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elios

join:2005-11-15
Springfield, MO
reply to lutful

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

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