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Alternator suddenly red hot?

 
Old 07-07-2019, 09:13 PM
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Default Alternator suddenly red hot?

I desperately need some wisdom to sort this out before MATG.

I've been running a 16 or 17in Spal fan for a few years on my '96. It draws about 21 amps. Many track and street days with it. Only problem was burned up relay at MATG last year that smoked the fan signal ground circuit in my MS3 Basic. Selected a different output and have both signal ground circuits for the fans going to one large 40amp aftermarket relay. 12v+ into the relay actuation circuit comes from the main fuze block. 12v+ input for the switched circuit is fused inline with a 30amp blade fuse and comes from the big 12v+ alternator post. Output goes to the Spal. Spal ground wire goes to ground gang post on engine beside the throttle body.

I did a track day in December with it in this configuration after making the fan signal circuit change in the MS3.

Ran engine yesterday and burped coolant, fan cycling without issue. Today I was checking the A/C with some gauges and the engine idling. The fan was running ~80% of the time and then just stopped. I turned off the A/C and then the car.

The 12v+ wire from the alternator was warm enough it started to melt the corrugated loom a little. The relay was hot to the touch as well. It turns out the inline 30 amp fuse on the 12v+ from the alternator had popped.

That's odd.

The wire from the relay to the fan was not hot. The ground wire for the fan was not hot. Removed and replaced ground nut and inspected surfaces.

Replaced fuse and cranked engine. Turned on A/C and fan was again running fine. Let it run about 10 minutes with A/C on and fan running about 80% of the time. Relay cool. Wire cool. Everything is groovy. I'm wondering if it was just a poor ground and I fixed it.

NOPE. I was fiddling with the A/C gauges a bit then checked the relay again and the damn thing is hot again, and so is that fused wire again. WTF? It was just cool a minute ago and had been running a while just fine.

I turn off the car and remove the A/C gauges and brush the back of my hand against the alternator. HOLY **** THAT THING IS HOT! It was quite a bit warmer than the engine itself, which was about 180-200F.

I'm not sure if I have an alternator problem, a bad relay, a bad fan motor, too much resistance in a connection, or what? None of the wires to the relay are chafed or melted. The blade connectors are crimped, FWIW.

I'm puzzled how it is good for a few minutes and then inexplicably not good very suddenly.

For clarity, the alternator wasn't actually "red" hot.
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Old 07-07-2019, 09:42 PM
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It is really crappy practice to talk about electrical problems from afar. One needs to be "hands on" to make meaningful suggestions.

Having said that,

I would start with the fans, to see if there are any physical obstructions keeping them from rotating freely.
Next, ı would check how much power (amps) they are drawing.

These two steps would eliminate the biggest source of power consumption if they check out fine.

Supposing the fans are not the culprit, I would throw a new relay in there. Beats trying to diagnose a relay.

For the record, I use 2 relays to run one fan. Meaning, one relay turns on another, and the second relay is "fed" straight from the battery connector in the underhood fuse box, and has its own separate fuse. Yes, I am paranoid that way.

Also, please check your battery voltage while the car is running. It's a very good idea to hook up a voltmeter and leave it on the passenger seat if you do not have a voltage gauge. There was a time when my system voltage would intermittently spike to 16 or so. Turned out a rectifier was going south in the alternator. (That does not mean a new alt is required; a proper shop can repair that for the fraction of the cost of a new alternator)

I would also check the alt belt. Yes, I am not kidding.

Just keep an eye on system voltage if/when these things are happening.
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Old 07-07-2019, 11:27 PM
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Are you running a rx7 alternator or a nb style alternator?
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Old 07-08-2019, 12:54 AM
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What gauge wires are you running at each length? There was a thread awhile ago you offered some suggestions about fan wiring, and I was going to correct you but decided you probably knew what you were doing(tm).
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Old 07-08-2019, 01:08 AM
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Oh.. and a couple of things I would change just given your description -

The post by the throttle body is your sensor ground. Since you're using that as your power ground for your spals, there's a non-zero chance that's what killed your MS last year if you don't have a snubber/flyback diode. Either way, I'd move it off the engine and onto the body.

