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

[Duncan Disorderly]

7 minutes ago, Philip Lewis 3 said:

No sorry I disagree, do not use a BMS

 

I thought the BMS had its own way of managing the supply charge? You're correct, you can't run one through your normal charger, it's a self contained system and I can't even get my head around how using both could even happpen!

 

I need to read up more about them.

 

In the meantime, headroom is your friend.

 

[Philip Lewis 3]

No a BMS just watches the voltage and effectively disconnects that cell or cells once that voltage is reached, you only need a BMS when using a "dumb" charger i.e. a simple two pole DC charger such as a wall wart, your balance charger pumps out the total pack voltage through the charge leads and then wastes away or dumps into a resistance the excess for a fully charged cell through the balance wire which is why a balance charge can take a long time at the end, it can only charge at the rate it can dissipate any excess.

[Philip Lewis 3]

To sort of conclude my thoughts on this (for whatever they are worth) this is exactly how I would wire it up if/when I build one, a single cell going open circuit won't show up you would just have a much reduced capacity from those cells in parallel, the same as you would when parallel charging multiple batteries and a cell with a high resistance simply won't accept a charge but the other cells won't be able to be overcharged either as once the set voltage has been reached the charge will cut off.

 

Yes you can get much more complex, for instace a formula 1 car battery has every cell monitored (I've seen it) but we don't have their millions.

 

Just a suggestion Duncan, but I would only charge this to 4.1 volt a cell not 4.15, 4.1V is the natural chemistry Lion voltage which they pushed to 4.2V, chargers which have a Lion charge setting should be set to 4.1 V per cell, only reason is again for longevity I'm not saying you are doing any harm but you really aren't losing much capacity using 4.1V rather than 4.15 or 4.2V.  

 

I really can't see a better way of wiring this set up.

[Andy J]

This site was quite informative about charging and interconnecting lifep04 batteries.

[Neil R]

@Duncan Disorderly- many thanks for providing the inspiration, here's one I've put together over the last couple of weeks. It was finished earlier today, and so far the charging is keeping all the voltages nice and even, which gives me confidence I didn't kill anything when soldering. (I bought an ISDT Air 8 also). 

This is going to absolutely transform my flying, perhaps especially in terms of grabbing those last minute opportunities when nothing else has been charged.

Thanks again!

[Duncan Disorderly]

18 hours ago, Neil R said:

@Duncan Disorderly- many thanks for providing the inspiration, here's one I've put together over the last couple of weeks. It was finished earlier today, and so far the charging is keeping all the voltages nice and even, which gives me confidence I didn't kill anything when soldering. (I bought an ISDT Air 8 also). 

This is going to absolutely transform my flying, perhaps especially in terms of grabbing those last minute opportunities when nothing else has been charged.

Thanks again!

 

Wow that's really good! Better than mine, anyway. I hope it brings you the freedom to fly that mine's brought me. Going forwards, it's nice to only ever have to buy one or two new LiPos. Those ISDT Air 8 chargers are brilliant - I really lucked in there because I didn't do an awful lot of research other than a quick check to see it'd do what I needed.

[Duncan Disorderly]

I'll check in on this topic now and again to update the total number of 4C/12A charges those two 6S 3300s have suffered and whether there's actually been any suffering involved. Worth doing, I think, because there was consternation earlier in the thread about >1C charging. They're now on 143 cycles at 12A and are still showing no sign of anything degrading.

[Phil Green]

Old thread but just to add that I recently bought one of those cheap hand-held spot welders from Aliexpress,

it works great for strapping cell packs:  https://www.aliexpress.com/item/1005006226735630.html

Shaun ordered a job lot of 100 'used' A123 cells from ebay, he gave me 20 so I've just made up a 12v pack for general use, 5P4S,

using the supplied strapping - this will keep my little 500mAh packs going nicely all weekend at Old Warden  😉

No BMS, just a 4S balance lead for charging on a regular R/C charger.

Its like a small, light leisure battery, occasionally handy around the house or when camping too 😃

 

[Duncan Disorderly]

On 11/10/2024 at 21:17, Phil Green said:

this will keep my little 500mAh packs going nicely all weekend

 

Perfect for the job! Have fun at OW.

 

 

The latest test packs of the newest Li-ions (6S2P 8000mAh but unsure of manufacturer) were sustaining over 100A at WOT, so it won't be long before we're using them in the planes instead of LiPos. We've got Roger's Junior 60 on a Li-ion pack at the Coventry club, giving almost an hour in the air, so now it's just a matter of amp draw for our aerobats.

 

While I'm here updating this thread:

 

Russ's original box finally got too unbalanced at almost the 5 year mark, so he unsoldered it all, tested each cell, threw out the rubbish ones and resoldered the good ones - so it's still going after the rebuild with cells that he got second hand (for free IIRC) in the first place. So a couple of pence per flight (not that we're doing it this way because it's cheaper - but it is a lot cheaper!)

 

My pair of 6S 3300 LiPos' balance leads have all broken (only a couple remaining on each) and I can't be bothered to take them apart to the required extent to fix them. They're on 736 cycles each now and I'm just doing unbalanced charging at the field and seeing how long they can handle that for. I think that I might have made my point about charging at high C rates by now - they've worn out mechanically not chemically!

[Philip Lewis 3]

12 hours ago, Duncan Disorderly said:

The latest test packs of the newest Li-ions (6S2P 8000mAh but unsure of manufacturer) were sustaining over 100A at WOT, so it won't be long before we're using them in the planes instead of LiPos. We've got Roger's Junior 60 on a Li-ion pack at the Coventry club, giving almost an hour in the air, so now it's just a matter of amp draw for our aerobats.

