Printer Friendly Forum Posts - Automotive Auto Shutdown Relay Is Hot

I installed a Chevy 3.8 V-6 into my 2002 PT Cruiser. I'm currently troubleshooting various electrical problems. The Auto Shutdown Relay in the main fuse box in the engine compartment gets very hot. I'm thinking that the drivetrain conversion must have placed a bigger load on the Auto Shutdown Relay. It has to handle more sensors, more fuel injectors and who knows what else. I would like to add another relay in the same circuit to share the load. Is this the right thing to do, or is there a better method to resolve this problem? If adding another relay is the right thing to do, which type of relay should I use, and exactly how do I go about installing it and wiring it? Any support will be greatly appreciated. Thank you very much, Tommy.

First find out what the amp draw is.

Then read the relay specs.

If your Amp Draw is close to the specs of the relay you can add another by Paralleling all connections.

For example :

30 to 30

85 to 85

86 to 86

87 to 87

87a to 87a

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John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !

I will be checking on how many amps the relay is drawing today, I'll get back to you on that. Would that reading be taken from pin cavity 30? I had no idea of how to add a second relay for my application. That is really interesting. With that wire configuration, does the load get distributed equally to each relay, or, how does it get distributed? Thank you, Tommy.

from 30 or 87

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John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !

I'm either taking the amp reading the wrong way, or my tester can't handle that high of an amp reading. I'm using an IDEAL Test Pro 360 Series Multimeter. These are the settings for the ADC scale. 200m, 20m/10A, 200u. I had the selector switch on the 20m/10A scale. The red probe was plugged into the 10A input, and the black probe was plugged into the com input. I grounded the black probe to a good ground sourse, and with the plastic cover removed from the relay, I had the red probe on the cavity pin 30 location. Within a milli second a 20 amp fuse blew. So, what am I doing wrong? Thank you, Tommy.

You connected the power directly to ground with your meter instead, so the fuse had to do its job to protect the meter from melting down.
When measuring current, the meter is effectively like a piece of wire, so it's like shorting together whatever points you attach the probes to.

To take a current measurement, you have to connect your meter in series, which means you have to disconnect the wire that the current is passing through, and then use the meter between the two points to connect them back together for the measurement.

The 10 Amp scale may not be big enough on a Multimeter.

If the current is that high the tiny wire may fry on the meter leads.

I use a gauge I scrounged from an old fork lift with battery charger leads on it.

posted_image

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John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !

If you can locate the fuse for that circuit, see what size fuse it is; if it's higher than the one for your meter, you'll need something like Hotwaterwizard has. I've got one of those stashed away myself, for measuring the high current stuff. :)

If the fuse is small enough, indicating your meter is good enough to make the measurement, you can just remove the fuse and connect your meter across the fuse contacts to make the measurement, without having to disconnect or cut any wires.

Great Idea!

Why didn't I think of that?

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John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !

I have never had to take an amperage reading before. Now I know what I was doing wrong. Yes, the fuse that blew was a 20 amp fuse. So, I should have known that the 10 amp multimeter that I'm using is not sufficient enough to do the job. OK, to make sure I understand where I will need to take the readings from. I should remove the relay, and probe between pin cavity's 30 and 86. Is that correct? And this should be done with an amperage meter that has a 20 amp capacity since the circuit I'm probing is supplied with a 20 amp fuse. I like that amp gauge idea. I'm sure I can find an amp gauge here locally, thanks for the offer and outstanding support from all of you, Tommy.

OK, I finally got to take the amperage reading. I purchased a 0 to 60 amp dash gauge very much like the one hotwaterwizard posted. I removed the 20 amp fuse for this circuit like dualsport suggested and ran some modified wire clips in it's place with wires crimped to the clips which then runs to each of the terminals on the amp gauge. Started up the engine with the fuse installed first, until I felt the relay get hot. I then turned off the ignition switch and again removed the fuse and installed the clips in it's place. I then started up the engine and checked how much amps the system was drawing. It is drawing somewhere between 17 to 19 amps. Again, this is for the Auto Shutdown System. Right next to this relay is the fuel pump relay. It too gets hot, not as hot as the Auto Shutdown relay, but I think probably hotter than it should be. I ran out of time today, however, tomorrow I will be checking to see how many amps that system is drawing as well. As for the Auto Shutdown relay, does it look like I should split the load by adding in another relay to share the load? Let me know what you think. Thank you for your support, Tommy.

