How do most manufacturer's "NORMALLY" wire relays

[Soundguy]

But in actual common practice we do care which coil terminal is plus and which is minus for there is often a spike suppression diode across the coil. Sometimes external sometimes internal to the relay case. The diode suppresses the back EMF ( electromotive force) that flows out of the coil when the circuit is broken. This spike is a considerable amount of power,and must be dealt with to prevent damage to other sensitive circuit components. The collapse of the magnetic field in the coil winding is what generates this voltage. The diode shorts this voltage out .

yup and if hooked up backwards, the realy won't actuate at all, as controll current would be shunted...

 

[Silvic]

Question on Electrical Relay on engines

As I continue to troubleshoot this issue with the engine and the starter issue and the path through the relay I have another question about relays that I have no clue on.

As a precursor to my question: I know that a thread of wire or a bad connection can and will show a full 12 volts with no load being draw through that wire. As soon as a load is put on it, the voltage drops as the poor connection or single strand can not maintain the voltage.

Can something similar to that happen with a relay that is faulty or partially failing?

What I am finding is the control wire voltage to the starter solenoid connection is showing a voltage of 12 volts if the wire is disconnected from the solenoid connection whenever the start switch is engaged.
If the wire is connected to the solenoid as it normally should be then the voltage on that same wire is 12 volts varying to nothing in concert with the starter functioning and not functioning in short cycles of on then off for a second or two then on again, all while the starter switch is held to start. (Just like if you were to turn the start switch on and off manually; however in this case the switch is held to start continually.) Before someone says battery and lead to the starter, that is not the issue. It has been ruled out.

 

[k0ua]

To answer you question, yes a relay could have a high resistance in it contacts that would cause a large voltage drop when more current is attempted to be drawn thru it.

Ohm' law is written as E=IR or sometimes written as V=IR. This is a simple grade school algebra equation, but it defines all you need to know about the relationship between voltage (E for electromotive force, sometimes called voltage) current (represented by the I in the equation) and resistance represented by the R in the equation. If you know any two of the parameters you can solve for the third by manipulation of the parameters on each side of the equation.

As an example a set of relays contacts should be near 0 ohms of resistance, but what if they were a higher value? When a load is placed thru these contacts, then if the resistance of the contacts are high the voltage will drop.

 

[Soundguy]

Re: Question on Electrical Relay on engines

As I continue to troubleshoot this issue with the engine and the starter issue and the path through the relay I have another question about relays that I have no clue on.

As a precursor to my question: I know that a thread of wire or a bad connection can and will show a full 12 volts with no load being draw through that wire. As soon as a load is put on it, the voltage drops as the poor connection or single strand can not maintain the voltage.

Can something similar to that happen with a relay that is faulty or partially failing?

What I am finding is the control wire voltage to the starter solenoid connection is showing a voltage of 12 volts if the wire is disconnected from the solenoid connection whenever the start switch is engaged.
If the wire is connected to the solenoid as it normally should be then the voltage on that same wire is 12 volts varying to nothing in concert with the starter functioning and not functioning in short cycles of on then off for a second or two then on again, all while the starter switch is held to start. (Just like if you were to turn the start switch on and off manually; however in this case the switch is held to start continually.) Before someone says battery and lead to the starter, that is not the issue. It has been ruled out.

the control wire on that relay coul be part of a bad circuit.. even something int he key switch. if the circuit cannot carry the field coil current, then the relay will not actuate. It COULD be the relay itself drawing too much in the field coil.. but mor ethan likely it is something in the circuit ahead of it, like bad contacts on the key start switch... or bad connector.

you could test this with an ammeter and a test lamp to see if yuo can get steady current from key held in start thru meter thru test lamp as a test laod ( disconnected from relay.

if the current holds and does not vary ( thus voltage too ), then I would next look at the relay itself.

