In reply to G4OBK:
Hi Phil,
a very interesting reading about your experience with the new lipos.
Perhaps there may be a temperature drift at the overvoltage protection of the FT-857?
Therefore it could be useful to test both - the radio and the lipos - in a cold environment.
Good luck!
73 Lutz
In reply to DL3SBA:
That is a good point Lutz and a possible explanation…I await a cold night and an early rise to set up the rig and the LiPo battery in the garden when the temperature is below zero centigrade. Tonight 2c.
73 Phil
In reply to G4OBK:
Hi Phil.When you do the test why not leave a 7ah slab outside as well to do a comparison atb Geoff.
In reply to G4ERP:
Hi Richard
Many thanks for the info. As a chemist (though long retired from that profession) I am intrigued by the concept of the batteries becoming effectively overcharged when their temperature is reduced. Are you able to give me any pointers to references in the literature where I might be able to research this effect further? I have found no references to a requirement to restrict level of charge when used at low temperature in the manufacturer’s data sheets or patents and most of the original work seems to be published in subscription-only journals. I am left wondering what the safety issues are, given that LiPo’s are specified for use down to -20C and the proclivity of certain SOTA activators to use them at temperatures well below freezing!
Any help much appreciated
73 de Paul G4MD
In reply to G4MD:
Good afternoon, Paul.
I think I can say that the information came from a major manufacturer of Lithum-based batteries but if you want any more details, it had better be direct.
You may well find something written in the regulations relating to the air transportation of these devices.
73, Richard (drying out after a soggy walk along the Cotswold escarpment - TNX G3NYY and 2E0XTL for the summits)
In reply to G4ERP:
Hi Richard,
Many thanks for the pointers which have eventually led me to an extensive source of material that’s given me understanding of what’s going on - although it’s going to take days to fully digest!
Two things have rapidly become clear, however, and I state them here as several users of LiPo’s may be interested. Note however that this info is based on reputable manufacturer’s info, and may not apply to batteries from less reliable sources ;-0
There does not appear to be any safety risk associated with the use of LiPo batteries at low temperature
The loss of capacity at low temperatures is severe - possibly 15% at 0C, 50% at -10C and 75% at -20C. Terminal voltage is also depressed - as low as 3.5V for a fully charged cell at -20C.
Research is ongoing…
73 de Paul G4MD
Hi All
I was let down once again by my 14.8V 5000 mAH 4S1P LiPo battery on Tuesday when I activated NP-016 Dodd Fell Hill.
I did not have a voltmeter but I took a 7 AH Slab and that got me got me QRV no bother.
For the record the walk in was 3.25 miles (each way) in full sun with temperatures in the shade of -4c. At the summit the temperature was -2.5c. The LiPo was carried in three layers of bubble wrap inside a small thermal cold bag and still it would not activate my FT-857 when connected. I left the LiPo on top of the trig point in full sun whilst I operated using the Slab and then checked it after about 80 minutes when I went QRT. This time the LiPO worked indicating 16v on the display, so either a rest or a good warm in the sun did the trick. When I got home I checked the battery and found it was fully charged within two minutes of connecting it to the balanced charger.
I put the Lipo in my freezer a few days ago in temperatures of -17c for an hour. It worked perfectly when brought out. I’m coming to the conclusion that movement in transmit is affecting the charactistics of the Lipo and causing a large voltage drop for some considerable time - any comments from anyone if this could be and explanation?
It’s -3c at present and may get colder so the Lipo is outside now. I’ll give it a good shake before I try it out at 8.30am!
73
Phil
but I took a 7 AH Slab and that got me got me QRV no bother
SLABs - it’s the future!
Tom M1EYP
In reply to M1EYP:
Yes Tom - it may be so in my case. SLABs may be the future…
Very frustrating getting to the bottom of this.
