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23 June 2005 HE104MAN-V8 Manual
Tri-M Engineering Tel: 800.665.5600, 604.945.9565
1407 Kebet Way, Unit 100 Fax: 604.945.9566
Port Coquitlam, BC V3C 6L3 E-mail: info@tri-m.com
Canada Web site: www.tri-m.com
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(P6KE or 1.5KE) will not survive the high-energy discharge of a “load dump”. Special automotive
suppressors must be used to use up the 20A to 30A peak currents being shunted. Several
manufacturers, such as Motorola, Harris and Seimens, manufacture suppressors specifically for
automotive applications. Some devices provide “zener diode” style protection, while others
provide “back to back zener diode” bidirectional protection. Each type has advantages, but
unless they are used correctly, they will fail to protect the electronics. Ratings on the transient
suppressors can be confusing. A suppressor with an avalanche voltage of 24V to 32V will have a
clamp off voltage of over 40V. In addition, ambient temperature can vary from –40C to 70C and
can result in the avalanche voltage being several volts lower at –40C and a clampoff several volts
higher at 70C.
Not all vehicles have 12V battery systems. Some trucks use 24V batteries, aircraft use 28V and
trains from 45V to 85V. Transient suppressors for aircraft cannot use the 12V system automotive
components. Instead, a suppressor with an avalanche rating of 35V is needed to allow for low
ambient temperature compensation, but this results in clamp off of over 70V. Tri-M Engineering’s
High Efficiency PC/104 Vehicle Power Supply, employs a Diode Inc. (part#5KP43A), allowing an
input voltage range of 6V to 40V. If a high clamp off voltage cannot be tolerated, other techniques
must be used. A series device such as a MOSFET can act as a pre-regulator, but it also must be
selected to withstand transients. In addition a series device adds to in-efficiency and creates a
heat dissipation problem, especially at high ambients.
“Load dumps” occur infrequently in a vehicle’s lifetime, but any electronics wishing to survive in
this environment must be designed to withstand the assaults. “Load dumps” co-operate slightly
through, their worst-case voltage does not typically occur with worst-case source impedance. In
fact, although the total energy of a “load dump” may be 500 joules, a transient suppressor
capable of 70 joules typically will be adequate because of the distributed electronics in the
vehicles. That is, provided the suppressor ratings are the same or larger than other suppressors
throughout the vehicle. A quick thinking engineer can take advantage of this and design his
power supply to withstand higher voltages and thus let others’ transient suppressors do the work.
APPENDIX 5
BC104 Battery Charger and PM104 Power Management Units
1) Description
When the BC104 and PM104 units are both installed on either the V104 or HE104 (hereafter
referred to as PSU), as universal battery charger can be setup and the PSU unit made into an
UPS (uninterruptible power supply).
The BC104 is a constant current “buck” switching regulator with an adjustable “float” voltage. The
float voltage is adjusted via a potentiometer. The PM104 is programmed by the user using a
“control basic” called Pbasic. A sample program is supplied to show a typical NiCd charging
control. Before using the BC104 and the PM104 the battery charging program must be set up for
the intended battery pack. The sample program has separate settings for normal charge current
and trickle charge current. In addition, the charge termination methods should be set, including