 

[Silvic]

Re: Question on Electrical Relay on engines

Thanks
The start switch electronics unit was already ruled out when the problem did not go away when it was replaced. Manufacturer had thought that might be the problem as well. (of course there could be multiple cascading failures) Will try to figure out a way to get a test lead on the control circuit wires/relay prongs during a start sequence to see if they are fluctuating and thus cause the relay to drop in and out.

 

[Soundguy]

Yup, you are down to wires and relay

 

[bumperm]

Have you absolutely positively eliminated the battery as the cause of your voltage drop?

Easy to do, connect your voltmeter to the battery terminals (if connecting to the battery clamps, make sure they are clean and secure). Turn on the starter switch and watch the voltage. If it drops below about 10.5 to 11 volts, the battery is suspect. Note that a lead acid battery can have a "surface charge" that will show good voltage with no load, then drop to a low voltage when load is applied.

When checking wiring and connections, you can use a volt meter in the same manner, connecting one lead on each side of the connection or wire run under test. Apply load, the voltage shown is the voltage "dropped" (or lost if you will) across that component, connection, or wire run. Test ground connections the same way, one lead to chassis (known good ground), the other lead to the wire or component. Apply load, voltage drop should be nil to very low, unless there is a corroded or otherwise poor connection.

As to the relay with a back EMF diode hooked up the wrong way (from another post), sure, it'll shunt the current alright, but it depending on the diode and wiring, it will either blow a fuse, or fail the diode (most such diodes seem to fail shorted - and will conduct both ways, rather than failing open). Banded side of is the cathode and when used to suppress reverse or back EMF, the banded side goes to the positive side of the relay coil.

 

[Silvic]

Re: Question on Electrical Relay on engines

Yes the battery has been vetted as being fine. Not only by me using a hydrometer, and a load tester, but by three different battery shops as the manufacturer kept insisting that it was a battery problem. The last shop laughed me out after what I told them as they said I was crazy to keep testing a perfectly good battery. The manufacturer would not accept the earlier testing of the battery thus the continued testing. In addition a different battery was brought in and there was no change to the problem.

 

[bumperm]

Re: Question on Electrical Relay on engines

Okay, battery is fine.

Next step is to jump across the two heavy terminals on the starter solenoid. In the old days, this was commonly done with a screwdriver (one you don't mind having a little arc burn on - so not your Snap-On one). If the starter springs to life and starts cranking, remove screwdriver (terminals could also be jumped with heavy wire etc.). Now you know that starter is good.

If it doesn't crank, then problem is either battery (yeah, I know), or starter, wiring/connections between starter and battery positive terminal, ground connections between battery negative terminal and chassis, or ground strap or connection between engine and chassis.

If it *did* crank in the above test, then problem is limited to starter relay (contactor), or control (key switch) circuitry. To troubleshoot:

When key switch is turned does relay click, if yes, key switch to relay is good, problem is likely starter relay bad contacts. If no, relay or ign. control circuit has problem - to verify, jumper power or ground as appropriate to energize starter relay (small terminals).

bumper

 

[k0ua]

Re: Question on Electrical Relay on engines

Okay, battery is fine.

Next step is to jump across the two heavy terminals on the starter solenoid. In the old days, this was commonly done with a screwdriver (one you don't mind having a little arc burn on - so not your Snap-On one). If the starter springs to life and starts cranking, remove screwdriver (terminals could also be jumped with heavy wire etc.). Now you know that starter is good.

If it doesn't crank, then problem is either battery (yeah, I know), or starter, wiring/connections between starter and battery positive terminal, ground connections between battery negative terminal and chassis, or ground strap or connection between engine and chassis.

If it *did* crank in the above test, then problem is limited to starter relay (contactor), or control (key switch) circuitry. To troubleshoot:

When key switch is turned does relay click, if yes, key switch to relay is good, problem is likely starter relay bad contacts. If no, relay or ign. control circuit has problem - to verify, jumper power or ground as appropriate to energize starter relay (small terminals).

bumper

Excellent synopsis.