When using in the RV industry what's called EQUALIZE MODE to help desulfate flooded lead acid batteries, typical charging voltage may be near 15 Volts DC. The AC voltage reading of any particular volt meter, is subject to the style, design and quality of the volt meter and the quality/shape of the charging voltage waveform, as its (battery charger output) typically NOT WELL FILTERED OR REGULATED MORE PULSING AND RIPPLING NOTTTTTTTTT STEADY STATE PURE DC........
Sooooo your meter may read different AC voltage then some other, and a different charger may yield different voltage also. Best I recall mine have read 14 + to 15 VDC (when in Equalize Desulfate mode) Ive never paid much attention to AC voltage
John T
Sooooo your meter may read different AC voltage then some other, and a different charger may yield different voltage also. Best I recall mine have read 14 + to 15 VDC (when in Equalize Desulfate mode) Ive never paid much attention to AC voltage
John T
OP
OP
Geo-TH,In
Well-known Member
JT,
I always thought my charger was desulfating when it was flashing a certain way and I measured an AC voltage.
When the ACV goes away it is in the equalization mode.
Not 100% of what mode I'm in. I just know it could take weeks of ACV before the charger goes into what I thought was equalization mode.
Shocking....lol
I always thought my charger was desulfating when it was flashing a certain way and I measured an AC voltage.
When the ACV goes away it is in the equalization mode.
Not 100% of what mode I'm in. I just know it could take weeks of ACV before the charger goes into what I thought was equalization mode.
Shocking....lol
The top of the line quality Four Stage (Bulk Absorption Float Equalize/Desulfate) Chargers many RV's use ONLY run the Equalize (higher voltage near 15 VDC) X minutes every 24 hours and thats all automatic. Still good but less expensive Three Stage (Bulk Absorption Float) RV house battery Chargers DO NOT have an Equalize/Desulfate Cycle. Basic off the shelf wally world or Auto Zone cheaper charges likely ?? DO NOT HAVE THREE LET ALONE FOUR REGULATED STAGES....They are just chargers..
John T
John T
If its indeed ??? a Four Stage so called Smart Charger with automatic regulated Bulk Absorption Float and Equalize/Desulfate Cycles YESSSSSSS thats similar to the Smart Chargers used in many RV's and NO they ARE NOT CHEAPIES LOL I know, Ive bought three or four of them
John T
John T
MarkB_MI
Well-known Member
- Location
- Motown USA
George, your El-Cheapo DMM is probably a peak-averaging meter and it's going to be tripped up by the pulsing waveform produced by your charger's desulfate mode. Hook it up to a true RMS meter and I'll bet the AC voltage will be negligible.
Destroked 450
Well-known Member
- Location
- Harned, Ky
So whats the advantage of a desulfating battery charger
John, coming from the phone biz where we have lots and lots of huge batteries, equalizing is not the same as the desulfate mode. Equalizing was when we apply an slight DC over voltage to the battery to make sure that ALL/Each individual cell was forced to be charged. This was so some cells in the series cluster did not absorb more of the charge at the expense of the higher resistance cells. Or at least thats what we were taught in our battery plant technology? Where de-sulfate uses a high frequency a/c pulse to remove the coating on the cells. But this is very old training from back in the dinosaur days.
Thanks for the info. In the RV circles Ive heard those two terms (Equalize & Desulfate) often used interchanged but like you I understood a high frequency pulse can help desulfate while the Smart Four Stage chargers Ive used run an automatic so called Equalize cycle once for x minutes each 24 hours at which time the voltage is like 15 volts which some still refer to as Desulfate
Thanks again for the information
John T
Thanks again for the information
John T
None of the theories I have read nor any of the circuits I have seen use AC voltage/current for desulfination. They all use pulse DC. I put one of my desulfinators on a scope when I first got it years ago to see what the output looked like. It was DC with a short higher voltage pulse although I do not remember the pulse frequency or voltage. Definitely not AC.
I know some meters have 1/2 rectifiers that do not do well with DC on an AC setting. The better meters, analog type, have a diode/resistor bridge to compensate for the expected 1/2 wave input but getting pure DC. I am not sure how the digital meters handle the analog to digital conversion but I assume they still use a 1/2 rectifier circuit with or without a bridge.
