The Electronic Speed Control
|Tom Wright 2||09/02/2011 02:52:59|
3908 forum posts
Steve catching a thermal 4) is a very good point ,with most esc you can programme the motor cut off point high enough to leave bags of reserve for the RX ,unless you intend to use a small lipo,then RX power reserve could be a problem if you get away in a good one.
|Steve Houghton||09/02/2011 13:17:14|
586 forum posts
Thanks Tom. This begs one final ESC question (trying not to drift off topic too much):
If the LVC cut-off point is reached and the motor cuts, does an ESC with BEC:
a) allow a LiPo to be flattened through the BEC by the RX and servos, since it is getting dangerously near to its minimum discharge voltage but probably has enough voltage to continue powering RX and servos?
b) have a secondary LVC cut-off point for the BEC as well?
I suspect the answers are (a) yes and (b) no, since it's probably better to loose a LiPo than lose the whole model if the RX power was suddenly cut.
This could be an argument for fitting a separate RX battery.
|Tim Mackey||09/02/2011 13:44:49|
20920 forum posts
A) It could, but it would take an awful long time to do so - the usual 3v per cell cut off occurs at high current draw, so the pack is "artificially" depressed as it were. Once the LVC kicks in, and that large current draw is removed, the voltage will rise almost immediately to a level way above that needed for the BEC circuitry to work.I have never timed it, but you would need to be up for a long long time I suspect.
Its no argument for a separate battery for me I am afraid, especially as we are not discussing a purpose built duration thermaling machine here - or are we ?
|Tom Wright 2||09/02/2011 14:21:26|
3908 forum posts
Hi Steve If you know what your esc motor cut setting is you could get a good idea how much capacity will be left to power the rx and servos,again this depend on the size of the lipo.as a rough example say you use a 3a lipo and set the cut off point at 50% you would have more than 1amp available which should give you at least 2hrs before the lipo voltage gets near critical.In theory you could even more than that as i have built extra margins into the example.
|Richard Wood||09/02/2011 15:39:39|
1098 forum posts
Be wary of an LBEC in an ESC if using more than a 2S LiPo.
The BEC rating of the ESC should be stated more clearly on some makes.
For example - my nice shiny Scorpion 55A ESC states 5V/4A BEC
on the case.
Check the catalogue & the large print says it works at 6 - 15V.
Further on in small asterisked type it states that the full rating only
applies to a 2S & to derate by 50% for a 3S & to use a seperate
UBEC for 4S.
A bit misleading.
Scorpion are probably not the only one - best to check ratings
before using a BEC.
|Tom Wright 2||09/02/2011 15:47:37|
3908 forum posts
Steve following on from the above ,four of us had a thermal soaring season last year flying 3and4m bubble dancer / avia type formats,We all retired so got out every day when it was not blowing a gale or raining .Over 400 flights were achieved with no separate batts ,no brown outs ,or critically low lipo voltages.We did use digital battery checkers,before each flight,and got many 40min flights after after motor cut off.
We did make a rule not to follow thermals above 1500 ft after Pete got disoriented at 3000ft!
|malcolm woodcock 1||26/11/2017 14:56:00|
|409 forum posts|
Quick question on this old thread, I've several old ESCs without any markings on them, can anyone tell me if I can run a check on them to find out what amps I can run through them?
|Denis Watkins||26/11/2017 15:23:49|
|4631 forum posts|
No way Malcolm
If they were yours as original
You can only try to recall the type of plane they were in
As unmarked stuff is usually from ARTF
|Geoff S||26/11/2017 15:44:31|
|3759 forum posts|
You'd probably be safe using them with a 3S LiPO then all you need to know what current they can draw safely. You can check that using a Watt meter and monitoring the current and temperature as you increase the load say by fitting different props to the motor you're using for the test.
Unless they're very small, they're probably good for 30 amps perhaps even more. I woudln't be too keen using them on a model I treasure
|Romeo Whisky||10/08/2020 16:44:01|
|731 forum posts|
There is a lot of useful information for beginners with electric flight here ...
2203 forum posts
Not exactly up to date though is it - rather a lot of opinion seems to have leaked in, much of which seems to be based on historic lower performing packs...
"...Charging at too high a rate is a significant fire risk, so when charging, for safety reasons, the maximum charge rate should be 1C, regardless of the battery's C rating. Although some manufacturers claim their batteries can be charged faster than 1C, this will shorten the battery life and the risk of fire is unacceptably increased.
...It does mean that if you have several different sizes and capacities of batteries that you must double-check the charge rate setting on the charger before you connect the battery to be charged. For charging - 1C maximum!
...Most ordinary LiPo packs will specify a C rating of 20C to 30C and this is adequate for average sport flying. It is best to ignore the higher C rating, as this is only to be used for a short burst of a few seconds."
Whist charging at higher rates can shorten your pack life if taken to extremes there is no problem with using 2-3C if you need to - I never leave a battery unattended anyway, so the safety angle just doesn't ring true to me. And as for the recommendation to avoid higher C-ratings...
Edited By MattyB on 10/08/2020 17:07:31
|Richard Clark 2||11/08/2020 18:16:06|
|426 forum posts|
Ridiculously over-cautious seeing it was written in November 2018.
I now charge my high C rating cells (mostly 70C Thunder Power ones) at 4C. Thunder Power say 12C is ok. I tried it a couple of times and they stay at ambient temperature.
Edited By Richard Clark 2 on 11/08/2020 18:23:57
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