What size inline fuse are you using? ATM, ATO, ATX?
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Old 07-08-2019, 06:31 AM
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Fuse is 30 amp ATO.

There is just one fan.

Original stock '96 alternator has been back in it since the rx7 alternator upgrade failed shortly after installation. It had a regulator problem and went high on voltage (17v+) after a couple of days. Stock '96 alternator was never trouble previously.

Fan should draw no more than 22 amps if running to spec, if my spec check is accurate.

Fan spins freely by hand, except for the resistance of the magnets. I checked it right before event occurred because I just installed the radiator.

Fan was actually grounded to relay mounting post behind headlight the first time, and I moved it to the throttle body sensor ground after it got hot the first time. I thought it would complicate the story to add that detail and my description was getting long. I'll try not to omit anything else moving forward.

Wires I added are a larger gauge than the ones coming out of the Spal, so I thought they were fine. I will attempt to determine the gauge number.

I was not watching the voltage during the event but can put a multimeter on it tonight.

IDK if the multimeter has any way to measure amperage draw from the fan. I'm willing to purchase an amp meter for diagnosis.

I'll need to refer back to your posts and see what questions I have missed.
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Old 07-08-2019, 06:56 AM
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I'll move the ground back to the body, remove the fan and shroud and ensure it spins freely again.

I'll check the belt tension.

The most perplexing thing for me is that it ran for several minutes without heating that relay or wire and then began getting hot very quickly.

I will run the car with a voltmeter attached.

Thinking back before yesterday, the fan did vary slightly in speed once as I was burping the coolant, but it was slight. I thought it odd because there were no other intermittent loads on the circuit. A/C was off that day.

Would a bad relay cause enough resistance to make the entire alternator really hot?

Why would the wires to the fan itself remain cool if the fan was the problem?

Why would the fan circuit need wires more than one size larger than provided by Spal on the fan itself? Just resistance due to length?

Are crimp/butt connections a problem? Shall I solder and shrink everything?
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Old 07-08-2019, 07:23 AM
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Picture of 40 amp relay. Maybe it isn't good for continuous duty.
Attached Thumbnails Alternator suddenly red hot?-20190707_190418.jpg  
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Old 07-08-2019, 07:35 AM
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Be sure to watch the alternator voltage (at the post), not simply the battery voltage.
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Old 07-08-2019, 08:04 AM
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Originally Posted by sixshooter View Post
I'll move the ground back to the body, remove the fan and shroud and ensure it spins freely again.

I'll check the belt tension.

The most perplexing thing for me is that it ran for several minutes without heating that relay or wire and then began getting hot very quickly.

I will run the car with a voltmeter attached.

Thinking back before yesterday, the fan did vary slightly in speed once as I was burping the coolant, but it was slight. I thought it odd because there were no other intermittent loads on the circuit. A/C was off that day.

Would a bad relay cause enough resistance to make the entire alternator really hot?

Why would the wires to the fan itself remain cool if the fan was the problem?

Why would the fan circuit need wires more than one size larger than provided by Spal on the fan itself? Just resistance due to length?

Are crimp/butt connections a problem? Shall I solder and shrink everything?
With all this new info, I am beginning to blame the relay while reserving the right to monitor alt output voltage.

Also, I solder end shrink tube everything. Paranoia has its advantages.

Also also, Ted, when I said battery voltage, it was a generic term. I meant voltage produced by the alternator. I swear on baby Jesus. Really.

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Old 07-08-2019, 08:28 AM
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The low hanging fruit to grab is another 40 amp relay. I'm willing to do that immediately because if it isn't the source of the trouble I can have a spare relay on hand for the future. I'll install that and monitor voltage and temperatures of wires for a bit.

And I'll move the fan ground back to the chassis.
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Old 07-08-2019, 08:38 AM
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Originally Posted by Godless Commie View Post

Also also, Ted, when I said battery voltage, it was a generic term. I meant voltage produced by the alternator. I swear on baby Jesus. Really.
Right, I believe you ~wink~

One thing I have learned through the years of mentoring junior engineers is that you have to be absolutely clear with instruction. Hence the single sentence replies I usually provide. Unfortunately, this place is the ultimate proof to the "you can lead a horse to water" saying.

