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Old Yesterday, 01:24 PM
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Oman
Joined Aug 2014
109 Posts
Question
chargers different watts

hii guys
i was looking for proper charger in HK website and somthing stop me from going farther which is :
some charger specification says max charging 200 watts and some says 50 watts and some max charging current 5A and other 10A
can anyone clarify it what is the difference if we speak about charging time
which charger i should select to charge my lipos 3s 2200mAh
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Old Yesterday, 02:22 PM
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United States, CA, Livermore
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There are some very good write-ups about chargers which you should seek out.

Basically, Power measured in Watts is what you want to look at. here are some general guidlines.

Small chargers (50 to 80 watts like the Thunder AC 680) are ok for small 1S battieres used in micro planes and helicopters.

Medium charger (200-300 Watts) are good for batteries like yours, 3S 2200's

Once you get into bigger batteries like 6S 5000's you want at least 500W and 1000W is better.

Power is Amps*Volts. P=IV.

A 3S batter charges to 12.6V

3C charging for a 2200 requires 6.6 Amps

Power need is then 6.6 Amps times 12.6Volts equals=83 Watts

So if you want to do two at the same time you need 166 Watts.

Current is important but especially with cheaper, low power chargers, they will say 10Amps and 80W. But if you charge a 3S battery, the max current will be less because 80W/12.6V=6.35Amps.

Charger will never exceed their power rating. If you try, they automatically turn down the current. So current ratings can be deceptive.

Hopefully these examples will show you how to figure these things out for yourself.

Also, be aware that once you get over the 80W size, most chargers require a separate DC power supply and depending on the charger, you might need more than 12volts. For example, my iCharger 306is rated at 1000W. It will run with a 12V supply but will only output 500W. To get the full 1000W, its needs 24V.
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Old Yesterday, 02:56 PM
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May I suggest you read this: http://www.tjinguytech.com/charging-how-tos

It should help you to understand about battery charging.

Glen
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Old Yesterday, 03:11 PM
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Oman
Joined Aug 2014
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Quote:
Originally Posted by rhodesengr View Post
There are some very good write-ups about chargers which you should seek out.

Basically, Power measured in Watts is what you want to look at. here are some general guidlines.

Small chargers (50 to 80 watts like the Thunder AC 680) are ok for small 1S battieres used in micro planes and helicopters.

Medium charger (200-300 Watts) are good for batteries like yours, 3S 2200's

Once you get into bigger batteries like 6S 5000's you want at least 500W and 1000W is better.


Power is Amps*Volts. P=IV.

A 3S batter charges to 12.6V

3C charging for a 2200 requires 6.6 Amps

Power need is then 6.6 Amps times 12.6Volts equals=83 Watts

So if you want to do two at the same time you need 166 Watts.

Current is important but especially with cheaper, low power chargers, they will say 10Amps and 80W. But if you charge a 3S battery, the max current will be less because 80W/12.6V=6.35Amps.

Charger will never exceed their power rating. If you try, they automatically turn down the current. So current ratings can be deceptive.

Hopefully these examples will show you how to figure these things out for yourself.

Also, be aware that once you get over the 80W size, most chargers require a separate DC power supply and depending on the charger, you might need more than 12volts. For example, my iCharger 306is rated at 1000W. It will run with a 12V supply but will only output 500W. To get the full 1000W, its needs 24V.
thank you very much ended
the cheaper charger was already in my wish list which is 50 watts only
so i understand from you that my lipos need at least 100 watts when separate charging to avoid deceptive current rating
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Old Yesterday, 03:13 PM
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Oman
Joined Aug 2014
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Quote:
Originally Posted by ggcrandall1 View Post
May I suggest you read this: http://www.tjinguytech.com/charging-how-tos

It should help you to understand about battery charging.

Glen
surely i will read it very soon
thank u mate for assistance
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Old Yesterday, 03:54 PM
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Originally Posted by ali74 View Post
thank you very much ended
the cheaper charger was already in my wish list which is 50 watts only
so i understand from you that my lipos need at least 100 watts when separate charging to avoid deceptive current rating
Yes, you have it right.

However it really isn't deceptive, but all charger ratings should be read as Xamps or Xwatts whichever is reached first. When you do the math you realize that for the higher cell count batteries it is the watt limit that is usually reached first.

