Inverter Power Ratings [RE-wrenches]

[Allan Sindelar]

Wrenches,
I am forwarding Rick Cullen's response, as his post to the Wrenches was
rejected:
Allan at PosNRG

----- Original Message -----
From: "Todd Cory, Mt. Shasta Energy Services" <toddcory at jps.net>
> If heat kills electronics (and I believe this to be correct) then how
> can those solar boost 50's run at a level too hot to touch and not
> self-destruct? I finally put a button thermoswitch on mine running a
> small muffin fan. The stock unit just gets too hot for me to feel good
> about.
>
> Todd
>
Rick's response:
It is true that heat shortens the life of electronics --- all electronics.
As a general rule of thumb a 10degC rise in temperature shortens life by
1/2.

But, this does not necessarily mean that a "hot to the touch" heatsink
yields an unreliable product. I believe that the Solar Boost charge
controllers have proven themselves to be quite reliable since we repair very
few for the many thousands shipped. Very hot to a human's touch is perhaps
60-70degC. In the case of the Solar Boost 50 and 3048 products the heatsink
may be hot because it is effectively unloading waste heat (several % of the
total processed). If the heat was not effectively dissipated as it is with
our oversized heatsink, device temperatures could run too hot leading to a
reliability problem. In a Solar Boost controller, the FET's and other power
devices will never run at greater than ~75degC. This is quite a bit of
derating as they are specified to operate reliably at up to 175degC or
nearly 350degF. The FET's in an SB50 are capable of handling up to 74A each,
but we choose to run them at only 12.5A max. While the heatsink may seem
hot, there is actually quite a bit of device derating and design margin.

Inherent reliability problems occur when devices used to construct a product
are not held to within their individual voltage, current, power or
temperature limits. Running the devices at or close to their limits reduces
reliability whereas providing lots of design margin improves reliability.
With regard to temperature, the "rock and hard spot" for us manufacturers is
to run the devices hard enough so that the product is cost effective and has
a reasonable design life, but not so hard that the product is unreliable. I
believe that RV Power Products has chosen the appropriate operating point
along the analog continuum of goodness-and-badness relative to how hard
individual devices are run.

While the Solar Boost products are designed to be run hard, the fan Todd is
using can only help overall reliability. If the fan produced the equivalent
heat reduction of a 10degC lower ambient temperature, then on average, life
will double. Keep in mind that there are many items other than temperature
that can lead to product reliability issues.

Rick Cullen
RV Power Products, Inc.
Providing quality MPPT solar charge controllers
Phone 760-597-1642 x102
Fax 760-597-1731

mail to: rick at rvpowerproducts.com
www.rvpowerproducts.com

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