battery/charging system - Mitsubishi-Forums.com
 
LinkBack Thread Tools
post #1 of 6 (permalink) Old 06-04-2019, 05:01 PM Thread Starter
Newbie
 
Join Date: Jun 2019
Posts: 4
battery/charging system

Despite the fact that my smart charger suggests the battery in a 2002 4 cylinder Mitsubishi Eclipse is ok, I donít think it is. How do I truly test the battery to find out if it is taking a charge and holding it.



So there are really two questions.



How do I know for sure the alternator is working? I have a scope (not automotive). Perhaps I could look across the output of the battery cables unhooked from the battery to see if there is a ripple (indicating a bad diode). I could look at voltage at the same time. I would love to measure the current, but am uncertain as to how to do that. I probably need to know the max current my multimeter can tolerate without frying it and couple it in series between the battery cables and the battery.

To test the battery, I suppose I need to place the battery under load and watch the rate of discharge. Maybe the most simple way is to take the battery to autozone and have them test it? Do I trust their setup to test the battery correctly?

Maybe the battery my friend has is a rebuilt battery. How an I tell if it is? How do I tell if one I purchase, as a replacement for the one she has, Is rebuilt?

Enough. Any help will be appreciated.
whburling is offline  
Sponsored Links
Advertisement
 
post #2 of 6 (permalink) Old 06-04-2019, 07:37 PM
Member
 
Join Date: Mar 2019
Posts: 60
Quote:
Originally Posted by whburling View Post
Despite the fact that my smart charger suggests the battery in a 2002 4 cylinder Mitsubishi Eclipse is ok, I don’t think it is. How do I truly test the battery to find out if it is taking a charge and holding it.
To test if the battery is holding its charge, you are going to have to take a measurement over a few hours.
a) 2A for a day should just drain a 48Ah battery. Side lights (parking lights) might do. So your own calculations, adding up the power of all the bulbs concerned. The voltage should go down from approx 12.5V to say 10V and then tail off fairly quickly.
b) Try starting the car a few times, but don't let it run. That way, the battery did not get charged in between. Try a few the next day. Look at the voltage across the battery when the engine is cranking, because there is a the greatest load then. See how the battery drains. If it ain't start in the morning, it isn't holding much charge, is it!

Quote:
Originally Posted by whburling View Post
How do I know for sure the alternator is working? I have a scope (not automotive). Perhaps I could look across the output of the battery cables unhooked from the battery to see if there is a ripple (indicating a bad diode). I could look at voltage at the same time. I would love to measure the current, but am uncertain as to how to do that. I probably need to know the max current my multimeter can tolerate without frying it and couple it in series between the battery cables and the battery.
The alternator output ripple current should be even from peak to peek. A longer gap is an open circuit diode. I can't remember what a shorted diode like like. An interesting thing about alternators is the voltage on the collector of the output of the control block. It's connected to one side of the alternator exciter windings. It's used to control the alternator output current, and hence the voltage. It tends to oscillate more than I expected. A low voltage means more output current. Turn on all the lights and heaters to prove this.

A battery under charge should measure 13.8V and the current depends on how much charge the battery has left. A battery at 12V is not charging!

Measure the current by measuring the village drop along the wire that goes to the battery. Do not try to put your lovely multimeter in series with 10A charging current or >100A cranking current. Start the multimeter at a 10V range. Calculating the power into the headlights might help calibrate the arrangement.

Quote:
Originally Posted by whburling View Post
To test the battery, I suppose I need to place the battery under load and watch the rate of discharge. Maybe the most simple way is to take the battery to autozone and have them test it? Do I trust their setup to test the battery correctly?
See above for loading the battery. Professionals often have a "battery tester" which is a high power heating element that will stimulate creaking indefinitely. It has a built in volt meter, and a poorly charged battery goes to zero pretty quickly.

Quote:
Originally Posted by whburling View Post
Maybe the battery my friend has is a rebuilt battery. How an I tell if it is? How do I tell if one I purchase, as a replacement for the one she has, Is rebuilt?
I suppose you should go to a reputable dealer to be reasonably sure. A rebuilt battery will hold slightly less charge, and supply less cranking power: measure the bills while cranking. Perhaps you have storage scope? 🙂
Quote:
Originally Posted by whburling View Post
Enough. Any help will be appreciated.
Long reply? You have only yourself to blame 😉
Ian61 is offline  
post #3 of 6 (permalink) Old 06-05-2019, 08:40 AM
Member
 
Join Date: Mar 2019
Posts: 60
Reading back my reply, I obviously need to proof read more. So

So *do* your own calculations,

If it *won't* start in the morningis

measuring the *voltage* drop

measure the *volts* while cranking
Ian61 is offline  
 
post #4 of 6 (permalink) Old 06-05-2019, 11:48 AM Thread Starter
Newbie
 
Join Date: Jun 2019
Posts: 4
thank you Ian61


You put a great deal of thoughtful effort into your answer. i am very grateful.



how did you look at the output ripple? did you put a scope across the battery leads? did you disconnect the battery from the leads as I suspect the battery acts as a huge capacitor and would hence smooth out the ripple.



I would love to see the ripple using my STORAGE scope. Should I take precautions to protect the scope? i am just looking at voltage ripple, so I assume my scope can at least measure 15 volts. maybe i beltter look at the scope specs.



Thank you once again


bil
whburling is offline  
post #5 of 6 (permalink) Old 06-05-2019, 06:36 PM
Member
 
Join Date: Mar 2019
Posts: 60
Hi 🙂
Try measuring the ripple at the alternator terminals. Here's a link:
https://www.picoauto.com/library/aut...le-diode-test/
Whereas the battery is a big capacitor, you still get ripple on the capacitor just after the half- or full-wave rectification in an AC power adaptor, and the ripple is greatest when the supply is fully loaded. So turn on all the headlights and the heater fan.
As for voltages harming the scope, just check it's spec. If you have a *proper* scope, none of this digital rubbish, then you use a 1Mohm probe, select AC coupling, and set the vertical gain at 200mV per cm. Otherwise just read the spec.
Ian61 is offline  
post #6 of 6 (permalink) Old 06-05-2019, 06:49 PM
Member
 
Join Date: Mar 2019
Posts: 60
And hey, I came here to get advice on things from people who know better than I do, so why wouldn't I talk about things I know a bit about when it helps? Let us know how you get on.
Ian61 is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Mitsubishi-Forums.com forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome