Overheating mosfet

jimeryan22

Hi all... Any of you knowledgable chaps able to give me a reason why my recently wired mosfet starts to get far too hot and basically go the way of burning out as soon as the battery is plugged in..? This is without trigger pulls.. I'm pretty sure it's wired perfect

DeBurca

It should not heat up as it is a passive device and should only be active when it receives a signal via the trigger switch

I assume that the MosFet is in the negative line (black wire) and not the posative (red wire) as most people think

jimeryan22

DeBurca wrote: »

It should not heat up as it is a passive device and should only be active when it receives a signal via the trigger switch

I assume that the MosFet is in the negative line (black wire) and not the posative (red wire) as most people think

Should of known you'd have the know how kev.. I have it the same as the bottom pic here.. Left side
http://img196.imageshack.us/img196/930/7str.jpg

Southern Dandy

Very odd, the mosfet should not be even remotely warm when not in use, signal voltage only passes when the trigger contacts meet, I have seen mosfets with incorporated heatsinks, but these are generally homemade.

It may be the result of a poor electrical connection somewhere on the mosfet, if it the cable is soldered then I would look into a weak joint, these can cause excess heat especially at the battery side, other than that it could be a dodgy component or circuit board. Maybe check your battery also.

What brand is the mosfet?, might still be under warranty.

jimeryan22

Southern Dandy wrote: »

Very odd, the mosfet should not be even remotely warm when not in use, signal voltage only passes when the trigger contacts meet, I have seen mosfets with incorporated heatsinks, but these are generally homemade.

It may be the result of a poor electrical connection somewhere on the mosfet, if it the cable is soldered then I would look into a weak joint, these can cause excess heat especially at the battery side, other than that it could be a dodgy component or circuit board. Maybe check your battery also.

What brand is the mosfet?, might still be under warranty.

Hi mate.. Yeah it is a home made one not by me... with heat sinks, I opened it up...
But. You may have hit something with the trigger switch, I have one ordered coming brand new.. So am I right in saying that, even if only 1 contact is touching slightly that when batt is inserted that it heats up as if someone's holding the trigger..? Here's a pic of mosfet

jimeryan22

Lads...? Oh and kev, posted that postal order there just when we were talking earlier so please god youll get it in the morning

DeBurca

Can I assume that you connected it as is shown in the photo

jimeryan22

DeBurca wrote: »

Can I assume that you connected it as is shown in the photo

Yep. Spot on

jimeryan22

Pics for kevin

Southern Dandy

Your mosfet does not look like it has a heatsink, unless you removed it. The trigger contact cables or comminication cables, do not carry the full voltage like before, it just tells the fet when and when not to allow voltage to the motor, so I doubt it is the trigger contacts.

You could also have a dodgey transistor, but heat building when idol is strange, has to be a connection or mosfet assembly issue. Am not doubting the person who built it but has he installed these in other aegs and had the same problem?.

jimeryan22

Southern Dandy wrote: »

Your mosfet does not look like it has a heatsink, unless you removed it. The trigger contact cables or comminication cables, do not carry the full voltage like before, it just tells the fet when and when not to allow voltage to the motor, so I doubt it is the trigger contacts.

You could also have a dodgey transistor, but heat building when idol is strange, has to be a connection or mosfet assembly issue. Am not doubting the person who built it but has he installed these in other aegs and had the same problem?.

It's funny you say that... After looking at it.. I think it might be actually assembled wrong... Been looking at a few diagrams, the MOSFET itself like

Southern Dandy

jimeryan22 wrote: »

It's funny you say that... After looking at it.. I think it might be actually assembled wrong... Been looking at a few diagrams, the MOSFET itself like

Theres no diode either by the looks if it, There should be 2 resistors also, I think.

DeBurca

Southern Dandy wrote: »

Theres no diode either by the looks if it, There should be 2 resistors also, I think.

Its hard to tell as what appears to be 2 resistors are under the heat shrink
As Southern Dandy said there is no heatsink and it could be a faulty tranny
But one thing for sure it should not be getting hot all on its own just because you connect the battery