No idea if that is as good. The ACT principle is covered by patents?
What is does is calculate the actual capacity of the battery in amp.hrs, which you can check against that stated on the case. Once it falls by more than a given percentage, it is replacement time. Never known it to be wrong. But of course with me it usually just confirms what I already knew, with my own batteries. But handy for testing one you don't know.
With a smear of vaseline, it helps keep the acid fumes from corroding the connenctions.
And each end of the engine block to chassis straps.
I think our local garage's battery tester is BFO wire wound resistor (foot long 1" dia) attached to a frame with a couple of hefty hinged probes. A volt meter is wired across the resistor. Firmly push one probe onto one terminal, whack the other onto the other hold for a few seconds as 100 odd amps flow and watch the voltage... Hopefully the first probe on doesn't weld itself to the terminal, the other might if you are a bit slow whacking it on and pulling it off. B-)
Yes - that's the old way. The ACT unit is more the size of a DVM - and no sparks when you connect it. Or things glowing red hot. ;-)
It's a superb device.
So it all depends how quickly you whack off? ;-)
Yes that's the type of battery tester that I've seen used. Very primitive!
Considerably better. But unless it draws a significant current, how does it test the ability of the battery to supply that current? Can you extrapolate and say "if the battery terminal voltage drops from A to B when a small current is drawn, then there will be a correspondingly larger voltage drop to C if a proportionally larger current is drawn"? In other words, are voltage drop and current always proportional: does a lead-acid battery behave as an infinite current source in series with a fixed resistance, and does that fixed resistance remain constant as the battery discharges?
Evidently there is, given that ACT units give useful results :-)
Yes works exactly the same read the item description or look it up on youtube its from China so Patents dont apply ;(
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Opinions vary as they usually do with these things. I heard IBM, but military is just as good a theory :)
I have the DBPower branded very similar version. It started a dead 2l VW diesel twice without any effort on its part.
The only thing that makes me nervous is it being a very high density lithium battery in a hot car - so I tend to take it out in summer. But summer usually gives me less problems than winter.
they claim to measure the conductance of the battery
I'd guess it draws a *very* heavy current for an instant. Judging by the clever crock clip design - to give it a very low impedance connection.
As has been suggested
Several miles in winter when headlights tend to get used more may not be enough to restore the energy taken from the battery to start the car.
A cheap DVM will show the state of charge of the battery.
Checking battery voltage with and without the engine running will show if the alternator is performing.
The only thing I would add is that it is possible to get a false negative in test 1. The alternator can be producing a significant charging current, sufficient to raise the voltage under test conditions, but still unable to produce sufficient current to maintain battery charge in ordinary driving. Especially in the dark or in Winter. To be sure you need to actually measure how much current the altenator can produce at highish revs, most easily with a DC clamp meter.
If it is an older car, with a simple ignition circuit, does the ignition light come on when you turn the ignition on?
If not, check the wiring and bulb.
Other possibilities:
Poor earth connection- battery to chassis or engine to chassis.
Assuming you've not added something recently which is drawing current while the ignition is not only off, but the key is removed, a wiring issue. Look at the door switch wires, they often get damaged.
Alternator
Or simply switch on all the normal loads like headlamps and heater etc and check the voltage again. With the engine at a fast idle. If the alternator can't balance the load the voltage will be low too.
True enough but FUBAR one is the more commonly used one when discussing computer kit and software, often turned into a verb or adverb by tagging ED on the end as in, "This version of windows is well and truly fubared!" (Vista and win10 references mostly).
A less epithetic alternative is the word "borked", derived from a typo of "broked", a mistranslation of "broken" often used by people who's first language is not English where it's quite possible the 'typo' was deliberately applied to emphasise the point (it seems to have passed into common usage by native English speaking people now).
Getting back on topic, the symptoms suggest either a buggered battery or, seeing as the battery in question is only a few weeks old, a problem of the car's electrics where something like a boot illumination lamp is permanently lit and slowly draining the battery so that it doesn't get a chance to be properly charged by the car alternator during typical daily use. Once a lead acid battery is being operated in a permanent state of deep discharge, it doesn't take very long before its capacity reduces to that of an old shagged out battery.
A fairly simple way of checking whether or not the alternator is working is to check the effect on tickover speed[1] when switching the headlights on with the main beam flashing switch lever operated to maximise the electrical loading (switching the screen heater on is optional but can be handy to exaggerate the difference between tickover and higher engine revs headlamp brightness). A working alternator will produce a noticeable increase in headlamp brightness when the accelerator pedal is depressed to increase the tickover to around 2000 rpm or so.
[1] This effect is most noticeable with petrol engined vehicles, less so with diesels. The "Rev it up test" is maybe the better option with a diesel engined vehicle.
Even if it's only testing with a 1A pulse of test current, you still need BFO croc clips to provide an ultra low contact resistance connection. The test leads don't have to be FHD if they include seperate voltage sensing wires to eliminate volt drop due to the test current pulses. Unless you use separately clipped on voltage sensing leads (a four wire test setup), you *do* need to employ BFO croc clips to get accurate battery impedance figure readings in the sub 10 milli-ohm range.
One way to measure battery impedance without the use of heavy discharge current pulses is to apply a high frequency ripple current via a current transformer with its current winding in series with the feed powering the tester allowing the tester to superimpose several amps of high frequency ripple current onto the net 100mA or so required to run the tester which circuitry will be bypassed at HF with a suitable capacitor that will act as an ultra low impedance return path for the HF ripple current or bi- polar test pulses.
Once the tester has measured the effective impedance (resistance) and voltage, along with user input regarding the battery type (SLI, GEL or AGM) it can make a pretty accurate guestimate of its condition in terms of effective capacity and state of charge.
Thanks for the many replies.
On the basis of advice, I disconnected the battery five days ago (Sunday), charged it up, and left it disconnected. This morning (Thursday) I reconnected it; the engine started immediately without issue (and the same for multiple subsequent starts).
The battery reads about 12.3v while connected and the same disconnected. At idle, it reads just about 14.3v.
I couldn't read anything between the battery earth and the chassis.
So it sounds to me that the battery is fine.
What do you suggest for the next step in the investigation?
Daniele
My ACT has very special crock clips. A series of spikes packed close together which will dig in to the lead battery posts. To get the most accurate reading, you need to disconnect the battery and clip to the posts
- rather than clip to the terminals.
As was said, check the voltage at the battery with the engine at a fast idle and the headlights on main beam, heater and heated rear window on.
Anything less than about 13.5v probably means it's not charging properly.
If that is OK, you need to measure what current is being taken from the battery with the engine stopped and everything switched off. That should be something like 50 mA maximum.
But many DVMs will blow their fuse or worse if used for this.
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