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elios

join:2005-11-15
Springfield, MO

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

ok so im trying to see if there is way to convert 24volts at 47amps to say 30volts at 40amps or even some thing close at 40amps

im trying to power a lipo charger but it limits the input current to 40amps my psu has more then the power to get the charge rate
but since it gets limited to 24v at 40amps im only getting 960watts or so out of it

ideas?
the other option is get diffrent charger for bit more then a 50amp input but then i would still like get another volt to 2 volts out of my PSU setup which is 2x HP server 47amp PSUs in series
the PSU model is
HP DPS-600PB series ESP135
if i could get another volt out of each for 26v at even a slightly lower amp rate that would work fine to with the bigger changers input amp rate

thanks

public

join:2002-01-19
Santa Clara, CA
said by elios:

ok so im trying to see if there is way to convert 24volts at 47amps to say 30volts at 40amps or even some thing close at 40amps

Of course it is possible to design a dc/dc converter that does that.
In your case the problem is likely voltage drop over interconnections at high current.
Cheap off the shelf designs are rarely more than 90% efficient.


SparkChaser
Premium
join:2000-06-06
Downingtown, PA
kudos:4
reply to elios
Hmmm.... 24*47=1128, 30*40=1200


elios

join:2005-11-15
Springfield, MO
reply to public
even 80% would get me there
i only need to get at lest 26v and 44amps


elios

join:2005-11-15
Springfield, MO
reply to SparkChaser
said by SparkChaser:

Hmmm.... 24*47=1128, 30*40=1200

derp your right

the idea is to get as close to max out put from the charger
at ~89% to 90% efficient for the charger
so the voltage needs to be as close to 25.2v and 40amps as i can get
since thats the voltage and current going in to the packs

whats best case i can get if we limit the charger input to 40 amps? 50 amps?

edit thinking about it if i just get the one with the 50amp input i can just leave every thing as it is

but if just look at one limited to 40amps
could you build a DC/DC converter for less then 60bucks that could handle 26v and 40amps with a 24v 47amp input?


Jason
Stowage Class Traveler
Premium,Mod
join:2001-01-24
38.2967 Lat
kudos:3
reply to public
said by public:

Of course it is possible to design a dc/dc converter that does that.
In your case the problem is likely voltage drop over interconnections at high current.
Cheap off the shelf designs are rarely more than 90% efficient.

I dunno.. We regularly only get a 1.2-1.5V drop when passing 3-4 thousand amps in our equipment.

Of course, this is wired with 8 pairs of 444mcm DLO cable as the interconnects

Our 10,000 amp systems have a voltage drop about the same with only 4, 750mcm cables as the interconnections.
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leibold
Premium,MVM
join:2002-07-09
Sunnyvale, CA
kudos:10
Reviews:
·SONIC.NET
reply to elios
You will get a better result (smaller space requirement, less complexity and therefore more reliable, more efficient and therefore less heat) if you are using the correct power supply to begin with instead of trying to convert a mismatched supply and load with a DC-DC converter.

Therefore my number 1 suggestion would be to just get the right power supply. The cost for the DC-DC converter and the correct power supply are about the same (either is likely to set you back more than $60).

However if all you need is an additional volt or two out of those existing power supplies that is less then 10% more output voltage. If you can get the schematics for the power supply this is very likely doable without exceeding the specs for any of the parts used inside. Some precision power supplies have external voltage feedback (compensating for wire losses by measuring the output voltage near the load instead of internally) which makes it possible to raise the output voltage without any alteration of the power supply itself (a simple voltage divider for the feedback).
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elios

join:2005-11-15
Springfield, MO
thats not a bad idea ill have to see what i can dig up
i did get a hold of the guy that mods them in series where i got it from
he says they out put closer to 25.2 volts with out a load
if i could get 26 out of it another 0.4v on each psu
i would be set
he also said the Over current protection doesnt kick in till 50amps

but yea i think ill just suck it up return the charger and pay the 60 extra for one with the higher input current limit

public

join:2002-01-19
Santa Clara, CA
said by elios:

but yea i think ill just suck it up return the charger and pay the 60 extra for one with the higher input current limit

For $60 retail you will not get a quality charger. If you are considering modifications, why not modify the charger to accept wider input range?

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

1 edit
reply to elios
said by elios:

... if there is way to convert 24volts at 47amps to say 30volts at 40amps or even some thing close at 40amps

You will need a "multi-phase boost converter" to provide that much current at very high efficiency. Intersil 78225 for example can run upto 8 phases, each providing upto 10A at 95% efficiency.

As others have already pointed out, you will get somewhat less than (24Vx47A)/30V amps out of the "boost" converter circuit. However, your typical "server" power supply will die very quickly if you run it at max current even with fan at full blast.

