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Topic: MOSFET N channel transistor curiosity (Read 1 time) previous topic - next topic

PerryBebbington

I didn't come to a conclusion, I was waiting for you to find out more.

17Nico17

Ok, I come tomorrow with these information ;)

PerryBebbington

Sorry, something I forgot, probably because I don't play with motors much. I was reminded reading another discussion. Measure the resistance across the motor. Turn the motor slowly by hand and look for the lowest reading. Divide the supply voltage by the lowest reading to get the stall current.

17Nico17

Off course, you are right, this is obvious now you talk about it! ;)
I measure 1.8 ohm minimal value. It is around 2.0-2.2 most of the time and 1.9 et 1.8 in a precise position for both motors. :)

I deduce that stall current is 6.15A (I will have 11.1v). This is in the case my motors are turning 100% speed and are blocked. In reality I will only use 7-8v maxi (wheels will be too fast after). So in practice if I have 4.5A per motor it would be the maximum. ;)

I guess that it is good news!!


PerryBebbington

It sounds a lot more reasonable!

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In reality I will only use 7-8v
How are you varying the voltage?

17Nico17

I make the tension varie using the Arduino. In practice, according to the first tests I have done, 11.1v will be too much and will make the balls to quick. I can consider in a very very extrem case having 11.1/1.8 = 6A but I guess that I will never have that.

A 15A diode should be sufficient then. Or 20A if we need more security.

Remains to find one...  :)

PerryBebbington

#36
Feb 22, 2020, 02:39 pm Last Edit: Feb 22, 2020, 02:39 pm by PerryBebbington
Quote
I make the tension varie using the Arduino. In practice, according to the first tests I have done, 11.1v will be too much and will make the balls to quick. I can consider in a very very extrem case having 11.1/1.8 = 6A but I guess that I will never have that.
If you mean you use PWM to vary the voltage then that's what I was afraid you were going to say. PWM does not vary the voltage, it varies the time the voltage is applied for; the full voltage is still applied to the load. If you meant something else then please explain because I can't think of anything else you might mean.

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A 15A diode should be sufficient then. Or 20A if we need more security.
No harm in higher, possible harm in too low.


17Nico17

Hi PerryBebbington! Hope you had a great WE ;)

Yes, I see what you mean, the medium voltage is lower but I will still have +12v some time to time depending on PWM signal. So I have to take into account the maximal intensity!

About that, I have some news and they seem to confirm the 20A I had in the datasheet. Under 1.2v voltage, I have 2.5A following the power supplier of my friend. We tried at 3v but it was higher than 6A and his power supply maxi current is 6A so it was overwelmed by the demand.

I would give around 25A for the stall current even if I measured only 1.8 ohm minimal value for both motor....

So, I definitely need a 50A diode...

PerryBebbington

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Hope you had a great WE
Thanks  :) You too!


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Yes, I see what you mean, the medium voltage is lower but I will still have +12v some time to time depending on PWM signal. So I have to take into account the maximal intensity!
Correct.

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So, I definitely need a 50A diode...
OK, do that. I can't help thinking it's higher than needed, but better higher than not high enough.

17Nico17

#39
Feb 24, 2020, 11:00 am Last Edit: Feb 24, 2020, 11:06 am by 17Nico17
Thanks! :) Yes, I agree. I have found this one. Is this kind suitable?

https://www.mouser.com.gt/datasheet/2/427/vs-80cpq150-48561.pdf

I see that this has 2 diodes inside? 2x 40A? Do you think this can be ok? And how do I have to connect it? Can I use the two diodes together?

I try to find the same with only 2 legs for 50A or 60A but no success....

I also have this kind, but seems strange that this little thing takes 100A??

https://www.mouser.fr/datasheet/2/240/Littelfuse_TVS_Diode_P6KE_Datasheet.pdf-741008.pdf


PerryBebbington

That'll be OK.

Connect 1 and 3 together and connect to negative, connect 2 to positive.

Note that it says 2 is connected to 'base'. I assume (you should check) there is a metal tab on the underside for cooling, I expect that this tab is connected to 2, so be careful not to short it to anything.

PerryBebbington

Which country are you in? I think you said you are French, is that right? (Can't tell from your English, that's perfect!) Mouser is a US company, I was wondering if they are local to you or not.

17Nico17

Ok, I will go with this one then! Thank you for the english compliment, better writting than speaking... :P

Ok, I see what you mean for the base, I will make sure this does not contact any other part of my system ;)

Thank you for all PerryBebbington! I do not know if I will find this one in France (Yes, I am in Toulouse), but I will find something equivalent I guess thanks to the datasheet of this one.

I guess that this topic is 100% solved, I will just send a message when I will have completed the system to just confirm it's working or not for the ones who would have the same issue as mine in the future ;) My Arduino program suits me. I need to begin the mechanical part now and receive some remaining parts.

Thank you again!! And see you soon for another topic maybe :P ;)

PerryBebbington

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Thank you for the English compliment, better writing than speaking
Well, there's the thing with non-native English speakers; they learn English better than the English! Probably because, as a non-native speaker, you were not subject to a local English dialect. I speak 2 versions of English; the 'correct(!)' version and a local dialect. I imagine you know 2 versions of French; official French and some local version.

Is there a French component supplier? Or maybe you can use RS Components in the UK.   


17Nico17

Ahah ok, I have noticed that, even in profesional world. Some english guys seem to not always follow the rules :P But as a french, I always have a doubt..

Yes, same in French, so many guys do so many mistakes, sometimes it is difficult to understand the sens of the sentence... I also talk a french special dialect but not all the words, just some expressions from the west of France (The Charentais!)

I will find a solution do not worry. Just needed the main charateristics of the component. Let's do the mechanical part now, I guess that in 1 month the whole system will be working! ;)

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