6S8P Li-Ion high-C LiPo field charging solution in a case (fly all day on two LiPos)

[Duncan Disorderly]

My friend Russ put one of these together in 2019 and it's still going strong today. The moment I saw it I knew it was the solution. It only took me four years to get around to making mine.

 

I fly aerobatic electric models up to 6000W/50cc size, so I've bought more than my fair share of LiPos over the years. There had to be a better way - and there is. It's a 40,000mAh (just scale it to suit your needs) Li-Ion pack at 24v connected to one or two ISDT 20A chargers, to allow a pair of 6S 5000mAh LiPo packs to be charged simultaneously at 4C, all housed in a Screw-fix metal carry case.

 

For a single charger system it cost £285 including various delivery charges but not including my time. Each pack took about 2 hours to solder up, with about the same again to sort out the cases & wiring. I should note here that I'm a known incompetent relating to all building matters, so Russ supervised me and very kindly finished off the wiring and cases when I fell over exhausted at the end of the day due to inhalation of too many solder fumes. I made three packs in all - two for me and one for my mate Pete. Final pic is the 12S flying day version but usually it's just one charger and a pair of LiPos for 6S flying.

 

I'll try and get some better pics of how it's wired in the box. There be fuses. I've got the component list knocking around somewhere if anybody wants to make one. It doesn't take much to spend £285 on LiPos, and the advantages are huge: you can leave it charged up all the time and it doesn't complain. This totally changes how you go about flying. Charge the box as soon as you get home, leave the LiPos at storage charge at the field (I generally land at 3.75). The Li-Ions will last forever because they're barely breaking a sweat - Russ built a 2nd box a year ago and can't tell which one he's using. So you can go flying at the drop of a hat, and leave all the decisions about which plane you're going to fly until the minute before you leave the house. No more "Oh if I knew the weather was going to be like this I'd have charged those other batteries." It's like having a can of petrol, only less smelly. And the bit I was nervous about - the high C rate charging - has proved to be worry free. At the moment I'm flying 6S 3300mAh Heavy Duty Turnigy packs and charging them at 12A, which takes about 10 minutes. I cap my flights at 7mins30 so you can pretty much fly non-stop if you don't mind being a patch-hog. Previously I've always, always, always charged at 1C or below, like I was a member of some death-cult, but I'm 250 charges in and I see no performance issues or increasing internal resistance - the Zippy 4500s hover around 0.9 and the Turnigys around 1.3 per cell. Happy batteries - and they had a couple of hundred cycles on them pre-chargebox. Only charging to 4.17 makes an amazing difference to battery life. That Phil Lewis knows his onions.

 

I've been using this for 4 months now and waited to see how things turned out before posting. I can honestly say that, for me, there is no other way of going about electric flight. Just my two 4 port chargers would have paid for this box, let alone the dozens of LiPos.

 

This is the first topic I've started so please excuse the mess. Long time lurker. Thought I'd contribute for once.

 

Oh... and definitely use the balsa sticks to assemble the initial cells all nice and tidy. The masking tape was like herding cats.

 

 

[Frank Skilbeck]

Neat, where did you get the Li-ion batteries from please.

[Duncan Disorderly]

https://www.cellsupply.co.uk/21700-batteries

[Geoff S]

How heavy is it?  The problem I've had recharging at the field is lugging a massive lead/acid battery about - usually an old car starter battery that will no longer deliver an adequate current, but is OK at the charge currents we need to charge LiPos.

 

Obviously, yours is set up to charge just one type of LiPo. Most of us use a variety of, mostly, 3S, 4S and perhaps 6S of various sizes so would need to have a slightly different connection regimen, which is not a problem.  Moreover, I, for one, only charge at 1C.

 

Perhaps I should open up a couple of 10s electric bike batteries that have broken connections which I've found very tricky to repair reliably.

