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PMC DC input voltage range


David Pickett
 

Jerry,


I know that the nominal d.c.input of the PMC box is 12 V, but what is the tolerance (i.e. what voltage range will it accept)?


Thanks,


David


hubbell_jerry@...
 

Hi David,

Thanks for your question. The minimum voltage required by the on-board voltage regulators is around 11 Vdc. The maximum safe voltage is probably around 16-18 Vdc, but the regulators are rated for 20-25 Vdc depending on the specific regulator. There are 4 voltage regulators on-board, 2 10Vdc for the motors, a 5 Vdc for the communications and 3.3 Vdc for the CPU and logic circuitry. I would not suggest exceeding 20 Vdc. on the input. The higher the voltage is above the nominal 12 Vdc (13.8 Vdc in reality from a battery) the more heat is generated in the voltage regulators that must be dissipated. This would likely shorten the life of the regulators and cause a failure. 

Jerry Hubbell
Director Electrical Engineering
Explore Scientific, LLC.


David Pickett
 

Thank you for this, Jerry. From your response, I
suspect that the limiting factor is actually the
way the regulators are mounted and how much heat
they can therefore dissipate, as you suggest,
which is not the same as the maximum quoted for
the devices on the assumption that all heat
generated is well "sunk". I would personally have
thought that 15v might be a more appropriate
maximum unless they are bolted to substantial
heat sinks. This would normally be slightly
higher than the terminal voltage of a Lead-Acid
battery under charge. As far as the lower level
is concerned, 11 volts sounds a bit marginal for
a regulator supplying 10v to a motor. It also
points to the unsuitability of NiMH batteries
with their range of 1.4 - 1.2 V per cell (8 x 1.25 = 10v).

David

At 19:14 09-10-17, hubbell_jerry@... [ESPMC-Eight] wrote:


Hi David,

Thanks for your question. The minimum voltage
required by the on-board voltage regulators is
around 11 Vdc. The maximum safe voltage is
probably around 16-18 Vdc, but the regulators
are rated for 20-25 Vdc depending on the
specific regulator. There are 4 voltage
regulators on-board, 2 10Vdc for the motors, a 5
Vdc for the communications and 3.3 Vdc for the
CPU and logic circuitry. I would not suggest
exceeding 20 Vdc. on the input. The higher the
voltage is above the nominal 12 Vdc (13.8 Vdc in
reality from a battery) the more heat is
generated in the voltage regulators that must be
dissipated. This would likely shorten the life
of the regulators and cause a failure.

Jerry Hubbell
Director Electrical Engineering
Explore Scientific, LLC.


hubbell_jerry@...
 

Hi David,

The thermal design of the PMC-Eight is fairly robust as the design is such that the heat is routed out from the thermal pads using vias coupled to the ground plane to the edge connectors bolted to the heavy aluminum case. I have not done any thermal studies with the input voltage higher than about 14 Vdc.

Jerry Hubbell
Director Electrical Engineering
Explore Scientific, LLC.


David Pickett
 

Sounds good! And, of course, it will be used most of the time in the open air at the low temperatures of midnight!

At 23:10 09-10-17, hubbell_jerry@... [ESPMC-Eight] wrote:

Hi David,

The thermal design of the PMC-Eight is fairly robust as the design is such that the heat is routed out from the thermal pads using vias coupled to the ground plane to the edge connectors bolted to the heavy aluminum case. I have not done any thermal studies with the input voltage higher than about 14 Vdc.

Jerry Hubbell
Director Electrical Engineering
Explore Scientific, LLC.