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Battery advice


#1

Hi, Have been thinking of going down the Li-po route to supply my FT-857, but to get something ‘meaty’ ie a 30C, 14. volt 5 - 7.5 mAh battery - the cost is going up and up, especially as I need a charger aswell. Then I’ve got to reduce the voltage a bit etc.
So, Ideas on doing thios with metal hydride batteries? If I get 11 of them (1.2V each) and sourse something like a 9mAhr set up, will this work and would you guys recommend it?
Your opinion is greatfully awaited,
Regards,
John


#2

In reply to G1STQ:

The reason a lot of people use LiPo cells is because they weigh next to nothing in comparison to other battery technologies. For less weight you pay more. Of course less weight on the back is worth every penny.

So 2x 14.8A 4000mA LiPo cells + a suitable charger from eBay comes to £56.45 inc p&p from China. That’s for a fast smart charger. Slower chargers are cheaper.

Yes you need to reduce the voltage when the pack is fully charged. So for each silicon power diode you use you lose 0.9V. For simplicity people use a bridge rectifier as it’s easy to mount etc.

1x 100v PIV 25A bridge (from Maplin therefore not cheap) £2.11
2x switch 16A rocker £2.98

I’ll assume you have wire and small heatsink etc. So the cost comes to £61.54 for two batteries and a switchable dropper.

The total weight will come to somewhere around 750g for both batteries combined plus whatever your bridge-n-switches weigh.

How much will your NiMH system weigh?
How much will it cost?

If price matters more than weight then don’t buy the LiPos.

Andy
MM0FMF


#3

In reply to G1STQ:

Hi John.

I used Li-Po’s last week in the lake district with my FT-817 and they worked great. I have two 15C 11.1v 1800mAh batteries. I have them as I also fly R/C planes. Of course the issue with Li-Po’s is the charger also. You need a balancing charger unless you want to charge each cell individually. Also Li-Po’s should never be discharged below 3v per cell (9v in my 3 cell pack). The good thing with the 817 is its ability to run from 8v-15v. Not sure about the 857. I used to use a 12v 2Ah SLAB but the Li-Po’s are obviously much lighter.

I wonder what kind of current draw your 857 has at your recommended power level? I am guessing at least a couple of amps in which case you will need some high capacity NiMh sub c’s for just an hour of operating. The charged open circuit voltage will be 1.36 to 1.4v (more immediately after charging) so no more than 11 cells. A charger will be cheap enough. R/C peak chargers nowadays usually have a 1-12 cell charger circuit. They use a DC-DC converter to take 12v DC and turn it into the 17 or so volts required to charge 12 cells in series.

If you can find out the average current your 857 will use at your specified power output it would help calculate the sort of operating time you could expect from (say) 11 sub c’s of 3300mAh capacity.

Not sure what you meant by ‘a 9mAhr set up’.

Good luck! John M0UKD.


#4

In reply to M0UKD:

“I wonder what kind of current draw your 857 has at your recommended power level? I am guessing at least a couple of amps”

I reckon mine draws 22 amps! I get at least an hour out of a fully charged 7AH slab.


#5

In reply to G1STQ:

Hi, John.

If you’re contemplating going down the NiMH route then be careful where you source your cells. Certainly I would recommend using 11 cell Sub-C packs but as far as capacity is concerned, my experience is that anything over 4aH needs treating with caution. They don’t seem capable of sourcing the current - probably because the manufacturers have pushed the geometry too far and the internal resistance has suffered. Many of the higher capacity cells have now disappeared from sale.

FWIW I always took two 3.3 or 4.3aH packs with me. One pack would easily run the FT-857 on ssb for 45 minutes at 50W. I got at least 100 activations out of a pack before the capacity started to drop. I hope that helps.

73, Richard


#6

In reply to the thread:

There is a lot of attention paid to reducing weight as much as possible. I do not strongly criticise this, after all I joined the backpackers club the year it was formed (1974, I think!) and went the route of carrying a guest soap and cutting half the handle off a toothbrush, but I think that the idea can be carried too far - as I did back then! Much better is to have a really decent rucsac that will distribute the weight properly, and just aclimatise yourself to carrying the weight. A 12 volt 7 a.h SLAB is £14.99 from Amazon, including carriage, and its care and feeding is much simpler. It’s heavier, of course, but 2.2 kg really isn’t going to break your back, and you are spared the worry and expense of the more advanced technology.

Just a thought to be tossed into the ring!

