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Old 17th Mar 2024, 11:01 am   #1
Malcolm T
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Default Portable Summits On The Air. Charging NiMh batteries.

Can anyone point me in the direction of info re charging NiMh batteries for portable use.
Not sure if wind generator or solar charger would be best route to follow or both ?.
Thank you.
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Old 18th Mar 2024, 12:04 am   #2
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Default Re: Portable SOTA. Charging NiMh batteries.

Not sure how large your anticipated system would be.

Sources like this seem to have coherent answers regarding solar:

https://electronics.stackexchange.co...ng-solar-panel

Instinct says that solar would give a more stable linear charge than wind, for your purposes

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Old 18th Mar 2024, 9:27 am   #3
Malcolm T
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Default Re: Portable SOTA. Charging NiMh batteries.

Thanks for the link.

No more than 10 watts max but i would like to stay under 5 for qrp .I found many years ago how running 100 watts from /p locations can seriously reduce ones battery life in a vehicle !.
There is such a choice today in batteries and each type seems to require a different charging regime .
The only battery i have used in the past is either the vehicle battery or a spare lead acid , but to lug one a Km or two is out of the question hence the question here.
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Old 18th Mar 2024, 10:39 am   #4
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Default Re: Portable SOTA. Charging NiMh batteries.

SOTA means Summits On The Air. So the equipment meant has to go in or on a rucksack quite often. Quite often as a solo expedition. An ex-colleague carried gear up every 'Munro' - 3000ft peak in Scotland. As he chose to use 2m exclusively due to the gear he had, some contacts were into repeaters where nothing simplex was available, so wouldn't be counted by today's more organised summit-baggers, but James was the first to actually get radio gear up the whole lot. Including the inaccessible pinnacle.

So photovoltaics, battery radio gear, small wind turbine, antenna, etc. all have to be portable together. Or you're just limited to the endurance of the battery alone. Doing it on HF makes lightweight wire antennae possible often from a couple of telescopic fishing poles, and you have a better chance of finding someone to contact so you're likely to want to stick around a bit longer.

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Old 18th Mar 2024, 10:57 am   #5
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Default Re: Portable SOTA. Charging NiMh batteries.

Yes I need to get a system together .
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Old 18th Mar 2024, 11:07 am   #6
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Default Re: Portable SOTA. Charging NiMh batteries.

The widely accepted meaning of SOTA is 'state of the art' which is what I thought the question was asking A SOTA portable power supply wouldnt use NiMh hence my suggestion of lithiums - a 4S LiFePo4 pack equates almost exactly to a 12v lead-acid in terms of CC the CV charge, with near identical bulk, absorption & float voltages, making them very suitable for irregular charging systems like solar & hand gens. An NiMh charge is difficult to control with an irregular charge as the delta-peak would be masked. LiFePo4 has a very low ESR suitable for high current peaks and a very low self-discharge and hence a long 'charged shelf-life' All by-the bye though as I had the wrong SOTA!
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Old 18th Mar 2024, 11:53 am   #7
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Default Re: Portable SOTA. Charging NiMh batteries.

I haven't done any fell top operation for a while (and never seriously as a SOTA competitor) but I have considered the idea of using 'universal' Lithium-Ion battery packs which just have an input (charging) socket and a DC output lead usually terminated in a DC power plug which most portable radios will have a matching socket for.

A reasonable '12V' Li-Ion pack will weigh a lot less than the 6 x SP12 size NiMHs it takes to power my FT290R2 and probably have greater capacity as well.

The only thing to wonder is how the ones claiming to have '12V' output actually achieve that because it is not a multiple of the basic Li-Ion cell voltage (3.6-3.7V) - very possibly they may use a DC-DC converter which could potentially be a bad source of RFI.

One with a stated output of 14.4V is more likely to use a simple array of 'Bare' Li-Ion cells, although it will probably still have a charge management chip which comes into play only when the pack is being charged, and possibly prevents it from being run down below a critical level as well.
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Old 18th Mar 2024, 1:04 pm   #8
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Default Re: Portable SOTA. Charging NiMh batteries.

