Mail Archives: geda-user/2013/07/21/13:22:57
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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><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"gmail_extra"><br><br><div class=
=3D"gmail_quote">On Sun, Jul 21, 2013 at 12:01 PM, Stuart Brorson <span dir=
=3D"ltr"><<a href=3D"mailto:sdb AT cloud9 DOT net" target=3D"_blank">sdb AT cloud9=
.net</a>></span> wrote:<br>
<blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p=
x #ccc solid;padding-left:1ex">Good points. =A0I agree that 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 class=3D"HOEnZb"><font color=
=3D"#888888"><br>
<br>
Stuart</font></span><div class=3D"HOEnZb"><div class=3D"h5"><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>
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