Observing DC Spikes with an Old Scope

[Bazz4CQJ]

I always have one or two old car batteries around to power up my 12V ham radio gear. Old batteries tend to suffer from sulfation, and some years ago I bought a “pulsator” which claimed to achieve some level of sulfate removal, and I’m convinced it did do that. I see that many battery chargers on sale now have some such feature built in to them.

My unit puts out “spikes” at about 14kHz. The duration of the spike is right at the limit of what my old 20MHz scope can resolve, i.e. the duration is no greater than the width of the beam. I think it peaks at about 16V. I think I measured it simply by putting the scope across the battery. Can anyone suggest a better way of connecting the scope?

Thanks
B

[trobbins]

If I am seeing this right, then perhaps a high intensity display setting in a dark room and use a digital camera/video to 'record' the transient and hope the permeance of the screen is your friend

[joebog1]

Bazz,
OLD car batteries are just that. YES they can be "desulphated " to some degree, but thats why we change them in our cars. I have fitted and constructed many wet acid solar systems in the past, and some people dont know the meaning of Ampere Hours. They decided it was "much " bigger than they had off the mains, or simply never had electricity before.
The pulsating spikes do sort of work to a very minor degree, really ? nope not much at all.
I know why you like lead acid!!, they have superlow impedance when newish, but that fades away quickly when stored or used as deep cycle batteries.
Radio uses them as deep cycle, by that I mean long small drain over hours.
Car batteries are designed to give 7 or 8 hundred amps for a few seconds, then be charged back up and essentially not used untill next start.
Its a painful thing when halfway through a contact the power dies.

Sulphation is a "fancy " name for high impedance.
Not much can be done about it.

Joe

[Bazz4CQJ]

Mmmm... permeance is a word you don't hear too often; noted

Joe, we will have to agree to differ on pulsators. Re sulfation, I think you will find that everyone, including the "little Englanders", agreed to consign the spelling with "ph" to the dustbin of history some years ago .

IIRC, the final push for it came from problems with "reading for the blind" apps.

B

[MotorBikeLes]

Sorry bazz, this Manx residing little Englander still insists on the ph. Putting a f in its place is just too much USA for me. My billion should have twelve zeros, not nine.
I was in dentist's chair this morning, and he asked his nurse for a spatula. After she rummaged, he said "we don't seem to have many spatulas".
I commented that whilst spatulas was accepted as correct English, for me it was still spatulae. After eight decades, well seven since they first pushed Latin in my direction, I don't forgo these things easily.
Sulphation. All discharged lead acid batteries contain lead sulphate, but we only say they are sulphated when they stand long enough for the "loosely deposited" compound to slowly crystallise into a hard, dense, well ordered crystal block.
Constant charging and discharging MAY reduce the crystal deposit size, but never completely. I understand EDTA (yes, I can spell it, but won't bother you now) can reduce the effect, but never tried it.
I bought a small charger with all the built in tests and routines. Like you I wondered about the pulse effect, but when I connected my 35MHz HP scope, I saw nothing. I assume the battery's capacitance is so high it just hides it.
Les.

[Bazz4CQJ]

Well, it's exactly because I had to do Latin too, that I'm so keen to put the boot in to all things classical like "ph"

I seem to recall that there are three or four processes that contribute to LA battery death, so even if the pulsators do de-sulfate, they will do nothing about the other issues, so there will be limited gains. Truth be told, this activity is probably no more than my Yorkshire gene busily at work, wringing the last penny's worth of value out of something that should be at the recycling centre.

B

[trobbins]

Doh, I meant persistence not permeance, sorry.

[joebog1]

Goddamn I arpolgize Bazz, I dint mean nuffin bah wrongly spellin ya Lars Anjelees baddery !!.

Cheers

transporteee Joe

[Trigon.]

Originally Posted by Bazz4CQJ

I think you will find that everyone, including the "little Englanders", agreed to consign the spelling with "ph" to the dustbin of history some years ago

Hmmm...not really.

The 'sulfer' brigade are ideed gaining ground, they outnumbered the 'sulphur' traditionalists in American English texts in the early 1940s :-



- but they're not there yet in British English texts !



https://writingexplained.org/sulfur-...to_Use_Sulphur

Cheers !

[Bazz4CQJ]

@Trobbins - I too thought that permeance was a useable word in that context, but on checking it turns out to mean "the property of allowing the passage of lines of magnetic flux". But thanks for the idea of using a camera.

Re sulfate, before the mods step in, one final comment. The British authorities dealing with such matters signed up to this a few years ago. UK Gov docs now refer to sulfate. The data going only to the year 2000 is not useful now. On a hobbyist forum, we can each do what we like on this issue. I hate it when people talk about "tubes" .

B

[Trigon.]

One final, final comment...

UK Gov docs now refer to sulfate.

No doubt that is the goal, but try a Google search with the following string:-

"sulphate" site:https://www.gov.uk/government/publications/

There are plenty of departments that didn't get the memo! Documents only a few months old...

Cheers !