My Fluke 77 will measure zero volts from a battery when in the AC mode. My Harbor Freight meter will measure correctly on the DC setting but similar to what you were getting on the AC setting. This is the reading on a 12v battery only with not charger or desulfinator attached.
My true RMS meter read correctly, the inexpensive Speco analog was off by a factor of two ( which fits with a non-bridged 1/2 wave rectifier), my Simpson 260 was accurate, my expensive Triplet 630 was off by 2X. Some of my other meters dating to the 1930s were accurate, others off by 2X.
None of the reading changed with a desulfinator attached to the battery, those meters will not respond fast enough to pick up the short pulse of dc, you need a scope for that.
Normally I trust the HF meters but the fault with digital anything, meters, calculators, etc., is that it is easy to believe what the display reads even if it does not make sense. Always do a real world check.
You are not measuring an AC voltage, you are just looking at an inaccurate output from your meter as well as using the meter incorrectly. Put a blocking capacitor in series with the meter and I expect you will get an AC voltage reading of zero. Some meters, Simpson, Triplett have a setting with a blocking capacitor. I expect others, such as Fluke, are always using a blocker of some type. When trying to sort out AC or pulsating DC from a DC bias, always use either a scope or a blocker of some sort.
Try measuring the battery voltage only, no desulfinator mode, and see what you get for an AC voltage. Some desulfinators do raise the voltage fairly high and that may show but I think it is unlikely your meter could measure the desulfinating pulse. However, there are may types and protocols associated with desulfination and your may well have a very long pulse that is picked up by the HF meter but it seems unlikely especially given the reading I got with my meters on a battery alone.
With the advent of modern electronics and PWM and buck boost power supplies, you do not have to go to an RV dealership to get a fancy expensive 3 or 4 stage charger. I have not looked at the battery charger aisle at Walmart but they may have a selection.
PS
I left in some spelling and gramatical errors so the spelling police on this board will have something to do.
All photos with the meters connected to a 12v battery only.
This post was edited by electro on 01/12/2022 at 06:53 pm.
I know some meters have 1/2 rectifiers that do not do well with DC on an AC setting. The better meters, analog type, have a diode/resistor bridge to compensate for the expected 1/2 wave input but getting pure DC. I am not sure how the digital meters handle the analog to digital conversion but I assume they still use a 1/2 rectifier circuit with or without a bridge.
My Fluke 77 will measure zero volts from a battery when in the AC mode. My Harbor Freight meter will measure correctly on the DC setting but similar to what you were getting on the AC setting. This is the reading on a 12v battery only with not charger or desulfinator attached.
My true RMS meter read correctly, the inexpensive Speco analog was off by a factor of two ( which fits with a non-bridged 1/2 wave rectifier), my Simpson 260 was accurate, my expensive Triplet 630 was off by 2X. Some of my other meters dating to the 1930s were accurate, others off by 2X.
None of the reading changed with a desulfinator attached to the battery, those meters will not respond fast enough to pick up the short pulse of dc, you need a scope for that.
Normally I trust the HF meters but the fault with digital anything, meters, calculators, etc., is that it is easy to believe what the display reads even if it does not make sense. Always do a real world check.
You are not measuring an AC voltage, you are just looking at an inaccurate output from your meter as well as using the meter incorrectly. Put a blocking capacitor in series with the meter and I expect you will get an AC voltage reading of zero. Some meters, Simpson, Triplett have a setting with a blocking capacitor. I expect others, such as Fluke, are always using a blocker of some type. When trying to sort out AC or pulsating DC from a DC bias, always use either a scope or a blocker of some sort.
Try measuring the battery voltage only, no desulfinator mode, and see what you get for an AC voltage. Some desulfinators do raise the voltage fairly high and that may show but I think it is unlikely your meter could measure the desulfinating pulse. However, there are may types and protocols associated with desulfination and your may well have a very long pulse that is picked up by the HF meter but it seems unlikely especially given the reading I got with my meters on a battery alone.
With the advent of modern electronics and PWM and buck boost power supplies, you do not have to go to an RV dealership to get a fancy expensive 3 or 4 stage charger. I have not looked at the battery charger aisle at Walmart but they may have a selection.
PS
I left in some spelling and gramatical errors so the spelling police on this board will have something to do.
All photos with the meters connected to a 12v battery only.
