How to Test a Relay

[Adam]

My car's blower motor relay may be bad (or the cause of noisy fan). So I
found the following video...

How to Test a Relay the Correct Way
https://www.youtube.com/watch?v=ire7vyDqelg

However, I don't have a cordless drill battery (used in the video).
Will the following battery charger...

UPG D1724 Sealed Lead Acid Battery Charger (6V/12V Switchable Single-
Stage With Alligator Clips)
https://www.amazon.com/gp/product/B001G8AIMU/ref=ox_sc_act_title_1?
smid=A10QFO4IXVZNRN&psc=1

work ? Other frugal ideas ?

 

[Tom Biasi]

On 2/9/2020 7:31 PM, Adam wrote:

My car's blower motor relay may be bad (or the cause of noisy fan). So I
found the following video...

How to Test a Relay the Correct Way
https://www.youtube.com/watch?v=ire7vyDqelg

However, I don't have a cordless drill battery (used in the video).
Will the following battery charger...

UPG D1724 Sealed Lead Acid Battery Charger (6V/12V Switchable Single-
Stage With Alligator Clips)
https://www.amazon.com/gp/product/B001G8AIMU/ref=ox_sc_act_title_1?
smid=A10QFO4IXVZNRN&psc=1

work ? Other frugal ideas ?

An automotive cube uses 12 volts. Any 12 volt DC source will see if the
coil pulls in the contacts.
There is much more to checking a relay properly.
Pull in current, dropout current, contact resistance, and more.
But if just want to see if you can hear the armature pull in that it
will do that.

 

[Adam]

On Sun, 09 Feb 2020 20:06:16 -0500, Tom Biasi wrote:

On 2/9/2020 7:31 PM, Adam wrote:

My car's blower motor relay may be bad (or the cause of noisy fan). So
I found the following video...

How to Test a Relay the Correct Way
https://www.youtube.com/watch?v=ire7vyDqelg

However, I don't have a cordless drill battery (used in the video).
Will the following battery charger...

UPG D1724 Sealed Lead Acid Battery Charger (6V/12V Switchable Single-
Stage With Alligator Clips)
https://www.amazon.com/gp/product/B001G8AIMU/ref=ox_sc_act_title_1?
smid=A10QFO4IXVZNRN&psc=1

work ? Other frugal ideas ?

An automotive cube uses 12 volts. Any 12 volt DC source will see if the
coil pulls in the contacts.
There is much more to checking a relay properly.
Pull in current, dropout current, contact resistance, and more.
But if just want to see if you can hear the armature pull in that it
will do that.

According to the video, I think I also need to check resistance.

Will that battery charger on Amazon work ?

 

[Tom Biasi]

On 2/9/2020 8:38 PM, Adam wrote:

On Sun, 09 Feb 2020 20:06:16 -0500, Tom Biasi wrote:

On 2/9/2020 7:31 PM, Adam wrote:

My car's blower motor relay may be bad (or the cause of noisy fan). So
I found the following video...

How to Test a Relay the Correct Way
https://www.youtube.com/watch?v=ire7vyDqelg

However, I don't have a cordless drill battery (used in the video).
Will the following battery charger...

UPG D1724 Sealed Lead Acid Battery Charger (6V/12V Switchable Single-
Stage With Alligator Clips)
https://www.amazon.com/gp/product/B001G8AIMU/ref=ox_sc_act_title_1?
smid=A10QFO4IXVZNRN&psc=1

work ? Other frugal ideas ?

An automotive cube uses 12 volts. Any 12 volt DC source will see if the
coil pulls in the contacts.
There is much more to checking a relay properly.
Pull in current, dropout current, contact resistance, and more.
But if just want to see if you can hear the armature pull in that it
will do that.

According to the video, I think I also need to check resistance.

Will that battery charger on Amazon work ?

Any 12 vdc source will work.
to check coil resistance you need an ohm meter.
The relay in the video has a diode.
So ohm meter polarity is important.
In a proper test the diode characteristics would also be checked.

