 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 |
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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. |
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 SparkChaserPremium
join:2000-06-06
Downingtown, PA
kudos:3 | reply to elios
Hmmm.... 24*47=1128, 30*40=1200 |
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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 |
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elios
join:2005-11-15
Springfield, MO | reply to SparkChaser
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? |
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 JasonStowage Class TravelerPremium,Mod
join:2001-01-24
38.2967 Lat
kudos:3
 ·AT&T U-Verse
Host:
Wireless Security
| 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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 leiboldPremium,MVM
join:2002-07-09
Sunnyvale, CA
kudos:6
 ·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 |
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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? |
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lutful... of ideasPremium
join:2005-06-16
Ottawa, ON Reviews:
·TekSavvy DSL
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. |
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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  |
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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 |
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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 |
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TheMGPremium
join:2007-09-04
Canada
kudos:1
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 |
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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 |
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lutful... of ideasPremium
join:2005-06-16
Ottawa, ON Reviews:
·TekSavvy DSL
| 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? |
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lutful... of ideasPremium
join:2005-06-16
Ottawa, ON Reviews:
·TekSavvy DSL
| 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. |
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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
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SparkChaserPremium
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.
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"Facts do not cease to exist because they are ignored." - Aldous Huxley
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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 |
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