECONDS it takes on one of these testers to eliminate that from the list , it is time well spent . Just think of the time wasted if you were going to start chasing an UNFUSED PARASIDIC DRAIN . It's also one less chance for a comeback . Thanks for your information .

[@wave3151]

9.9v with battery loading test with DMM, 8.7(?)v In Rush Voltage with Scope test Why is that so different ? simply DMM can't update that fast of Scope or something else? Which method is more reliable or preferrable ? Thanks

[@aaronarmelin616]

what brand DMM is being used in the video?

[@MotorAgeMagazine]

The DMM shown in the video is made by UEI and my personal meter.

[@leomcalla29]

hi, what should be the minimum on the loaded voltage. you gave 9.6v for the DVM and 8.5v for the scope.

[@MotorAgeMagazine]

The short answer is "both"! The digital multimeter doesn't sample as fast as a scope, and doesn't catch the inrush voltage like the scope does.

[@leomcalla29]

Motor Age thank you, after watching the video a second time I got it. thanks again!

[@bmw-e30]

A battery tester shows that my battery only has 50% of its original cranking amps and voltage generally in the morning shows 12.2volts. While this is low and the battery is on the way out, it still has no problem starting the car. Is this state hard on an alternator I wonder or does it matter?

[@MotorAgeMagazine]

MsCelicagt4 Yes, it is. I am betting a higher than normal amperage demand on the alternator, which means more heat...not good.

[@bmw-e30]

Thank you very much for reply.

[@alejandroamaro8303]

i want to get an oscilloscope. but have no direction since i dont know brands or where to start with. any suggestion ? great video btw

[@MotorAgeMagazine]

+Alejandro Amaro Choosing a scope is like choosing a girl. It's all about the features you want and what you can afford. Scopes range from pocket sized one channel units to PC-based 8 channel scopes. Check your shop's scan tool - many have scopes built in or offer add on modules for the existing tool.

[@alejandroamaro8303]

+Motor Age but would the pocket sized ones update fast enough catch a glitch on say.. a TPS sensor as i do a sweep test ? Im a begginer DYIer and am learning automotive electrical systems. i want a scanner and a scope but cant afford good ones yet. i just want something reliable with good update frequencies so i can be sure i make a right call on stuff. btw, thanks for all the time you put into making your videos. i am learning alot from them

[@MotorAgeMagazine]

Oh yeah, the UScope is a highly capable scope. But I will admit, I like at least two channels so that I can compare. For example, if you do a relative compression test you'll know you have a weak cylinder with one channel but not WHICH one. With a second channel, I can add a reference signal (like an ignition trigger) that will tell me so much more.

[@alejandroamaro8303]

+Motor Age oh. so 2 chanels is better? ive seen some with 8 channels

[@MotorAgeMagazine]

My personal recommendation is 2 channels at a minimum for every day shop use.

[@nickayivor8432]

PRODIGY Sir Pete Meier Motor Age My teacher Thank you very much for sharing it Take care and have a great Evening PRODIGY Sir Pete Meier Motor Age From Nick Ayivor from London England UK 🇬🇧

[@rq11561]

first one