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lutful
... of ideas
Premium
join:2005-06-16
Ottawa, ON
kudos:1
reply to elios

Re: PSU's and DC-DC convters or Is There An EE In The House!?

said by elios:

as to any one wondering WHY i need 40amps to charge lipos my helis run on 6 cell 3000mAh to 3300mAh lipo packs
... with a 39~40amp charge rate i can do 6 packs at once in about 30min

If you are trying to charge N separate M-cell lithium-polymer battery packs in parallel using a single charger - please reconsider your strategy! You really should use a separate charger per pack with taps to monitor each cell of the pack to avoid a potential disaster.

Anyway typical RC Li-poly packs can easily be fast charged at 5C rate which translates to 15A for your 6S/3000mAh packs. Buy 6 AC input 25.2V/15A capable smart Li-Poly chargers and plug them into a 6-outlet power bar. Now the packs should be ready to fly in less than 15 minutes, right?


elios

join:2005-11-15
Springfield, MO

2 edits
said by lutful:

said by elios:

as to any one wondering WHY i need 40amps to charge lipos my helis run on 6 cell 3000mAh to 3300mAh lipo packs
... with a 39~40amp charge rate i can do 6 packs at once in about 30min

If you are trying to charge N separate M-cell lithium-polymer battery packs in parallel using a single charger - please reconsider your strategy! You really should use a separate charger per pack with taps to monitor each cell of the pack to avoid a potential disaster.

Anyway typical RC Li-poly packs can easily be fast charged at 5C rate which translates to 15A for your 6S/3000mAh packs. Buy 6 AC input 25.2V/15A capable smart Li-Poly chargers and plug them into a 6-outlet power bar. Now the packs should be ready to fly in less than 15 minutes, right?

works totally fine thanks Ohm's Law
all packs are in parallel and all the cells are in parallel to the balancer

im not new to charging lipos
just highpower charging setups
why i need to charge that many packs?
this


the big one needs 2x 6cell packs in series for 12 cell and the small one uses one 6 cell
both same capacity 3000 to 3300 mAh 6S packs
6 packs = 2 flights each at ~5min a flight + short breaks i can fly all day



SparkChaser
Premium
join:2000-06-06
Downingtown, PA
kudos:3
Reviews:
·Verizon FiOS
said by elios:

works totally fine thanks Ohm's Law
all packs are in parallel and all the cells are in parallel to the balancer

You'll use one of these? »www.revolectrix.com/cellpro_adapters.htm

OT what helio do you have. I've see the color in the hobby shop but I'm not sure what it is. I went to the the shop to buy some small Lipos for a project and saw the helicopters and have been thinking about since.
--
--
--
"Facts do not cease to exist because they are ignored." - Aldous Huxley


elios

join:2005-11-15
Springfield, MO

3 edits
the big one is a Compass 6HV a 600 class (590 to 630mm main blades) and the "small" one is a T-Rex 500 ESP a 500 class (425mm main blades)
btw the 6HV i measured using ~3500watts with a peak of 4000watts it weighs in at 3.2kg

this is what im going to use
»www.revolectrix.com/MPA_XH.htm
its designed for 40amp loads and is fused

lots of fun man but not cheap by any means but dont let that stop you

if you want get in to the hobby get a get mCX2 ~120 bucks comes with every thing and pick up a few extra lipos for it total cost should be around 150

if you think its some thing you really want to do after that pick up as much TX as you can afford and a sim like Phoenix RC
at lest get a DX6i or better i fly a Spektrum DX8

feel free pm me if you need any help and check out »www.helifreak.com

also »www.modelaircraft.org/ if you go want to fly some thing 'big' you should join the AMA you can also look up clubs near you most love to have people stop by and watch

next project im saving for will be a Goblin 700 or 770 which swings 700mm to 770mm mains

fun fact since all the cells are in parallel in when setup like that ie pack 1's cell 1 is in parallel with pack 2's cell 1 etc
the MORE packs you put on the more the internal resistance of the cells even out and the better balanced all the cells are

lipos also have some nifty tricks do the chemistry of them
since the higher the capacity of the cell the lower the internal resistance of the cell
AND the internal resistance goes up as function of the voltage

this site has some good stuff on the how and why it works
»www.icharger.co.nz/articles/Arti···-me.aspx


SparkChaser
Premium
join:2000-06-06
Downingtown, PA
kudos:3
Reviews:
·Verizon FiOS
Thanks for the info. That MCX2 sounds pretty good. Eflite are the batteries I been using along with their balanced charger but only 0.6A

