[Focbox] 60A Continuous rating

I All !

I’m using a focbox with a 4kW motors and a 12S Lipo Battery. Everything works fine but the Focbox mosfets gets hot really fast: from 48°C to 76°C in less than 90secondes, pulling maximum 60Amps motor and average 40°C.

You can see the datas here:

The Focbox was inside a box so no cooling but even though, I didn’t expect it to get so warm so quickly.

What I don’t understand is that the Focbox is rated for 60Amps continuous. Is it only under perfect conditions with a really big fan blowing directly on the fets ? Or maybe is it because my focbox has an issue somehow ?

Any advice/ opinion is welcome here :slight_smile:

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If it doesnt limit its amps till it cools down your good

But you are not pulling all the 60 amps per focbox, maybe you should just put a new silicon pad for cooling. Where are you skating? How many degrees of temperature outside in you country My conf is dual focbox 12s4p 30q bms 60 amps amps batt 60 no external cooling https://metr.at/r/XlbKl

It does limit the amp after reaching 80°C which is the cutoff start limit I set up.

The focbox is not used inside a eskate but inside a Epaddle board, so on the water. The motor makes a propeller spin.

Spatt, from your data, I see that the temperature of your focbox doesn’t rise as quickly as mine.

I guess thats the reason why, maybe you should have gone with a higher voltage and a diffrent esc


You don’t really want to go higher than 50V when dealing with water, but indeed, maybe a different ESC would be better. But the Vesc architecture is so good, it’s hard to change to something way more restrictive

I read that water is more stressful for escs than ground. Btw focbox is rated for 60 amps for sure with a different cooling system, more efficient, and you are pulling more amps constantly than me…

You can choose for a different cooling system using water for example… you should study something like that.

Yea that makes sense lol

Yes, I’m planning on mounting the Focbox to an aluminium plate on direct contact with the water. However, I’m wondering if there is not something wrong with the mosfet of temp sensor that would cause this lightning increase of temp.

You can wait for someone more expert in focbox than me, but if you see carefully your log when the temperature raise it doesn’t drop quickly as mine so it seems like your stock cooling plate is not working at all! I would check first silicon pads, make also a photo of how and where you put your focbox, if you put it over the lipo pack for example, something that doesn’t let the focbox cool down.because after the 30 amps drowned it’s 0 amps so the cooling is really too slow

The focbox Alu plate is in contact with a big aluminium plate (A4 size) that is in direct contact with sea water, so this big Alu plate is always at 20°C. I have bought new silicon pads with 8W/mk thermal conductivity and will try it as soon as I receive it. Also, I will now use this Silicon pad between the Focbox and the big Alu plate that touches the water. If this doesn’t work out, the Focbox is probably the problem…

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No you are right original focbox cooling is like a joke… that’s why we have made heatsink cases/plates and etc stuff. I am running on 90A batt amps had never seen more than 50ºC on mosfets


Did you make any modifications to the focbox besides the added cooling?

Not much, I have added some solder on some places as it was bit lacking

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with the silicon between focbox and the aluminum plate in contact with water I think it will be for sure better.

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Do you have a picture of your setup ? I’m really interested in knowing how to increase significantly the continuous limit current.

Basically this stuff:


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Interesting, but it really looks like the one already integradted to the focbox

definitely a lot more resistance with a prop in water than thane on a street. FocBox was designed for esk8, but i think if you can somehow add better cooling you’d be fine.

Is there any possibility of mounting a sealed aluminum heatskink waterside so that the heat can sink faster? You’re in the water, you should take advantage of it.