[Duncan Disorderly]

I made two boxes for myself because I live in a field and have to walk 300m to my car for about 5 months of the year, so being able to carry my plane + batteries + everything else I need in one trip was important. So one box in the winter when I'm walking, two boxes in the summer when I can get my car to the house. I haven't weighed it but it's nowhere near the weight of a lead acid. Each cell is approx 68g and the packs I made have 48 cells in them, so 3.3kg plus the case, chargers & LiPos. Maybe 5kg all up?

 

I charge all sorts of LiPos with it. Fellow fliers at the patch are beginning to realise that they don't need to go home when they're out of batteries, as I seldom use all the electrons up. The chargers will charge anything you have the leads for!

 

As I said, I never used to charge at above 1C. Never. It was one of my golden rules and I've only ever flown electric. Then Russ asked me why not, and because I'd never gone there, all I could say was "...because I read that you shouldn't." But the empirical evidence was right in front of me and increasingly hard to ignore. Hundreds and hundreds and hundreds of cycles on the same batteries, all being charged at 3C or above. Nothing going pop or boom or even puff. The Zippys in the pics have over 400 cycles on them and you can still put a ruler down the side. I simply ran out of reasons why I shouldn't do it because there weren't really any there to begin with, other than "I'm scared" (which I was). Caveat: use batteries that can be charged at above 1C. They cost a little more but not much really if you put any value on your time or their longevity - and 40C Zippys and 60C Turnigys aren't exactly posh, daft-money batteries. For me, a good portion of the reason for doing it falls apart if you're going to wait an hour per recharge, though if that works for you then that's all that matters.

 

Well worth recycling the bike batteries to have a go cost-free and see if it suits you too. It's a different routine and takes a while to bed in, but I wouldn't go back now.

[Philip Lewis 3]

Hi Duncan, and thanks for the compliment - I appreciate that.

 

I can certainly second the attestation that this works and works as described, I've seen it working since Russ made it many years ago now.

 

Distilled down to the simplest level (and part of the beauty of this is exactly that, it's utter simplicity), this is an alternative solution to a generator or leisure battery for those who want to charge at the field but so much lighter and more convenient than either, it will charge any battery you like as it's just the power supply to a charger so the restriction is only what your chosen charger can charge, heck it would even recharge a car battery to at least get it to start your car.

 

Thanks for posting this Duncan it's a pause for thought moment, my current (sic) thinking is maybe to use this in a hybrid arrangement, charge a few packs before leaving and the rest as needed when I get there which would certainly avoid charging packs that then don't get used and then have to be taken down to storage charge again.

 

It's quite popular in Japan to operate this way except that they seem to use a few massive LiPo packs to supply the power, this is a very viable alternative to that, probably much cheaper as well although I did consider doing it this way when HK used to sell Multistar low discharge rate LiPo's with some massive capacities many years ago but not available now, old bike batteries should also work well.

 

What are you using to fuse it though? My guess it 24 Volt lorry fuses?

 

 

  

Edited January 23 by Philip Lewis 3
Spelling

[Duncan Disorderly]

Hi Phil

 

That's exactly how I tend to use it - pre-load a couple of LiPos at home and charge the rest at the field. I was at the point of needing to buy a new load of LiPos and figured that it was a good time to jump in and try it. Russ just quietly gets on with it but I think it should be shouted from the rooftops, especially to the heavy users out there. Wish I'd had it when I was flying F3A.

 

However, using LiPo packs as the source isn't a good idea. All that discharging to storage milarkey partially defeats the objective. The whole point of this setup is to have it charged and ready to go at all times, which needs a more considerate cell supplying it!

 

Wake up, look out of window, go flying.

[Dickw]

Back in 2012 I put together a 4s2p 30Ah 12v LiFe pack from 8 x 15 Ah electric bike cells. I have been using it for field charging since then. It is a bit down on capacity now, but stil useable. 

The great thing about Lithium based cells is how light they are compared with lead acids. The other great thing is the superior performance - I get more charge out of my 30Ah than I ever did out of 80Ah lead acids, and it has lasted years longer.

 

I also now have a 38Ah 12v LiFe battery as well.

 

Dick

 

[Duncan Disorderly]

That's fantastic to get 12 years out of your batteries! I have a feeling this was a good idea.