The batteries were left out last night in my garden in temperatures of -3c. One completely exposed one in a plastic bag. I took out my FT-857 to see if they would supply current and bingo they worked. The temperature then was -1c. So for some reason they do not like being walked to the top of a summit, even when they are wrapped in swaddling clothes, but they will function when left outside stationary in similar or colder temperatures.
It is looking like movement is affecting these particualr LiPo’s and they are failing due to this.
73 Phil
In reply to G4OBK:
(This time I’ll post it under the correct username!)
The problem will be obvious once we know what it is! However, something smells wrong somewhere. I’ve got a pair of 3S1P packs that have worked at at least -10C if not lower. They’re not particular well wrapped up, just a layer of bubble wrap and into the rucksack. I’ve not exhausted them on my activations and I’ve done a few when I’ve not charged them between outings. I think this mirrors a lot of other people’s experience.
So that suggests there is another failure mode in play here. Given that everything seems fine business when at room temperature, I’m thinking there’s a connection that’s going OC when cold. Possibly one of the inter cell connections is dodgy and when subjected to prolonged cold and vibration it fails. Once allowed to warm up, it may expand enough to make contact again. Just a thought without seeing the packs in question.
Andy
MM0FMF
In reply to G4OBK:
Hi Phil
Chemically speaking, there is nothing in a LiPo that shaking or movement could affect, so a mechanical problem may be to blame - like Andy and several others, I have used LiPo’s well below freezing with no problems.
The other possibility is still the rig - after over an hour’s operating on the SLAB, it would no doubt have been considerably warmer than when first switched on so a temperature sensitive overvoltage protection system in the '857 could still be the culprit! Perhaps you could try putting the radio in the freezer instead of the LiPo. Once you can replicate the problem you could try the LiPo with a couple of diodes in series to drop it’s voltage and if the problem goes away Bingo!
Looking forward to the next chapter in the saga…
vy 73 de Paul G4MD
Yes Paul - Andy may be on the right track, but if so both batteries have got the same dodgy connections - unlikely I would say, although they did come from the same source. I won’t risk putting the radio in the freezer, too expensive a risk, but I will try it in sub zero overnight temperatures and see how that checks out.
I’m looking to buy one of the 11.2v LiPo’s as well now.
73 Phil
In reply to G4OBK:
I’m looking to buy one of the 11.2v LiPo’s as well now.
I’m looking the other way Phil. When the 3 cell LiPos I use get down to the 11.1V plateau, they still give ample power out, but the audio on the 857 goes distorted. The sub-standard tonal report you gave me the other day on CW would have been far worse had I been using SSB. John M0JDK witnessed the result when I was on Harter Fell on Monday. I’m looking at either going to 4 cell batteries with diode droppers or perhaps adding a NiMH D booster cell (readily available at 10AH) to the 3 cell LiPos I have to raise the voltage by 1.2V.
If you hear a loud bang, you’ll know I’ve got it wrong!
73, Gerald
P.S. Has anyone used a NiMH cell to boost a LiPo before? I know Nigel G6SFP uses NiMH to successfully boost a SLAB, but I don’t recall anyone saying they have combined NiMH and LiPo technologies.
In reply to G4OBK:
Hi, Phil.
Is the 3S pack for use with the FT-857? I had’t realised that was what Gerald was using. Do you know which one you’re going for?
I’m currently load testing some new 3S packs - but not at the currents you would be drawing. This is for use in a couple of weeks when I’m going walking. Funnily enough, I also planned to see how good they are at low temperatures if I get time.
73, Richard
In reply to G4OIG:
Hi Gerald
adding a NiMH D booster cell (readily available at 10AH) to
the 3 cell LiPos I have to raise the voltage by 1.2V
I would advise extreme caution with this! We take great care to ensure our LiPo’s individual cells are well balanced, to effectively add another cell of widely differing properties to the battery could have unexpected results. A brief survey of available info indicates that the internal resistance of both LiPo’s and NiMH cells varies widely between manufacturers, testing of the actual cells to be used may be necessary to determine compatibility; bearing in mind that the terminal voltage and internal resistance of the two different chemistries change at differing rates as the cells discharge.
