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| Motion control, S-curves and other stuff >> controlling lift with DC motor |
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| krisRaba:
--- Quote from: capt bullshot on October 24, 2019, 10:11:44 am --- --- Quote from: krisRaba on October 24, 2019, 10:00:24 am ---I have added 2x 4,7uH in series with motor windings and just as expected, current ripple has been decreased. It is not enormous change, something about 25%, but always something is better than nothing :-+ Does it mean that effective inductance of motor is about 37,6uH? I think so and it sounds quite realistic. It would be 36,5% of 103uH presented in datasheet and they were talking about 30-80% for calculations.. --- End quote --- Yes, I'd agree using the same rough (and probably incorrect) calculation pointing to the ballpark range. Good enough for a plausible estimate. --- End quote --- The formula from mentioned earlier FAQ is ΔIppmax=Vcc/(2*Ltot*freq), where Ltot=Lint+0.3..0.8*Lmot+Lext [mH], freq in [kHz], so it can be correctly estimated that way, I think. Given change in ΔIppmax is caused by given change in Ltot, the rest is kept unchanged. |
| capt bullshot:
--- Quote from: krisRaba on October 24, 2019, 11:03:00 am --- --- Quote from: capt bullshot on October 24, 2019, 10:11:44 am --- --- Quote from: krisRaba on October 24, 2019, 10:00:24 am ---I have added 2x 4,7uH in series with motor windings and just as expected, current ripple has been decreased. It is not enormous change, something about 25%, but always something is better than nothing :-+ Does it mean that effective inductance of motor is about 37,6uH? I think so and it sounds quite realistic. It would be 36,5% of 103uH presented in datasheet and they were talking about 30-80% for calculations.. --- End quote --- Yes, I'd agree using the same rough (and probably incorrect) calculation pointing to the ballpark range. Good enough for a plausible estimate. --- End quote --- The formula from mentioned earlier FAQ is ΔIppmax=Vcc/(2*Ltot*freq), where Ltot=Lint+0.3..0.8*Lmot+Lext [mH], freq in [kHz], so it can be correctly estimated that way, I think. Given change in ΔIppmax is caused by given change in Ltot, the rest is kept unchanged. --- End quote --- Okay, I did a very simple linear calculation without even looking at that formula you mentioned (4.7uH * 2 * (1/0.25)) ( = 37.6 uH). So I can't be horribly wrong ;) |
| krisRaba:
--- Quote from: capt bullshot on October 24, 2019, 11:50:17 am ---Okay, I did a very simple linear calculation without even looking at that formula you mentioned (4.7uH * 2 * (1/0.25)) ( = 37.6 uH). So I can't be horribly wrong ;) --- End quote --- Yeah, this is how I did it at the first time as well - value estimated just from proportions ;) Then I only posted my response to your "(and probably incorrect)" senstence to show it doesn't have to be wrong because in mentioned formula relation is also linear (so no sqrt or ^2 etc) :-+ |
| capt bullshot:
--- Quote from: krisRaba on October 24, 2019, 12:39:32 pm --- --- Quote from: capt bullshot on October 24, 2019, 11:50:17 am ---Okay, I did a very simple linear calculation without even looking at that formula you mentioned (4.7uH * 2 * (1/0.25)) ( = 37.6 uH). So I can't be horribly wrong ;) --- End quote --- Yeah, this is how I did it at the first time as well - value estimated just from proportions ;) Then I only posted my response to your "(and probably incorrect)" senstence to show it doesn't have to be wrong because in mentioned formula relation is also linear (so no sqrt or ^2 etc) :-+ --- End quote --- Yes, linear the relation is, no doubt, so linear estimation is correct. I'm still wondering if the ratio applied (1/ 0.25) is correct for this kind of relative change, or if I have to apply something like 1/x or (1 - x) on the 25% change, but meh, it's just an estimate, and I'm not in the mood to think about basic math ;) |
| krisRaba:
--- Quote from: krisRaba on October 24, 2019, 11:03:00 am ---The formula from mentioned earlier FAQ is ΔIppmax=Vcc/(2*Ltot*freq), where Ltot=Lint+0.3..0.8*Lmot+Lext [mH], freq in [kHz], so it can be correctly estimated that way, I think. Given change in ΔIppmax is caused by given change in Ltot, the rest is kept unchanged. --- End quote --- You have two situations: ΔIppmax=Vcc/(2*Ltot1*freq) -> without additional inductance, Ltot1= Lmot_eff, where Lmot_eff = (0.3..0.8*Lmot) and 0,75*ΔIppmax=Vcc/(2*Ltot2*freq) -> with additional inductance (Lint=2x4,7uH), Ltot2=Lint+Lmot_eff, where Lmot_eff = (0.3..0.8*Lmot) then you can replace ΔIppmax in second one with the first one, so you get 0,75*(Vcc/(2*Ltot1*freq)) = Vcc/(2*Ltot2*freq) and then you can remove things that are on both sides by multiplying both sides of the equation with (2*freq/Vcc) so this is what remains 0,75/(Ltot1) = 1/(Ltot2) so finally Ltot1 = 0,75*Ltot2 so (Lmot_eff) = 0,75 * (Lint+Lmot_eff) (1-0,75)*(Lmot_eff) = 0,75 * Lint uhm.. s#!t.. (Lmot_eff) = 0,75 * Lint / 0,25 = 0,75 * 9,4uH / 0,25 = 28,2uH... ekhm... something is wrong here :palm: :scared: Eh, whatever :-DD |
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