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Motor Kv - the truth


Tim Mackey
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Ha! what about AD149's germanium audio outputs, they used to pop off if you looked at them the wrong way. My apprenticeship started in 1958, I wonder how many of you remember the KB Rhapsody radio mains battery portable. You had to be very careful with these as when connected wrong way round the chassis was live, the cable had no polarity identification, so much so we used keep stocks of new cases, cos a lot used to get thrown up in the air accompanied by some very strange language!! Ah well happy days...
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Brian,
Thanks for your reply. To be absolutely honest, I’m not exactly sure we need to read quite that much into this. Re. the motor wires, as I previously said, for me the most important thing would be to increase the conductor size, if I wanted to extend the length, to try and keep the volt drop to a reasonable level. If they got hot, I definitely would. I would always twist them together, if for no other reason than to keep them tidy.

When we get the battery leads, there could be a little supposition on my part. I’ll have a bit of a guess, but I reckon the large capacitor on the ESC input is a reservoir capacitor. The battery supply is pulsing to some extent, so the cap is charging up when the switch is off, and discharging into the ESC and motor when the switch is on. This is like the smoothing capacitor across the output of a rectifier bridge, the difference being that the bridge is a most likely a fixed frequency, usually 100Hz, and a close approximation to a sine wave whilst the ESC is probably a varying frequency and goodness knows what sort of wave form. And therein may be a problem. As always, I think it’s quite possible the manufacturers have made the controller as minimalist as possible. My Aveox ESC, and this is a company I would rate as one of the better ones, was obviously operating right on the limit. Electronic components do not generally like heat, for one thing it tends to reduce their working life span. I may be wrong, but as I think as this capacitor seems to work pretty hard it needs to be a top quality, low ESR, adequate capacitance size unit. In other words, one that can withstand ripple current. However, if this comes at a cost, maybe that’s a few pence too much.

If we increase the total resistance, that’s the resistance plus reactance, the impedance, by making the wires longer, I quite agree, this makes the cap work harder; if it was going flat out in the first place, then perhaps there’s not a lot of room for expansion. If we chose our components carefully I’m sure, at least for a reasonable increase in length we should be able to keep the balance, though. Without some test equipment it might be difficult to decide what the correct components are, but as I suggested, I’d increase the wire size for a start, run the controller for given periods of time from min. to max. output and then start checking what’s hot and what’s not with a contact thermometer. If I felt that increasing the capacitance would help I’d certainly look closely at any cans that I were adding on.

‘Fraid this has gotten off the beaten track again, however overheating ESCs can be a topical issue; although this may be improving as modellers are perhaps getting more familiar with cooling techniques etc. And if it’s also a fact that very few modellers wish to change their standard installation anyway, maybe this is all not such a big deal at the end of the day.

Hope this is making some sense….. PB
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Still off the actual thread topic (sorry) but..

A useful temperature module for your ESC, battery etc. (Handy also for IC temp measurement). From ebay and much cheaper than you can make yourself. It is also able to measure voltage, is programmable and has audible warning.

Edited By Brian Parker on 18/06/2010 10:28:09

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  • 3 weeks later...
The tread has been silent for some time.
 
I believe that contributions of those who have posted, is sufficient for someone to sumate how in principle they work, and perhaps the effect of the options available relative to inrunner and outrunners.
 
Please volunteer to provide that easy (for me) to understand description for ordinary non electronic engineer modellers.
 
Erfolg
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