[Duncan Disorderly]

Phil - yes they're car fuses. Can't remember their rating. I'll take some more pics soon.

[PeterF]

I put together a field pack of HobbyKing 6 parallel 6S 16,000mAh cells, these were the green 10C packs for multiro that were not sold for long as they did not appear very popular. This gives me a wapping 96Ah at nominal 24V. HK were selling these off cheaply so a good bargain for <£300 and much more capacity than a lead acid leisure battery for less weight. All day flying with some large models. It is the way to go.

[Philip Lewis 3]

16 minutes ago, Duncan Disorderly said:

The whole point of this setup is to have it charged and ready to go at all times, which needs a more considerate cell supplying it!

I certainly agree with that, lead acid as a source has two big problems, one weight and the second they don't like to be deep discharged so the capacity on the label isn't actually usable either, which means half the weight you are lagging around you can't even use.

 

Definitely a use for competition flying, if I have three rounds to fly I always take four packs in case I have to re fly a round, it would certainly have a use there.

 

I 100% agree your comments on LiPo's as a source, I have no idea what they actually do or how they treat them.

 

I've used LiFe PO4 packs as TX and RX packs for years now, never worn one out yet and they have always been kept fully charged so I can't see why Lion would be different, heck my phone is four years old now and fully charged every day and still as good as new.

 

I would guess that for those not wanting to go this DIY route that LiFe PO4 leisure batteries (think narrow boats and camper vans) would be an alternative, essentially a ready made pack, Victron Energy would be one such supplier, straight replacement for lead acids so I guess 4 cell packs, two in series would of course give you 24 volts. 

 

This is a really interesting discussion of an alternative method not often really considered, well done for raising the profile of the alternative whether replacement or as hybrid approach.

[Duncan Disorderly]

PeterF - yes I nearly jumped in with those huge Multistar LiPos and that's a really good price for all those mAhs! However, it was still a LiPo fuelling a LiPo, so I was still caught in the discharge cycle and having to second guess if tomorrow would be a good flying day. Substituting Li-ions for LiPos was the final piece of the jigsaw, as it means they can stay permanently charged (they settle down to about 4.16), seemingly without issue**, so are always ready to go. That was the bit that changed the way I went flying because it's much more like having an IC plane (or "one of the very few advantages of having an IC plane", but let's not go there...)

 

You must have some absolutely MASSIVE planes!

 

 

**mine are new. I'm going on Russ's version using the 18650 cells (all 120 of 'em) which is now 4 years old, so roughly 3000-3500 LiPos charged with that box.

[Neil R]

Thanks v much DD for the interesting and inspiring post; I'm now very interested in putting one of these packs together. Which exact cell did you pick please? - was it the one of the LG M50 variants? I'm also really hoping you will post those extra piccies of the wiring within the case, I haven't quite worked out yet where the fuses would go. Thanks! 

Edited January 24 by Neil R

[PeterF]

10 hours ago, Duncan Disorderly said:

PeterF - yes I nearly jumped in with those huge Multistar LiPos and that's a really good price for all those mAhs! However, it was still a LiPo fuelling a LiPo, so I was still caught in the discharge cycle and having to second guess if tomorrow would be a good flying day. Substituting Li-ions for LiPos was the final piece of the jigsaw, as it means they can stay permanently charged (they settle down to about 4.16), seemingly without issue**, so are always ready to go. That was the bit that changed the way I went flying because it's much more like having an IC plane (or "one of the very few advantages of having an IC plane", but let's not go there...)

 

You must have some absolutely MASSIVE planes!

 

 

**mine are new. I'm going on Russ's version using the 18650 cells (all 120 of 'em) which is now 4 years old, so roughly 3000-3500 LiPos charged with that box.

Well the strategy is that I keep them at storage charge and at that charge I can take them to the field and use them for a flying session using my normal sized planes. However, if I go with a larger plane (largest is Tony Nijhuis Vulcan using 2 x 8S 6,250mAh) I charge the field pack up in the morning. I have a 40A charger so I can get it from storage to full in less than 1 hour at the same time as charging the batteries to take with me, load the car etc etc.

