I have a thing for antique tools as I am sure many of you do as well. I bought an antique Atlas battery tester for $5, granted, I could probably find some new gadget from Amazon that could do the same job, but I really like the analog vibe this thing gives off. I do have a question about how it works; if you look at the instructions it calls for you to attach the clips to the battery of course, but then it says to push down the timer switch and it will remove the surface charge from the battery. I have never heard of this before; is it like degaussing? Why would that be necessary? I’m going to clean it up and see inside that everything is clean and attached before I try it on a battery. I just wanted to share this with you guys.
If you check the voltage of a battery fresh off a charger or from a vehicle that was just running it will be high, this is the surface charge, to check the battery we get rid of it, by applying a slight load to it it to get it down to its true state of charge, this can be done by a load tester or by turning high beams etc on for a few minutes. Remember a fully charged batter is 12.65 volts
Surface charge is when the battery holds an elevated voltage for a relatively short time after charging. This voltage is not a true representation of the actual state of charge, so you want to get rid of it to see the voltage the battery would stabilize at. You can wait until it has sat unused for hours, or you can draw some current from it to get done quickly.
It appears to be a light load tester. These will defintely show if a battery is bad. However, passing a light load test doesn't always mean a battery is necessarily good. For many years testing batteries with a heavy load tester (carbon pile) was the standard of the industry. The newest testers actually measure battery internal resistance. I worked for a major truck manufacturer and we went to the internal resistance test after most of the car manufacturers had already switched. The heavy load test is still a good test, but it is operator dependent. The new testers aren't as operator dependent.
And not that accurate (depending on manufacture and price of tester), I still stick by my old VAT 40.
The VAT 40 would be my tester of choice. However, I did a lot of side by side testing with the new style tester and found it to be extremely accurate. The only thing I ran across was 2 new, badly discharged batteries that it failed . I put them on a slow charge for a day and they both passed the VAT 40 and the resistance tester.
Today oscilloscopes can be used for battery tests, here's an automated test for Picoscope automotive scopes, using the current draw from the starter during a normal start to test the health of the battery. No external load to apply, just measure what happens naturally. During this or similar testing you can also see abnormal heavy pulsing of the starter current/battery voltage indicating the starter is bad (brushes losing contact with the commutator). Disable spark/fuel so the engine can't start and you can compare the current draw/voltage drop caused by the starter working against the compression in each cylinder, quickly showing you if all cylinders have the same compression. Won't tell you if all are good or bad, just if there's a difference (so a leaking valve is obvious while a cam out of timing in a single cam engine won't be). Modern testing equipment can do amazing things. Old testing equipment still looks better.
The Jalopy Journal