Modelling the action of the combination of cells during discharge would be a very interesting exercise!
If you hear a loud bang, you’ll know I’ve got it wrong!
And a complex one…
73 de Paul G4MD
In reply to G4OIG:
I am using a Lipo and NiMH mixture since last september. The results are very good. For charging I have to seperate each battery type and charge the Lipo and the NiMH cell individual. The question I asked myself was to add one or two NiMH cells to a 11,1V Lipo:
discharged charged
3S Lipo 9,0V 12,6V
+ 1 NiMH cell 1,0V 1,4V
-----------------------------------
total voltage 10,0V 14,0V
3S Lipo 9,0V 12,6V
+ 2 NiMH cells 2,0V 2,8V
-----------------------------------
total voltage 11,0V 15,4V
I have choosen the combination with 2 NiMH cells, because the voltage range fits best to my transceiver, which needs 13,8V ± 15%.
I am using a combination with a 11,1V 20 Ah Lipo and 4 piece 11Ah NiMH cells for my QRO Rig (TS-480SAT) and I have built a smaller combination with a 11,1V 5Ah Lipo and 2 piece 4,6 Ah NiMH sub C cells for my QRP Rig (IC-703).
Up to now I have had no problems with this hybrid battery pack, but “if you hear a loud bang, you’ll know I’ve got it wrong!”
73 Lutz
In reply to DL3SBA:
Hi Lutz,
Many thanks for the information. I understand the issues involved (as highlighted by Paul G4MD) and you certainly have faced them head on in a big way. A 20AH LiPo on its own would worry me, let alone adding another 11AH of NiMH to it! The combination could start a car!
I am interested in using 10AH NiMH D cells as they are rated at 3C (peak current 30A) which is well within the 5.5A that the 857 takes at 25W output on 2m. I would use these with my 4AH LiPos which are 15C peak rated. The alternative is to use 14.8V LiPos and a diode dropper and accept the power lost in heat. Maybe I should try both ideas and see which performs best.
73, Gerald
In reply to G4OIG:
I think Lutz’s idea of extra NiMH cells top up the voltage is an excellent one for when you do need around 14V. I much prefer the idea of adding a cell than using a diode to drop the excess voltage even though the diode wont weigh anything like an extra cell or two do.
Andy
MM0FMF
In reply to MM0FMF:
Hi Andy.Like Phil I am using two 7.4 volt 5000 mah lipo batteries in series when fully charged they show 16.8 volts .Mine have not been charged for about 4 weeks now and when checked last night showed 14.8 volts.I left them out on the bird table overnight where the temp dropped to -2 checked again this morning and they still showed 14.8 volts.I connected the Icom Ic 706 and it still gave a full 100 watts on 40 metres when connected to a Yaesu 150 watt dummy load /watt meter.I wonder if one of Phil`s cells are faulty.I would gladly loan mine to Phil if he would like to do some comparison tests .ATB Geoff
In reply to MM0FMF:
… even though the diode wont weigh anything like an extra cell or two do.
Well the weight is not an issue Andy. You either have a 4S LiPo plus a couple of stud diodes on a small heat sink and a flying shorting lead or a 3S LiPo and a NiMH cell. Both would weigh something in the region of 450g.
Having heard from Lutz, I am minded to go the NiMH route on account of the fact that I have 3S LiPos already. If I continue to use the 857 on the hills rather than the 817, then the ones I have will become redundant.
The alternative route going to 4S LiPos can be achieved in two ways - either I can buy 4 packs which are 4S (I need 4 summits worth of power), in which case I need a new charger, or I buy 8 packs which are 2S and use them in series and accept additional charging time using my existing 2S/3S chargers. Ideally I would purchase 1S packs to add to the 3S packs I already have, but they just don’t appear to exist at 4000mAH and I’m not doing surgery on a couple of 2S packs to split them in two… for obvious reasons!
73, Gerald