e350coupe
 lvl.2
Canada
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Ok I have read this post from start to finish and want to add my 5 cents worth.
First of all although I spent the last 32 years working for the government I was trained and certified as an electrician in 1975 where I was recruited for a more profitable career. At the age of 5 I was making a telegraph system to talk on and by age 7-8 I had designed an alarm system to keep all my numerous older brothers out of my room and taking my acquired gadgets and candy from me.
Wattage does equal voltage times amperage. This is a straight forward fact. I try to explain this as, say you need to fill up a 5 gallon bucket full of water if you use a half inch hose with 35 psi of water pressure then it will take so many minutes. The dia. of the hose is the voltage, the psi is the amperage and the size of the 5 gallon bucket full is the wattage.
Now if this was a normal regular type of battery then the theory of maintaining the voltage at a constant, and increasing the current to the maximum amount permissible would in effect charge our batteries very quickly. However our batteries are not regular batteries and as explained by some people too much current will actually overheat and quickly destroy these batteries.
Think of this when you were a kid and got a candy bar every couple of days or so, no problem right, but then comes halloween and you eat all the candy you can that night, and the result you are quite sick the next day.
In this case the battery might very well want all the current it can get but I guarantee your battery will get sick and be useless the following day if you over charge these puppies.
Now lets see what DJI did with these chargers which in my case get warm but not hot. By setting the maximum output of 100 watts they are limiting the amount of candy that can be fed to the battery at a time. In this case I suspect that 4.2 amps it probably the maximum initial current that these batteries can safely take. We know that the cells are a combination of 6 cells and that they are in parallel otherwise they could not be able to monitored separately. If we take the 4.2 amps and divide by 6 we see that each cell is getting .7 of an amp at 22.2 or 22.8 volts.
This is probably the maximum current that these cells can take without getting sick, or die and require warranty under the 90 day policy even though the CSA (canadian standards association) stipulates every electronic item sold in Canada must have a 1 year warranty, but this is another topic for another day.
Lithium type batteries are a strange breed, they do not like to give out lots of current and they are not capable of accepting lots of current in their current configuration. This is why when used in automotive circumstances, that we see voltage from 320 upwards to 550 volts in automotive. By keeping the voltages high we are able to reduce the current in order to supply the necessary wattage.
Now I found the post quite interesting, however when the assumptions were made, it did not take into account that the type of battery is lithium ion or polymer of hybrid of some type.
As for the charger getting hot, in the electronic world, this is really not hot, just warm, I have worked in electrical vaults where the temperature is upwards of 200f and I can tell you that most people cannot hold something in the range of 120-130 for more then a few seconds.
I did read in the manual that you should not charge the battery and controller at the same time, I suspect the controller has a different voltage input then the battery does and this is the reason for this. I do know you can use the extra cable to have your battery charge the controller and thus this is how I know the controller battery is of a lower value.
Now to answer the question between charger or supply, the correct exam question is that the higher rated or supplying voltage is the charger. This is how the battery acts as a charger when you use the extra supplied cord and attach the depleted battery to the remote control and that it will charge the controller until the battery is completely exhausted. This is tried and tested and it was another forum member who suggested it. As long as the supply voltage is higher then the receiving battery then the unit will charge to its maximum capacity. We note our chargers are 25.2 volts and the batteries 22.2 to 22.8 volts if I remember correctly thus they all get charged. To prove this take 2 car batteries one fully charged and one say almost exhausted attach them in parallel and come back a little later the higher voltage battery will be depleted to charge the lower voltage and they will now be almost exactly the same voltage. Once again 2 buckets of water one full and one empty with a hose connecting them together go away and when you come back they will be exactly the same.
As for the 18 gauge wire issue, this is one thing that manufacturers always play around with. In school there are gauge sizes and current capacities that are commonly accepted. 12 gauge is 20 amps 14 gauge is 15 amps and so on, and on. These are ratings for solid wire and like a person posted the electricity travels on the outside of the wire thus stranded wire can handle higher current ratings for it's given size, then there is fine stranded wire use for flexibility, and cold conditions commonly used in welding cable, and finally supposedly oxygen free wire that is sealed with even finer strands to handle more flexible conditions such as vibration from a car etc.
Now the issue of 40 amps on an 18 gauge wire, I would not say it is not possible but I have extreme concerns and I personally would never, never, never, ever consider it. I just wired an add on circuit in a vehicle requiring 40 amps and I can tell you I used 8 gauge oxygen free high finely stranded cable, and this was over a length of 22 feet. I am not saying it impossible as I have seen 10 and 12 gauge jumper cables claiming a rating of 400 amps. So the correct answer would be possible but realistically not feasible.
Now my final opinion is that DJI has figured out that the maximum safe charging current for each cell of their batteries is .7 of an amp times the 6 cells and thus the 4.2 amp charger/power supply is their way of regulating the maximum current being provided to their batteries.
In short, they made it, they designed it, so don't fxxx with it. At least if you want warranty, and don't want these things to explode on you, been there and done that to.
Now can we all please just get along (oh and send my cheque for 22 million) |
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