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Good morning gentlemen.? I know that the PA of the BITX40 can handle 12V to 24V input.? My question is what can the rest of the board handle.? I have a 4 pack holder for 18650 batteries, and with them freshly charged they are at 16.5V output.? I don't want to burn up the board.? Does anyone know for sure what the circuits will handle?

Thanks

Jason

Hi Jason!

I would not go any higher than 13.8V. For the current design even that voltage is border line.

Q13 is working at the maximum ratings in terms of power dissipation.
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Ion

VA3NOI

Add an LM7812 between batteries and rig. ?Power the IRF510 directly from the battery.

The schematic in the circuit description shows the board has two voltage regulators?LM78L09 max Vin 35V, minimum Vin 10.7V, and?LM78L05ACZ max Vin 30V.

The Raduino has LM7805CT?max Vin 35V

Any common 12V voltage source like a car battery's 12.7V, or alternator charging voltage of about 13.8V is fine. Something like 16.5V should also be fine. But you should find those regulators and monitor the for excessive heat. If it burns you, or you can't keep your finger on it, it's too hot. Back off the input voltage.

The bigger the difference in voltage between source and regulator equals more energy lost as heat. Closely matching source voltage with the regulator equals low heat, and more efficiency.?

Fine for the regulators. ?Not fine for some of the other stuff, like Q13, which will get awfully hot and quite possibly blow at 16v. ?Add an LM7812 for all but the IRF510 if exceeding 12v by much. ?

I wouldn't trust a car's electrical system with engine running, or when switching on an inductive load like a fan motor. ?There can be voltage spikes. ?Automotive electronics are typically rated at 30-40v peak for a reason.

Farhan's in here somewhere saying that the board's designed for 13.8V nominal with a max of 15.

/g/BITX20/message/18201?p=Created,,,20,1,0,0::Relevance,,voltage,20,2,0,4105151

You can run one of the lithium variants as long as you don't fully charge them. ?Since lithium cobalt (typical 'LiPo' cells) hold much of their energy at higher voltage, you'll lose capacity. ?If you want to run lithium, run LiFePO4 - it has a flat discharge curve, carries most of its energy at around 3.2V per cell, and you'll have about 90% capacity/run time if you run it between 10 and 14V in a 4S string.

73

Andy

I left my BitX40 running all day on RX and I came back to TX later in the afternoon... No TX output.... Found Q13 was dead. My BitX40 was powered at 13.8v for about 8 hours on RX only and it was a warm day today with a max about 30 deg C.

I replaced the dead q13 with a 2n2222 (normal sized not SMD) and all is good with the world again.
I did also tune up a 100W AM transmitter during the day while the bitX40 was connected to another antenna, and I think I read somewhere someone else had an issue with the high level rf destroying a transistor in his BitX40. So I may have done it myself by transmitting on another radio or the 13.8v for 8 hours on a warm day killed q13 either way it shouldn't happen again to this Bitx40.
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Mike VK3XL

Here's Raj's post 19105 of Dec 16, 2016:

73 Raj vu2zap?

The track between K1 pin 12 and K2 pin 14 is only used during receive, not during transmit. ?I'd never heard of that incandescent lamp trick, wasn't sure I wanted a fragile bit of tungsten between me and my antenna. ?But AA1OF flagged me that the resistance goes up drastically with temperature. ?The first line of the document in the link that follows reads: "Tungsten-filament incandescent lamps exhibit a very-high positive temperature coefficient of resistance with the cold filament resistance being approximately 10% of the hot filament resistance."? ?Wow, very cool!

?

Those little mini 12v bulbs won't have much of a filament, likely fine through all of HF. ?

Somewhat off topic: ?When I was going to school at Oregon State in the 1970's, the EE dept storage room still had boxes of ancient Edison bulbs with carbon filaments. ?Had used them as RF dummy loads back in the day. ?The coiled up tungsten filaments of 120v household bulbs just didn't work as well. ?But a 120v 40w tungsten bulb had worked fine as a dummy load on my 40m 35w 6146 single tube crystal oscillator as a novice back in high school.

Jerry, KE7ER