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Thread: Pick me a Mosfet for a RC Boat

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    Default Pick me a Mosfet for a RC Boat

    As the titles says "PIC ME A MOSFET for RC Boat"

    Now I need a N Channel mosfet ( RC controlled boat) that can switch 12 V DC device ( 11.1 V Pi Po battery) that uses around 10 to 30 Amps but on Start up can peak over 60 to 80 Amps. Yes this is a simple device than normally use a micro switch to turn the motor on but after a few minutes the micro switch even the 10 amp (Cant fit bigger one if available) one can and will eventually burn out.
    This mosfet would be good as the Heavy load between the Li Po battery and the Hungry motor will be controlled by the mosfet and the control current will only be switch by the micro switch.
    thanks
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    The trick here is the low operating voltage of the Battery (Li-po 11.1V) and the peak/spike current 60-80-amps. The threshold voltage is the minimum gate-to-source voltage that is needed to create a conducting path between the source and drain terminals. You can get few FETS over 20v that have currents up to 100 amps but i think they are no good for me because of the minimum voltage which is around 11.1v
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    This one will do the job, I use it in a 12v 20A regulator.
    The specs suit your purpose,
    Cheers, Tiny
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    Quote Originally Posted by Tiny View Post
    This one will do the job, I use it in a 12v 20A regulator.
    The specs suit your purpose,
    Good man, thank you very much. I got shock how many they are available but was hard to get the correct one.
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    Quote Originally Posted by Tiny View Post
    This one will do the job, I use it in a 12v 20A regulator.
    The specs suit your purpose,
    Oh! that 60 amps only, the starting surge can get over that and it dies as I used a IRFZ44n that is rated @ 49 AMPS and it died after I tested it a few times and because of this a 100 Amp one should be ok but can I get one @100A that will work on a Li Pol battery 11.1 Volts.
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    Are you sure that it is peaking that high? seems unlikely, considering the size of the wiring in RC's.

    Anyway let's look at how many Watts.
    You estimate a surge of 100A at 11.1v.
    11.1V x 100A = 1,110 W

    Mosfet
    60V x 60A = 3,600 W

    I think this type of mosfet will handle it.
    It's only a couple of dollars to find out.
    Cheers, Tiny
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    Quote Originally Posted by Tiny View Post
    Are you sure that it is peaking that high? seems unlikely, considering the size of the wiring in RC's.

    Anyway let's look at how many Watts.
    You estimate a surge of 100A at 11.1v.
    11.1V x 100A = 1,110 W

    Mosfet
    60V x 60A = 3,600 W

    I think this type of mosfet will handle it.
    It's only a couple of dollars to find out.
    Yes I agree!
    Normally I buy 6 at a time when something is that cheap. Possible the mosfet I was using were duds or had it wiring wrong.

    I will buy them and try

    Thanks
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    Don't forget to put a small heat sink on it so it has somewhere to dissipate the surge heat.

    EDIT: If you're not confident in your wiring plan, then post up a simple diagram & we'll see if it meets requirements.
    Remember there are no dumb questions, just dumb not to ask if you're not sure.
    Last edited by Tiny; 31-01-19 at 06:34 PM.
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    Let us know if it worked for you.
    It still says 10V Ugs. Generally I find that for the max current you still need the 10V but the 11.1 V from the battery should be fine until the battery drops to 9V where you want to stop using it.
    I also do not see a problem using 2 of those MOSFETs parallel for that simple switching purpose.
    Last edited by nomeat; 31-01-19 at 11:45 PM.
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    Quote Originally Posted by nomeat View Post
    I also do not see a problem using 2 of those MOSFETs parallel for that simple switching purpose.
    Not a bad idea to share the surge that way. Cool
    Cheers, Tiny
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    Quote Originally Posted by Tiny View Post
    Don't forget to put a small heat sink on it so it has somewhere to dissipate the surge heat.

    EDIT: If you're not confident in your wiring plan, then post up a simple diagram & we'll see if it meets requirements.
    Remember there are no dumb questions, just dumb not to ask if you're not sure.
    Thank you Tiny. I will tell my Daughter the diagram and she will put it on this site as I have no clue how to draw it and put it here. what I'm say I can draw it on paper but not on the puter. I Blame the stroke for this

    I will do this this arvo
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    Quote Originally Posted by nomeat View Post
    Let us know if it worked for you.