Here is the local store, prices seem good on the MCX2 »www.hobbyhut.com/SearchResults.a···rch=mcx2


elios

join:2005-11-15
Springfield, MO

1 recommendation

thats the one get the "RTF" itll come with a TX that looks like game controller, 1S lipo and charger that runs on 2xAA
you can replace this with a real TX later down the road like a DX6i, DX7s, DX8, DX18

and imo get at lest 2 extra 1S 120mAh packs for it if not 4 or so they dont cost much and you only get ~5min a pack
im guessing you already know about not over discharging them
so use a timer dont just fly till the LVC
you can also get cables to charge the lipos with the charger you have already and do up to 6 at once

nice thing is its small and very stable so you can fly in the living room its not good out side unless its DEAD CALM

and if you do break it you can get parts to repair it


elios

join:2005-11-15
Springfield, MO
reply to SparkChaser
thats a nice local shop wish the one here was that nice your guys even carry Compass
i have mail order every thing from Nankin Hobbies they are the US distributor for Compass

let me know how works out send me a pick with your new heli

lutful
... of ideas
Premium
join:2005-06-16
Ottawa, ON
kudos:1
reply to elios
said by elios:

said by lutful:

said by elios:

... i can do 6 packs at once ...

If you are trying to charge N separate M-cell lithium-polymer battery packs in parallel using a single charger - please reconsider your strategy! ...

works totally fine thanks Ohm's Law ...

Each battery pack, even when their internal cells are perfectly balanced, will start with slightly different electrical characteristics which will change at slightly different rates with each charge cycle.

The exact time when charger needs to move a particular battery pack from constant current mode (CC) to constant voltage mode (CV) will gradually drift apart.

That is why it is much better to have completely independent CC-CV charger for each pack.


elios

join:2005-11-15
Springfield, MO
read the link i posted
people have been doing this for years
and the more packs in parallel the less drift there is
again this only works with lipos do to way the chemistry works
since as a cells voltage goes up its IR goes up as well and cell will take less amps

also the each cell is in parallel with the same cell for the other packs
and the IR is avenged and again the more cells in parallel the better the balance
»www.icharger.co.nz/articles/Arti···-me.aspx

lutful
... of ideas
Premium
join:2005-06-16
Ottawa, ON
kudos:1

1 edit
said by elios:

read the link i posted
people have been doing this for years
...
»www.icharger.co.nz/articles/Arti···-me.aspx

OK, I read that link and a few others. This site is similar with some more photos and details and some warnings too:
»sites.google.com/site/tjinguytec···charging


... If something were to go wrong during the charge cycle it could effect multiple packs
... you loose the ability to monitor each pack independently
... it is possible that a large amount of current can flow between the packs as they equalize themselves ... most cases this will not damage the batteries but it can damage the wiring.

... Parallel charging large packs on lesser capable chargers will give little to no benefit, aside from only having to set up charger one time ... Parallel charging is really done best on larger chargers.


Imagine taking this approach to this ridiculous extreme:
AC-DC power supply: 28V/100A output
DC parallel charger: 25.2V/100A capable
Parallel adapter for 8 lipo batteries

Alternative solution which packages 8 separate 25.2V/15A capable charger modules in one box will actually be cheaper and will provide benefits too:

- ability to mix and match 2S/3S/.../6S packs
- less risk of wrong cable hookup
- proper CC-CV charging for each pack
- proper monitoring of each individual pack

Perhaps no company is packaging such a solution yet is because "people are doing it for years" another way.


elios

join:2005-11-15
Springfield, MO

2 edits
well the thing is more then 5C change rates will damage the packs
so no point in charging over 4C really

the idea is you can charge more packs at a lower C over all and get them done in the same

if you have packs massively out of balance well you shouldnt be flying them any way

almost no one charges at over 4C its just not good for the packs

i dont care about mixing packs cell counts both my models use the same packs 6S 3000mAh to 3300mAh
and even when i go get a 700 itll use 6S packs too just 4500mAh

i have some 3S packs for other stuff but i can keep charging them on my 150w charger since i can easily get 2C out it for 3S and they will never be bigger then 3200mAh

the issue of SUPER high amp chargers is more of the size of the cable and the size of the power supply
to get 100amps of output you need at lest that much in if not a lot more
for that you would need a 2kw or more power supply which in the US would HAVE to run 220v
and you would need 6 guage cable every where and high current connectors

its an issue of cost and input power

»epbuddy.com/index.php?main_page=···s_id=389

this charger can do up to 70amps using 2 channels but each channel needs 25v to 30v and 45amps
again needing 2kw+ of power to run the thing
the really limit is the power coming out of your wall

lutful
... of ideas
Premium
join:2005-06-16
Ottawa, ON
kudos:1
Click for full size
said by elios:

well the thing is more then 5C change rates will damage the packs so no point in charging over 4C really ... almost no one charges at over 4C its just not good for the packs

I actually said that in my first response when I thought you were trying to rapid charge packs at 40A.

