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Interesting problem


#1

Last Saturday I activated Place Fell, G/LD-027, and started with 2 metres SSB, intending to go on to FM and then 5 and 7 megs. At first all went well,but my fifth contact, Mike GW0DSP, reported problems with my modulation being distorted and difficult to tune in. It seemed better when I reduced power so I signed with him and went on to call CQ. It was at this point that I noticed that the battery voltage had dropped to 10.0 on receive. Clearly there was something wrong with the battery, which had been charged up two days earlier, so I terminated the activation and descended.

Yesterday I tested the battery and it seemed alright with plenty of life in it; I charged it up fully and found it ran the rig perfectly well, even at 50 watts output. The battery is a Yuasa 12 volt 7 ampere hour gel cell. I have had it for about five years so I suppose it doesn’t owe me anything! The question is, does the first sign of a battery passing its use-by date consist of a voltage drop at low temperatures (it was just below freezing at the summit) or must I look elsewhere for the cause of the problem?

73

Brian G8ADD


#2

In reply to G8ADD:

I have had it for about five years so I suppose it

doesn’t owe me anything! The question is, does the first sign of a
battery passing its use-by date consist of a voltage drop at low
temperatures (it was just below freezing at the summit) or must I look
elsewhere for the cause of the problem?

73

Brian G8ADD

Wow!! five years old. Maybe a hint of the problem there. I tend to renew my SLABS approx after 1 year of regular use. Bear in mind that I also use them in the shack at times for experimenting.

I find that even a new SLAB suffers a bit of voltage drop in freezing conditions.

It’s a case of the old saying Brian, if in doubt, throw it out…but test it first, hi.

73
Mike GW0DSP

P.S. Do you use the heavy discharge SLABS or just the typical Yuasa alarm type battery? I find that the latter die very quickly from buckled plates if used with the 857 although they are fine with the 817.


#3

In reply to G8ADD: I was aware that the more modern cell types (even NiCads) don’t work so well at low temperatures, but I was not aware SLABS were also affected. Mind you, I’ve only used mine (A 4.2 AH from Maplin) on the FT817. You could always try cooling it in a fridge and checking capacity and internal resistance.

Good luck, Dave, M0DFA/G6DTN


#4

In reply to GW0DSP:

Hi, Mike, yes its the ordinary alarm type slab but it has not seen heavy use, the occasional outing with the 817 when I had it, and I run a florescent tube off it when camping, usually I use a 13 Ah sealed lead-acid battery with the 857 but thought that the smaller battery would be better because of the weight of extra clothing I was carrying (there had been overnight snow!)

Dave, the fridge suggestion is a good idea, I will try it!

73

Brian G8ADD


#5

In reply to G8ADD:
Hi Brian.I had a similar problem when doing Kinder Scout.My 817 kept cutting off and the battery indicator told me the battery was down to 8 volts although I had charged it the night before.I did not realise at the time that it was the internal battery that was down and it was the rig that was not accpting power from the rear socket.It was not untill I got home and dicovered you could not charge the internal battery from the rear socket that I found out it was an internal fault with the rig.It has now been repaired under warranty.Fault on main board. all the best Geoff.


#6

In reply to G6MZX:

Geoff, I had the same problem with my 817 but it was out of the warrenty period so I had a look at it myself and found that a track on the PC board from the power socket had lifted and broken, apparently this can happen if you are in the habit of running it at 5 watts! I soldered a strip of tinned copper wire along the track which increased its robustness and I didn’t get the problem again.

73

Brian G8ADD


#7

In reply to G8ADD:

Battery performance is a function of temperature. This is one of the reasons cars are harder to start when it’s very cold. Not only is the oil “stiff” and so the engine is harder to turn, but the power available from the battery is much reduced. Typically a lead-acid battery will have at best 65% efficiency at 0C compared to 25C. It drops faster as the temperature drops further.

The other thing to remember is that the rate quoted is the 20hr rate. For my 2.8Ahr battery the 1hr rate is only 1.6A. Which means I can pull 1.6A continuous for 1hr AT 25C. At 0C I can only pull 1.04A for an hour. That’s for a new battery. With repeated charge/discharge cycles the capacity will be reduced further.

The only reason why I’ve not noticed any problems with my 817 is that it doesn’t need anywhere near 13.8V to produce full output. Just as well as I’ve operated at temperatures when it was -11C in the valley in bright sunlight and my SLA has worked well enough for 2x HF activations followed by 25mins of 2.5W 2m FM activity.

Likewise charging at too high a temperature will drastically shorten SLA life. You need either a temperature compensated charger or if you stuff a fixed voltage on them, charging them in the garage in the cold is better than charging in a toasty warm shack. My own 2.8Ahr SLAB still seems to be cutting the mustard after over 100 activations and 2 years use but it doesn’t need to provide the full waft as already explained.

Andy
MM0FMF


#8

In reply to G8ADD:

Hi Brian,

I have used my SLABs at sub-zero temperatures without any problems, even on The Cheviot where there was a northerly wind blowing with the wind chill taking it down to minus 10C. I couldn’t eat my pizza, but the SLABs ran okay!

When getting set up for SOTA I did buy a number of SLABs and one of them turned out to be useless. It worked fine for several months and took charge and provided power okay. Then it started to suddenly drop down to around 10 volts after a few minutes operating. I suspect a cell has gone weak and maybe yours has gone the same way.

The issue with the PC board track may not have been due to running 5 watts all the time. John GW4BVE warned me that this can happen when the power lead flexes and puts a strain on the power socket which then breaks the connection to the track. I have strapped the power lead to the case of the rig a couple of inches from the plug to take the strain and have had no problem in 2 years of activations.

73, Gerald

P.S. Another cause of your battery failure could be your intention to go to 2m FM after SSB. Just a thought… :wink:


#9

In reply to G6MZX:
HI Geoff
A common problem with the FT-817. I also had to repair the PCB track connection to the external power socket after it broke on mine. This was around 2 years ago and it’s been OK since.

For Brian I think it’s time to replace the SLAB. Haven’t they gone up in price though over the last year or so.
73 Phil


#10

In reply to G4OIG:

Related to this battery question just for information if anybody visits northern Scandinavia in winter. The cars can normally be started at -30 C temperatures, but you should be prepared also to the case that the car does not start. That means warm clothes so that you can stay outside a few hours at these temperatures.

73, Jaakko OH7BF/F5VGL