If you are tied to that charger, you could get a good quality 24V/50A AC-DC module designed for industrial/telecom systems. They are usually adjustable between 22V-28V. Check Digikey, Mouser, etc.

Otherwise get a multi-chemistry lithium battery charger which directly uses AC input and gives you high enough current output (that does not damage the pack). These are available for both RC hobbyists and electric bikes.


elios

join:2005-11-15
Springfield, MO

2 edits
reply to public
said by public:

said by elios:

but yea i think ill just suck it up return the charger and pay the 60 extra for one with the higher input current limit

For $60 retail you will not get a quality charger. If you are considering modifications, why not modify the charger to accept wider input range?

:p i mean 60 MORE im getting a Power Lab 6 as a gift i can return it and pay 60 MORE for the Power Lab 8
website for the chargers
»www.revolectrix.com/

these are the best charges out and the input current is limited in the software which is not easily mod-able lol

i over payed for the charger i have now which is enimic for what im flying now its only 150w and 12v input so it maxes out around 4amps for a 6S pack so the PL8 will be 10x as powerful


elios

join:2005-11-15
Springfield, MO
reply to lutful
the issue was/is the Power Lab 6 has input current limit of 40amps
and to get near full output of the charger which is 1000watts
on a 6S lipo which is 25.2v full
i was hoping to get 38amp charge rates
wile the PSU set up has more then the power to do it I THOUGHT it was limited to 24v
the PSU could out put 47amps but the charger limits the current to 40amps

24*40=960 - ~10% you end up with only ~31amps for 6S packs

but my issue is solved im going to pay the extra for the Powerlab 8 which has a 50amp input current limit
and i found out the guy that mods the PSUs ups the pots in them to out put 25.2v

so im good to go up to 39amps close enough to 40 for 6S packs

as to any one wondering WHY i need 40amps to charge lipos
my helis run on 6 cell 3000mAh to 3300mAh lipo packs
and my biggest one atm runs on 12 cell using 2 packs
with a 39~40amp charge rate i can do 6 packs at once in about 30min


elios

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

Otherwise get a multi-chemistry lithium battery charger which directly uses AC input and gives you high enough current output (that does not damage the pack). These are available for both RC hobbyists and electric bikes.

chargers with built in AC input or ones that come with small AC power supplies are FAR to small again the charger i have now is like that and only 150watts see other posts for the math on that
the power Powerlab6 is 1000watt and 8 is 1344watt
but they ether need to be run off a set of deep cycle Pb cell batteries or a 24v to 30v bench supply
so here is what im ending up with

»www.revolectrix.com/pl8_specs_tab.htm

TheMG
Premium
join:2007-09-04
Canada
kudos:3
Reviews:
·NorthWest Tel

1 edit
reply to elios
I would suggest looking around eBay. You can sometimes find good quality industrial power supplies for a decent price.

A few years ago I obtained a couple of Astec (now Emerson Power) MP series power supplies for $60 each. One is 12V 50A the other is 24V 23.5A. These are adjustable, have external voltage sensing, current-limited. They are designed for continuous usage at maximum load, and also support current-sharing between multiple power supplies (meaning power supplies of same voltage output can be paralleled for higher power).

So yeah, looks around and you might find a good deal on a power supply that will do the trick.

Edit: here you go, 24V 62.4A, adjustable up to at least 26.4V according to the datasheet, probably a little bit more in actucality. They guarantee a minimum adjustment range of +/-10% of nominal, but in reality you can do a bit more. It is also designed for continuous use at 100% load.

»www.ebay.ca/itm/Astec-VS1-L5-02-···782cff8e

public

join:2002-01-19
Santa Clara, CA
reply to elios
said by elios:

power Powerlab6 is 1000watt and 8 is 1344watt
but they ether need to be run off a set of deep cycle Pb cell batteries or a 24v to 30v bench supply
so here is what im ending up with

»www.revolectrix.com/pl8_specs_tab.htm

None of the Revo products use heavy enough gauge wires or quality high current connectors.
Industrial grade supply would be one like this
»www.eltekvalere.com/wip4/powerpa···at=11355

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

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

the power Powerlab6 is 1000watt and 8 is 1344watt
but they ether need to be run off a set of deep cycle Pb cell batteries or a 24v to 30v bench supply

OK, I had a look at the Powerlab and it is supposed to charge multiple packs in parallel with taps coming from each pack using separate 9-pin connectors.

Instead of a 30V/50A bench supply, which will be really expensive, consider my original suggestion of an adjustable 24V AC-DC module from Vicor, TDK-Lambda, etc. Set the output to match maximum safe voltage rating of the Powerlab.


elios

join:2005-11-15
Springfield, MO

2 edits
reply to lutful
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:4
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:4
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.