 

LiFePO4 is the way to go but at the time the cost of the end of line Multistar packs was much lower than an equivalent LiFePO4 pack. You can get LiFePO4 leisure batteries, 12V 100Ah for about £350 now with a built in BMS for charging and discharging as others have mentioned. You could even get bare prismatic cells and build your own, I would certainly consider this if I was doing it now and not multiple years ago.

[Dickw]

If you are interested in LiFePo4:-
These are the cells I bought back in 2012, and a photo is attached showing them built into my field box.
https://eclipsebikes.com/battery-cells-accessories-c-70_69/headway-lifepo4-40152s-32v-15ah-p-197.html

 

This is the battery I bought 2 of a couple of years ago to make into a 12v 48Ah battery. If I use this in conjunction with my 100 watt solar panel it will keep me going for a whole weekend flying away from home (including battery heating boxes).
https://www.bmstechnologies.co.uk/product/tn-power-lithium-12v-24ah-leisure-battery-lifepo4-tn24/

 

Different sizes and types are available, and in both cases they can be bought cheaper elsewhere, but those websites will give you lots of options and proper data to aid your research.

 

Dick

[leccyflyer]

Really interesting thread guys, thank you so much for posting your experiences. The ready made high capacity LiFePO4 leisure batteries look eye wateringly expensive, but so are ordinary car batteries these days when you come to replace one. As Duncan said in the OP perhaps the hardest thing to break through in terms of a large increase in practical usability at the field for a whole day's flying with a minimal number of lipos is the 1C charging. I'd be very uncomfortable charging at 4C to be honest, but I do like the idea of charging to 4.17v/cell. Will follow this with interest.

[Ron Gray]

Very interesting and would be very tempted but as I now have an EV I use that, plus we are about to equip our flying site with a solar 'powered' charging station. Great work.

[Duncan Disorderly]

2 hours ago, Neil R said:

Thanks v much DD for the interesting and inspiring post; I'm now very interested in putting one of these packs together. Which exact cell did you pick please? - was it the one of the LG M50 variants? I'm also really hoping you will post those extra piccies of the wiring within the case, I haven't quite worked out yet where the fuses would go. Thanks! 

 

It was the LG M50LT 21700 that I ended up using. 144 of them inc VAT and delivery cost £508.10 (Aug 2023), which made up the three packs. Stupidly, I didn't order any spares but every single cell was at 3.55v on arrival, not even 0.01v variation, let alone any dead ones. Cell Supply do much better prices wholesale, so buy over 50 cells if you can.

 

The fuses are lorry fuses at 40A just wired inline between battery and the XT90 sockets on the side of the case to prevent anything going bang. Probably OTT but why not? Pics to follow.

[Duncan Disorderly]

1 hour ago, Dickw said:

If you are interested in LiFePo4:-
These are the cells I bought back in 2012, and a photo is attached showing them built into my field box.
https://eclipsebikes.com/battery-cells-accessories-c-70_69/headway-lifepo4-40152s-32v-15ah-p-197.html

 

This is the battery I bought 2 of a couple of years ago to make into a 12v 48Ah battery. If I use this in conjunction with my 100 watt solar panel it will keep me going for a whole weekend flying away from home (including battery heating boxes).
https://www.bmstechnologies.co.uk/product/tn-power-lithium-12v-24ah-leisure-battery-lifepo4-tn24/

 

Different sizes and types are available, and in both cases they can be bought cheaper elsewhere, but those websites will give you lots of options and proper data to aid your research.

 

Dick

 

 

Looks like you got there over a decade before me! That's a work of art. It's very good to know others are out there doing this stuff too. Will check out LiFePo4 as they're not on my radar usually

[Jake Bullit]

Looks great.

I've recently been making a few molicel P45b flight packs.

 

Bought a cheap portable spot welder which works great and has less chance of heat damaging the cells.

