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Shocking a battery

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electro
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PostPosted: Thu Jan 13, 2022 3:17 pm    Post subject: Re: Shocking a battery Reply to specific post Reply with quote

You missed the point of my post. The error on the HF meter and my Triplet and Speco meters is absolutely due to 1/2 wave rectification. The Triplett and Simpson both use 2 diodes arranged as two legs of a Wheatstone bridge, the other legs are calibration resistors. I assume that arrangment is to balance any shifts in the voltage drop of the diodes as they age. However, the current to the meter is still through only one diode and is 1/2 wave. The meter is expecting a 50% pulse width from the diode, the 1/2 wave part of the full wave AC signal, but is getting a 100% width because it is getting the DC current out of the battery. That is why the voltage reads twice what you would expect. The pulse width is twice as long and the current to the meter is twice as much. The meter then reads increased current as increased voltage although the real voltage is still 12 volts dc. The question I have is why one meter, the Simpson, read 13 volts on both the AC and DC settings but the Triplett read 13 volts on the dc setting and 26 on the ac setting. The schematics for both meters are essentially the same. I never use the any of the Simpsons I have and the meter may well be bad.

I know how a DVM works at least to the level of a block diagram. George fell prey to what the Lean Six Sigma folks call a Gauge R&R error, the measurement or gauge was not accurate or reproducible. The HF meter is not measuring any AC current since there is none in his desulfinator. He is just getting an erroneous reading from a cheap meter on the AC mode while connected to a 12v dc source. My photos of my HF meter show exactly the same error.

A scope would be fast enough to sort out the pulse but I expect it is only an few milliseconds long and is DC not AC. The battery is esentially a large voltage clamp device with a slight time delay, it would clamp any votage spike more than a few milliseconds long. Try connecting a 28 volt source to a 12 volt battery, or even better, a 28 volt AC source to a 12 volt battery and see how long that 28 volt power supply lasts. That battery can easily clamp several hundred amps if the pulse lasted very long. That is one reason why the pulses are so short.

One of my photos shows a reading off of my Weston true rms meter just for historical interest, I do not expect it or any common meter would be fast enough to pick up such a short pulse with any accuracy.

If I were George, I would just trust the LED when it lights and indicates a desulfinating mode.
 
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MarkB_MI
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PostPosted: Thu Jan 13, 2022 4:48 pm    Post subject: Re: Shocking a battery Reply to specific post Reply with quote

> The meter is expecting a 50% pulse width from the diode, the 1/2 wave part of the full wave AC signal, but is getting a 100% width because it is getting the DC current out of the battery. That is why the voltage reads twice what you would expect. The pulse width is twice as long and the current to the meter is twice as much.

That might be true if the input is DC coupled. Most meters are AC coupled on their AC ranges; a series capacitor blocks the DC component of the input.

> A scope would be fast enough to sort out the pulse but I expect it is only an few milliseconds long and is DC not AC.

I'm not sure what you mean about the pulse being 'not AC'. I assume you mean it only goes positive, which is correct.

> The battery is esentially a large voltage clamp device with a slight time delay, it would clamp any votage spike more than a few millisI aeconds long.

I assume the charger is sourcing a tremendous amount of current during the desulfation pulse, maybe as much as a 100 amps, but for a very brief duration. The pulse duration has to be short because the charger can only source that much current for an instant.

> One of my photos shows a reading off of my Weston true rms meter just for historical interest, I do not expect it or any common meter would be fast enough to pick up such a short pulse with any accuracy.

It appears this meter is DC-coupled and reads the sum of the AC and DC components. Compared to the DC battery voltage, the desulfation pulse will contribute negligible voltage because it's so brief. Older TRMS meters (if indeed it is one) measure the temperature rise of a resistor heated by the input waveform. Since the pulse contributes little power, it's probably not measurable by such a meter. It would be measurable by a fast digital-to-analog converter.
 
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Geo-TH,In
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PostPosted: Fri Jan 14, 2022 4:39 am    Post subject: Re: Shocking a battery Reply to specific post Reply with quote

Simply put, when my cheapie meter doesn't read an ACV, the
charger is done desulfating and my ACV is GONE!
It's that simple... In a few weeks I'll post a pic and show you.
 
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electro
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PostPosted: Fri Jan 14, 2022 5:45 pm    Post subject: Re: Shocking a battery Reply to specific post Reply with quote

Mark,
I agree the average meter, analog or digital, is not going to read a short pulse like what I would expect on a desulfinator so I have trouble George's meter is giving the information He thinks it is.

My Fluke has a blocking capacitor which is why it reads zero when measuring DC on the AC range. It also uses 1/2 wave for the input to the 4 bit integrator. The Simpson and Triplett meters both have a blocking capacitor on a separate input jack called "Output" but there is no blocker on the normal AC voltage setting alone. That is why they erroneously read an AC voltage when there is none. I would have thought all DVMs would have a blocker but apparently not in the case of the free HF meter.

The true RMS meter I showed is a true RMS meter, thermocouple type. I do have a peak to peak meter but was not able to get it working although I doubt it would have a short enough response to be useful. If I am ambitious, I will hook a desulfinator to one of my scopes and see how long the pulse lasts.

For George, I got the same reading you did with my free HF meter on the AC setting using a 12 volt battery only with NO desulfinator. No AC voltage or DC pulse in that battery. I am at a loss to explain your results other than what I have already said. I feel like the explanation is obvious at least in this case. I find it hard to believe your meter is sensitive enough in terms of response time to react to a short DC pulse and a longer pulse would require many more amps than your small charger could supply. But I may be wrong and am willing to learn if you can educate me as to other ways you could get the results you are showing.

Voltage is either AC or DC. If it regularly changes polarity then it is AC, if it does not change polarity, no matter how it may vary, it is DC. If it is a steady voltage then it is pure or filtered DC, if it varies but never changes polarity then it is still DC and is commonly called pulsating DC. Because the voltage pulsates does not make it AC. It has to change polarity.

There are likely many phases to your desulfinator, it may be putting out pulses only, DC, or it may raise the base line voltage to the battery in addition to DC pulses, or it may stop charging all together followed by a series of pulses, there are many desulfinating protocols.

If you have a scope then put that on the charger and see what the waveform looks like. The photos I posted clearly show the HF meter is inaccurate when fed DC voltage while on the AC mode.

To answer your original question,my HF meter shows around 28 volts, desulfinating or not, desulfinating charger plugged in or not. Desulfinator hooked to the battery or not. All the same.

Mark has given good explanations as to the pitfalls and considerations with the use of both analog and DVMs. I still think you are being fooled by your HF meter.


Some links to show the waveform and voltages:

https://thesai.org/Downloads/Volume8No7/Paper_72-Impact_of_Pulse_Voltage_as_Desulfator.pdf


https://www.researchgate.net/publication/320886624_Desulfation_of_lead-acid_battery_by_high_frequency_pulse



If I was the reviewer I would have sent the first paper back for revision but it does clearly show the waveform. The second paper also has the scope tracing although it is a bit crowded. Both show pulsed DC not AC. People often complain about chargers not being pure DC and assume the pure DC chargers would somehow charge better. Early desulfinators were pulsed at 120 cps, i.e. unfiltered DC output and they seemed to be better than the filtered pure DC. Modern desulfinators seem to use a range in the low Mhz area which is supposed to be some sort of mechanical resonance frequency. Who knows but they do seem to work to some extent.

This post was edited by electro on 01/14/2022 at 05:47 pm.

 
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