My VHF activation of G/DC-003 came to an abrupt end this afternoon when the radio screen went completely blank in the middle of a QSO. I checked fuses and connections from the battery but nothing would bring the radio back to life.
I only had 3 QSOs in the log but with my HT I managed a 4th with Don, G0RQL, which gained me a point as this is my first activation of the summit in 2024.
Arriving back home I checked the radio on the shack PSU and was relieved to find it was working perfectly.
On the drive back home I had begun to hope the BMS had shut the battery down and it might be working now. I was pleased to see 13.2 volts on the terminals but the radio still refused to do anything. Further tests revealed the open circuit voltage of 13.2 dropped to around 6 when it was connected to the radio. The battery, a RoyPow 12aH LiFePo4, was fully charged before the activation. The specification says it has a maximum continuous discharge current of 12 amps which I knew a 50W transmission would be very close to if not exceed. My tests on the radio (Yaesu 987D) which is new to me, using the battery over the last week had been without problems. I had used it on 2m FM but only to see what repeaters it could reach from my home QTH. I had used it on FT8 too which involves 15 second transmissions but of course that is USB so the current was probably less than during my rag-chewing on 2m FM today.
An entirely avoidable error of course. My power leads did not have an ammeter in them, which I will now add.
I’ve already ordered a replacement battery, an Eco-Worthy 20aH LiFePo4 which they say can manage a 20 amp discharge and has over-current protection. It was £80 but I got £10 off for registering with Eco-Worthy. But I will still keep an eye on the ammeter when activating. It isn’t a SOTA battery except on drive on summits but I will use it for POTA and BOTA.
For the superstitious, today was my 13th activation of G/DC-003. I don’t believe in “Unlucky 13” but I am glad my next activation will be the 14th!
John, I can barely keep an eye on the S-meter, SWR meter and logging app, while trying to extract callsigns from the noise/QRM/QSB/pile-up, so good luck with adding an ammeter into the equation. Couldn’t you just wind the power in a little and keep your life simple?
If you thought the current was close enough to exceed the max continuous current then why did you operate it at that level? If you operate the radio for long periods such that PA devices and drivers get hot, then the current consumption may rise a bit. If you were just below when cold, you would probably over when hot.
25W would drop the PA current by half in theory and would be 1/2S point less at the far end of the QSO. In the real world the reduction is not so extreme but it would certainly drop the consumption by several amps to a much safer value for continuous modes.
FT8 is a constant envelope modulation. You can see that because output power meter stays at the same level. The duty cycle is 100% unlike unprocessed SSB voice of around 20%. So it’s exactly the same as FM and will have been running your battery and BMS near or above the continuous limit.
In aviation they use the term CFIT for what you have done.
I think the ammeter will only need to be looked at occasionally. I may wire it in temporarily just to see what current is drawn on different modes and with different antenna. My IC-7300 shows the current in the finals which changes between bands and different SWRs.
I take heart from the last two Moon landings where the lander has fallen on its side. You don’t find what’s achievable unless you try. However, I guess the Moon landers had more instrumentation than my experiment had.
I agree with Fraser. Over many years running 2m SSB using a number of different rigs with and without amplifiers, I’ve found 25 to 30 watts to be about optimal for 2m SSB from a summit. In my opinion, the same is alao true for HF. This power seems to offer the best performance relative to battery current drain. Also don’t forget that some rigs like the 897 and the 857 have a fairly high current take on receive, so that needs to be considered. For that very reason I have reverted to an 817 with a linear, both for 2m and HF. My alternatives on HF are an IC-703 and a KX3, both pretty current efficient on receive.
Pity about the battery John. An expensive item, but an essential one.
Gerald, thank you and I don’t doubt cranking back the power wouldn’t have made much difference but I just wanted to see what my new toy could do when let loose.
Unfortunately, the 12aH battery I bought is not available now. They do a 6aH but given the receive current, which you mention, is around 1 amp this is too small I think.
I’m going to try the bigger is better route!
But there is always something to learn on an activation. Today, I learned when using a beam you need to sit virtually touching the mast so you can swing it easily. A simple lesson but one I hadn’t fully appreciated until today.
Once the new battery arrives I will have another go!
I do sometimes wonder. I travelled on the Herald of Free Enterprise several times and also was on HMS Antelope once. Both subsequently sunk with loss of life.
I have found that the little CB amplifier I use on 10m (a pair of FETs in push-pull) is quite sensitive to voltage. With an Avo 8 on 10A range in series to meaure the current, it produces about 30 Watts. Take the meter out (same battery) and it produces over 40W.