73

Brian G8ADD


#7

In reply to G8ADD:
Is it really necessary to run 50 Watts? “smaller” rigs with lesser requirements can surely get the job done? e.g. K2 with (if you have to) 15 W out on SSB, and a much lower Amps requirement, as well as a vastly lower receive draw.

A K1 & KX-1 worked fine in Malta with 3W to 4 W out, using 8x AA NiMHd batteries, but only if you “do” CW, of course. They last “all day”.

Regards,
Les (g0nmd)


#8

In reply to G0NMD:

This depends on conditions, in poor conditions more power is desirable, in good conditions it could be done on QRP. It also depends on mode, CW will get through on lower power, but not everybody wants to operate on CW. Another factor is that if you are prepared to carry the extra weight of, say, an FT857D, you will also have facilities like the DSP to help you and for the CW devotees that blue flashing light that tells you that you are correctly tuned in (apropos - is that really useful?) Finally, if you are using an inefficient antenna, say a short doublet on Top Band, the extra power will make up for the fact that relatively few summits have room for a 266-foot dipole.

Really, I suppose, you also have to ask what the “job” is? Low power might be enough for a qualifying activation but if you want to bag some DX or an S2S with somebody across the pond then more power becomes desirable. In the end it is up to the activator.

73

Brian G8ADD


#9

In reply to G8ADD:

It’s interesting to work out how much energy the activator expends carrying their gear.

Those of an engineering/physics bent may wish to calculate the approximate energy required to carry a 2.2kg battery on the walk I did on Sunday last. I walked approx 15.2km and the ascent was 850m, my stride is 0.79m, I estimate for each step the bag rises and falls 0.1m. Then compare it to the 530gm my LiPos weigh for the a little more energy density than the 2.2kg SLAB has.

Or you can consider it differently. For every kg of battery you don’t have to carry you can carry a kg of something else. e.g. different radios, more antennas, yummy chocolate comestibles.

Everything is a compromise. Output power used, operating modes, bands used etc. There is no right answer. Other than the one your back/shoulders/legs/feet give after a long walk up a big hill with a pack on your back.

Andy
MM0FMF


#10

In reply to MM0FMF:
Plenty of food for thought, and thanks for all the replies.
At the end of the day a slab taken on a short activation is not really a big problem, however - I am looking forward to having a go at some of the bigger ones over the winter and so I guess every bit of weight saved is a bonus.
I am also doing a few DX trials on non-sota hills and so extra capacity is a good thing as, for example on Monday night I was on a peak from 1900 to midnight trying to get States, India and Japan.
Did’nt make it mind - but atleast I had a go, and this is what the radio hobby is all about for me.
Might try a waist pack to carry the battery load and not on my back.
I’ll let you all know how I’m getting on trying 50-100W on Snowdon in January!


#11

In reply to G1STQ:

Belated comment: I use LiPOs in combo with NiMH to good effect with the 857 and I can run 100W output no problem - see http://www.flickr.com/photos/18897403@N00/4491202158/

The NiMH are Fuji 10AH cells. As Richard says, make sure that NiMH cells are of good quality. Mine rarely drop below 1.2V by the end of an activation when piggybacked onto 4AH 3 cell LiPOs.

73, Gerald


#12

In reply to G4OIG:

Tiny little Li-Poly safety note … I had one small 11.7V 750maH Li-Poly battery burst into flames while powering my Elecraft KX1. Fortunately, I had it external to the radio on a 20cm pigtail, I was operating from our deck overlooking our gravel driveway, and I was able to detach it and fling it over the rail onto the rocks, where it fizzed, popped, and flamed for a couple of minutes or so. Given the Li part of the name, I decided not to turn the hose on it.

I’ve used several since [different brand] with no problems. The flaming one was designed for use in radio controlled model aircraft, boats, and other vehicles. And, yes, I do have a proper charger for them.

Did my first activation last Sun and got my first chaser points today. This is quite a bit more fun than it seemed it would be when Mike, KD9KC, introduced me to it.

73,

Fred, K6DGW
Auburn CA


#13

In reply to G4OIG:

Tiny little Li-Poly safety note … I had one small 11.7V 750maH Li-Poly battery burst into flames while powering my Elecraft KX1. Fortunately, I had it external to the radio on a 20cm pigtail, I was operating from our deck overlooking our gravel driveway, and I was able to detach it and fling it over the rail onto the rocks, where it fizzed, popped, and flamed for a couple of minutes or so. Given the Li part of the name, I decided not to turn the hose on it.

I’ve used several since [different brand] with no problems. The flaming one was designed for use in radio controlled model aircraft, boats, and other vehicles. And, yes, I do have a proper charger for them.

