Voltage Drop In 12V Circuits And How To Minimise Impact.
Voltage drop in 12V circuits – how serious is voltage drop in 12V circuits and what can we do to minimise the issue?
A: Voltage drop in 12V circuits is a major issue. Voltage is what causes current to flow – without voltage electrons would just rattle around in the same place. This means that without the necessary voltage, energising current is not going to travel through a conductor.
12V is a modest voltage and that makes it especially prone to voltage drop if installations aren’t handled carefully. A particular issue is that even a well installed 12V DC circuit is going to run into voltage drop issues over time as resistance builds up through corrosion in terminations at either end of the run, as well as in junction boxes mid-run.
A circuit that has been installed for decades, especially in an environment that’s humid and/or salty, is certain to end up delivering 9V instead of 12V. And don’t expect the damage to be obvious as it is in the images here. Voltage drop is the sum of the subtraction of multiple instances of resistance across a circuit – in a complex circuit that could be very hard to find.
Establishing voltage drop might require use of an over-sized, low resistance bridging cable. With the bridge supplementing existing cable, if devices downstream of the supply suddenly start functioning perfectly, voltage drop becomes the most likely culprit.
A key consideration when building 12V circuits is considering the voltage drop introduced by the environment and by connections and terminations when the circuit is new. Electronic security devices are tolerant of voltage drop, so getting this right shouldn’t be too hard. You’re trying to keep maximum drop at around 5 per cent for a circuit at full load. Sensitive circuits should be kept within 1.5 per cent, which is not as easy as it sounds, but is unlikely to be necessary with most security systems.
There are things techs can do to ensure voltage drop doesn’t become an issue. Choose devices that are tolerant of voltage drop. Buy slightly over-sized, higher quality conductors that are resistant to moisture, install them carefully, pay attention to the quality of terminations throughout the cable run, and include checks in the maintenance program.
You should also keep your cable runs within length specification and make the effort to measure drop across typical circuits. If an environment is complex or challenging, keep cable runs shorter. If you need to go longer, increase conductor size more than necessary. Measure voltage in the field to get a feel for how these choices impact on circuit voltage.
Other techniques include managing temperature by venting junction and controller boxes, or keeping cable in the bottom of a space, rather than at the top. In some cases, you may be able to power devices from a remote source, reducing cable length.
Depending on your skill level and the nature of the circuit, you can also decrease voltage drop by decreasing load current, but you’ll need to make sure the circuit remains capable of powering field devices.
You can learn more about measuring DC voltage here or read more SEN news here.
“Voltage Drop In 12V Circuits And How To Minimise Impact.”