I haven’t taken any more measurements, but in this case the voltage drop across the ammeter has a significant effect, and the reading is clearly understating the “normal” current draw.
Your radio may behave differently, and a good digital meter with short test leads might be a lot less intrusive, but it is something to bear in mind…
(There are clamp-on ammeters for measuring dc current without breaking the circuit which would be ideal, but I don’t own one yet…)
When I used to run an 857, I produced a housing for 4 x 4.2AH LiFePO4 batteries to create a 16AH pack. For this I bought a voltmeter and an ammeter complete with a shunt resistor. The resistance of the shunt is low so I never noticed any effect having the meter in circuit. I’m rather surprised the AVO did not similarly present a low resistance.
I run my 857 from a 4.2Ah LiFePO4 (no bms) and previously used a serial power monitor that would track usage and show the present current, but mostly these days I just rely on the plug in low voltage alarm. For a given power setting I know what the draw will be, and I also find that 20-30W is the best compromise. It’s a rare day you’ll need 50W instead of 20, although today someone was getting me 42 so I cranked it to full power and improved the report the 53. More than half of contacts can be made readability 5 with 5W or less in my experience.
On the topic of maybe turning down the power, I was activating a local SOTA summit last week using my G90 which had just been returned from being repaired, and which had had a “factory reset”, so I wasn’t too sure that settings were as I wanted them to be on all bands and USB/LSB modes.
At one point in the activation, there was a lull in chaser activity, so I ran a couple of checks on various settings: imagine my surprise when I found that - despite my having got RS reports of between 53 and 59 around Europe on 20 meters - the power level was at 1W and the speech compressor was off! Normally, I operate at between 10W and 15W and compressor on - but these reports from several chasers show that even at 1W SSB good contacts can be made.
OK, having a half-decent antenna and a good take-off on a summit will help, but even so… who really needs 50W when activating SOTA?
Indeed John. I also recommend the use of a rotating guy ring such as that sold by Sotabeams (other makes may be available) for the pole when using a beam. I used to use the simple guy rings, but found the mast could be hard to rotate and I had a few shatter. I now use a rotating guy ring regardless of what I have mounted on the pole… even an HF vertical.
strange behaviour of the BMS. In case of overload or low voltage it should shut off to 0.
Depends the voltage from the load current? If yes, whats with the wires and the plug?
I have exposed the BMS and I think there is evidence of overheating. Although it was showing 13.2 volts open-circuit on the day of the activation the next day it was reading zero.
The description of the battery says it should have overload protection. I might investigate (carefully!) a bit further later.
It is common for a BMS to disconnect itself from the battery when it cuts out. Then you need to apply power to the output, or bridge the battery to the output momentarily to bring it back to life. (I have a tact switch with a 330 - 1k ohm series resistor to do this)
There is no reason to believe that 12A would fry those fets. The primary current limit is via the two parallel R0006 resistors, you can increase the current limit by lowering that R.
The BMS might also cut the pack off because a cell voltage goes too low during current peaks.
You can also monitor the actual current with your voltmeter or oscilloscope across the R0006s
Very, very many thanks. Your post made me go back and look at the battery again and discover it all seems to be working now.
Using a dummy load and power set to a sensible 20W the radio worked perfectly with the battery voltage dropping from 13.2 volts to 12.8 volts under load which is what I would expect.
It must have a very clever idiot-proof BMS. I still have a larger battery on order which I will keep for higher power or longer activations and I will keep this one, once I’ve glued it back together, for everything else.
73
John
I’m not a “big battery” guy but I am big on batteries.
Historically I have had RF issues with BMS’s and non resonant antennas. I believe triggering short circuit safety systems (presumed not confirmed) and the same behaviour presumably in USB battery banks. No issues where resonant antennas are used.
Just my 2p may not be of any interest or use perhaps?
The battery, a RoyPow 12aH LiFePo4, was fully charged before the activation. The specification says it has a maximum continuous discharge current of 12 amps which I knew a 50W transmission would be very close to if not exceed. My tests on the radio (Yaesu 987D) which is new to me, using the battery over the last week had been without problems. I had used it on 2m FM but only to see what repeaters it could reach from my home QTH. I had used it on FT8 too which involves 15 second transmissions but of course that is USB so the current was probably less than during my rag-chewing on 2m FM today.
It isn’t a SOTA battery except on drive on summits but I will use it for POTA and BOTA.
