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Relays and timers | DoItYourself.com

It's really amazing how often expensive power contactor relays are thrown away because one of many sets of contacts has become intermittent or unable to make contact. Most often, many of the contacts on the relay have never even been used. Such debris can quickly become a treasure if they can be applied to a system where only one or two contacts are needed to turn on the "hot" side (s).

For one thing, such devices can be used to create a safety relaxation to prevent damage due to power failure. If an equipment starts when a wave is in progress, this safety precaution can turn it off until it is manually restarted to prevent the equipment from restarting without monitoring when power is restored.

Given that some high-power relays sell for a few hundred dollars, they may not be a bad thing to stick to, even if they are partially disabled. But this is only useful for the experienced electric do-it-yourself. If you are planning a project on incorporating power relays, remember that the power MUST be turned off before you start thinking.


Relays 101

Let's start with the basic relays and how they work. A relay is an electrical switch that lets a low current circuit control an appliance, fan, heater, air conditioner or other device that draws very large current, requires higher voltage, or both.

For example, when someone starts their car as soon as the key is turned, 12 VDC is sent to a small square box under the hood and activates a relay, which makes the connection between the two flaps on the side of the relay. Less than 500 milliamps (or 0.5 amps) is required to activate the relay, but then 150 amps are sent directly from the battery by starting through the starter motor to reverse it.

It says right now what must be known when choosing the right relay or contactor relay – for the example above, the set of contacts must have the capacity to handle at least 200 Amp and at least 12 VDC or more. For the flush rating, the voltage is all that is needed (in this case 12 volts from the car battery).

In another scenario, a contactor relay may be needed to power a table saw that must draw 18 amps if connected to 115 VAC or 9 Amp wired to 230 VAC. The motor would only consume half the power if it is connected to 230 volts, so this would probably be the alternative and would require a contact with 230 VAC at least with at least 10 Amp capacity, although a larger Amp value does not matter.

If the motor is connected with a 12/3 cable containing three wires plus the ground wire, a coil value of either 115 or 230 VAC can be used to activate the relay. But if it is connected via a 12/2 cable with only two wires (one red, the other black) and ground, it means that all you get at the engine are both "hot" sides, giving a single alternative of 230 VAC for classifying the coil.

 relay device

In recent years, since I have done repairs on medical devices running on battery power (usually two 12 volt batteries connected in series) I have encountered many more relays with a 24 VDC coil rating. 24 volts is not bad because a lot of gadgets that we buy nowadays turn off power packages or transformers that output that voltage.

Of course, I save some energy packs, chargers, and turns off transformers when I dispose of the broken or outdated equipment they power. If I then need a relay activated with a 24 volt coil, I will only use a shutdown transformer or current adapter with a current rating that matches or exceeds the class required by the coil in that relay.

If something else, such as when a solenoid valve, or timer, is running at 24 volts, it can all be connected to that transformer, provided the power rating is sufficient. All of these components can then be fixed inside an electrical box where they can be properly connected. Again, this is not for the inexperienced DIYer in electrical work. If you are experienced enough to try such projects, DO NOT forget to turn off the power – charging can be very dangerous, even deadly. If you are not a certified electrician, consult one before you begin.

  Different Types of Power Relays

Using Timer Relays

A time delay relay is another object that I have come across and found extremely useful. As the name says it is mainly a relay. Their main purpose is to control the activation of certain components or equipment, but only at a very specific preset time and for a very precise time. They are available in four basic ways of contact operation:

1. NOTC – Usually open / closed

The coil is not activated – the contact is open.

Activate the coil – the connector remains open until the preset time has elapsed.

The contact remains closed as long as the coil remains activated.

Voltage voltage – opens the contact.

2nd NCTO – Normally Closed / Time Opened

The coil is not activated – the connector is closed.

Activate the coil – the connector remains closed until the preset time has elapsed.

After the preset time delay has elapsed, the contact opens and remains open until the coil is de-energized.

3rd NOTE – Normally open / time open:

The coil is not activated – the contact is open.

Activate the coil – the connector closes.

Voltage-free voltage – the contact remains closed until the preset duration has elapsed.

After the preset time delay has passed, the contact opens.

4th NCTC – Normally Closed / Timed

The coil is not activated – the connector is closed.

Activate the coil – the contact opens.

Disabling the coil / connector remains open until the preset time has elapsed.

After the preset time delay has passed, the contact opens.

Double Throw Contacts

Most power relays have "double throw" sets of contacts, which means the contact makes a connection to one side of a set of contacts while creating an open circuit to the other side while inactive, but with the exact opposite that occurs when the coil is activated. So if you have a NOTC relay that is dual throw with a common contact connection with another contact at the same time, the connected contact would be NCTO, but operate at the same set time delay.

The same applies to the NOTO and NCTC relays. These can be set to open a circuit, close a circuit, transfer from one circuit to another, all at an exact predetermined time and for a predetermined period.

These basics are just the tip of the iceberg when it comes to DIY electrical tinkering. If you're working on some cool creations, share them with our readers in our project section!

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