Category: SOTA

LiFePO4 Portable Power Kit

LiFePO4 Portable Power Kit

Recently I was researching an alternative to Sealed Lead Acid Batteries (SLAB), the cause of this research…back pain. While SLAB’s have performed ok for my car portable use, I was reminded just how heavy a 50AH SLAB is after straining my back putting it back on the shelf. So having seen a number of posts and videos on the Internet about the weight advantage I needed to give alternatives some serious thought.

I suspect like me, many of you will have heard of Lithium batteries but what I hadn’t realised is that there are different types and specifications. I was looking for three things in a new battery; appropriate voltage for amateur radio use (13 to 14 volts), low voltage sag (little voltage drop when under load), and a high number of recharge cycles (reduced cost of ownership).

Lithium ChemistryNominal Voltage
(4 cells in series)
Recharge Cycles
Lithium Titanate9.6v3000-7000
Lithium Nickel Cobalt Aluminium Oxide 14.4v500
Lithium Cobalt Oxide14.4v500-1000
Lithium Manganese Oxide14.8v300-700
Lithium Nickel Manganese Cobalt Oxide14.8v1000-2000
Lithium Iron Phosphate (LiFePO4)13.2v1000-2000

 

I hope you agree that Lithium Iron Phosphate (LiFePO4) came out as the most suitable. I was also fortunate that while away on a DX’pedition to the Isle of Barra with Bob (M0KLO) he kindly lent me his KX3 and a small radio model style 13v LiFePO4 4.2AH battery pack to try. It was certainly compact in size, light weight, and an ability to maintain voltage during transmit but the total capacity of 4.2AH I felt was a bit small for what I had in mind. 

A battery of about 15AH seemed to be about the size suitable for my needs based on my initial transmit tests with a Yaesu FT-891 “field” radio which suggested about 8 amps on transmit was a good target if I wanted 3 hours of operating time on a single charge. Remember that this is not an exact science as less current is drawn when listening as to transmitting and whether you use CW, Data, or SSB.

A search on the Internet provided a range of options from which I produced a shortlist:

  1. “radio control” style soft battery packs to make up a battery of 17AH. Various comments on the Internet suggested quality control of these packs is variable. Costs today (Mar’2018) for a 8.4AH pack is £ 52.83 + p/p. Due to the manufacturing process if one of the internal cells develops a fault the whole battery is a right off. Requires a balance charger to maintain cells. https://hobbyking.com/en_us/zippy-flightmax-8400mah-4s2p-30c-lifepo4-pack-xt90.html

 

  1. Electric Golf Cart suppliers have a good selection of LiFePO4 batteries in capacities from 15-40AH available with chargers and 3-5 year guarantees. Mainly sealed units with an internal Battery Management System (BMS), while this is perhaps convenient it has the drawback that if a cell or the BMS develops a fault the battery may be a right off. Generally supplied with a simple charger. Costs depending on capacity and warranty term but are generally £150  to £300 per unit. NB: Always double check golf cart batteries, are they definitely LiFePO4?www.topcaddy.co.uk/category/batteries/lithium-batteries/

 

  1. Electric Bikes commonly use LiFePO4 packs of various sizes (8,10,12,15AH), individual cells can be purchased and made into a pack. All of the required components can be purchased online or from an electric bike components supplier. Costs increase as cells capacity increases. For 4x15AH cells + cable bits to make 13.2 battery (Mar’2018) approximately £100. Simple chargers are available similar to the ones provided by the Golf Cart suppliers, but would recommend radio model style balance chargers suitable for LiFePO4 batteries.
    LiFePO4 (UK) Battery supplier
    http://eclipsebikes.com/index.php?cPath=25_10
    ISDT T6 LiFePO4 charger
     https://hobbyking.com/en_us/isdt-t6-lite-600w-charger.html?___store=en_us
    ISDT Battery Checker
    https://hobbyking.com/en_us/bg-8s-smart-battery-checker.html

 

I decided on option 3, if there was a problem with an individual cell I could replace it at minimum cost and it allowed me to take control of the management of the battery pack and individual cells. As a self-build I could also choose on different form-factors depending on requirements and components. It is also a simple task to increase the capacity of the pack by putting another one in parallel if needed at a later date. I also purchased a radio control style charger (ISDT T6).  This charger provides greater control of charging and also includes storage charge and discharge options and very importantly it allows charging of cells without a balance lead connected as I would be Bottom Balancing. Note that some LiFePO4 chargers will refuse to work without a balance lead connected. I also purchased the ISDT Battery Checker for more precise measurement of individual cell voltages on charge, storage, and discharge.

The rationale for bottom balancing is that I want the cells to converge to the same state of charge when discharged, before use and I charge the whole battery as one, rather than have the charger bulk charging the cells and top balancing them when using balance leads. I’ve included the following YouTube links for the background to bottom balance and not using a BMS. 