 

[whit3rd]

On Sunday, February 9, 2020 at 4:31:52 PM UTC-8, Adam wrote:

My car's blower motor relay may be bad (or the cause of noisy fan).

However, I don't have a cordless drill battery (used in the video).

You have a car, with a battery that makes perfectly acceptable 12V.

Will the following battery charger...

UPG D1724 Sealed Lead Acid Battery Charger (6V/12V Switchable Single-
Stage With Alligator Clips)
work ?

Maybe. It's possible to make chargers that don't generate +12V unless
attached to a battery, or that turn off if/when peak voltage exceeds a full battery charge.

 

[Adam]

On Sun, 09 Feb 2020 19:32:13 -0800, whit3rd wrote:

On Sunday, February 9, 2020 at 4:31:52 PM UTC-8, Adam wrote:
My car's blower motor relay may be bad (or the cause of noisy fan).

However, I don't have a cordless drill battery (used in the video).

You have a car, with a battery that makes perfectly acceptable 12V.

Maybe best to just use the car battery then. Just connect with alligator
clips.

Will the following battery charger...

UPG D1724 Sealed Lead Acid Battery Charger (6V/12V Switchable Single-
Stage With Alligator Clips)
work ?

Maybe. It's possible to make chargers that don't generate +12V unless
attached to a battery, or that turn off if/when peak voltage exceeds a
full battery charge.

 

[John Robertson]

On 2020/02/09 4:31 p.m., Adam wrote:

My car's blower motor relay may be bad (or the cause of noisy fan). So I
found the following video...

How to Test a Relay the Correct Way
https://www.youtube.com/watch?v=ire7vyDqelg

However, I don't have a cordless drill battery (used in the video).
Will the following battery charger...

UPG D1724 Sealed Lead Acid Battery Charger (6V/12V Switchable Single-
Stage With Alligator Clips)
https://www.amazon.com/gp/product/B001G8AIMU/ref=ox_sc_act_title_1?
smid=A10QFO4IXVZNRN&psc=1

work ? Other frugal ideas ?

OK, the video is fine as far as it goes, but it really is not the last
word in properly testing a relay as the real test is do the contacts
work under load.

So, what I would do if I was suspicious of this relay, and I didn't want
to remove the cover to visually inspect the contacts, is I would first
hook the relay to 12VDC with the +12VDC source connected to terminal 86,
and the negative side of the 12VDC supply to terminal 87. The diode
shown in the wiring diagram on the relay shows that the relay will not
operated if these are wired backwards as the diode would block the
current flow.

Next I would find a load of a couple of amps - perhaps a car light bulb.
You want something that is 24Watts - which is roughly 2 amps at 12VDC.
You then wire up the lamp so that the switch inside the relay - contacts
30 & 87 - are in series with the light and the 12VDC source. And you
also hook up a voltmeter across terminals 30 & 87 - to measure voltage
across the contacts.

Now power/energize the relay - the 12V lamp should light and the voltage
across the terminals 30 & 87 should drop to as close to zero VDC as
possible. Anything under 0.100VDC would probably be OK, with actually
0.00VDC being the ideal. If you see around 0.50 or more VDC across those
two terminals then the relay contacts are corroded and the relay is
unlikely to operate anything drawing heavier current well at all. It
should be replaced.

Without testing relay contacts under a reasonable load you really don't
know if the contacts will operate well enough to do the job that is
required. These relays are usually rated at around 25A, so a 2A load is
roughly ten percent and will give you some idea of the contact condition
if you measure the voltage drop across them.

John :-#)#

 

[John Robertson]

On 2020/02/09 4:31 p.m., Adam wrote:

My car's blower motor relay may be bad (or the cause of noisy fan). So I
found the following video...

How to Test a Relay the Correct Way
https://www.youtube.com/watch?v=ire7vyDqelg

However, I don't have a cordless drill battery (used in the video).
Will the following battery charger...

UPG D1724 Sealed Lead Acid Battery Charger (6V/12V Switchable Single-
Stage With Alligator Clips)
https://www.amazon.com/gp/product/B001G8AIMU/ref=ox_sc_act_title_1?
smid=A10QFO4IXVZNRN&psc=1

work ? Other frugal ideas ?