This post was edited by electro on 01/12/2022 at 06:53 pm.
Billy Shafer
Well-known Member
I would be very careful about shocking a battery. I have seen too many explode. If you are going to do it. Wear protection.
MarkB_MI
Well-known Member
- Location
- Motown USA
> I know some meters have 1/2 rectifiers that do not do well with DC on an AC setting. The better meters, analog type, have a diode/resistor bridge to compensate for the expected 1/2 wave input but getting pure DC. I am not sure how the digital meters handle the analog to digital conversion but I assume they still use a 1/2 rectifier circuit with or without a bridge.
It's not a matter of half-wave versus full-wave rectification. It's how the AC signal is converted to a digital value. Non-true RMS meters assume a sinusoidal waveform, and detect the peak value of the rectified input waveform. The TRMS value of a sine wave is peak value times 0.707 (the square root of 2 divided by 2). For a non-sinusoidal wave form such as a square wave or pulse, a peak-averaging multimeter will produce an erroneous value. For a square wave, the peak and RMS values are the same. For a pulsing signal, like the charger desulfation mode, the peak voltage will be much greater than the RMS value.
Your Fluke 77 is a peak-averaging DMM. Your Simpson 260 does not read true RMS, but by its analog nature isn't as easily tricked as a peak-averaging DMM. Back in the day they made true RMS analog voltmeters for laboratory purposes; they were quite expensive.
To determine the true RMS voltage of a waveform, a digital meter has to determine how much heat the waveform can generate. I think back in the early days of digital multimeters they used an actual resistor and measured how much heat it put out. This was inherently inaccurate, which is why peak-averaging meters were preferred for most applications. I believe modern TRMS meters sample the entire waveform and digitize it, then calculate the RMS value of the sampled waveform. (Early day analog to digital converters weren't fast enough to do this, at least those cheap enough to put in an affordable meter.)
It's not a matter of half-wave versus full-wave rectification. It's how the AC signal is converted to a digital value. Non-true RMS meters assume a sinusoidal waveform, and detect the peak value of the rectified input waveform. The TRMS value of a sine wave is peak value times 0.707 (the square root of 2 divided by 2). For a non-sinusoidal wave form such as a square wave or pulse, a peak-averaging multimeter will produce an erroneous value. For a square wave, the peak and RMS values are the same. For a pulsing signal, like the charger desulfation mode, the peak voltage will be much greater than the RMS value.
Your Fluke 77 is a peak-averaging DMM. Your Simpson 260 does not read true RMS, but by its analog nature isn't as easily tricked as a peak-averaging DMM. Back in the day they made true RMS analog voltmeters for laboratory purposes; they were quite expensive.
To determine the true RMS voltage of a waveform, a digital meter has to determine how much heat the waveform can generate. I think back in the early days of digital multimeters they used an actual resistor and measured how much heat it put out. This was inherently inaccurate, which is why peak-averaging meters were preferred for most applications. I believe modern TRMS meters sample the entire waveform and digitize it, then calculate the RMS value of the sampled waveform. (Early day analog to digital converters weren't fast enough to do this, at least those cheap enough to put in an affordable meter.)
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.
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.
MarkB_MI
Well-known Member
- Location
- Motown USA
> 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.
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.
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/public..._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.
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/public..._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.
We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.
Copyright © 1997-2025 Yesterday's Tractor Co.
All Rights Reserved. Reproduction of any part of this website, including design and content, without written permission is strictly prohibited. Trade Marks and Trade Names contained and used in this Website are those of others, and are used in this Website in a descriptive sense to refer to the products of others. Use of this Web site constitutes acceptance of our User Agreement and Privacy Policy TRADEMARK DISCLAIMER: Tradenames and Trademarks referred to within Yesterday's Tractor Co. products and within the Yesterday's Tractor Co. websites are the property of their respective trademark holders. None of these trademark holders are affiliated with Yesterday's Tractor Co., our products, or our website nor are we sponsored by them. John Deere and its logos are the registered trademarks of the John Deere Corporation. Agco, Agco Allis, White, Massey Ferguson and their logos are the registered trademarks of AGCO Corporation. Case, Case-IH, Farmall, International Harvester, New Holland and their logos are registered trademarks of CNH Global N.V.
Yesterday's Tractors - Antique Tractor Headquarters
Website Accessibility Policy