Bottom or Top Balancing
https://youtu.be/0KSFitqvap0

One example of how to Bottom Balance a battery pack
https://youtu.be/J2WvQre8sAQ

To achieve bottom balance I discharged the individual cells to 2.7 volts each and measured the voltage variation (after a settling period of 24hr) between the cells using the ISDT Battery Checker via the balance leads to achieve a variation between cells of a couple of mV. I then charged the cells to 3.4 volts per cell using the chargers (ISDT T6) upper storage charge setting of 3.4v and a charge current of 1/10th the pack capacity i.e 15AH divided by 10 = 1.5 Amps. The cell voltage variation at 3.4v across the pack was 8mV. I’ve found that if the individual cell charge voltage is increased to 3.6v, the cell voltage difference will also increase to 100+ mV. Also if the charge current is increased for example to 5A then the cell voltage variation will increase at top of charge. This in itself is not a problem and is predicted however monitor the voltage to make sure no individual cell goes beyond the 3.6v manufacturers specification.

My final choice was for 2×2 rather than the 4×1 cell pack, mainly because it fits neatly into a box that I subsequently purchased and it also fits better the compartment underneath the boot-floor of my car. The red/black leads with PowerPoles fitted are for the high current connection to the radio, and are also used when charging and discharging, the white leads are the low current balance leads that are used for voltage monitoring. If the ISDT T6 Lite is used to perform a discharge the balance leads are connected and the T6 will not let a cell go below 2.8v. While using the battery pack with my radio a small voltmeter is connected to the balance leads which cycles continually indicating pack and individual cell voltages during use. The audible alarm is set to 2.7v, if any cell reaches this lower limit an alarm sounds and I stop transmitting and disconnect the battery to prevent further discharge. After use the pack gets a storage charge and stored in a dry and cool place in the garage. 

Enjoy your radio
Glen G0SBN/P

SOTA – Scafell Pike

SOTA – Scafell Pike

So today was an education, in more ways than one. First lesson was never trust your brother in law when he says we’re going out for a walk in the lakes, come along bring your radio; it not going to be anything heavy duty… Second lesson was always be prepared, and if there are ‘two’ SOTA summits nearby make sure you activate both of them; now remember this as I did actually say ‘two’ summits. 

So it was a 3:30 am start, now this in itself is not a good start. I don’t do early mornings but this is the middle of the flipping night man ! Anyway we headed off to the lakes and duly ended up at the Wastwater car park around 7am. We then set off for Scafell. 

 

Chris (my brother in law) had a plan to ‘not take the normal’ routes and to try and get to the summit via what looked like a gulley called ‘Lords Rake’ which all seemed feasible. After all he had it planned and we had a map etc.. Happy days. 

Some where along the way we got kind off track as it were and actually ended up on the opposite side of the gulley to Lords Rake, what did that mean.. well. It meant we had to scale to the summit of Scafell via what I believe is called ‘Deep Crag’. This wasn’t exactly walking it was more like rock climbing! The walls of the crag were wet and slippery from the night before and this made even more sketchy.

That said, we made it ! The celebration at the top was part elation and part relief! 

So about the radio / SOTA stuff, well remember I said ‘two summits’ right?

Well Scafell was in the SOTA database as G/LD-002 and I operated from the top and activated this ‘summit’ with about 6 contacts as we only had a very brief time up there before heading on…Where to you ask ?

Well across the way we could see Scafell Pike and the plan was to get across there and then come back via Lingmell Gill. 

Now Scafell Pike has quite a decent path defined up from the valley floor and doesn’t look to be too much of a climb, the only issue was we were not on the valley floor we were on Scafell. This link here will give you and idea of what we had to come.. 

We headed off Scafell and duly made our way back to Lords Rake which was just over from where we climbed up deep crag to get to the first summit, and yes you guessed it we had to descend Lords Rake… Not good. Very precarious with lots of loose rock and slippery surfaces with next to no hand holds. 

That said we managed it, scary ? Yes. Hard work? Yes. We then headed off to Scafell Pike via Mickledoor which wasn’t too bad and gave us some great views! Scafell Pike is a 10 point summit (G/LLD-001) which actually has a fairly well defined path up to it that attracts lots of visitors. Except we decided to take the brother in laws scenic route as I have said! Once at the top I didn’t have long as we had planned to descend via Lingmell and we had yet to eat lunch!

Never the less 2M came good and I managed 9 contacts total with 1 summit to summit contact with David (G0EVV/P) who was on G/LD-003.

So as it turns out Scafell is now NOT a SOTA summit despite it being more difficult to ascend than the pike and I only found this out when I got home and tried to upload my log. It has been DOWNGRADED ! to a hump in the HEMA Awards scheme. A Hump !! Can you believe that ! 

I’m glad I activated both peaks today or I would have 1 measly HEMA point for a 20 hour day out walking !! 

Here is the brief list of QSO’s for today 
MW6ISC : Op – Steve : Wales  
2E0MOW / M : Chris : Unknown 
G0EVV / P : Op – David : Helvellyn G/LD-003 (S2S) 
G6NHW / A : Op – Pete : Unknown 
M0LKO : Op – Andrew : Ulverston 
M6XVE : Op – Sheri : Ulverston 
G4YLB : Op – Jim : Unknown 
GM3 VMB : Op – Peter : Lockerbie 
2E0LDF : Op – Reg : Cockermouth 

Steve Nelson
2E0EFP