Glen
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Old Yesterday, 04:22 PM
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Originally Posted by ali74 View Post
thank you very much ended
the cheaper charger was already in my wish list which is 50 watts only
so i understand from you that my lipos need at least 100 watts when separate charging to avoid deceptive current rating
Well 50Watts/12.6V=3.96amps. So if you are charging a 3S battery, you are only going to get 3.96 Amps even if they say it is a 10amps charger.

It is not so much that the ratings are deceptive. You just need to understand them. At low voltage (1S), you will tend to hit the current limit first. At high voltage, you will tend to hit the Power limit first.

You just have to look at both ratings. For example, an i106B is rated at 10amps and 250W and 6S max. 6S is about 25V so 25V*10Amps=250watts so that model will give full current and full power at max voltage. But at lower voltage, you will get full current but not full power. At 3S, 12.6V*10A=126Watts.

It also depends on your battery size and how fast you want to charge. Right now you have 3S 2200's. So you have to understand the whole C thing. The write-up the other guy posted is the one I meant and should help. But basically,

charge time=60 minutes/C

1C charging takes 60 minutes
2C charging takes 30 minutes
3C takes 20 minutes
etc.

The charging current is battery mAh/1000*C
So for 3C charging : 2200/1000*3=6.6amps
Power would be 6.6 * 12.6=83Watts so a 50 Watt charger will not 3C charge one of your batteries.

Working it backwards 50Watts/12.6Volts=3.97Amps so no matter what they say the current rating is, when charging a 3S battery, the charger will only push 4 amps. The C is then 4/2.2=1.82. The time required would be 60/1.82=33.

So if you are willing to wait around 33 minutes to charge one 3S 2200 battery, 50 watts is ok.

Really there are no short cuts here. You need both current and power ratings and decide how fast you want to charge your batteries and how many you want to charge at once. Then you can figure the requirements for both current and power. The charger need to be rated higher for both current and power than what you need for your desired charge.

I know not everyone can do all this figuring so easily. That is why I posted some general guidelines. For 3S batteries, 200-300 watts is a good target to set your sites on. You can get by with less but you will be waiting a lot longer to charge.
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Old Today, 02:44 AM
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Oman
Joined Aug 2014
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[QUOTE=rhodesengr;30241466]Well 50Watts/12.6V=3.96amps. So if you are charging a 3S battery, you are only going to get 3.96 Amps even if they say it is a 10amps charger.

thank you Rhodesenger it is more than enough informations for me as beginner in RC
because you are one of the experts may i ask you if i have a 3s battery 20C and another 3s 30C . So the difference in C rating does affect the motor's performance????
i already knew the C rating affects the charging time means higher C rating less charging time. I hope my clue is right
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Old Today, 03:22 AM
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ali74 ..... all above is great info ... but I feel can also mislead ...

Many people use 50W chargers for packs like yours, I have two 50W chargers on my bench and a 60W charger ordered to add to the bench.

The 50W chargers do a good job and it is only a time factor that is the real factor. As another showed - 50W charger will max out at 50 / voltage of pack ... so a 3S pack like yours ... max amps is 50 / 12.6 = 3.96A.

Some say that is not enough ... but for me it is ... I only charge at 1C rate usually ... and I set charger for a 3S 2200 pack at 2.2A. It charges in reasonable time and I know I am not stressing the pack.

If you intend to go for larger packs and bigger models - then high wattage chargers are called for and of course the benefit then is higher rates for small packs IF they can take it. But if you have no intention to go for 5S packs ... 5000mAh and so on - then the 50W chargeer will do the job fine. I actually have 5S 3000mAh packs as well as many 4S 1000 up to 3000mAh ... I'm fine with my low power 50W jobs.

Another point : I do not like putting all eggs in one basket. That is having one charger .. which would be the case if I bought higher rated than 50W. The 50W chargers being less cost allows me to have 'redundancy' - I know that even if a charger fails - I still have another ... they also do not have any problem used with car ciggy socket at the field.

I see you mention C rate ... do not confuse quoted C rate of ie 20C ... 30C ... with Charge rate. The quoted rates of 20C ... 30C... etc. are DISCHARGE rates.
Charge rates are typically significantly lower ... often 2C .. some quote 5C ...

If you were to try charging at 20C ... 30C ... even if chargeer was capable - you would have very short life of packs and possibly a very dangerous action.

I know I am presenting a case that many would argue against .. but I only rarely need a higher rate charger ...

