Power supplies

[RobW]

Thinking about replacing my 20 year old power supply. It is still working ok but starting to get a bit noisy so rather replace before it fails at a meeting.

Current one is only 10amps output which does not really pose a problem as I currently charge at 1C so max I need is 7.2amps for my 7200mah 1S i use in my GT12. Use a lower rate for 1/10th off road.

Only thought is new chargers seem to be coming onto market with 30/40A outputs and many new lipos seem to be able to be charged at 4/5C. So if I want to future proof myself a bit, what is the maths involved? Is it as simple as needing a 40A power supply to power a 40A charger IF I ever wanted to use the charger to its full capabilty in some time in the future or do you need more to cope with inefficiencies in supply and charger or does it depend on number of cells?

Any advise on the maths or recommendations on power supplies appreciated.

Rob

[badger5]

Hi Rob, if you're charging at 1S or 2S then the amps going to the charger will be less than to the cells. From memory charging 2S at 5A my power supply is giving approx 3A. You could say that it would be easy to work out using the VIR equation but I'm not sure how efficient chargers are as they can get a bit warm.
When I get chance I'll test my SkyRC charger with my power supply and let you know.

[RobW]

Thanks, Richard

[MiCk B.]

Hi,

Best to think about it in watts, rather then amps (and volts).

Watts is volts by amps.

12v at 1 amp is 12w of power, same as 6v at 2amps.
Both provide the same amount of power.

So charging to 8.4v at 6 amps is 8.4 x 6 = 50.4w
So you charger is supplying 50w to the pack, your supply, will need (ideally) to supply 50w to the charger, in reality it will be more due to losses.
So for some headroom take charger needs 60w to supply 50w.

So 60w at 12v ~ 60/12 = You need a supply giving out 5a at 12v.

So if you want to charge at 10a (8.4x10 = 84w)
You'll need a supply to give 7.5a (at 12v)(90/12)

A 15 to 20a supply with give you lots to play with.

A 20a supply will give you 240w at 12v.

This will allow you to charge at 27a at 8.4v (230/8.4)


You can also use the above to see how many chargers you can run off your supply.

(Always safe to assume there will be some loss in conversation, mains to 12v to charger.)

MiCk B. :-)

[JonyNitro]

Hi few people I know use cool ice psu and rate them very good and good decent option, I use a efuel Psu bit pricey but dam good.

Thanks above for the Math

[RobW]

Thanks guys, for making maths simple and recommendations. Got to say efuel ones look pretty smart. 30a one for £100-ish looks like plenty.

Rob