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 SHIT 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.

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.

Are you running a rx7 alternator or a nb style alternator?

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).

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?

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.

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?

Picture of 40 amp relay. Maybe it isn't good for continuous duty.

Be sure to watch the alternator voltage (at the post), not simply the battery voltage.

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.

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.

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.

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.

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.



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?

You may want to consider getting a relay base, that'll help the vibration issue and simplify wiring into some good ol' butt splices. 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.

This is what I use for amp draw:

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

https://cimg0.ibsrv.net/gimg/www.mia...ae91d2a70c.jpg

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.

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?

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.

volts x amps = watts

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

Attachment 228100

re: regulator crowbar et al - I don't think our alternators/fans are that smart. I don't really see a regulator failing intermittently - should be working or dead. Also voltage regulation at idle RPM's is difficult, I wouldn't put too much stock in it.

That doesn't inspire a lot of confidence, then. I thought I was on to something good.

What about the voltage reference circuit for the alternator? Maybe it is reading from an inaccurate source, a source being dragged down by load and poor connections? Gotta check the diagrams and see where that sucker is conneted.

Ordered:
80a relay listed above
140a NA8 replacement alternator (because why replace with stock amperage?)

What I would do - next time it goes from fast to slow, blip the throttle for a second. Alternator is two electromagnets that push against each other, power (and voltage) output is set by the field strength of that electromagnet. Since we're not at a constant RPM, fields have to vary accordingly - which get annoying because if you're trying to suck 5-6hp out of an engine at idle you're putting a significant drag which'll lead to stalling. This is where I put in that whole "don't pay no mind to idle voltages" concept in - alternators aren't meant to self excite too much at idle rpms - and therefore not suck HP. Old GM 1-wire alternators used in big V8's don't even charge until they're nearly at 3000 RPM (granted - in part because of pulley size and V-belt's like to squeal unless tensioned properly, moreso than newer micro-v belts). Newer ECU controlled alternators basically tell the alt's to turn off at idle or steady state cruise (with the heavy consumption accessories off) when battery voltages are good to save gas.

Either way - I wouldn't trust any observations made below 2k rpm - too much handwaving to explain away why - unless it was something obvious like 18v.

For my knowledge, what is the difference between an FD alternator and a 140a stock replacement? Does one offer better low rpm voltage?

IDK other than mounting lugs and plug location being slightly different.

Gooflophaze, my Miata idles about 1050-1100 rpm because I like it there where it is smooth and not affected as much by loads. I'm not particularly concerned about idle fuel economy, if you know what I mean.

What are your thoughts on my idea of inaccurate signal reference voltage to the alternator?

So we get into the details I want to handwave away - because I don't have direct experience with them, just theory. I'm a digital guy with enough analog knowledge to be dangerous. But my understanding is signal reference should be internal to the alt - or at least Savington corrected me a few months ago. However a higher idle might be working against you in this case.

Regulator basically has a target it wants to be at. The further away from it, the more duty cycle (though I'm using a digital term here I'm pretty sure it's just an op-amp output) to the field it pushes, which in return pushes more drag on the alternator and more voltage out to the battery. There's a bare minimum of voltage in the coil, and at that low point it basically says "phhhbt why even try?" - that's your freewheeling voltage. Once that freewheeling voltage goes above a threshold (because RPM has increased) it wakes up and says "oh hey cool I can actually get on with work now" and gives more voltage to the fields which in turn produces more power (and drag) from the alt. As you approach redline, it's backing off that voltage because power = force * speed, more speed less force. If your regulator was bad, you'd get voltage differences consummate with engine speed (well, that's one failure mode - there are plenty of others).

So immediately after startup you have your ASE / cold idle targets. Since the battery is partially drained from running the starter it's lower voltage and the alt regulator wants to charge it cuz it's dumb and sees a voltage diffference - but your tune makes it more transparent. Since you have a higher idle, you might be dipping into that partial-exciting range, which charges the battery up, then it decides "nah I'm good" and voltage/RPM dips below the "feed me Seymore" threshold and you're pulling volts from the battery.

So.. handwaving / shoulder shrugging.

Interesting.

Idea!!! The relay and wire were not hot at idle when I was burping the cooling system and initially charging the air conditioning. When I was trying to finish charging the AC system I was manually revving the throttle body steadily for a period of time. Maybe the voltage regulator is bad but it wasn't evident at idle? Maybe revving it up made it get excited and reveal a bad regulator?

Alternator reference is the R/W wire, which is tapped on the downstream side of the main alternator to fuse box run. You can see upwards of several tenths of a volt drop across this run depending on load in a healthy application.