I suggest look at what time you have available to charge ... how many packs you will be charging ... what is the likely max size pack you will use ...

It's sort of ... no need for a pick-up truck if all you are doing is weekend shopping !!

Cheers
Nigel
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Old Today, 05:20 AM
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Another thing to consider if you're using a DC charger is the wattage/amp rating of the power supply that powers the charger. If you're charging 3s packs and down, then things are simple; just match the power supplies' watt/amp rating plus maybe 10% as a safety margin with the charger. But, if you're going to be charging 4s and up, your power supply must be able to sustain a higher watt/amp rating. As an example, say you're charging a 3s pack at 5 amps - a power supply rated at 6 amps would be fine. But, if you're charging a 6s pack at the same 5 amp rate, you would need a power supply capable of 11 amps or more. This is of course assuming a power supply output of 12 volts. I know that when I'm charging one of my 6s packs at 7 amps (maximum my charger will do), my 14 amp power supply gets too hot to touch. I have to back off the charge current to no more than 5.5 amps and even then the power supply is pretty hot.
The reason for all this is because at higher charge voltages, the booster circuit in the charger needs more current in order to produce the higher voltage; nothing is free.
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Old Today, 06:29 AM
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The simple matter is to compare WATTS output of Power Supply to the Max WATTS capability of charger.

A lot of people think ... 5A max on charger - so a 5A power supply is fine. No it is not. That is only sufficient at the rated voltage ie 12v and is actually with no margin.

My B6 are supplied by : a) a 10A 120W supply, b) 6A 70W supply. These to their resprctive chargers allow the higher voltages that the packs demand and still deliver at the max overall Watts of the charger. The best of course is a) as it runs cool, it has plenty of spare overhead capacity.

So my advice ...if a charger says 50W / 12v ... then go for at least 70W / 12v supply. The 120W / 12v I have for a) is excellent but it is overkill, larger and heavier.
Multiply charger WATTS by 1.5 to give a sensible margin for supply.

Nigel
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Old Today, 07:46 AM
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Oman
Joined Aug 2014
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[QUOTE=solentlife;30245221]ali74 ..... all above is great info ...
Okey Nigel you have seen my charger in another thread which is max 50 watts so this figure of watt will it enough for my lipo 4S 4000mAh 40C which is still new unbox waiting my next scratch giant plane to be finished ??? if i dont care about charging time
Mr rhodesengr posted some figure calculations if i follow means 4S 4000mAh needs 201.6 watts
i hope i calculated it right

sorry Nigel finger mistake i did
i didn't mean sow
sorry again
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Old Today, 08:02 AM
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Quote:
Originally Posted by ali74 View Post
...will it enough for my lipo 4S 4000mAh 40C which is still new unbox waiting my next scratch giant plane to be finished ??? if i dont care about charging time
50W / (4 x 4.2V) = 2.98A

4Ah / 2.98A = 1.34h

Add losses due to charging inefficiency and balancing, subtract any charge that was in the battery before charging.. It would take probably an hour and a half to charge a 4s 4000mAh battery with a 50W charger. But it can be done without any adverse effects.
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Old Today, 08:02 AM
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Oman
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[QUOTE=babblefish;30245509]Another thing to consider if you're using a DC

problem with DC charger which have high watt they are costly and need separate high DC power supply rarely find in our local market and if found it will be also costly
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Old Today, 10:00 AM
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Quote:
Originally Posted by jkettu View Post
50W / (4 x 4.2V) = 2.98A

4Ah / 2.98A = 1.34h

Add losses due to charging inefficiency and balancing, subtract any charge that was in the battery before charging.. It would take probably an hour and a half to charge a 4s 4000mAh battery with a 50W charger. But it can be done without any adverse effects.

But that time calculation assumes battery is efectively zero charged at start.

As we all know a battery should be at least storage charge level and that means the charge time is reduced significantly.

Lipo 'fuel table' ...

Near zero : 3.209v
10% : 3.683v
20% : 3.747v
30% : 3.791v
40% : 3.812v
50% : 3.839v
60% : 3.883v
70% : 3.936v
80% : 3.999v
90% : 4.085v
100% : 4.199v

So lets assume lipo is at 30% level ... an average sort of fig ... that means :

4 x 70% = 2.8Ah now ... at 2.98A = less than 1 hour if no exceptional balancing needed.

Nigel
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