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Comments by Jan
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Understanding battery capacity: Ah is not A
- 16 September 2013Matt,
As long as you are talking about "amps per hour", you do not understand it. "Per" means you are doing division, so something like "watts per hour" is very different from "watt hours", which is watts *times* hours. Units like amps and watts are already rates (coulombs per second and joules per second, respectively).
As for your main question, I specifically went over it in the post, and you got it right in your follow up post, except for the "per hour" part: a 2Ah, 10C battery can deliver 20 amps.
- Jan
Small things in the pipeline
- 9 September 2013Hello.
We have what should be a final configuration for the corresponding sensor board, so we just have to do initial production and make the product web pages and documentation. We should have that done by the end of the week.
- Jan
Understanding battery capacity: Ah is not A
- 15 August 2013How well different battery types handle high loads is generally a very relevant consideration, but your ~2 A discharge rate is not that much for these batteries, so the alkalines having 5x the capacity should far outweigh the variations in high-discharge rate characteristics.
This is not that complicated, and your latest question is whether 26 is bigger than 17. If you gave two more similar numbers, like 17 and 19, you should just try it and time it if it matters much if one does 8 hours and the other does 8.5.
- Jan
Understanding battery capacity: Ah is not A
- 14 August 2013Robert,
Your question boils down to: do D alkaline cells store more than 3.3 Ah? http://www.allaboutbatteries.com/Energy-tables.html lists 17 Ah, so if that's correct, it's no contest.
By the way, your 0.2 Ah/day will use up that 3.3 Ah in about two weeks even without any pumping, so that is not a viable option, anyway.
- Jan
Servo control interface in detail
- 14 August 2013Hello.
Thanks for that data point. I just did a quick search on Hitec's site (www.hitecrcd.com), and I see no claim there of the HSR-1425CR being digital. They say it is the continuous rotation version of their HS-425HB, which doesn't lead to anything in their search results, but HS-425BB is listed under analog servos.
If the servo is analog, the waveforms showing current in this article are consistent with your observation that the servo gives you more power out with a higher pulse rate. If Hitec is not documenting this, I think there is not much value in doing further characterizations since we do not know how much the servos can vary from unit to unit.
- Jan
Continuous-rotation servos and multi-turn servos
- 8 August 2013Hi, Merv.
1) You cannot get the servo to do anything without using the signal wire. You might get the behavior you want from a regular gearmotor (motor with gearbox, without the servo electronics).
2) Making a servo hit its mechanical limits is quite likely to damage the servo.
- Jan
Understanding battery capacity: Ah is not A
- 6 August 2013Andy,
You are correct about the calculation for the four hour estimate, and I think the "12AH/20HR" means that the 12 Ah capacity is based on a 20-hour discharge (i.e. discharged at 12/20 A, or 600 mA). In general, you will get less than the 12 Ah out of the battery if you discharge it faster, but you will probably still get close to the four hours.
- Jan
LPS331AP pressure sensor test flight
- 30 July 2013Hello.
Which specific sensor are you talking about? Have you looked at the datasheets? What characteristics do you care about?
- Jan
Servo control interface in detail
- 16 July 2013RC,
I'm happy you like the articles. I was ready for more of a discussion after Brad's post, but looks like he did not want to follow up on it. Your claim would be more credible if you were basing it on more than a Wikipedia article that starts with a disclaimer about not citing any references or sources. You acknowledge that "the terms get used kind of interchangeably these days" in the field; are you saying all those people are wrong because they do not use your more narrow definition? That could be an interesting discussion, but you would have to back it up with a lot more than "that's how I learned it".
I'm not sure what your point is with all the sine wave business; you realize that is just restating your claim and that rectangular waves (with non-50% duty cycles) can be expressed as sums of sine waves, too, right?
It would also help if you addressed the other examples I gave (test equipment, textbooks). For example, it would be interesting if you were involved with some old function generator design team at a reputable manufacturer and could tell us about an internal discussion about "square" vs. "rectangular" and you knew that the only reason the feature got called "square" was because "rectangular" couldn't fit on a button, and everyone else in the industry just followed suit. Of course, even then, you would still end up acknowledging that "square wave" is in some sense the more generic term for "rectangular wave".
- Jan
Understanding battery capacity: Ah is not A
- 8 July 2013David,
I'm not sure what you are asking. Is your safety guy saying the fuse approach is not acceptable? If you're thinking about using a 12 V lead-acid battery, those are commonly used in alarm systems, and I doubt they all need to get building permits. If they do accept the fuse or other current/power-limiting device right at the battery, the capacity shouldn't really matter, and you could use a 40 Ah battery (it would be the size of a car battery) to give you 4 A for 10 hours.
- Jan