- Charging gel cells in series - 1 Update
- HP 339A Info - 3 Updates
- Measuring audio amp output power - 1 Update
| pedro <me@privacy.net>: Aug 03 07:16PM +0800 On Fri, 26 Jun 2015 10:46:48 -0700 (PDT), captainvideo462009@gmail.com wrote: >On Friday, June 26, 2015 at 12:08:38 PM UTC-4, captainvi...@gmail.com wrote: >> I have a customer who wants to buy twelve 12.0 volt 8.0 AH gel cells from me. He uses these in his fire alarm panels and wants to keep a quantity in stock for when one of these panels goes down for battery failure. I've explained to him about the need for trickle charging these while they're sitting on the shelf, and rather than sell him 12 individual trickle chargers I was wondering if anyone knows of a cost effective series charger whereby I could put perhaps 6 in series and charge them all at the same time. I would probably not want to go above 6 and I would not do this with anything other than new batteries all of the same type and rating. Thanks, Lenny >I was under the impression that parallel charging was not the way to go because it is difficult if not virtually impossible to equalize the current through each battery. Batteries having a lower terminal voltage would draw more current. The inverse would then be true with a higher terminal voltage. In series the entire string gets the same amount of current. Lenny Lead-acid batteries charging is VOLTAGE-controlled, unlike NiXX. So parallel charging - well, floating actually - is what is required. Refer to the cell manufacturer for the appropriate voltage and do as Tom Miller suggested. |
| Phil Allison <pallison49@gmail.com>: Aug 02 07:42PM -0700 Phil Hobbs wrote: Phil Allison wrote: > >> The square wave/attenuator trick does all of that. > > ** Like hell it does. > Really? Why not? ** Passing test 2 is essential, it shows the instrument complies with the definition of THD+N used in audio. Unlike your test, it identifies if the notch has the required narrow bandwidth and that the high frequency response is correct. Your test, if done at 8kHz or above, will show a significant under reading error on a faultless instrument due to progressive attenuation of the harmonics. BTW: A *far simpler* test of overall THD reading accuracy is to mix a small sine wave signal of known amplitude from another oscillator with the internal one. Long as the new frequency is set clear of the notch filter's effect, the correct reading in percentage is easily calculated. .... Phil |
| jurb6006@gmail.com: Aug 02 09:32PM -0700 >"due to progressive attenuation of the harmonics. " Seems you have answered a question I have not yet asked. Like, if the reading is to be considered valid there has to be a specified bandwidth otherwise you are excluding the meaningful or including the useless. Like, you do not need to know the content at 4.8 GHz. So 100 KHz is the cutoff then ? I never checked. Seems reasonable, that would be the fifth harmonic of 20 KHz. If anyone can hear that we should all line up to kiss their ass and give them time to advertise the tickets. Anyway, my buddy took it home today. It is his actually, but we just umm, don't care which place a certain piece of equipment is at all the time. But now I want to get more specific on this mixing a square wavee into the sine wave thing to do an ersatz calibration check. Right now it is reading pretty high distortion on its internal oscillator, and actually reading lower on my Wavetek. I haven't been to all the ranges of the internal oscillator yet, nor on the Wavetek. At 1 KHz, the Wavetek read like 0.48 %. the internal oscillator was like 27 %. This does not seem right, maybe a ground problem or bypass caps or something because it just doesn't seem all that likely. I would like to have a distortion meter to check the oscillator on this distortion meter. Yup. The wavefoprm looks alright by eye. I did not try nulling it with the Wavetek nor doing the Lissajous thing to see if I oculd get a decent circle. but it looked alraght and back then I did see a decent sine wave. the high distortion reading came after it had an all night burn in. Then, unfortunately it was time to go. He has to learn how do run the thing. Hey, I didn't know initially. I know the theory behind it but operation is another thing. I got it figured out pretty much and next will come the finer points. Like, yeah it measures, but does it measure accurately ? Next question. This thing FILTERS, not really nulls out the fundamental. this allowws it to accurately measure through a system that has phase shift. Otherwise an OP AMP would make the best distortion meter. So it gets lovcked to that frequency by something that resembles a PLL at least remotely. Now, if I have 1 V P-P sine going in there at 1 KHz, if I took another generator, not locked or anything to the fundamental one, and injected a 2 KHz sine wave into it, the distortion meter should read that accurately, correct ? I mean I am putting in a controlled amount of the second harmonic, but it is not locked in any phase relationship and in fact is not even frequency locked. WILL THAT WORK ? That thing wiht the mixing a square wave with the sine wave, I want to try that. But the ratio, is it RMS voltage or P-P ? A sine wave makes it easy because it is the same as the fundamental. Adding it at the second harmonic at 10 % the amplitude clearly should read 10 % on the meter, correct ? In fact, now that I think of it I shold be able to add ANY frequency to it not at the fundamental and the meter should read that. Read the dB scale or the percentage, whatever snokes ya up. (yeah, I hear some are starting to describes THD in -dB instead of percent) Anyway, now that I think of it, all I need is a second generator. Interesting. |
| Phil Allison <pallison49@gmail.com>: Aug 02 11:17PM -0700 > >"due to progressive attenuation of the harmonics. " > So 100 KHz is the cutoff then ? ** It's the typical -3dB point of the metering circuit. > I never checked. Seems reasonable, that would be the fifth harmonic of 20 KHz. ** Correct - 2nd, 3rd & 5th harmonics plus noise are read by the meter when if 20kHz is the fundamental. By convention, this has long been is deemed adequate to quantify non-linearity in audio circuits. > Next question. This thing FILTERS, not really nulls out the fundamental. ** A notch filter IS a filter, adjusting the centre frequency to match an incoming sine wave is called " nulling". The 339A has a notch filter. > So it gets lovcked to that frequency by something that resembles a PLL at least remotely. ** The auto nulling feature tracks the incoming frequency, long as it varies slowly. Without it, small temperature drifts in the oscillator and notch filter makes manual nulling very tedious or impossible when dealing with low THD percentages. > Now, if I have 1 V P-P sine going in there at 1 KHz, if I took another generator, not locked or anything to the fundamental one, and injected a 2 KHz sine wave into it, the distortion meter should read that accurately, correct ? ** Yep - a pair of say 10kohms in a Y arrangement allows the signals to combine at the input to the 339A. The level of both will be cut in half, of course. > I mean I am putting in a controlled amount of the second harmonic, but it is not locked in any phase relationship and in fact is not even frequency locked. > WILL THAT WORK ? ** Yep. > Anyway, now that I think of it, all I need is a second generator. ** Best set the level of the second generator to not more than say 10% of the main one, so the auto-nulling system is not confused. .... Phil |
| Phil Allison <pallison49@gmail.com>: Aug 02 06:08PM -0700 Cursitor Doom wrote: > Yes, I recall 0.707 of the peak signal level. So for example if I set an > amp to some arbitrary output and feed into an 8 ohm load and measure say > 10V peak-to-peak on a scope, then I'm getting about 6.25W RMS out. ** The "peak" value is referenced to the zero line, so there are negative and positive ones. The "peak to peak" value has no polarity and is easier to read off a scope screen but to get the rms value of a sine wave one divides by 2.83 ( 2 x sq.rt 2) So in your example, that value is 3.54Vrms and the power is 1.56 watts. .... Phil |
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