Did you do what Hotwaterwizard suggested and try to find out what the current rating of that relay is? Might be marked on the relay- if it's not rated for a high enough current rating, it'll have a larger resistance across the contacts, and dissipate more heat as all that current flows through it. If the condition of the relay is marginal and has high contact resistance, it'd generate more heat also.

If your fuse is rated for 20A, and you're measuring 17 to 19A, it's safe to assume the relay wasn't expected to handle that much. They usually wouldn't design it with fuse values that close to the operating range, so it was probably meant to handle lower current.

Since your setup is modified, and expect more current, you could parallel another relay across the existing one to share the load, as mentioned-

Yes, I looked at the relay and there are no ratings listed on it. It is an Omron brand. These are the numbers I found on it: 21911C and 05269988AA. I tried looking on line and could not find any info on it. Help me to understand how sharing the load with another relay works? If I added another relay by using the parallel method, would that resolve the amperage draw problem? The 2 relays would still be operating off the same 20 amp fuse. By adding a second relay in parallel, would that lower the amperage draw within the circuit? I would think the amperage draw would still remain the same. I can see that the relays would run much cooler being that they are sharing the load. If the amperage remains the same, what other options are there that will lower the amperage reading on the 20 amp circuit? Thank you, Tommy.

Relays that stay on most of the time stay hot anyways. The coil disipates heat and warms up the relay from the friction of the electrons flowing thru the wire. You may be worrying for no reason.

LETS SEE IF WE CAN FIND OUT WHAT THE NORMAL OPERATING TEMPERATURE IS ON SOME COMMON TYPE RELAYS UNDER CONTINUOUS DUTY.

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John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !

hotwaterwizard wrote:

Relays that stay on most of the time stay hot anyways. The coil disipates heat and warms up the relay from the friction of the electrons flowing thru the wire. You may be worrying for no reason.
LETS SEE IF WE CAN FIND OUT WHAT THE NORMAL OPERATING TEMPERATURE IS ON SOME COMMON TYPE RELAYS UNDER CONTINUOUS DUTY.

Yes, I hope you find something. Thank you, Tommy.

Here is what I have so far

relay operating temperature

Relay Tutorials

https://www.bcae1.com/relays.htm

https://www.classictruckshop.com/clubs/earlyburbs/projects/bosch/relay.htm

https://www.6066gmcguy.org/BoschRelay.htm

Relay Datasheets

https://www.alliedelec.com/Images/Products/Datasheets/BM/OMRON_ELECTRONICS_LLC/Omron-Electronics-Llc_Industrial-Control_8213028.pdf

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John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !

I took a quick look. That is good info. Looks like the Omron relays operate between 40 F to 158 F. When I get time, I will take a better look. Thank you for the info, Tommy.

I found out why the Auto Shutdown Relay is heating up. When the modifications were made to my engine harness, the 6 items listed below were all tied into the Auto Shutdown Relay. Too many systems on one circuit. I will be splitting up these systems by installing 3 relays. Probably one relay for the Fuel Injectors, one for the Ignition Control Module and the 3rd one for the 02 sensors. The maining systems will continue working off the Auto Shutdown Relay. Thank you for your support, Tommy.

1) Engine PCM

2) Fuel Injectors - Pink wire circuit 639, J8 - 15 amps (separate on it's own)

3) Ignition Control Module - Pink wire circuit 239, G8 - 15 amps

4) 02 sensors - Pink wire circuit 539, J6 - 20 - amp

5) MAF sensor - Pink wire circuit 539, J6 - 20 amps

6) Evap purge solenoid valve - Pink wire circuit 239, G8 - 15 amps

Not sure if you were planning to use the same fuse line or not, but don't forget the supply side of the relay has limitations on current also; you may want to run a separate fused lines for the extra relays.
If your original line with the 20A fuse is now having to supply 19A on a regular basis from your modifications, the wiring and any other connections may be overloaded also, not just the relay.

dualsport, yes, the company who fabricated my engine harness is now putting together a 3 relay pack with separate fuses. Once installed, I'll check the amps draw for every circuit, including the existing circuit. Hopefully this 3 pack relay assembly will resolve the overloading problem. Thank you for your support, Tommy.