Funny you should say that Duncan, I'm about to test that out right now, I've got some decent quality 5,000 mah Molicell packs that are rated at 45 amp constant discharge as well as some other slight smaller 4,500 mah 50 amp constant rated packs, I've got an old 8 cell plane to initially test them in which I don't care what happens to, my initial thought are that if you used 6 cell LiPo's you probably need to use 8 cell Li-ion and likewise for an 8 cell LiPo plane use 10 cell Li-ion, that's because I'm expecting the Li-ion to sag to a much lower voltage per cell under the same large load, I have the capability to measure voltage under load V amps drawn V RPM live so should be able to get some decent telemetry data, sadly the FIA rules (around standing max voltage) are likely to make this unviable for competition use.

 

The other issue is C of G (something that doesn't trouble the drone users), you might not even be able to get the Li-ion pack far forward enough, as a direct comparison my ten cell LiPo packs weigh 1100 grams, a twelve cell Li-ion pack of the same capacity would weigh in at around 840 grams.

 

An interesting experiment though especially as the Li-on pack is about 40% cheaper as well.   

 

Also the solid state lithium packs look rather interesting!

Edited October 13, 2024 by Philip Lewis 3

[Duncan Disorderly]

17 hours ago, Philip Lewis 3 said:

I'm about to test that out right now

Brilliant - I'll leave that one up to you!

 

17 hours ago, Philip Lewis 3 said:

if you used 6 cell LiPo's you probably need to use 8 cell Li-ion

That sounds very sensible

 

17 hours ago, Philip Lewis 3 said:

sadly the FIA rules (around standing max voltage) are likely to make this unviable for competition use.

Well, yes... internationally... but nobody would mind domestically if you based it on total wattHours instead, as you wouldn't be getting any advantage. And nobody would check anyway!

 

17 hours ago, Philip Lewis 3 said:

The other issue is C of G

That's interesting cos I'm forever extending battery trays towards the back of the plane or adding tail weight - no matter which airframe - so lighter packs would suit me fine!

 

17 hours ago, Philip Lewis 3 said:

Also the solid state lithium packs look rather interesting!

Indeed - these are good times to be flying electric

 

I'll come and get that Elixir any day now!

[Philip Lewis 3]

2 hours ago, Duncan Disorderly said:

Well, yes... internationally... but nobody would mind domestically if you based it on total wattHours instead, as you wouldn't be getting any advantage. And nobody would check anyway!

 

That's interesting cos I'm forever extending battery trays towards the back of the plane or adding tail weight - no matter which airframe - so lighter packs would suit me fine!

 

Duncan you're confusing capacity with power, and I also don't really understand why the FAI have a volt limit as that doesn't limit power either, watts is power and double the current draw with the same voltage and you double the power, and while I'm having a rant why is pattern limited to 10 cell but heli's can use 12 cells?

 

Yes I agree I always seem to have the same trouble of getting the battery tray far enough back and I absolutely cannot seem to get myself to actually add weight, just that it might be the opposite problem with these, we'll see. 

[Dickw]

19 minutes ago, Philip Lewis 3 said:

 

............. and I also don't really understand why the FAI have a volt limit as that doesn't limit power either, watts is power and double the current draw with the same voltage and you double the power, and while I'm having a rant why is pattern limited to 10 cell but heli's can use 12 cells?

..............................

I assume part of the reason for a 12 cell limit with Lipos is electrical safety, as 50v is generally regarded as a safe "touch" voltage.

I can understand why some power related competition classes have lower cell count limits but no idea of any reason where power is not a factor.

 

Dick

[Philip Lewis 3]

41 minutes ago, Dickw said:

I assume part of the reason for a 12 cell limit with Lipos is electrical safety, as 50v is generally regarded as a safe "touch" voltage.

I can understand why some power related competition classes have lower cell count limits but no idea of any reason where power is not a factor.

 

Dick

Yes I get that and I don't disagree with it, I also get some other classes limiting in other ways but I just don't understand the logic of limiting Pattern to 10 cell if 12 is considered OK from a safety perspective for Heli's, mainly because 6 cell packs are much more readily available.

[Duncan Disorderly]

14 hours ago, Duncan Disorderly said:

based it on total wattHours

 

11 hours ago, Philip Lewis 3 said:

Duncan you're confusing capacity with power,

 

What I typed was "total watts" and the robots did the rest!  (They were probably continuing an earlier conversation about capacities, saw me type "watts" and thought "we know what to do here"... Apologies, I'm normally good at checking my posts for errors)

 

So e.g. put a 3kW/4hp limit and it's up to you how to multiply the amps and volts. A voltage limit doesn't control anything (other than volts, obviously)!

[Learner]

1 hour ago, Duncan Disorderly said:

 

 

What I typed was "total watts" and the robots did the rest!  (They were probably continuing an earlier conversation about capacities, saw me type "watts" and thought "we know what to do here"... Apologies, I'm normally good at checking my posts for errors)

 

So e.g. put a 3kW/4hp limit and it's up to you how to multiply the amps and volts. A voltage limit doesn't control anything (other than volts, obviously)!

I imagine the 10s cut off was originally brought out for cost capping.

Checking for 10s is very easy, whereas checking power output could get very complicated especially If someone is wanting to bend the rules.

[Dickw]

13 hours ago, Philip Lewis 3 said:

Yes I get that and I don't disagree with it, I also get some other classes limiting in other ways but I just don't understand the logic of limiting Pattern to 10 cell if 12 is considered OK from a safety perspective for Heli's, mainly because 6 cell packs are much more readily available.

I am with you on the availability of packs.
In F5B we were limited to 10s for quite understandable power/performance related reasons, but that did make finding suitable battery packs an issue. I do have some 5+5 packs, but most of mine are based on 6+4 configuration because those were the easiest packs to source.

 

Dick