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how to calculate charger watt power vs volts???

Old 10-14-2015, 11:38 PM
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Flysohigh
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Default how to calculate charger watt power vs volts???

I have a icharger 308 and it can put out 1300w at 23.5v but how can i determine at 14v how much watts it can put out? My PSU is 40a 600w?
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Old 10-15-2015, 02:21 AM
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fhhuber
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Watts = volts * amps

So if output is 50 watts max (typical of a lot of chargers) then 50 / (full charge volts) = max current output.
Note: Actual practice it will output a bit more and taper down as the pack fills, but its really close.
For 4S LiPo (16.8 v full charge) the 50 watt charger I have, when set for 5 amp rate, will automatically go to 3.3 amps for a nearly empty pack and tapers down as the pack fills.

Most modern chargers you can tell it to TRY to charge at a higher rate and they'll automatically reduce rate to prevent damaging the charger. But its always best to set for something the charger should be able to deliver.


****************

Then there's the input power demand... which is typically 10% to 50% more than output, depending on charger efficiency at the step-up/down between source and output.
Because of how much this varies its hard to predict without having the same charger and actually taking measurements.
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Old 10-15-2015, 03:23 AM
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Flysohigh
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i thought you would just cut in half the charger output power based on input voltage ...

i.e. 24v input to charger from psu puts out 1200watts , 12v input to charger from psu puts out 600watts?? am i missing something?
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Old 10-15-2015, 06:02 AM
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These are the specs from the manual:

Specifications
  • Input voltage range: 10.030.0VDC
  • Maximum input current limit: <60A, CH1/2<40A
  • Maximum charge/discharge current: [email protected] Mode [email protected] Mode
  • Maximum charge power capacity: 1300W (Channel 800W @input > 23.5V)
  • Maximum discharge power capacity: 120W (Channel 80W)
  • Maximum regenerative discharge power capacity: 1300W (Channel 800W)
  • Maximum extra discharge power capacity: 2100W (Channel 1050W @35V/30A)
  • Maximum current drain for balancing: [email protected] Mode [email protected] Mode
  • USB charging port: 5V/1A(current-limiting protection 1.2A)

In this case though the spec of the charger doesn't really matter. The 'weak link' is your power supply. The power supply can only do 40A / 600W so allowing for efficiency the maximum charger output would be around 500-550W or so.

You should set a current input limit of 40A (or a little less) in the charger software to avoid accidentally attempting to pull too much from the PSU... or better yet upgrade the PSU.

With a good enough PSU the limit becomes the input current rating of the charger which according to the spec is 60A in dual mode or 40A in single channel.
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Old 10-15-2015, 09:16 AM
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While one charger MIGHT have 1200 watt input and 600 watt output under some condition... Its not reliable to assume 50% loss in the charger.
Less loss would be more normal.

Just changing input voltage to the charger would be expected to change the AMPS demanded. (assuming you are staying within the charger's acceptable input voltage range)

12v input for 1200 watt (charger) demand would mean 100 amp demand
Watts / Volts = Amps.

Just changing input voltage, but keeping the same load on the charger you would expect:

24v input, 1200 watt (* change in efficiency) demand at 50 amps (* change in efficiency)

You could actually run tests to determine the change of efficiency with input voltage change. But that change would depend on the charger. It might be significant... it might not. And it can easily depend on voltage of the pack being charged.
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Old 10-15-2015, 09:54 AM
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JetPlaneFlyer
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Originally Posted by fhhuber View Post
While one charger MIGHT have 1200 watt input and 600 watt output under some condition... Its not reliable to assume 50% loss in the charger.
Less loss would be more normal.
I think you misunderstand my last post, no one suggested a 50% loss through the charger.

The Power supply in question is only 600W, therefore the charger cannot ever output more than 600W regardless of it's theoretical maximum rating. In reality the 500-550W I suggested will be the realistic maximum charger output due to efficiency losses through the charger.
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Old 10-15-2015, 12:35 PM
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Flysohigh
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Originally Posted by JetPlaneFlyer View Post
I think you misunderstand my last post, no one suggested a 50% loss through the charger.

The Power supply in question is only 600W, therefore the charger cannot ever output more than 600W regardless of it's theoretical maximum rating. In reality the 500-550W I suggested will be the realistic maximum charger output due to efficiency losses through the charger.
Ok so with this being said lets say output from my charger at 500w, i would then only be able to put out 250 roughly from each port? And is this regardless if the input from the power supply is at 12v or 24v?
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Old 10-15-2015, 12:41 PM
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Originally Posted by Flysohigh View Post
Ok so with this being said lets say output from my charger at 500w, i would then only be able to put out 250 roughly from each port? And is this regardless if the input from the power supply is at 12v or 24v?
The 500W would be shared between the two ports, so that could be 250W per port or 500W on a single port.. that's entirely dependant on how you set up your charging.

The voltage of the PSU makes no difference in this case. the limitation is that the PSU is only rated for 600W. You cant get more power out of the charger than you put in, that would break the most fundamental laws of physics!
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Old 10-15-2015, 12:51 PM
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PS.. there are a few people around who sell converted computer server supply units for use in powering high output chargers. These are the most cost effective solution.

One of the most common server supplies is the HP DPS-600PB. Many sell these units configured in series which gives a 24V 47A supply. That would be enough to 'almost' (but not quite) max out your charger.

Modifying them yourself is also perfectly possible if you are good with a soldering iron.
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Old 10-15-2015, 02:08 PM
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Flysohigh
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With that said i will be putting up for sale my PSU chargery s600 40amp...i had a 62amp 800w server supply but man it was loud!!!
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Old 10-15-2015, 02:21 PM
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Yeah, they can tend to ne noisy because they are designed for use in server rooms where no one can hear them. Some have temperature controlled fans which is much better, or there are a few tricks to slow the fans down a bit.
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Old 10-18-2015, 02:22 AM
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PS conversion thread here
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