Oh, and it is really unlikely that a relay will cause a fan to be noisy
- that is more likely bearing failure, or foreign matter in the motor
assembly somewhere...

John :-#)#

 

On Monday, 10 February 2020 00:31:52 UTC, Adam wrote:

My car's blower motor relay may be bad (or the cause of noisy fan). So I
found the following video...

How to Test a Relay the Correct Way
https://www.youtube.com/watch?v=ire7vyDqelg

However, I don't have a cordless drill battery (used in the video).
Will the following battery charger...

UPG D1724 Sealed Lead Acid Battery Charger (6V/12V Switchable Single-
Stage With Alligator Clips)
https://www.amazon.com/gp/product/B001G8AIMU/ref=ox_sc_act_title_1?
smid=A10QFO4IXVZNRN&psc=1

work ? Other frugal ideas ?

Nearly all relay failures are switching points gone high resistance. So test that. To power the coil... you have a car battery right?

 

[Adam]

On Sun, 09 Feb 2020 22:41:33 -0800, John Robertson wrote:

On 2020/02/09 4:31 p.m., Adam wrote:

My car's blower motor relay may be bad (or the cause of noisy fan). So
I found the following video...

How to Test a Relay the Correct Way
https://www.youtube.com/watch?v=ire7vyDqelg

However, I don't have a cordless drill battery (used in the video).
Will the following battery charger...

UPG D1724 Sealed Lead Acid Battery Charger (6V/12V Switchable Single-
Stage With Alligator Clips)
https://www.amazon.com/gp/product/B001G8AIMU/ref=ox_sc_act_title_1?
smid=A10QFO4IXVZNRN&psc=1

work ? Other frugal ideas ?


Oh, and it is really unlikely that a relay will cause a fan to be noisy
- that is more likely bearing failure, or foreign matter in the motor
assembly somewhere...

John :-#)#

Blower Motor
https://us.lexusownersclub.com/forums/topic/61767-blower-motor/

Relays are cheap compared to other parts so I don't mind starting with
the relay.

 

[Adam]

On Mon, 10 Feb 2020 03:09:49 -0800, tabbypurr wrote:

On Monday, 10 February 2020 00:31:52 UTC, Adam wrote:
My car's blower motor relay may be bad (or the cause of noisy fan). So
I found the following video...

How to Test a Relay the Correct Way
https://www.youtube.com/watch?v=ire7vyDqelg

However, I don't have a cordless drill battery (used in the video).
Will the following battery charger...

UPG D1724 Sealed Lead Acid Battery Charger (6V/12V Switchable Single-
Stage With Alligator Clips)
https://www.amazon.com/gp/product/B001G8AIMU/ref=ox_sc_act_title_1?
smid=A10QFO4IXVZNRN&psc=1

work ? Other frugal ideas ?

Nearly all relay failures are switching points gone high resistance. So
test that. To power the coil... you have a car battery right?

Yes, I'll probably use the car battery. Hopefully, no shock.

 

[pfjw@aol.com]

Late in on this:

a) The only way a relay could affect fan noise would be if it is chattering - thereby causing the fan to chatter. Brush-type DC motors are generally not fond of low-frequency intermittent voltage.

b) And, if an automotive relay is in any way questionable - replace it outright. The alternative might be a 3:00 am breakdown during a blinding snowstorm. To this end, I know a number of individuals (including me) that carry spare relays for critical functions when on road-trips or off the beaten path. And, I know where those of that nature live in both vehicles.

There is frugal - spending money wisely.
There is parsimonious - which is frugality taken to the extreme.
There is being miserly - which has high potential for negative consequences..

Be frugal, and/but try not to be stupid about it.

My road-trip "Spares Kit" includes: Fuel Pump, Headlight, and Main Systems relays. High and Low beam, turn-signal and brake lamps, if applicable. Fuses. Black electricians tape. Good gloves. Very, very good Jumper cables. Flat-fix x 2. Canvas tarp.

Come to kindly terms with your Ass, for it bears you - John Muir.

Peter Wieck
Melrose Park, PA