i know how to make them but i dont know about all the numbers. can someone explain?

say i have a charger that charges 4 2s batteries at once at 5 amps each, how would i determine the minimum power needed from a power supply?

Basic equation: Voltage x Amps = Watts

For the case mentioned, including allowance for charger efficiency:

4 lipos x 8.4V full charge x 5A / 80% charger efficiency = 210 watts

Most power supply manufacturers recommend ~30% extra for reliable operation: 273 watts.

OHM's Law.. basic electronics..

I have been using my converted Server PS now for almost 3 years ..its a 125amp with 13.8volts DC..I run 5 chargers varying from 10 amps 8.4v to 25 amps 8.4v..My voltage never falls below..13.6V. had issues with ICE chargers a few years ago not liking the 11.5V a computer PS supplied.dumped the ICE's anyway..fell into follow the pack thing and Never again..I do my own thing and many people follow my leads at my 2 tracks..

The guy that got the 2 dells yes u bought a box for 299 as i can buy these ps for $37 each

why do some people use 24 volts?
I have never tried 24 volt input into any of my chargers.

my icharger 208b says it can handle up to 36vdc
my Thunder power tp610c says up to 18vdc
I would guess the higher input voltage allows the charger to run more efficiently Is this True?
And has anyone ran the 2 12v psu in series for 24v,with one pcu still running 12v to a seperate set of posts?
see diagram

Some of the big boy chargers require 24 volt (or higher even) supplies to generate full output power. Including PowerLabs, and the bigger iCharger, Hyperion, and ThunderPower models. Because of input current limits, generally it’s cheaper/easier to go up in volts than amps to get high power. Helps with efficiency too as you suspected.

It’s mostly needed for the high voltage batteries (>4S) that are more common with planes and helis. Usually for smaller lipos the amperage limit is hit first before the power limit.

I am mainly charging 4s batteries for my 1/8 Losi late model
I only have 3 batteries and was wanting to be sure I would be able charge between open laps,heat and main races.
These batteries are ran down to cutoff in about 5 minutes.
45 minute to 1hr charge times aren't always possible.This is why I want to be able to charge at higher amperage when needed.

Bingo.

Also, battery chargers are basically Switch-Mode Power Supplies.

When you step a voltage down "Buck" or up "Boost", it requires a specific set of routines and circuitry.

Those 24v chargers get to use smaller (cheaper) transistors due to high-voltages not requiring as much thermal design concerns, they also requires less sophisticated Boost sections due to the input voltage being so high.

Whereas a 12v charger requires a rather significant, complex Boost regulator and parts (large high-value capacitors, FET's of significant amperage, etc) comparably, to charge Higher-Voltage batteries.

This is where efficiency kicks in. Boost regulators are not as efficient as Buck. Buck regulators can be upwards of 95% efficient, boost only 85%~+. That's a lot of power when we're talking double-digit numbers of amps.

Your 208B charging a 4S provides a good example of required power supply voltage. Assuming for the moment you and your lipos are OK with going to 11, the charger can output 20 amps into a 4S, peak of 336 watts (20A x 16.8V max).

336 is below the 350W charger rating, but wait, check the chart on the bottom of page 10 in the manual. To achieve the 336W output requires a power supply of just over 15.5V.

On a true 12V power supply the 208B is limited to just over 250W of output, or around 14.9 amps for a 4S. On a typical 13.8V bench supply around 290W, or just over 17 amps.


For 2S the power limits probably wouldn't matter, as you would be current limited by the 20A. But if you had a 8S helicopter, then that extra power could come in handy.

I would like to have my 3 chargers all operate off the one power supply(2 in series).I know I probably won't need full amperage to all at once,but i want to have headroom just in case.
The kicker is......
my team orion clubman charger ,12-15VDC input
thunder power 11-18VDC input
icharger 4.5-32VDC input
so 24 VDC won't be ok for 2 out of 3
That's why I'm curios about running 12v and 24v off the 2 psu's in series.
or should I just get a 3rd psu for the clubman and thunder (14.8v would be nice)
just a thought!

Haven’t done it myself, seems like it should work, if I remember correctly I've read where it has been done. I'd assume the 12V should come off of the correctly grounded unit.

Hi zeeman, looking at the picture of your power supply is there a picture or diagram to show how to modify it other than just the resistor on the outside. or Dave h you might know.