Observing DC Spikes with an Old Scope

[Bazz4CQJ]

Yes, I have always worked under the belief that it is a slow process, as in one week or two.

B

[PETERg0rsq]

Originally Posted by Bazz4CQJ

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

I am afraid if you want to "analyse" the spike, then only solution is a faster scope. That is the reason scopes go up to 400MHz or more, not to see 400MHz waves, but to see very fast transients.
Of course you will then need very fast probes, or look at probing techniques to get accurate response on screen!

However for measuring the pulse width you may be better of with a time interval meter (good frequency counters have this function built in), but not sure if they will measure the pulse width you may have. For example the Racal 1991 claims it can measure a pulse width down to 6.25nS

For voltage measurement you should be able to cobble together a voltage following amplifier, that charges up a capacitor to the peak pulse voltage, using an op-amp.

[cmjones01]

Since the battery is almost certainly presenting a low impedance to the pulses and therefore making the resulting voltage spikes hard to see, why not try probing the current going in to the battery from the charger instead? That should show it a lot more clearly. As a first lash-up, just try a couple of turns of wire wrapped round one battery wire, then connected to the scope input. Of course, it won't show you any DC current going in to the battery, but it should show any pulses of current quite clearly. Some experimentation with the number of turns and/or burden resistor may be necessary, or use of a proprietary current probe.

Chris

[duncanlowe]

Originally Posted by 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?"

I have a few related devices. A couple of them (different versions from the same brand) start with pulsing, if the battery is low. Then they go on to the constant current then constant voltage phases. The voltage then gets slightly reduced to a float charge which it remains in for several days. If the option for reconditioning is selected, it then moves on to putting pulses on top of the float voltage. I don't know how long it does that for, it may be continuous.

I also have a couple of the standalaone desuplhators. One built from a kit, one bought from CPC as they were on clearance. Both apply pulses all the time. The kit one uses a 555 timer driving a MOSFET. The current through the MOSFET also passes through an inductor. When the FET switches off, the inductive spike is passed, via capacitor, back into the battery. That unit also has a low voltage cutout, so if for whatever reason any charger isn't keeping the battery topped up, it doesn't completely drain the battery again. I do have a circuit diagram for that, but I'm not sure that it's OK to post it given it's a commercial product (even if no longer for sale).

[Bazz4CQJ]

Originally Posted by duncanlowe

I do have a circuit diagram for that, but I'm not sure that it's OK to post it given it's a commercial product (even if no longer for sale).

I guess that issue is for the mods to consider; post it and see what happens

B

[Reelman]

I’m sure I remember reading in the 80s that this would revive batteries suffering from the “S” word… obviously only works with non-sealed batteries so I include for completeness.

1) remove acid
2) replace by a solution of borax
3) “charge” until obvious a reaction is taking place
4) drain, refill with correct SG acid and charge.

Not tried it and it is from memory.

Peter

[pmmunro]

Originally Posted by 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

Thanks Bazz

PMM

[Bazz4CQJ]

@PMM - all I've managed to find are copies of 2 pictures I took of the assembled board. There's less to it than I remembered, one IC (TA7555P) and one FET. I now recall that I had a suspicion that the circuit was not original and had been already been published on the net; I'll look at one or two PDF's I have on file.

Also found a circuit for a scope attachment which I forgotten I had.

B

[Techman]

I now think I know what this bit of home made kit is/was that I posted about a few months ago and no one commented on. It put out high(ish) frequency pulses and looks to have leads that would clamp onto a lead acid battery. It was powered by a 9 volt battery.

[Techman]

That wasn't the best picture of the innards and I couldn't seem to edit and add a better one to that previous post:-

[GMB]

I have discovered another version of the desulphator circuit which is much simpler and maybe like the first PDF posted in #28.

It's just a 555 driving a MOSFET that delivers a charging pulse from a 2200uF capacitor at about 40-50V. The circuit I found uses 10uS pulses at 100Hz repetition rate. This is much more like what some commercial chargers do, albeit they use a lower voltage with longer pulses.

The actual voltage you will see will depend on the various impedances. With a dead battery it will be the supply voltage, and when recovered it will be hard to spot.

[duncanlowe]

The unit I have looks very similar to the device in post 28, though it's not the same. My version has an extra chip to provide the low voltage cutout, and a few other components around the board are in different places. But much of it is so similar they must be related.

Attached is a snapshot of the circuit diagram from the instructions.

[majoconz]

You can always get your batteries rebuilt.....

https://www.youtube.com/watch?v=PdMWBv8kAo0

It must have been the Health and Safety man's day off.....