Alternator Output Drops Above 45 C After 75 km

Bret Cahill wrote on 7/19/2017 12:15 PM:

Does this only happen during the day and not at night? What is the voltage on the system when you start running and when the engine fails, also with and without lights? I'm not sure how you can restart the engine if the voltage is so low the engine won't run. I'm thinking it is an issue with the engine control computer rather than the electrical system.

You can get voltmeters off eBay that plug into your lighter socket.

--

Rick C

I avoid driving at night when it's really hot.

LED headlights would solve the problem and are actually cheaper than voltage regulators if you can believe that.

I'll check it out.

The battery restarts the engine just fine. Autozone tested it claiming everything is A-OK with the charging system. Of course, the engine had been off for a couple of minutes so that test wasn't too useful.

I should have thought of that.

I'll wire up a plug to a multi meter next trip into the heat. I should have thought of that too. Thanks again.

You can conceptualize w/o language but you cannot think w/o language.

Bret Cahill

Bret Cahill wrote on 7/19/2017 2:43 PM:

I'm trying to figure out if it *is* the heat. Heck, it could be something blocking the exhaust or something with the fuel supply.

How do you know LED headlights will solve the problem if you don't know what the problem is?

If your alternator stops working because of the heat, the battery will run down. The system voltage can't droop without the battery loosing charge. So if the engine starts ok something else is wrong.

Do the headlights dim? That's an indication of low voltage to the headlights.

It can also be something as mundane as the ignition coil. Do you have one or several? If one it could be that. Or if you have an ignition resistor that can be opening in the heat. The symptom will be the engine starts while you turn the key to start, but as soon as you release it to ON, the engine dies.

--

Rick C

out lights_.

ust be some thresh hold where the rectifier or voltage regulator is really sensitive to even small changes in temps.

This never happens below 40 C so heat is definitely one leg of the 2 legged stool.

I always think it's a clogged fuel filter at first. Later down the road I remember trying changing the filter so this issue is not a clogged fuel fil ter.

Maybe the fuel pump creates enough of a vacuum so that the pressure drops b elow vapor pressure which should be quite high at 50 - 60C. Then the pump could lose suction. The problem with that theory is the fuel system shoul d not be affected by a load on the electrical system, especially a cam driv en fuel pump.

ltage regulators if you can believe that.

hat

Halogens draw a lot of power which hastens the onset / aggravates the mis f iring enormously but _only when it is really hot_.

he

everything is A-OK with the charging system. Of course, the engine had be en off for a couple of minutes so that test wasn't too useful.

n

The distributor ignition module is a suspect component. Maybe a combinatio n of heat + a load on the electrical system for a slightly different voltag e is too much for it.

There isn't any easy way to dismiss that theory.

ghts.

I don't remember ever having dim lights.

have thought of that too. Thanks again.

e

One. The resistances check out OK at lower temperatures. Maybe something opens up in the heat.

It'll start immediately and stay running until there's some combination of too much electrical load + too much heat.

Bret Cahill

Bret Cahill wrote on 7/19/2017 8:49 PM:

Sure there are lots of ways. Try taking some measurements.

Then there is nothing wrong with the voltage. Forget the alternator, regulator and system voltage.

Duh, that's the point. It can be opening up at high temps. Same with the resistor.

I'm talking about after it fails and won't run. Above you said you have to wait 2 minutes until it will start. You need to check things *then*. No point in checking them when they are working.

Does the engine stumble, lose power and die or just quit like you turned it off?

--

Rick C

99% of the time alternator problems are caused by brushes. First suspect with any vehicle that has 50K+ miles on it. (although some new alternators don't have brushes... and some go for 200K before they wear enough)

Warm temps can cause the metal in the holders or the insulating material to expand causing the brushes to bind in the slip ways. If the brushes are at the end of their life, the small amount of run-out (wobble) can kick the brushes up into the slip holders where they stay until it cools enough so the spring can push it back into contact with the rings.

How many miles on the car?

Brushes are cheap - ~$4 ($8 in NY to fix my OM's car) take it to a garage and they replace the alternator for $300, or claim they rewound the rotor for about that same amount.

Pressed in diodes on the alternator housing can also cause that, if they are rusted between the diode case (steel) and aluminum alternator.

How about replacing it with a 140A alternator...

:-} ...Jim Thompson

-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

| 1962 |

I'm looking for work... see my website.

Thinking outside the box...producing elegant & economic solutions.

default wrote on 7/20/2017 6:18 AM:

There is nothing wrong with his alternator. He has not measured anything to show there *is* a problem. His engine stops running when it is hot out and he jumped to a conclusion that it had to be an alternator problem. At this point he has reported no measurements that would support the idea that the problem is the charging system. He has said the light do not dim and the engine starts fine after things sit for a couple of minutes, so I don't see how it can be the charging system.

--

Rick C

I had the same problem. I would squirt some Cold Spray onto the fuel pump and away we go... Vapor lock? Bad vent on gas cap?

+1

Apparently the exact terminal voltage has to be set according to temperature - I assume there's a circuit in there somewhere with a thermistor.

AFAICR: there's appnotes about this on Jim Thompson's website - analogue solutions or something.

Slip ring brushes last a lot longer on field rotor alternators - I've only seen them on motorcycles, but the latest thing is interleaved poles only rotor coupled to the field assembly via a coaxial pole arrangement. No brushes at all.

Last time I had that was the middle HT lead to the distributor had a spark eroded copper core - trim it back to make a proper connection and it worked fine.

Some of the motorcycles I had - you could hear the vent whistling!

More like battery management sensing an over heated battery and dropping back the charging voltage..

The module is normally mount under and very close to the battery compartment..

Missing guards and rust in areas no longer blocking hot air from hitting the compartment area could be heatnig up the module and giving it a false sense.

Or, it just could be bad!

Jmaie

If it is an older high-mileage vehicle it probably still has brushes. My 91 Dodge Pickup does...

Town I lived in some years ago had this place that specialized in alternator repairs. I'd hear people at work talking about their car problems and mention the alternator place. If they are to be believed rotors frequently require "rewinding," a $300 service. (in the 80's)

I later fixed a friend's car that he'd gotten an estimate for a "bad rotor," and only had to replace the brushes.

I rewound one rotor my old Honda motorcycle. Rotor failure is rare - most vehicles use the slight current from the alternator indicator light or a resistor to excite the thing to get it charging, but when it starts working a separate set of small diodes (3) on the positive output side of the alternator supplies the exciting current - that way a failure in the alternator doesn't cause the battery to discharge through the rotor if the alternator has no output.

Motorcycles have it rough. The alternator is directly driven from the crank shaft so all the heat of the (usually) air cooled engine is present in the alternator and there are no fans to aid cooling just the air the rotor stirs up to distribute heat. Modern bikes frequently have PM alternators with the field on the outside of the coils.

Assuming you catch it before they break up and rip up the commutator.

Almost a frequent occurrence in power tools.

Y'know, the cool thing about experienced mechanics is that they see these things ALL THE TIME, and while they may not have the foggiest notion of the theory behind the problems, and they may even be dead wrong about the "why" part of it, they usually have a pretty damned good idea of what parts to fix/change/bang on to make the problem go away.

So why ask on an electronics group?

AFAIK generators have been failing at hot since well before there were any semiconductors in the loop -- maybe it's just some grotty old electromechanical problem, like the heat making the brushes get slack on the slip rings, or something equally mundane.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com

I'm with you, Tim! I've never seen such a lengthy thread about something that should have been resolved in a few days ;-) ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 

             I'm looking for work... see my website. 

Thinking outside the box...producing elegant & economic solutions.