Comments by Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 18 December 2017

    Hi, Cindy.

    Your math generally seems right, though the "56 mA per use" is not correct; it's that times the two minutes to get back to units for total capacity. But the 56 mA is probably a more useful figure, as long as you realize it's not "per use" but the average rate over the two minutes. Maybe the motor only runs for 10% of that, and the remaining time the current is negligible, so the peak current draw might be over half an amp but only for ten seconds.

    It sounds like the 5V, 1A adapter will likely be sufficient. In general, it's fine to use a bigger adapter since it's not going to force the currrent into your system.

    - Jan

  • Free shipping, phase two: lots more free shipping

    Free shipping, phase two: lots more free shipping

    - 1 November 2017

    Hi, Dave.

    If you meet us half way, you can get in on the free shipping! Hawaii has other benefits, too.

    I know it's not the same as free shipping, but our international shipping rates are going down, and we keep working on getting them lower. Please also support your local distributors, and maybe bug them for free shipping!

    - Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 18 October 2017

    Hi,

    Your initial calculations seem right, except for the last one being a bit off: for 8 of those D cells I get 17*8*1.5=204; divide that by 4.8 and I get 42.5, not 43.75. Maybe you were approximating that 17 is basically half of 35 since 43.75 is half of the earlier 87.5.

    For the last part, you can be pretty sure about the battery side. If you have 2Ah * 1.2V * 3 = 7.2Wh and you're getting many hours out of it, you can be sure the load is actually less than 3.6W. Maybe that's some conservative upper limit, perhaps at a higher voltage like 4.8V (1.6V per cell), and the actual consumption might be half that at 3.5V and drop even more as the battery voltage goes down. If there isn't some fancy flashing pattern, it should be really easy to just measure the current at different voltages.

    - Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 11 October 2017

    Hi.

    For the first question, yeah, your power should basically scale with the number of motors. Keep in mind that you won't necessarily get to use that extra power the way you want to, which brings us to your second question, where the answer totally depends on your system. Even if you have a system in which your output power is constrained to be the exact same in both scenarios, your system efficiencies will not be the same, and more importantly, the motors would not be operating at the same efficiency points. Back to real life systems, if you have more power available, your robot will move faster at top speed or accelerate more quickly, so your output power is unlikely to be constrained to the same value in both situations.

    - Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 22 September 2017

    Hello.

    If you understand the system you are putting the battery into, you should be able to tell if anything would be affected badly. The 10 Ah battery should last about four times as long as the 2.5 Ah battery, and if you don't change anything, charging should take about four times as long. If you are putting the battery into a system you do not understand or control, things could be more complicated, depending on how smart or helpful your device is. For instance, you might be fine waiting 20 hours instead of five hours for charging, but your device might have a timeout after six hours or it might think there is a problem and stop working normally.

    - Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 30 August 2017

    Hello, Don.

    You generally cannot force a current out of a battery and into something. If you have a load that wants to use 3A when you connect it to 12V, the battery should be capable of delivering that.

    - Jan

  • Electrical characteristics of servos and introduction to the servo control interface

    Electrical characteristics of servos and introduction to the servo control interface

    - 14 June 2017

    Hi, Gustavo.

    Your question is not clear. If you are asking about characteristics of servos, as in can you stick 1.2k in series between your RC control signal and the servo (NOT between signal and ground, which would be in parallel with the servo), it's a little more than I'm comfortable with (I would use something like 220 ohms) but should probably be fine. Things like the particular servo you have and the wiring lengths will matter, so you should try to look at the signal on the servo side with an oscilloscope to make sure it looks decent.

    If you are asking about the characteristics of receivers or other servo controllers, as in can you put a 1.2k resistor in parallel (NOT series) between signal and ground, that will depend on your receiver, and 1.2k is a little on the small side (I would use about 10k for a pull-down resistor). You can again look at the signal with an oscilloscope to see if the resistor is deforming the signal too much.

    - Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 31 May 2017

    Hi, Kerron.

    Yes, that's right: 24V could damage a device expecting 18V, and the current part should be okay. (So you should use your device with an 18V voltage regulator, and make sure that it can comfortably take a 24V input and deliver at least the 1.67A you need.)

    - Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 22 May 2017

    Hi.

    It looks like you either did not read the blog post or did not get the point of it. 20A is about how fast you can get the energy out, not the capacity of the cell. 3.7V and 2.2 Ah give you 8.14 Wh per cell, and that multiplied by 1234 gives you just over the 10 kWh.

    - Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 16 May 2017

    Hi.

    A 12V adapter connected directly to the battery is unlikely to be an appropriate charger. A 12V battery showing you 9V is definitely not good and charged. I am not sure how you are measuring the 0.2amps, that will be a function of your load, and a good battery should definitely be able to supply much more than that. The voltage will gradually go down as your battery discharges. You can probably find a datasheet for the battery you are using and get more specific information. You will need to regulate to 5V anyway, so your main concern should be not discharging your battery too much. And you should get a switching regulator, which should need less than 500mA to output 1A when going from 12V to 5V.

    - Jan

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