Capacitors TX board - Printable Version

Capacitors TX board - Printable Version

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Capacitors TX board - engolling - 20-03-2018

Hello,
I have a question concerning the capacitors on the TX 3.12 board.

C3: Is there any reason why this capacitor is chosen so big? Neither the 7809 requires such a big output capacitance nor the AMS1117 such a input capacitance.

Another problem is I can't get such a big capacitor with a 2,54mm grid. So if there is no specific reason which I don't see at the moment? If not I would use 100µF for C3. This should be sufficient.

I noticed if you power the TX board without a battery but with a non stabilized power supply it could be necerssary to add an additional capacitor on the input of the 7809 voltage regulator.

RE: Capacitors TX board - werk_ag - 21-03-2018

Hi,

100 to 220uF is just fine.
On schematics, C3 have a value of 470uF mainly because of the possible use of a fan for the Radiation Shield.

Quote:I noticed if you power the TX board without a battery but with a non stabilized power supply it could be necerssary to add an additional capacitor on the input of the 7809 voltage regulator.

Here a small trick, which help to avoid the inefficient 7809 regulator.

- If you have the 7809 already installed, remove it.
- On the TX board, do a shunt between input and output pins of the 7809 regulator.
- Take a step down converter module like the one below. They cost less than $1

[Image: m6K-zF7pP4CF4DmAKCFp5Ig.jpg]

- Connect your power source to the module input, and adjust voltage output to 9V.
- Connect the output of the module, to TX power in.
- If you are using +Bat pin to monitor the battery voltage in a solar system, just keep it connected to positive (+) battery terminal.

I think you catch the idea...

RE: Capacitors TX board - engolling - 21-03-2018

Hello Werk,

thank you for your Feedback. I understand perfectly what you mean. So I was asking myself why the 7809 is used for battery applications.
In my case it would not matter since I will have mains supply at my TX station to power all my heating systems.

Engolling

RE: Capacitors TX board - werk_ag - 21-03-2018

(21-03-2018, 08:11)engolling Wrote: Hello Werk,

... So I was asking myself why the 7809 is used for battery applications.

The main reason is limiting the power voltage applied to the transmitter module. Specs say that it can be powered to up to 12V, however my experience says that 12V is the maximum allowed and they don't last too much when powered by 12V, by other side the output of most of the cheap solar controllers aren't regulated to 12V and often you can measure 14.8V or more, so not having 7809 regulator will make that the AMS1117 regulator will have to dissipate more power, producing more heat.

RE: Capacitors TX board - engolling - 22-03-2018

Hello Werk,

thanks for your explanation, but I think this was a misunderstanding. I know why the voltage regulator is used, but I was asking myself why this linear regulator is used for a potentially battery powered application since it is not very efficient.
So I was wondering if you chose it because of the small voltage ripple of a linear regulator.

In using a switching regulator i could suggest this ones:
https://www.aliexpress.com/item/5pcs-DC-DC-Converter-Step-Down-Buck-40-5V-to-0-9-30V-Adjustable-Power-Supply/32670818900.html?spm=2114.search0104.3.15.24bb7ccfQ8RIhM&ws_ab_test=searchweb0_0,searchweb201602_2_10320_10152_10321_10065_10151_10344_10068_10342_10547_10343_10322_10340_10548_10341_10193_10696_10194_10084_10083_10618_10304_10307_10302_10180_5711215_10313_10059_10184_10534_100031_10319_10103_10624_10623_443_10622_10186_10621_10620,searchweb201603_49,ppcSwitch_5&algo_expid=75982715-6f45-4595-a974-adcc596fe0d3-2&algo_pvid=75982715-6f45-4595-a974-adcc596fe0d3&priceBeautifyAB=0

They a pin compatible to the already used 7809 and could be a good alternative.

Regards,
engolling

RE: Capacitors TX board - Shred - 23-03-2018

There are other drop-in switching regulators too. I installed a "Traco Power 1-2409" and have never had a problem with it. I think it reduced the standby power consumption from 28mA to 21mA.

If you're really interested in reducing the Tx power consumption, getting rid of the LED and installing a switch to cut power to the Arduino USB interface are more worthwhile modifications.

On the other hand: I think most of us have just gone with larger solar panels and batteries. It's much easier and leaves room for future enhancements.

RE: Capacitors TX board - werk_ag - 23-03-2018

(22-03-2018, 22:23)engolling Wrote: So I was wondering if you chose it because of the small voltage ripple of a linear regulator.

Hi,
I chosen the linear regulator just by simplicity and price. At the time where the TX board was designed, DC-DC converters were not so common and cheap as they are today.

RE: Capacitors TX board - engolling - 02-05-2018

Quick feedback from my side: The adjustable DCDC replacement step down converters from ebay or ali express are also working fine as the 7809 linear regulators.
Up to now I did not check the difference of current consumption, but if I find some time I will do a measurement.

Regards,
Engolling