question about charger and power supply

[ReadyToFly]

hi there,

I'm trying to understand how those parameters on the power supply and charger works please.

i have a few questions:

1) to find out how many watts a PS has, all i have to do is multiply the V (voltage) by the A (amper)? for example, a PS that is 12v and 5A is 60 watts (12 x 5)?

2) if my charger is 50 watts and i want to charge a 2200, 11.1 battery, the maximum A i can use is 4.5A (50 / 11.1)?

3) however, if i have a power supply that is 40watts (8V, 5A), the maximum A that i can have with the same charger will be only 3.6a (40 / 11.1)?

4) if the answer to all previous question is YES, can i say that the WATTS that determines how many A i can use during the charge is the smallest WATTS between the charger and the power supply?

thanks.

[Kozmyk]

1) Yes
2) Yes ... but you're better off using the max charge voltage of 4.2V/cell rather than the nominal cell voltage 3.7V/cell
3) Yes (see 2)
4) Yes and probably a little less because the charger efficiency won't be 100%. Another factor will be the Max current output of the charger.
For example - A charger may have a power rating of 250W but a Max current limit of 10A.
Into a 3s lipo the charger won't manage 250W > 10A*12.6V=126W.
Into a 6s lipo the full 10A tips the scale at 10A*25.2= 252W

You're other limiting factor is the C rating of the pack.
For your 2200mAh pack 1C = 2.2A
1C charging puts the least strain on your pack though depending on the particular spec you Could charge it at a higher rate. Most commonly that would be 2C - 4.4A but there are more packs coming onto the market now that claim to be able to take up to 5C charge but most of us are still wary of that thus far.
If in doubt, charge at 1C.

[ReadyToFly]

thanks a lot.

it seems i found the right person to clarify my doubts.

1) so, the max A i can have with a 50w charger and a 2200mah, 3s, battery is 50 / (4.2 x 3) = 3.9a ?

2) also, when buying a charger, i must pay close attention to its maximum A? the biggest, the best?

3) is it the same for the power supply?

4) how about the charger/power supply V (voltage)? does it have to be within a certain range or must it be bigger or smaller than anything?

thanks a lot again!!!

[Kozmyk]

You're in luck. I can't sleep ...

1) Yes
2) The Charger's output current must be enough to do the job.
3) The PSU should be at least equal in power to the charger and preferably a bit larger
4) For lipos the charger output voltage is rated in the number of cells it can charge up to 4s, 6s, 8s, 10s, 12s.
For PSUs they are the mains equivalent of 12V lead acid batteries and so usually put out 13.8V though this may vary from 12V to 15V commonly. The charger is capable of taking in a nominal 12V supply and then putting out a higher charger voltage.


When buying you have to juggle the factors:

Watts + Amps + s capacity(no. of cells) vs current application vs future requirements vs cost

For starters a 50W 1s-6S charger with a small PSU will do you fine for a couple of 3s 2200mAh.
If you decide shortly after that you want to charge more 2200s you could get another 50Wcharger.
Then you'll wish you'd got a bigger PSU to start with.
If you've got plenty of time of spare you won't be worrying about charge time EXCEPT that you'll probably want to be able to go flying at fairly short notice, British weather being what it is.
So now you're at a point where you can get a pack charged in 30 mins if you go 2C or 1 hour at 1C
NB. Even though its a 2200 you should only be discharging down to 20% capacity so you only have to replace 80%
I started out with a Lipro Quad 6 which is 4 x 50W chargers in one box. I can be out of the door with 4 charged 3s 2200 inside an hour.
I bought a PRO PEAK 200W POWER SUPPLY and it's been fine so far for me but it has a chequered track record.
A soon as I got a heli that used 6s 3300mAh lipos I was down to 80 min to replace 80%.
I could have gone for the next step which would have been a 250W to 300W charger but I decided to jump one bigger this time.
I'm currently in the process of rigging up two of those HP Server PSUs for some heavy duty charging.