I think what we are looking for here is current. I am not sure how a relay can cause an increase in current, but we will let the investigation pan out there.

My hypothesis is that the alternator is generating a voltage in excess of a crowbar like input protection circuit in the fan. This is resulting in excess current. These things can have thermal time constants, which could explain the time delay. The alternator post is not tightly regulated in the voltage domain.
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Old 07-08-2019, 08:53 AM
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Still having my morning caffeine, so bear with as I might end up tossing edits in here..

Multimeter - usually wont read more than a handful of amps without blowing up, certainly not enough to measure the fan. Spec is probably fine, though inrush current is probably going to be a lot more than 21a.
Wire gauge - consider that a fuse is just a really small gauge wire over a short distance. I tend to overkill on fan wiring, 14-12awg.
Solder - while I don't recommend it - I don't like the look of that crimp, what little of it can be seen. Looks uneven, and with that exposed wire, wonder if it's fatiguing - work hardening - cracking. Use some heat shrink to strain relief.
Relay - pop the cover off, contactors are probably black. When the contactors close they arc which produces carbon which creates resistance. A little sandpaper will clean it up.
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Old 07-08-2019, 09:12 AM
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All helpful information, thanks. My background is mechanical and not electrical or electronic, so don't assume anything with me.

I'm ordering a couple of relays with a higher amp rating in case this one's not really rated for continuous duty.

https://www.amazon.com/dp/B01IX7NV0C/ref=cm_sw_r_sms_awdo_t1_12ZiDbTNTNRE5 https://www.amazon.com/dp/B01IX7NV0C/ref=cm_sw_r_sms_awdo_t1_12ZiDbTNTNRE5


I will solder and shrink connections where I can and re-crimp the others to ensure security of the connections.

Not sure what a crowbar is but I assume it is a voltage or current limiting device of some sort. I get you believe the alternator may be over producing voltage and will attempt to monitor this once I begin running and testing. If there was a limiting device in the fan motor would it not create heat in the wiring to the fan in this case?
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Old 07-08-2019, 09:22 AM
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You may want to consider getting a relay base, that'll help the vibration issue and simplify wiring into some good ol' butt splices.
https://www.amazon.com/ONLINE-LED-STORE-Pack-Interlocking/dp/B01KVZ2MCW/ref=sr_1_3?keywords=relay+base&qid=1562591954&s=automotive&sr=1-3 https://www.amazon.com/ONLINE-LED-STORE-Pack-Interlocking/dp/B01KVZ2MCW/ref=sr_1_3?keywords=relay+base&qid=1562591954&s=automotive&sr=1-3
I don't think respeccing the relay is necessary - if it says 40a it should be able to do 80a for a short amount of time. Electromechanical is a bit more tolerant like that. edit: should also mention these should be at your local auto parts store.

As far as alternator overproducing.. that should really only be the case if the battery isn't well connected. Might want to doublecheck your 80a fuse in the underhood box, make sure its bolted connections are nice and tight.
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Old 07-08-2019, 09:38 AM
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Originally Posted by gooflophaze View Post
Multimeter - usually wont read more than a handful of amps without blowing up, certainly not enough to measure the fan. Spec is probably fine, though inrush current is probably going to be a lot more than 21a.
This is what I use for amp draw:

https://www.miataturbo.net/attachmen...ine=1368199791


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Old 07-08-2019, 09:51 AM
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I've had a CS144 alternator and leads get hot before in my Pontiac, which has next to no draw. Bad voltage regulator was overcharging and cooking the battery.
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Old 07-08-2019, 12:10 PM
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Originally Posted by Godless Commie View Post
This is what I use for amp draw:


That's what I was contemplating purchasing.

A failing voltage regulator could go from just fine to higher voltage intermittently, couldn't it? And the fan speed wouldn't reflect it if it has this crowbar device?
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Old 07-08-2019, 12:28 PM
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Forgive my electrical ignorance, but why the hell would a fan pull 22 freaking amps?? The 1 HP electric motor I just bought for my belt grinder only pulls about 14, and that's at startup.
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Old 07-08-2019, 12:41 PM
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volts x amps = watts

12v x 22a = 264 watts
120v x 14a = 1680 watts
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