Degradation in this path can result in a true alternator voltage that is volts higher than what is reported by say a megasquirt or measured at the battery. If the fan is connected directly to the alternator, it will see this full voltage.

Theory, but easy to test.

You can evaluate pretty much the entire path from the alternator to the fan by measuring the voltage between the alternator and the fan with the fan running. Hot relays or wires mean either the resistance is high (bad connections/contacts) or the current is high. Both of these situations result in power dissipation, with the power going as the SQUARE of the current. Power increases linearly with resistance. IOW, current dissipates more power when increased than an equal increase (%) in resistance.

I doubt it is the relay contacts. Adding resistance to the circuit will not cause high amps at the alternator, but rather low voltage at the fan, causing it to run slow. On a DC motor, voltage is proportional to speed, and current is proportional to torque. It would also cause the relay to get hot due to the extra power dissipated in the contacts.

DNM

Correct me if I am wrong, but I was under the impression using the alternator output terminal for anything other than the battery cable is a bad idea.

I am not an engineer - just play one on TV - but I believe the battery should be included in every circuit so it can act as a buffer for instantaneous loads, spikes and whatnot.
The primary duty of the alternator is charging the battery. Your ATM for all things electrical is the battery.


Also,

Steve, your idea of checking the voltage reference source seems very logical to me.
I would still monitor system voltage, tho.

yes

I feel validated!

So you're not wrong but not for that reason. The battery acts as a resistive load that the alternator is always "fighting". If the battery disconnects then you get a load dump which basically spikes the voltage and does very bad things - like an arm wrestler that suddenly lets go and gets punched in the face. Wiring-wise, though - 6awg wire alternator - 80a main relay - 6awg starter - 4awg(?) battery. Adding another ring terminal to the alternator doesn't take the battery out of the circuit.. but thinking about it, it does increase the draw across the 6awg cable from the alt to the main fuse if the alternator isn't excited - but if that wire isn't getting hot, I don't see how it could do harm.

Should also mention the main 80a fuse isn't solely for the alternator - there are two common rails it provides for the rest of the fuse box, but I can't recall specifically which fuses are fed off of which side.

Would it present a problem if I have added additional wires between the battery and alternator and from the alternator to the 80 amp fuse in the fuse block? After the wiring issue last year at MATG additional wires were run parallel to stock to "help" ensure the paths were adequate.

I don't think you need to all the way to the battery itself to wire a fan.

Here's what I did back in the day: I used the 6 mm bolt that holds the main fuse, which gave me unfused B+.
I then made an auxiliary fuse box, and fed that power wire into it.

https://cimg0.ibsrv.net/gimg/www.mia...80358f98ed.jpg

Not the best pic in the world, but you get the idea...


And, this is my 144 Amp alternator.
I installed a second, 35 mm2 wire (pretty massive by Japanese car maker standards) between the alt and the battery.
Ground side is seriously beefed up, as well.

https://cimg8.ibsrv.net/gimg/www.mia...d2bf25c192.jpg


https://cimg9.ibsrv.net/gimg/www.mia...3d01a91ea8.jpg

The second line between the alt and bat has yellow tape on it, so I could identify which is which at a glance. You can barely see the ring terminal of the original wire on the alt lug.

I also have a second wire going from the alternator to the battery, and an extra wire going from the alternator to the 80 amp fuse Bolt.

Is the one from the alternator to the 80 amp fuse a problem for me?

I'm trying to see what difference it makes if the power going from the alternator to the battery and back to the fuse is somehow better than going straight from the alternator to the fuse.

Where does this 140A alternator come from? A stock Miata alternator is about 60, I thought?

--Ian

Simplify. More wires, more joints, more points of failure.

I strongly believe the "chain" should be battery -> alternator -> fuse (box) -> power consuming whatever doodad.

I'll let @Joe Perez convince you for the whys and assorted intricacies for such practice.

That's one way of doing it. It's also common to see the starter motor in between the battery and the alternator.

Provided that the conductors are of adequate size, and the connections clean and tight, it kind of doesn't matter what the exact topology is. The only majorly important rule as to positive-side wiring are that you want to keep the connection between the battery and the starter as short & simple as possible. Beyond that, everyone knows the usual stuff about good ground returns and whatnot.

True, but those two never play together. It's either the starter, or the alternator.

This whole thread and not one word about the condition of the battery. Have you checked that?

My brief search on the consequences of too small a battery for an electrical system netted enough information that I would be alarmed. I always thought your battery was a little undersized.

It's plenty big for a lawn tractor. 340cca

It's been on an electronic battery tender/charger and cranks the car without issue.

