You can't test a 12Ah battery like that. The test would not be valid in that it would give little indication of the actual output capacity in normal use, and you would risk damaging the battery.
Bill
A multimeter of any kind does not include the load necessary to perform a discharge test. If you think you could connect a multimeter set to a current measuring range across a battery, all that would happen is that you would blow the meter's internal fuse. The resistance across the terminals of a multimeter when set to a high current range is effectively zero, because it is across a shunt resistance made from a length of copper sheet or similar.
If you can't use it for more than a few seconds how can it measure battery capacity? You would have to take it off before the battery had discharged, so you would not have made a measurement. Let us say you give it ten seconds. At 60A that is 0.16Ah.Not much of a test for a 12Ah battery.
Deep discharge batteries are not designed for rapid discharge. Most will suffer severe voltage drop at excessive discharge.
The gadgets garages use are designed to simulate the load a starter motor puts on a car battery. This is an entirely different situation to the testing of a 12Ah deep discharge battery.
Bill
In message , harryagain writes
But hardly the sort of thing that every DIYer has in his toolbox.
I've so far failed to burn mine out (although I do admit that the leads look a bit too flimsy for a continuous 10A).
No, but that's not what they are designed for. However, a little playing with a wire shunt will allow your 10A meter to read (say) 10A when the real current is 50A.
They probably do, but the average DIYer will probably do some elementary tests first with his cheap multimeter.
Of course!
It doesn't, it's just a cheap bit of kit. It gives an indication that the battery is not completely knackered. The condition of the battery can only be determined with the equipment I described. I know how mutlitmeter work thanks.
A multimeter tells you nothing useful about a battery.
I dunno why you drivel on about your theories. This is what happens in the real world.
And means precisely nothing.
Why don't you cease your drivel? This is what is done in the real world. And has been for decades.
In message , harryagain writes
The gist of your contributions seems to be that you can't do any meaningful tests at all whatsoever on a battery unless you use exactly the 'right' test equipment. You are simply wrong. The sensible use of a cheap multimeter, plus a little ingenuity, should enable you to get a fair idea whether it's worth going to the bother of getting 'proper' tests done, or whether the battery is essentially a 'no-hoper'.
You need to know the battery capacity in amp.hr. This is commonly measured at the 20 hour rate - so the load needed to check this will vary according to the size. If you work out the load needed and make it up using, say, suitable bulbs a fully charged battery in good condition will give near enough that amp.hour figure.
For example, a 60 amp hour battery would be discharged using a 3 amp (36 watt) load which should run for 20 hours.
The instructions with my tester say that if the capacity of the battery is less than 65% of the stated one it should be replaced.
But bear in mind that the discharge rate radically affects the result of this test. A realistic test will discharge at a similar rate to the intended load.
Bill
Yes, for car batteries. Deep discharge batteries are entirely different. Small ones (12Ah) need especial care or they can be damaged.
Your lack of knowledge here doesn't surprise me because it is in line with the ignorance you have displayed when discussing other topics, but your arrogance does still surprise me. Most ignorant people know they are ignorant so they know when to keep quiet. I've noticed that you always seem happy to offer an opinion (which you dress as hard fact) even when it is quite clear that your knowledge on the topic is close to zero. This is a characteristic of the bar room buffoon and the barrack room lawyer. You are a loud-mouthed ignoramus.
Bill
Not so. You are checking the battery is to spec. If the capacity is correct (or near) the chances are very high it is fine.
But obviously you need to use the correct battery for the job.
A perfect 40 amp.hr battery may not work so well as a slightly faulty 80 amp.hr one in practice. As it were.
That is an appropriate test for a *CAR* battery.
He is right and you are wrong yet again.
The guy came to service my alarm today and although he does have a battery tester it self calibrates to the battery under test and applies the right continuous shunt load for a few seconds monitors the voltage drop with a final estimate of the Ah capacity and health of the cells.
It used to be done with a shunt load and a voltmeter. But you have to use the right shunt for the battery capacity or the battery dies!
Regards, Martin Brown
That is likely the same one as I have. Made by ACT? I bought mine to keep on top of a load of car batteries being used for location filming. Probably too expensive for DIY - but I'd expect any decent battery place to have one. Even Halfords.
Says suitable for lead acid 12v 1.2 - 200 amp hour batteries both 'wet' and SLA, so covers just about any you'd find.
I used to look after batteries of all types in the NHS from traction to standby, starters for very large diesel engines and emergancy lighting systems. So I reckon I know some thing about them after forty years.
I pointed out the deep discharge battery business in my first reply to the OP
In message , harryagain writes
Presumably you had access to all the proper test equipment required to do your job correctly and efficiently. However, is this blinding you from that fact that such equipment may not be absolutely necessary for some of the simpler tests at home?
>
Bill knows more about this stuff than you will ever learn. I dont know what planet you live on but I would rather be on Bill's.
Just a follow up to thank all for their contributions. It looks like I unwittingly got an unsuitable UPS type battery. I know how this happened, I made the fatal mistake of looking at the batteries I had removed, rather than checking the spec from scratch !!!!!
Vaguely reminds me of an air accident investigation programme where a windscreen fell out because the fitter used like for like, (thus propagating a mistake) rather than check the spec
p.s. anyone guess my new years resolution ;)
Can't recall the brand didn't really see it for long enough but a grey box ~ 10x10x25 cm with LCD display - and yes it was a generic tests all Ah ratings 12v or 6v all types of lead acid batteries. This one might not go up as far as 200Ah - really didn't look big enough.
Regards, Martin Brown
Might be a different make then - although I thought ACT had a patent.
Or a later model - mine is black, several years old. Size 110 x 55 x 35mm. The giveaway is the unusual crock clips to ensure an ultra low impedance connection.
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