[Duncan Disorderly]

47 minutes ago, leccyflyer said:

Really interesting thread guys, thank you so much for posting your experiences. The ready made high capacity LiFePO4 leisure batteries look eye wateringly expensive, but so are ordinary car batteries these days when you come to replace one. As Duncan said in the OP perhaps the hardest thing to break through in terms of a large increase in practical usability at the field for a whole day's flying with a minimal number of lipos is the 1C charging. I'd be very uncomfortable charging at 4C to be honest, but I do like the idea of charging to 4.17v/cell. Will follow this with interest.

 

Yes, I knew it'd be the above 1C charging that would split the jury and it's what took me so long to do it, I think. I've got tons of LiPos so I just took an old pair of 6S 4500 and an old pair of 6S 3300 (which are the ones I use most) and spanked the living daylights out of them when charging them up - and continue to do so. Even so, I still find myself staring at the charger thinking, "Am I really going to put 12 amps through this?" because old habits die hard. I still charge at 1C at home, don't ask me why because I don't know any more. I thought I knew but it turned out that I didn't. I mean, I cannot deny what is staring me in the face, no matter how much I read up on it. I don't want it to work either, because it's challenged my knowledge and I like the comfort of what I know not having to change! Can you set one LiPo aside to try it out? IMHO it's charging them over 4.16 or 4.17 that kills them (Phil Lewis posted a table somewhere that blew my mind - can you post it here please Phil?). Or draining every last volt out of them. Stay between 4.16 and 3.80 and it appears that they last forever. Maybe it's also something to do with the the fact that they're only having to hold a full charge for 10 minutes before they're back down to 3.80 again, rather than overnight? I don't know, but whatever test I throw at those batts they just smile back at me. I do have good throttle management but I also fly big aerobatics, so they're always being 'gently pushed'. And don't forget that the spec on these batteries is a 5C charge and, unlike the discharge C rate nonsense, I actually believe it may well be somewhere around there. Rest assured that the moment I find out otherwise I'll let you know!

[Duncan Disorderly]

5 minutes ago, Jake Bullit said:

Looks great.

I've recently been making a few molicel P45b flight packs.

 

Bought a cheap portable spot welder which works great and has less chance of heat damaging the cells.

 

Russ tried frying one before and it was good for 30 sec. Took about 5 sec per cell but we borrowed an enormous industrial iron that sped things up. I guesss for flight packs they're going to be pushed a lot harder than these ever will be so every weld matters. No planes fall out of the sky if I get mine wrong!

[Duncan Disorderly]

Hopefully showing the fuses...

 

Setup with both chargers. They're so tiny. Pete made up some XT60 to banana sockets so we could use all our existing charging leads (though I notice I've set it up the wrong way round) as none of us had XT60s on anything.

 

Probably a bit heavy to carry comfortably with two packs in one box, though possible. I just bought two boxes and duplicated the system for heavy use days - and having one to lend out has already converted a couple of people.

[Philip Lewis 3]

13 minutes ago, Duncan Disorderly said:

 

IMHO it's charging them over 4.16 or 4.17 that kills them (Phil Lewis posted a table somewhere that blew my mind - can you post it here please Phil?). Or draining every last volt out of them. Stay between 4.16 and 3.80 and it appears that they last forever. Maybe it's also something to do with the the fact that they're only having to hold a full charge for 10 minutes before they're back down to 3.80 again, rather than overnight? 

I'll take a look and see if I've still got it/can find it again later on as I'm currently working (though not very hard) using a company PC at the moment.

 

I wouldn't say that they would last forever but I do recall that charging to 95% according to the information should double the amount of charging cycles a pack can take before it becomes of no more use, charging to only 95% is also completed much quicker as the charger doesn't struggle to cram the last bit in. 

 

Given that we all accept that keeping a LiPo fully charged is detrimental to it I would say it must follow that your second point above (only being at full charge for a few minutes) definitely has some validity and certainly will do more good than harm just difficult to quantify.

 

Max charge rate is an interesting one, some of my packs say max charge 5C but others say 2C, what is the difference and why is the maximum charge rate so low compared to the discharge rate? Lion can certainly take incredible charge rates, think Formula one, recharged in seconds!