    I also do not see a problem using 2 of those MOSFETs parallel for that simple switching purpose.
    You are the third Person to say this to uses say TWO in parallel IRFZ44N (49Amp) I questioned why 2 but you said the magic work PARALLEL. Did not know you can do this. Yes it just a simple switch "eg" off or on FULL BORE

    I will put my diagram this arvo and maybe you could modify it for two mosfets in parallel
    Last edited by Mr 672A; 01-02-19 at 09:32 AM.
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    Here we Go. Please Amen it with two Mosfets in Parallel. ( I might have a fair idea but!! )

    Good Job Done, by my Daughter

    Last edited by Mr 672A; 01-02-19 at 04:01 PM.
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    I think the power dissipated in the MOSFET will be determined by the current and the channel 'on' resistance Rds-on
    IE I^2.Rds
    so 40A in a IRFZ44N (17.5mOhm) will produce about 30W of heat to be removed which is a lot meaning you'd need the heatsink to be large and water cooled as well to stay well below the rated max device temperature of 175C.
    Doubling the current produces 4 times the heat so it gets out of hand very quickly.

    Finding a FET with a much lower Rds would help a lot too

    Something like IRF1405ZPBF which is rated N Channel, 150 A, 55 V, 0.0049 ohm and priced about $3 from Element14
    Or PSMN2R5-60PLQ 150A 60V 0.002 ohm - this one will be dissipating only about 3W at 40A compared to 28W for IRFZ44N

    Need to consider the gate sensitivity too if planning to trigger them from a logic level source (which the schematic doesn't suggest)

    Search for suitable devices on RS Components
    Last edited by Skepticist; 02-02-19 at 09:58 AM. Reason: added examples

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    Quote Originally Posted by Skepticist View Post

    Something like IRF1405ZPBF which is rated N Channel, 150 A, 55 V, 0.0049 ohm and priced about $3 from Element14
    Or PSMN2R5-60PLQ 150A 60V 0.002 ohm - this one will be dissipating only about 3W at 40A compared to 28W for IRFZ44N

    Need to consider the gate sensitivity too if planning to trigger them from a logic level source (which the schematic doesn't suggest)
    Will look at that two later this week end. So for my case the less resistance the better. I've seem them used before on Similar situations (two mosfets) and they use no heatsinks? and similar motors so how can they get away with it?
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    The lower the resistance, the lower the heat losses for a given current and there are high current mosfets available with Rds less than 0.001 ohm (at a cost of course) so you can get away without using a heatsink apart from the copper on the PCB. A good example is the PWM ESC modules available for RC applications.

    This surface mounted one is 500 microOhms and rated for 30V, 300A
    You'd need about 35 IRFZ44N's in parallel to get the total Rds that low!
    Last edited by Skepticist; 02-02-19 at 11:52 AM.

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    IPT004N03LATMA1 N-Channel MOSFET, 300 A, 30 V OptiMOS, 8+Tab-Pin HSOF Infineon

    Well done Skepticist, that surface mount mosfet above looks like it would do the job with no trouble on it's own.

    ......................................
    Mr 672A; Your diagram is very simple so I have kept to the kiss principle.
    It is after all just a simple switch you want.

    I've added in the parallel mosfet, however I don't think you need it, especially if you go with the surface mount Infineon.



    Last edited by Tiny; 02-02-19 at 05:55 PM.
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    The 10k resistor is only to ensure the FET turns off by tying the gate to the source when there's no gate input. The gate would be floating without the trigger closed otherwise causing all sorts of random stuff.

    The SMD FET and the PSMN2R5-60PLQ are 'logic level' gate threshold which means they can be switched fully on by a TTL or CMOS high logic level which is something like +4-5V. The max range for Vgs is typically -20 to +20V and a lot of FETs require a Vgs of about 10V so it's best to check the data sheet.
    Last edited by Skepticist; 02-02-19 at 04:49 PM.

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    Quote Originally Posted by Skepticist View Post
    The 10k resistor is only to ensure the FET turns off by tying the gate to the source when there's no gate input. The gate would be floating without the trigger closed otherwise causing all sorts of random stuff.
    Fixed. ^^^
    Yes! right you are, forgot when going simple that you still need the bridge.

    On my regulators I use a much more complex switch, with pots, resistors & caps connecting back to the source, most of it due to using a dump load.

    Cheers, Tiny
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    Quote Originally Posted by Tiny View Post
    IPT004N03LATMA1 N-Channel MOSFET, 300 A, 30 V OptiMOS, 8+Tab-Pin HSOF Infineon

    Well done Skepticist, that surface mount mosfet above looks like it would do the job with no trouble on it's own.
    Well If I can get away with one 300 A, 30 V OptiMOS, 8+Tab-Pin HSOF Infineon I will defiantly use it, secondly if not for some reason I will use Tiny twin Mosfets Diagram modify from my original one mosfet one. but Skepticist one that will need a bread board to construct it. well that will be the third option.
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