FYI some electric cars and military gear safely charge lithium polymer packs at 10C and some UAVs/drones (not that different than your RC helis) are actually rapid charged at 20C. That is possible because they implement proper per-cell safety monitoring and true CC-CV algorithm.

However, the system I imagined would definitely have adjustable constant current which could be set for example between 0.1C to 10C for each pack based on its electrical specs and application needs.

said by elios:

needing 2kw+ of power to run the thing the really limit is the power coming out of your wall

Yes ... but X independent smart charger modules can be packaged more easily in an enclosure with 120V/240V switchable AC input and internal bus that could distribute upto 30A. System controller could ensure maximum 15A@120V or 30A@240V current draw for all active chargers.

Anyway, I found 2 off-the-shelf LT automotive chips (used by Mitsubishi) which could be used for the RC industry. Each independent charger module could handle upto 12S packs at 50.4V/20A with these chips and total system cost for 8 pack solution should be less than single monster parallel balance charger with required accessories.


elios

join:2005-11-15
Springfield, MO
the check the cell chemistry on the fast charge cars there not Lipo they are using Li-Fe/A123 which you CAN charge an insane rates

we use Li-Fe for things like TX, RX and ignition packs
the trade off is Li-Fe weighs more and has lower per cell voltage
not ideal for flight packs

there just isnt a need for that kind of a charger
when with a 40amp charger you can do 6 packs at once
even bird that needs 2 at time thats 3 flight
12 packs and you can fly back to back all day long

and with the Powerlab you can link up to 16 of them lol to run of the setting of 1 IF you REALLY need that much

your avg RC guy rarely needs more then a 20amp to 30 amp charger
and the guys wanting setups like me are few and at the top end of the hobby

lutful
... of ideas
Premium
join:2005-06-16
Ottawa, ON
kudos:1
said by elios:

check the cell chemistry on the fast charge cars there not Lipo they are using Li-Fe/A123 which you CAN charge an insane rates

Many production hybrid cars have been switching over to lithium polymer since Hyundai did it back in 2008:
»green.autoblog.com/2008/07/09/hy···battery/
The Elantra LPI HEV will be the first car in the world to use lithium polymer rechargeable batteries ... significant advantages over lithium–ion batteries including higher energy density, lower manufacturing costs, being more robust to physical damage and they can also take more charge–discharge cycles ...

said by elios:

... with the Powerlab you can link up to 16 of them lol to run of the setting of 1 IF you REALLY need that much

Powerlab appears to be the end of innovation for RC folks.

Anyway, your original problem is solved by a multi-phase DC-DC boost converter: more phases = more current @ constant voltage.


elios

join:2005-11-15
Springfield, MO
it pretty much is untill we get a new battery type any way


elios

join:2005-11-15
Springfield, MO

1 recommendation

reply to lutful
got my stuff in and setup
PSU is putting out 25.5v so should be good to go
only tested up to 30amps on the charger so far but looks good


SmokChsr
Who let the magic smoke out?
Premium
join:2006-03-17
Saint Augustine, FL
reply to lutful
said by lutful:

The exact time when charger needs to move a particular battery pack from constant current mode (CC) to constant voltage mode (CV) will gradually drift apart.

The packs I'm working with the protection circuit in the battery pack does all the decision making for the pack. All the pack wants from the charger is the proper voltage to charge with. After that the circuit will do all the cell balancing and even cut the charger off if it allows the voltage to get too high. Since my charger doesn't even approach 1C, I don't know if they will regulate the charging current to keep it from getting to high.

With a 40A charger that should put him a bit above a 2C charge with 6 packs connected. Even worse it could try to go above 10C if only one pack is connected.

PS I'm using 8cell 10AH packs for ENG lighting. Replacing the old standard 24 cell 4000mAh NiCad battery belt. Ahh so nice 3X the run time and half the weight.

lutful
... of ideas
Premium
join:2005-06-16
Ottawa, ON
kudos:1
said by SmokChsr:

The packs I'm working with the protection circuit in the battery pack does all the decision making for the pack ... don't know if they will regulate the charging current

Yes. Since I usually quote Linear Tech, let me try Texas Instruments this time ... bqSWITCHER™ series are highly integrated Li-ion and Li-polymer switch-mode charge management devices ... high-accuracy current and voltage regulation, charge preconditioning, charge status, and charge termination, in a small, thermally enhanced QFN package

»www.ti.com/product/bq24100

Of course, RC li-poly packs do not incorporate such ICs and brute-force parallel chargers can't adjust the charge current for each pack.