[SiriusHardware]

Getting back to Baz's original post, what is the actual aim, to find out the length of the pulses? Or something else?

[Bazz4CQJ]

Yes, really just to find out what sort of pulse voltage and duration. The first pulsator I bought was a kit from a company in Scotland some years ago (now sadly gone). It powers itself from the battery which it is pulsing and I can hear it whine (reminds of the old Pye Vanguard) and AM radios really don't like it. As above, I reckon it pulses at ~14kHz, to maybe 16V, but the duration is very short; more a spike than a pulse.

These days, quite a high percentage of the modern battery chargers on the market have a pulsator function built in to them, and sometime soon I'll take a look at one of those and find out what they do.

It may well be that with the limited equipment I have, taking a photograph may prove useful. I did wonder about inserting a small transformer between pulsator and battery; just a couple of turns on the primary on a ferrite ring (any inductance will introduce error) and a few more turns on the secondary for the scope?

B

[pmmunro]

Bazz,

I also bought a desulphator from the company which I think you must have. If I remember correctly they/he was based in Portsoy.

If so, would you still have the information that came with it please? Mine has gone missing.

PMM

[GMB]

I am in the midst of piles of traction batteries - all totally dead - that I am trying to revive to save the kilo-pound bill for new ones.

I am currently using a modern charger that does the pulsing treatment but not in the way of the devices you decsribed. I will take a look at the waveform when I get a minute. I was also considering building one of the published circuits for desulphating.

So far I had huge success with one battery which was resurrected by the pulsing technique of the modern charger. The device seems to apply about 24V (to a 12V battery) in pulses but it gives up quite quickly. Another battery is resisting the attempt but the trouble is that the charger assesses the battery and then, if dead, applies the pulses until it see significant current flowing at which point it goes to a more regular mode of charging (so gives up the desulphating). It then applies its standard algorithm and on seeing only 7V declares the battery dead. It may be true but I would like to be able to tell it to try harder. The problem is that the modern clever chargers are afraid that a vehicle's electronics might still be connected and also that it may be overheating the battery so may be less agressive than would give a good result.

The desulphator circuits I have seen basically store energy in a small choke which is then discharged into the battery. The voltage you get will depend on the battery and although the pulses occur at a kHz rate the discharge is said to generate oscillations in the MHz range - so are effective short-wave jammers I suspect. An old 'scope may struggle to see the high frequency oscillations as they may be rather fast and short lived and not repeating very often.

[SiriusHardware]

I don't know how deep you want to go Baz, but if you are prepared to delve into the machine and find the transistor or FET which controls the pulsing and then follow its base or gate back to the digital output which will inevitably drive it, it might be easier to scope the width of the pulse signal there.

If the unit runs on the battery which is being conditioned I wonder how it generates any higher voltage to generate an overvoltage pulse - are you sure it doesn't work by applying a periodic very short duration heavy load / near short across the battery? Edit: I see there have been suggestions of a coil to store the requisite 'extra' voltage to apply across the battery.

[G6Tanuki]

I've tried various desul[ph|f]ating approaches over the years with 'tired' lead-acid cells [from little 1.2AH SLA burglar-alarm batteries, through UPS/motorcycle/electric-lawnmower/car/truck/boat batteries] and never had much success; Sul[ph|f]ation never seems to be defeated by the pulse-type devices and even the brute-force approach which shoved 10A at up to 240V [ahem] pulses into a 'stalled' battery followed by what amounted to a dead-short for 5 seconds never achieved lasting results.

I suspect that - as has been mentioned upthread - even a horribly-sul[ph|f]ated battery has enough residual internal capacitance to act as an effective short-circuit to high-frequency short-duration pulses. Even a totally-failed battery still looks like a Farad or two!


My instinct would be to weigh the batteries in for scrap. Lead has one of the highest recycling-percentages of any material [anything between 70 and 99% according to where you source your data and your definitions] - which must tell you something...

[Bazz4CQJ]

The unit came from Curtistown Marine, who were in business for some time, and I believed to be "reputable". The quality of the kit was very good, but it did not include a circuit diagram and I never traced it out (so far).

@PMM - I'll see what records I can find, but I'm sure there was no diagram. I'd guess it was 15-20 years ago.

B

[Philips210]

I built the Lead-Acid Battery Revitaliser from Elektor Electronics, September 2001 issue. I don't recall having much success with it. In the text it mentions the voltage spikes are typically below 15V amplitude for a battery in reasonable condition. For one with high internal resistance the spikes can be high as 50V.

I still have the unit stored away somewhere. I'll try to find it and check the output pulses.

Regards,
Symon

[GMB]

If you want to see a typical circuit, here is an random example: http://www.reuk.co.uk/wordpress/stor...y-desulfation/

UPDATE: I scoped my charger and it seems the pulsing stage is rather short lived so it is not doing it any more. It is now using a constant current charge where the voltage can rise up to about 24V. I think without more high voltage pulses this will fail.

The reference I posted above says it can take several weeks to work, so to people who claim the pulsers don't work I ask "did you wait that long?"