Help with Relays

f1rocket · #1 03-19-2009, 10:12 AM

I need help for this electronically challenged brain of mine. I'm not even sure how to ask the question but I'll give it a try. Maybe some kind electrical engineer will take pity on me and provide an answer.

I am trying to drive a warning light when my 2-10 double-pole switch is in the middle position. In this situation, terminals 3 and 4 are open. Under all other conditions, terminals 2 and 5 are always grounded and terminals 1 and 6 are always powered. In the up position, 3 is open and in the down position, 4 is open. So the condition I am trying to pop the the light on for is when 3 and 4 are both open.

Okay, so I figure I need a relay to get this accomplished. I start looking at relays and some have 4 terminals and some have 8 terminals and I get totally confused. I found an 12 V/ 3A automative relay on Radio Shack seems like just what I need but the terminal designations have numbers on them and they don't make any sense. Here is a link to the spec sheet.

My question is 1) Is this the appropriate relay to accomplish what I am trying to do? 2) If not, which relay is? or 3) if so, how do I wire this relay up?

Thank you in advance. These electrons are very confusing!

DGlaeser · #2 03-19-2009, 10:49 AM

On the relay you show, when power is applied across terminals 30 and 87 (the ones that form a 'T'), the relay closes and contacts 86 and 87 are connected.

A diagram of the circuits involved would be most helpful. Getting the warning light ONLY in the middle position is a bit involved because the 2-10 is the progressive ON-ON-ON switch (typically used as a master switch).

To get the light to come on in either the middle or up postion (i.e. the master switch is ON):
In the MIDDLE position, contact 1 & 2 close (and stay closed in the UP position). If 1 is always powered, then in the middle position, 2 would also be powered. If you connected switch terminal 2 to terminal 30 of the relay, and grounded terminal 87 of the relay, it should close when your switch is in the middle or up position.
Your warning light should have one side connected to power and the othe side connected to terminal 86 of the relay. Terminal 87 of the relay should go to ground.

If you really want the light on in ONLY the middle position, you'll need a different realy - one that has a NC (normally closed) contact - easily obtained. But that circuit would need to be powered all the time to keep the light off. Knowing more about your circuits would be required.

f1rocket · #3 03-19-2009, 11:33 AM

Thanks Dennis. I have a 2-10 switch in front of the Master (also a 2-10 switch) to select which or both batteries are powering the starter. I have a PDF wiring diagram put together. I'll post it when I get home.

Yes, I need the light on just in the middle position but I'm not keen about powering the relay all the time. That would likely drain my battery between flights. Maybe I'll have to compromise and power it as you suggest, when the switch in on the "both" (middle) or "auxiliary" (up) battery position.

Thanks for helping me.

Don Jones · #4 03-19-2009, 11:45 AM

Quote:

Originally Posted by DGlaeser

On the relay you show, when power is applied across terminals 30 and 87 (the ones that form a 'T'), the relay closes and contacts 86 and 87 are connected.

Terminals 30 and 87 are the actual switch circuit(contacts) inside the relay. 30 is usually the power(or ground) source for the circuit you are switching. 87 goes to what ever you are turning off and on with the relay. The coil which pulls the relay down is on terminals 85 & 86. Some of these relays have a diode across these(85 & 86) terminals to prevent spikes, so polarity might matter. So if you apply power to 85 and ground to 86, the relay closes connecting 30 & 87.

DGlaeser · #5 03-19-2009, 01:50 PM

Quote:

Originally Posted by Don Jones

Terminals 30 and 87 are the actual switch circuit(contacts) inside the relay. 30 is usually the power(or ground) source for the circuit you are switching. 87 goes to what ever you are turning off and on with the relay. The coil which pulls the relay down is on terminals 85 & 86. Some of these relays have a diode across these(85 & 86) terminals to prevent spikes, so polarity might matter. So if you apply power to 85 and ground to 86, the relay closes connecting 30 & 87.

Don's right. must've had my tongue wrapped around my eyeteeth when I looked at the diagram...

f1rocket · #6 03-19-2009, 04:49 PM

Here's the link to my battery diagram. I'm trying to drive a light off the "Battery Source" switch when it is in the center, or "both" position. Thanks.

Norman CYYJ · #7 03-19-2009, 07:51 PM

If your switch contacts are open in the centre position no problem Just put a lamp or an LED across them. When the switch is then closed the lamp will turn off. If using an LED put a 1k resistor in series with it and it will never blow out.

f1rocket · #8 03-20-2009, 07:12 AM

Norman,

I'm not sure I understand how this will work with a progressinve 2-10 switch. Can you elaborate? Also, I want the light to come on when the contacts are open, not go off. Thanks.

bcondrey · #9 03-20-2009, 08:09 AM

Rather than thinking about the switch behavior, look at the circuits being switched. If you're trying to determine that both battery contactors are closed (GND supplied to both coils), try this:
- connect terminal 85 to the switched power side of either battery contactor (those contactor outputs are connected together)
- connect terminal 86 to the switched side of the coil (GND supplied to turn on) for either of the battery contactors
- connect terminal 30 to the switched side of the coil for the other battery contactor
- connect terminal 87 to whatever load you have to turn on. GND will be supplied to it only when both battery contactors are turned on.

Bob
RV-10 N442PM (flying)

DGlaeser · #10 03-20-2009, 08:28 AM

I don't see a 'simple' way to do what you want - just wires and a light.

The 'complex' way to do it is to add 2 relays in parallel with the solenoids - each one is activated with it's twin. Their contacts are hooked in series between the light and power source. When both relays are closed the light comes on. If either is off (it's solenoid twin is off) then the light is off.
You can get auto relays for a couple of bucks each, so the cost isn't high, it's just a bunch more wiring.

2 questions for my edification:
What drives the need for 2 batteries?
Does the Battery Link ACR manage the charging of the aux battery when the aux contactor is off?