My plan is to use 4 x 22000mAh on the frame and 4 x 16000mAh in a flight cockpit/ballast bag.
If you are going to use batteries in series, they should be of the same age, manufacturer, capacity and type.
That’s because all cells in a series pack have to be able to support the full load current which is running through every one of them.
Since I have to parallel them as well it is important that all paralleled packs must have the same charged voltage… They don’t have to be the same capacity (mAh).
If batteries are connected in parallel, each will stay at exactly the same voltage as the other at all times. If your packs are different capacity (mAh), the larger one will provide a greater share of the power than the smaller one, in order that it’s voltage drops at the same rate.
I will also use on each balance lead cell voltage checker, which are buzzing if any separate cell is going below a certain voltage (3.3 volt default). They are really loud…
What is the current rating of the connectors on the batteries, and wire gauge? Length of the wires will be important due to voltage drops from the further packs, and the temperature of the cables will also be high potentially. The video link is a little frustrating to listen to, but it shows cables and XT90 connectors being stressed - maybe someone did the same for your batteries? XT90 - Measured and tested - YouTube
Worth considering that the power loss in the connectors and cables is I2R, so double the current, quadruple the power loss, and there will be a point where that runs away as there is a linear relationship between temperature and resistance for the power loss equation.
I’m a bit concerned about people thinking it’s ok to extend the wires between their batteries and ESCs. Do the ESCs used on this project not specify a maximum wire length between battery and ESC?
The Turnigy dlux 250A I used on my project specifies the wires should be no longer that 6 inches, not because of current concerns, but EMF generated in the wires supplying the ESC. The longer the battery wires the more the ESC gets pounded to destruction.
It’s supposed to be ok to extend the wires between the ESC and motor though.
I expect one or two of you have seen this video, note the extended wire running from the ESC down to the batteries.
There could be a number of reasons that an ESC can burn up. Top of my list being… Well… Turnigy…
The EMF your referring to, I know as ‘voltage ripple’. In practice, I’ve never seen it rise above 2 volts (as logged on a Castle Creations HV160, with 1.5 meter battery wire run pulling 200A)
Say your ESC is rated to 12S or 50V.
Hot off the charger your battery is 50.4V. Add an extra 2-5 volts induced for long cable ripple voltage and your ESC input could be spiking as high as 55v. Your capacitors and MOSFETs are the voltage sensitive components inside the ESC. They will be the bits that fail violently.
You could add additional capacitors at the ESC to absorb the hammering if you have data confirming it’s a problem.
Turnigy and other ‘Lucky Dragon’ brands are built to a price with components running on the edge of their spec. That additional couple of volts from a long cable run could be enough to tip it into the grave.
Pull one apart and get the model numbers off the MOSFETs and capacitors. Compare their data sheets to say one out of a known, quality brand like Castle Creations. Be curious to hear back from any one who has done this.
I’m not sure where these Hobby-Wing ESC’s sit. I’ve never used them before, but their quality has crossed my mind
Primary concern is the bridge capacitors. With higher series resistance due to the cables, they will be doing more work, will get hot, and are more likely to fail. Most ESCs have questionable capacitors, both in terms of working voltage (must be significantly higher than nominal supply voltage), and ESR (if they are to be useful to the bridge).
Cheers Lukas.
In my case it was only the three external 470uF 100v 105º of the ESC that burst thus stopping the unit from working which, was handy, as I was in the air at the time; and naturally wouldn’t have wanted the fireworks shown in the link I pasted earlier.
The two internal 470uF caps of my ESC were ok, but unfortunately replacing the three external caps with the correctly rated types didn’t get my unit working again so, the internal control circuit must have sustained some damage.
The Turnagy dlux 250A that I have uses 36 IRFB3207 MOSFETS.
The bloke in the link below seems knowledgeable on the subject of long battery wires, it is from 2008 though.
Too long battery wires will kill your ESC over time !
Voltage spikes higher than battery voltage will destroy components and/or the standard input capacitors will be destroyed over time because they get warmer/hot. Using thicker wire will not help, it’s a wire [inductance] problem, not a [resistance] problem.
Controllers already have capacitors on-board to compensate for ’ standard ’ length battery wire [inductance]. But that may not be enough capacitance when adding extra battery-wire.
If you lengthen the battery wires, add extra capacitors with the same voltage in parallel with ESC. As a rule of thumb, for every 4inch/10cm extra length/distance between battery and ESC, add 220uF extra capacitance near the ESC.
Do those that have added extra wire have an estimate on how much they think they added and did not extra add extra caps see any extra ESC heating yet??
Cheers
yo