High Country Tek DVC80 - Manual (Page 150)

P/N: 021-00154, Rev. A.6 - updated for V4.7 Tools Page | 150
breaks or restrictions in the current's path through the chassis as they add resistance to the circuit and thereby
lower the current flow and the resultant magnetic force produced. If more than one circuit uses the same wires,
they interact, just as would happen if an undersized hose were used to return the fluid from many valves to tank.
The pressure drop across the restriction in the wire is the resistance multiplied by the sum of all the currents
using the wire. This voltage drop is seen by all of the circuits using the wire. The expected currents should be
added up and an appropriately sized wire selected, or individual wires to each load/circuit can be used. The
gauge and length of the wire affects its resistance. Even a short machine can have long wires if they are routed
poorly. Note that corroded contacts in any circuit can have very high resistance. Also use waterproof parts if
there is any chance of water contacting the circuit.
Protection with Fuses and Special switches
Safe electronics require the use of fuses to protect equipment and people. Fuses seldom are fast enough to
protect electronic components from damage, but they will usually limit potential fire damage and avoid burning
up the wiring. HCT’s products all provide internal protection circuits for the HCT modules in your system in the
advent of a wiring mistake or other over voltage condition. Note that fuses, circuit breakers, connectors, relays
and switches all have resistance. Fuses and circuit breakers are typically the worst offenders and should be
accounted for even at moderate current values (1 to 10 amps), while the others are typically quite small and are
only a problem at high currents.
Use so-called "inductive load" rated switches when driving coils. The coil inductance tries to keep the current
constant when you turn off the switch. Trying to instantly turn off current to a coil will result in an arc across the
switch if no means of arc suppression is employed. That is basically how spark plugs work.
All of HCT’s products that are used for controlling valve spool movement by controlling the coil current provide
for this arc suppression and do not require an external switch to apply the coil current. Refer to the Pulse Width
Modulation (PWM) write-up in the Appendices for a full discussion.
Get the entire valve shift you need
Valve coils have a resistance. This resistance demands a certain amount of voltage to drive enough current to
create the magnetic force to shift the spool fully. The valve manufacturers typically build their coils to have
enough resistance that they will not draw too much current and burn up, but will be able to run off of typical 12 or
24volt power sources. The amount of voltage you have to work with is the battery, alternator or power supply
voltage. Extra resistance spread throughout the circuit may reduce the conducted current and prevent proper
valve operation. Valve coils are made of copper wire and have resistance, so forcing current through them
causes them to heat up. Copper wire increases its resistance when it gets hot. This heating phenomenon is
most troublesome for currents over one amp. Coils can also become hot when hot fluid is run through the valve
or if located next to a running engine. It is hard to predict coil temperature and even harder to get the resistance
vs. temperature curve from the manufacturer, not to mention getting the resistance or voltage drop
specifications on all valve drivers, fuses and switches etc.
These resistance variations can prove troublesome to getting a system to work properly and reliably especially
one with many valves. HCT’s products incorporate circuits to regulate the current to a valve’s coil independent
of circuit resistance variations within a machine and machine-to-machine. The Pulse Width Modulation (PWM)
technique used by HCT solves this problem
. Without this capability one would resort to the cut and try
approach, which can be used with some success. However, this requires that the person commissioning the
machine must know what to look for if the electronics is not fully shifting the valve. Some coils increase their
resistance by over 50% when very hot and no longer draw enough current to fully shift at normal alternator
voltages. 10volt coils can often be substituted for 12volt coils when this happens, but the coil current will usually
be higher for full shift on the lower voltage valve, which compounds problems with wire resistance.
Trouble shooting the electronics in your system
Electrons are usually invisible and silent, which makes it hard to find leaks or restrictions. A well-equipped
troubleshooter must have a digital volt / ohm / amp meter, mating connectors or break out boxes, and may need
an oscilloscope to see quickly changing voltages or pulses. We recognize that this is probably asking too much,
so HCT’s products incorporate LEDs to help troubleshoot your system with our products.