Did my first activation last Sun and got my first chaser points today. This is quite a bit more fun than it seemed it would be when Mike, KD9KC, introduced me to it.

73,

Fred, K6DGW
Auburn CA


#14

In reply to G4OIG:

Tiny little Li-Poly safety note … I had one small 11.7V 750maH Li-Poly battery burst into flames while powering my Elecraft KX1. Fortunately, I had it external to the radio on a 20cm pigtail, I was operating from our deck overlooking our gravel driveway, and I was able to detach it and fling it over the rail onto the rocks, where it fizzed, popped, and flamed for a couple of minutes or so. Given the Li part of the name, I decided not to turn the hose on it.

I’ve used several since [different brand] with no problems. The flaming one was designed for use in radio controlled model aircraft, boats, and other vehicles. And, yes, I do have a proper charger for them.

Did my first activation last Sun and got my first chaser points today. This is quite a bit more fun than it seemed it would be when Mike, KD9KC, introduced me to it.

73,

Fred, K6DGW
Auburn CA


#15

In reply to G1STQ:

If you haven’t given up on Li, take a look at the model PST-MP3500-I from powerstream.com. It uses DC-DC converters on both input and output, so it can be safely recharged from unregulated sources (such as raw solar cells) and delivers constant output voltage until dead. About 2x the power density of MH and 3x lead-acid. I have no connection with the company, just a satisfied customer.

73, Elwood, WB0OEW


#16

In reply to G1STQ:

John,

One word…LiFePO4. They have a much better voltage profile then a Li-po.

W2VV and I have experience with NiMH and LiFePO4 and It sure seems like the NiMH cells are not really happy with a full on assult from an 857 at 100w.
W2VV ran his with 11 NiMH cells as 10 would not cut it at full load.

I would suggest a LiFePO4 pack as yu will not have to worry about voltage and the chargers are cheap. Also, unlike any high capacity NiMH your LiFePO4 cells will not self discharge much at all on the shelf.

Check out the packs at:

I run similar cells that have 10 ah capacity and they are just great. My pack does not use a balancer or any protection chips…the cells are that stable! I have checked the individual cell balance and they really dont go out of balance if you charge them at 1c or less…you can discharge them as hard as you like.

Today you can even get LiFePO4 in polymer format.

I am a bit afraid of the regular lithium cells.

73,
Tom-N2YTF


#17

In reply to all:

For info - A nice bat-pack I have be interested in

http://www.powerstream.com/PST-MP3500.htm

73 Luc ON6DSL


#18

In reply to ON6DSL:

$172 !!!

:frowning:

Andy
MM0FMF


#19

In reply to MM0FMF:
Hi Andy,
The batteries I have as spares are a bit (lots) cheaper. I picked up three HP lap top batteries at a car boot for 50P for three!
They are LiLo, rated at 14.8V 4300mAh. Carefully brought them back to life, after removing internal charging circuitry, and they are performing quite well running my 857 at 50W power level.
I use my existing BC6 charger to charge them.
I have used them on a couple of activations, and they seem to perform ok.

73,
Frank


#20

In reply to G3RMD:

You can get some bargains by salvaging used packs as long as you apply some caution. I have a number of 18650 LiPo cells I bought at some rallies. They were sold as new 3.7V 2200mAh. They looked new. Now rally deals are always a gamble. Are they new? Are they out of spec? Are the faulty etc. However, I made a pack up with 3 in series and charged them with the same 3S charger I use for my RC packs. They charged nicely and I was pleased with the deal.

Then I used them with vengeance and they seemed OK. When I came to charge them they wouldn’t charge. I was a little miffed as they seemed OK to start with. Being bored one night, I dissected one and there was a tiny PCB in series with the connections. The battery cell was showing 2.7V but the leads out showed 0V. The other 2 cells were the same. So I removed the PCB and rebuilt the pack and it seems to be OK apart from the fact the voltage when the charger stops is a bit low being near 12V rather than 12.5ish. That’s probably a result of over discharge to 2.7V per cell.

I don’t know why all 3 PCBs failed but they all failed at the same time. Possibly I drew too much current through them, although I was using the pack to power my Icom X21 handy at the time. Anyway, I shall remove the PCB from the other cells and will just use them as 18650 cells. The end result is a nominal 12.5V 2200mAh pack that weighs less than 125g and has the volume of a packet of cigarettes. All for the princely sum of £3.50 each (including JST connector).

Andy
MM0FMF