Mail Archives: geda-user/2013/07/21/13:37:54
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Although I did find a 20 watt TO-220 heatsink HS380-ND
I think maybe thermal is a higher priority than vibration and shock.
On Sun, Jul 21, 2013 at 1:22 PM, Rob Butts <r DOT butts2 AT gmail DOT com> wrote:
> Thanks guys, all great points!
>
> This is a controller for my latest endeavor. I'm putting a small 12 volt
> trolling motor on the back of a kayak and controlling the steering via a
> joystick. I'm using a 12 volt dc 14 Nm gear motor to turn the trolling
> motor. This gear motor has a stall current of 26-32 amps and a nominal
> current of about 8 amps. The trolling motor will be mounted in such a way
> that the torque will not be much. The spec says peak power is 36.5 watts
> and nominal is 24 watts but if I'm pushing 8 amps at nominal power 12 volts
> aren't those h-bridges seeing 96 watts?
>
> Having worked in gte's government systems environmental lab for a few
> years I've seen first hand how vibration and shock play a roll in system
> reliability. The vibration shouldn't be too bad especially where I'd mount
> the board on rubber mounts but I'm thinking the TO-263 package will be
> better with the beefiest heatsink I found for that package
> DV-T263-101E-ND. And this way I can make use of the big pad for the output.
>
> Thoughts?
>
>
> On Sun, Jul 21, 2013 at 12:01 PM, Stuart Brorson <sdb AT cloud9 DOT net> wrote:
>
>> Good points. I agree that environment -- shock & vibe -- also play a
>> role in deciding whether to stand the part up, or lay it down. I
>> would imagine that the amount of space you have over the board will
>> also play a role.
>>
>> As for standing the part up, there are heatsinks which are mounted to
>> the PCB, and the tab is screwed to the heatsink. What do you think
>> about them w.r.t. the shock/vibe issue you raise? I think you have
>> expertise in design for extremely harsh environments, and know more
>> about this than I do.
>>
>> The one problem with laying the part down is that in general I don't
>> know how to calculate the heat dissipation of a large PCB pad. With
>> standing parts and commercial heatsinks, the heatsink comes with a
>> rating allowing you to compute whether it will handle all the power
>> dissipated by the part. For computing the dissipation allowed by a
>> PCB pad I generally look around for an app note with a recommended
>> footprint. Maybe there is some commerical thermal analysis program
>> out there which can compute the thermal dissipation of an aribtrary
>> pad?
>>
>> The good news is that this Infineon part comes in a TO-263 variant.
>> It is designed to lay down, and use the tab as the heat sink. I found
>> a TI app note which gives specs for the thermal conductivity of the
>> TO-263 package, and a clear drawing of the recommended footprint.
>>
>> http://www.ti.com/lit/an/**snva328a/snva328a.pdf<http://www.ti.com/lit/an/snva328a/snva328a.pdf>
>>
>> Maybe Rob should consider this package?
>>
>> Stuart
>>
>>
>>
>>
>> On Sun, 21 Jul 2013, Bob Paddock wrote:
>>
>> On Sun, Jul 21, 2013 at 10:27 AM, Stuart Brorson <sdb AT cloud9 DOT net> wrote:
>>>
>>> 1. Since the output is on both pin 4 and pin 8 (the tab), you can
>>>> stand the part upright, with the tab in the air,
>>>>
>>>
>>> 2. You can lay the part down on the board,
>>>>
>>>
>>> Which one you want to do will be largely determined by how much power
>>>> the part will dissipate.
>>>>
>>>
>>> The other major determining factor for stand/lay, be sides space and
>>> power dissipation, is the system environment.
>>>
>>> If the unit is subject to high vibration levels (this is a motor boat
>>> control?)
>>> or high G levels (dropping the motor when mounting), standing parts
>>> tend to break (or be ripped in the case of G forces) their leads at
>>> the solder junction after a while.
>>> Alas no way to know how long "a while" might be.
>>>
>>> I've seen this failure most with standing electrolytic caps. Some
>>> have had the leads break *inside* the case so the part looked fine.
>>> :-(
>>>
>>> I've learned the hard way it is best to lay parts down when you can.
>>> Don't overlook the stress of bending the leads to get that done, as
>>> that can also lead to system failures.