If you think you may be expanding your heli fleet and/or your lipo collection sooner than later then you may want to consider a larger charger than 50W. There's quite a selection in the 150W to 300W range.
Just one example Voltz 6250 (250W) and Voltz PS (350W)

Whether you decide to start with a low cost low power charge rig and see what happens later or go medium sized to cover your requirements for a while to come is up to you.

[ReadyToFly]

thanks a lot.

i actually already have two accucel 6 so i can charge my 2200 batteries at 2c quite quickly.

what i wanted in this post was to get some theoretical knowledge on how things work.

I'm thinking of having a bigger heli, but this PS / charger thing bothers me a lot. i checked the prices on HK and I'd have to spend a lot of money to fly a trex550 - for example - as frequently as i fly a trex450. i say that because their batteries are way more expensive and the charger/ps are too. the guys who have bigger helis here in my city have to wait a long time between flights so the battery is ready again. i don't like the idea of spending all the afternoon in the field just to have 3 or 4 5min flights.

that's why I've been considering buying a glow model like a trex600, but there are a lot of people who says that it is a bad idea because the electric helis are the future.

it seems lots of people are using computer PS to feed their chargers. when buying one of those ps, the only thing to pay attention is the V and A? the output cable of those PS usually has a 3rd wire that would have no use on the RC chargers, right?

thanks a lot for you patience and valuable information.

regards.

[Kozmyk]

Finding the time

For extended numbers of flights you need multiple packs and field charging at a rate that will bring your 1st pack to full charge by the time your last pack is spent.
That's going to be 3 or 4 packs minimum plus a field supply for your charger/s - leisure batteries, generator, mains supply at field.

My LOGO 400 on 6s
3300mAh x 80% = 2640mAh
2640/3300 x 60mins OR 80% x 1C = 48mins @ 1C(3.3A 83W) , 24mins @ 2C(6.6A 166W)
OR
A TRex550 on 6s
5000mAH x 80% = 4000mAh
4000/5000 x 60mins OR 80% x 1C = 48mins @ 1C(5A 126W) , 24mins @ 2C(10A 252W)

An idealised schedule where you have no waiting your turn, no talking to others, no coffee breaks, no watering the bushes.
Oh! and no crashes
Using a dual port charger OR 2 single port chargers capable of at least 166W per port(3300mAh @2C) OR 252W (5000mAh @ 2C)

fly pack1 12:00 - 12:05
heli cool down, pack cool down and potch 12:05 - 12:10
start pack1 on charge @ 2C 12:10
fly pack2 12:10 - 12:15
heli cool down, pack cool down and potch 12:15 - 12:20
start pack2 on charge @ 2C 12:20
fly pack3 12:20 - 12:25
heli cool down, pack cool down and potch 12:25 - 12:30
fly pack 4 12:30 - 12:35
start pack3 on charge @ 2C 12:30 OOPS!! still waiting for pack1 to finish
Pack1 finished charging 12:34
fly pack1 12:40 - 12:45
Rinse and repeat

That could give you 7 flights per hour ... theoretically.

OR ... alternatively

fly pack1 12:00 - 12:05
fly pack2 12:06 - 12:11
start packs1&2 on parallel charge @ 2C (13.2A 332W) 12.12
fly pack3 12:15 - 12:20
fly pack4 12:21 - 12:26
start packs3&4 on parallel charge @ 2C (13.2A 332W) 12.28
packs 1&2 charged by 12:36

See where this is going?
Even with parallel charging it'll take more than 4 packs to get more than 7 flights per hour even without cooldowns.
Unless you charge at over 2C
5C charging with 6 or 8 packs ... you do the maths.

Regarding Server PSUs
You're really only looking at using the 12V output.
There are loads of server PSUs out there but the popular (and cheap) one for us at the moment is the Compaq HP DL580 Proliant ESP114 Server PSU. That kicks out 12V at 50Amps.
There's a +3.3V and a +5V with usable current and a -12V and a +5VSB standby with really small current capacity.
The +5V COULD be utilised if you really wanted. Maybe an Rx pack charging supply for instance.