Quote:
Originally Posted by SiriusHardware View Post
The only thing to wonder is how the ones claiming to have '12V' output actually achieve that because it is not a multiple of the basic Li-Ion cell voltage (3.6-3.7V)
The 12v ones are 4S LiFePo4 which does very nicely equate to a 12v lead-acid G
3v3 nominal and 3v6 charge per cell. I'm still using my stash of genuine A123 LiFePo4 cells from a race bike project ten years ago!

Last edited by Phil__G; 18th Mar 2024 at 1:25 pm.
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Old 18th Mar 2024, 1:40 pm   #9
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Default Re: Portable SOTA. Charging NiMh batteries.

Sorry i should have typed Summits On The Air instead of just SOTA .
Thanks for the replies it does narrow down the field somewhat
So i shall be looking into LiFePo4 then , seems like a good system . If the pack has on-board management system then yes i wonder too about QRM.
This all very new to me so a learning curve
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Old 18th Mar 2024, 1:54 pm   #10
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Default Re: Portable Summits On The Air. Charging NiMh batteries.

Thread title updated.
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Old 18th Mar 2024, 5:04 pm   #11
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Default Re: Portable SOTA. Charging NiMh batteries.

Quote:
Originally Posted by Malcolm T View Post
if the pack has on-board management system then yes i wonder too about QRM.
No QRM Malcolm, most BMSs are simple linear DC, no oscillating regulators and only really come into play when charging. Under normal discharge circumstances the BMS does nothing pending the first cell to reach low-voltage-cutoff.
Depending on the BMS type, your 12v output comes either directly from the battery contacts, or via a saturated powerfet in the BMS, theres no PWM or anything, its just on or off.
A further benefit is that LiFePo4's are much more tolerant of abuse and hence safer than Lithium Polymer etc.

Roughly what capacity is needed? are we talking four A123 cells or a lithium Leisure Battery?
Maybe somewhere in between, say a lithium motorcycle battery? (beware some are very low capacity, 2Ah or so....)
or like this https://uk.eco-worthy.com/products/l...sphate-battery ??

Last edited by Phil__G; 18th Mar 2024 at 5:21 pm.
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Old 18th Mar 2024, 6:58 pm   #12
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Default Re: Portable Summits On The Air. Charging NiMh batteries.

Thanks Phil
Well weight is everything ,
I was thinking of a single battery , say 12v 7 Ah , looking at yuasa it would weigh 2.2kg but a LiFePh is only 1 Kg so i could have two and one in use whilst other is charging or a stand by if one goes down.
Or connect up two for 14 Ah but i wonder if that would be a wise thing to do ?.
The idea is to trickle charge whilst in use or use one then swap for the fully charged one ,i dont know yet , early days . Thanks for the link , battery power is not cheap is it !
Where are those eco batteries made ?.
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Old 18th Mar 2024, 7:06 pm   #13
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Default Re: Portable Summits On The Air. Charging NiMh batteries.

Yes LiFePo4 batteries are definitely the way to go, they have great energy density (in terms of Watt Hours per Kilogram) and low internal resistance so even small ones can provide high current. As far as power budgets are concerned, the Military standard approach is to assume a 9:1 receive/transmit ratio but that might not apply if you are sat on a trig point calling CQ most of the time.

Have a look at what the drone and radio controlled race cars sectors are using these days for compact and lightweight power.
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Old 18th Mar 2024, 8:38 pm   #14
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Default Re: Portable Summits On The Air. Charging NiMh batteries.

Thanks for the replies.
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Old 19th Mar 2024, 12:49 am   #15
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Default Re: Portable Summits On The Air. Charging NiMh batteries.

Its ok to parallel two if they are both fresh off the charger, ie in an identical charge state.
Well, actually thats not strictly necessary as the expected transfer current is brief but if SoC is very different, ie one flat & one fresh, then the transfer current could be significant.
They can also be charged in parallel - in fact you could permanently connect two and treat it as one battery, this is normal practise with lithiums in caravans & camper vans.
Lithium packs configurations are described in terms of xSyP, eg 4S2P which is four series pairs of two cells in parallel - in other words the cells are paralleled inside the battery - they parallel just fine, no problems.
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Old 19th Mar 2024, 6:28 am   #16
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Default Re: Portable Summits On The Air. Charging NiMh batteries.

We've locked onto a tangent of lithium chemistry, BMS devices, and the vintage content has been worked-out. Time to close.

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