>>>
>>>
>
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<div dir=3D"ltr"><div>Although I did find a 20 watt TO-220 heatsink HS380-N=
D<br><br></div>I think maybe thermal is a higher priority than vibration an=
d shock.<br></div><div class=3D"gmail_extra"><br><br><div class=3D"gmail_qu=
ote">
On Sun, Jul 21, 2013 at 1:22 PM, Rob Butts <span dir=3D"ltr"><<a href=3D=
"mailto:r DOT butts2 AT gmail DOT com" target=3D"_blank">r DOT butts2 AT gmail DOT com</a>></s=
pan> wrote:<br><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex=
;border-left:1px #ccc solid;padding-left:1ex">
<div dir=3D"ltr"><div><div><div>Thanks guys, all great points!<br><br></div=
>This is a controller for my latest endeavor.=A0 I'm putting a small 12=
volt trolling motor on the back of a kayak and controlling the steering vi=
a a joystick.=A0 I'm using a 12 volt dc 14 Nm gear motor to turn the tr=
olling motor.=A0 This gear motor has a stall current of 26-32 amps and a no=
minal current of about 8 amps.=A0 The trolling motor will be mounted in suc=
h a way that the torque will not be much.=A0 The spec says peak power is 36=
.5 watts and nominal is 24 watts but if I'm pushing 8 amps at nominal p=
ower 12 volts aren't those h-bridges seeing 96 watts?<br>
<br></div>Having worked in gte's government systems environmental lab f=
or a few years I've seen first hand how vibration and shock play a roll=
in system reliability.=A0 The vibration shouldn't be too bad especiall=
y where I'd mount the board on rubber mounts but I'm thinking the T=
O-263 package will be better with the beefiest heatsink I found for that pa=
ckage DV-T263-101E-ND.=A0 And this way I can make use of the big pad for th=
e output.<br>
<br></div>Thoughts?<br></div><div class=3D"HOEnZb"><div class=3D"h5"><div c=
lass=3D"gmail_extra"><br><br><div class=3D"gmail_quote">On Sun, Jul 21, 201=
3 at 12:01 PM, Stuart Brorson <span dir=3D"ltr"><<a href=3D"mailto:sdb AT c=
loud9.net" target=3D"_blank">sdb AT cloud9 DOT net</a>></span> wrote:<br>
<blockquote class=3D"gmail_quote" style=3D"margin:0pt 0pt 0pt 0.8ex;border-=
left:1px solid rgb(204,204,204);padding-left:1ex">Good points. =A0I agree t=
hat environment -- shock & vibe -- also play a<br>
role in deciding whether to stand the part up, or lay it down. =A0I<br>
would imagine that the amount of space you have over the board will<br>
also play a role.<br>
<br>
As for standing the part up, there are heatsinks which are mounted to<br>
the PCB, and the tab is screwed to the heatsink. =A0What do you think<br>
about them w.r.t. the shock/vibe issue you raise? =A0I think you have<br>
expertise in design for extremely harsh environments, and know more<br>
about this than I do.<br>
<br>
The one problem with laying the part down is that in general I don't<br=
>
know how to calculate the heat dissipation of a large PCB pad. =A0With<br>
standing parts and commercial heatsinks, the heatsink comes with a<br>
rating allowing you to compute whether it will handle all the power<br>
dissipated by the part. =A0For computing the dissipation allowed by a<br>
PCB pad I generally look around for an app note with a recommended<br>
footprint. =A0Maybe there is some commerical thermal analysis program<br>
out there which can compute the thermal dissipation of an aribtrary<br>
pad?<br>
<br>
The good news is that this Infineon part comes in a TO-263 variant.<br>
It is designed to lay down, and use the tab as the heat sink. =A0I found<br=
>
a TI app note which gives specs for the thermal conductivity of the<br>
TO-263 package, and a clear drawing of the recommended footprint.<br>
<br>
<a href=3D"http://www.ti.com/lit/an/snva328a/snva328a.pdf" target=3D"_blank=
">http://www.ti.com/lit/an/<u></u>snva328a/snva328a.pdf</a><br>
<br>
Maybe Rob should consider this package?<span><font color=3D"#888888"><br>
<br>
Stuart</font></span><div><div><br>
<br>
<br>
<br>
On Sun, 21 Jul 2013, Bob Paddock wrote:<br>
<br>
<blockquote class=3D"gmail_quote" style=3D"margin:0pt 0pt 0pt 0.8ex;border-=
left:1px solid rgb(204,204,204);padding-left:1ex">
On Sun, Jul 21, 2013 at 10:27 AM, Stuart Brorson <<a href=3D"mailto:sdb@=
cloud9.net" target=3D"_blank">sdb AT cloud9 DOT net</a>> wrote:<br>
<br>
<blockquote class=3D"gmail_quote" style=3D"margin:0pt 0pt 0pt 0.8ex;border-=
left:1px solid rgb(204,204,204);padding-left:1ex">
1. =A0Since the output is on both pin 4 and pin 8 (the tab), you can<br>
stand the part upright, with the tab in the air,<br>
</blockquote>
<br>
<blockquote class=3D"gmail_quote" style=3D"margin:0pt 0pt 0pt 0.8ex;border-=
left:1px solid rgb(204,204,204);padding-left:1ex">
2. =A0You can lay the part down on the board,<br>
</blockquote>
<br>
<blockquote class=3D"gmail_quote" style=3D"margin:0pt 0pt 0pt 0.8ex;border-=
left:1px solid rgb(204,204,204);padding-left:1ex">
Which one you want to do will be largely determined by how much power<br>
the part will dissipate.<br>
</blockquote>
<br>
The other major determining factor for stand/lay, be sides space and<br>
power dissipation, is the system environment.<br>
<br>
If the unit is subject to high vibration levels (this is a motor boat contr=
ol?)<br>
or high G levels (dropping the motor when mounting), standing parts<br>
tend to break (or be ripped in the case of G forces) their leads at<br>
the solder junction after a while.<br>
Alas no way to know how long "a while" might be.<br>
<br>
I've seen this failure most with standing electrolytic caps. =A0Some<br=
>
have had the leads break *inside* the case so the part looked fine.<br>
:-(<br>
<br>
I've learned the hard way it is best to lay parts down when you can.<br=
>
Don't overlook the stress of bending the leads to get that done, as<br>
that can also lead to system =A0failures.<br>
<br>
</blockquote>
</div></div></blockquote></div><br></div>
</div></div></blockquote></div><br></div>
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