Alternator smoking after jump start...

Do not have the source vehicle running while jumping. You just want the battery voltage only. The output from the source alternator can fry the jumped vehicle.

 

Well 275,000 miles is a lot but you stressed and killed it. You asked your alt to run your truck, keep your battery charged, charge his dead batteries and start his truck. An 8 cylinder diesel. There is a reason he has 2 batteries and a much larger alt than you do.

There is a limit to what your alternator was built for. You certainly found it. When jumping a larger engine you can charge up his batteries but shut off your engine before he tries to start his engine. Some won't start any other engine while theirs is running. Have the battery take the load, don't kick the shit out of your alternator.

 

NO! Never ever EVER have the jumper vehicle running while the dead vehicle is cranking. Especially when jumping a larger vehicle. That's what fried it.

Revving to charge the dead batteries is taxing but *usually* not too bad depending on battery resistance(proportional to amp rating) and how dead that battery is. But having your alternator running while he was cranking means that your Taco's little 140A alt was taxed with both charging his dead batteries AND feebly attempting to supply the 1200A his starter was pulling. It's a matter of voltage and amperage.

Think of it like air pressure. Voltage is electrical "pressure". Pressure is the result of resistance to flow. Your battery, regardless of amperage rating, stores/supplies juice at 12.6v at full charge(nominally). Your alternator is a pump that supplies juice at 13.5+ volts to overcome that "pressure" and push current into the pressure tank(your battery). With only a few volts of "pressure" difference, minimal current flows. Just enough to keep the the battery topped off as designed, until it eventually hits equilibrium and the flow trickles to a stop. If course it never fully stops since your engine and vehicle uses some of that to keep running.

When you add the dead vehicle to the circuit while running, electrons follow the path of least resistance and flow into the dead battery as if it's yours, again until everything equalizes. Just like when you use electrics in your vehicle, you open a path for current to flow, voltage drops a bit, and the alternator picks up the slack to keep it where it needs to be.

NOW....try to crank that dead vehicle on your alternator and you open the flood gates for all that juice to flow right to his massive 1200amp diesel starter motor and glow plugs etc. Now with almost zero resistance, voltage drops through the floor, your battery is maxed out(considering his is dead), and the little hamster in your alternator loses its furry little mind ramping up the output to compensate until it strokes out. All that amperage(flow) creates incredible amounts of heat and incinerates the insulation in your alternator windings, brushes, diodes, regulator, etc, which are only sized/designed to handle 140A max to maintain an 800A battery, not charge 2 dead 1000A batteries AND start a V8 diesel. Cue the zaps and smoke. The batteries are designed to flow many hundreds of amps, your alternator is not.

It's like trying to run an industrial plant off of a little Honda generator. kaboom.

Like BKinzey said, there's a reason his truck needs multiple huge batteries and a bigger alternator. Not to mention the possibility of a short causing his dead batteries in the first place.

TL;DR: Big truck starter pulls LOTS of power, overloads your battery, alternator sizzles trying to compensate. Your battery is probably cooked too, or at least *severely* degraded in life expectancy. You're honestly lucky it didnt overheat and explode. It may have if the truck wasn't running. Sucks man, you were only trying to help. But don't do that ever again.

 

To the OP, you said the smoke came out of your alternator, NAPA sells replacement smoke, go get a box sized for your truck.

 

Here it is.

 

I must be missing something here...

The vehicle you are jumping doesn't matter, within reason of course. Old diesel trucks can have small alternators just like the one in the Taco. What difference does it make?

It fried because it had 275k miles. What difference is jumping a dead diesel truck with two batteries vs. charging a secondary battery in the Taco vs. stalling the winch on your bumper? None. The alternator is going to max out and it is designed to operate like that. Sure it will get angry after a while and depending on the conditions could overheat but probably isn't going to occur while idling.

It was on it's death bed and this just kicked it.

Stop the internet scare tactic...people have been jump starting vehicles since they have had electric starters. Your Uber Taco isn't special...

 

How many miles have ya'll's alternators lasted on your trucks before needing to be replaced? Anything else I should be expecting to lose ~275-300k? Water pump and everything is original on this truck. Nothing has been replaced but spark plugs, brakes, etc.

This truck has been amazing so far. My dad has had to borrow it so many times when his 5.4 Triton F-150 is in the shop lol. No surprise that it was an F-250 on the side of the road that needed help.

 

so did he get it started lol

 

Yeah lol. He felt really bad when he saw what happened to my truck and kept apologizing and offered to pay my repair bill. But from the looks of it, he can barely afford to keep his work truck together and running so I’m not gonna put that on him, not his fault

 

Meh, it'll probably cause damage over time if you do it a lot. I don't know how many times I've held a gas soaked rag over a tractor's intake to get it started in the winter. It's also great when someone runs the fuel tank dry. Way better than cracking the lines and bleeding air out.

 

If an alternator goes 100k that is decent. Most jap ones like Denso longer. My father has a 2.7 Taco and his went around a quarter mil. That's pretty good.

 

You are.

If that's true, then why doesn't that F250 have a smaller alt and only one battery? The demands of starting that engine exceeds the capabilities of the Tacoma's alternator.

 

The thing is its the batteries that provide the starting current for the engine, not the alternator.

 

The alternator does not start the vehicle, the batteries do. The Alt simply tops them back up after the fact. Jumping simply puts the batteries in parallel. Typically the bad batteries aren't completely flat, just need a little extra juice to the starter get them over the top.

 

I learned this many years ago: "Everything electrical runs on smoke. If you let the smoke out, it won't work anymore." True eh?

 

The British have this solved.

 

So one person understands starting and charging systems.

So what happens when my house bank is dead on my boat and I start the engine? If the BS that is being spouted is true, then my alternator would fry every time I start by propulsion engine and charge the battery bank.

I'll repeat again because not everyone understands alternator function. It isnt putting out anywhere near the max current at idle. You would have to hold the engine revs up for that to work. The it benefits from increased cooling so it still isn't a problem.

Suggest many people read instead of typing crap that future readers will take as being true.

Did you know 5g caused Corona? I read it in a forum...

 

Because it is a diesel and the glow plugs circuit needs more current during startup. Plus a diesel needs more current because of the higher compression. The base model only has one alternator. You have to upgrade to get two.

Alternator size and number has nothing to do with starting needs.

Try passing the 101 course before you try schooling me honcho...

 

Out with the old, in with the reman. Good to go now. Thanks for the input everyone!

 

Yuck. Is that all oil and dirt?

Not quite the worst one I've seen. When the bearings come apart and the shaft goes sideways and then it catches fire, apparently they don't take it as a core anymore