I am not an electrical engineer, so I don’t know whether this was a good idea or not. I’m curious to hear yalls’ thoughts.
Since both weight and space are concerns on longer hiking and camping trips, I abjure the idea of bringing single-purpose batteries. Why should I bring a battery that only powers the KX2? I also need a battery bank to top up my cell phone, so shouldn’t I be able to use that for everything?
I’m not inclined to homebrew a LiFePo4 battery bank–see previous re: not an electrical engineer. Nor am I keen to use a step-up voltage adapter to make a 5V battery bank supply 12V for the KX2 since I’ve heard that can have bad effects on the output RF. I took the easy route and bought a USB-C Power Delivery-capable power bank. PD is a protocol for negotiating power supply between devices, and there are various little boards you can buy that act as configurable terminators for homebrew devices. I don’t like that they’re mostly naked PCBs, and cases for them are hard to come by, and I’m lazy, so instead of using one of those I found a cable that includes a built-in terminator for 12V PD, cut the end off, and soldered on a barrel adapter. As an added bonus, I can power the KX2 from a USB-C PD wall charger when I’m using it in my shack at home… or could, if I had anywhere to put an antenna at home…
I don’t think there’s any step up/step down conversion involved so it seems safe to me. I’ve made several contacts over FT8 using this arrangement, but given the insane amount of error correction involved with that I doubt I’d notice any negative effects anyway.
Time to learn then. Enjoyment gained from using homebrewed equipment greatly exceeds that from using stuff you bought. ISTR the license document says one of the conditions of the licence is self-training in radio communication.
If at some point you decide to go the LIPO route, there are little (smaller than a matchbox) voltage monitor display units (<$10) that connect to the charger lead not the main output lead and have a USB socket on them that can be used to plug your normal phones charger cable into, whether that is a micro-USB or USB-C socket on the phone.
Does the KX2 draw enough to keep the battery bank on? I am using a step up USB cable to power my MTR3B and most battery banks shut down after 30 seconds or so because of this. I finally find a bank with “trickle” mode which stays on and works great with the MTR. Into my 40m monoband EFHW, the noise doesnt sound any different between the step up cable and a 9v battery. But, I am not an expert so your mileage may vary. I wonder if the PD negotiation keeps it from shutting down?
There is a lot going on in the market. A device like the one Jens suggested is available in German supermarkets (e.g. Aldi) again and again for about 70 Euros. They have a 12V output that delivers 10A. That would be nice for a small PA.
I can’t say whether they switch off on reception due to the low power consumption of the KX2. Does anyone have any experience of this?
I don’t have a KX2 but just checked my power bank: Without switching anything on, there’s 12V available at the output when I connect a multimeter. So it should be OK with a radio with low current draw on RX.
The 10A in the spec is not really a hard limit: I used the power bank with my FT-891 before I bought my big LiFePo4 pack, and managed to operate the TRX with 100 W for about 15 minutes. With 20 W out, I could get about an hour of operating time.
I just tried this for use with my MTR3b. I purchased the USB-C cable that you linked and then soldered on a 4x1.7mm DC plug onto it. For some reason I am only getting 5v out of anything I plug it into. My battery bank does support PD.
Not sure how else to troubleshoot this as the USB-C cable has a metal housing (really nice quality) and I can’t get to the internals without destroying it.
One thing to check is that your battery bank supports 12V PD output. I understand 12V output is less commonly supported, so I made sure to find a bank that explicitly supports it. Otherwise, I think it may back off to the standard 5V output.
Yes it does support 12v/1.3amp PD output. I also tried it with a 30w PD wall plug too. 5v from that as well.
I wonder if the 12v negotiation takes into account the load the device at the other end is requiring? The KX2 might be drawing enough to get the PD trigger in the cable to request 12v where the MTR might not be drawing enough?
Very curious. I think the PD voltage negotiation occurs irrespective of the current draw–at least mine has only ever drawn 12V when tested with a multimeter. What battery bank and wall charger do you have?