Update-

I was wrong about the extra wire from the battery. It goes to the main 80 amp fuse and not the alternator. It is 6 gauge and can be seen at the battery and the fuse block (red wire).

There's an added 10 gauge wire going from the alternator to the 80 amp fuse (yellow).

The high current supply to the fan relay has been moved from the alternator to the output of the 80 amp fuse and the extra length of wire has been removed. It is a 12 gauge wire (orange by the fuse). All of the wires to and from the relay and fan are 12 gauge (also yellow) except the ones from Spal which appear to be slightly smaller. Chart attached says 12 gauge wire is good for up to 35 amps.

I moved the fan ground back to the chassis beside the headlight.

I didn't solder any wires yet in lieu of the crimps but did re-crimp a few to make sure they were tight.

I cranked it up and checked voltage with the multimeter. 14.5 volts at high warmup idle. Not good. Not terrible.

Measuring with A/C and high fan 14.5 volts. Measuring with engine manually revved up faster 14.5 volts. Measuring at driver's footwell fuse block 14.4x volts.

I'm guessing something is off in the voltage regulator and it possibly goes to an even higher voltage occasionally and causes the problem with hot wiring and relays and probably other things.

If the fan has this "crowbar" device that limits voltage I'm guessing it helped create extra heat in those specific wires when fighting the alternator.

Pictures of some of my mess, before, after, and during the alterations.

Is the alternator still getting really hot? How about the wiring/relay?

I didn't let it run long enough to get hot. I'm thinking it probably jumps up to an even higher voltage sometimes. New alternator should arrive Friday.

If you have/had an unstable output, it is possible that the instability is/was caused by having the fan connected directly to the alt terminal. I won't get into the maths associated with the voltage feedback on the internally regulated alternator, but it is conceivable.

IOW, moving the alternator tap may solve all your problems.

Interesting.

It is still out of range at 14.5v so I'm glad it's being replaced. Having higher available amperage won't bother me either.

UPDATE:

Still weird.

Alternator has been replaced with the higher amperage unit. It, interestingly, produces 14.0 volts during operation. The battery makes 12.7 by itself. The fuse holder wire was still getting warm along with the relay. The wire from the relay to the fan was cool and so was the wire from the ground to the fan. The 30 amp fuse popped after a few cycles.

The voltage drop across the relay during operation was .05 volts. The voltage drop across the fuse was about .3 volts. The voltage at the fan was 13.65.

Sooo, I changed out the inline fuse holder with one utilizing a larger 10 gauge wire and I switched to the 80 amp relay. The fuse holder wire still became warm, as did the relay. Then after a few cycles the 30 amp fuse popped.

I haven't yet purchased the amp meter. I'm contemplating the fan now, as it is the last man standing.

Suggestions?

I've had surprisingly good results from the super-cheap shunt type ammeters you can buy from Amazon / eBay. The ones that Chinese hobbyists buy from Uzbekistan, because quality Chinese-made units are too expensive.

Ex:

What crimp tool are you using?

Snap-on

https://cdn.vehicleservicepros.com/f...aacb9d1379.jpg

That's a better choice. The only one I saw locally was $90 @ Lowe's.

I went ahead and ordered another fan because I'm running out of things to try. And running out of time. Who knows what other issues will present themselves in the shakedown?

I'm weary of this. I appreciate the help from you all.

Had I known you were made of money, I'd have soaked you for the pen.

Hahaha! It was a birthday gift from my buddy Gary many years ago. He's a flashy name brand tool kinda guy. I can't hang. Gotta max out the 401k and IRA's for both of us prior to car stuff.

One of his cars:


Another one:

This is the fan I'm using. Spal VA18-AP71/LL-59A 12V.

It spins freely but there's some evidence of it having rubbed its housing at times, possibly due to sway bar contact or fabricated aluminum shroud bending at times. I think I will ensure shroud rigidity by riveting some small aluminum angle across its back in select locations.

EDIT: I trimmed the marked section where the plastic was flaking with a razor and sandpaper but it still popped the fuse. Fan seems to pop the fuse mostly on startups.

https://cimg5.ibsrv.net/gimg/www.mia...d561391ec6.jpg

New fan should arrive Tuesday.

Sounds like the right thing. 30 A with 0.05V drop gives contact resistance of less than 2mOhms. Relay still seems solid. Fan seems to be drawing too much current.

Your Spal fan is supposed to pull 20 - 22 A.

Seems logical. Presupposing an unregulated supply, electric motors (along with many other things) tend to draw much more current while first starting up than when running in a steady-state configuration. 'Tis called inrush current.